# Posts Tagged proton

## Recent Postings from proton

### Excesses of Cosmic Ray Spectra from A Single Nearby Source [Cross-Listing]

Growing evidence reveals universal hardening on various cosmic ray spectra, e.g. proton, positron, as well as antiproton fraction. Such universality may indicate they have a common origin. In this paper, we argue that these widespread excesses can be accounted for by a nearby supernova remnant surrounded by a giant molecular cloud. Secondary cosmic rays ($\rm p$, $\rm e^+$) are produced through the collisions between the primary cosmic ray nuclei from this supernova remnant and the molecular gas. Different from the background, which is produced by the ensemble of large amount of sources in the Milky Way, the local injected spectrum can be harder. The time-dependent transport of particles would make the propagated spectrum even harder. Under this scenario, the anomalies of both primary ($\rm p$, $\rm e^-$) and secondary ($\rm e^+$, $\rm \bar{p}/p$) cosmic rays can be properly interpreted. We further show that the TeV to sub-PeV anisotropy of proton is consistent with the observations if the local source is relatively young and lying at the anti-Galactic center direction.

### Can sea quark asymmetry shed light on the orbital angular momentum of the proton?

A striking prediction of several extensions of the constituent quark model, including the unquenched quark model, the pion cloud model and the chiral quark model, is a proportionality relationship between the quark sea asymmetry and the orbital angular momentum of the proton. We investigate to which extent a relationship of this kind is corroborated by the experiment, through a systematic comparison between expectations based on models and predictions obtained from a global analysis of hard-scattering data in perturbative Quantum Chromodynamics. We find that the data allows the angular momentum of the proton to be proportional to its sea asymmetry, though with a rather large range of the optimal values of the proportionality coefficient. Typical values do not enable us to discriminate among expectations based on different models. In order to make our comparison conclusive, the extrapolation uncertainties on the proportionality coefficient should be reduced, hopefully by means of accurate measurements in the region of small proton momentum fractions, where the data is currently lacking. Nevertheless, the unquenched quark model predicts that quarks account for a proton spin fraction much larger than that accepted by the conventional wisdom. We explicitly demonstrate that such a discrepancy can be reabsorbed in the unknown extrapolation region, without affecting the description of current data, by imposing the unquenched quark model expectation as a boundary condition in the analysis of the data itself. We delineate how the experimental programs at current and future facilities may shed light on the region of small momentum fractions.

### The proton and helium anomalies in the light of the Myriad model

A hardening of the proton and helium fluxes is observed above a few hundreds of GeV/nuc. The distribution of local sources of primary cosmic rays has been suggested as a potential solution to this puzzling behavior. Some authors even claim that a single source is responsible for the observed anomalies. But how probable these explanations are? To answer that question, our current description of cosmic ray Galactic propagation needs to be replaced by the Myriad model. In the former approach, sources of protons and helium nuclei are treated as a jelly continuously spread over space and time. A more accurate description is provided by the Myriad model where sources are considered as point-like events. This leads to a probabilistic derivation of the fluxes of primary species, and opens the possibility that larger-than-average values may be observed at the Earth. For a long time though, a major obstacle has been the infinite variance associated to the probability distribution function which the fluxes follow. Several suggestions have been made to cure this problem but none is entirely satisfactory. We go a step further here and solve the infinite variance problem of the Myriad model by making use of the generalized central limit theorem. We find that primary fluxes are distributed according to a stable law with heavy tail, well-known to financial analysts. The probability that the proton and helium anomalies are sourced by local SNR can then be calculated. The p-values associated to the CREAM measurements turn out to be small, unless somewhat unrealistic propagation parameters are assumed.

