Two-particle correlations in azimuthal angle and pseudorapidity in central $^7$Be+$^9$Be collisions at the CERN Super Proton Synchrotron

New Challenges to Hydrodynamics from Azimuthal Anisotropy at RHIC

This paper presents $v_{4}/v_{2}^2$ ratio as a function of transverse momentum ($p_{t}$), pseudorapidity ($η$) and collision centrality in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). It is found that $v_{4}/v_{2}^2$ is larger than Hydrodynamic calculations, the centrality and transverse dependence of this ratio can not be fully described by Hydrodynamics, and the pseudorapidity dependence is opposite to what one expects from Hydrodynamics. The $p_{t}$ dependence of $v_{1}$ is also presented. It is found that $v_{1}(p_{t})…

Fluctuations of the azimuthal particle distribution in NA49 at the CERN SPS

Event-by-event fluctuations and correlations in azimuthal angle are currently widely investigated in various experiments. In this paper the $Φ$ measure (earlier used in experiments to evaluate fluctuations in transverse momentum) is now applied to azimuthal angle $ϕ$. Properties of this $Φ_ϕ$ function are investigated through fast generators and with complex models such as Pythia, Hijing, and UrQMD. Preliminary results of NA49 on $Φ_ϕ$ are also presented. The system size dependence (p+p, C+C, Si+Si and 6 centralities of Pb+Pb) at the highest SPS energy (158$A$ GeV) is shown, as well as the ene…

Event-plane decorrelation over pseudo-rapidity and its effect on azimuthal anisotropy measurement in relativistic heavy-ion collisions

Within A Multi-Phase Transport model, we investigate decorrelation of event planes over pseudorapidity and its effect on azimuthal anisotropy measurements in relativistic heavy-ion collisions. The decorrelation increases with increasing η gap between particles used to reconstruct the event planes. The third harmonic event planes are found even anticorrelated between forward and backward rapidities, the source of which may root in the opposite orientation of the collision geometry triangularities. The decorrelation may call into question the anisotropic flow measurements with pseudorapidity gap…

Energy and System-size Dependence of Two-particle Azimuthal Correlations of High-pT Charged Hadrons at the CERN SPS

Angular correlations of high-pT hadrons can serve as a probe of interactions of partons with the dense medium produced in high-energy heavy-ion collisions but other sources of such correlations exist which can be non-negligible SPS energies. In an attempt to determine the primary source, NA49 has performed an energy and system-size scan of two-particle azimuthal correlations in central Pb+Pb, Si+Si and p+p collisions at 158A GeV, as well as central Pb+Pb collisions at 20A, 30A, 40A and 80A GeV. Moreover, results at 158A GeV have been compared to UrQMD simulations.

Two-particle Azimuthal Correlations of High-pT Charged Hadrons at the CERN SPS

Two-particle azimuthal correlations of high-pT hadrons can serve as a probe of interactions of partons with the dense medium produced in high-energy heavy-ion collisions. First NA49 results on such correlations are presented for central and mid-central Pb+Pb collisions at 158A GeV beam energy, for different centrality bins and charge combinations of trigger and associate particles. These results feature a flattened away-side peak in the most central collisions, which is consistent with expectations of the medium-interaction scenario. A comparison with CERES Pb+Au results at the same energy, as…

Limiting fragmentation in high-energy nuclear collisions at the CERN Large Hadron Collider

The hypothesis of limiting fragmentation (LF) or it is called otherwise recently, as extended longitudinal scaling, is an interesting phenomena in high energy multiparticle production process. This paper discusses about different regions of phase space and their importance in hadron production, giving special emphasis on the fragmentation region. Although it was conjectured as a universal phenomenon in high energy physics, with the advent of higher center-of-mass energies, it has become prudent to analyse and understand the validity of such hypothesis in view of the increasing inelastic nucleo…

Study of azimuthal correlations between D mesons and charged particles with the ALICE experiment

A study of azimuthal correlations between D$^0$, D$^+$, and D$^{*+}$ and charged particles in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV is presented. D mesons were reconstructed from their hadronic decays at central rapidity ($|y| < 0.5$) in the transverse momentum range $3 \leq p_{\rm T}^{\rm D} \leq 16$ GeV/$c$ and they were correlated with charged particles reconstructed in the pseudorapidity range $|η| < 0.8$. Perspectives for the measurement in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.5 TeV after the ALICE upgrade are presented as well.

