Forward-backward multiplicity correlation strengths have been measured with the STAR detector for Au+Au and $\textit{p+p}$ collisions at $\sqrt{s_{NN}}$ = 200 GeV. Strong short and long range correlations (LRC) are seen in central Au+Au collisions. The magnitude of these correlations decrease with decreasing centrality until only short range correlations are observed in peripheral Au+Au collisions. Both the Dual Parton Model (DPM) and the Color Glass Condensate (CGC) predict the existence of the long range correlations. In the DPM the fluctuation in the number of elementary (parton) inelastic collisions produces the LRC. In the CGC longitudinal color flux tubes generate the LRC. The data is in qualitative agreement with the predictions from the DPM and indicates the presence of multiple parton interactions.
The centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor 2 from peripheral (70-80%) to central (0-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.
Forward-backward multiplicity correlations of target fragments in nucleus-emulsion collisions at a few hundred MeV/nucleon
本文研究了150 A MeV He-乳胶、290 A MeV C-乳胶、400 A MeV C-乳胶、400 A MeV Ne-乳胶和500 A MeV Fe-乳胶相互作用中靶蒸发碎片（黑径迹粒子）和靶反冲质子（灰径迹粒子）的前向-后向多重数和关联。结果表明，灰、黑和重电离径迹粒子的前向和后向平均多重数随靶尺寸的增大而增大。前向黑径迹粒子、后向黑径迹粒子和后向灰径迹粒子的平均多重数与粒子大小和能量无关，但前向灰径迹粒子的平均多重数随粒子大小和能量的增加而增加。后向灰径迹粒子多重数分布服从指数衰减规律，衰减常数随目标尺寸的增大而减小。前后向多重数关联遵循线性规律，与弹丸尺寸和能量无关，在某些重目标数据集中观察到饱和效应。
Recently, Chatterjee et al used a hadronic transport model to estimate the resolution with which various experimental quantities select the impact parameter of relativistic heavy ion collisions at collision energies relevant to the Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC). Measures based on particle multiplicity at forward rapidity were found to be significantly worse than those based on midrapidity multiplicity. Using the same model, we show that a slightly more sophisticated measure greatly improves the resolution based on forward rapidity particles; this …
Forward-backward emission of target evaporated evaporated fragments at high energy nucleus-nucleus collisions
研究了12 A GeV的$^{4}$ He、3.7 A GeV的$^{16}$ O、60 A GeV的$^{16}$ O、1.7 A GeV的$^{84}$ Kr和10.7 A GeV的$^{197}$ Au乳胶重靶（AgBr）相互作用中靶蒸发碎片在前半球和后半球发射的多重数分布、多重数矩、标度方差、熵和约化熵.结果表明，靶蒸发碎片在前半球和后半球的多重数分布可用高斯分布拟合。在前半球和后半球发射的目标蒸发粒子的多重数矩随着矩{ \em q}的阶数的增加而增加，并且对于前半球和后半球的所有相互作用，二阶多重数矩分别与总能量无关。标度方差，多重性波动的直接测量，是接近一个所有的相互作用，可以说，有一个微弱的相关性之间产生的粒子。在实验误差范围内，前半球和后半球发射的靶蒸发碎片的熵是相同的。
Multiplicity and Pseudorapidity Distributions of Charged Particles and Photons at Forward Pseudorapidity in Au + Au Collisions at sqrt{s_NN} = 62.4 GeV
本文给出了sqrt{sNN} = 62.4GeV的Au + Au碰撞中带电粒子和光子的多重数和赝快度分布的中心依赖测量。带电粒子和光子分别在赝快度区域2.9 < eta < 3.9和2.3 < eta < 3.7测量。我们研究了粒子产生随参与核子数和二体碰撞数的标度。在测量的赝快度范围内的光子和带电粒子的产生已被证明是符合能量无关的限制碎裂行为。光子被观察到遵循一个中心独立的限制碎裂行为，而对于带电粒子，它是中心依赖。本文对核-核碰撞中带正电荷的强子、带负电荷的强子、光子、π介子、净质子的赝快度分布和p+p碰撞的赝快度分布进行了比较研究。从这些比较中，我们得出结论，重子的包容性带电粒子分布是负责所观察到的限制碎裂的中心性依赖。介子遵循能量无关的有限碎裂行为，而重子的行为似乎是能量相关的。
We report the collision-centrality dependence of cumulants of event-by-event net-proton, net-charge and net-kaon distributions in Au+Au collisions for center-of-mass energy $\sqrt{s_{NN}}$ = 54.4 GeV from the STAR experiment. Strong collision-centrality dependence is observed for cumulants ($C_{n}, n$ $\leq$ 4) of the net-particle distributions. The cumulant ratios $C_{3}/C_{2}$, $C_{4}/C_{2}$ and $C_{6}/C_{2}$ exhibit a weak collision-centrality dependence. The $C_{6}/C_{2}$ of net-proton and net-charge distributions for most central gold nuclei collisions at $\sqrt{s_{NN}}$ = 54.4 GeV show p…
