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1/β vs. momentum for π±, K±, and p(p¯) from 200 GeV d+Au collisions. Separations between pions and kaons, kaons and protons are achieved up to pT≃1.6 and 3.0 GeV/c, respectively. The insert shows m2=p2(1/β2−1) for 1.2<pT<1.4 GeV/c. Clear separation of pions, kaons and protons is seen.
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Identified mid-rapidity particle spectra of π±, K±, and from 200 GeV p+p and d+Au collisions are reported. A time-of-flight detector based on multi-gap resistive plate chamber technology is used for particle identification. The particle-species dependence of the Cronin effect is observed to be significantly smaller than that at lower energies. The...
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Citations
... Similar "collective" behavior in the pattern of soft particle production that is attributed to QGP evolution in large systems has been observed [44][45][46][47][48][49], suggesting the possibility of final-state effects. However, clear evidence of jet quenching has not been established [50][51][52][53][54][55]. This puzzle has led to intense discussion of the origin of the apparent collectivity [56][57][58][59] and the nature of the medium produced in small systems. ...
The search for the smallest quark-gluon plasma (QGP) droplets in nature has motivated recent small collisions system programs at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). Unambiguous identification of jet quenching due to final-state interactions is key to confirming quark-gluon plasma (QGP) formation in these reactions. We compute the nuclear modification factors RAA and Rp(d)A of charged hadrons and heavy flavor mesons in large (Au-Au, Xe-Xe, Pb-Pb) and small (d−Au, p−Pb, O-O) colliding systems, respectively. Our results include the Cronin effect and initial-state parton energy loss in cold nuclear matter. In the final state, hard partons undergo collisional energy loss and branching that was recently derived using soft-collinear-effective-theory with Glauber gluons (SCETG). In large colliding systems, medium-modified quantum chromodynamics evolution of the fragmentation functions dominates the nuclear correction. As the system size decreases, we find that cold nuclear matter effects, collisional energy loss, and QGP-induced radiations can become equally important. A systematic scan over the medium size and mass or flavor dependence of RAA provides the opportunity to separate these individual contributions and identify QGP signatures in small systems. Predictions for RAAh, RAAD, RAAB in O-O collisions at s=0.2 and 7 TeV are presented with and without the formation of a QGP and contrasted with the corresponding Rp(d)A calculations. Single-hadron measurements at RHIC and the LHC will not only test the O-O predictions for both light and heavy flavor production but also shed light on the possibly very different dynamics of p−A and A−A reactions at similar soft particle production multiplicities.
... The experimental data measured in pp MB collisions [42,54,[71][72][73][74] at √ s = 62.4 GeV, 200 GeV, 2.76 TeV, and 5.02 TeV were used for obtaining the dE T /dy / dN/dy )-dN/dy /S ⊥ correlation considering only π ± , K ± , p andp, and the corresponding neutral hadrons in Eqs. (4) and (5). ...
Previous extensive studies on the dependence of the average transverse momentum, its slope as a function of the hadron mass, and the average transverse expansion on the particle multiplicity per unit rapidity and unit transverse overlap area of the colliding partners are extended to the ratio of the energy density to the entropy density. The behavior of the ratio between the average transverse momentum and the square root of the particle multiplicity per unit rapidity and unit transverse overlap area 〈pT〉/〈dN/dy〉/S⊥ as a function of collision energy for a given centrality or as a function of centrality for a given collision energy supports the predictions of color glass condensate and percolation based approaches. The dependence of the ratio of the energy density 〈dET/dy〉/S⊥ to the entropy density 〈dN/dy〉/S⊥ at different collision centralities for A−A collisions from the Alternating Gradient Synchrotron, the Super Proton Synchrotron, the BNL Relativistic Heavy Ion Collider, and the CERN Large Hadron Collider energies is presented. The trend of this ratio towards a plateau at the highest RHIC energies followed by a steep rise at LHC energies is in agreement with theoretical predictions made 40 years ago that indicate this behavior as a signature of a phase transition. This pattern strongly depends on the collision geometry, converging towards the dependence that characterizes the pp minimum bias collisions for the most peripheral A−A collisions. Expected similarities between pp and Pb-Pb collisions at LHC energies are confirmed.
