Charged-particle jet yields have been measured in semicentral Pb$-$Pb collisions at center-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}} = 5$ TeV with the ALICE detector at the LHC. These yields are reported as a function of the jet transverse momentum, and further classified by their angle with respect to the event plane and the event shape, characterized by ellipticity, in an effort to study the path-length dependence of jet quenching. Jets were reconstructed at midrapidity from charged-particle tracks using the anti-$k_{\rm T}$ algorithm with resolution parameters $R =$ 0.2 and 0.4, with event-plane angle and event-shape values determined using information from forward scintillating detectors. The results presented in this letter show that, in semicentral Pb$-$Pb collisions, there is no significant difference between jet yields in predominantly isotropic and elliptical events. However, out-of-plane jets are observed to be more suppressed than in-plane jets. Further, this relative suppression is greater for low transverse momentum ($<$ 50 GeV/$c$) $R =$ 0.2 jets produced in elliptical events, with out-of-plane to in-plane jet-yield ratios varying up to 5.2$\sigma$ between different event-shape classes. These results agree with previous studies indicating that jets experience azimuthally anisotropic suppression when traversing the QGP medium, and can provide additional constraints on the path-length dependence of jet energy loss.
Charged-particle jet yields, R=0.2
Charged-particle jet yields, R=0.4
q2-large/q2-small, R=0.2
The transverse-momentum ($p_{\rm T}$) spectra and coalescence parameters $B_2$ of (anti)deuterons are measured in pp collisions at $\sqrt{s} = 13$ TeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest $p_{\rm T}$ in the event ($p_{\rm T}^{\rm{ lead}} > 5$ GeV/$c$) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions and the jet signal is obtained as the difference between the Toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the Transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons inside the jet cone as compared to the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase space distributions of nucleons are generated using PYTHIA 8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in PYTHIA 8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the $B^{\rm Jet}_2$ is not reproduced by the models, which instead give a decreasing trend.
Transverse momentum spectra for the transverse azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).
Transverse momentum spectra for the toward azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).
Transverse momentum spectra for the away azimuthal regions. Events with a leading track with PT>5 GEV at midrapidity are selected. The spectrum is shown in Figure 1 (left panel).
The production of K$^*$(892)$^\pm$ meson resonance is measured at midrapidity ($|y|<0.5$) in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using the ALICE detector at the LHC. The resonance is reconstructed via its hadronic decay channel K$^*$(892)$^\pm \rightarrow \rm{K^0_S \pi^\pm}$. The transverse momentum distributions are obtained for various centrality intervals in the $p_{\rm T}$ range of 0.4-16 GeV/$c$. The reported measurements of integrated yields, mean transverse momenta, and particle yield ratios are consistent with previous ALICE measurements for K$^*$(892)$^0$. The $p_{\rm T}$-integrated yield ratio 2K$^*$(892)$^\pm$/($\rm{K^+ + K^-}$) in central Pb-Pb collisions shows a significant suppression (9.3$\sigma$) relative to pp collisions. Thermal model calculations overpredict the particle yield ratio. Although both simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas MUSIC+SMASH tends to overpredict them. These observations, along with the kinetic freeze-out temperatures extracted from the yields of light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which increases towards central collisions. The $p_{\rm T}$-differential yield ratios 2K$^*$(892)$^\pm$/($\rm{K^+ + K^-}$) and 2K$^*$(892)$^\pm$/($\rm{\pi^+ + \pi^-}$) are suppressed by up to a factor of five at $p_{\rm T}<2$ GeV/$c$ in central Pb-Pb collisions compared to pp collisions at $\sqrt{s} =$ 5.02 TeV. Both particle ratios and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor shows a smooth evolution with centrality and is below unity at $p_{\rm T}>8$ GeV/$c$, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 0-10\% centrality.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 10-20\% centrality.
$p_{\rm T}$-distributions of $\rm{K}^{*}$ (average of particle and anti-particle) meson measured in Pb-Pb collisions at \sqrt{s_{NN}}$ = 5.02 TeV for 20-40\% centrality.
