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.
Studies of the correlations of the two highest transverse momentum (leading) jets in individual Pb+Pb collision events can provide information about the mechanism of jet quenching by the hot and dense matter created in such collisions. In Pb+Pb and pp collisions at $\sqrt{s_{_\text{NN}}}$ = 5.02 TeV, measurements of the leading dijet transverse momentum ($p_{\mathrm{T}}$) correlations are presented. Additionally, measurements in Pb+Pb collisions of the dijet pair nuclear modification factors projected along leading and subleading jet $p_{\mathrm{T}}$ are made. The measurements are performed using the ATLAS detector at the LHC with 260 pb$^{-1}$ of pp data collected in 2017 and 2.2 nb$^{-1}$ of Pb+Pb data collected in 2015 and 2018. An unfolding procedure is applied to the two-dimensional leading and subleading jet $p_{\mathrm{T}}$ distributions to account for experimental effects in the measurement of both jets. Results are provided for dijets with leading jet $p_{\mathrm{T}}$ greater than 100 GeV. Measurements of the dijet-yield-normalized $x_{\mathrm{J}}$ distributions in Pb+Pb collisions show an increased fraction of imbalanced jets compared to pp collisions; these measurements are in agreement with previous measurements of the same quantity at 2.76 TeV in the overlapping kinematic range. Measurements of the absolutely-normalized dijet rate in Pb+Pb and pp collisions are also presented, and show that balanced dijets are significantly more suppressed than imbalanced dijets in Pb+Pb collisions. It is observed in the measurements of the pair nuclear modification factors that the subleading jets are significantly suppressed relative to leading jets with $p_{\mathrm{T}}$ between 100 and 316 GeV for all centralities in Pb+Pb collisions.
absolutely normalized dijet cross sections from pp collisions
absolutely normalized dijet yields scaled by 1/<TAA> in 0-10% central PbPb collisions
absolutely normalized dijet yields scaled by 1/<TAA> in 10-20% central PbPb collisions
Parton energy loss in the quark-gluon plasma (QGP) is studied with a measurement of photon-tagged jet production in 1.7 nb$^{-1}$ of Pb+Pb data and 260 pb$^{-1}$ of $pp$ data, both at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV, with the ATLAS detector. The process $pp \to \gamma$+jet+$X$ and its analogue in Pb+Pb collisions is measured in events containing an isolated photon with transverse momentum ($p_\mathrm{T}$) above $50$ GeV and reported as a function of jet $p_\mathrm{T}$. This selection results in a sample of jets with a steeply falling $p_\mathrm{T}$ distribution that are mostly initiated by the showering of quarks. The $pp$ and Pb+Pb measurements are used to report the nuclear modification factor, $R_\mathrm{AA}$, and the fractional energy loss, $S_\mathrm{loss}$, for photon-tagged jets. In addition, the results are compared with the analogous ones for inclusive jets, which have a significantly smaller quark-initiated fraction. The $R_\mathrm{AA}$ and $S_\mathrm{loss}$ values are found to be significantly different between those for photon-tagged jets and inclusive jets, demonstrating that energy loss in the QGP is sensitive to the colour-charge of the initiating parton. The results are also compared with a variety of theoretical models of colour-charge-dependent energy loss.
The differential cross-section of photon-tagged jets as a function of jet $p_{\mathrm{T}}$ in pp collisions.
The yields of photon-tagged jets as a function of jet $p_{\mathrm{T}}$ in Pb+Pb collisions for different centrality intervals.
The nuclear modification factor of photon-tagged jets as a function of jet $p_{\mathrm{T}}$ for different centrality intervals.
Data from Au + Au interactions at sqrt(s_NN) = 130 GeV, obtained with the PHENIX detector at RHIC, are used to investigate local net charge fluctuations among particles produced near mid-rapidity. According to recent suggestions, such fluctuations may carry information from the Quark Gluon Plasma. This analysis shows that the fluctuations are dominated by a stochastic distribution of particles, but are also sensitive to other effects, like global charge conservation and resonance decays.
The normalized variance $v(Q)$as a function of $n_{ch}$.
The normalized variance $v(R)$ as a function of $n_{ch}$.
The normalized variance $v(Q)$ for different centrality classes.
Distributions of event-by-event fluctuations of the mean transverse momentum and mean transverse energy near mid-rapidity have been measured in Au+Au collisions at sqrt(s_NN) = 130 GeV at RHIC. By comparing the distributions to what is expected for statistically independent particle emission, the magnitude of non-statistical fluctuations in mean transverse momentum is determined to be consistent with zero. Also, no significant non-random fluctuations in mean transverse energy are observed. By constructing a fluctuation model with two event classes that preserve the mean and variance of the semi-inclusive p_T or e_T spectra, we exclude a region of fluctuations in sqrt(s_NN) = 130 GeV Au+Au collisions.
The $N_{tracks}$ distribution for the $0-10\%$ centrality class (data points) compared to the $N_{mix}$ distribution from the mixed event sample (curve).
The $M_{p_T}$ distributions for four different centrality classes. The curves are the random baseline mixed event distributions.
The residual distribution between the data and mixed event $M_{p_T}$ in units of standard deviations for all centrality classes. The total ${\chi}^2$ and the number of degrees of freedom for the $0-5\%$, $0-10\%$, $10-20\%$, $20-30\%$ centrality classes are 89.0/39, 155.7/40,163.3/47, and 218.4/61, respectively.
