Posts Tagged proton

Recent Postings from proton

Twist Three Generalized Parton Distributions for Orbital Angular Momentum

We study the orbital angular momentum contribution to the spin structure of the proton. It is well known that the quark and gluon spin contributions do not add up to the proton spin. We motivate the connection between the Generalized Transverse Momentum Distribution (GTMD) $F_{14}$, and orbital angular momentum by exploring the underlying quark proton helicity amplitude structure. The twist three Generalized Parton Distribution (GPD) $\tilde{E}_{2T}$, was shown to connect to OAM. We study these functions using a diquark model calculation. The GTMD $F_{14}$ is unique in that it can describe both Jaffe-Manohar and Ji OAM depending on choice of gauge link, i.e. whether final state interactions are included or not. We perform a calculation of $F_{14}$ in both scenarios.

Measuring the Weak Charge of the Proton via Elastic Electron-Proton Scattering

The Qweak experiment which ran at Jefferson Lab in Newport News, VA, measured the weak charge of the proton $Q_W^p$ via elastic electron-proton scattering. Longitudinally polarized electrons were scattered from an unpolarized liquid hydrogen target. The Standard Model predicts a small parity-violating asymmetry of scattering rates between electron right and left helicity states due to the weak interaction. An initial result using 4% of the data was published in October 2013 with a measured parity-violating asymmetry of $-279\pm 35(\text{stat})\pm 31$ (syst) parts per billion (ppb). This asymmetry, along with other data from parity-violating electron scattering experiments, provided the world's first determination of the weak charge of the proton. The weak charge of the proton was found to be $Q_W^p=0.064\pm0.012$, in agreement with the Standard Model prediction of $Q_W^p(SM)=0.0708\pm0.0003$. The results of the full dataset are expected to decrease the statistical error from the initial publication by a factor of 4-5. The level of precision of the final result makes it a useful test of Standard Model predictions and particularly of the "running" of $\sin^2\theta_W$ from the Z-mass to low energies. This thesis focuses on reduction of systematic error in two key systematics for the Qweak experiment. First, techniques for measuring and removing false asymmetries arising from helicity-correlated electron beam properties at the few ppb level are discussed. Second, as a parity-violating experiment, Qweak relies on accurate knowledge of electron beam polarimetry. To help address the requirement of accurate polarimetry, a Compton polarimeter built specifically for Qweak. Compton polarimetry requires accurate knowledge of laser polarization inside a Fabry-Perot cavity enclosed in the electron beam pipe. A new technique was developed for Qweak that nearly eliminates this systematic error.

Wigner distribution and orbital angular momentum of a proton

The Wigner distributions for u and d quarks in a proton are calculated using the light front wave functions (LFWFs) of the scalar quark-diquark model for nucleon constructed from the soft-wall AdS/QCD correspondence. We present a detail study of the quark orbital angular momentum(OAM) and its correlation with quark spin and proton spin. The quark density distributions, considering the different polarizations of quarks and proton, in transverse momentum plane as well as in transverse impact parameter plane are presented for both u and d quarks.

Beam-Energy and Centrality Dependence of Directed Flow of Identified Particles [Cross-Listing]

These proceedings present directed flow ($v_1$) measurements in Au+Au collisions from STAR's Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider, for $p$, $\bar{p}$, $\Lambda$, $\bar\Lambda$, $K^\pm$, $K^0_S$ and $\pi^\pm$. At intermediate centrality, protons show a minimum in directed flow slope, $dv_1/dy\,|_{y\leq0.8}$, as a function of beam energy. Proton $dv_1/dy$ changes sign near 10 GeV, and the directed flow for $\Lambda$ is consistent with the proton result. The directed flow slope for net protons shows a clear minimum at 14.5 GeV and becomes positive at beam energies below 10 GeV and above 30 GeV. New results for net-kaon directed flow slope resemble net protons from high energy down to 14.5 GeV, but remain negative at lower energies. The slope $dv_1/dy$ shows a strong centrality dependence, especially for $p$ and $\Lambda$ at the lower beam energies. Available model calculations are in poor agreement.

Beam-Energy and Centrality Dependence of Directed Flow of Identified Particles

These proceedings present directed flow ($v_1$) measurements in Au+Au collisions from STAR's Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider, for $p$, $\bar{p}$, $\Lambda$, $\bar\Lambda$, $K^\pm$, $K^0_S$ and $\pi^\pm$. At intermediate centrality, protons show a minimum in directed flow slope, $dv_1/dy\,|_{y\leq0.8}$, as a function of beam energy. Proton $dv_1/dy$ changes sign near 10 GeV, and the directed flow for $\Lambda$ is consistent with the proton result. The directed flow slope for net protons shows a clear minimum at 14.5 GeV and becomes positive at beam energies below 10 GeV and above 30 GeV. New results for net-kaon directed flow slope resemble net protons from high energy down to 14.5 GeV, but remain negative at lower energies. The slope $dv_1/dy$ shows a strong centrality dependence, especially for $p$ and $\Lambda$ at the lower beam energies. Available model calculations are in poor agreement.

A direct probe of the intrinsic charm content of the proton

Measurement of $Z$ bosons produced in association with charm jets $(Zc)$ in proton-proton collisions in the forward region provides a direct probe of a potential non-perturbative (intrinsic) charm component in the proton wave function. We provide a detailed study of the potential to measure $Zc$ production at the LHCb experiment in Runs 2 and 3 of the LHC. The sensitivity to valence-like (sea-like) intrinsic charm is predicted to be $\langle x \rangle_{\rm IC} \gtrsim 0.3\%(1\%)$. The impact of intrinsic charm on Higgs production at the LHC, including $Hc$, is also discussed in detail.

