Nuclear Shadowing Research Articles

Photonuclear and Two-Photon Interactions at High-Energy Nuclear Colliders

Ultraperipheral collisions (UPCs) of heavy ions and protons are the energy frontier for electromagnetic interactions. Both photonuclear and two-photon collisions are studied at collision energies that are far higher than those available elsewhere. In this review, we discuss physics topics that can be addressed with UPCs, including nuclear shadowing, nuclear structure, and searches for physics beyond the Standard Model.

Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at [formula omitted] TeV

The differential invariant yield as a function of transverse momentum (pT) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0–10%), semi-central (30–50%) and peripheral (60–80%) lead–lead (Pb–Pb) collisions at sNN=5.02 TeV in the pT intervals 0.5–26 GeV/c (0–10% and 30–50%) and 0.5–10 GeV/c (60–80%). The production cross section in proton–proton (pp) collisions at s=5.02 TeV was measured as well in 0.5<pT<10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to pT=5 GeV/c and close to the mean value for larger pT. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon–nucleon collisions is evaluated by measuring the nuclear modification factor RAA. The measurement of the RAA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The RAA shows a suppression with respect to unity at intermediate pT, which increases while moving towards more central collisions. Moreover, the measured RAA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low pT in heavy-ion collisions at LHC.

S(c)helling in Kashmir: Bargaining under the Nuclear Shadow

Twenty years ago in the mountains of Kashmir, India and Pakistan fought one of the two limited wars between nuclear powers.1 The Kargil conflict between May­­–July 1999 marked a watershed moment, n...

Mechanisms of B Meson Suppression in Ultrarelativistic Heavy Ion Collisions

Different mechanisms of B meson suppression in lead ion collisions at an energy of the Large Hadron Collider $$\sqrt {{{s}_{{NN}}}} $$ = 5.02 TeV have been comparatively analyzed. It has been shown that the experimentally observed weak momentum dependence of the B meson suppression factor can be reproduced by the HYDJET++ model including the nuclear shadowing of initial parton distributions and radiative and collisional energy losses of heavy quarks in hot matter. A significant difference in the effects of the initial and final states on light and heavy hadron suppression has been revealed.

Provocation, war and restraint under the nuclear shadow: The Kargil conflict 1999

ABSTRACT The Kargil conflict was a limited war between India and Pakistan fought along the Kashmir Line of Control during the spring/summer of 1999. Named for the principal town in the combat zone on the Indian side, it was the first open warfare between India and Pakistan as declared nuclear weapons states and included the first combat employment of the Indian Air Force since 1971. Despite its intensity, it was also characterised by considerable restraint on both sides. The potential for conventional escalation, however, was high and the possibility of nuclear confrontation could not be excluded. It had significant long-term ramifications for both countries and constitutes an important part of the backdrop to their relations today.

PHENIX study of the initial state with forward hadron measurements in 200 GeV p(d)+A and 3He+Au collisions

Forward hadron measurements in p(d)+A provide a signal to study nuclear shadowing, initial state energy loss and/or gluon saturation effects as a function of rapidity, centrality and energy. High pT identified π0 measurements are an essential first step toward measuring prompt photon production. The π0 measurements are enabled by the PHENIX MPC-EX detector, a Si-W preshower detector located in front of the Muon Piston Calorimeter (MPC), expanding the neutral pion reconstruction capabilities in the rapidity range 3.1 <η < 3.8 out to high energies, E < 80 GeV. Previous PHENIX measurements of punch-through charged hadrons in the muon arms in the rapidity range 1.4 < |η| < 2.2 were significantly improved through the capability of the forward silicon vertex detector (FVTX) to determine the transverse momentum and rapidity with high precision and reject background from secondary hadrons.PHENIX collected d+Au data with the MPC-EX in the 2016 run at sNN=200,62,39and19.6GeV; and p+p and p+Au(Al) data with the FVTX in 2015 at 200 GeV. In this talk, we will present first results for high pTπ0 production from the sNN=200GeV dataset, the status of the prompt photon measurement, as well as charged hadron nuclear modification factors in p+Au(Al) and 3He+Au.