Forward-rapidity azimuthal and radial flow of identified particles for $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions

A strong azimuthal flow signature at RHIC suggests rapid system equilibration leading to an almost perfect fluid state. The longitudinal extent of the flow behavior depends on how this state is formed and can be studied by measuring the pseudorapidity and transverse momentum dependence of the second Fourier component ($v_{2}(p_{T})$) of the azimuthal angular distribution. We report on a measurement of identified-particle $v_{2}$ as a function of $p_{T}$ (0.5-2.0 GeV/c), centrality (0-25%, 25-50%), and pseudorapidity ($0\leqη<3.2$) for $\sqrt{s_{NN}} = 200 \rm GeV$ Au+Au collisions. The BRAHMS …

Transverse momentum fluctuations and Δη-Δϕcorrelations in p+p interactions at the CERN SPS energies

The NA61/SHINE experiment aims to discover the critical point of strongly interacting matter and study the properties of the onset of deconfinement. These goals are to be achieved by performing a two dimensional phase diagram (T-μ_B) scan by measurements of hadron production properties in proton-proton, proton-nucleus and nucleus-nucleus interactions as a function of collision energy and system size. Close to the critical point an increase of fluctuations is predicted. In this contribution preliminary results on transverse momentum fluctuations and two-particle pseudorapidity/azimuthal angle c…

Dipole asymmetry at $\sqrt{s_{NN}} = 200$ GeV Au+Au Collisions from STAR experiment at RHIC

We report the first measurements of azimuthal anisotropy at midrapidity originated from the dipole asymmetry due to fluctuations in the initial geometry in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, based on data from the STAR experiment at the Relativistic Heavy Ion Collider. The signal is almost symmetric in pseudorapidity and we report it as a function of pseudorapidity and transverse momentum for different centrality. Results are compared with available model predictions

Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for $pp$ collisions at $\sqrt{s}=5.02$ and $13$ TeV and $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ATLAS detector

ATLAS measurements of two-particle correlations are presented for $\sqrt{s} = 5.02$ and $13$ TeV $pp$ collisions and for $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV $p$+Pb collisions at the LHC. The correlation functions are measured as a function of relative azimuthal angle $Δϕ$, and pseudorapidity separation $Δη$, using charged particles detected within the pseudorapidity interval $|η|{<}2.5$. Azimuthal modulation in the long-range component of the correlation function, with $|Δη|{>}2$, is studied using a template fitting procedure to remove a "back-to-back" contribution to the correlation function …

Studies of Heavy Flavor Jets Using $D^0$-hadron Correlations in Azimuth and Pseudorapidity in Au+Au Collisions at 200 GeV at the STAR Experiment

Heavy flavor (HF) quarks (charm, bottom) are important probes of the medium produced in relativistic heavy-ion collisions because they are formed in the early stage and propagate throughout the lifetime of the QGP medium. HF-meson spectra and azimuthal anisotropy ($v_{2}$) measurements have been reported by experiments at RHIC and the LHC, and they suggest strong interactions of HF quarks with the medium. $D^{0}$-hadron correlations on relative pseudorapidity and azimuth ($Δη,Δϕ$) provide a method for disentangling correlation structures on ($Δη,Δϕ$), related to jets and bulk phenomena directl…

Measurements of long-range two-particle correlation over a wide pseudorapidity range in p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV

Correlations in azimuthal angle extending over a long range in pseudorapidity between particles, usually called the "ridge" phenomenon, were discovered in heavy-ion collisions, and later found in pp and p$-$Pb collisions. In large systems, they are thought to arise from the expansion (collective flow) of the produced particles. Extending these measurements over a wider range in pseudorapidity and final-state particle multiplicity is important to understand better the origin of these long-range correlations in small-collision systems. In this Letter, measurements of the long-range correlations …

