Kaon interferometric probes of space-time evolution in Au+Au collisions at sqrt(s_NN) = 200 GeV
PHENIX Collaboration, S. Afanasiev
备注：
344 authors, 6 pages text, 3 figures, RevTeX 4. Submitted to PRL. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html
Bose-Einstein correlations of charged kaons are measured for Au+Au collisions at sqrt(s_NN) = 200 GeV and are compared to charged pion probes, which have a larger hadronic scattering cross section. Three dimensional Gaussian source radii are extracted, along with a one-dimensional kaon emission source function. The centrality dependences of the three Gaussian radii are well described by a single linear function if N_part^1/3 with zero intercept. Imaging analysis shows a deviation from a Gaussian tail at r >~ 10 fm, although the bulk emission at lower radius is well-described by a Gaussian. The presence of a non-Gaussian tail in the kaon source reaffirms that the particle emission region in a heavy ion collision is extended, and that similar measurements with pions are not solely due to the decay of long-lived resonances.
Three-dimensional source images for mid-rapidity, low transverse momentum kaon and pion pairs have been extracted from central Au+Au collisions data at \sqrt{s_{NN}} = 200 GeV by the STAR experiment at RHIC. The pion source function displays significant non-Gaussian features implying a finite pion emission duration. On the other hand, the kaon source function is essentially Gaussian, consistent with instantaneous emission from the fireball.
Measurement of femtoscopic correlations in heavy-ion collisions can provide information about spatial and temporal parameters of the particle emission region at kinetic freeze-out. In this work we present the measurement of two-pion and two-kaon femtoscopic correlations in 200 GeV Au+Au collisions at RHIC. The collision centrality and transverse momentum dependence of the three-dimensional radii, $R_{out}$, $R_{side}$ and $R_{long}$ is discussed.
Particle correlations at small relative momenta can be used to measure the space$-$time characteristics of particle production on the femtoscopic (fm=10$^{-15}$ m) level in high-energy collisions. Such correlations arise due to quantum statistics and final state interactions. We report correlations of two charged identical kaons measured in p$-$Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV by the ALICE experiment at the LHC. The femtoscopic invariant radii and correlation strengths are extracted from the one-dimensional kaon correlation functions and are compared to those obtained in pp and Pb…
Invariant pT spectra and rapidity densities covering a large rapidity range(-0.1 < y < 3.5) are presented for $π^{\pm}$ and $K^{\pm}$ mesons from central Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4 GeV. The mid-rapidity yields of meson particles relative to their anti-particles are found to be close to unity ($π^-/π^+ \sim 1$, $K^-/K^+ \sim 0.85$) while the anti-proton to proton ratio is $\bar{p}/p \sim 0.49$. The rapidity dependence of the $π^-/π^+$ ratio is consistent with a small increase towards forward rapidities while the $K^-/K^+$ and $\bar{p}/p$ ratios show a steep decrease to $\sim$ 0.…
In this work we report on the production of charged pions, kaons, and (anti) protons in pp and Pb-Pb collisions at sqrt{s_NN}= 2.76 TeV for 3 < pT < 20 GeV/c. The evolution of the nuclear modification factor, RAA, with collision centrality and transverse momentum is discussed.
