通讯机构：
[Zhang, DL; Chen, K ; Wang, HL] C;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, PLAC, Wuhan 430079, Peoples R China.;Hubei Prov Engn Res Ctr Silicon Pixel Chip & Detec, Wuhan 430079, Peoples R China.
关键词：
CMOS readout of gaseous detectors;Front-end electronics for detector readout;Gaseous imaging and tracking detectors;Time projection Chambers (TPC)
摘要：
<jats:title>Abstract</jats:title>
<jats:p>Within the project of building a time projection chamber using 100 kg of high-pressure
<jats:sup>86</jats:sup>SeF<jats:sub>6</jats:sub> gas to search for the neutrinoless double-beta decay in the NvDEx
collaboration, we are developing a CMOS charge sensor, named Topmetal-S, which is tailored for the
experiment to detect the ions without gas amplification. In this work, the performance of
the sensor is presented. The equivalent noise charge of the sensor is measured to be about 120 to
140 e<jats:sup>-</jats:sup> depending on the operating point, with the charge injection capacitance
calibrated against external capacitors. The signal waveforms are investigated with various chip
parameters and experimental settings. In addition to electrons, both negatively and positively
charged ions could be detected, and their waveforms are studied using air and SF<jats:sub>6</jats:sub>
gases. Using the sensor, the mobility of negative ions in ambient air in the atmospheric pressure
is measured to be 1.555 ± 0.038 cm<jats:sup>2</jats:sup> · V<jats:sup>-1</jats:sup> · s<jats:sup>-1</jats:sup>. Our study
demonstrates that the Topmetal-S chip could be used as the ion detection charge sensor for the
experiment. Further work is ongoing to reduce the noise of the sensor and to develop a
small readout plane with tens of thesensors.</jats:p>
作者机构：
[Huang, Huan Zhong] Univ Calif Los Angeles, Dept Phys & Astrophys, Los Angeles, CA 90095 USA.;[Shi, Shusu; Luo, Xiaofeng; Liu, Feng] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Peoples R China.;[Shi, Shusu; Luo, Xiaofeng; Liu, Feng] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.;[Wang, Fuqiang] Purdue Univ, Dept Phys, W Lafayette, IN 47907 USA.;[Xu, Nu] Lawrence Berkeley Natl Lab, Nucl Sci Div, Berkeley, CA 94720 USA.
通讯机构：
[Shusu Shi] K;Key Laboratory of Quark & Lepton Physics (MOE) and Institute of Particle Physics, Central China Normal University, Wuhan 430079, China<&wdkj&>Author to whom correspondence should be addressed.
关键词：
high-energy nuclear collisions;collectivity;chirality;criticality;QCD;critical point;phase boundary;strangeness;thermalization;viscosity;baryon density
摘要：
<jats:p>We celebrate the legacies of our friend and mentor Professor Lianshou Liu who was one of the pioneers for the phenomenology of multi-particle interactions and initiated the physics of relativistic heavy-ion collisions in China. In this article, we discuss some of the recent exciting experimental observations on the collective phenomena including collectivity, chirality, criticality, strangeness production, and thermal equilibrium in high-energy nuclear collisions. Future directions, especially the physics at high baryon density, will be discussed with a focus on the first-order phase boundary and hyperon–nucleon interactions.</jats:p>
通讯机构：
[Liu, J; Zhang, DL ; Gao, CS; Wang, HL] C;[Wang, Z ] G;Guizhou Normal Univ, Sch Phys & Elect Sci, Guiyang, Peoples R China.;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, PLAC, Wuhan, Peoples R China.;Hubei Prov Engn Res Ctr Silicon Pixel Chip & Detec, Wuhan, Peoples R China.
