Backward Rapidity Research Articles

D meson production in p+Pb collisions with the analytical transverse momentum distribution from the color dipole models* *Supported by the National Natural Science Foundation of China Joint for Large Scientific Units (U1832120), the Hebei Province Outstanding Youth Fund (A2020210012), the S&T Program of Hebei (Grant No. 236Z4601G), and the Scientific Research Foundation for the Introducing Returned Overseas Chinese Scholars of

D meson production in proton–lead (p+Pb) collisions is globally investigated within the color dipole framework. To simplify the Fourier transform, the analytical transverse momentum distribution functions extracted from different color dipole models are used. With the Glauber–Gribov method, the impact parameter dependence is considered for the nuclear modification of the gluon density. We obtain from comparison with recent experimental data from the LHCb and ALICE Collaborations that the theoretical results from the Kovchegov, Lu and Rezaeian (KLR) model are in good agreement with the experimental data at small P T, and the results from the Golec–Biernat–Wüsthoff (GBW) and Bartels, Golec-Biernat and Kowalski (BGK) model are reasonable at all rapidity bins. Then, the influence of the initial-state energy loss effect on D meson production in p+Pb collisions is analyzed. A clear reduction of the nuclear modification factor is shown at backward rapidity. Finally, the predictive results for D0 and D+ production differential cross section versus rapidity (Y) in p+Pb collisions are given.

Bulk properties of the system in Au–Au collisions at 3 GeV and their dependence on collision centrality and particle rapidity

We analyze the transverse momentum spectra of proton (p), deuteron (d), triton (t), and helium (3He and 4He) in different centrality intervals in various rapidity slices in gold–gold (Au–Au) collisions at sNN=3 GeV. We apply the blast-wave model with Tsallis statistics (TBW) to transverse momentum spectra of the particles, which fits well the data of STAR Collaboration. The freezeout parameters such as kinetic freezeout temperature, transverse flow velocity, and kinetic freezeout volume are extracted. Our findings reveal that central collisions exhibit higher values for the kinetic freezeout temperature, transverse flow velocity, and kinetic freezeout volume (which means that the central collisions are more hot and expansive), and observed that they decrease from central to peripheral collisions, and the former two parameters decrease from backward rapidity regions to mid-rapidity. This indicates a rapid expansion of the system in central collisions and in backward rapidities. The above parameters are mass-dependent, and the former increases, while the latter two decrease for heavier particles, reflecting the multiple kinetic freezeout and volume differential freezeout scenarios. Besides, the entropy parameter (q) is extracted, and it increases from peripheral to central and from backward to mid-rapidity regions.

Two-Pion Bose–Einstein Correlations in Au+Au Collisions at sNN = 3 GeV in the STAR Experiment

The correlation femtoscopy technique makes it possible to estimate the geometric dimensions and lifetime of the particle emission region after the collision of ions. Measurements of the emission region characteristics not only at midrapidity but also at backward (forward) rapidity can provide new information about the source and make it possible to impose constraints on the heavy-ion collision models. This work is devoted to revealing the dependence of the spatial and temporal parameters of the emission region of identical pions in Au+Au collisions at sNN = 3 GeV from the fixed-target program of the STAR experiment. The extracted femtoscopic radii, Rout, Rside, Rlong, Rout−long2, and the correlation strength, λ, are presented as a function of collision centrality, pair rapidity, and transverse momentum. Physics implications will be discussed.

Fraction of χ_{c} Decays in Prompt J/ψ Production Measured in pPb Collisions at sqrt[s_{NN}]=8.16 TeV.