### Estimation of Stopped Protons at RHIC BES Energies [Cross-Listing]

The recent net-proton fluctuation results of the STAR experiment from beam energy scan (BES) program at RHIC have drawn much attention to explore the QCD critical point and the nature of deconfinement phase transition. There have been many speculations that the non-monotonic behaviour around 19.6 GeV in STAR results may be due to the existence of QCD critical point. However, the experimentally measured proton distributions contain protons from heavy resonance decays, from baryon stopping and from the production processes. Further, these proton distributions are used to estimate the net-proton number fluctuations as it is difficult to disentangle the protons from the above sources. Assuming that any criticality in the system could affect the particle production, in order to study the dynamical fluctuations at different center of mass energies, it will be interesting to devise a method which accounts for the produced baryons i.e. the protons here. In the present work we present a method to estimate the number of stopped protons at RHIC BES energies for central $0\%-5\%$ Au+Au collisions within STAR acceptance and discuss its implications on the net-proton fluctuation results.

### Estimation of Stopped Protons at RHIC BES Energies

The recent net-proton fluctuation results of the STAR experiment from beam energy scan (BES) program at RHIC have drawn much attention to explore the QCD critical point and the nature of deconfinement phase transition. There have been many speculations that the non-monotonic behaviour around 19.6 GeV in STAR results may be due to the existence of QCD critical point. However, the experimentally measured proton distributions contain protons from heavy resonance decays, from baryon stopping and from the production processes. Further, these proton distributions are used to estimate the net-proton number fluctuations as it is difficult to disentangle the protons from the above sources. Assuming that any criticality in the system could affect the particle production, in order to study the dynamical fluctuations at different center of mass energies, it will be interesting to devise a method which accounts for the produced baryons i.e. the protons here. In the present work we present a method to estimate the number of stopped protons at RHIC BES energies for central $0\%-5\%$ Au+Au collisions within STAR acceptance and discuss its implications on the net-proton fluctuation results.

### Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ in Compton scattering

The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$, are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined.

### Calculation of gluon contribution to the proton spin by using the non-perturbative quantization \{a} la Heisenberg

The contribution of gluon fields to the proton spin is calculated. The calculations are performed following non-perturbative Heisenberg's quantization technique. In our approach a proton is considered as consisting of three quarks connected by three flux tubes. The flux tubes contain colour longitudinal electric and transversal electric and magnetic fields. The longitudinal electric field causes the interaction forces between quarks. The quantum superposition of the transversal fields causes the appearance of the angular momentum density. From our calculations, we obtain that the contribution of the gluon field from the flux tubes to the proton spin is of the order of $15\%$. The dimensionless relation between the angular momentum and the mass of the gluon fields is obtained. The experimental verification of this relation is discussed. Simple numerical relation between the proton mass, the speed of light and the proton radius, which is of the same order as the Planck constant, is discussed.

### Calculation of gluon contribution to the proton spin by using the non-perturbative quantization \a la Heisenberg [Replacement]

The contribution of crossed gluon fields in flux tubes connecting quarks to the proton spin is calculated. The calculations are performed following non-perturbative Heisenberg's quantization technique. In our approach a proton is considered as consisting of three quarks connected by three flux tubes. The flux tubes contain colour longitudinal electric and transversal electric and magnetic fields. The longitudinal electric field causes the interaction forces between quarks. The quantum superposition of the transversal fields causes the appearance of the angular momentum density. The dimensionless relation between the angular momentum and the mass of the gluon fields is obtained. The contribution to proton spin from rotating quarks and flux tubes connecting quarks is estimated. Simple numerical relation between the proton mass, the speed of light and the proton radius, which is of the same order as the Planck constant, is discussed.

### Activation cross-sections of proton induced reactions on vanadium in the 37-65 MeV energy range

Experimental excitation functions for proton induced reactions on natural vanadium in the 37-65 MeV energy range were measured with the activation method using a stacked foil irradiation technique. By using high resolution gamma spectrometry cross-section data for the production of $^{51,48}$Cr, $^{48}$V, $^{48,47,46,44m,44g,43}$Sc and $^{43,42}$K were determined. Comparisons with the earlier published data are presented and results predicted by different theoretical codes (EMPIRE and TALYS) are included. Thick target yields were calculated from a fit to our experimental excitation curves and compared with the earlier experimental yield data. Depth distribution curves to be used for thin layer activation (TLA) are also presented.