A direct probe of the intrinsic charm content of the proton [Replacement]

Measurement of $Z$ bosons produced in association with charm jets $(Zc)$ in proton-proton collisions in the forward region provides a direct probe of a potential non-perturbative (intrinsic) charm component in the proton wave function. We provide a detailed study of the potential to measure $Zc$ production at the LHCb experiment in Runs 2 and 3 of the LHC. The sensitivity to valence-like (sea-like) intrinsic charm is predicted to be $\langle x \rangle_{\rm IC} \gtrsim 0.3\%(1\%)$. The impact of intrinsic charm on Higgs production at the LHC, including $Hc$, is also discussed in detail.

A direct probe of the intrinsic charm content of the proton [Replacement]

Measurement of $Z$ bosons produced in association with charm jets $(Zc)$ in proton-proton collisions in the forward region provides a direct probe of a potential non-perturbative (intrinsic) charm component in the proton wave function. We provide a detailed study of the potential to measure $Zc$ production at the LHCb experiment in Runs 2 and 3 of the LHC. The sensitivity to valence-like (sea-like) intrinsic charm is predicted to be $\langle x \rangle_{\rm IC} \gtrsim 0.3\%(1\%)$. The impact of intrinsic charm on Higgs production at the LHC, including $Hc$, is also discussed in detail.

Gluon Polarization in Longitudinally Polarized $pp$ Collisions at STAR [Cross-Listing]

The STAR Collaboration is performing a wide range of measurements to determine the gluon helicity distribution in the proton. Gluon-gluon and quark-gluon scattering dominate jet production in proton-proton collisions at RHIC, so the longitudinal double-spin asymmetry, $A_{LL}$, for jet production places significant constraints on the gluon polarization in the proton. In recent years STAR has recorded large longitudinally polarized $pp$ data sets at both $\sqrt{s} = 200$ GeV and $510$ GeV. The 2009 STAR inclusive jet $A_{LL}$ measurements at $\sqrt{s} = 200$ GeV show the first experimental evidence of non-zero gluon polarization over the Bjorken-$x$ range, $x > 0.05$. Furthermore, data collected at $\sqrt{s} = 510$ GeV during the 2012 and 2013 RHIC runs allow access to the gluon polarization at lower $x$. In this talk, I will present the final results of the 2009 inclusive jet $A_{LL}$ measurement at $200$ GeV, the analysis status of the 2012 inclusive jet $A_{LL}$ measurement at $510$ GeV, and the status of di-jet and other STAR measurements that are sensitive to gluon polarization.

Gluon Polarization in Longitudinally Polarized $pp$ Collisions at STAR

The STAR Collaboration is performing a wide range of measurements to determine the gluon helicity distribution in the proton. Gluon-gluon and quark-gluon scattering dominate jet production in proton-proton collisions at RHIC, so the longitudinal double-spin asymmetry, $A_{LL}$, for jet production places significant constraints on the gluon polarization in the proton. In recent years STAR has recorded large longitudinally polarized $pp$ data sets at both $\sqrt{s} = 200$ GeV and $510$ GeV. The 2009 STAR inclusive jet $A_{LL}$ measurements at $\sqrt{s} = 200$ GeV show the first experimental evidence of non-zero gluon polarization over the Bjorken-$x$ range, $x > 0.05$. Furthermore, data collected at $\sqrt{s} = 510$ GeV during the 2012 and 2013 RHIC runs allow access to the gluon polarization at lower $x$. In this talk, I will present the final results of the 2009 inclusive jet $A_{LL}$ measurement at $200$ GeV, the analysis status of the 2012 inclusive jet $A_{LL}$ measurement at $510$ GeV, and the status of di-jet and other STAR measurements that are sensitive to gluon polarization.

LHCb results from proton ion collisions

Proton-lead and lead-proton data taking during 2013 has allowed LHCb to expand its physics program to heavy ion physics. Results include the first forward measurement of Z production in proton-lead collisions as well as a measurement of the nuclear modification factor and forward-backward production of prompt and displaced J/$\psi$, $\psi$(2S) and $\Upsilon$. Angular particle correlations have also been measured for events of varying charged particle activity.

LHCb results from proton ion collisions [Cross-Listing]

Proton-lead and lead-proton data taking during 2013 has allowed LHCb to expand its physics program to heavy ion physics. Results include the first forward measurement of Z production in proton-lead collisions as well as a measurement of the nuclear modification factor and forward-backward production of prompt and displaced J/$\psi$, $\psi$(2S) and $\Upsilon$. Angular particle correlations have also been measured for events of varying charged particle activity.

LHCb results from proton ion collisions [Cross-Listing]

Proton-lead and lead-proton data taking during 2013 has allowed LHCb to expand its physics program to heavy ion physics. Results include the first forward measurement of Z production in proton-lead collisions as well as a measurement of the nuclear modification factor and forward-backward production of prompt and displaced J/$\psi$, $\psi$(2S) and $\Upsilon$. Angular particle correlations have also been measured for events of varying charged particle activity.