Measurements of three-dimensional correlation functions of like-sign low transverse momentum kaon pairs from Au+Au collisions at top RHIC energy $\sqrt s_{NN}$=200 GeV are presented. The extracted kaon source function is narrower than the pion one and does not have the long tail along the pair transverse momentum direction. This indicates a much smaller role of long-lived resonance decays and/or of the emission duration on kaon emission. Three-dimensional Gaussian shape of the kaon source function can be adequately reproduced by Therminator simulations with resonance contributions taken into a…
Femtoscopic correlations between charged pions and kaons for different charge combinations are measured in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV with ALICE at the LHC. The three-dimensional pion-kaon ($π-{\rm K}$) correlation functions and double ratios in the out-side-long pair rest frame are studied in different centrality bins. The $π-{\rm K}$ femtoscopic source size parameter ($R_{\rm out}$) and emission asymmetry ($μ_{\rm out}$) are extracted. It is observed that the average source size of the system and the emission asymmetry between pions and kaons increase from peripheral …
In this paper, the first femtoscopic analysis of pion-kaon correlations at the LHC is reported. The analysis was performed on the Pb-Pb collision data at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV recorded with the ALICE detector. The non-identical particle correlations probe the spatio-temporal separation between sources of different particle species as well as the average source size of the emitting system. The sizes of the pion and kaon sources increase with centrality, and pions are emitted closer to the centre of the system and/or later than kaons. This is naturally expected in a system with strong …
Observation of the centrality-dependent difference in directed flow between charged kaons and $K^{*0}$ resonances in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 14.6, 19.6 and 27 GeV
We present the results of three-dimensional femtoscopic analyses for charged and neutral kaons recorded by ALICE in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. Femtoscopy is used to measure the space-time characteristics of particle production from the effects of quantum statistics and final-state interactions in two-particle correlations. Kaon femtoscopy is an important supplement to that of pions because it allows one to distinguish between different model scenarios working equally well for pions. In particular, we compare the measured 3D kaon radii with a purely hydrodynamical calc…
Femtoscopy is providing information on system size and its dynamics in heavy-ion collisions. At ultra-relativistic energies, such as those obtained at the LHC, significant production of pions, kaons and protons enables femtoscopic measurements for these particles. In particular the dependence of system size on pair momentum and particle type is interpreted as evidence for strong collective flow. Such phenomena are naturally modeled by hydrodynamics. We present calculations within the 3+1D hydrodynamic model coupled to statistical hadronization code THERMINATOR 2, corresponding to Pb--Pb collis…
We report systematic measurements of bulk properties of the system created in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum spectra of $π^{\pm}$, $K^{\pm}$, and $p$($\bar{p}$) are studied at mid-rapidity $(\lvert y \rvert < 0.1)$ for different centrality classes. We also present mid-rapidity measurement of particle yields $(dN/dy)$ and particle ratios in Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 GeV. The kinetic freeze-out parameters ($T_{kin}$ and $\langle β\rangle$) are extracted from parti…
We report the measurement of the directed flow ($v_{1}$) for charged kaons in Au+Au collisions at $\sqrt{s_{NN}}$ =7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV as a function of rapidity and compare these results for pions, protons and antiprotons. These new kaon results may help to constrain the medium properties and collision dynamics including the in-medium kaon potential and baryon number transport in these collisions.
Kaons and protons carry large parts of two conserved quantities, strangeness and baryon number. It is argued that their correlation and thus also fluctuations are sensitive to conditions prevailing at the anticipated parton-hadron phase boundary. Fluctuations of the $(\mathrm{K}^+ + \mathrm{K}^-)/(\mathrm{p}+\bar{\mathrm{p}})$ and $\mathrm{K}^+/\mathrm{p}$ ratios have been measured for the first time by NA49 in central Pb+Pb collisions at 5 SPS energies between $\sqrt{s_{NN}}$= 6.3 GeV and 17.3 GeV. Both ratios exhibit a change of sign in $σ_{\mathrm{dyn}}$, a measure of non-statistical fluctu…
