Physics performance of the STAR zero degree calorimeter at relativistic heavy ion collider

The zero degree calorimeter(ZDC) at RHICSTAR was installed in the year 2000.After running for more than 10 years,the performance of the STAR-ZDC cannot maintain a proper status because of the radiation damage.The ZDC on RHIC-BRAHMS had been moved to STAR in 2011 after some tests.We present here the result of the tests as well as the physical performance of those ZDC modules between the 2011 and 2015 RHIC runs.The excellent energy resolution of the ZDC in heavy ion collision provides a good candidate for future detector development,such as the CSR experiment at CAS-Lanzhou facility.

Yield ratio of hypertriton to light nuclei in heavy-ion collisions from √sNN=4.9 GeV to 2.76 TeV

We argue that the difference in the yield ratio S3=NΛ3H/NΛ/N3He/Np measured in Au+Au collisions at √sNN=200 GeV and in Pb-Pb collisions at √sNN=2.76 TeV is mainly owing to the different treatment of the weak decay contribution to the proton yield in the Au+Au collisions at √sNN=200 GeV.We then use the coalescence model to extract from measured S3 the information about the Λ and nucleon density fluctuations at the kinetic freeze-out of heavy-ion collisions.We also show,using available experimental data,that the yield ratio S2=NΛ3H/NΛNd is a more promising observable than S3 for probing the local baryon-strangeness correlation in the produced medium.

Alternative methods for measurement of the global polarization of Λhyperons

We propose alternative methods for measurement of the global polarization of Λ hyperons. These methods involve event averages of proton and Λ momenta in the laboratory frame. We carry out simulations using these methods and show that all of them work equally well in obtaining the global polarization of Λ hyperons.

Photoproduction of J/ψ in non-single-diffractive p+p collisions

Significant enhancements of J/ψ production at very low transverse momenta were recently observed by the ALICE and STAR collaborations in peripheral hadronic A+A collisions. The anomalous excess points to coherent photon-nucleus interactions in violent hadronic heavy-ion collisions, which were conventionally studied only in ultra-peripheral collisions. Assuming that the coherent photoproduction is the underlying mechanism responsible for the excess observed in peripheral A+A collisions, its contribution in p+p collisions with nuclear overlap, i.e. nonsingle-diffractive collisions, is of particular interest. In this paper, we perform a calculation of exclusive J/ψ photoproduction in non-single-diffractive p+p collisions at the RHIC and LHC energies based on the pQCD motivated parametrization using the world-wide experimental data, which could be further employed to improve the precision of the phenomenological calculations for photoproduction in A+A collisions. The differential rapidity and transverse momentum distributions of J/ψ from photoproduction are presented. In comparison with the J/ψ production from hadronic interactions, we find that the contribution of photoproduction is negligible.