The spin of the proton in chiral effective field theory

Proton spin is investigated in chiral effective field theory through an examination of the singlet axial charge, $a_0$, and the two non-singlet axial charges, $a_3$ and $a_8$. Finite-range regularization is considered as it provides an effective model for estimating the role of disconnected sea-quark loop contributions to baryon observables. Baryon octet and decuplet intermediate states are included to enrich the spin and flavour structure of the nucleon, redistributing spin under the constraints of chiral symmetry. In this context, the proton spin puzzle is well understood with the calculation describing all three of the axial charges reasonably well. The strange quark contribution to the proton spin is negative with magnitude 0.01. With appropriate $Q^2$ evolution, we find the singlet axial charge at the experimental scale to be ${\hat a}_0 = 0.31^{+0.04}_{-0.05}$, consistent with the range of current experimental values.

Heavy quarks in proton-nucleus collisions - the hybrid formalism

We explore the quark mass effects on inclusive hadron production in proton-nucleus collisions at high energies. We consider two processes. First, we compute the single inclusive cross-section for production of hadrons with open heavy flavour in the proton forward direction at leading order. Next, in the same kinematics, we calculate the heavy-quark contribution to single inclusive production of light or unidentified hadrons at next-to-leading-order. For both studies we exploit the hybrid formalism, that is the collinear factorisation on the proton side while high-density and high-energy effects are resummed on the side of the nucleus.

Comment on "Evidence for narrow resonant structures at $W\approx$ 1.68 GeV and $W\approx$ 1.72 GeV in real Compton scattering off the proton" [Cross-Listing]

We comment on the statement by Kuznetsov et al. that the structure around W=1.72 GeV seen in the beam asymmetry in Compton scattering off the proton is not observed in the total cross section of $\eta$ photoproduction on the neutron.

Comment on "Evidence for narrow resonant structures at $W\approx$ 1.68 GeV and $W\approx$ 1.72 GeV in real Compton scattering off the proton"

We comment on the statement by Kuznetsov et al. that the structure around W=1.72 GeV seen in the beam asymmetry in Compton scattering off the proton is not observed in the total cross section of $\eta$ photoproduction on the neutron.

Comment on "Evidence for narrow resonant structures at $W\approx$ 1.68 GeV and $W\approx$ 1.72 GeV in real Compton scattering off the proton" [Replacement]

We comment on the statement by Kuznetsov et al. that the structure around W=1.72 GeV seen in the beam asymmetry in Compton scattering off the proton is not observed in the total cross section of $\eta$ photoproduction on the neutron.

Comment on "Evidence for narrow resonant structures at $W\approx$ 1.68 GeV and $W\approx$ 1.72 GeV in real Compton scattering off the proton" [Replacement]

We comment on the statement by Kuznetsov et al. that the structure around W=1.72 GeV seen in the beam asymmetry in Compton scattering off the proton is not observed in the total cross section of $\eta$ photoproduction on the neutron.

Comment on "Evidence for narrow resonant structures at $W\approx$ 1.68 GeV and $W\approx$ 1.72 GeV in real Compton scattering off the proton" [Replacement]

We comment on the statement by Kuznetsov et al. that the structure around W=1.72 GeV seen in the beam asymmetry in Compton scattering off the proton is not observed in the total cross section of $\eta$ photoproduction on the neutron.

Effect of correlation on cumulants in heavy-ion collisions [Cross-Listing]

We study the effects of correlation on cumulants and their ratios of net-proton multiplicity distribution which have been measured for central (0-5\%) Au+Au collisions at Relativistic Heavy Ion Collider (RHIC). This effect has been studied assuming individual proton and anti-proton distributions as Poisson or Negative Binomial Distribution (NBD). In-spite of significantly correlated production due to baryon number, electric charge conservation and kinematical correlations of protons and anti-protons, the measured cumulants of net-proton distribution follow the independent production model. In the present work we demonstrate how the introduction of correlations will affect the cumulants and their ratios for the difference distributions. We have also demonstrated this study using the proton and anti-proton distributions obtained from HIJING event generator.

Self-similarity of proton spin and z-scaling

The concept of z-scaling previously developed for analysis of inclusive reactions in proton-proton collisions is applied for description of processes with polarized particles. Hypothesis of self-similarity of the proton spin structure is discussed. The possibility of extracting information on spin-dependent fractal dimensions of hadrons and fragmentation process from the cross sections and asymmetries is justified. The double longitudinal spin asymmetry A_{LL} of jet and pi0-meson production and the coefficient of polarization transfer D_{LL} measured in proton-proton collisions at sqrt s = 200 GeV at RHIC are analyzed in the framework of z-scaling. The spin-dependent fractal dimension of proton is estimated.

Centrality dependence of elliptic flow of multi-strange hadrons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

We present recent results of the mid-rapidity elliptic flow ($v_2$) for multi-strange hadrons and the $\phi$ meson as a function of centrality in Au + Au collisions at the center of mass energy $\sqrt{s_{NN}}$ = 200 GeV. The transverse momentum dependence of $\phi$ and $\Omega$ $v_2$ is similar to that of pion and proton, indicating that the heavier strange ($s$) quark flows as strongly as the lighter up ($u$) and down ($d$) quarks. These observations constitute a clear piece of evidence for the development of partonic collectivity in heavy-ion collisions at the top RHIC energy. In addition, the mass ordering of $v_2$ breaks between the $\phi$ and proton at low transverse momenta in the 0-30\% centrality bin, possibly due to the effect of late hadronic interactions on the proton $v_2$.