摘要：
A beam monitor system is being developed for the cool storage ring (CSR) external-target experiment (CEE) at the Heavy Ion Research Facility in Lanzhou (HIRFL). The beam monitor is required to measure the lateral position of each beam particle with spatial resolution less than 50 mu m andwith beam rates up to 1 MHz. As the beam intensity increases, the build-up of slow-moving positive ions created from the ionization of the detector gas by the beam leads to a significant distortion of the nominal electric field in the drift region. In this work, simulation studies of the beam monitor are performed, in particular the space charge effect and the correction strategy. It shows that the space charge at the nominal drift electric field of 700 V/cm modifies the electric field in the sensitive volume by roughly 5% in both the drift and transverse directions. The distortion on the measured position is up to 0.35 mm in the 5s region of the beam profile. The expected spatial resolution of 500 MeV/u U ion is 34.5 mu m considering the pixel noise of 400 e(-) and the 100 mu m x 1 mm pixel size of the charge sensor chip in the selected gas mixture.
摘要：
本文讨论了RHIC-STAR相对论重离子碰撞实验近年来重要的结果.主要包括高能重离子碰撞中夸克物质的集体运动性质和能量扫描实验中各阶集体流的研究,守恒荷的高阶矩与强相互作用相变临界点的探索,以及重味、奇异粒子和轻核产生的测量.我们发现STAR实验最高能量的重离子碰撞中形成了热化的夸克物质,多个信号表明当碰撞能量低于39 Ge V之时,可能进入了强相互作用相图的临界区.最后对未来重离子碰撞实验的运行计划和研究重点做了展望.
通讯机构：
[Chaosong Gao; Hulin Wang] P;PLAC, Key Laboratory of Quark & Lepton Physics (MOE), Central China Normal University, Wuhan, 430079, China<&wdkj&>Hubei Provincial Engineering Research Center of Silicon Pixel Chip & Detection Technology, Wuhan, 430079, China
摘要：
Within the project of building a beam monitor for the CSR external-target experiment (CEE) at HIRFL, charge sensors that are used in the gaseous ionization detector and in line with the Topmetal principle, are being developed and studied. It integrates in the same chip a topmost metal, which senses the drifting charges, and the readout circuitry. This paper presents the design and preliminary characterization of the first full-sized Topmetal-CEE chip, the Topmetal-CEEv1, which follows this design principle while tailored to the CEE physics programs. It features an enlarged 1 mm x 89 mu m topmost metal per pixel, in-pixel discrimination and sparsified readout, as well as an amplitude measurement with the Time-over-Threshold (TOT) method. The studies are carried out with the injected pulses and the alpha particles from Am-241. The major functionalities of the chip are verified. Its performance pertaining to the usage as charge sensing and readout chip in the beam monitor of CEE are also preliminarily evaluated. It will be used in the upgraded prototype of the beam monitor, superseding the common-purpose Topmetal-II- chip.
通讯机构：
[Zhao, CX ; Gao, CS; Liu, J ; Wang, HL] C;[Wang, Z ] G;Cent China Normal Univ, Key Lab Quark & Lepton Phys, PLAC, MOE, Wuhan 430079, Peoples R China.;Hubei Prov Engn Res Ctr Silicon Pixel Chip & Detec, Wuhan, Peoples R China.;Guizhou Normal Univ, Sch Phys & Elect Sci, Guiyang, Peoples R China.
摘要：
The cool storage ring (CSR) external-target experiment (CEE) will be the first large-scale nuclear physics experiment at the Heavy Ion Research Facility in Lanzhou (HIRFL). The beam monitor, designed to measure the lateral position of each beam particle, will improve the precision of primary vertex reconstruction otherwise determined by the time projection chamber (TPC) and multi-wire drift chambers (MWDCs). The beam monitor mainly contains two gaseous ionization sub-detectors, each measuring one lateral coordinate of the beam. The design requirements include the spatial resolution of <50 mu m, the two-particle separation capability of <1 mu s, the rate capability of >10(6) pps, and small material budget. It features novel front-end pixel chips for both charge sensing and readout functions. The first prototype, utilizing the common-purpose Topmetal-II-chips, has been developed and tested; the second one, deploying the custom-designed Topmetal-CEEv1 chips, is currently being assembled. In this paper we will present the detector specifications, design and test of the prototypes, in particular the charge sensing and readout chips.