$\sqrt{s_{\rm NN}}$ = 5.02 TeV下pp和p-Pb碰撞中重味强子衰变电子与带电粒子的方位角关联

Azimuthal correlations of heavy-flavor hadron decay electrons with charged particles in pp and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

本研究测量$\sqrt{s_{\rm{NN}}} = 5.02$ TeV下pp和p$-$Pb碰撞中重味衰变电子与带电粒子的方位角关联，通过拟合分析重夸克碎裂强子化，对比冷核物质效应并与蒙特卡洛模型计算比较。

Measurement of the azimuthal anisotropy of neutral pions in PbPb collisions at sqrt(s(NN)) = 2.76 TeV

First measurements of the azimuthal anisotropy of neutral pions produced in PbPb collisions at a center-of-mass energy of sqrt(s(NN)) = 2.76 TeV are presented. The amplitudes of the second Fourier component (v2) of the neutral pion azimuthal distributions are extracted using an event-plane technique. The values of v2 are studied as a function of the neutral pion transverse momentum (pt) for different classes of collision centrality in the kinematic range 1.6 < pt < 8.0 GeV, within the pseudorapidity interval abs(eta) < 0.8. The CMS measurements of v2(pt) are similar to previously reported neut…

Measurement of higher-order harmonic azimuthal anisotropy in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV

Measurements are presented by the CMS Collaboration at the Large Hadron Collider (LHC) of the higher-order harmonic coefficients that describe the azimuthal anisotropy of charged particles emitted in sqrt(s[NN]) = 2.76 TeV PbPb collisions. Expressed in terms of the Fourier components of the azimuthal distribution, the n = 3-6 harmonic coefficients are presented for charged particles as a function of their transverse momentum (0.3 < pt < 8.0 GeV), collision centrality (0-70%), and pseudorapidity (abs(eta) < 2.0). The data are analyzed using the event plane, multiparticle cumulant, and Lee-Yang …

Study of Transverse Spherocity and Azimuthal Anisotropy in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV using A Multi-Phase Transport Model

Transverse spherocity is an event shape observable having a very unique capability to separate the events based on their geometrical shapes. Recent results from experiments at the LHC suggest that transverse spherocity is an important event classifier in small collision systems. In this work, we use transverse spherocity for the first time in heavy-ion collisions and perform an extensive study on azimuthal anisotropy of charged particles produced in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV using A Multi-Phase Transport Model (AMPT). The azimuthal anisotropy is estimated using the 2-…

Pseudorapidity dependence of the anisotropic flow of charged particles in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV

We present measurements of the elliptic ($\mathrm{v}_2$), triangular ($\mathrm{v}_3$) and quadrangular ($\mathrm{v}_4$) anisotropic azimuthal flow over a wide range of pseudorapidities ($-3.5< η< 5$). The measurements are performed with Pb-Pb collisions at $\sqrt{s_{\text{NN}}} = 2.76$ TeV using the ALICE detector at the Large Hadron Collider (LHC). The flow harmonics are obtained using two- and four-particle correlations from nine different centrality intervals covering central to peripheral collisions. We find that the shape of $\mathrm{v}_n(η)$ is largely independent of centrality for the f…

Centrality and pseudorapidity dependence of elliptic flow for charged hadrons in Au+Au collisions at sqrt(sNN) = 200 GeV

This paper describes the measurement of elliptic flow for charged particles in Au+Au collisions at sqrt(sNN)=200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The measured azimuthal anisotropy is presented over a wide range of pseudorapidity for three broad collision centrality classes for the first time at this energy. Two distinct methods of extracting the flow signal were used in order to reduce systematic uncertainties. The elliptic flow falls sharply with increasing eta at 200 GeV for all the centralities studied, as observed for minimum-bias collisions at s…

Two-particle correlations in azimuthal angle and pseudorapidity in inelastic p+p interactions at the CERN Super Proton Synchrotron

Results on two-particle $ΔηΔϕ$ correlations in inelastic p+p interactions at 20, 31, 40, 80, and 158~GeV/c are presented. The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The data show structures which can be attributed mainly to effects of resonance decays, momentum conservation, and quantum statistics. The results are compared with the EPOS and UrQMD models.