The fraction of χ_{c1} and χ_{c2} decays in the prompt J/ψ yield, F_{χ_{c}→J/ψ}=σ_{χ_{c}→J/ψ}/σ_{J/ψ}, is measured by the LHCb detector in pPb collisions at sqrt[s_{NN}]=8.16 TeV. The study covers the forward (1.5<y^{*}<4.0) and backward (-5.0<y^{*}<-2.5) rapidity regions, where y^{*} is the J/ψ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6±0.3 and 20.8±0.5 nb^{-1}, respectively. The result is presented as a function of the J/ψ transverse momentum p_{T,J/ψ} in the range 1<p_{T,J/ψ}<20 GeV/c. The F_{χ_{c}→J/ψ} fraction at forward rapidity is compatible with the LHCb measurement performed in pp collisions at sqrt[s]=7 TeV, whereas the result at backward rapidity is 2.4σ larger than in the forward region for 1<p_{T,J/ψ}<3 GeV/c. The increase of F_{χ_{c}→J/ψ} at low p_{T,J/ψ} at backward rapidity is compatible with the suppression of the ψ(2S) contribution to the prompt J/ψ yield. The lack of in-medium dissociation of χ_{c} states observed in this study sets an upper limit of 180MeV on the free energy available in these pPb collisions to dissociate or inhibit charmonium state formation.

Production of η and η′ mesons in pp and pPb collisions

The production of η and η′ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of 5.02 and 13TeV and proton-lead collisions are studied at a center-of-mass energy per nucleon of 8.16TeV. The studies are performed in center-of-mass (c.m.) rapidity regions 2.5&lt;yc.m.&lt;3.5 (forward rapidity) and −4.0&lt;yc.m.&lt;−3.0 (backward rapidity) defined relative to the proton beam direction. The η and η′ production cross sections are measured differentially as a function of transverse momentum for 1.5&lt;pT&lt;10GeV and 3&lt;pT&lt;10GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for η and η′ mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of η mesons are also used to calculate η/π0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as η and η′ meson fragmentation. ©2024 CERN, for the LHCb Collaboration 2024 CERN

Prompt photon production in proton–nucleus collisions at LHC: a comparison among color dipole models* *Supported by the National Natural Science Foundation of China (Grant No. U1832120), the Natural Science Foundation for Outstanding Young Scholars of Hebei Province (Grant No. A2020210012), the S&T Program of Hebei (Grant No. 236Z4601G), and the Scientific Research Foundation for the Introducing Returned Overseas Chinese Scholars

The nuclear modification factor for prompt photon production in proton–nucleus collisions is investigated within color dipole formalism. By means of the Glauber–Gribov approach, the nuclear effects are studied in various rapidity bins with the evolution equation-based saturation models and the phenomenological dipole models. The theoretical results are compared with the experimental data provided by PHENIX, ATLAS and CMS Collaborations. At forward rapidity and midrapidity, a reasonable agreement with the experimental data is shown for the theoretical results with the modified Kharzeev, Levin and Nardi model, and the Kowalski and Teaney model. Then, we analyze the influence of the initial state energy loss effect on the nuclear modification factor and find that it is obvious only at backward rapidity together with small p T. Finally, the theoretical results are also compared with those of JETPHOX Monte Carlo program and the predictive results for the LHCb at very forward rapidities are presented.

Measurements of azimuthal anisotropies at forward and backward rapidity with muons in high-multiplicity p–Pb collisions at [formula omitted] TeV

The study of the azimuthal anisotropy of inclusive muons produced in p–Pb collisions at sNN=8.16 TeV, using the ALICE detector at the LHC is reported. The measurement of the second-order Fourier coefficient of the particle azimuthal distribution, v2, is performed as a function of transverse momentum pT in the 0–20% high-multiplicity interval at both forward (2.03<yCMS<3.53) and backward (−4.46<yCMS<−2.96) rapidities over a wide pT range, 0.5<pT<10 GeV/c, in which a dominant contribution of muons from heavy-flavour hadron decays is expected at pT>2 GeV/c. The v2 coefficient of inclusive muons is extracted using two different techniques, namely two-particle cumulants, used for the first time for heavy-flavour measurements, and forward–central two-particle correlations. Both techniques give compatible results. A positive v2 is measured at both forward and backward rapidities with a significance larger than 4.7σ and 7.6σ, respectively, in the interval 2<pT<6 GeV/c. Comparisons with previous measurements in p–Pb collisions at sNN=5.02 TeV, and with AMPT and CGC-based theoretical calculations are discussed. The findings impose new constraints on the theoretical interpretations of the origin of the collective behaviour in small collision systems.