... Apart from pions and kaons, leading baryons can carry a large fraction of the energy producing similar reactions. The experimental data [40][41][42] of such reactionsavailable up to a few tens of TeV per nucleon in the center-of-mass frame -show a transverse momentum p T distribution that decreases exponentially, The slope Q, which is related to the average p T , changes slowly with the energy of the collision and the rapidity region. The average transverse momentum is of the order of tenths of GeV/c (see figure 2). ...
In extensive air shower experiments, the number of muons crossing a detector at a given position, as well as their arrival time, arrival direction, and energy, are determined by a more fundamental 3-dimensional distribution linked to the hadronic core of the shower. Muons are produced high up in the atmosphere after the decay of mesons in the hadronic cascade. The distributions of production depth, energy, and transverse momentum of muons are enough to fully predict the muon component of air showers in any particular observational condition. By using air-shower simulations with the state-of-the-art hadronic interaction models, the mentioned distributions at production are analyzed as a function of zenith angle, primary mass, and hadronic interaction model, and their level of universality is studied and assessed in an exhaustive manner for the first time.
... With 2σ separation, protons/(pions + kaons) and kaons/pions were identified up to 3 and 1.6 GeV/c, respectively. Although the acceptance of the prototype was only 1/120 of the TOF system, several important physics results were achieved from the acquired data thanks to the extended particle identification capability [61,62]. With the success of the TOFr physics run, the STAR collaboration decided that all TOF MRPC modules were to be produced in China. ...
Pairs of lepton and antilepton (dilepton) in a continuous mass range are one of the most experimentally challenging and golden probes of the quark-gluon plasma (QGP) produced in heavy ion collisions because they do not strongly interact with the hot and dense medium, and reflect the properties of the medium at the time the dilepton is generated. The measurements of dileptons require lepton identification with high purity and high efficiency at large detector acceptance. STAR is one of two large experiments at the relativistic heavy ion collider with a primary goal of searching for the QGP and studying its properties. The STAR experiment launched a comprehensive dielectron (e+e−) program enabled by the time-of-flight (TOF) detector that had been fully installed in 2010. In this article, we review the decade-long R&D, the construction and performance of the STAR TOF detector, and dielectron measurements, including thermal dielectron production and dielectron production from the Breit–Wheeler process. Future perspectives are also discussed.
... Simulated events were generated using PYTHIA 6.4.28 [98] with the PERUGIA 2012 tune [99]. The parameter PARP (90), which controls the energy dependence of the underlying event process low-p T cutoff, was adjusted from 0.24 to 0.213 in PERUGIA 2012 in order to match previous STAR measurements of the π AE cross sections in 200 GeV pp collisions [100,101]. This modification was first introduced in Ref. [102], where it was shown to provide a very good description of a wide range of jet and event properties in 510 GeV pp collisions. ...
The STAR Collaboration reports measurements of the transverse single-spin asymmetries, AN, for inclusive jets and identified “hadrons within jets” production at midrapidity from transversely polarized pp collisions at s=200 GeV, based on data recorded in 2012 and 2015. The inclusive jet asymmetry measurements include AN for inclusive jets and AN for jets containing a charged pion carrying a momentum fraction z>0.3 of the jet momentum. The identified hadron within jet asymmetry measurements include the Collins effect for charged pions, kaons, and protons, and the Collins-like effect for charged pions. The measured asymmetries are determined for several distinct kinematic regions characterized by the jet transverse momentum pT and pseudorapidity η, as well as the hadron momentum fraction z and momentum transverse to the jet axis jT. These results probe higher momentum scales (Q2 up to ∼900 GeV2) than current, semi-inclusive deep-inelastic scattering measurements, and they provide new constraints on quark transversity in the proton and enable tests of evolution, universality, and factorization breaking in the transverse-momentum-dependent formalism.