Centrality dependence of elliptic flow of multi-strange hadrons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

We present recent results of the mid-rapidity elliptic flow ($v_2$) for multi-strange hadrons and the $\phi$ meson as a function of centrality in Au + Au collisions at the center of mass energy $\sqrt{s_{NN}}$ = 200 GeV. The transverse momentum dependence of $\phi$ and $\Omega$ $v_2$ is similar to that of pion and proton, indicating that the heavier strange ($s$) quark flows as strongly as the lighter up ($u$) and down ($d$) quarks. These observations constitute a clear piece of evidence for the development of partonic collectivity in heavy-ion collisions at the top RHIC energy. In addition, the mass ordering of $v_2$ breaks between the $\phi$ and proton at low transverse momenta in the 0-30\% centrality bin, possibly due to the effect of late hadronic interactions on the proton $v_2$.

Hanbury-Brown-Twiss measurements at large rapidity separations, or can we measure the proton radius in p-A collisions?

We point out that current calculations of inclusive two-particle correlations in p-A collisions based on the Color Glass Condensate approach exhibit a contribution from Hanbury-Brown-Twiss correlations. These HBT correlations are quite distinct from the standard ones, in that they are apparent for particles widely separated in rapidity. The transverse size of the emitter which is reflected in these correlations is the gluonic size of the proton. This raises an interesting possibility of measuring the proton size directly by the HBT effect of particle pairs produced in p-A collisions.

Hanbury-Brown-Twiss measurements at large rapidity separations, or can we measure the proton radius in p-A collisions? [Replacement]

We point out that current calculations of inclusive two-particle correlations in p-A collisions based on the Color Glass Condensate approach exhibit a contribution from Hanbury-Brown-Twiss correlations. These HBT correlations are quite distinct from the standard ones, in that they are apparent for particles widely separated in rapidity. The transverse size of the emitter which is reflected in these correlations is the gluonic size of the proton. This raises an interesting possibility of measuring the proton size directly by the HBT effect of particle pairs produced in p-A collisions.

Evaluation of the forward Compton scattering off protons: I. Spin-independent amplitude [Replacement]

We evaluate the forward Compton scattering off the proton, based on Kramers-Kronig kind of relations which express the Compton amplitudes in terms of integrals of total photoabsorption cross sections. We obtain two distinct fits to the world data on the unpolarized total photoabsorption cross section, and evaluate the various spin-independent sum rules using these fits. For the sum of proton electric and magnetic dipole polarizabilities, governed by the Baldin sum rule, we obtain the following average (between the two fits): $\alpha_{E1}+\beta_{M1}=14.0(2)\times 10^{-4}\,\mathrm{fm}^3$. An analogous sum rule involving the quadrupole polarizabilities of the proton is evaluated too. The spin-independent forward amplitude of proton Compton scattering is evaluated in a broad energy range. The results are compared with previous evaluations and the only experimental data point for this amplitude (at 2.2 GeV). We remark on sum rules for the elastic component of polarizabilities.

Evaluation of the forward Compton scattering off protons: I. Spin-independent amplitude [Replacement]

We evaluate the forward Compton scattering off the proton, based on Kramers-Kronig kind of relations which express the Compton amplitudes in terms of integrals of total photoabsorption cross sections. We obtain two distinct fits to the world data on the unpolarized total photoabsorption cross section, and evaluate the various spin-independent sum rules using these fits. For the sum of proton electric and magnetic dipole polarizabilities, governed by the Baldin sum rule, we obtain the following average (between the two fits): $\alpha_{E1}+\beta_{M1}=14.0(2)\times 10^{-4}\,\mathrm{fm}^3$. An analogous sum rule involving the quadrupole polarizabilities of the proton is evaluated too. The spin-independent forward amplitude of proton Compton scattering is evaluated in a broad energy range. The results are compared with previous evaluations and the only experimental data point for this amplitude (at 2.2 GeV). We remark on sum rules for the elastic component of polarizabilities.

Evaluation of the forward Compton scattering off protons: I. Spin-independent amplitude [Replacement]

We evaluate the forward Compton scattering off the proton, based on Kramers-Kronig kind of relations which express the Compton amplitudes in terms of integrals of total photoabsorption cross sections. We obtain two distinct fits to the world data on the unpolarized total photoabsorption cross section, and evaluate the various spin-independent sum rules using these fits. For the sum of proton electric and magnetic dipole polarizabilities, governed by the Baldin sum rule, we obtain the following average (between the two fits): $\alpha_{E1}+\beta_{M1}=14.0(2)\times 10^{-4}\,\mathrm{fm}^3$. An analogous sum rule involving the quadrupole polarizabilities of the proton is evaluated too. The spin-independent forward amplitude of proton Compton scattering is evaluated in a broad energy range. The results are compared with previous evaluations and the only experimental data point for this amplitude (at 2.2 GeV). We remark on sum rules for the elastic component of polarizabilities.

Evaluation of the forward Compton scattering off protons: I. Spin-independent amplitude [Cross-Listing]

We evaluate the forward Compton scattering off the proton, based on Kramers-Kronig kind of relations which express the Compton amplitudes in terms of integrals of total photoabsorption cross sections. We obtain two distinct fits to the world data on the unpolarized total photoabsorption cross section, and evaluate the various spin-independent sum rules using these fits. For the sum of proton electric and magnetic dipole polarizabilities, governed by the Baldin sum rule, we obtain the following average (between the two fits): $\alpha_{E1}+\beta_{M1}=(14.0\pm 0.20)\times 10^{-4}\,\mathrm{fm}^3$. An analogous sum rule involving the quadrupole polarizabilities is evaluated here too. The spin-independent forward amplitude of proton Compton scattering is evaluated in a broad energy range. The results are compared with previous evaluations and the only experimental data point for this amplitude (at 2.2 GeV). We also remark on sum rules for the elastic component of polarizabilities.