Exclusive vector meson production at an electron-ion collider

Coherent exclusive vector meson electroproduction is a key physics channel at an electron-ion collider. It probes the gluon structure of nuclei over a wide range of $Q^2$, and can be used to measure nuclear shadowing and to search for gluon saturation and/or the colored glass condensate. In this paper, we present calculations of the kinematic distributions for a variety of exclusive vector meson final states: the $\rho$, $\phi$, J/$\psi$, $\psi'$ and the $\Upsilon$ states. The cross-sections for light and $c\overline c$ mesons are large, while $\Upsilon$ states should be produced in moderate numbers at a medium energy EIC (the proposed U.S. designs) and in large numbers at the LHeC. We investigate the acceptances for these states, as a function of detector rapidity coverage. A large-acceptance detector is needed to cover the full range photon-nucleon collision energies produced at an EIC; a forward detector is required to observe vector mesons from the most energetic photon interactions, and thereby probe gluons at the lowest possible Bjorken-$x$ values.

The Strategy Trap: India and Pakistan under the Nuclear Shadow- A Book Review

The Strategy Trap: India and Pakistan under the Nuclear Shadow- A Book Review

Effects of shadowing in Pb + Pb collisions at energies available at the CERN Large Hadron Collider within the HIJING code

The charged particle central rapidity density per participant nucleon pair ( $(\mathrm{d} N_{ch}/\mathrm{d} \eta)/(0.5\langle N_{part} \rangle)$ ) as a function of the average number of participants ( $ N_{part}$ ) for $ \mathrm{Au}+\mathrm{Au}$ ( $ \mathrm{Cu}+\mathrm{Cu}$ ) collisions at $ \sqrt{s_{\mathrm{NN}}}=62.4$ and 200 GeV, and $ \mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ and 5.02 TeV is investigated within an improved HIJING (ImHIJING/Cas) model. Compared to the standard HIJING version, it incorporates: i) more consistent parton densities, ii) a QCD running coupling, defined by the exact solution of the renormalization group equation, and iii) a spatial dependent nucleon shadowing, triggered by collective nucleon interactions with an incoming nucleon, and simulated by the collective cascade recipe. Predictions are compared using four different settings of nuclear shadowing of partons, based on the standard HIJING1.0(2.0) parameterizations. It is shown that ImHIJING/Cas/Set2 (that with both quark and soft gluon shadowing of strength $ s_{q(g)}$ can nicely reproduce the measured centrality dependence of $ (\mathrm{d} N_{ch}/\mathrm{d} \eta)/(0.5\langle N_{part} \rangle)$ at RHIC energy. As for LHC, a reduction of $ s_{g}$ by $ \sim 40$ % at very peripheral (90-100%) $ \mathrm{Pb}+\mathrm{Pb}$ collisions, as compared to free nucleon-nucleon collisions, is found to reproduce the measured data. The values of $s_{q(g)}$ used in ImHIJING/Cas/Set2 calculations for most central 0-3(5)% $ \mathrm{Au}+\mathrm{Au} (\mathrm{Pb}+\mathrm{Pb})$ collisions at RHIC(LHC) energy, are found to be consistent with those employed in Set2 that reproduce the measured structure function ratios ( $ 12F^{Pb}_{2}/207F^{C}_{2}$ ) as a function of x.

Production of open-charm mesons in relativistic heavy-ion collisions

We present a theoretical framework to study open charm production in relativistic heavy-ion collisions. The coupling strength between the charm quarks and the QGP constituents, quantified by the spatial diffusion coefficient $2\pi TD_{s}$, is obtained by performing a phenomenological fit analysis to the lattice QCD calculations, resulting in $2\pi TD_{s}=const.$ (\textbf{Model-A}) and $2\pi TD_{s}=1.3 + (T/T_{c})^2$ (\textbf{Model-B}). We find that the relative azimuthal distribution of the initially back-to-back generated $c\bar{c}$ pairs presents a broadening behaviour, which is more pronounced for $c\bar{c}$ pairs with small initial $p_{\rm T}$, and when the Model-B approach is adopted. The competition between the initial drag and the subsequent collective effects tends to restrict the time dependence of charm quark $R_{\rm AA}$. Concerning the theoretical uncertainty on final D-meson nuclear modification, the nuclear shadowing and pp baseline components are dominat at high and low $p_{\rm T}$ ($p_{\rm T}\lesssim3~{\rm GeV/{\it c}}$), respectively. The measured D-meson $R_{\rm AA}(p_{\rm T})$ favors Model-A assumption for the diffusion coefficient both at RHIC and LHC, while their $v_{2}(p_{\rm T})$ prefer Model-B at moderate $p_{\rm T}$. These results confirm the necessity to consider the temperature- and/or momentum-dependence of $2\pi TD_{s}$ to describe well the D-meson $R_{\rm AA}$ and $v_{\rm 2}$ simultaneously.