Measurement of the Prompt D^{0} Nuclear Modification Factor in p-Pb Collisions at sqrt[s_{NN}]=8.16 TeV.

The production of prompt D^{0} mesons in proton-lead collisions in both the forward and backward rapidity regions at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=8.16 TeV is measured by the LHCb experiment. The nuclear modification factor of prompt D^{0} mesons is determined as a function of the transverse momentum p_{T}, and the rapidity in the nucleon-nucleon center-of-mass frame y^{*}. In the forward rapidity region, significantly suppressed production with respect to pp collisions is measured, which provides significant constraints on models of nuclear parton distributions and hadron production down to the very low Bjorken-x region of ∼10^{-5}. In the backward rapidity region, a suppression with a significance of 2.0-3.8 standard deviations compared to parton distribution functions in a nuclear environment expectations is found in the kinematic region of p_{T}>6 GeV/c and -3.25<y^{*}<-2.5, corresponding to x∼0.01.

Measurement of ψ (2S) production as a function of charged-particle pseudorapidity density in pp collisions at sqrt{s} = 13 TeV and p–Pb collisions at sqrt{s_{textrm{NN}}} = 8.16 TeV with ALICE at the LHC

Production of inclusive charmonia in pp collisions at center-of-mass energy of sqrt{s} = 13 TeV and p–Pb collisions at center-of-mass energy per nucleon pair of sqrt{s_{textrm{NN}}} = 8.16 TeV is studied as a function of charged-particle pseudorapidity density with ALICE. Ground and excited charmonium states (J/ψ, ψ(2S)) are measured from their dimuon decays in the interval of rapidity in the center-of-mass frame 2.5 < ycms< 4.0 for pp collisions, and 2.03 < ycms< 3.53 and −4.46 < ycms< −2.96 for p–Pb collisions. The charged-particle pseudorapidity density is measured around midrapidity (|η| < 1.0). In pp collisions, the measured charged-particle multiplicity extends to about six times the average value, while in p-Pb collisions at forward (backward) rapidity a multiplicity corresponding to about three (four) times the average is reached. The ψ(2S) yield increases with the charged-particle pseudorapidity density. The ratio of ψ(2S) over J/ψ yield does not show a significant multiplicity dependence in either colliding system, suggesting a similar behavior of J/ψ and ψ(2S) yields with respect to charged-particle pseudorapidity density. Results for the ψ(2S) yield and its ratio with respect to J/ψ agree with available model calculations.

W±-boson production in p–Pb collisions at sqrt{s_{textrm{NN}}} = 8.16 TeV and Pb–Pb collisions at sqrt{s_{textrm{NN}}} = 5.02 TeV

The production of the W± bosons measured in p–Pb collisions at a centre-of-mass energy per nucleon–nucleon collision sqrt{s_{textrm{NN}}} = 8.16 TeV and Pb–Pb collisions at sqrt{s_{textrm{NN}}} = 5.02 TeV with ALICE at the LHC is presented. The W± bosons are measured via their muonic decay channel, with the muon reconstructed in the pseudorapidity region −4 < {eta}_{textrm{lab}}^{mu } < −2.5 with transverse momentum {p}_{textrm{T}}^{mu } > 10 GeV/c. While in Pb–Pb collisions the measurements are performed in the forward (2.5 < {y}_{textrm{cms}}^{mu } < 4) rapidity region, in p–Pb collisions, where the centre-of-mass frame is boosted with respect to the laboratory frame, the measurements are performed in the backward (−4.46 < {y}_{textrm{cms}}^{mu } < −2.96) and forward (2.03 < {y}_{textrm{cms}}^{mu } < 3.53) rapidity regions. The W− and W+ production cross sections, lepton-charge asymmetry, and nuclear modification factors are evaluated as a function of the muon rapidity. In order to study the production as a function of the p–Pb collision centrality, the production cross sections of the W− and W+ bosons are combined and normalised to the average number of binary nucleon–nucleon collision 〈Ncoll〉. In Pb–Pb collisions, the same measurements are presented as a function of the collision centrality. Study of the binary scaling of the W±-boson cross sections in p–Pb and Pb–Pb collisions is also reported. The results are compared with perturbative QCD calculations, with and without nuclear modifications of the Parton Distribution Functions (PDFs), as well as with available data at the LHC. Significant deviations from the theory expectations are found in the two collision systems, indicating that the measurements can provide additional constraints for the determination of nuclear PDFs and in particular of the light-quark distributions.