... Apart from pions and kaons, leading baryons can carry a large fraction of the energy producing similar reactions. The experimental data [32][33][34] of such reactionsavailable up to a few tens of TeV per nucleon in the center-of-mass frame -show a transverse momentum p T distribution that decreases exponentially, ...
In extensive air shower experiments, the number of muons crossing a detector at a given position, as well as their arrival time, arrival direction, and energy, are determined by a more fundamental 3-dimensional distribution linked to the hadronic core of the shower. Muons are produced high up in the atmosphere after the decay of mesons in the hadronic cascade. The distributions of production depth, energy, and transverse momentum of muons are enough to fully predict the muon component of air showers in any particular observational condition. By using air-shower simulations with the state-of-the-art hadronic interaction models, the mentioned distributions at production are analyzed as a function of zenith angle, primary mass, and hadronic interaction model, and their level of universality is studied and assessed in an exhaustive manner for the first time.
... Similar "collective" behavior in the pattern of soft particle production that is attributed to QGP evolution in large systems has been observed [44][45][46][47][48][49], suggesting the possibility of final-state effects. However, clear evidence of jet quenching has not been observed [50][51][52][53][54][55][56]. This puzzle has led to intense discussion of the origin of the apparent collectivity [57][58][59][60] and the nature of the medium produced in small systems. ...
The search for the smallest quark-gluon plasma (QGP) droplets in nature has motivated recent small collisions system programs at RHIC and LHC. Unambiguous identification of jet quenching due to final-state interactions is key to confirming QGP formation in these reactions. We compute the nuclear modification factors and of charged hadrons and heavy flavor mesons in large (Au-Au, Xe-Xe, Pb-Pb) and small (d-Au, p-Pb, O-O) colliding systems, respectively. Our results include the Cronin effect and initial-state parton energy loss in cold nuclear matter. In the final state, hard partons undergo collisional energy loss and branching that was recently derived using Soft-Collinear-Effective-Theory with Glauber Gluon (SCET). In large colliding systems, medium-modified QCD evolution of the fragmentation functions dominates the nuclear correction. As the system size decreases, we find that cold nuclear matter effects, collisional energy loss, and QGP-induced radiations can become equally important. A systematic scan over the medium size and mass/flavor dependence of provides the opportunity to separate these individual contributions and identify QGP signatures in small systems. Predictions for , , in O-O collisions at TeV are presented with and without the formation of a QGP and contrasted with the corresponding calculations. Upcoming single-hadron measurements at the LHC will not only test the O-O predictions for both light and heavy flavor production, but will shed light on the possibly very different dynamics of p-A and A-A reactions at similar soft particle production multiplicities.
... Then the particle path can be calculated and extended to the ToF system. Figure 4a [57] shows the relationship between the inversed velocity (1/β) measured by the ToF system and the momentum (p) obtained from TPC. The ToF provides good PID capabilities with 1.6 GeV/c for π/K and 3 GeV/c for K/p separation. ...
... The mass peaks of 3 He and 4 He can be separated obviously, which reveals the importance of the ToF system. [57]. Insert: the distribution of the square of the mass for momentum in the range of 1.2 and 1.4 GeV/c. ...
With the advantages of high-performance, easy to build and relatively low cost, the multigap resistive plate chamber has been arousing broad interests over the last few decades. It has become a new standard technology for the time of flight system in high energy physics experiments. In this article, we will give a description of the structure and the operating principles of the MRPC detector and focus on reviewing the applications on the time of flight system in several famous experiments. The performances, including time resolution and particle identification, are discussed in detail. Some recent advances and points of view for the future development of the next generation MRPC are also outlined.