We studied the centrality selection effect on cumulants (up to fourth order) and the cumulants ratios of net-proton multiplicity distributions in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7.7, 19.6 and 200 GeV from UrQMD model. The net-proton cumulants are calculated with collision centralities by using charged particle multiplicity from different pesudorapidity ($η$) region. By comparing the results from various collision centralities, we found that the autocorrelation effects are not significant in the results with collision centralities "refmult-3" and "refmult-2", which are using mid-…
STAR's measurement of Long-range forward-backward multiplicity correlations as the signature of "dense partonic matter" in the Heavy Ion collisions at $\sqrt{s_{NN}}=$200 GeV.}
Two-particle pseudorapidity correlations are measured in 2.76 TeV Pb+Pb, 5.02 TeV pPb and 13 TeV pp collisions. Correlation function is measured using charged particles in the pseudorapidity range $|η|<2.4$ with transverse momentum $p_T>0.2$ GeV, and it is measured as a function of event multiplicity, defined by number of charged particles with $|η|<2.5$ and $p_T>0.4$ GeV. The correlation function is decomposed into a short-range component (SRC) and a long-range component (LRC). The SRC differs significantly between the opposite-charge pairs and same-charge pairs, and between the three collisi…
The recently proposed participant dissipating effective-energy approach is applied to describe the dependence on centrality of the multiplicity of charged particles measured in heavy-ion collisions at the collision energies up to the highest LHC energy of 5 TeV. The effective-energy approach relates multihadron production in different types of collisions, by combining, under the proper collision energy scaling, the constituent quark picture with Landau relativistic hydrodynamics. The measurements are shown to be well described in terms of the centrality-dependent effective energy of participan…
It is argued that the superposition approach, where partons are independently emitted from longitudinally extended sources in the early stage, is fully compatible with the experimental results for the forward-backward multiplicity correlations in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76 \textrm{ TeV}$. The pertinent correlation analysis is based on the PhD Thesis of Ref. [1], which includes an unpublished analysis of data taken by the ALICE Collaboration. Our calculations show that in the experimentally covered pseudorapidity range $Δη=1.2$, the initial sources in the backward and forward bins …
The pseudorapidity density of charged particles ($\mathrm{d}N_\mathrm{ch}/\mathrm{d}η$) at mid-rapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.02 TeV. It increases with centrality and reaches a value of $1943 \pm 54$ in $|η|<0.5$ for the 5% most central collisions. A rise in $\mathrm{d}N_\mathrm{ch}/\mathrm{d}η$ as a function of $\sqrt{s_{\rm NN}}$ for the most central collisions is observed, steeper than that observed in proton-proton collisions and following the trend established by measurements at lower energy. The centra…
In this Letter, the ALICE Collaboration presents the first measurements of the charged-particle multiplicity density, $\rm{d}N_{\rm{ch}}/\rm{d}η$, and total charged-particle multiplicity, $N_{\rm{ch}}^{\rm{tot}}$, in Xe-Xe collisions at a centre-of-mass energy per nucleon--nucleon pair of $\sqrt{s_{\rm NN}}$ = 5.44 TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of $-3.5 < η< 5$. The values of $\rm{d}N_{\rm{ch}}/\rm{d}η$ at mid-rapidity and $N_{\rm{ch}}^{\rm{tot}}$ for central collisions, normalised to the number of nucleons participat…
