arXiv subjects
Publications and source records attributed to Adam Bzdak.
The azimuthal cumulants, $c_2\{2\}$ and $c_2\{4\}$, originating from the global conservation of transverse momentum in the presence of hydro-like elliptic flow are calculated. We observe the sign change of $c_2\{4\}$ for small number of produced particles. This is in a qualitative agreement with the recent ATLAS measurement of multi-particle azimuthal correlations with the subevent cumulant method.
We calculate the $k$-particle ($k=2,4,6,8$) azimuthal cumulants resulting from the conservation of transverse momentum. We find that $c_2\{k\}>0$ and depending on the transverse momenta, $c_2\{k\}$ can reach substantial values even for a relatively large number of particles. The impact of our results on the understanding of the onset of collectivity in small systems is emphasized.
The dependence of multi-proton correlation functions and cumulants on the acceptance in rapidity and transverse momentum is studied. We find that the preliminary data of various cumulant ratios are consistent, within errors, with rapidity and transverse momentum independent correlation functions. However, rapidity correlations which moderately increase with rapidity separation between protons are slightly favored. We propose to further explore the rapidity dependence of multi-particle correlation functions by measuring the dependence of the integrated reduced correlation functions as a function of the size of the rapidity window.
Following previous work [1], we propose to analyze the rapidity dependence of transverse momentum and transverse-momentum multiplicity correlations. We demonstrate that the orthogonal polynomial expansion of the latter has the potential to discriminate between models of particle production.
It is argued that the multiplicity distribution in proton-proton ($pp$) collisions, which is often parameterized by the negative binomial distribution, may result from the multiplicity distribution measured in electron-positron ($e^{+}e^{-}$) collisions, once the fluctuating energy carried by two leading protons in $pp$ is taken into account.
A model in which the soft collisions of the nucleon are described in terms of interactions of its two constituents (a quark and a diquark) is proposed. When adjusted to describe precisely the elastic proton-proton scattering data and supplemented with the idea of wounded constituents, the model accounts rather well for the centrality dependence of particle production in the central rapidity region at RHIC energies.
In this paper we discuss the relation of particle number cumulants and correlation functions. It is argued that measuring couplings of the genuine multi-particle correlation functions could provide cleaner information on possible non-trivial dynamics in heavy-ion collisions. We extract integrated multi-proton correlation functions from the presently available experimental data on proton cumulants. We find that the STAR data contain significant four-proton correlations, at least at the lower energies, with indication of changing dynamics in central collisions. We also find that these correlations are rather long-ranged in rapidity. Finally, using the Ising model, we demonstrate how the signs of the multi-proton correlation functions may be used to exclude certain regions of the phase diagram close to the critical point.
We investigate possible effects of correlations between stopped nucleons on higher order proton cumulants at low energy heavy-ion collisions. We find that fluctuations of the number of wounded nucleons $N_{\mathrm{part}}$ lead to rather nontrivial dependence of the correlations on the centrality; however, this effect is too small to explain the large and positive four-proton correlations found in the preliminary data collected by the STAR collaboration at $\sqrt{s}=7.7$ GeV. We further demonstrate that, by taking into account additional proton clustering, we are able to qualitatively reproduce the preliminary experimental data. We speculate that this clustering may originate either from collective/multi-collision stopping which is expected to be effective at lower energies or from a possible first-order phase transition, or from (attractive) final state interactions. To test these ideas we propose to measure a mixed multi-particle correlation between stopped protons and a produced particle (e.g. pion, antiproton).
In this note, using the colour string model, we study the configuration space distribution of stopped nucleons in heavy-ion collisions. We find that the stopped nucleons from the target and the projectile end up separated from each other by the distance increasing with the collision energy. In consequence, for the center of mass energies larger than 6 or 10 GeV (depending on the details of the model) it appears that the system created is not in thermal and chemical equilibrium, and the net baryon density reached is likely not much higher than that already present in the colliding nuclei.
We evaluate $n$-particle ($n=2,3,4,5$) transverse momentum correlations for pions and kaons following from the decay of statistical clusters. These correlation functions could provide strong constraints on a possible existence of thermal clusters in the process of particle production.
In this contribution we will discuss how the study of various fluctuation observables may be used to explore the phase diagram of the strong interaction. We will briefly summarize the present study of experimental and theoretical research in this area. We will then discuss various corrections and issues which need to be understood and applied for a meaningful comparison of experimental measurements with theoretical predictions. This contribution is dedicated to Andrzej Bialas on the occasion of his $80^{\mathrm{th}}$ birthday.
We study the effect of intrinsic fluctuations of the proton saturation momentum scale on event-by-event rapidity distributions. Saturation scale fluctuations generate an asymmetry in the single particle rapidity distribution in each event resulting in genuine n-particle correlations having a component linear in the rapidities of the produced particles, $y_1\cdots y_n$. We introduce a color domain model that naturally explains the centrality dependence of the two-particle rapidity correlations recently measured by ATLAS while constraining the probability distribution of saturation scale fluctuations in the proton. Predictions for n = 4, 6 and 8 particle correlations find that the four and eight-particle cumulant change sign at an intermediate multiplicity, a signature which could be tested experimentally.
The two-particle short-range correlation functions in rapidity, azimuthal angle and transverse momentum, following from the decay of statistical clusters are evaluated and discussed.
In this note we extend previous work on efficiency corrections for cumulant measurements [1,2]. We will discuss the limitations of the methods presented in these papers. Specifically we will consider multiplicity dependent efficiencies as well as a non-binomial efficiency distributions. We will discuss the most simple and straightforward methods to implement those corrections.
Intrinsic fluctuations of the proton saturation momentum generate asymmetric rapidity distributions on an event-by-event basis. We argue that the asymmetric component, $\left $, of the orthogonal polynomial decomposition of the two-particle rapidity correlation function is a sensitive probe to this distribution of fluctuations. We present a simple model connecting the experimentally measured $\left $ to the variance, $σ$, of the distribution of the logarithm of the proton saturation scale. We find that $σ\approx 0. 5-1$ describes the asymmetric component of the rapidity correlations recently measured by the ATLAS collaboration.
The recently measured centrality dependence of high energy jets in proton-lead collisions at the LHC is investigated. We hypothesize that events with jets of very high energy (a few hundred GeV) are characterized by a suppressed number of soft particles, thus shifting these events into more peripheral bins. This naturally results in the suppression (enhancement) of the nuclear modification factor, $R_{pA}$, in central (peripheral) collisions. Our calculations suggest that a moderate suppression of the order of $20\%$, for $10^{3}$ GeV jets, can quantitatively reproduce the experimental data. We further extract the suppression factor as a function of jet energy and test our conjecture using available $R_{pA}$ data for various centralities.
We calculate the genuine long-range multi-particle rapidity correlation functions, $C_{n}(y_1,...,y_n)$ for $n=3,4,5,6$, originating from fluctuations of the fireball longitudinal shape. In these correlation functions any contribution from the short-range two-particle correlations, and in general up to $(n-1)$-particle in $C_n$, is suppressed. The information about the fluctuating fireball shape in rapidity is encoded in the cumulants of coefficients of the orthogonal polynomial expansion of particle distributions in rapidity.
We compute analytically the multi-particle eccentricities, ε_m {2n}, for systems dominated by fluctuations, such as proton-nucleus collisions at the Large Hadron Collider. In particular, we derive a general relation for <ε_2^{2n}>. We further discuss the relations between various multi-particle eccentricities and demonstrate that ε_2{2} > ε_2{4} \simeq ε_2{6} \simeq ε_2{8}, in agreement with recent numerical calculations in a Glauber model.