关键词：
Analogue electronic circuits;CMOS readout of gaseous detectors;Front-end electronics for detector readout
摘要：
<jats:title>Abstract</jats:title>
<jats:p>This paper presents the design and test results of a low noise Phase Locked Loop (PLL) Application Specific Integrated Circuit (ASIC), which is designed for the data transmission system in a pixel chip for a beam monitor of the Cooling Storage Ring (CSR) external target experiment at HIRFL in China. The proposed PLL consists of a differential ring oscillator, a digital divider, a three-state phase frequency detector, a current charge pump, a second-order loop filter and current mode level buffers. A prototype PLL ASIC has been fabricated in a standard 130 nm CMOS process. The test results show that the frequency of the output clock is about 2.2 GHz with a phase noise of −90 dBc/Hz at a frequency offset of 1 MHz and a root mean square jitter of 1.15 ps. The core circuit of the PLL consumes about 30 mW under the power supply of 1.2 V.</jats:p>
摘要：
A prototype beam monitor was designed to provide tracking information for heavy-ion projectiles for the cool storage ring (CSR) external target experiment (CEE) at the Heavy Ion Research Facility in Lanzhou (HIRFL). High granularity and direct charge sensing are the main features of this device. It measures the beam position in a two-dimensional (2D) plane transverse to the beam direction on an event-by-event basis. The current design consists of two field cages inside a single vessel that operates independently and has electrical drift fields in orthogonal directions. Preliminary tests of the prototype were performed using a
$${{}^{241}\mathrm{Am}}$$
$$\alpha$$
source. The results show that a spatial resolution of less than 40
$${\upmu \mathrm{m}}$$
and a time resolution of less than 600ns can be achieved.
关键词：
Beam-line instrumentation (beam position and profile monitors;beam-intensity monitors;bunch length monitors);CMOS readout of gaseous detectors;Front-end electronics for detector readout
摘要：
The Cooler-Storage-Ring External-target Experiment (CEE) which is being constructed since 2020 is a spectrometer to study the properties of nuclear matter at high baryon density region. We present the design and simulation results of a sensor named Topmetal-CEE which is being developed for an online beam monitor of the CEE. A prototype of the Topmetal-CEE has been designed in a standard CMOS 130 nm process and is being fabricated. The Topmetal-CEE prototype has 180 channels with a pitch of 100 μm. In each channel, electrons are collected by a charge collection electrode which is a top-most metal exposed to the surrounding media, amplified by a charge sensitive amplifier, and then fed into a discriminator. The output of the discriminator is split into two paths which record Time of Arrival (ToA) and Time over Threshold (ToT) of the collected signal, respectively. In order to reduce the dead time, 180 channels are split into two separate parts and then the information in each part is read out by a data-driving priority readout scheme independently. Each channel has its own address encoded by an address encoder. The ToA, ToT and address of each channel are framed and encoded, and then transferred off chip with a serial speed of 4.4 Gbps.
作者：
Agakishiev, H.*;Aggarwal, M. M.;Ahammed, Z.;Alakhverdyants, A., V;Alekseev, I;...
期刊：
中国物理C,2021年45(4):198-241 ISSN：1674-1137
通讯作者：
Agakishiev, H.
作者机构：
[Kechechyan, A.; Agakishiev, H.; Averichev, G. S.; Efimov, L. G.; Alakhverdyants, A., V; Kizka, V; Rogachevskiy, O., V; Panebratsev, Y.; Shahaliev, E.; Fedorisin, J.; Bunzarov, I; Zoulkarneev, R.; Zoulkarneeva, Y.; Tokarev, M.; Filip, P.; Lednicky, R.; Dedovich, T. G.; Vokal, S.] Joint Inst Nucl Res, Dubna 141980, Russia.;[Underwood, D. G.; Krueger, K.; Bridgeman, A.; Spinka, H. M.] Argonne Natl Lab, Argonne, IL 60439 USA.;[Ullrich, T.; Pile, P.; Lamont, M. A. C.; Ljubicic, T.; Le Vine, M. J.; Xu, Z.; Ogawa, A.; Ruan, L.; Tang, A. H.; Videbaek, F.; Fisyak, Y.; Beavis, D. R.; Lauret, J.; Bland, L. C.; Longacre, R. S.; Webb, J. C.; Christie, W.; Arkhipkin, D.; Fine, V; Debbe, R. R.; Lebedev, A.; Burton, T. P.; Dunlop, J. C.; Gordon, A.; Landgraf, J. M.; Love, W. A.; Yip, K.; Didenko, L.; Guryn, W.; Van Buren, G.; Lee, J. H.] Brookhaven Natl Lab, Upton, NY 11973 USA.;[Perkins, C.; Crawford, H. J.; Engelage, J.; Judd, E. G.] Univ Calif Berkeley, Berkeley, CA 94720 USA.;[Sanchez, M. Calderon de la Barca; Draper, J. E.; Cebra, D.; Brovko, S. G.; Mall, O., I; Sangaline, E.; Reed, R.; Romero, J. L.; Salur, S.; Haag, B.; Liu, H.] Univ Calif Davis, Davis, CA 95616 USA.
