Experimental Study Of Hypertriton In Relativistic Heavy Ion Collisions

Quantum chromodynamics is a gauge filed theory to describe strong interactions.QCD has two basic properties: Quark Confinement and Asymptotic freedom.According to the Lattice QCD,a new phase of matter,known as quark-gluon-plasma,could be created under condition of extremely high temperature and low baryon density.Large relativistic heavy ion colliders were built in order to search for this new form of matter.The Relativistic Heavy Ion Collider(RHIC)in Brookhaven National Laboratory(BNL)is located in the Long Island of New York.There are two experiments which are still in operation at RHIC: the STAR experiment and the PHENIX experiment.The STAR and PHENIX experiments have accumulated lots of experimental evidence to prove that a new form of matter with extremely high temperature,high density,and strong interaction has been created,which is called s QGP.Since strange quark and strange particles have been discovered in 1950 s,the HyperonNucleon(YN)interaction has become a new frontier of particle and nuclear physics.On one aspect,the research on YN interaction will help us to understand the Baryon-Baryon interaction.On another aspect,YN interaction is believed to be dominated in neutron stars,which makes it also important in cosmology.The Relativistic Heavy Ion Collider provides a good opportunity for the YN research especially for the study of hyper triton,the lightest hypernuclei,which is the most abundantly produced in collisions.Hypertriton has two main decay modes: the mesonic decay and non-mesonic decay.The total branching ratio of mesonic decay is larger than 98%.In this dissertation,we will focus on the two main decay channels,i.e.the two body and three body ? decay channels.The STAR minimum biased data with center-of-mass energyps and 200 Ge V collected in year 2010 and 2011 are used for the reconstruction of signals.We calculated the lifetime and ratio of branching ratios for after detector e ciency,acceptance and event number correction.Here the ratio is defined as B.R.(2-body)/B.R.(2-body plus 3-body).The lifetime result is ,and the ratio is .Traditional theory tells us a hypertriton is a weakly bounded state of a deutron and a?.Thus,the lifetime of would be close to that of a free ?,which is 263 ps.Some early experimental results are indeed close to free ? lifetime but mostly with large error bars.Since2000,with help of TPC technology,results from RHIC-STAR,LHC-Alice and GSI-Hyp HI,including the result from this dissertation,show results which are significantly smaller than lifetime of a free ?.This indicates our understanding of structure may need modification.The STAR zero degree calorimeter(ZDC)cannot be maintained in a proper status after its installation for over 10 years due to radiation.Considering that the ZDC modules on BRAHMS are idle since 2006,we planned to move those modules to STAR as replacements for the current STAR-ZDC modules.After calibration for the high voltage,the new modules have been installed at STAR since 2010.In this dissertation,we calculated the energy resolution of the ZDC modules and results show that for 200 Ge V Au+Au collisions,the energy resolutions for both sides are around 27%.This resolution is a little higher when compared to the test beam result in the very beginning,which is 20%.However,with a resolution of 27%,the ZDC modules are still in good status.The heavy flavor tracker(HFT)was fully installed in 2014 and started data collection since then.In order to include HFT hits information into High Level Trigger(HLT)system,we tested the reconstruction e ciency and CPU time consumption with HLT-HFT code.The result shows a good reconstruction e ciency if the primary vertex could be accurately determined,while the CPU time consumption is far from being accepted.