### Partonic structure of proton in the resonance region

We separate the contributions of parton distributions from higher twist corrections to the deeply inelastic lepton-proton scattering in the resonance region using the Jefferson Lab data at low $Q^2$. The study indicates that the concept of the valence quarks and their distributions are indispensable even at $Q^2<1GeV^2$. The quark-hadron duality is also discussed.

### Skyrme model study of proton and neutron properties in a strong magnetic field

The proton and neutron properties in a uniform magnetic field are investigated. The Gell-Mann-Nishijima formula is shown to be satisfied for baryon states. It is found that with increasing magnetic field strength, the proton mass first decreases and then increases, while the neutron mass always increases. The ratio between magnetic moment of proton and neutron increases with the increase of the magnetic field strength. With increasing magnetic field strength, the size of proton first increases and then decreases, while the size of neutron always decreases. The present analyse implies that in the core part of the magnetar, the equation of state depend on the magnetic field, which modifies the mass limit of the magnetar.

### Skyrme model study of proton and neutron properties in a strong magnetic field [Cross-Listing]

The proton and neutron properties in a uniform magnetic field are investigated. The Gell-Mann-Nishijima formula is shown to be satisfied for baryon states. It is found that with increasing magnetic field strength, the proton mass first decreases and then increases, while the neutron mass always increases. The ratio between magnetic moment of proton and neutron increases with the increase of the magnetic field strength. With increasing magnetic field strength, the size of proton first increases and then decreases, while the size of neutron always decreases. The present analyse implies that in the core part of the magnetar, the equation of state depend on the magnetic field, which modifies the mass limit of the magnetar.

### Extraction of the proton charge radius from experiments

Static properties of hadrons such as their radii and other moments of the electric and magnetic distributions can only be extracted using theoretical methods and not directly measured from experiments. As a result, discrepancies between the extracted values from different precision measurements can exist. The proton charge radius, $r_p$, which is either extracted from electron proton elastic scattering data or from hydrogen atom spectroscopy seems to be no exception. The value $r_p = 0.84087(39)$ fm extracted from muonic hydrogen spectroscopy is about 4% smaller than that obtained from electron proton scattering or standard hydrogen spectroscopy. The resolution of this so called proton radius puzzle has been attempted in many different ways over the past six years. The present article reviews these attempts with a focus on the methods of extracting the radius.

### Recent results for the proton spin decomposition from lattice QCD

The exact decomposition of the proton spin has been a much debated topic, on the experimental as well as the theoretical side. In this talk we would like to report on recent non-perturbative results and ongoing efforts to explore the proton spin from lattice QCD. We present results for the relevant generalized form factors from gauge field ensembles that feature a physical value of the pion mass. These generalized form factors can be used to determine the total spin and angular momentum carried by the quarks. In addition we present first results for our ongoing effort to compute the angular momentum of the gluons in the proton.

### Recent results for the proton spin decomposition from lattice QCD [Cross-Listing]

The exact decomposition of the proton spin has been a much debated topic, on the experimental as well as the theoretical side. In this talk we would like to report on recent non-perturbative results and ongoing efforts to explore the proton spin from lattice QCD. We present results for the relevant generalized form factors from gauge field ensembles that feature a physical value of the pion mass. These generalized form factors can be used to determine the total spin and angular momentum carried by the quarks. In addition we present first results for our ongoing effort to compute the angular momentum of the gluons in the proton.

### Proton distribution radii of $^{12-19}$C illuminate features of neutron halos

Proton radii of $^{12-19}$C densities derived from first accurate charge changing cross section measurements at 900$A$ MeV with a carbon target are reported. A thick neutron surface evolves from $\sim$ 0.5 fm in $^{15}$C to $\sim$ 1 fm in $^{19}$C. The halo radius in $^{19}$C is found to be 6.4$\pm$0.7 fm as large as $^{11}$Li. Ab initio calculations based on chiral nucleon-nucleon and three-nucleon forces reproduce well the radii.