We present the first measurement of event-by-event fluctuations in the kaon sector in Pb-Pb collisions at $\sqrt {s_{\rm NN}}=$ 2.76 TeV with the ALICE detector at the LHC. The robust fluctuation correlator $ν_{\rm dyn}$ is used to evaluate the magnitude of fluctuations of the relative yields of neutral and charged kaons, as well as the relative yields of charged kaons, as a function of collision centrality and selected kinematic ranges. While the correlator $ν_{\rm dyn}[\rm K^+,\rm K^-]$ exhibits a scaling approximately in inverse proportion of the charged particle multiplicity, $ν_{\rm dyn}[…
Non-identical particle femtoscopy measures the size of the system emitting particles ("radius") in heavy-ion collisions as well as the difference between mean emission space-time coordinates of two particle species ("emission asymmetry"). The system created in such collisions at the LHC behaves collectively and its dynamics is well described by hydrodynamic models. A significant emission asymmetry between pions and kaons, coming from collective flow, enhanced by contribution from flowing resonances is predicted. We present calculations within the (3+1)D viscous hydrodynamic model coupled to st…
The measurement of primary $π^{\pm}$, K$^{\pm}$, p and $\overline{p}$ production at mid-rapidity ($|y| <$ 0.5) in proton-proton collisions at $\sqrt{s} = 7$ TeV performed with ALICE (A Large Ion Collider Experiment) at the Large Hadron Collider (LHC) is reported. Particle identification is performed using the specific ionization energy loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/$c$ for pions, from 0.2 up to 6 GeV/$c$ for kaons and fr…
We calculate the cumulants and correlation functions of net-kaon multiplicity distributions in Au+Au collisions at $\sqrt{s_{NN}} = 7.7$ GeV using a multiphase transport model (AMPT) with both a new coalescence mechanism and all charge conservation laws. The AMPT model can qualitatively describe the centrality dependences of the net-kaon cumulants and cumulant ratios measured by the STAR experiment. By focusing on the stage evolution of the cumulants, cumulant ratios, and correlation functions, we reveal several key effects on the fluctuations and correlations of strangeness during the dynamic…
Correlations of two charged identical kaons (${\rm K}^{\rm ch}{\rm K}^{\rm ch}$) are measured in pp collisions at $\sqrt{s}=7$~TeV by the ALICE experiment at the Large Hadron Collider (LHC). One-dimensional ${\rm K}^{\rm ch}{\rm K}^{\rm ch}$ correlation functions are constructed in three multiplicity and four transverse momentum ranges. The ${\rm K}^{\rm ch}{\rm K}^{\rm ch}$ femtoscopic source parameters $R$ and $λ$ are extracted. The ${\rm K}^{\rm ch}{\rm K}^{\rm ch}$ correlations show a slight increase of femtoscopic radii with increasing multiplicity and a slight decrease of radii with incr…
Transverse momentum ($p_{\rm{T}}$) spectra of pions, kaons, and protons up to $p_{\rm{T}} = 20$ GeV/$c$ have been measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV using the ALICE detector for six different centrality classes covering 0-80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at $p_{\rm{T}} \approx 3$ GeV/$c$ in central Pb-Pb collisions that decreases towards more peripheral collisions. For $p_{\rm{T}} > 10$ GeV/$c$, the nuclear modification factor is found to be the same for all three particle species in each centrality interval within system…
In late 2017, the ALICE experiment recorded a data sample of Xe--Xe collisions at the unprecedented energy in A--A systems of $\sqrt{s_{\rm{NN}}} = 5.44\text{ TeV}$. The $p_{\rm T}$ spectra at mid-rapidity ($|y| < 0.5$) of pions, kaons and protons are presented. The preliminary $p_{\rm T}$ spectra are obtained by combining independent analyses with the Inner Tracking System (ITS), the Time Projection Chamber (TPC), and the Time-Of-Flight (TOF) detectors. This paper focuses on the details of the analysis performed with TOF and in particular on the performance implications of the special Xe--Xe …
Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at sqrt(sNN) = 5.02 TeV. Charged pions, kaons, and protons in the transverse-momentum range pt approximately 0.1-1.7 GeV and laboratory rapidity abs(y) < 1 are identified via their energy loss in the silicon tracker. The average pt increases with particle mass and the charged multiplicity of the event. The increase of the average pt with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that EPOS LHC, which incorporates additional hydrodyna…
The production of charged pions, kaons and (anti)protons has been measured at mid-rapidity ($-0.5 < y < 0$) in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using the ALICE detector at the LHC. Exploiting particle identification capabilities at high transverse momentum ($p_{\rm T}$), the previously published $p_{\rm T}$ spectra have been extended to include measurements up to 20 GeV/$c$ for seven event multiplicity classes. The $p_{\rm T}$ spectra for pp collisions at $\sqrt{s}=7$ TeV, needed to interpolate a pp reference spectrum, have also been extended up to 20 GeV/$c$ to measure the nucl…