通讯机构：
[Agakishiev, H.] J;Joint Inst Nucl Res, Dubna 141980, Russia.
关键词：
relativistic heavy ion collisions;dihadron correlations;jet-medium interactions;anisotropic flow background;event plane
摘要：
<jats:title>Abstract</jats:title>
<jats:p>Dihadron azimuthal correlations containing a high transverse momentum (
<jats:inline-formula>
<jats:tex-math><?CDATA $ p_{T} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M2.jpg" xlink:type="simple" />
</jats:inline-formula>) trigger particle are sensitive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the traversing parton and the medium, i.e. jet-quenching. Previous measurements revealed a strong modification to dihadron azimuthal correlations in Au+Au collisions with respect to <jats:italic>p</jats:italic>+<jats:italic>p</jats:italic> and <jats:italic>d</jats:italic>+Au collisions. The modification increases with the collision centrality, suggesting a path-length or energy density dependence to the jet-quenching effect. This paper reports STAR measurements of dihadron azimuthal correlations in mid-central (20%-60%) Au+Au collisions at
<jats:inline-formula>
<jats:tex-math><?CDATA $ \sqrt{s_{\rm{NN}}} = 200 $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M3.jpg" xlink:type="simple" />
</jats:inline-formula> GeV as a function of the trigger particle's azimuthal angle relative to the event plane,
<jats:inline-formula>
<jats:tex-math><?CDATA $ \phi_{s} = | \phi_{t}- \psi_{{\rm{EP}}}| $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M4.jpg" xlink:type="simple" />
</jats:inline-formula>. The azimuthal correlation is studied as a function of both the trigger and associated particle
<jats:inline-formula>
<jats:tex-math><?CDATA $ p_{T} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M5.jpg" xlink:type="simple" />
</jats:inline-formula>. The subtractions of the combinatorial background and anisotropic flow, assuming Zero Yield At Minimum (ZYAM), are described. The correlation results are first discussed with subtraction of the even harmonic (elliptic and quadrangular) flow backgrounds. The away-side correlation is strongly modified, and the modification varies with
<jats:inline-formula>
<jats:tex-math><?CDATA $ \phi_{s} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M6.jpg" xlink:type="simple" />
</jats:inline-formula>, with a double-peak structure for out-of-plane trigger particles. The near-side ridge (long range pseudo-rapidity
<jats:inline-formula>
<jats:tex-math><?CDATA $ \Delta\eta $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M7.jpg" xlink:type="simple" />
</jats:inline-formula> correlation) appears to drop with increasing
<jats:inline-formula>
<jats:tex-math><?CDATA $ \phi_{s} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M8.jpg" xlink:type="simple" />
</jats:inline-formula> while the jet-like component remains approximately constant. The correlation functions are further studied with the subtraction of odd harmonic triangular flow background arising from fluctuations. It is found that the triangular flow, while responsible for the majority of the amplitudes, is not sufficient to explain the
<jats:inline-formula>
<jats:tex-math><?CDATA $ \phi_{s} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M9.jpg" xlink:type="simple" />
</jats:inline-formula>-dependence of the ridge or the away-side double-peak structure. The dropping ridge with
<jats:inline-formula>
<jats:tex-math><?CDATA $ \phi_{s} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M10.jpg" xlink:type="simple" />
</jats:inline-formula> could be attributed to a
<jats:inline-formula>
<jats:tex-math><?CDATA $ \phi_{s} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M11.jpg" xlink:type="simple" />
</jats:inline-formula>-dependent elliptic anisotropy; however, the physics mechanism of the ridge remains an open question. Even with a
<jats:inline-formula>
<jats:tex-math><?CDATA $ \phi_{s} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M12.jpg" xlink:type="simple" />
</jats:inline-formula>-dependent elliptic flow, the away-side correlation structure is robust. These results, with extensive systematic studies of the dihadron correlations as a function of
<jats:inline-formula>
<jats:tex-math><?CDATA $ \phi_{s} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M13.jpg" xlink:type="simple" />
</jats:inline-formula>, trigger and associated particle
<jats:inline-formula>
<jats:tex-math><?CDATA $ p_{T} $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M14.jpg" xlink:type="simple" />
</jats:inline-formula>, and the pseudo-rapidity range
<jats:inline-formula>
<jats:tex-math><?CDATA $ \Delta\eta $?></jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpc_45_4_044002_M15.jpg" xlink:type="simple" />
</jats:inline-formula>, should provide stringent inputs to help understand the underlying physics mechanisms of jet-medium interactions in high energy nuclear collisions.
