High Energy Proton-nucleus Collisions Research Articles

Dissociation cross sections of ψ(3770), ψ(4040), ψ(4160), and ψ(4415) mesons with nucleons

We study the dissociation of ψ(3770), ψ(4040), ψ(4160), and ψ(4415) mesons in collision with nucleons, which takes place in high-energy proton-nucleus collisions. The quark interchange between a nucleon and a cc¯ meson leads to the dissociation of the cc¯ meson. We consider the reactions: pR→Λc+D¯0 , pR→Λc+D¯*0 , pR→Σc++D− , pR→Σc++D*− , pR→Σc+D¯0 , pR→Σc+D¯*0 , pR→Σc*++D− , pR→Σc*++D*− , pR→Σc*+D¯0 , and pR→Σc*+D¯*0 , where R stands for ψ(3770), ψ(4040), ψ(4160), or ψ(4415). A reaction of a neutron and a cc¯ meson corresponds to a reaction of a proton and the cc¯ meson by replacing the up quark with the down quark and vice versa. Transition-amplitude formulas are derived from the S-matrix element. Unpolarized cross sections are calculated with the transition amplitudes for scattering in the prior form and in the post form. The cross sections relate to nodes in the radial wave functions of ψ(3770), ψ(4040), ψ(4160), and ψ(4415) mesons.

Evolution of eccentricities induced by geometrical and quantum fluctuations in proton-nucleus collisions

We compute the azimuthal eccentricities arising from initial stage fluctuations in high energy proton-nucleus collisions at proper times $\tau \geq 0^+$. We consider two sources of fluctuations, namely the geometrical structure of the proton and the fluctuation of color fields carried by both proton and nucleus. Describing these effects with Gaussian models allows us to analytically calculate the one- and two-point correlators of energy density, from which the eccentricities are obtained. We compute the proper time evolution of these quantities by approximating the Glasma dynamics in terms of linearized Yang-Mills equations, which we solve by assuming free field propagation and adopting the dilute-dense limit.

Gluon saturation in proton and its contribution to single inclusive soft gluon production in high energy proton-nucleus collisions

The leading order single inclusive soft gluon production in high energy proton-nucleus (pA) collisions has been studied by various approaches for more than two decades. The first correction due to the gluon saturation in proton was analytically attempted recently through a diagrammatic approach in which only partial results were obtained. An important feature of the first saturation correction is that it includes both initial state and final state interactions. In this paper, we present the complete result derived from the Color Glass Condensate framework. Our approach is to analytically solve the classical Yang-Mills equations in the dilute-dense regime and then use the Lehmann-Symanzik-Zimmermann (LSZ) reduction formula to obtain gluon production from classical gluon fields.

First saturation correction in high energy proton-nucleus collisions. Part III. Ensemble averaging

In high energy proton-nucleus collisions, the gluon saturation effects from the nucleus are fully incorporated into the light-like Wilson lines. The gluon saturation effects from the proton, which are anticipated to be important either in the extreme high energy limit or towards the dense-dense (nucleus-nucleus) collision regimes, have been studied perturbatively within the Color Glass Condensate effective theory in previous papers of this series. A configuration-by-configuration expression for the single inclusive semi-hard gluon production including the first saturation correction was obtained. In this paper, we perform ensemble averaging in the McLerran-Venugopalan model and the Dipole Approximation. We find that, in the saturation correction, the effects of the initial state interactions are negligible while the final state interactions play most important role and give a positive-valued contribution to the semi-hard gluon spectrum. Furthermore, we show that the single gluon spectrum scales approximately 1/ {k}_{perp}^4 at small k⊥, suggesting that a resummation of higher order saturation corrections is required to regulate the infrared region of the gluon spectrum.