### Comparison of Yields of neutron rich nuclei in Proton and Photon induced $^{238}$U fission

A comparative study of fission of actinides specially $^{238}$U, by proton and bremsstrahlung photon is performed. Relative mass distribution of $^{238}$U fission fragments have been explored theoretically for both proton and photon induced fission. The integrated yield along with charge distribution of the products are calculated to find out the neutron richness in comparison to the nuclei produced by r-process in nucleosynthesis. Some r-process nuclei in intermediate mass range for symmetric fission mode are found to be produced almost two order of magnitude more for proton induced fission than photofission, although rest of the neutron rich nuclei in the asymmetric mode are produced in comparable proportion for both the processes.

### The bending of the proton plus helium flux in primary cosmic rays measured by the ARGO-YBJ experiment in the energy range from 20 TeV to 5 PeV [Cross-Listing]

The measurement of proton plus helium and all-particle energy spectra in the range $20\,$ TeV to $5 \,$PeV and $80 \,$TeV to $5 \,$PeV respectively are presented. Data taken by the ARGO-YBJ detector in the 2010 year have been analyzed. The ARGO-YBJ experiment (Tibet, P. R. China) has been taking data for more than five years by means of a full-coverage array of RPC detectors. The discrimination between showers produced by light and heavy primaries has been performed by looking at the lateral particle density close to the core region. A Bayesian unfolding technique was therefore applied to the measured quantities in order to evaluate the cosmic ray energy spectrum. The proton plus helium spectrum clearly shows a bending at about $1 \,$PeV, while the all-particle spectrum is consistent with previous observations.

### The bending of the proton plus helium flux in primary cosmic rays measured by the ARGO-YBJ experiment in the energy range from 20 TeV to 5 PeV

The measurement of proton plus helium and all-particle energy spectra in the range $20\,$ TeV to $5 \,$PeV and $80 \,$TeV to $5 \,$PeV respectively are presented. Data taken by the ARGO-YBJ detector in the 2010 year have been analyzed. The ARGO-YBJ experiment (Tibet, P. R. China) has been taking data for more than five years by means of a full-coverage array of RPC detectors. The discrimination between showers produced by light and heavy primaries has been performed by looking at the lateral particle density close to the core region. A Bayesian unfolding technique was therefore applied to the measured quantities in order to evaluate the cosmic ray energy spectrum. The proton plus helium spectrum clearly shows a bending at about $1 \,$PeV, while the all-particle spectrum is consistent with previous observations.

### The bending of the proton plus helium flux in primary cosmic rays measured by the ARGO-YBJ experiment in the energy range from 20 TeV to 5 PeV [Replacement]

The measurement of proton plus helium and all-particle energy spectra in the range $20\,$ TeV to $5 \,$PeV and $80 \,$TeV to $5 \,$PeV respectively are presented. Data taken by the ARGO-YBJ detector in the 2010 year have been analyzed. The ARGO-YBJ experiment (Tibet, P. R. China) has been taking data for more than five years by means of a full-coverage array of RPC detectors. The discrimination between showers produced by light and heavy primaries has been performed by looking at the lateral particle density close to the core region. A Bayesian unfolding technique was therefore applied to the measured quantities in order to evaluate the cosmic ray energy spectrum. The proton plus helium spectrum clearly shows a bending at about $1 \,$PeV, while the all-particle spectrum is consistent with previous observations.

### The bending of the proton plus helium flux in primary cosmic rays measured by the ARGO-YBJ experiment in the energy range from 20 TeV to 5 PeV [Replacement]

The measurement of proton plus helium and all-particle energy spectra in the range $20\,$ TeV to $5 \,$PeV and $80 \,$TeV to $5 \,$PeV respectively are presented. Data taken by the ARGO-YBJ detector in the 2010 year have been analyzed. The ARGO-YBJ experiment (Tibet, P. R. China) has been taking data for more than five years by means of a full-coverage array of RPC detectors. The discrimination between showers produced by light and heavy primaries has been performed by looking at the lateral particle density close to the core region. A Bayesian unfolding technique was therefore applied to the measured quantities in order to evaluate the cosmic ray energy spectrum. The proton plus helium spectrum clearly shows a bending at about $1 \,$PeV, while the all-particle spectrum is consistent with previous observations.

