Energy Heavy Ion Collision Experiments Research Articles

Present and future of QGP research in high energy heavy ion collision experiments

from p-p and p-Pb collisions at LHC at different centre of mass energies have been used as references to the results from Pb-Pb collisions. These results are further compared with detailed and elaborate measurements performed with Au-Au collisions at p sNN = 200 GeV at RHIC. The basic properties of the matter created at LHC have been found to be similar to that at RHIC, e.g., the matter in Pb-Pb collisions at LHC also behaves like a strongly coupled partonic liquid as inferred for the Au-Au collisions at top RHIC energy. However, with higher collision energy at LHC, a new set of probes in heavy ion collisions like jets and higher states of quarkonia open up new avenues in detailed understanding of the properties of the matter. Recent findings of the collective behaviour at p-Pb collisions at LHC however questions the existing theoretical understanding of the medium formation in p-Pb and Pb-Pb collisions. RHIC and LHC explore the high temperature and nearly zero net-baryon density region of the phase diagram, another extremes are being explored at the beam energy scan (BES) programme at RHIC and the upcoming CBM experiment at FAIR. The BES-I results demonstrate that at lower p sNN , several findings that were interpreted as the signatures of the formation of de-confined partonic matter at top RHIC energy were found to be absent. The interpretation of these results require thorough understanding of the role of baryons in the matter created at lower p sNN . The CBM experiment at FAIR aims to explore the matter created at low collision energy by the use of bulk and rare probes.

Design and performance simulation of a segmented-absorber based muon detection system for high energy heavy ion collision experiments

A muon detection system (MUCH) based on a novel concept using a segmented and instrumented absorber has been designed for high-energy heavy-ion collision experiments. The system consists of 6 hadron absorber blocks and 6 tracking detector triplets. Behind each absorber block a detector triplet is located which measures the tracks of charged particles traversing the absorber. The performance of such a system has been simulated for the CBM experiment at FAIR (Germany) that is scheduled to start taking data in heavy ion collisions in the beam energy range of 6–45AGeV from 2019. The muon detection system is mounted downstream to a Silicon Tracking System (STS) that is located in a large aperture dipole magnet which provides momentum information of the charged particle tracks. The reconstructed tracks from the STS are to be matched to the hits measured by the muon detector triplets behind the absorber segments. This method allows the identification of muon tracks over a broad range of momenta including tracks of soft muons which do not pass through all the absorber layers. Pairs of oppositely charged muons identified by MUCH could therefore be combined to measure the invariant masses in a wide range starting from low mass vector mesons (LMVM) up to charmonia. The properties of the absorber (material, thickness, position) and of the tracking chambers (granularity, geometry) have been varied in simulations of heavy-ion collision events generated with the UrQMD generator and propagated through the setup using the GEANT3, the particle transport code. The tracks are reconstructed by a Cellular Automaton algorithm followed by a Kalman Filter. The simulations demonstrate that low mass vector mesons and charmonia can be clearly identified in central Au+Au collisions at beam energies provided by the international Facility for Antiproton and Ion Research (FAIR).

Collective expansion and hadronization in high energy heavy ion collision experiments**Supported by Ministry of Education of China (306022) and National Natural Science Foundation of China (10635020)

An overview of research status of soft physics in high energy heavy-ion collision experiments and recent experimental results are presented.

Correlations and fluctuations in high energy heavy ion collision experiments**Supported by Ministry of Education of China (306022) and National Natural Science Foundation of China (10635020,10705012)

An overview of research status of soft physics in high energy heavy-ion collision experiments and recent experimental results are presented. The experimental status on fluctuations and correlations has been reviewed and the outlook for research status of soft physics in LHC/ALICE has been introduced in this paper.

Collision geometry and particle production in high energy heavy ion collision experiments**Supported by Ministry of Education of China (306022) and National Natural Science Foundation of China (10635020)

An overview of research status of soft physics in high energy heavy-ion collision experiments and recent experimental results are presented. This paper includes four parts: 1) Theoretical predictions of quarkgluon plasma and introduction for high energy heavy ion collision experiments. 2) Experimental status on collision geometry. 3) Experimental status on particle production. 4) Conclusion and outlook for research status of soft physics in LHC/ALICE.

Development of a time projection chamber using gas electron multipliers (GEM–TPC)

We developed a prototype time projection chamber using gas electron multipliers (GEM–TPC) for high energy heavy ion collision experiments. To investigate its performance, we conducted a beam test with three kinds of gases (Ar(90%)–CH 4(10%), Ar(70%)–C 2H 6(30%) and CF 4). Detection efficiency of 99%, and spatial resolution of 79 μ m in the pad-row direction and 313 μ m in the drift direction were achieved. The test results show that the GEM–TPC meets the requirements for high energy heavy ion collision experiments. The configuration and performance of the GEM–TPC are described.

Effective Photon Mass in Nuclear Matter and Finite Nuclei

Electromagnetic field in nuclear matter and nuclei are studied. In the nuclear matter, because the expectation value of the electric charge density operator is not zero, different in vacuum, the U(1) local gauge symmetry of electric charge is spontaneously broken, and consequently, the photon gains an effective mass through the Higgs mechanism. An alternative way to study the effective mass of photon is to calculate the self-energy of photon perturbatively. It shows that the effective mass of photon is about 5.42 MeV in the symmetric nuclear matter at the saturation density ρ0 = 0.16 fm -3 and about 2.0 MeV at the surface of 238U. It seems that the two-body decay of a massive photon causes the sharp lines of electron–positron pairs in the low energy heavy ion collision experiments of 238 U + 232 Th .