First saturation correction in high energy proton-nucleus collisions. Part I. Time evolution of classical Yang-Mills fields beyond leading order

In high energy proton-nucleus collisions, the single- and double-inclusive soft gluon productions at the leading order have been calculated and phenomenologically studied in various approaches for many years. These studies do not take into account the saturation and multiple rescatterings in the field of the proton. The first saturation correction to these leading order results (the terms that are enhanced by the combination {alpha}_s^2{mu}^2 , where μ2 is the proton’s color charge squared per unit transverse area) has not been completely derived despite recent attempts using a diagrammatic approach. This paper is the first in a series of papers towards analytically completing the first saturation correction to physical observables in high energy proton-nucleus collisions. Our approach is to analytically solve the classical Yang-Mills equations in the dilute-dense regime using the Color Glass Condensate effective theory and compute physical observables constructed from classical gluon fields. In the current paper, the Yang-Mills equations are solved perturbatively in the field of the dilute object (the proton). Next-to-leading order and next-to-next-to-leading order analytic solutions are explicitly constructed. A systematic way to obtain all higher order analytic solutions is outlined.

First saturation correction in high energy proton-nucleus collisions. Part II. Single inclusive semi-hard gluon production

Exploiting recently obtained analytic solutions of classical Yang-Mills equations for higher order perturbations in the field of the dilute object (proton), we derive the complete first saturation correction to the single inclusive semi-hard gluon production in high energy proton-nucleus collisions by applying the Lehmann-Symanzik-Zimmermann reduction formula. We thus finalize the program started by Balitsky (see ref. [1]) and independently by Chirilli, Kovchegov and Wertepny (see ref. [2]) albeit using a very different approach to carry out our calculations. We extracted the functional dependence of gluon spectrum on the color charge densities of the colliding objects; thus our results can be used to evaluate complete first saturation correction to the double/multiple inclusive gluon productions.

The proton structure via double parton scattering

In this talk we present the results of the investigation on the so called double parton distribution functions (dPDFs), accessible quantities in high energy proton-proton and proton nucleus collisions, in double parton scattering processes (DPS). These new and almost unknown distributions encode information on how partons inside a proton are correlated among each other and represent a new tool to explore the three dimensional partonic structure of hadrons. In the present contribution, results of the calculations of dPFDs are presented also including phenomenological investigations on the impact of double correlations in experimental observables, showing how the latter could be observed in the next LHC run. In addition we discuss how present information on experimental observables could be related to the transverse proton structure.

Probing double parton scattering via associated open charm and bottom production in ultraperipheral pA collisions

In this article, we propose a novel channel for phenomenological studies of the double-parton scattering (DPS) based upon associated production of charm c{bar{c}} and bottom b{bar{b}} quark pairs in well-separated rapidity intervals in ultraperipheral high-energy proton–nucleus collisions. This process provides direct access to the double-gluon distribution in the proton at small-x and enables one to test the factorized DPS pocket formula. We have made the corresponding theoretical predictions for the DPS contribution to this process at typical LHC energies and beyond and we compute the energy-independent (but photon momentum fraction dependent) effective cross section.

Testing Production Scenarios for (Anti-)(Hyper-)nuclei with Multiplicity-dependent Measurements at the LHC

The production of light anti- and hyper-nuclei provides unique observables to characterise the system created in high energy proton-proton (pp), proton-nucleus (pA) and nucleus-nucleus (AA) collisions. In particular, nuclei and hyper-nuclei are special objects with respect to non-composite hadrons (such as pions, kaons, protons, etc.), because their size is comparable to a fraction or the whole system created in the collision. Their formation is typically described within the framework of coalescence and thermal-statistical production models. In order to distinguish between the two production scenarios, we propose to measure the coalescence parameter B$_{A}$ for different anti- and hyper-nuclei (that differ by mass, size and internal wave-function) as a function of the size of the particle emitting source. The latter can be controlled by performing systematic measurements of light (anti-)(hyper-)nuclei in different collision systems (pp, pA, AA) and as a function of the multiplicity of particles created in the collision. While it is often argued that the coalescence and the thermal model approach give very similar predictions for the production of light nuclei in heavy-ion collisions, our study shows that large differences can be expected for hyper-nuclei with extended wave-functions, as the hyper-triton. We compare the model predictions with data from the ALICE experiment and we discuss perspectives for future measurements with the upgraded detectors during the High-Luminosity LHC phase in the next decade.