Observation of charge-dependent azimuthal correlations in pPb collisions and its implication for the search for the chiral magnetic effect

Charge-dependent azimuthal particle correlations with respect to the second-order event plane in pPb and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV have been studied with the CMS experiment at the LHC. The measurement is performed with a three-particle correlation technique, using two particles with the same or opposite charge within the pseudorapidity range abs(eta) < 2.4, and a third particle measured in the hadron forward calorimeters (4.4 < abs(eta) < 5). The observed differences between the same and opposite sign correlations, as functions of multiplicity and e…

Beam energy dependence of pseudorapidity distributions of charged particles produced in heavy-ion collisions at RHIC and LHC energies

Heavy-ion collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory and the Large Hadron Collider at CERN probe matter at extreme conditions of temperature and energy density. Most of the global properties of the collisions can be extracted from the measurements of charged particle multiplicity and pseudorapidity ($η$) distributions. We have shown that the available experimental data on beam energy and centrality dependence of \Eta-distributions in heavy-ion (Au+Au or Pb+Pb) collisions from \sNN=7.7 GeV to 2.76 TeV are reasonably well described by the AMPT model, whic…

Measurement of the azimuthal anisotropy for charged particle production in sqrt(s_NN) = 2.76 TeV lead-lead collisions with the ATLAS detector

Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at sqrt(s_NN) = 2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 mb^-1. This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle (phi), with the coefficients v_n denoting the magnitude of the anisotropy. Significant v_2-v_6 values are obtained as a function of transverse momentum (0.5<pT<20 GeV), pseudorapidity (|eta|<2.5) and centrality using an event plane method. The v_n values f…

Beam-energy dependence of the azimuthal anisotropic flow from RHIC

Recent STAR measurements of the anisotropic flow coefficients (v$_{n}$) are presented for Au+Au collisions spanning the beam energy range $\sqrt{s_{NN}} = 7.7 - 200$ GeV. The measurements indicate dependences on the harmonic number ($n$), transverse momentum ($p_T$), pseudorapidity ($η$), collision centrality and beam energy ($\sqrt{s_{NN}}$) which could serve as important constraints to test different initial-state models and to aid precision extraction of the temperature dependence of the specific shear viscosity.

Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider

Measurements of multi-particle azimuthal correlations (cumulants) for charged particles in p-Pb and Pb-Pb collisions are presented. They help address the question of whether there is evidence for global, flow-like, azimuthal correlations in the p-Pb system. Comparisons are made to measurements from the larger Pb-Pb system, where such evidence is established. In particular, the second harmonic two-particle cumulants are found to decrease with multiplicity, characteristic of a dominance of few-particle correlations in p-Pb collisions. However, when a $|Δη|$ gap is placed to suppress such correla…

Two-particle correlations in pseudorapidity in a hydrodynamic model

Two-particle pseudorapidity correlations of hadrons produced in Pb+Pb collisions at 2.76 TeV at the CERN Large Hadron Collider are analyzed in the framework of a model based on viscous 3+1-dimensional hydrodynamics with the Glauber initial condition. Based on our results, we argue that the correlation from resonance decays, formed at a late stage of the evolution, produce significant effects. In particular, their contribution to the event averages of the coefficients of the expansion in the Legendre basis explain 60-70% of the experimental values. We have proposed an accurate way to compute th…

ALICE probes of local parity violation with charge dependent azimuthal correlations in Pb-Pb collisions

We report on the measurement of two and three particle azimuthal correlations in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV recorded with ALICE at the LHC. While two particle azimuthal correlations mainly provide an important information on possible background correlations, the three particle correlator probes the charge separation of hadrons with respect to the collision reaction plane which is expected for local parity violation in strong interactions. The two and three particle correlations are presented as a function of collision centrality and differentially vs. pseudorapidity and transver…