On the proton charge extensions

We examine how corrections to $S$-state energy levels, $ E_{nS}$, in hydrogenic atoms due to the finite proton size are affected by moments of the proton charge distribution. The corrections to $E_{nS}$ are computed moment by moment. The results demonstrate that the next-to-leading order term in the expansion is of order $r_p / a_B $ times the size of the leading order $ \langle r_p^2 \rangle $ term. Our analysis thus dispels any concern that the larger relative size of this term for muonic hydrogen versus electronic hydrogen might account for the outstanding discrepancy of proton radius measurements extracted from the two systems. Furthermore, the next-to-leading order term in powers of $r_p / a_B $ that we derive from a dipole proton form factor is proportional to $\langle r_p^3 \rangle $, rather than $\langle r_p^4 \rangle$ as would be expected from the scalar nature of the form factor. The dependence of the finite-size correction on $\langle r_p^3 \rangle $ and higher odd-power moments is shown to be a general result for any spherically symmetric proton charge distribution. A method for computing the moment expansion of the finite-size correction to arbitrary order is introduced and the results are tabulated for principal quantum numbers up to $n=7$.

Neutrino oscillations in accelerated states

We discuss the inverse $\beta$-decay of accelerated protons in the context of neutrino oscillations. The process $p\rightarrow n \ell^+ \nu_\ell$ is kinematically allowed because the accelerating field provides the rest energy difference between initial and final states. The rate of $p\to n$ conversions can be evaluated in either the laboratory frame (where the proton is accelerating) or the co-moving frame (where the proton is at rest and interacts with an effective thermal bath of $\ell$ and $\nu_\ell$ due to the Unruh effect). By explicit calculation, we show the rates in the two frames disagree when taking into account neutrino oscillations, because the weak interaction couples to charge eigenstates whereas gravity couples to neutrino mass eigenstates. The contradiction could be resolved experimentally, potentially yielding new information on the origins of neutrino masses.

Neutrino oscillations in accelerated states [Cross-Listing]

We discuss the inverse $\beta$-decay of accelerated protons in the context of neutrino oscillations. The process $p\rightarrow n \ell^+ \nu_\ell$ is kinematically allowed because the accelerating field provides the rest energy difference between initial and final states. The rate of $p\to n$ conversions can be evaluated in either the laboratory frame (where the proton is accelerating) or the co-moving frame (where the proton is at rest and interacts with an effective thermal bath of $\ell$ and $\nu_\ell$ due to the Unruh effect). By explicit calculation, we show the rates in the two frames disagree when taking into account neutrino oscillations, because the weak interaction couples to charge eigenstates whereas gravity couples to neutrino mass eigenstates. The contradiction could be resolved experimentally, potentially yielding new information on the origins of neutrino masses.

Strong diquark correlations inside the proton [Cross-Listing]

Quantum Chromodynamics is thought to be the relativistic quantum field theory that describes the strong interaction of the Standard Model. This interaction produces mesons but it is also able to generate quark-quark (diquark) correlations inside baryons. In this work, we employ a continuum approach to QCD based on Dyson-Schwinger equations to calculate the electromagnetic form factors of the proton and analyze in a deeper way the consequences of having strong diquark correlations. Comparison with the experimental data reveals that the presence of strong diquark correlations within the proton is sufficient to understand empirical extractions of the flavour-separated form factors. The explained reduction of the ratios $F_{1}^{d}/F_{1}^{u}$ and $F_{2}^{d}/F_{2}^{u}$ at high $Q^{2}$ in the quark-diquark picture are responsible of the precocious scaling of the $F_{2}^{p}/F_{1}^{p}$ observed experimentally.

Strong diquark correlations inside the proton [Cross-Listing]

Quantum Chromodynamics is thought to be the relativistic quantum field theory that describes the strong interaction of the Standard Model. This interaction produces mesons but it is also able to generate quark-quark (diquark) correlations inside baryons. In this work, we employ a continuum approach to QCD based on Dyson-Schwinger equations to calculate the electromagnetic form factors of the proton and analyze in a deeper way the consequences of having strong diquark correlations. Comparison with the experimental data reveals that the presence of strong diquark correlations within the proton is sufficient to understand empirical extractions of the flavour-separated form factors. The explained reduction of the ratios $F_{1}^{d}/F_{1}^{u}$ and $F_{2}^{d}/F_{2}^{u}$ at high $Q^{2}$ in the quark-diquark picture are responsible of the precocious scaling of the $F_{2}^{p}/F_{1}^{p}$ observed experimentally.

Strong diquark correlations inside the proton [Cross-Listing]

Quantum Chromodynamics is thought to be the relativistic quantum field theory that describes the strong interaction of the Standard Model. This interaction produces mesons but it is also able to generate quark-quark (diquark) correlations inside baryons. In this work, we employ a continuum approach to QCD based on Dyson-Schwinger equations to calculate the electromagnetic form factors of the proton and analyze in a deeper way the consequences of having strong diquark correlations. Comparison with the experimental data reveals that the presence of strong diquark correlations within the proton is sufficient to understand empirical extractions of the flavour-separated form factors. The explained reduction of the ratios $F_{1}^{d}/F_{1}^{u}$ and $F_{2}^{d}/F_{2}^{u}$ at high $Q^{2}$ in the quark-diquark picture are responsible of the precocious scaling of the $F_{2}^{p}/F_{1}^{p}$ observed experimentally.