NATO RESILIANCE, DETER AND PROFESIONAL MILITARY EDUCATION

Our professional military education still lags in the attention it gives to contemporary deterrence problems. We try to provide a comprehensive framework for officer education across the strategic, operational, and tactical domains but curiously fails to highlight the need to teach deterrence in the professional military education classrooms. In this respect, we have to prepare our students for deterrence and escalation issues. It is critical to adapt their core curricula to include vital content on deterrence, escalation, cross-domain conflict, and crisis management under the nuclear shadow. Deterrence is not completely neglected in our core curricula, same individual academic or research faculty offer electives, even first-rate elective classes but still for a small number of students.

Shadowing in low-energy photonuclear reactions

The photonuclear reaction in the multi-GeV region occurs because of the electromagnetic and hadronic interactions. The latter originates due to the hadronic fluctuation, i.e., vector meson, of the photon. The total cross section of the reaction is shadowed because of the vector meson--nucleus (hadronic) interaction. To estimate it quantitatively, the cross section of the photonuclear reaction was calculated in the low energy region ($\ensuremath{\sim}1--3$ GeV) using the simple vector-meson dominance (SVMD) model, i.e., the low-lying vector mesons (${\ensuremath{\rho}}^{0}, \ensuremath{\omega}$, and $\ensuremath{\phi}$ mesons) were considered. The nuclear shadowing is reinvestigated using the generalized vector meson (GVMD) model, where the higher $\ensuremath{\rho}$ meson effective state (${\ensuremath{\rho}}^{\ensuremath{'}}$ meson) is taken into account along with the low-lying vector mesons. Using the GVMD model, the total cross section of the photonuclear reaction are calculated in the above mentioned energy region. The calculated results are compared with the measured spectra.

Aspects of hard QCD processes in proton–nucleus collisions

Hard processes in high-energy proton–nucleus collisions are a powerful tool in order to investigate several importants aspects of QCD in a nuclear medium, such as nuclear shadowing, parton multiple scattering or medium-induced gluon radiation. I review in these proceedings recent progress in that field.

Coherent J/ψ photoproduction in ultra-peripheral PbPb collisions at [formula omitted] with the CMS experiment

The cross section for coherent J/ψ photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, Xn0n, is measured with the CMS experiment in ultra-peripheral PbPb collisions at sNN=2.76TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159μb−1, collected during the 2011 PbPb run. The J/ψ mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dσXn0ncoh/dy(J/ψ)=0.36±0.04(stat)±0.04(syst) mb in the rapidity interval 1.8<|y|<2.3. Using a model for the relative rate of coherent photoproduction processes, this Xn0n measurement gives a total coherent photoproduction cross section of dσcoh/dy(J/ψ)=1.82±0.22(stat)±0.20(syst)±0.19(theo) mb. The data strongly disfavor the impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/ψ photoproduction in γ+Pb interactions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing.

Dynamical model of antishadowing of the nuclear gluon distribution

We explore the theoretical observation that within the leading twist approximation, the nuclear effects of shadowing and antishadowing in non-perturbative nuclear parton distribution functions (nPDFs) at the input QCD evolution scale involve diffraction on nucleons of a nuclear target and originate from merging of two parton ladders belonging to two different nucleons, which are close in the rapidity space. It allows us to propose that for a given momentum fraction $x_P$ carried by the diffractive exchange, nuclear shadowing and antishadowing should compensate each other in the momentum sum rule for nPDFs locally on the interval $\ln (x/x_P) \le 1$. We realize this by constructing an explicit model of nuclear gluon antishadowing, which has a wide support in $x$, $10^{-4} < x < 0.2$, peaks at $x=0.05-0.1$ at the level of $\approx 15$\% for $^{208}$Pb at $Q_0^2=4$ GeV$^2$ and rather insignificantly depends on details of the model. We also studied the impact parameter $b$ dependence of antishadowing and found it to be slow.

