PDF《Hidden-charm Pentaquark States in》

arXiv:1601.

02835v1 [hep-ph]

12 Jan

2016 Hidden-charm Pentaquark States in Heavy Ion Collisions at the Large Hadron Collider Rui-Qin Wang,1,2 Jun Song,3 Kai-Jia Sun,2 Lie-Wen Chen,2 Gang Li,1 and Feng-Lan Shao1, ?

1 College of Physics and Engineering, Qufu Normal University, Shandong 273165, China

2 Department of Physics and Astronomy and Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University, Shanghai 200240, China

3 Department of Physics, Jining University, Shandong 273155, China In the framework of the quark combination, we derive the yield formulas and study the yield ratios of the hidden-charm pentaquark states in ultra-relativistic heavy ion collisions. We propose some interesting yield ratios which clearly exhibit the production relationships between di?erent hidden-charm pentaquark states. We show how to employ a speci?c quark combination model to evaluate the yields of exotic P+ c (4380), P+ c (4450) and their partners on the basis of reproducing the yields of normal identi?ed hadrons, and execute the calculations in central Pb+Pb collisions at √ sNN = 2.76 TeV as an example. PACS numbers: 25.75.Dw, 25.75.Nq, 25.75.-q I. INTRODUCTION The LHCb Collaboration at the Large Hadron Collider (LHC) has recently announced two exotic resonances P+ c (4380) and P+ c (4450), consistent with pentaquark states, via the J/ψp invariant mass spectrum in Λ0 b decays in p+p reactions [1]. Thereupon, the study for the internal con?gurations of such resonances becomes a subject of an intensive discussion in literatures. The so-far suggested interpretations for P+ c (4380) and P+ c (4450) include molecular states bound of a charmed baryon and an anticharmed meson [2, 3], molecular states with J/ψ and an excited nucleon [4], composites containing colored baryonlike and mesonlike constituents [5], pentaquark states with one heavy-light diquark, one light-light diquark and a charm antiquark [6C8], pentaquark states with color-antitriplet diquark cu and color-triplet ? cud [9, 10], and so on. There are also some works about needing further con?rmation of whether such resonance is just a kinematical e?ect or a real exotic resonance by analyzing other processes, such as Λ0 b → K? χc1 p [11C14]. Further exploring for the intrinsic dynamical nature of such exotic resonances and searching for their partners are necessary for understanding some longstanding questions in hadronic physics, which requires more theoretical and experimental e?orts. Heavy ion collisions with ultra-relativistic collision energies, especially those at the LHC, provide preferable conditions for the creation of particles in heavy ?avor sectors. The studies of heavy ?avor exotic resonances in heavy ion collisions not only are complementary to those in the LHCb experiments, but also o?er unique insights into some of the fundamental questions in hadronic physics [15, 16]. As is well known, the Quark Combination Mechanism (QCM) is an e?ective phenomenological method to deal with the hadronization of the partonic system produced early in high energy heavy ion collisions. It has shown successes in reproducing multiplicities, yield ratios, momentum distributions, elliptic ?ows, etc., of normal identi?ed light, strange and heavy ?avor hadrons [17C23], and has also many applications in describing the production properties of exotic resonances [15, 16, 24C27]. Due to the produced bulk decon?ned ?reball and the hadronization through the quark combination in high energy heavy ion collisions, various kinds of exotic hadrons can be formed. The purpose of this paper is to investigate the yield ratios and estimate the yields of various hidden-charm pentaquark states with di?erent valence quark ingredients and di?erent intrinsic quantum numbers in the framework of the QCM in ultra-relativistic heavy ion collisions at the LHC. This can provide useful references for the exotic hadron search in future experiments and is helpful for understanding the production mechanism of the exotic resonances in heavy ion collisions. The rest of the paper is organized as follows. In Sec. II, we derive the yield formulas and study the yield ratios of hidden- charm pentaquark states from the basic ideas of the QCM. During the derivation, a few assumptions, approximations and/or simpli?cations are used and they are all clearly presented. In Sec. III, we show how to employ a speci?c quark combination model to estimate the yields of di?erent hidden-charm pentaquark states, and give the estimated results in central Pb+Pb collisions at √ sNN = 2.76 TeV as an example. Sec. IV summaries our work. ?Electronic address: shao?@mail.sdu.edu.cn