Transverse momentum spectra of electrons from Au+Au collisions at sqrt(s_NN) = 130 GeV have been measured by the PHENIX experiment at RHIC. The spectra show an excess above the background from photon conversions and light hadron decays. The electron signal is consistent with that expected from semi-leptonic decays of charm. The yield of the electron signal dN_e/dy for p_T > 0.8 GeV/c is 0.025 +/- 0.004 (stat.) +/- 0.010 (sys.) in central collisions, and the corresponding charm cross section is 380 +/- 60 (stat.) +/- 200 (sys.) micro barns per binary nucleon-nucleon collision.
Transverse momentum spectra of electrons in PHENIX from Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV.
Transverse momentum spectra of electrons in PHENIX from Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV.
Transverse momentum spectra of electrons in PHENIX from Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV. The upper limit for 1.9 GeV/$c$ is 4.10224e-05.
Two particle azimuthal correlation functions are presented for charged hadrons produced in Au + Au collisions at RHIC sqrt(s_NN) = 130 GeV. The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values v_2 show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone, epsilon, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low p_T. A breakdown of this epsilon scaling is observed for charged hadrons with p_T > 1.0 GeV/c for the most central collisions.
Azimuthal correlation functions for charged hadrons as a function of centrality and $p_T$ selection. The solid curves represent Fourier fits following Eq. (2). Error bars are statistical only.
$v_2$ vs. centrality for several $p_T$ selections. [F] and [A] indicate results obtained with the fixed-$p_T$ and assorted-$p_T$ methods respectively. Systematic errors are estimated to be $\sim 5$%; they are dominated by the normalization of the correction function for real tracks. For the centrality range 0-5%, the data points are statistically uncertain and the points are omitted.
$v_2$ vs. centrality for several $p_T$ selections. [F] and [A] indicate results obtained with the fixed-$p_T$ and assorted-$p_T$ methods respectively. Systematic errors are estimated to be $\sim 5$%; they are dominated by the normalization of the correction function for real tracks. For the centrality range 0-5%, the data points are statistically uncertain and the points are omitted.
Measurements of the suppression and correlations of dijets is performed using 3 $\mu$b$^{-1}$ of Xe+Xe data at $\sqrt{s_{\mathrm{NN}}} = 5.44$ TeV collected with the ATLAS detector at the LHC. Dijets with jets reconstructed using the $R=0.4$ anti-$k_t$ algorithm are measured differentially in jet $p_{\text{T}}$ over the range of 32 GeV to 398 GeV and the centrality of the collisions. Significant dijet momentum imbalance is found in the most central Xe+Xe collisions, which decreases in more peripheral collisions. Results from the measurement of per-pair normalized and absolutely normalized dijet $p_{\text{T}}$ balance are compared with previous Pb+Pb measurements at $\sqrt{s_{\mathrm{NN}}} =5.02$ TeV. The differences between the dijet suppression in Xe+Xe and Pb+Pb are further quantified by the ratio of pair nuclear-modification factors. The results are found to be consistent with those measured in Pb+Pb data when compared in classes of the same event activity and when taking into account the difference between the center-of-mass energies of the initial parton scattering process in Xe+Xe and Pb+Pb collisions. These results should provide input for a better understanding of the role of energy density, system size, path length, and fluctuations in the parton energy loss.
The centrality intervals in Xe+Xe collisions and their corresponding TAA with absolute uncertainties.
The centrality intervals in Xe+Xe and Pb+Pb collisions for matching SUM ET FCAL intervals and respective TAA values for Xe+Xe collisions.
The performance of the jet energy scale (JES) for jets with $|y| < 2.1$ evaluated as a function of pT_truth in different centrality bins. Simulated hard scatter events were overlaid onto events from a dedicated sample of minimum-bias Xe+Xe data.
PHENIX has measured the centrality dependence of charged hadron p_T spectra from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction of the contribution from hard scattering to high p_T hadron production. For central collisions the yield at high p_T is shown to be suppressed compared to binary nucleon-nucleon collision scaling of p+p data. This suppression is monotonically increasing with centrality, but most of the change occurs below 30% centrality, i.e. for collisions with less than about 140 participating nucleons. The observed p_T and centrality dependence is consistent with the particle production predicted by models including hard scattering and subsequent energy loss of the scattered partons in the dense matter created in the collisions.
Number of participants and binary collisions and their systematic errors for the individual centrality selections used in this analysis. Also given is the ratio of the number of binary collisions for the most central sample relative to the one for each sample. The last column quantifies the ratio of binary collisions to participant pairs.
The ratio $p/h$ represents the proton plus anti-proton yield relative to the total charged hadron multiplicity. This shows the $p_T$ dependence of $p/h$ for minimum bias events.
The ratio $p/h$ represents the proton plus anti-proton yield relative to the total charged hadron multiplicity. This shows the centrality dependence of $p/h$ for $p_T >$ 1.8 GeV/$c$.
Two-pion correlations in sqrt(s_NN)=130 GeV Au+Au collisions at RHIC have been measured over a broad range of pair transverse momentum k_T by the PHENIX experiment at RHIC. The k_T dependent transverse radii are similar to results from heavy ion collisions at sqrt(s_NN) = 4.1, 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii (R_out/R_side) is consistent with unity and independent of k_T.
HBT radii for pion pairs as a function of $k_T$ measured at mid-rapidity for various energies for Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV. Values used are from the Longitudinal Co-Moving System (LCMS) frame.
HBT radii for pion pairs as a function of $k_T$ measured at mid-rapidity for various energies for Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV. Values used are from the Pair Center-of-Mass System (PCMS) frame.
The top panel shows the measured $R_{side}$ from identical pions for PHENIX. The bottom panel shows the ratio $R_{out}/R_{side}$ as a function of $k_T$. Longitudinal Co-Moving System (LCMS) frame for $\pi^+$
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