Azimuthal correlations of prompt D mesons with charged particles in pp and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at $\sqrt{s}$ = 5.02 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with the ALICE detector at the LHC is reported. The D$^{\rm 0}$, D$^{\rm +}$, and D$^{\rm *+}$ mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval 3 < $p_{\rm T}$ < 24 GeV/c and correlated with charged particles having $p_{\rm T}$ > 0.3 GeV/c and pseudorapidity $|η| <$ 0.8. The properties of the correlation peaks appearing in the near- and a…

Hydrodynamic Flow in PbPb Collisions Observed via Azimuthal Angle Correlations of Charged Hadrons

Azimuthal angle correlations of charged hadrons were measured in $\sqrt s_{NN}$ = 2.76 TeV PbPb collisions by the CMS experiment. The distributions exhibit anisotropies that are correlated with the event-by-event orientation of the reaction plane. Several methods were employed to extract the strength of the signal: the event-plane, cumulant and Lee-Yang Zeros methods. These methods have different sensitivity to correlations that are not caused by the collective motion in the system (non-flow correlations due to jets, resonance decays, and quantum correlations). The second Fourier coefficient o…

Transverse Spin Asymmetries in the $p^{\uparrow}p\to pπ^0 X$ Process at STAR

A significant sample of $p^{\uparrow}p\to pπ^0 X$ events has been observed at STAR in $\sqrt{s}=200$ GeV transversely polarized $pp$ collisions, where an isolated $π^0$ is detected in the forward pseudorapidity range $2.65<η<3.9$ along with the forward-going proton $p$, which scatters with a near-beam forward pseudorapidity into Roman Pot detectors. The sum of the $π^0$ and the scattered proton energies is consistent with the incident proton energy of 100 GeV, indicating that no further particles are produced in this direction. It is postulated that the forward incident proton may have fluctua…

Evidence for transverse momentum and pseudorapidity dependent event plane fluctuations in PbPb and pPb collisions

A systematic study of the factorization of long-range azimuthal two-particle correlations into a product of single-particle anisotropies is presented as a function of pt and eta of both particles, and as a function of the particle multiplicity in PbPb and pPb collisions. The data were taken with the CMS detector for PbPb collisions at sqrt(s[NN]) = 2.76 TeV and pPb collisions at sqrt(s[NN]) = 5.02 TeV, covering a very wide range of multiplicity. Factorization is observed to be broken as a function of both particle pt and eta. When measured with particles of different pt, the magnitude of the f…

Centrality dependence of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at sqrt(s[NN]) = 2.76 TeV

Measurements from the CMS experiment at the LHC of dihadron correlations for charged particles produced in PbPb collisions at a nucleon-nucleon centre-of-mass energy of 2.76 TeV are presented. The results are reported as a function of the particle transverse momenta (pt) and collision centrality over a broad range in relative pseudorapidity [Delta(eta)] and the full range of relative azimuthal angle [Delta(phi)]. The observed two-dimensional correlation structure in Delta(eta) and Delta(phi) is characterised by a narrow peak at (Delta(eta), Delta(phi)) approximately (0, 0) from jet-like correl…

Pseudorapidity and centrality dependence of the collective flow of charged particles in Au+Au collisions at sqrt{s_NN} = 130 GeV

This paper describes the measurement of collective flow for charged particles in Au+Au collisions at sqrt{s_NN}} = 130 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). An azimuthal anisotropy is observed in the charged particle hit distribution in the PHOBOS multiplicity detector. This anisotropy is presented over a wide range of pseudorapidity (eta) for the first time at this energy. The size of the anisotropy (v_{2}) is thought to probe the degree of equilibration achieved in these collisions. The result here,averaged over momenta and particle species, is observed…