The size of the particle emission region in high-energy collisions can be deduced using the femtoscopic correlations of particle pairs at low relative momentum. Such correlations arise due to quantum statistics and Coulomb and strong final state interactions. In this paper, results are presented from femtoscopic analyses of $π^{\pm}π^{\pm}$, ${\rm K}^{\pm}{\rm K}^{\pm}$, ${\rm K}^{0}_S{\rm K}^{0}_S$, ${\rm pp}$, and ${\rm \overline{p}}{\rm \overline{p}}$ correlations from Pb-Pb collisions at $\sqrt{s_{\mathrm {NN}}}=2.76$ TeV by the ALICE experiment at the LHC. One-dimensional radii of the sys…
Three-dimensional analyses of the pion source revealed a heavy, non-Gaussian tail in the direction of the pair transverse momentum. The interpretation of these pion sources in terms of pure hydrodynamical evolution is, however, complicated by the strong contribution of feed-down from long-lived resonances to the source. On the other hand, kaons provide a much cleaner probe of the expanding fireball. Here we present a recent three-dimensional kaon correlation analysis using Cartesian harmonics decomposition technique. In contrary to pions, the three-dimensional source function of kaons is large…
In this Letter, comprehensive results on ${\rmπ}^\pm$, K$^\pm$, K$^0_S$, p, $\rm\bar{p}$, $\rm Λ$ and $\rm \barΛ$ production at mid-rapidity ($0 < y_{\rm cms} < 0.5$) in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, measured by the ALICE detector at the LHC, are reported. The transverse momentum distributions exhibit a hardening as a function of event multiplicity, which is stronger for heavier particles. This behavior is similar to what has been observed in pp and Pb-Pb collisions at the LHC. The measured $p_{\rm T}$ distributions are compared to results at lower energy and with predicti…
In this Letter we report the first results on $π^\pm$, K$^\pm$, p and $\mathrm {p\overline{p}}$ production at mid-rapidity ($\left|y\right|<0.5$) in central Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, measured by the ALICE experiment at the LHC. The $p_{\rm T}$ distributions and yields are compared to previous results at $\sqrt{s_{\rm NN}}$ = 200 GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with $\sqrt{s_{\rm NN}}$, which in hydrodynamic models is expected as a consequence of the increasing particl…
Fluctuations of conserved quantities such as net-baryon, net-charge, and net-strangeness numbers have generated considerable interest in the study of the thermodynamic properties of the hot and dense QCD matter. Theoretical calculations suggest that the off-diagonal cumulants of conserved charges along with the diagonal cumulants can help better constrain the freeze-out parameters and, therefore, help to map the QCD phase diagram. In this proceeding, we briefly outline the recent STAR measurements on the second-order off-diagonal cumulants of net-charge, net-proton, and net-kaon multiplicity d…
Many data in the high energy physics are, in fact, sample means. It is shown that when this exact meaning of the data is taken into account and the most weakly bound states are removed from the hadron resonance gas, the acceptable fit to the whole spectra of pions, kaons and protons measured at midrapidity in central Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV [Phys.Rev.Lett.109,252301(2012)] is obtained. The invariant distributions are predicted with the help of the single-freeze-out model in the chemical equilibrium framework. Low $p_{T}$ pions and protons are reproduced simultaneously as…
A microscopic approach has been employed to study the kaon productions in heavy ion collisions. The momentum integrated Boltzmann equation has been used to study the evolution of strangeness in the system formed in heavy ion collision at relativistic energies. The kaon productions have been calculated for different centre of mass energies ($\sqrt{s_{\mathrm {NN}}}$) ranging from AGS to RHIC. The results have been compared with available experimental data. We obtain a non-monotonic horn like structure for $K^+/π^+$ when plotted with $\sqrt{s_{\mathrm {NN}}}$ with the assumption of an initial pa…
STAR's measurements of directed flow ($v_1$) for pions, kaons (charged and $K_s^0$), protons and antiprotons for Au + Au collisions at $\sqrtsNN = 200$ GeV are presented. Negative $v_1(y)$ slope is observed for pions, antiprotons, protons and kaons. The proton $v_1(y)$ slope at midrapidity is found extremely small. Sizable difference is seen between $v_1$ of protons and anti-protons in 5-30% central collisions. Anti-flow can explain the negative slope, however, it has difficulties explaining the centrality dependence of the difference between the $v_1(y)$ slopes of protons and anti-protons. Th…