### The bending of the proton plus helium flux in primary cosmic rays measured by the ARGO-YBJ experiment in the energy range from 20 TeV to 5 PeV [Replacement]

The measurement of proton plus helium and all-particle energy spectra in the range $20\,$ TeV to $5 \,$PeV and $80 \,$TeV to $5 \,$PeV respectively are presented. Data taken by the ARGO-YBJ detector in the 2010 year have been analyzed. The ARGO-YBJ experiment (Tibet, P. R. China) has been taking data for more than five years by means of a full-coverage array of RPC detectors. The discrimination between showers produced by light and heavy primaries has been performed by looking at the lateral particle density close to the core region. A Bayesian unfolding technique was therefore applied to the measured quantities in order to evaluate the cosmic ray energy spectrum. The proton plus helium spectrum clearly shows a bending at about $1 \,$PeV, while the all-particle spectrum is consistent with previous observations.

### The bending of the proton plus helium flux in primary cosmic rays measured by the ARGO-YBJ experiment in the energy range from 20 TeV to 5 PeV [Replacement]

The measurement of proton plus helium and all-particle energy spectra in the range $20\,$ TeV to $5 \,$PeV and $80 \,$TeV to $5 \,$PeV respectively are presented. Data taken by the ARGO-YBJ detector in the 2010 year have been analyzed. The ARGO-YBJ experiment (Tibet, P. R. China) has been taking data for more than five years by means of a full-coverage array of RPC detectors. The discrimination between showers produced by light and heavy primaries has been performed by looking at the lateral particle density close to the core region. A Bayesian unfolding technique was therefore applied to the measured quantities in order to evaluate the cosmic ray energy spectrum. The proton plus helium spectrum clearly shows a bending at about $1 \,$PeV, while the all-particle spectrum is consistent with previous observations.

### How bright is the proton? A precise determination of the photon PDF

It has become apparent in recent years that it is important, notably for a range of physics studies at the Large Hadron Collider, to have accurate knowledge on the distribution of photons in the proton. We show how the photon parton distribution function (PDF) can be determined in a model-independent manner, using electron-proton ($ep$) scattering data, in effect viewing the $ep\to e+X$ process as an electron scattering off the photon field of the proton. To this end, we consider an imaginary BSM process with a flavour changing photon-lepton vertex. We write its cross section in two ways, one in terms of proton structure functions, the other in terms of a photon distribution. Requiring their equivalence yields the photon distribution as an integral over proton structure functions. As a result of the good precision of $ep$ data, we constrain the photon PDF at the level of 1-2% over a wide range of $x$ values.

### How bright is the proton? A precise determination of the photon PDF [Replacement]

It has become apparent in recent years that it is important, notably for a range of physics studies at the Large Hadron Collider, to have accurate knowledge on the distribution of photons in the proton. We show how the photon parton distribution function (PDF) can be determined in a model-independent manner, using electron-proton ($ep$) scattering data, in effect viewing the $ep\to e+X$ process as an electron scattering off the photon field of the proton. To this end, we consider an imaginary BSM process with a flavour changing photon-lepton vertex. We write its cross section in two ways, one in terms of proton structure functions, the other in terms of a photon distribution. Requiring their equivalence yields the photon distribution as an integral over proton structure functions. As a result of the good precision of $ep$ data, we constrain the photon PDF at the level of 1-2% over a wide range of $x$ values.

### How bright is the proton? A precise determination of the photon PDF [Replacement]

It has become apparent in recent years that it is important, notably for a range of physics studies at the Large Hadron Collider, to have accurate knowledge on the distribution of photons in the proton. We show how the photon parton distribution function (PDF) can be determined in a model-independent manner, using electron-proton ($ep$) scattering data, in effect viewing the $ep\to e+X$ process as an electron scattering off the photon field of the proton. To this end, we consider an imaginary BSM process with a flavour changing photon-lepton vertex. We write its cross section in two ways, one in terms of proton structure functions, the other in terms of a photon distribution. Requiring their equivalence yields the photon distribution as an integral over proton structure functions. As a result of the good precision of $ep$ data, we constrain the photon PDF at the level of 1-2% over a wide range of $x$ values.