Heavy flavor collectivity in small systems

The presence of correlations between particles significantly separated in pseudorapidity in proton-proton and proton-nucleus collisions revealed surprises in the early LHC data. Are the physical processes responsible for the observed long-range pseudorapidity correlations and their azimuthal structure the same in small collision systems as in heavy ion collisions? Whereas in the case of heavy ion collisions "flow" is interpreted as generated by initial geometric inhomogeneities, calculations indicate that initial-state momentum correlations are present and could contribute to the observed azim…

Elliptic Flow in Au+Au Collisions at RHIC

Elliptic flow is an interesting probe of the dynamical evolution of the dense system formed in the ultrarelativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). The elliptic flow dependences on transverse momentum, centrality, and pseudorapidity were measured using data collected by the PHOBOS detector, which offers a unique opportunity to study the azimuthal anisotropies of charged particles over a wide range of pseudorapidity. These measurements are presented, together with an overview of the analysis methods and a discussion of the results.

High transverse momentum triggered correlations over a large pseudorapidity acceptance in Au+Au collisions at sqrt(s_NN)=200 GeV

A measurement of two-particle correlations with a high transverse momentum trigger particle (p_T^{trig} > 2.5 GeV/c) is presented for Au+Au collisions at sqrt(s_NN) = 200 GeV over the uniquely broad longitudinal acceptance of the PHOBOS detector (-4 < Δη< 2). A broadening of the away-side azimuthal correlation compared to elementary collisions is observed at all Δη. As in p+p collisions, the near-side is characterized by a peak of correlated partners at small angle relative to the trigger particle. However, in central Au+Au collisions an additional correlation extended in Δηand known as the `r…

Measurement of azimuthal anisotropy of muons from charm and bottom hadrons in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The elliptic flow of muons from the decay of charm and bottom hadrons is measured in $pp$ collisions at $\sqrt{s}=13$ TeV using a data sample with an integrated luminosity of 150 pb$^{-1}$ recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the tra…

Energy Dependance of Azimuthal Correlations (and more) in Nucleus-Nucleus Collisions at the CERN SPS

Analysing two-particle azimuthal and pseudorapidity-azimuth correlations of high-pT hadrons, experiments at the RHIC have obtained results - "the double hump", "the ridge" etc. - which provide interesting information about properties of the hot, dense medium produced in central high-energy heavy-ion collisions as well as of its interaction with products of hard scattering. However, not all of the observed effects have been fully explained by theory or models yet; such explanations are hampered in part by the lack of good reference from lower collision energies. In an attempt to further our und…

Forward Physics at STAR: Status of analysis on forward and mid rapidity correlation measurements in p+p and d+Au

Measurements of the production of high energy pi0 mesons at large pseudorapidity, coincident with charged hadrons at mid-rapidity, for proton+proton and deuteron+gold collisions at sqrt(s)_NN=200 GeV are reported. The p+p cross section for inclusive pi0 production follows expectations from next-to-leading order perturbative QCD. Both the inclusive cross section and the di-hadron azimuthal correlations are consistent with a model where parton showers supplement leading-order pQCD. A suppression of the back-to-back azimuthal correlations was observed in d+Au, qualitatively consistent with the gl…

Transverse momentum and pseudorapidity dependences of $'\bm{Mach-like}'$ correlations for central Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

The transverse momentum and pseudorapidity dependences of partonic {`\it{Mach-like}'} shock wave have been studied by using a multi-phase transport model (AMPT) with both partonic and hadronic interactions. The splitting parameter $D$, i.e. half distance between two splitting peaks on away side in di-hadron azimuthal angular ($Δϕ$) correlations, slightly increases with the transverse momentum of associated hadrons ($p^{assoc}_T$), which is consistent with preliminary experimental trend, owing to different interaction-lengths/numbers between wave partons and medium in strong parton cascade. On …

Baseline study for net-proton number fluctuations at top energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider with the Angantyr model