Forward-backward multiplicity correlation and fluctuation in 197Au + 197Au collisions at fixed target Elab = 10A, 20A, 30A and 40A GeV in the UrQMD model

We use the ultra-relativistic quantum molecular dynamics (UrQMD) model to study the multiplicity correlations and fluctuations of charged hadrons emitted in the forward and backward rapidity hemispheres in 197Au + 197Au collisions at four different incident beam energies, namely Elab=10A,20A, 30A and 40A GeV. Dependence of the correlation and fluctuation parameters on the incident beam energy, collision centrality, rapidity gap and rapidity window size are examined. Both short and long-ranged correlations contribute to our UrQMD simulated results. In the framework of the UrQMD model the short-ranged correlations can be interpreted in terms of resonance decays and/or cluster formation. The long-ranged correlations on the other hand, perhaps originate from multiple rescattering suffered by the hadrons and decay of longitudinally stretched strings in the rapidity space. Our simulation based analysis can be used to set a reference base-line for any future experimental study on the forward-backward multiplicity correlation for the colliding system and collision energies involved in the present case.

Vortex rings in heavy-ion collisions at energies sNN=3–30 GeV and possibility of their observation

The ring structures that appear in Au+Au collisions at collision energies $\sqrt{s_{NN}}=$ 3 -- 30 GeV are studied. The calculations are performed within the model of three-fluid dynamics. It is demonstrated that a pare of vortex rings are formed, one at forward and another at backward rapidities, in ultra-central Au+Au collisions at $\sqrt{s_{NN}}>$ 4 GeV. The vortex rings carry information about early stage of the collision, in particular about the stopping of baryons. It is shown that these rings can be detected by measuring the ring observable $R_\Lambda$ even in rapidity range $0<y<0.5$ (or $-0.5<y<0$) on the level of 0.5--1.5\% at $\sqrt{s_{NN}}=$ 5 -- 20 GeV. At forward/backward rapidities, the $R_\Lambda$ signal is expected to be stronger. Possibility of observation of the vortex-ring signal against background of non-collective transverse polarization is discussed.

Λ Polarization and Vortex Rings in Heavy-Ion Collisions at NICA Energies

We review recent studies of vortical motion and the resulting polarization of Λ hyperons in heavy-ion collisions at NICA energies, in particular, within the model of three-fluid dynamics (3FD). This includes predictions of the global Λ polarization and ring structures that appear in Au+Au collisions. The global Λ polarization in Au+Au collisions is calculated, including its rapidity and centrality dependence. The contributions of the thermal vorticity and meson-field term (proposed by Csernai, Kapusta, and Welle) to the global polarization are considered. The results are compared with data from recent STAR and HADES experiments. It is predicted that the polarization maximum is reached at sNN≈ 3 GeV if the measurements are performed with the same acceptance. It is demonstrated that a pair of vortex rings are formed, one at forward rapidities and another at backward rapidities, in ultra-central Au+Au collisions at sNN&gt; 4 GeV. The vortex rings carry information about the early stage of the collision, in particular, the stopping of baryons. It is shown that these rings can be detected by measuring the ring observable RΛ, even in the midrapidity region at sNN= 5–20 GeV. At forward/backward rapidities, the RΛ signal is expected to be stronger. The possibility of observing the vortex-ring signal against the background of non-collective transverse polarization is discussed.

J/ψ and ψ(2S) production in small systems with PHENIX

The nuclear modification of J/ψ production has been studied at forward and backward rapidity in the collision systems p+Al, p+Au, and 3He+Au. A comparison of results for p+Au and 3He+Au is presented, with a focus on possible differences caused by the different particle multiplicity in the final state. The modification of ψ(2S) production in p+Au collisions has also been studied at forward and backward rapidity as a function of centrality. The ψ(2S) results complement earlier results at mid-rapidity at RHIC energies and results obtained at LHC energies, revealing a strong rapidity dependence of the ψ(2S) nuclear modification at RHIC energies that is indicative of final state effects.

Interactions between heavy quarks and tilted QGP fireballs in 200 A GeV Au+Au collisions* *Supported by the National Natural Science Foundation of China (11935007, 12175122, 2021-867), Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008), Natural Science Foundation of Hubei Province (2021CFB272), Education Department of Hubei Province of China with Young Talents Project (Q20212703), Open Foundation of Key Laboratory

Heavy quark observables are applied to probe the initial energy density distribution with violation of longitudinal boost invariance produced in relativistic heavy-ion collisions. Using an improved Langevin model coupled to a (3+1)-dimensional viscous hydrodynamic model, we study the nuclear modification factor () and directed flow () and elliptic flow () coefficients of heavy mesons and their decayed electrons at an RHIC energy. We find that the counter-clockwise tilt of nuclear matter in the reaction plane results in a positive (negative) heavy flavor in the backward (forward) rapidity region, whose magnitude increases with the heavy quark transverse momentum. The difference in the heavy flavor between different angular regions is also proposed as a complementary tool to characterize the asymmetry of the medium profile. Our model results are consistent with currently available data at the RHIC and provide predictions that can be tested by future measurements.

Anisotropic Flows of Charmonium in the Relativistic Heavy-Ion Collisions

We review recent studies about anisotropic flows (v1,v2,v3) of charmonium in the quark-gluon plasma produced in relativistic heavy-ion collisions. Collective flows of the bulk medium are developed due to the anisotropic pressure gradient of the medium. Strongly coupled with the bulk medium, charm quarks carry collective flows from the expanding medium, which will be inherited by the regenerated charmonium via the coalescence process. In event-by-event collisions where nucleon positions fluctuate from the smooth distribution, there is triangularity in the medium initial energy density. Triangular flows of the bulk medium and heavy flavor particles can be developed due to the initial fluctuations. In the longitudinal direction, the rapidity-odd distribution of the initial energy density is induced by the rotation of the medium in non-central heavy-ion collisions. Charmonium suffers biased dissociation along positive and negative x-directions in forward (backward) rapidity. The directed flow of charmonium becomes non-zero. The directed, elliptic and triangular flows (v1,v2,v3) of charmonium come from the anisotropic initial distributions of the medium energy density in the transverse and longitudinal directions.

System scan of the multiplicity correlation between forward and backward rapidities in relativistic heavy-ion collisions using a multi-phase transport model * *Supported in part the National Natural Science Foundation of China (11890710, 11890714, 11875066, 11925502, 11961141003), the Strategic Priority Research Program of CAS (XDB34000000), National Key R&D Program of China (2018YFE0104600, 2016YFE0100900), and Guangdong Major Project of Basic and Applied

A systematic study on forward–backward (FB) multiplicity correlations from large systems to small ones through a multi-phase transport model (AMPT) has been performed and the phenomenon that correlation strength increases with centrality can be explained by taking the distribution of events as the superposition of a series of Gaussian distributions. It is also found that correlations in the plane can imply the shape of the event. Furthermore, long-range correlations originate from the fluctuations associated with the source information. FB correlations allow us to decouple long-range correlations from short-range correlations, and may provide a chance to investigate the α-clustering structure in initial colliding light nuclei as well. It seems the tetrahedron 16O + 16O collision gives a more uniform and symmetrical fireball, that emits the final particles more isotropically or independently in the longitudinal direction, indicating that the forward–backward multiplicity correlation could be used to identify the pattern of α-clustered 16O in future experiments.

Accessing subnuclear fluctuations and saturation with multiplicity dependent J/ψ production in p+p and p+Pb collisions

We study the production of J/ψ vector mesons as a function of charged hadron multiplicity in p+p and p+Pb collisions at LHC energies. We employ the color glass condensate framework, using running coupling Balitsky-Kovchegov evolved dipole amplitudes, to compute gluon and cc¯-pair production. We use fragmentation functions to obtain charged hadrons, and explore two different hadronization schemes for the J/ψ: non-relativistic quantum chromodynamics and the improved color evaporation model. In our framework, event-by-event multiplicity fluctuations of both hadrons and J/ψ are driven by geometric and saturation scale normalization fluctuations. Studying the correlation between J/ψ and hadron multiplicity, we show that the characteristic difference between forward and backward rapidity in p+Pb collisions is a result of different degrees of saturation probed at different rapidities. We demonstrate that experimental data on heavy-flavor production as a function of event activity provide stringent constraints on the fluctuating proton structure.

The ϕ meson production in small collision systems observed by PHENIX

The measurements of light hadron production in small collision systems (such as p+Al, p+Au, d+Au, 3He+Au) may allow to explore the quarkgluon plasma formation and to determine the main hadronization mechanism in the considered collisions. Such research has become particularly crucial with the observation of the light hadrons collective behavior in p/d/3He+Au collisions at √SNN = 200 GeV and in p+Al collisions at the same energy at forward and backward rapidities. Among the large variety of light hadrons, ϕ meson is of particular interest since its production is sensitive to the presence of the quark-gluon plasma. The paper presents the comparison of the obtained experimental results on ϕ meson production to different light hadron production in p+Al and 3He+Au at √SNN = 200 GeV at midrapidity. The comparisons of ϕ meson production in p+Al, p+Au, d+Au, and 3He+Au collisions at √SNN = 200 GeV at midrapidity to theoretical models predictions (PYTHIA model and default and string melting versions of the AMPT model) are also provided. The results suggest that the QGP can be formed in p/d/3He+Au collisions, but the volume and lifetime of the produced medium might be insufficient for observation of strangeness enhancement effect. Conceivably, the main hadronization mechanism of ϕ meson production in p+Al collisions is fragmentation, while in p/d/3He+Au collisions this process occurs via coalescence.

Centrality dependence of J/\u03c8 and \u03c8(2S) production and nuclear modification in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 8.16 TeV

The inclusive production of the J/ψ and ψ(2S) charmonium states is studied as a function of centrality in p-Pb collisions at a centre-of-mass energy per nucleon pair sqrt{s_{mathrm{NN}}} = 8.16 TeV at the LHC. The measurement is performed in the dimuon decay channel with the ALICE apparatus in the centre-of-mass rapidity intervals −4.46 < ycms< −2.96 (Pb-going direction) and 2.03 < ycms< 3.53 (p-going direction), down to zero transverse momentum (pT). The J/ψ and ψ(2S) production cross sections are evaluated as a function of the collision centrality, estimated through the energy deposited in the zero degree calorimeter located in the Pb-going direction. The pT-differential J/ψ production cross section is measured at backward and forward rapidity for several centrality classes, together with the corresponding average 〈pT〉 and leftlangle {p}_{mathrm{T}}^2rightrangle values. The nuclear effects affecting the production of both charmonium states are studied using the nuclear modification factor. In the p-going direction, a suppression of the production of both charmonium states is observed, which seems to increase from peripheral to central collisions. In the Pb-going direction, however, the centrality dependence is different for the two states: the nuclear modification factor of the J/ψ increases from below unity in peripheral collisions to above unity in central collisions, while for the ψ(2S) it stays below or consistent with unity for all centralities with no significant centrality dependence. The results are compared with measurements in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV and no significant dependence on the energy of the collision is observed. Finally, the results are compared with theoretical models implementing various nuclear matter effects.