Gluon density fluctuations in dilute hadrons

Motivated by the relation existing between the gluon density in a hadron and the multiplicity of the particles measured in the final state of hadron-nucleus collisions, we study systematically the fluctuations of the gluon density in onia, which are the simplest dilute hadrons, of different sizes and at various rapidities. We argue that the small and the large-multiplicity tails of the gluon distributions present universal features, which should translate into properties of the multiplicity of the particles measured in the final state of high-energy proton-nucleus collisions, or of deep-inelastic scattering at a future electron-ion collider. We propose simple physical pictures of the rare events populating the tails of the multiplicity distribution that allow us to derive analytical formulas describing these universal behaviors, and we compare them to the results of Monte Carlo simulations.

Nucleon 3D structure from double parton scattering: a Light-Front quark model analysis

Double parton distribution functions (dPDFs) represent a tool to explore the 3D partonic structure of the proton. They can be measured in high energy proton-proton and proton nucleus collisions and encode information on how partons inside a proton are correlated among each other. dPFDs are studied here in the valence region by means of a constituent quark model scenario within the relativistic Light Front approach, where two particle correlations are present without any additional prescription. Furthermore, a study of the QCD evolution at high energy scale, of the model results, has been completed in order to compare our predictions with future data analyses. In closing, results on the evaluation of the so called σeff, crucial ingredient for the description of double parton scattering, where dPDFs can be accessed, are presented and discussed.

Effect of the fluctuating proton size on the study of the chiral magnetic effect in proton-nucleus collisions

High energy proton-nucleus (pA) collisions provide an important constraint on the study of the chiral magnetic effect in QCD matter. Naively, in pA collisions one expects no correlation between the orientation of event plane as reconstructed from the azimuthal distribution of produced hadrons and the orientation of magnetic field. If this is the case, any charge-dependent hadron correlations can only result from the background. Nevertheless, in this paper we point out that in high multiplicity pA collisions a correlation between the magnetic field and the event plane can appear. This is because triggering on the high hadron multiplicity amounts to selecting Fock components of the incident proton with a large number of partons that are expected to have a transverse size much larger than the average proton size. We introduce the effect of the fluctuating proton size in the Monte Carlo Glauber model and evaluate the resulting correlation between the magnetic field and the second-order event plane in both pA and nucleus-nucleus (AA) collisions. The fluctuating proton size is found to result in a significant correlation between magnetic field and the event plane in pA collisions, even though the magnitude of the correlation is still much smaller than in AA collisions. This result opens a possibility of studying the chiral magnetic effect in small systems.

Multiparticle Collectivity from Initial State Correlations in High Energy Proton-Nucleus Collisions

Qualitative features of multiparticle correlations in light-heavy ion (p+A) collisions at RHIC and LHC are reproduced in a simple initial state model of partons in the projectile coherently scattering off localized domains of color charge in the heavy nuclear target. These include (i)the ordering of the magnitudes of the azimuthal angle nth Fourier harmonics of two-particle correlations v_{n}{2}, (ii)the energy and transverse momentum dependence of the four-particle Fourier harmonic v_{2}{4}, and (iii)the energy dependence of four-particle symmetric cumulants measuring correlations between different Fourier harmonics. Similar patterns are seen in an Abelian version of the model, where we observe v_{2}{2}>v_{2}{4}≈v_{2}{6}≈v_{2}{8} of two, four, six, and eight particle correlations. While such patterns are often interpreted as signatures of collectivity arising from hydrodynamic flow, our results provide an alternative description of the multiparticle correlations seen in p+A collisions.

Forward J/ψ and D meson nuclear suppression at the LHC

Using the color glass condensate formalism, we study the nuclear modification of forward J/ψ and D meson production in high energy proton-nucleus collisions at the LHC. We show that relying on the optical Glauber model to obtain the dipole cross section of the nucleus from the one of the proton fitted to HERA DIS data leads to a smaller nuclear suppression than in the first study of these processes in this formalism and a better agreement with experimental data.

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.