</jats:p>
摘要：
相对论重离子碰撞（又称高能核-核碰撞）为研究极端条件下核物质内禀性质、致密星体内部结构和大爆炸之后宇宙的早期演化过程提供了途径.强相互作用的量子色动力学（QCD）理论预言存在着解禁闭的新物质状态夸克-胶子等离子体（QGP）.经过近30年的努力,在极端相对论能区的核-核对撞实验中,包括RHIC和LHC的实验,科学家找到了QGP存在的证据.目前,高能核物理的一个重要的科学问题是高重子密度区的相结构,包括寻找相边界和可能存在的QCD临界点.量子热动力学基本原理告诉我们只有找到相边界或临界点才能最终确定新的物质相QGP的存在.我们首先回顾了高能核物理实验的研究现状,其中包括RHIC能量扫描实验中的强子集体运动、手征特性的研究和QCD临界点的寻找.然后对利用我国重离子加速器群,如Heavy Ion Research Facility in Lanzhou （HIRFL）和High Intensity heavy-ion Accelerator Facility （HIAF）以及CSR-External-target Experiment等开展高能核物理实验研究进行了展望.
作者机构：
[Zhang, Liang; Liu, Feng] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;[Zhang, Liang; Liu, Feng] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;[Li, Cheng; Jiang, Kun] Univ Sci & Technol China, Dept Modern Phys, Hefei 230026, Anhui, Peoples R China.;[Zhang, Liang; Wang, Fuqiang; Jiang, Kun] Purdue Univ, Dept Phys & Astron, W Lafayette, IN 47907 USA.;[Wang, Fuqiang] Huzhou Univ, Sch Sci, Huzhou 313000, Zhejiang, Peoples R China.
通讯机构：
[Liu, Feng] C;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.
摘要：
Background: Measurements of two-particle azimuthal angle correlations are a useful tool to study the distribution of jet energy loss; however, they are complicated because of the significant anisotropic flow background.
作者机构：
[Zhang, Chao; Zheng, Liang; Liu, Feng; Shi, Shusu; Lin, Zi-Wei] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China;[Zhang, Chao; Zheng, Liang; Liu, Feng; Shi, Shusu; Lin, Zi-Wei] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China;[Zheng, Liang] China Univ Geosci, Wuhan 430074, Hubei, Peoples R China;[Lin, Zi-Wei] East Carolina Univ, Dept Phys, Greenville, NC 27858 USA
通讯机构：
[Shi, Shusu] C;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China. Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.
摘要：
A multiphase transport (AMPT) model has been successful in explaining a wide range of observables in relativistic heavy ion collisions. In this work, we implement a newer set of free proton parton distribution functions and an impact parameter-dependent nuclear shadowing in the AMPT model. After refitting the parameters of the two-component initial condition model to the experimental data on pp and pp¯ total and inelastic cross sections from s∼ 4 GeV to 13 TeV, we study particle productions in pp and AA collisions. We show that the updated AMPT model with string melting can reasonably describe the overall particle yields and transverse momentum spectra for both pp and AA collisions at RHIC and LHC energies after we introduce a nuclear scaling of the minijet transverse momentum cutoff for AA collisions at LHC energies that is motivated by the color glass condensate. Since heavy flavor and high−pT particles are produced by perturbative-QCD processes and thus directly depend on parton distribution functions of nuclei, the updated AMPT model is expected to provide a more reliable description of these observables.
作者机构：
[Luo, Xiaofeng; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;[Luo, Xiaofeng; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;[Luo, Xiaofeng] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA.;[Nara, Yasushi] Akita Int Univ, Akita 0101292, Japan.;[Nara, Yasushi] Frankfurt Inst Adv Studies, D-60438 Frankfurt, Germany.
通讯机构：
[Luo, Xiaofeng] C;[Luo, Xiaofeng] U;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA.
关键词：
heavy-ion collisions;elliptic flow;equation of state;QCD phase transition
作者机构：
[Luo, Xiaofeng; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;[Luo, Xiaofeng; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;[Luo, Xiaofeng] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA.;[Nara, Yasushi] Akita Int Univ, Akita 0101292, Japan.;[Nara, Yasushi] Frankfurt Inst Adv Studies, D-60438 Frankfurt, Germany.
关键词：
heavy-ion collisions;elliptic flow;equation of state;QCD phase transition
摘要：
We perform a systematic study of elliptic flow (v_2)in Au+Au collisions at √S_(NN)=5 GeV by using a microscopic transport model, JAM. The centrality,pseudorapidity, transverse momentum and beam energy dependence of v_2 for charged as well as identified hadrons are studied. We investigate the effects of both the hadronic mean-field and the softening of equation of state (EoS) on elliptic flow. The softening of the EoS is realized by imposing attractive orbits in two body scattering, which can reduce the pressure of the system. We found that the softening of the EoS leads to the enhancement of v_2, while the hadronic mean-field suppresses v_2 relative to the cascade mode. It indicates that elliptic flow at high baryon density regions is highly sensitive to the EoS and the enhancement of V_2 may probe the signature of a first-order phase transition in heavy-ion collisions at beam energies of a strong baryon stopping region.
作者机构：
[Luo, Xiaofeng; Zhang, Chao; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;[Luo, Xiaofeng; Zhang, Chao; Liu, Feng; Chen, Jiamin] Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.;[Nara, Yasushi] Akita Int Univ, Akita 0101292, Japan.;[Nara, Yasushi] Frankfurt Inst Adv Studies, D-60438 Frankfurt, Germany.
通讯机构：
[Luo, Xiaofeng] C;Cent China Normal Univ, Inst Particle Phys, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Key Lab Quark & Lepton Phys MOE, Wuhan 430079, Hubei, Peoples R China.
摘要：
We present a detailed analysis of the beam energy dependence of the mechanisms for the generation of directed and elliptic flows in Au + Au collisions focusing on the role of hadronic rescattering and spectator shadowing within a microscopic transport model jam with different equations of state. A systematic study of the beam energy dependence is performed for Au + Au collisions at sNN=2.3−62.4 GeV. The transition of the dynamical origin of the directed flow is observed. We find that the initial Glauber-type nucleon-nucleon collisions generate negative v1 for nucleons at midrapidity due to the presence of spectator matter, and this negative nucleon v1 is turned to be positive by the meson-baryon interactions at the beam energy region of sNN<30 GeV. In contrast, above 30 GeV there is no spectator shadowing at midrapidity, and initial nucleon-nucleon collisions do not generate directed flow, but subsequent rescatterings among produced particles generate negative v1 for nucleons. It is demonstrated that negative pion-directed flows are mostly generated by the interaction with the spectator matter. It is also shown that the squeeze-out effect is largely suppressed in the case of softening, which leads to the enhancement of elliptic flow around sNN=5−7 GeV. The elliptic flow at midrapidity above 10 GeV is not influenced by the squeeze-out due to spectator matter, while its effect is seen at the forward rapidity range of y/yc.m.>0.5, which decreases as beam energy increases.
