Effect Of Magnetic Fields On Pairs Of Oppositely Charged Particles In Ultrarelativistic Heavy-ion Collisions

A ultra-strong magnetic field will be generated during the ultra-relativistic heavy ion collision.The magnitude of this magnetic field is approximately 1015T by theo-retically calculation.But it is difficult to measure such huge magnetic field since the existence of the magnetic filed is very short and it attenuate to 0 very quickly.Several probes of the magnetic field have been proposed,such as the anisotropic charmonium production,the separation in the global polarization between ∧ and ∧,the directed flow of charm quarks,and recently,the pT broadening of e+e-spectra.The magnetic has not been directly detected in experiment.So,through our deep research,we inspect the imprint left by the magnetic field on pairs of particles with opposite chargesThe charged particles are deflected by the magnetic field under the action of the Lorentz force in the relativistic heavy ions collision.The deflection direction is oppo-site for opposite charged particles.So we propose the observation △α,which is the projection of the angle between the positive and negative particle motion directions in the reaction plane,as a probe for detecting extremely strong magnetic fields.Without a magnetic field,the △α distribution is symmetric with respect to △α= π,since the probability has to be the same when the two decay daughters are swapped.After turn-ing on the magnetic field,△α will decrease,then the △α distribution symmetry will be broken.So,the asymmetry can be extracted to measure the magnetic field.Polar-ization and Balance function methods are proposed to quantify this asymmetry.The polarization method is to measure the polarization of s r.w.t reaction plane,where the s is defined to be s≡e+×e-/|sinζ|.For the balance function method,we slightly modify the bal-ance function,and then define BP(△α)and BN(△α),then we introduce the Skewness to measure the asymmetry of BP(△α)and BN(△α).In order to present the sensitivity of our methods dependent on the magnetic field,we compare the sensitivity from our methods with the pT broadening method.It show us our methods proposed are more sensitive.Strong interaction is described by quantum chromodynamics(QCD).QCD has two basic properties:Color confinement and Asymptotic freedom.According to the Lat-tice QCD calculation,a new phase of matter,know as quark-gluon-plasma(QGP),could be created under extremely high temperature and large baryon density.In order to in?vestigate the properties of this new matter,scientists build the Large relativistic heavy ion colliders(RHIC)and the detecter system of STAR.It helps scientists to learn much knowledge to QGP in experiment.In theory,the AMPT model is introduced to de-scribed the dynamic evoluton of heavy ion collision.We adopt the AMPT model,using the φ meson as a probe,introducing a nuclear modification factor,and comparing the collision systems with different energies and symmetry.We observe that the evolution from cold nuclear matter effect to hot nuclear matter effect when the size of system becomes larger.We discuss the STAR high level trigger system(HLT)in experiment.During the increase of the luminosity of RHIC and the limit of data acquisition capability,we de-velop the STAR HLT.HLT is contrast to low level trigger system.It contains large threshold value of trigger time,so HLT can get the information from TPC,TOF and MTD which is very important for track reconstruction.These information can help us to select the events for proper physical analysis.It obviously improves the efficiency of our physical analysis.In the process of track reconstruction,due to the existence of space charge and grid leakage effect,we discuss the correction method to space charge and grid leakage.