Recoil Polarization Measurements of the Proton Electromagnetic Form Factor Ratio to High Momentum Transfer [Cross-Listing]

The electromagnetic form factors of the nucleon characterize the effect of its internal structure on its response to an electromagnetic probe as studied in elastic electron-nucleon scattering. These form factors are functions of the squared four-momentum transfer $Q^2$ between the electron and the proton. The two main classes of observables of this reaction are the scattering cross section and polarization asymmetries, both of which are sensitive to the form factors in different ways. When considering large momentum transfers, double-polarization observables offer superior sensitivity to the electric form factor. This thesis reports the results of a new measurement of the ratio of the electric and magnetic form factors of the proton at high momentum transfer using the recoil polarization technique. A polarized electron beam was scattered from a liquid hydrogen target, transferring polarization to the recoiling protons. These protons were detected in a magnetic spectrometer which was used to reconstruct their kinematics, including their scattering angles and momenta, and the position of the interaction vertex. A proton polarimeter measured the polarization of the recoiling protons by measuring the azimuthal asymmetry in the angular distribution of protons scattered in CH$_2$ analyzers. The scattered electron was detected in a large-acceptance electromagnetic calorimeter in order to suppress inelastic backgrounds. The measured ratio of the transverse and longitudinal polarization components of the scattered proton is directly proportional to the ratio of form factors $G_E^p/G_M^p$. The measurements reported in this thesis took place at $Q^2=$5.2, 6.7, and 8.5 GeV$^2$, and represent the most accurate measurements of $G_E^p$ in this $Q^2$ region to date.

Kinetic Alfv\'en waves generation by large-scale phase-mixing

One view of the solar-wind turbulence is that the observed highly anisotropic fluctuations at spatial scales near the proton inertial length $d_p$ may be considered as Kinetic Alfv\'en waves (KAWs). In the present paper, we show how phase-mixing of large-scale parallel propagating Alfv\'en waves is an efficient mechanism for the production of KAWs at wavelengths close to $d_p$ and at large propagation angle with respect to the magnetic field. Magnetohydrodynamic (MHD), Hall-Magnetohydrodynamic (HMHD), and hybrid Vlasov-Maxwell (HVM) simulations modeling the propagation of Alfv\'en waves in inhomogeneous plasmas are performed. In linear regime, the role of dispersive effects is singled out by comparing MHD and HMHD results. Fluctuations produced by phase-mixing are identified as KAWs through a comparison of polarization of magnetic fluctuations and wave group velocity with analytical linear predictions. In the nonlinear regime, comparison of HMHD and HVM simulations allows to point out the role of kinetic effects in shaping the proton distribution function. We observe generation of temperature anisotropy with respect to the local magnetic field and production of field-aligned beams. The regions where the proton distribution function highly departs from thermal equilibrium are located inside the shear layers, where the KAWs are excited, this suggesting that the distortions of the proton distribution are driven by a resonant interaction of protons with KAW fluctuations. Our results are relevant in configurations where magnetic field inhomogeneities are present, as, for example, in the solar corona where the presence of Alfv\'en waves has been ascertained.

Role of pentaquark components in $\phi$ meson production proton-antiproton annihilation reactions [Replacement]

The pentaquark component is included in the proton wave functions to study phi meson production proton-antiproton annihilation reactions. With all possible configurations of the uuds subsystem proposed for describing the strangeness spin and magnetic moment of the proton, we estimate the branching ratios of the annihilation reactions at rest proton-antiproton to phi + X (X=pi, eta, rho, omega) from atomic proton-antiproton S- and P-wave states by using effective quark line diagrams incorporating the 3P0 model. The best agreement of theoretical prediction with the experimental data is found when the pentaquark configuration of the proton wave function takes the flavor-spin symmetry, [4]_FS [22]_F [22]_S.

Role of pentaquark components in $\phi$ meson production proton-antiproton annihilation reactions

The pentaquark component is included in the proton wave functions to study phi meson production proton-antiproton annihilation reactions. With all possible configurations of the uuds subsystem proposed for describing the strangeness spin and magnetic moment of the proton, we estimate the branching ratios of the annihilation reactions at rest proton-antiproton to phi + X (X=pi, eta, rho, omega) from atomic proton-antiproton S- and P-wave states by using effective quark line diagrams incorporating the 3P0 model. The best agreement of theoretical prediction with the experimental data is found when the pentaquark configuration of the proton wave function takes the flavor-spin symmetry, [4]_FS [22]_F [22]_S.