### Revealing proton shape fluctuations with incoherent diffraction at high energy [Replacement]

The differential cross section of exclusive diffractive vector meson production in electron proton collisions carries important information on the geometric structure of the proton. More specifically, the coherent cross section as a function of the transferred transverse momentum is sensitive to the size of the proton, while the incoherent, or proton dissociative cross section is sensitive to fluctuations of the gluon distribution in coordinate space. We show that at high energies the experimentally measured coherent and incoherent cross sections for the production of $J/\Psi$ mesons are very well reproduced within the color glass condensate framework when strong geometric fluctuations of the gluon distribution in the proton are included. For $\rho$ meson production we also find reasonable agreement. We study in detail the dependence of our results on various model parameters, including the average proton shape, analyze the effect of saturation scale and color charge fluctuations and constrain the degree of geometric fluctuations.

### Revealing proton shape fluctuations with incoherent diffraction at high energy [Replacement]

The differential cross section of exclusive diffractive vector meson production in electron proton collisions carries important information on the geometric structure of the proton. More specifically, the coherent cross section as a function of the transferred transverse momentum is sensitive to the size of the proton, while the incoherent, or proton dissociative cross section is sensitive to fluctuations of the gluon distribution in coordinate space. We show that at high energies the experimentally measured coherent and incoherent cross sections for the production of $J/\Psi$ mesons are very well reproduced within the color glass condensate framework when strong geometric fluctuations of the gluon distribution in the proton are included. For $\rho$ meson production we also find reasonable agreement. We study in detail the dependence of our results on various model parameters, including the average proton shape, analyze the effect of saturation scale and color charge fluctuations and constrain the degree of geometric fluctuations.

### Revealing proton shape fluctuations with incoherent diffraction at high energy

The differential cross section of exclusive diffractive vector meson production in electron proton collisions carries important information on the geometric structure of the proton. More specifically, the coherent cross section as a function of the transferred transverse momentum is sensitive to the size of the proton, while the incoherent, or proton dissociative cross section is sensitive to fluctuations of the gluon distribution in coordinate space. We show that at high energies the experimentally measured coherent and incoherent cross sections for the production of $J/\Psi$ mesons are very well reproduced within the color glass condensate framework when strong geometric fluctuations of the gluon distribution in the proton are included. For $\rho$ meson production we also find reasonable agreement. We study in detail the dependence of our results on various model parameters, including the average proton shape, analyze the effect of saturation scale and color charge fluctuations and constrain the degree of geometric fluctuations.

### Revealing proton shape fluctuations with incoherent diffraction at high energy [Cross-Listing]

The differential cross section of exclusive diffractive vector meson production in electron proton collisions carries important information on the geometric structure of the proton. More specifically, the coherent cross section as a function of the transferred transverse momentum is sensitive to the size of the proton, while the incoherent, or proton dissociative cross section is sensitive to fluctuations of the gluon distribution in coordinate space. We show that at high energies the experimentally measured coherent and incoherent cross sections for the production of $J/\Psi$ mesons are very well reproduced within the color glass condensate framework when strong geometric fluctuations of the gluon distribution in the proton are included. For $\rho$ meson production we also find reasonable agreement. We study in detail the dependence of our results on various model parameters, including the average proton shape, analyze the effect of saturation scale and color charge fluctuations and constrain the degree of geometric fluctuations.

### Tomographic image of the proton

We determine, based on the latest experimental Deep Virtual Compton Scattering experimental data, the dependence of the spatial size of the proton on the quark's longitudinal momentum. This results in a three-dimensional momentum-space image and tomography of the proton.