We report the beam energy and collision centrality dependence of fifth and sixth order cumulants ($C_{5}$, $C_{6}$) and factorial cumulants ($\kappa_{5}$, $\kappa_{6}$) of net-proton and proton distributions, from $\sqrt{s_{NN}} = 3 - 200$ GeV Au+Au collisions at RHIC. The net-proton cumulant ratios generally follow the hierarchy expected from QCD thermodynamics, except for the case of collisions at $\sqrt{s_{NN}}$ = 3 GeV. $C_{6}/C_{2}$ for 0-40% centrality collisions is increasingly negative with decreasing $\sqrt{s_{NN}}$, while it is positive for the lowest $\sqrt{s_{NN}}$ studied. These observed negative signs are consistent with QCD calculations (at baryon chemical potential, $\mu_{B} \leq$ 110 MeV) that include a crossover quark-hadron transition. In addition, for $\sqrt{s_{NN}} \geq$ 11.5 GeV, the measured proton $\kappa_{n}$, within uncertainties, does not support the two-component shape of proton distributions that would be expected from a first-order phase transition. Taken in combination, the hyper-order proton number fluctuations suggest that the structure of QCD matter at high baryon density, $\mu_{B}\sim 750$ MeV ($\sqrt{s_{NN}}$ = 3 GeV) is starkly different from those at vanishing $\mu_{B}\sim 20$MeV ($\sqrt{s_{NN}}$ = 200 GeV and higher).
Event-by-event proton multiplicity distributions for 0-40$\%$, 0-5$\%$ and 50-60$\%$ Au+Au collisions at $\sqrt{s_{NN}} = 3 GeV. The distributions are not corrected for proton and antiproton detection efficiency.
Proton factorial cumulants K4, K5 and K6 in 0-40$\%$ and 50-60$\%$ Au+Au collisions from $\sqrt{s_{NN}}$ = 3 - 200 GeV. At $\sqrt{s_{NN}}$ = 3 GeV, measurement is done with halfrapdity coverage (-0.5 $<$ y $<$ 0) while for rest of energies the rapidity coverage is (-0.5 $<$ y $<$ -0.5).
Proton factorial cumulants K4, K5 and K6 from UrQMD model (0-40$\%$ and 50-60$\%$ centrality) for Au+Au collisions from $\sqrt{s_{NN}}$ = 3 - 200 GeV. UrQMD calculation for 3 GeVis with rapidity coverage (-0.5 $<$ y $<$ 0) while for rest of energies the rapidity coverage is (-0.5 $<$ y $<$ -0.5). In addition, two-component model (0-40$\%$) calculations for facorial cumulants are also given.
Transverse momentum spectra and yields of hadrons are measured by the PHENIX collaboration in Au + Au collisions at sqrt(s_NN) = 130 GeV at the Relativistic Heavy Ion Collider (RHIC). The time-of-flight resolution allows identification of pions to transverse momenta of 2 GeV/c and protons and antiprotons to 4 GeV/c. The yield of pions rises approximately linearly with the number of nucleons participating in the collision, while the number of kaons, protons, and antiprotons increases more rapidly. The shape of the momentum distribution changes between peripheral and central collisions. Simultaneous analysis of all the p_T spectra indicates radial collective expansion, consistent with predictions of hydrodynamic models. Hydrodynamic analysis of the spectra shows that the expansion velocity increases with collision centrality and collision energy. This expansion boosts the particle momenta, causing the yield from soft processes to exceed that for hard to large transverse momentum, perhaps as large as 3 GeV/c.
The sources of systematic uncertainties in $\langle p_T \rangle$ and $dN$/$dy$.
The $dN$/$dy$ at midrapidity for hadrons produced at midrapidity in each centrality class.
The resulting inverse slopes in MeV after fitting an $m_T$ exponential to the spectra in the range $m_T$-$m_0$ < 1 GeV in each event centrality classes. The pion resonance region is excluded in the fits. The equivalent $p_T$ fit range for each particle is shown accordingly.
We present transverse momentum (p_T) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at \sqrts = 200 GeV for four centrality classes. Nucleon-gold collisions were selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, \nu, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that the yield per nucleon-nucleon collision saturates with \nu for high momentum particles. We also present the charged hadron to neutral pion ratios as a function of p_T.
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
<p>Charged hadron spectra for centrality selected d+Au collisions.</p>
Measurements of anisotropic flow Fourier coefficients ($v_n$) for inclusive charged particles and identified hadrons $\pi^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ produced at midrapidity in Cu+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). The particle azimuthal distributions with respect to different order symmetry planes $\Psi_n$, for $n$~=~1, 2, and 3 are studied as a function of transverse momentum $p_T$ over a broad range of collisions centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three harmonics. The charged-particle results are compared to hydrodynamical and transport model calculations. We also compare these Cu$+$Au results with those in Cu$+$Cu and Au$+$Au collisions at the same $\sqrt{s_{_{NN}}}$, and find that the $v_2$ and $v_3$, as a function of transverse momentum, follow a common scaling with $1/(\varepsilon_n N_{\rm part}^{1/3})$.
$v_1$ ($p_T$) for charged hadrons measured with respect to the Cu spectator neutrons at midrapidity in Cu + Au collisions at $\sqrt{S_{NN}}$ 200 GeV.