Double parton scattering in the color glass condensate: Hanbury-Brown-Twiss correlations in double inclusive photon production

We introduce a technique to study double parton scattering (DPS) in the Color-Glass-Condensate (CGC) approach. We show that the cross-section of the DPS in the CGC approach is calculable in terms of new nonperturbative objects, generalized double transverse momentum-dependent parton distribution (2GTMD) functions. We investigate the production of pairs of prompt photons from two partons in the projectile hadron in high-energy proton-nucleus collisions. We show that even for independent partons in the projectile, the prompt photon correlation function exhibits Hanbury Brown and Twiss (HBT) correlations. The width of the HBT peak is controlled by the transverse distance between the parton of the pair, which is of the order of the proton size. Thus, the HBT measurements in two-particle production such as prompt photon pairs provide useful information about the nonperturbative 2GTMDs.

Prospects of direct search for dark photon and dark Higgs in SeaQuest/E1067 experiment at the Fermilab main injector

In this review, we present the current status and prospects of the dark sector physics search program of the SeaQuest/E1067 fixed target dimuon experiment at Fermilab Main Injector. There has been tremendous excitement and progress in searching for new physics in the dark sector in recent years. Dark sector refers to a collection of currently unknown particles that do not directly couple with the Standard Model (SM) strong and electroweak (EW) interactions but assumed to carry gravitational force, thus could be candidates of the missing Dark Matter (DM). Such particles may interact with the SM particles through “portal” interactions. Two of the simple possibilities are being investigated in our initial search: (1) dark photon and (2) dark Higgs. They could be within immediate reach of current or near future experimental search. We show there is a unique opportunity today at Fermilab to directly search for these particles in a highly motivated but uncharted parameter space in high-energy proton–nucleus collisions in the beam-dump mode using the 120 GeV proton beam from the Main Injector. Our current search window covers the mass range 0.2–10 GeV/c2, and in the near future, by adding an electromagnetic calorimeter (EMCal) to the spectrometer, we can further explore the lower mass region down to about [Formula: see text][Formula: see text]1 MeV/c2 through the di-electron channel. If dark photons (and/or dark Higgs) were observed, they would revolutionize our understanding of the fundamental structures and interactions of our universe.

Centrality dependence of forward J/ψ suppression in high energy proton–nucleus collisions

The production of forward J/ψ mesons in proton-nucleus collisions can provide important information on gluon saturation. In a previous work we studied this process in the Color Glass Condensate framework, describing the target using a dipole cross section fitted to HERA inclusive data and extrapolated to the case of a nuclear target using the optical Glauber model. In this work we study the centrality dependence of the nuclear suppression in this model and compare our results with recent LHC data for this observable.

Initial state azimuthal anisotropies in small collision systems

Strong multiparticle azimuthal correlations have recently been observed in high energy proton-nucleus collisions. While final state collective effects can be responsible for many of the observed effects, the domain structure in the classical color field of a high energy nucleus, naturally also leads to such multiparticle correlations. We describe recent calculations of the momentum space 2-particle cumulant azimuthal anisotropy coefficients νn{2}, n=2,3,4 from fundamental representation Wilson line distributions describing the high energy nucleus. We find significant differences between Wilson lines from the MV model and from JIMWLK evolution. We also discuss the relation of this calculation to earlier work on the ridge correlation obtained in the “glasma graph” approximation, and to the “color electric field domain model.”

Di-photon correlations in p+A collisions at the LHC

We study the long-range in rapidity near-side and away-side azimuthal collimation, the so-called “ridge” structure for di-photon correlations in high-energy proton-nucleus (p+A) collisions. We show that based on the initial-state Color-Glass-Condensate at leading-log approximation, the ridge-like structure for di-photon correlations disappears at the LHC energies. Nevertheless, the near-side and away-side correlations coming from the remanent of double and single fragmentation contributions respectively, survive upto Δη≈1÷3 in rapidity interval between two produced photons at RHIC and the LHC. Therefore, an experimental observation of ridge-like structure in di-photon correlations at the LHC similar to the one observed in di-hadron correlations in p+p(A) collisions, may suggest that final-state effects play important role in the formation of the ridge.