Measurement of exclusive $\gamma\gamma\rightarrow \ell^+\ell^-$ production in proton-proton collisions at $\sqrt{s} = 7$ TeV with the ATLAS detector

This Letter reports a measurement of the exclusive $\gamma\gamma\rightarrow \ell^+\ell^- (\ell=e, \mu)$ cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of $4.6$ fb$^{-1}$. For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be $\sigma_{\gamma\gamma\rightarrow e^+e^-}^{\mathrm{excl.}} = 0.428 \pm 0.035 (\mathrm{stat.}) \pm 0.018 (\mathrm{syst.})$ pb for a phase-space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum $p_\mathrm{T}>12$ GeV and pseudorapidity $|\eta|<2.4$. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum $p_\mathrm{T}>10$ GeV and pseudorapidity $|\eta|<2.4$, the cross-section is determined to be $\sigma_{\gamma\gamma\rightarrow \mu^+\mu^- }^{\mathrm{excl.}} = 0.628 \pm 0.032 (\mathrm{stat.}) \pm 0.021 (\mathrm{syst.})$ pb. When proton absorptive effects due to the finite size of the proton are taken into account in the theory calculation, the measured cross-sections are found to be consistent with the theory prediction.

Measurement of exclusive $\gamma\gamma\rightarrow \ell^+\ell^-$ production in proton-proton collisions at $\sqrt{s} = 7$ TeV with the ATLAS detector [Replacement]

This Letter reports a measurement of the exclusive $\gamma\gamma\rightarrow \ell^+\ell^- (\ell=e, \mu)$ cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of $4.6$ fb$^{-1}$. For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be $\sigma_{\gamma\gamma\rightarrow e^+e^-}^{\mathrm{excl.}} = 0.428 \pm 0.035 (\mathrm{stat.}) \pm 0.018 (\mathrm{syst.})$ pb for a phase-space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum $p_\mathrm{T}>12$ GeV and pseudorapidity $|\eta|<2.4$. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum $p_\mathrm{T}>10$ GeV and pseudorapidity $|\eta|<2.4$, the cross-section is determined to be $\sigma_{\gamma\gamma\rightarrow \mu^+\mu^- }^{\mathrm{excl.}} = 0.628 \pm 0.032 (\mathrm{stat.}) \pm 0.021 (\mathrm{syst.})$ pb. When proton absorptive effects due to the finite size of the proton are taken into account in the theory calculation, the measured cross-sections are found to be consistent with the theory prediction.

Jet measurements in polarized p+p collisions at STAR at RHIC [Cross-Listing]

Jet productions in polarized p+p collisions at $\sqrt{s} = 200$ GeV and $\sqrt{s} = 500$ GeV provide powerful probes to study gluons inside the proton. The Solenoidal Tracker at RHIC (STAR) has the capability, with nearly full azimuthal ($2\pi$) coverage, to reconstruct jets at mid-rapidity ($|\eta| < 1$). The latest STAR inclusive jet longitudinal double-spin asymmetry $A_{LL}$ measured in 200 GeV p+p collisions provides better constraints on the polarized gluon distribution $\Delta g(x)$ for $0.05<x<0.2$. A recent global QCD fit which includes the 2009 RHIC results provides the first evidence of non-zero gluon contribution to the proton spin. The new inclusive jet cross section using the anti-$k_{T}$ algorithm provides potential insights into the unpolarized gluon distribution function, and the new inclusive jet $A_{LL}$ measurement in 510 GeV p+p collisions shows consistent $x_{T}$ scaling with the 200 GeV result. Future measurements with continuing high energy polarized proton-proton running at $\sqrt{s} = 500$ GeV at RHIC and detector upgrades in the forward direction will explore the gluonic contribution to the proton spin at low $x$ region.

Jet measurements in polarized p+p collisions at STAR at RHIC

Jet productions in polarized p+p collisions at $\sqrt{s} = 200$ GeV and $\sqrt{s} = 500$ GeV provide powerful probes to study gluons inside the proton. The Solenoidal Tracker at RHIC (STAR) has the capability, with nearly full azimuthal ($2\pi$) coverage, to reconstruct jets at mid-rapidity ($|\eta| < 1$). The latest STAR inclusive jet longitudinal double-spin asymmetry $A_{LL}$ measured in 200 GeV p+p collisions provides better constraints on the polarized gluon distribution $\Delta g(x)$ for $0.05<x<0.2$. A recent global QCD fit which includes the 2009 RHIC results provides the first evidence of non-zero gluon contribution to the proton spin. The new inclusive jet cross section using the anti-$k_{T}$ algorithm provides potential insights into the unpolarized gluon distribution function, and the new inclusive jet $A_{LL}$ measurement in 510 GeV p+p collisions shows consistent $x_{T}$ scaling with the 200 GeV result. Future measurements with continuing high energy polarized proton-proton running at $\sqrt{s} = 500$ GeV at RHIC and detector upgrades in the forward direction will explore the gluonic contribution to the proton spin at low $x$ region.

Jet measurements in polarized p+p collisions at STAR at RHIC [Replacement]

Jet production in polarized $p+p$ collisions at $\sqrt{s} = 200$ GeV and $\sqrt{s} = 500$ GeV provides a powerful probe to study gluons inside the proton. The Solenoidal Tracker at RHIC (STAR) has the capability, with nearly full azimuthal ($2\pi$) coverage, to reconstruct jets at mid-rapidity ($|\eta| < 1$). The latest STAR inclusive jet longitudinal double-spin asymmetry $A_{LL}$ measured in 200 GeV $p+p$ collisions provides better constraints on the polarized gluon distribution $\Delta g(x)$ for $0.05<x<0.2$ than previous measurements. A recent global QCD fit (DSSV 2014) which includes the 2009 RHIC results provides the first evidence of non-zero gluon contribution to the proton spin. A new inclusive jet cross section using the anti-$k_{T}$ algorithm provides potential insights into the unpolarized gluon distribution function, and the new inclusive jet $A_{LL}$ measurement in 510 GeV $p+p$ collisions shows consistent $x_{T}$ scaling with the 200 GeV result. Future measurements with continuing high energy polarized proton-proton running at $\sqrt{s} = 500$ GeV at RHIC and detector upgrades in the forward direction will explore the gluonic contribution to the proton spin at low $x$ region.