Nuclear parton distributions

We review a microscopic model of the nuclear parton distribution functions, which accounts for a number of nuclear effects including Fermi motion and nuclear binding, nuclear meson-exchange currents, off-shell corrections to bound nucleon distributions and nuclear shadowing. We also discuss applications of this model to a number of processes including lepton-nucleus deep inelastic scattering, proton-nucleus Drell-Yan lepton pair production at Fermilab, as well as W+- and Z0 boson production in proton-lead collisions at the LHC.

Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects

We evaluate the prompt atmospheric neutrino flux at high energies using three different frameworks for calculating the heavy quark production cross section in QCD: NLO perturbative QCD, $k_T$ factorization including low-$x$ resummation, and the dipole model including parton saturation. We use QCD parameters, the value for the charm quark mass and the range for the factorization and renormalization scales that provide the best description of the total charm cross section measured at fixed target experiments, at RHIC and at LHC. Using these parameters we calculate differential cross sections for charm and bottom production and compare with the latest data on forward charm meson production from LHCb at $7$ TeV and at $13$ TeV, finding good agreement with the data. In addition, we investigate the role of nuclear shadowing by including nuclear parton distribution functions (PDF) for the target air nucleus using two different nuclear PDF schemes. Depending on the scheme used, we find the reduction of the flux due to nuclear effects varies from $10\%$ to $50 \%$ at the highest energies. Finally, we compare our results with the IceCube limit on the prompt neutrino flux, which is already providing valuable information about some of the QCD models.

Rapidity and centrality dependence of particle production for identified hadrons in Cu + Cu collisions atsNN=200GeV

The BRAHMS collaboration has measured transverse momentum spectra of pions, kaons, protons, and antiprotons at rapidities 0 and 3 for Cu+Cu collisions at sNN=200 GeV. As the collisions become more central the collective radial flow increases while the temperature of kinetic freeze-out decreases. The temperature is lower and the radial flow weaker at forward rapidity. Pion and kaon yields with transverse momenta between 1.5 and 2.5 GeV/c are suppressed for central collisions relative to scaled p+p collisions. This suppression, which increases as the collisions become more central, is consistent with jet quenching models and is also present with comparable magnitude at forward rapidity. At such rapidities, initial state effects may also be present and persistence of the meson suppression to high rapidity may reflect a combination of jet quenching and nuclear shadowing. The ratio of protons to mesons increases as the collisions become more central and is largest at forward rapidities.

J/ψ photoproduction in ultra-peripheral Pb-Pb and p-Pb collisions with the ALICE detector

Ultra-relativistic heavy ions generate strong electromagnetic fields which offer the possibility to study gamma-gamma, gamma-nucleus and gamma-proton processes at the LHC in ultra-peripheral Pb-Pb and p-Pb collisions (UPC). Exclusive photoproduction of J/ψ vector mesons is sensitive to the gluon distribution of the interacting target (proton or nucleus). This process is expected to be sensitive to saturation phenomena and nuclear gluon shadowing. Here we report on the ALICE measurement of J/ψ coherent photoproduction in Pb-Pb UPC at sNN=2.76 TeV at forward and central rapidities. Furthermore, we also present results on the J/ψ photoproduction in p-Pb UPC at sNN=5.02 TeV in the forward and backward rapidities, where the rapidity is measured in the laboratory frame with respect to the proton beam direction. The J/ψ mesons have been identified through their leptonic decays.

Jet Fragmentation and Energy Loss in Ultrarelativistic Heavy Ion Collisions

In this work we study the suppression of charged hadrons (π±, K±, p and ) in ultrarelativistic heavy ion (UHI) collisions, where the quark-gluon plasma (QGP) is believed to be produced. Jet energy loss in the QGP is the main explanation for jet quenching, which may suppress the number of hadrons produced while the jets traverse the dense and colorful medium created. By taking into account the energy loss of the partons traversing the medium and the nuclear shadowing of the parton distributions depending on the impact-parameter, we calculate the nuclear modification factor RAA for lead-lead collisions at the LHC. Finally, we estimate the opacity of the QGP in several centrality classes.