... Tracking efficiency depends on particle species; tracking efficiency for nonidentified charged tracks therefore depends on the relative population of different species. In order to assess the magnitude of this dependence, two different assumptions are made for the relative yield of charged pions, charged kaons, protons, and antiprotons comprising the charged track population: the relative yields measured in pp collisions [54,55] and those measured in Au+Au collisions [55][56][57]. The relative yields for Au+Au collisions are used in the principal analysis, giving tracking efficiency for primary charged tracks of 68% at p T = 0.5 GeV/c and 72% for p T > 1 GeV/c in central Au+Au collisions and 85% at p T = 0.5 GeV/c and 88% for p T > 1 GeV/c in peripheral Au+Au collisions. ...
The STAR Collaboration at the Relativistic Heavy Ion Collider reports the first measurement of inclusive jet production in peripheral and central Au+Au collisions at sNN=200 GeV. Jets are reconstructed with the anti-kT algorithm using charged tracks with pseudorapidity |η|<1.0 and transverse momentum 0.2<pT,jetch<30 GeV/c, with jet resolution parameter R=0.2, 0.3, and 0.4. The large background yield uncorrelated with the jet signal is observed to be dominated by statistical phase space, consistent with a previous coincidence measurement. This background is suppressed by requiring a high-transverse-momentum (high-pT) leading hadron in accepted jet candidates. The bias imposed by this requirement is assessed, and the pT region in which the bias is small is identified. Inclusive charged-particle jet distributions are reported in peripheral and central Au+Au collisions for 5<pT,jetch<25 GeV/c and 5<pT,jetch<30 GeV/c, respectively. The charged-particle jet inclusive yield is suppressed for central Au+Au collisions, compared to both the peripheral Au+Au yield from this measurement and to the pp yield calculated using the PYTHIA event generator. The magnitude of the suppression is consistent with that of inclusive hadron production at high pT and that of semi-inclusive recoil jet yield when expressed in terms of energy loss due to medium-induced energy transport. Comparison of inclusive charged-particle jet yields for different values of R exhibits no significant evidence for medium-induced broadening of the transverse jet profile for R <0.4 in central Au+Au collisions. The measured distributions are consistent with theoretical model calculations that incorporate jet quenching.
... The simulation sample used for detector response and background correction in this analysis was generated using PYTHIA 6.4.28 [19] with the CTEQ6L1 PDF [20] and the Perugia 2012 tune [4] with the PARP(90) parameter changed to 0.213, which is, throughout this article, referred to as PYTHIA 6 (STAR) [3]. PYTHIA 6 (STAR) is tuned with STAR published minimum bias identified particle spectra [21,22] resulting in agreement with the inclusive identified charged pion cross-sections at the 10% level [23]. The PYTHIA parameter PARP(90) is related to the energy scaling of the minimum bias and underlying event phenomena [4]. ...
... An energy dependence study of the Transverse region charged particle density shows a near-linear increase with the log of the collision energy, which contributes to the understanding of the energy scaling of the underlying event dynamics. These underlying event activity measurements, in combination with the previously reported minimum bias observables [21,22], provide valuable input and constraints to the predominantly phenomenological modeling in Monte Carlo event generators of the low-momentum QCD processes in p+p collisions. ...
Particle production sensitive to non-factorizable and non-perturbative processes that contribute to the underlying event associated with a high transverse momentum () jet in proton+proton collisions at =200 GeV is studied with the STAR detector. Each event is divided into three regions based on the azimuthal angle with respect to the highest- jet direction: in the leading jet direction ("Toward"), opposite to the leading jet ("Away"), and perpendicular to the leading jet ("Transverse"). In the Transverse region, the average charged particle density is found to be between 0.4 and 0.6 and the mean transverse momentum, , between 0.5-0.7 GeV/c for particles with 0.2 GeV/c at mid-pseudorapidity (1) and jet 15 GeV/c. Both average particle density and depend weakly on the leading jet . Closer inspection of the Transverse region hints that contributions to the underlying event from initial- and final-state radiation are significantly smaller in these collisions than at the higher energies, up to 13 TeV, recorded at the LHC. Underlying event measurements associated with a high- jet will contribute to our understanding of QCD processes at hard and soft scales at RHIC energies, as well as provide constraints to modeling of underlying event dynamics.