$v_2(p_T)$ for charged hadrons measured at midrapidity in Cu + Au collisions at $\sqrt{S_N{N}}$ = 200 GeV.
$v_3(p_T)$ for charged hadrons measured at midrapidity in Cu + Au collisions at $\sqrt{S_N{N}}$ = 200 GeV.
The PHENIX Collaboration has measured the ratio of the yields of $\psi(2S)$ to $\psi(1S)$ mesons produced in $p$$+$$p$, $p$$+$Al, $p$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV over the forward and backward rapidity intervals $1.2<|y|<2.2$. We find that the ratio in $p$$+$$p$ collisions is consistent with measurements at other collision energies. In collisions with nuclei, we find that in the forward ($p$-going or $^{3}$He-going) direction, the relative yield of $\psi(2S)$ mesons to $\psi(1S)$ mesons is consistent with the value measured in \pp collisions. However, in the backward (nucleus-going) direction, the $\psi(2S)$ is preferentially suppressed by a factor of $\sim$2. This suppression is attributed in some models to breakup of the weakly-bound $\psi(2S)$ through final state interactions with comoving particles, which have a higher density in the nucleus-going direction. These breakup effects may compete with color screening in a deconfined quark-gluon plasma to produce sequential suppression of excited quarkonia states.
Summary of the measured ratios of $\Psi$(2S)/$\Psi$(1S) mesons.
Summary of the measured ratios of $\Psi$(2S)/$\Psi$(1S) mesons.
Summary of the measured ratios of $\Psi$(2S)/$\Psi$(1S) mesons.
The first measurements of skewness and kurtosis of mean transverse momentum ($\langle p_\mathrm{T}\rangle$) fluctuations are reported in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$$=$ 5.44 TeV and pp collisions at $\sqrt{s} = 5.02$ TeV using the ALICE detector. The measurements are carried out as a function of system size $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle_{|\eta|<0.5}^{1/3}$, using charged particles with transverse momentum ($p_\mathrm{T}$) and pseudorapidity ($\eta$), in the range $0.2 < p_\mathrm{T} < 3.0$ GeV/$c$ and $|\eta| < 0.8$, respectively. In Pb$-$Pb and Xe$-$Xe collisions, positive skewness is observed in the fluctuations of $\langle p_\mathrm{T}\rangle$ for all centralities, which is significantly larger than what would be expected in the scenario of independent particle emission. This positive skewness is considered a crucial consequence of the hydrodynamic evolution of the hot and dense nuclear matter created in heavy-ion collisions. Furthermore, similar observations of positive skewness for minimum bias pp collisions are also reported here. Kurtosis of $\langle p_\mathrm{T}\rangle$ fluctuations is found to be in good agreement with the kurtosis of Gaussian distribution, for most central Pb$-$Pb collisions. Hydrodynamic model calculations with MUSIC using Monte Carlo Glauber initial conditions are able to explain the measurements of both skewness and kurtosis qualitatively from semicentral to central collisions in Pb--Pb system. Color reconnection mechanism in PYTHIA8 model seems to play a pivotal role in capturing the qualitative behavior of the same measurements in pp collisions.
Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in pp collisions at $\sqrt{s}$ = 5.02 TeV.
Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV.
Standardized skewness of $\langle p_\mathrm{T}\rangle$ as a function of $\langle\mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle^{1/3}_{|\eta|<0.5}$ in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV.
We report the measurement of cumulants ($C_n, n=1\ldots4$) of the net-charge distributions measured within pseudorapidity ($|\eta|<0.35$) in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=7.7-200$ GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider. The ratios of cumulants (e.g. $C_1/C_2$, $C_3/C_1$) of the net-charge distributions, which can be related to volume independent susceptibility ratios, are studied as a function of centrality and energy. These quantities are important to understand the quantum-chromodynamics phase diagram and possible existence of a critical end point. The measured values are very well described by expectation from negative binomial distributions. We do not observe any nonmonotonic behavior in the ratios of the cumulants as a function of collision energy. The measured values of $C_1/C_2 = \mu/\sigma^2$ and $C_3/C_1 = S\sigma^3/\mu$ can be directly compared to lattice quantum-chromodynamics calculations and thus allow extraction of both the chemical freeze-out temperature and the baryon chemical potential at each center-of-mass energy.
Efficiency corrected cumulants of net-charge distributions as a function of $\langle N_{part} \rangle$ from Au+Au collisions at different collision energies.
Efficiency corrected cumulants of net-charge distributions as a function of $\langle N_{part} \rangle$ from Au+Au collisions at different collision energies.
Efficiency corrected cumulants of net-charge distributions as a function of $\langle N_{part} \rangle$ from Au+Au collisions at different collision energies.
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