Search

We argue that the Drell-Yan process in the $x_A \ge 0.15$ kinematics recently studied at FNAL by the E906/SeaQuest experiment may allow to observe an analogous of the EMC effect for antiquarks. The effects of Fermi motion and energy loss are considered. The preliminary E906/SeaQuest data are inconsistent with the growth of the $\sigma_A/A\sigma_N$ ratio expected in the Fermi motion scenario at $x_A \ge 0.25$. The pattern of the $x_A$ dependence of the ratio seems also inconsistent with a scenario in which the dominant nuclear effect is a suppression of the cross section due to the energy loss experienced by a quark of the projectile proton involved in the Drell-Yan process. All together the data suggest the possibility of a modification of the antiquark parton distributions in nuclei, with a pattern similar to the one observed in the EMC effect. We argue that optimal kinematics to look for an antiquark EMC-like effect would be to measure the $\sigma_A^{DY}/A\sigma_N^{DY}$ ratios for $x_A$ = 0.2-0.4 and $x_p$ $\approx$ constant., Comment: 22 pages, 5 figures

We present a model of exclusive $\phi$-meson lepto-production $ep \to e'p'\phi$ near threshold which features the strangeness gravitational form factors of the proton. We argue that the shape of the differential cross section $d\sigma/dt$ is a sensitive probe of the strangeness D-term of the proton., Comment: 9 pages

Ultra-peripheral collisions (UPCs) involving heavy ions and protons are the energy frontier for photon-mediated interactions. UPC photons can be used for many purposes, including probing low-$x$ gluons via photoproduction of dijets and vector mesons, probes of beyond-standard-model processes, such as those enabled by light-by-light scattering, and studies of two-photon production of the Higgs., Comment: Letter of Interest submitted to Snowmass 2021

We study sub-threshold heavy quarkonium ($J/\psi$ and $\Upsilon$) photo-productions in $\gamma A$ collisions as an independent test of the universality of the nucleon-nucleon short range correlation (SRC) in nuclear scattering processes. Just below the $\gamma p$ threshold, the cross section is dominated by the mean field contribution of nucleons inside the nucleus. The SRC contributions start to dominate at lower photon energies, depending on the fraction of the SRC pairs in the target nucleus. We give an estimate of the cross sections in the sub-threshold region both for $J/\psi$ and $\Upsilon$. This may be helpful for future measurements at JLab as well as at the Electron-Ion Collider in the U.S., and especially in China., Comment: 7 pages, 5 figures

Three nucleon short range correlations~(SRCs) are one of the most elusive structures in nuclei. Their observation and the subsequent study of their internal makeup will have a significant impact on our understanding of the dynamics of super-dense nuclear matter which exists at the cores of neutron stars. We discuss the kinematic conditions and observables that are most favorable for probing 3N-SRCs in inclusive electro-nuclear processes and make a prediction for a quadratic dependence of the probabilities of finding a nucleon in 2N- and 3N- SRCs. We demonstrate that this prediction is consistent with the limited high energy experimental data available, suggesting that we have observed, for the first time, 3N-SRCs in electro-nuclear processes. Our analysis enables us to extract $a_3(A,Z)$, the probability of finding 3N-SRCs in nuclei relative to the A=3 system., Comment: 7 pages and 4 figures, to be published in Physical Review C

The unambiguous observation of a Chiral Magnetic Effect (CME)-driven charge separation is the core aim of the isobar program at RHIC consisting of ${^{96}_{40}}$Zr+${^{96}_{40}}$Zr and ${^{96}_{44}}$Ru+${^{96}_{44}}$Ru collisions at $\sqrt {s_{\rm NN}}\!=\!200$ GeV. We quantify the role of the spatial distributions of the nucleons in the isobars on both eccentricity and magnetic field strength within a relativistic hadronic transport approach (SMASH, Simulating Many Accelerated Strongly-interacting Hadrons). In particular, we introduce isospin-dependent nucleon-nucleon spatial correlations in the geometric description of both nuclei, deformation for ${^{96}_{44}}$Ru and the so-called neutron skin effect for the neutron-rich isobar i.e. ${^{96}_{40}}$Zr. The main result of this study is a reduction of the magnetic field strength difference between ${^{96}_{44}}$Ru+${^{96}_{44}}$Ru and ${^{96}_{40}}$Zr+${^{96}_{40}}$Zr by a factor of 2, from $10\%$ to $5\%$ in peripheral collisions when the neutron-skin effect is included. Further, we find an increase of eccentricity by up to 10$\%$ when deformation is taken into account while neither the neutron skin effect nor the nucleon-nucleon correlations result into a significant modification of this observable with respect to the traditional Woods-Saxon modeling. Our results suggest a significantly smaller CME signal to background ratio for the experimental charge separation measurement in peripheral collisions with the isobar systems than previously expected., Comment: 6 pages, 3 figures, v2: bug in the implementation of the deformation has been fixed. Conclusions remain intact