Jet measurements in polarized p+p collisions at STAR at RHIC [Replacement]

Jet production in polarized $p+p$ collisions at $\sqrt{s} = 200$ GeV and $\sqrt{s} = 500$ GeV provides a powerful probe to study gluons inside the proton. The Solenoidal Tracker at RHIC (STAR) has the capability, with nearly full azimuthal ($2\pi$) coverage, to reconstruct jets at mid-rapidity ($|\eta| < 1$). The latest STAR inclusive jet longitudinal double-spin asymmetry $A_{LL}$ measured in 200 GeV $p+p$ collisions provides better constraints on the polarized gluon distribution $\Delta g(x)$ for $0.05<x<0.2$ than previous measurements. A recent global QCD fit (DSSV 2014) which includes the 2009 RHIC results provides the first evidence of non-zero gluon contribution to the proton spin. A new inclusive jet cross section using the anti-$k_{T}$ algorithm provides potential insights into the unpolarized gluon distribution function, and the new inclusive jet $A_{LL}$ measurement in 510 GeV $p+p$ collisions shows consistent $x_{T}$ scaling with the 200 GeV result. Future measurements with continuing high energy polarized proton-proton running at $\sqrt{s} = 500$ GeV at RHIC and detector upgrades in the forward direction will explore the gluonic contribution to the proton spin at low $x$ region.

High-resolution hybrid simulations of kinetic plasma turbulence at proton scales

We investigate properties of plasma turbulence from magneto-hydrodynamic (MHD) to sub-ion scales by means of two-dimensional, high-resolution hybrid particle-in-cell simulations. We impose an initial ambient magnetic field, perpendicular to the simulation box, and we add a spectrum of large-scale magnetic and kinetic fluctuations, with energy equipartition and vanishing correlation. Once the turbulence is fully developed, we observe a MHD inertial range, where the spectra of the perpendicular magnetic field and the perpendicular proton bulk velocity fluctuations exhibit power-law scaling with spectral indices of -5/3 and -3/2, respectively. This behavior is extended over a full decade in wavevectors and is very stable in time. A transition is observed around proton scales. At sub-ion scales, both spectra steepen, with the former still following a power law with a spectral index of ~-3. A -2.8 slope is observed in the density and parallel magnetic fluctuations, highlighting the presence of compressive effects at kinetic scales. The spectrum of the perpendicular electric fluctuations follows that of the proton bulk velocity at MHD scales, and flattens at small scales. All these features, which we carefully tested against variations of many parameters, are in good agreement with solar wind observations. The turbulent cascade leads to on overall proton energization with similar heating rates in the parallel and perpendicular directions. While the parallel proton heating is found to be independent on the resistivity, the number of particles per cell and the resolution employed, the perpendicular proton temperature strongly depends on these parameters.

Higher order proton lifetime estimates in grand unified theories

Since the main experimentally testable prediction of grand unified theories is the instability of the proton, precise determination of the proton lifetime for each particular model is desirable. Unfortunately, the corresponding computation usually involves theoretical uncertainties coming e.g. from ignorance of the mass spectrum or from the Planck-suppressed higher-dimensional operators, which may result in errors in the proton lifetime estimates stretching up to several orders of magnitude. On the other hand, we present a model based on SO(10) gauge group which is subsequently broken by a scalar adjoint representation, where the leading Planck-suppressed operator is absent, hence the two-loop precision may be achieved.

High x Structure Function of the Virtually Free Neutron [Replacement]

The pole extrapolation method is applied for the first time to the data on semi-inclusive inelastic scattering off the deuteron with tagged spectator protons to extract the high Bjorken x structure function of the neutron. This approach is based on the extrapolation of the measured cross sections at different momenta of the spectator proton to the non-physical pole of the bound neutron in the deuteron. The advantage of the method is that it makes it possible to suppress nuclear effects in a maximally model independent way. The neutron structure functions obtained in this way demonstrate a surprising $x$ dependence at x\ge 0.6, indicating a possible rise of the neutron to proton structure function ratio. Such a rise may indicate new dynamics in the generation of high-x quarks in the nucleon. One such mechanism we discuss is the possible dominance of short-range isosinglet quark-quark correlations that can enhance the d-quark distribution in the proton.

High x Structure Function of the Virtually Free Neutron

The pole extrapolation method is applied for the first time to data on semi-inclusive deep-inelastic scattering off the deuteron with tagged spectator protons to extract the high Bjorken x structure function of the neutron. This approach is based on the extrapolation of the measured cross sections at different momenta of the detected spectator proton to the non-physical pole of the bound neutron in the deuteron. The advantage of the method is that it makes it possible to suppress nuclear effects in a maximally model independent way. The neutron structure functions obtained in this way demonstrate surprising x dependence at x> 0.6, indicating the possibility of a rise in the neutron to proton structure function ratio. Such a rise may indicate new dynamics in the generation of high x quarks in the nucleon. One such mechanism we discuss is the possible dominance of short-range isosinglet quark-quark correlations that can enhance the d-quark distribution in the proton resulting in d/u -> 1.

 

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