The multiplicity percentile dependence of cumulants, of net-proton number distributions in Au$-$Au collisions at $\sqrt{s_{NN}} = $ 200 GeV and Pb$-$Pb collisions at $\sqrt{s_{NN}} = $ 2.76 TeV has been investigated using the Angantyr model (the heavy-ion extension of the \textsc{Pythia 8} model). The effects of finite transverse momentum ($p_{\mathrm T}$) and pseudorapidity ($η$) acceptance on the net-proton cumulants have also been studied. Furthermore, the effects of the hydrodynamic expansion and feed down from weak decays were explored. It was found that radial flow has substantial impact…

NA61/SHINE results on fluctuations and correlations in p+p and Be+Be interactions at CERN SPS energies

The aim of the NA61/SHINE strong interaction program is to explore the phase diagram of strongly interacting matter. The main physics goals are the study of the onset of deconfinement and the search for the critical point of strongly interacting matter. These goals are pursued by performing a beam momentum (13$A$ - 158$A$ GeV/c) and system size (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La) scan. This contribution presents results on transverse momentum and multiplicity fluctuations from the Be+Be and p+p energy scan. Also, results on two-particle correlations in pseudorapidity and azimuthal angle obtained …

Two-particle azimuthal correlations in photonuclear ultraperipheral Pb+Pb collisions at 5.02 TeV with ATLAS

Two-particle long-range azimuthal correlations are measured in photonuclear collisions using 1.7 nb$^{-1}$ of 5.02 TeV Pb+Pb collision data collected by the ATLAS experiment at the LHC. Candidate events are selected using a dedicated high-multiplicity photonuclear event trigger, a combination of information from the zero-degree calorimeters and forward calorimeters, and from pseudorapidity gaps constructed using calorimeter energy clusters and charged-particle tracks. Distributions of event properties are compared between data and Monte Carlo simulations of photonuclear processes. Two-particle…

在质心能量为8.16 TeV的pPb碰撞中$Υ$(1S)介子方位角各向异性的研究

Study of azimuthal anisotropy of $Υ$(1S) mesons in pPb collisions at $\sqrt{s_\mathrm{NN}}$ = 8.16 TeV

该研究利用CMS实验数据，通过双粒子关联方法测量了8.16 TeV质子-铅碰撞中$Υ$(1S)介子的方位角各向异性，发现其小于同能量下粲偶素的结果，但与5.02 TeV铅-铅碰撞中$Υ$(1S)的测量值一致。

Investigating charm production and fragmentation via azimuthal correlations of prompt D mesons with charged particles in pp collisions at $\sqrt{s} = 13$ TeV

Angular correlations of heavy-flavour and charged particles in high-energy proton-proton collisions are sensitive to the production mechanisms of heavy quarks and to their fragmentation as well as hadronisation processes. The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV with the ALICE detector is reported, considering D$^{0}$, D$^{+}$, and D$^{*+}$ mesons in the transverse-momentum interval $3 < p_{\rm T} < 36$ GeV/$c$ at midrapidity ($|y| < 0.5$), and charged particles …

PbPb碰撞中$\sqrt{s_\mathrm{NN}}$ = 5.02 TeV下双喷注事件的方位角各向异性

Azimuthal anisotropy of dijet events in PbPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV

本研究利用CMS实验数据，通过提取高横动量双喷注的方位角各向异性系数$v_n$，探究了PbPb碰撞中致密部分子介质内依赖于路径长度的部分子能量损失，发现$v_2$值随碰撞中心度增加而增大。

Non-flow effects in three-particle mixed-harmonic azimuthal correlations in small collision systems

The Multi-particle technique has been used to unravel the nature of the long-range collectivity in small collision systems. A large three-particle mixed-harmonic correlation signal was recently observed by the ATLAS Collaboration, but the role of non-flow correlations is not yet studied. We estimate the influence of non-flow correlations to the three-particle correlators in $pp$ and $p$+Pb collisions using PYTHIA and HIJING models, and compare with the ATLAS results. The large non-flow effects from the jet and dijet production is found to be largely suppressed in $p$+Pb collisions using the su…

Heavy-flavour measurements in pp and Pb-Pb collisions with the ALICE experiment at the CERN LHC