Exciting new scientific opportunities are presented for the PANDA detector at the High Energy Storage Ring in the redefined $\overline{\text{p}} \text{p}(A)$ collider mode, HESR-C, at the Facility for Antiproton and Ion Research (FAIR) in Europe. The high luminosity, $L \sim 10^{31}$ cm$^{-2}$ s$^{-1}$, and a wide range of intermediate and high energies, $\sqrt{s_{\text{NN}}}$ up to 30 GeV for $\overline{\text{p}} \text{p}(A)$ collisions will allow to explore a wide range of exciting topics in QCD, including the study of the production of excited open charm and bottom states, nuclear bound states containing heavy (anti)quarks, the interplay of hard and soft physics in the dilepton production, probing short-range correlations in nuclei, and the exploration of the early, complete $\overline{\text{p}}$-p-annihilation phase, where an intially pure Yang-Mills gluon plasma is formed., Comment: 36 pages, 5 figures, Comments: 36 pages, 5 figures. An expanded version of arXiv:1808.09550 (which will appear in the memorial volume for Walter Greiner of the Springer-Nature FIAS Interdisciplinary Science series). This version prepared for Eur. Phys. Jour. A; v2: version accepted for publication by Eur. Phys. Jour. A

This document collects the proceedings of the PHOTON 2017 conference ("International Conference on the Structure and the Interactions of the Photon", including the 22th "International Workshop on Photon-Photon Collisions", and the "International Workshop on High Energy Photon Colliders") held at CERN (Geneva) in May 2017. The latest experimental and theoretical developments on the topics of the PHOTON conference series are covered: (i) $\gamma\,\gamma$ processes in e$^+$e$^-$, proton-proton (pp) and nucleus-nucleus (AA) collisions at current and future colliders, (ii) $\gamma$-hadron interactions in e$^\pm$p, pp, and AA collisions, (iii) final-state photon production (including Standard Model studies and searches beyond it) in pp and AA collisions, and (iv) high-energy $\gamma$-ray astrophysics. These proceedings are dedicated to the memory of Maria Krawczyk., Comment: 296 pages. CERN-Proceedings-2018-001 (CERN, Geneva, 2018), to appear. arXiv admin note: substantial text overlap with arXiv:1804.05614, arXiv:1708.06683, arXiv:1709.09044, arXiv:1708.00912, arXiv:1708.07173, arXiv:1709.02985, arXiv:1709.00176, arXiv:1709.05167, arXiv:1708.05756, arXiv:1708.09759, arXiv:1708.07531, arXiv:1703.08450, arXiv:1711.02551, arXiv:1511.07794, arXiv:1712.10104, arXiv:1708.05776, arXiv:1712.10202, arXiv:1709.07110, arXiv:1702.08730, arXiv:1709.02648, arXiv:1411.6397

Exciting new scientific opportunities are presented for the PANDA detector at the High Energy Storage Ring in the redefined $\bar{\text{p}} \text{p}(A)$ collider mode, HESR-C, at the Facility for Antiproton and Ion Research (FAIR) in Europe. The high luminosity, $L \sim 10^{31}$ cm$^{-2}$ s$^{-1}$, and a wide range of intermediate and high energies, $\sqrt{s_{\text{NN}}}$ up to 30 GeV for $\bar{\text{p}} \text{p}(A)$ collisions will allow to explore a wide range of exciting topics in QCD, including the study of the production of excited open charm and bottom states, nuclear bound states containing heavy (anti)quarks, the interplay of hard and soft physics in the dilepton production, and the exploration of the regime where gluons -- but not quarks -- experience strong interaction., Comment: 29 pages, 5 figures. To appear in the memorial volume for Walter Greiner of the Springer-Nature FIAS Interdisciplinary Science series

We present a detailed study of kinematical and dynamical conditions necessary for probing highly elusive three-nucleon short range correlations~(3N-SRCs) in nuclei through inclusive electron scattering. The kinematic requirements that should be satisfied in order to isolate 3N-SRCs in inclusive processes are derived. We demonstrate that a sequence of two short-range NN interactions represents the main mechanism for 3N-SRCs in inclusive processes. Within this mechanism we predict a quadratic dependence of the inclusive cross section ratios of nuclei to $^3$He in the 3N-SRC region to the same ratio measured in 2N-SRC domain. The extended analysis of the available data satisfying the necessary 3N-SRC kinematical conditions is presented. This analysis provides tantalizing signatures of scaling associated with the onset of 3N-SRC dominance. The same data are also consistent with the prediction of the quadratic relation between the ratios measured in the 3N and 2N-SRC regions for nuclei ranging $4 \le A \le 197$. This agreement made it possible to extract $a_3(A)$, the probability of 3N-SRCs relative to the A=3 nucleus. We find $a_3(A)$ to be significantly larger in magnitude than the analogous parameter, $a_2(A)$, for 2N-SRCs., Comment: 34 pages and 18 figures, version published in Physical Review C

We test the hypothesis that configurations of a proton with a large-$x$ parton, $x_p \gtrsim 0.1$, have a smaller than average size. The QCD $Q^2$ evolution equations suggest that these small configurations also have a significantly smaller interaction strength, which has observable consequences in collisions with nuclei. We perform a global analysis of jet production data in proton- and deuteron-nucleus collisions at RHIC and the LHC. Using a model which takes a distribution of interaction strengths into account, we quantitatively extract the $x_p$-dependence of the average interaction strength, $\sigma(x_p)$, over a wide kinematic range. By comparing the RHIC and LHC results, our analysis finds that the interaction strength for small configurations, while suppressed, grows faster with collision energy than does that for average configurations. We check that this energy dependence is consistent with the results of a method which, given $\sigma(x_p)$ at one energy, can be used to quantitatively predict that at another. This finding further suggests that at even lower energies, nucleons with a large-$x_p$ parton should interact much more weakly than those in an average configuration, a phenomenon in line with explanations of the EMC effect for large-$x_p$ quarks in nuclei based on color screening., Comment: 7 pages, 4 figures; Accepted for publication by Phys. Rev. D (Rapid Communications)

In hadronic collisions, interference between different production channels affects momentum distributions of multi-particle final states. As this QCD interference does not depend on the strong coupling constant, it is part of the no-interaction baseline that needs to be controlled prior to searching for other manifestations of collective dynamics. Here, we introduce a model that is based on the QCD theory of multi-parton interactions and that allows one to study interference effects in the production of $m$ particles in hadronic collisions with $N$ parton-parton interactions ("sources"). In an expansion in powers of $1/(N_c^2-1)$ and to leading order in the number of sources $N$, we calculate interference effects in the $m$-particle spectra and we determine from them the second and fourth order cumulant momentum anisotropies $v_n$. Without invoking any azimuthal asymmetry and any density dependent non-linear dynamics in the incoming state, and without invoking any interaction in the final state, we find that QCD interference alone can give rise to values for $v_n\lbrace 2\rbrace$ and $v_n\lbrace 4\rbrace$, $n$ even, that persist unattenuated for increasing number of sources, that may increase with increasing multiplicity and that agree with measurements in proton-proton (pp) collisions in terms of the order of magnitude of the signal and the approximate shape of the transverse momentum dependence. We further find that the non-abelian features of QCD interference can give rise to odd harmonic anisotropies. These findings indicate that the no-interaction baseline including QCD interference effects can make a sizeable if not dominant contribution to the measured $v_n$ coefficients in pp collisions. Prospects for analyzing QCD interference contributions further and their possible relevance for proton-nucleus and nucleus-nucleus collisions are discussed shortly., Comment: 49 pages, 15 figures, revised version to appear in JHEP