### The spin structure of the proton at low $x$ and low $Q^2$ in two-dimensional bins from COMPASS [Cross-Listing]

The longitudinal double spin asymmetries $A_1^p$ and the spin dependent structure function of the proton $g_1^p$ were extracted from COMPASS data in the region of low Bjorken scaling variable $x$ and low photon virtuality $Q^2$. The data were taken in 2007 and 2011 from scattering of polarised muons off polarised protons, resulting in a sample that is 150 times larger than the one from the previous experiment SMC that pioneered studies in this kinematic region. For the first time, $A_1^p$ and $g_1^p$ were evaluated in this region in two-dimensional bins of kinematic variables: $(x,Q^2)$, $(\nu ,Q^2)$, $(x,\nu)$ and $(Q^2,x)$. The following kinematic region was investigated: $4\times 10^{-5}<x<4\times 10^{-2}$, $0.001$~(GeV/$c$)$^2<Q^2<1$~(GeV/$c$)$^2$ and $14$~GeV$<\nu <194$~GeV. The obtained results were confronted with theoretical models.

### Avoiding common pitfalls and misconceptions in extractions of the proton radius [Cross-Listing]

In a series of recent publications, different authors produce a wide range of electron radii when reanalyzing electron proton scattering data. In the light of the proton radius puzzle, this is a most unfortunate situation. However, we find flaws in most analyses that result in radii around 0.84 fm. In this paper, we explain our reasoning and try to illustrate the most common pitfalls.

### Avoiding common pitfalls and misconceptions in extractions of the proton radius

In a series of recent publications, different authors produce a wide range of electron radii when reanalyzing electron proton scattering data. In the light of the proton radius puzzle, this is a most unfortunate situation. However, we find flaws in most analyses that result in radii around 0.84 fm. In this paper, we explain our reasoning and try to illustrate the most common pitfalls.

### Avoiding common pitfalls and misconceptions in extractions of the proton radius [Cross-Listing]

In a series of recent publications, different authors produce a wide range of electron radii when reanalyzing electron proton scattering data. In the light of the proton radius puzzle, this is a most unfortunate situation. However, we find flaws in most analyses that result in radii around 0.84 fm. In this paper, we explain our reasoning and try to illustrate the most common pitfalls.

### Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR [Replacement]

Simulation results for future measurements of electromagnetic proton form factors at \PANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel $\bar p p \to e^+ e^-$ is studied on the basis of two different but consistent procedures. The suppression of the main background channel, $\textit{i.e.}$ $\bar p p \to \pi^+ \pi^-$, is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance.

### Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR [Replacement]

Simulation results for future measurements of electromagnetic proton form factors at \PANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel $\bar p p \to e^+ e^-$ is studied on the basis of two different but consistent procedures. The suppression of the main background channel, $\textit{i.e.}$ $\bar p p \to \pi^+ \pi^-$, is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance.

### Hot spots and the hollowness of proton-proton interactions at high energies

We present a dynamical explanation of the hollowness effect observed in proton-proton scattering at $\sqrt s\!=\!7$ TeV. This phenomenon, not observed at lower energies, consists in a depletion of the inelasticity density at zero impact parameter of the collision. Our analysis is based on three main ingredients: we rely gluonic hot spots inside the proton as effective degrees of freedom for the description of the scattering process. Next we assume that some non-trivial correlation between the transverse positions of the hot spots inside the proton exists. Finally we build the scattering amplitude from a multiple scattering, Glauber-like series of collisions between hot spots. In our approach, the onset of the hollowness effect is naturally explained as due to the diffusion or growth of the hot spots in the transverse plane with increasing collision energy.

### A Determination of the Charm Content of the Proton [Replacement]

We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.

### A Determination of the Charm Content of the Proton [Replacement]

We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.

### A Determination of the Charm Content of the Proton

We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.

### A Determination of the Charm Content of the Proton [Cross-Listing]

We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.

### A Determination of the Charm Content of the Proton [Replacement]

We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.

### A Determination of the Charm Content of the Proton [Replacement]

We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.

### Electrophobic Scalar Boson and Muonic Puzzles

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed.

### Electrophobic Scalar Boson and Muonic Puzzles [Cross-Listing]

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed.

### Electrophobic Scalar Boson and Muonic Puzzles [Cross-Listing]

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed.

### Electrophobic Scalar Boson and Muonic Puzzles [Cross-Listing]

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed.

### Electrophobic Scalar Boson and Muonic Puzzles [Replacement]

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed.

### Electrophobic Scalar Boson and Muonic Puzzles [Replacement]

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed.