Low mass vector meson production at forward rapidity in p+p and d+Au collisions at sNN = 200 GeV from a multiphase transport model

Low mass vector meson production at forward rapidity in p+p and d+Au collisions at <math id="M1"><mrow><msqrt><mrow><msub><mi>s</mi><mrow><msub><mrow/><mrow><mtext>N</mtext><mi>N</mi></mrow></msub></mrow></msub></mrow></msqrt></mrow></math> = 200 GeV from a multiphase transport model 1 2 first-author 1 2 1 corresp chenjinhui@sinap.ac.cn chenjinhui@sinap.ac.cn chenjinhui@sinap.ac.cn 1 3 corresp ygma@sinap.ac.cn ygma@sinap.ac.cn ygma@sinap.ac.cn 1 1 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China University of Chinese Academy of Sciences, Beijing 100049, China University of Chinese Academy of Sciences, Beijing 100049, China Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China Low-mass vector meson ( ρ , ω , and ϕ ) production at forward rapidity in p+p and d+Au collisions at <math id="M2"><mrow><msqrt><mrow><msub><mi>s</mi><mrow><msub><mrow/><mrow><mtext>N</mtext><mi>N</mi></mrow></msub></mrow></msub></mrow></msqrt></mrow></math> = 200 GeV is studied within the framework of a multiphase transport model (AMPT). Detailed investigations, including the transverse momentum and the rapidity dependence of low-mass vector meson production in the AMPT model show that the hadron interaction process is important for a quantitative description of the ρ and ω data. But for the ϕ meson, the strange quark production in the AMPT model with the string melting scenario describes the data reasonably well, while the default AMPT model under predicts the data. The N( ϕ )/N( ρ + ω ) ratio from the AMPT model with the string melting scenario perfectly describes the data in p+p collisions. For the d+Au collisions, an increased trend of this ratio vs. transverse momentum and the number of participants is observed from the AMPT model. Our results indicate that a precise measurement of the N( ϕ )/N( ρ + ω ) ratio in d+Au and Au+Au collisions will shed more light on the strangeness production and its dynamics in Quark Gluon Plasma. Vector meson Handron interaction AMPT 1 Introduction 1 Low-mass vector meson (LVM) production in high energy p+p and d+Au collisions is a useful tool in understanding the dynamics of the hot matter created in the reaction. In p+p collisions, LVM provides data for tuning the event generator inspired by Quantum Chromodynamics (QCD) and is a good reference for heavy-ion collisions. In heavy-ion collisions, LVM, due to their short lifetime and strong decay in the medium, carry important information on the hot and dense state of matter formed in such collisions [ 1 1 - 6 6 1-6 ]. Strangeness enhancement [ 7 7 ] is a phenomenon associated with soft particles in bulk matter, which can be studied via ϕ meson production [ 8 8 - 16 16 8-16 ] and the N( ϕ )/N( ρ + ω ) ratio. There are well tuned QCD event generators in p+p collision, such as the PYTHIA [ 17 17 ]. Microscopic transport model calculations including the di-lepton channel, are also available in the literature. For example, the parton-hadron string dynamics (PHSD) covariant transport model [ 18 18 ], which shows a fair agreement with the STAR data [ 19 19 - 21 21 19-21 ]. We provided another study on LVM production based on a multi-phase transport model (AMPT) and we focused on the forward rapidity region. We found that the N( ϕ )/N( ρ + ω ) ratio is sensitive to strange quark dynamics and proposed further experiment measurement on LVM production at froward rapidity in high energy heavy-ion collisions. The article is organized as follows. Sect. 2 is a brief description of the AMPT model. Section 3 is the results and discussion. A final summary is given in Sect. 4. 2 THE AMPT MODEL 1 The AMPT model is a hybrid model including the following four main components [ 22 22 ]: the initial condition, the partonic interactions, the conversion from partonic matter into hadronic matter, and the hadronic interactions. The initial condition, which includes the spatial and momentum distributions of minijet partons and soft string excitation, are obtained from the HIJING model [ 23 23 ]. The scatterings among partons are modeled by Zhang’s parton cascade (ZPC) [ 24 24 ], which presently includes only two-body elastic scatterings with cross sections obtained from the pQCD with screening mass. After the freeze-out of partons, two different methods are used in order to describe the conversion from partonic matter into hadronic matter, leading to the two different versions of the AMPT model: 1) the default version and 2) the string-melting version. In the default AMPT model, partons are recombined with their parent strings when they stop the interaction, and the resulting strings are converted to hadrons using a Lund string fragmentation model [ 25 25 ]. In the AMPT model with string melting, a simple quark coalescence model, based on the quark spatial information, is used to combine partons into hadrons. After the hadronization process, in both the default and string-melting versions, the dynamics of the hadronic matter is then described by A Relativistic Transport (ART) model [ 26 26 ]. The details of the AMPT model can be found in Ref. [ 22 22 ]. In the present study, we use the version of AMPT-v1.26-v2.26 with the QCD coupling constant α s = 0.33, and the screening mass μ = 3.2 fm -1 to obtain a parton scattering cross section of 1.5 mb in the ZPC stage. These new parameters, i.e. the coupling constant and the screening mass, will help to describe charged particle multiplicity density and the elliptic flow in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) [ 27 27 ]. All the other parameters are from the AMPT manual [ 22 22 ]. 3 RESULTS AND DISCUSSION 1 3.1 Low mass vector meson production in p+p and d+Au collisions 2 Figure 1 Figure 1 shows the ρ , ω , and ϕ <math id="M3"><mrow><msub><mi>p</mi><mi>T</mi></msub></mrow></math> spectra from the AMPT model in comparison to the experimental data. From the figure, one can see that the default AMPT model describes the ρ + ω data better than the string melting version, while for the ϕ meson calculation, which was published elsewhere [ 29 29 ], the AMPT with string melting version describes the data better than the default version. The new findings are consistent with our earlier study on mid-rapidity identified particle production in d+Au collisions at <math id="M4"><mrow><msqrt><mrow><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt></mrow></math> = 200 GeV [ 30 30 ]: the final state interaction in the default AMPT version is important for proton and π production. However, for the ϕ meson, the strangeness production in the string melting version enhance the rate and describes the data better than the pure hadonic phase version. Figure 2 Figure 2 presents the ρ , ω , and ϕ rapidity in p+p collisions at <math id="M7"><mrow><msqrt><mrow><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt></mrow></math> = 200 GeV. For the ( ρ + ω ), the default AMPT describes the data well, while the AMPT with string melting version under predicts the data in the full rapidity range. For the ϕ meson, the AMPT model with string melting version does a better job than the default version. This is consistent with the findings from the <math id="M8"><mrow><msub><mi>p</mi><mi>T</mi></msub></mrow></math> spectra [c.f. Fig. 1 Fig. 1 ]. For a heavy system like d+Au collisions, as shown in Fig.3 Fig.3 , the default AMPT model predicts a higher yield for ( ρ + ω ) than the melting version, while for the ϕ meson, the string melting version, has a higher rate than the default version. In comparison to the available ϕ meson data [ 31 31 ], also discussed in the earlier paper [ 29 29 ], the AMPT model with the string melting version predicts the ϕ meson yield in the d-going direction well, while it slightly under-predicted the high <math id="M9"><mrow><msub><mi>p</mi><mi>T</mi></msub></mrow></math> yield in the Au-going direction. The reason may be due to the small quark mass used in the model calculation and the particles that are less affected by the radial flow [ 22 22 ]. Future experimental measurement on ρ and ω production will be helpful. 3.2 N( ϕ )/N( ρ + ω ) ratio vs. transverse momentum and impact parameter 3 Figure 4 Figure 4 shows the N( ϕ )/N( ρ + ω ) ratio as a function of <math id="M11"><mrow><msub><mi>p</mi><mi>T</mi></msub></mrow></math> in p+p and d+Au collisions. From the figure, one can see that the AMPT model with the sting melting version (the red solid lines) describes the ratio well in p+p collisions (the blue solid circles), while the default version (the dash blue lines) under-predicts the ratio. It may be due to the enhanced strangeness production in the melting version, while the default version is only involved in the pure hadronic transport process. The ratio from the d+Au collisions shows similar behaviour as observed in p+p system. It will be interesting to see how the data will be in future experiment in future. Figure 5 Figure 5 predicts the N( ϕ )/N( ρ + ω ) in d+Au collisions at <math id="M14"><mrow><msqrt><mrow><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt></mrow></math> = 200 GeV. Two different types of collisions were selected for systematic study: the nucleon+Au collision type and the d+Au collision type. One can see that the ratios increase as a function of N part in low N part and saturate at certain values of N part : in the n(p)+Au type collisions, the ratio becomes flat after N part > 3 while for the d+Au type collisions, the ratio becomes flat after N part > 5. Future experimented measurements on the ratio may help to pin down the possible difference. 4 Summary 1 Low-mass vector meson productions in p+p and d+Au collisions at <math id="M15"><mrow><msqrt><mrow><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt></mrow></math> = 200 GeV are studied within a multiphase transport model. 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C , 2015 , 92 : 044909 . doi: 10.1103/PhysRevC.92.044909 http://doi.org/10.1103/PhysRevC.92.044909 ϕ meson production in d+Au collisions at sNN=200GeV 10.1007/s41365-016-0093-7 This work was supported in part by the Major State Basic Researchsearch Development Program in China (No. 2014CB845401) and the National Natural Science Foundation of China (Nos. 11421505, 11520101004, 11275250 and 11322547) . 2016-03-31 2016-04-17 2016-04-21 2016-07-09 2016-08-20 2021-04-11 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2016 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-016-0093-7 http://dx.doi.org/10.1007/s41365-016-0093-7 . 2016 Nuclear Science and Techniques 04 27