The ALICE experiment at the CERN LHC has conducted first systematic studies of heavy-flavour hadron production in pp collisions at sqrt(s) = 7 TeV and in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. In pp collisions the differential production cross sections of D mesons at mid-rapidity, as well as the cross sections for electrons and muons from semileptonic heavy-flavour hadron decays at mid- and forward-rapidity, respectively, have been measured. These data provide a crucial testing ground for perturbative QCD calculations in the new LHC energy regime. In Pb-Pb collisions, the nuclear modificat…

On the clustering properties of produced particles in high-energy $pp$ collisions

Minijets provide useful information on parton interactions in the low transverse-momentum (low-$p_T$) region. Because minijets produce clusters, we study the clustering properties of produced particles in high-energy $pp$ collisions as a first step to identify minijets. We develop an algorithm to find clusters by using the k-means clustering method, in conjunction with a k-number (cluster number) selection principle in the space of pseudorapidity and azimuthal angles. We test the clustering algorithm using events generated by PYTHIA 8.1, for $pp$ collision at $\sqrt{s}=200$ GeV. We find that c…

Constraints on the chiral magnetic effect using charge-dependent azimuthal correlations in pPb and PbPb collisions at the LHC

Charge-dependent azimuthal correlations of same- and opposite-sign pairs with respect to the second- and third-order event planes have been measured in pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV and PbPb collisions at 5.02 TeV with the CMS experiment at the LHC. The measurement is motivated by the search for the charge separation phenomenon predicted by the chiral magnetic effect (CME) in heavy ion collisions. Three- and two-particle azimuthal correlators are extracted as functions of the pseudorapidity difference, the transverse momentum ($p_\mathrm{t}$) difference, and the $p_\mathr…

Measurement with the ATLAS detector of multi-particle azimuthal correlations in p+Pb collisions at sqrt(s_NN)=5.02 TeV

In order to study further the long-range correlations ("ridge") observed recently in p+Pb collisions at sqrt(s_NN) =5.02 TeV, the second-order azimuthal anisotropy parameter of charged particles, v_2, has been measured with the cumulant method using the ATLAS detector at the LHC. In a data sample corresponding to an integrated luminosity of approximately 1 microb^(-1), the parameter v_2 has been obtained using two- and four-particle cumulants over the pseudorapidity range |eta|<2.5. The results are presented as a function of transverse momentum and the event activity, defined in terms of the t…

质子-质子、质子-铅核与边缘铅核-铅核碰撞中方位角各向异性与平均横动量的相关性

Correlations between azimuthal anisotropy and mean transverse momentum in pp, pPb, and peripheral PbPb collisions

本研究利用CMS探测器采集的不同能量下pp、pPb和边缘PbPb碰撞数据，分析方位角各向异性与平均横动量的相关性随多重数的变化，并对比相关模型预测，为理解高能碰撞的初末态效应提供实验依据。

Longitudinal and azimuthal evolution of two-particle transverse momentum correlations in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV

This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators $G_{2}^{\rm CI}$ and $G_{2}^{\rm CD}$ in Pb--Pb collisions at $\sqrt{s_{\text{NN}}} = 2.76\;\text{\TeVe}$ by the ALICE collaboration. The two-particle transverse momentum correlator $G_{2}$ was introduced as a measure of the momentum current transfer between neighbouring system cells. The correlators are measured as a function of pair separation in pseudorapidity ($Δη$) and azimuth ($Δφ$) and as a function of collision centrality. From peripheral to c…

Measurement of azimuthal correlations between D mesons and charged hadrons with ALICE at the LHC

The comparison of angular correlations between charmed mesons and charged hadrons produced in pp, p-Pb and Pb-Pb collisions can give insight into the mechanisms through which charm quarks lose energy in a QGP medium, produced in ultra-relativistic heavy-ion collisions, and can help to recognize possible modifications of their hadronization induced by the presence of the QGP. The analysis of pp and p-Pb data and the comparison with predictions from pQCD calculations, besides constituting the necessary reference for interpreting Pb-Pb data, can provide relevant information on charm production an…