The present day experimental data on the $X(3872)$ decays do not allow to make clear conclusions on the dominating structure of this state. We discuss here an alternative way to study its structure by means of the two-step $\bar D^*$ (or $D$) production in $\bar p A$ reactions. If this process is mediated by $X(3872)$, the characteristic narrow peaks of the $\bar D^*$ (or $D$) distributions in the light cone momentum fraction at small transverse momenta will appear. This would unambiguously signal the $D \bar D^*$ + c.c. molecular composition of the $X(3872)$ state., Comment: Proceedings of the XVI International Conference on Hadron Spectroscopy, 13-18.09.2015, Newport News, USA

We investigate dijet production from proton-nucleus collisions at the Large Hadron Collider (LHC) as a means for observing superfast quarks in nuclei with Bjorken $x>1$. Kinematically, superfast quarks can be identified through directly measurable jet kinematics. Dynamically, their description requires understanding several elusive properties of nuclear QCD, such as nuclear forces at very short distances, as well as medium modification of parton distributions in nuclei. In the present work, we develop a model for nuclear parton distributions at large $x$ in which the nuclear dynamics at short distance scales are described by two- and three-nucleon short range correlations (SRCs). Nuclear modifications are accounted for using the color screening model, and an improved description of the EMC effect is reached by using a structure function parametrization that includes higher-twist contributions. We apply QCD evolution at the leading order to obtain nuclear parton distributions in the kinematic regime of the LHC, and based on the obtained distributions calculate the cross section for dijet production. We find not only that superfast quarks can be observed at the LHC, but also that they provide sensitivity to the practically unexplored three-nucleon SRCs in nuclei. Additionally, the LHC can extend our knowledge of the EMC effect to large $Q^2$ where higher-twist effects are negligible., Comment: 44 pages, 17 figures, final version to be published in EJPC

The production of charmonia in the antiproton-nucleus reactions at $p_{\rm lab}=3-10$ GeV/c is studied within the Glauber model and the generalized eikonal approximation. The main reaction channel is charmonium formation in an antiproton-proton collision. The target mass dependence of the charmonium transparency ratio allows to determine the charmonium-nucleon cross section. The polarization effects in the production of $\chi_{c2}$ states are evaluated., Comment: 4 pages, 3 figures, Proceedings of the 13th International Workshop on Meson Production, Properties and Interaction, Krakow, Poland, 29.05-3.06.2014

The possibility of using a tensor polarized deuteron target in electroproduction reactions creates new opportunities for studying different phenomena related to the short-range hadronic and nuclear physics. The use of tensor polarized deuteron allows to isolate smaller than average inter-nucleon distances for the bound two-nucleon system. In this report we consider several of high $Q^2$ reactions which are particularly sensitive to the short-range two-nucleon configurations in the deuteron. The one is the relativistic dynamics of electron-bound-nucleon scattering which can be studied in both inclusive and exclusive reactions, other is the strong final state interaction in close proximity of two nucleons that can be used as a sensitive probe for color-transparency phenomena., Comment: 8 pages and 6 figures, proceedings of the Tensor Polarized Solid Target Workshop March 10-12, 2014 (Jefferson Lab, Newport News, USA)

Applying exact QCD sum rules for the baryon charge and energy-momentum we demonstrate that if nucleons are the only degrees of freedom of nuclear wave function, the structure function of a nucleus would be the additive sum of the nucleon distributions at the same Bjorken x = AQ^2/2(p_Aq)< 0.5 up to very small Fermi motion corrections if x>0.05. Thus the difference of the EMC ratio from one reveals the presence of non-nucleonic degrees of freedom in nuclei. Using exact QCD sum rules we show that the ratio R_A(x_p,Q^2) used in experimental studies, where x_p = Q^2/2q_0 m_p deviates from one even if a nucleus consists of nucleons with small momenta only. Use of the Bjorken x leads to additional decrease of R_A(x,Q^2) as compared to the x_p plots. Coherent contribution of equivalent photons into photon component of parton wave function of a nucleus unambiguously follows from Lorentz transformation of the rest frame nucleus Coulomb field. For A~200 photons carry ~0.0065 fraction of the light momentum of nucleus almost compensates the difference between data analysis in terms of Bjorken x and x_p. Different role of higher twist effects for Q^2 probed at electron and muon beams is emphasized. Direct observations of large and predominantly nucleonic short-range correlations in nuclei pose a serious challenge for most of the models of the EMC effect for x>0.6. The data are consistent with a scenario in which the hadronic EMC effect reflects fluctuations of inter nucleon interaction due to fluctuations of color distribution in the interacting nucleons. The dynamic realization of this scenario is the model in which the 3q (3qg) configurations with x > 0.5 parton have a weaker interaction with nearby nucleons, leading to suppression of such configurations giving a right magnitude of the EMC effect. The directions for the future studies and challenging questions are outlined., Comment: The sign in the relation of x_Bj and x_p is corrected and the following discussion is adjusted accordingly. Discussion of the higher twist effects is added