Multiplicity distributions of charged particles and their event-by-event fluctuations have been compiled for relativistic heavy-ion collisions from the available experimental data at Brookhaven National Laboratory and CERN and also by the use of an event generator. Multiplicity fluctuations are sensitive to QCD phase transition and to the presence of critical point in the QCD phase diagram. In addition, multiplicity fluctuations provide baselines for other event-by-event measurements. Multiplicity fluctuation expressed in terms of the scaled variance of the multiplicity distribution is an inte…
We present a measurement of inclusive J/$ψ$ production in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, $p_{\rm T}$, in the backward ($-4.46 < y_{\rm cms} < -2.96$) and forward ($2.03 < y_{\rm cms} < 3.53$) rapidity intervals in the dimuon decay channel and in the mid-rapidity region ($-1.37 < y_{\rm cms} < 0.43$) in the dielectron decay channel. The backward and forward rapidity inte…
The initial geometry effect on forward-backward multiplicity correlations $C(N_{f},N_{b})$ is studied in relativistic collisions between light nuclei by using a multiphase transport model (AMPT). It is found that tetrahedron $^{16}$O + $^{16}$O gives a more uniform and symmetrical fireball which produces a more isotropic distribution of final particles after the expansion and evolution, and leads to a small $C(N_{f},N_{b})$. Forward-backward multiplicity correlation could be taken as a useful probe to distinguish the pattern of $α$-clustered $^{16}$O in experiments by comparing the neighboring…
Volume or centrality fluctuations (CF) is one of the main uncertainties for interpreting the centrality dependence of many experimental observables. The CF is constrained by centrality selection based on particle multiplicity in a reference subevent, and contributes to observables measured in another subevent. Using a Glauber-based independent source model, we study the influence of CF on several distributions of multiplicity $N$ and eccentricities $ε_n$: $p(N)$, $p(ε_n)$, $p(ε_n,ε_m)$ and $p(N,ε_n)$, where the effects of CF is quantified using multi-particle cumulants of these distributions. …
Centrality definition in A$+$A collisions at colliders such as RHIC and LHC suffers from a correlated systematic uncertainty caused by the efficiency of detecting a p$+$p collision ($50\pm 5\%$ for PHENIX at RHIC). In A$+$A collisions where centrality is measured by the number of nucleon collisions, $N_{\rm coll}$, or the number of nucleon participants, $N_{\rm part}$, or the number of constituent quark participants, $N_{\rm qp}$, the error in the efficiency of the primary interaction trigger (Beam-Beam Counters) for a p$+$p collision leads to a correlated systematic uncertainty in $N_{\rm par…
Fluctuations of various observables in heavy-ion collisions at ultra-relativistic energies have been extensively studied as they provide important signals regarding the formation of a Quark-Gluon Plasma (QGP). Because of the large number of produced particles in each event, a detailed study of event-by-event multiplicity fluctuations has been proposed as one of the signatures of the phase transition. In addition, the understanding of multiplicity fluctuations is essential for other event-by-event measurements. In the present work, we have calculated the scaled variance ($ω_{\rm ch}=σ^{\rm 2} /…
The multihadron production in nucleus-nucleus collisions and its interrelation with that in (anti)proton-proton interactions are studied by exploring the charged particle mean multiplicity collision-energy and centrality dependencies in the measurements to date. The study is performed in the framework of the recently proposed effective-energy approach which, under the proper scaling of the collision energy, combines the constituent quark picture with Landau relativistic hydrodynamics counting for the centrality-defined effective energy of participants and relating different types of collisions…