We report on the results of femtoscopic analyses of Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV and pp collisions at $\sqrt{s}$= 7 TeV with identical charged and neutral kaons. The femtoscopic correlations allow one to measure the space-time characteristics of particle production using particle correlations due to the effects of quantum statistics for identical particles and final state interaction for both identical and non-identical ones. Small contributions from resonance decays make kaon femtoscopy an ideal tool for the correlation studies. In conjunction with pion and proton femtoscopy, …
Transverse momentum spectra of $π^{\pm}$, $\rm K^{\pm}$ and p($\bar{\rm p}$) up to $p_{\rm T}$ = 20 GeV/$c$ at mid-rapidity in pp and Pb-Pb collisions at $\sqrt{s_{\rm NN}}=$ 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at $p_{\rm T} \approx 3 GeV/c$ in central Pb-Pb collisions. Below the peak, $p_{\rm T}$ < 3 GeV/$c$, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadron…
Balance functions have been measured for charged particle pairs, identified charged pion pairs, and identified charged kaon pairs in Au+Au, d+Au, and p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV at the Relativistic Heavy Ion Collider using the STAR detector. These balance functions are presented in terms of relative pseudorapidity, $Δη$, relative rapidity, $Δy$, relative azimuthal angle, $Δϕ$, and invariant relative momentum, $q_{\rm inv}$. In addition, balance functions are shown in terms of the three components of $q_{\rm inv}$: $q_{\rm long}$, $q_{\rm out}$, and $q_{\rm side}$. For charged p…
We investigate the squeezed back-to-back correlations (BBC) of $K^+$$K^-$, caused by the mass modification of the particle in the dense medium formed in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV and Au+Au collisions at $\sqrt{s_{NN}}=62.4$ GeV. Considering some kaons may be not affected by the medium, we further study the BBC functions of $K^+$$K^-$ when parts of all kaons have a mass-shift. Our results indicate that the BBC functions of $K^+$$K^-$ can be observed when only about 10$\%$ of all kaons have a mass-shift in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV and the peripheral collisions …
We present Hanbury-Brown Twiss measurements from the PHENIX experiment at RHIC for final results for charged kaon pairs from sqrt{s_{NN}} = 200 GeV Au+Au collisions and preliminary results for charged pion pairs from sqrt{s} = 200 GeV p+p collisions. We find that for kaon pairs from Au+Au, each traditional 3D Gaussian radius shows approximately the same linear increase as a function of N^{1/3}_{part}. An imaging analysis reveals a significant non-Gaussian tail for r \gtrsim 10 fm. The presence of a tail for kaon pairs demonstrates that similar non-Gaussian tails observed in earlier pion measur…
We present the first measurements of femtoscopic correlations between the K$^0_{\rm S}$ and K$^{\rm \pm}$ particles in pp collisions at $\sqrt{s}=7$ TeV measured by the ALICE experiment. The observed femtoscopic correlations are consistent with final-state interactions proceeding solely via the $a_0(980)$ resonance. The extracted kaon source radius and correlation strength parameters for K$^0_{\rm S}$K$^{\rm -}$ are found to be equal within the experimental uncertainties to those for K$^0_{\rm S}$K$^{\rm +}$. Results of the present study are compared with those from identical-kaon femtoscopic …
The first measurement of the production of pions, kaons, (anti-)protons and $ϕ$ mesons at midrapidity in Xe-Xe collisions at $\sqrt{s_{\rm NN}} = 5.44$ TeV is presented. Transverse momentum ($p_{\rm T}$) spectra and $p_{\rm T}$-integrated yields are extracted in several centrality intervals bridging from p-Pb to mid-central Pb-Pb collisions in terms of final-state multiplicity. The study of Xe-Xe and Pb-Pb collisions allows systems at similar charged-particle multiplicities but with different initial geometrical eccentricities to be investigated. A detailed comparison of the spectral shapes in…
Studying baryon number transport dynamics via hyperon-kaon correlations in $p + \mathrm{Au}$ collisions at $\sqrt{s_{_{\rm NN}}}=20$, $39$ and $62$ GeV
Key Laboratory of Nuclear Physics and Ion-beam Application (MOE), Fudan University（核物理与离子束应用教育部重点实验室，复旦大学）
Mid-rapidity production of $π^{\pm}$, $\rm{K}^{\pm}$ and ($\bar{\rm{p}}$)p measured by the ALICE experiment at the LHC, in Pb-Pb and inelastic pp collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum ($p_{\rm{T}}$) range from hundreds of MeV/$c$ up to 20 GeV/$c$. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0$-$90%. The comparison of the $p_{\rm{T}}$-integrated particle ratios, i.e. proton-to-pion (p/$π$) and kaon-to-pion (K/$π$) ratios, with similar measurements in…