The recent x>1 (e,e') and correlation experiments at momentum transfer Q^2 \ge 2 GeV^2 confirm presence of short-range correlations (SRC) in nuclei mostly build of nucleons. Recently we evaluated in a model independent way the dominant photon contribution to the nuclear structure. Taking into account this effect and using definition of x consistent with the exact kinematics of eA scattering (with exact sum rules) results in the significant reduction of R_A(x,Q^2)=F_{2A}(x,Q^2)/F_{2N}(x,Q^2) ratio which explains \sim 50% of the EMC effect for x\le 0.55 where Fermi motion effects are small. The remaining part of the EMC effect at $x\ge 0.5$ is consistent with dominance of the contribution of SRCs. Implications for extraction of the F_{2n}/F_{2p} ratio are discussed. Smallness of the non-nucleonic degrees of freedom in nuclei matches well the recent observation of a two-solar mass neutron star, and while large pn SRCs lead to enhancement of the neutron star cooling rate for kT\le 0.01 MeV., Comment: To be published in proceedings of PANIC 11

We estimate the contributions by double-parton interactions to the cross sections for pp->pi^0 pi^0 X and dA->pi^0 pi^0 X at RHIC. We find that such contributions become important at large forward rapidities of the produced pions. This is in particular the case for dA scattering, where they strongly enhance the azimuthal-angular independent "pedestal" component of the cross section, providing a natural explanation of this feature of the RHIC dA data. We argue that the discussed processes open a window to studies of double quark distributions in nucleons. We also briefly address the roles of shadowing and energy loss in dA scattering, which we show to affect the double-inclusive pion cross section much more strongly than the single-inclusive one. We discuss the implications of our results for the interpretation of pion azimuthal correlations., Comment: 24 pages, 14 figures. Some discussion added, one figure improved. Version to appear in Phys. Rev. D

Efficient detection of spectator fragments is key to the main topics at an electron-ion collider (eIC). Any process which leads to emission of fragments or $\gamma$'s breaks coherence in diffractive processes. Therefore this is equivalent to non-detection of rapidity gaps in pp collisions. For example, in coherent photoproduction of vector mesons their 4-momentum transfer distribution would image the "gluon charge" in the nucleus in the same way that Hofstadter measured its charge structure using elastic scattering of $\sim$100 MeV electrons. Whereas he could measure the $\sim$4 MeV energy loss by the electron due to excitation of nuclear energy levels (Figure 1), even the energy spread of the incident beam would prevent such an inclusive selection of quasielastic events at an eIC. The only available tool is fragment detection. Since, in our example, one finds that $\sim100$ of deexcitations go through $\gamma$'s or 1 neutron, rarely to 2 neutron and never to protons(due to Coulomb barrier suppression), the eIC design should emphasize their detection., Comment: 10 pages, 6 figures

We show that with a realistic treatment of spectator momentum distributions the RHIC detector trigger sensitivity is high even when RHIC is run below injection energies. In particular, a problem region with $\sqrt{s_{NN}}$=10 to 60 or 80 GeV assuming a simple Fermi step model is not found when using a more realistic one. We argue also that production of fast nucleons (with momenta $> p_F$ in the nucleus rest frame) provides complementary information about the collision process., Comment: 11 pages, 8 figures

We calculate production rates for several hard processes in ultraperipheral proton-nucleus and nucleus-nucleus collisions at the LHC. The resulting high rates demonstrate that some key directions in small $x$ research proposed for HERA will be accessible at the LHC through these ultraperipheral processes. Indeed, these measurements can extend the HERA $x$ range by roughly a factor of 10 for similar virtualities. Nonlinear effects on the parton densities will thus be significantly more important in these collisions than at HERA., Comment: Submitted to Phys. Rev. Lett., 4 pages, 5 figures