Time:Thursday, Jan. 15, 2015, 10:30 AM (Beijing time)

Location： Room9409

Speaker： Li Yi (易立),Purdue University

Title: Long-range pseudo-rapidity dihadron correlations measurement in d+Au

Abstract:

A long-range (large |\Delta\eta|) two-particle azimuthal (\Delta\phi) correlation (?idge? was observed in high-multiplicity p+p and p+Pb collisions at the LHC. Subtraction of two-particle correlations in high- and low-multiplicity events reveals a back-to-back double ridge (\Delta\phi=0 or \pi). A similar double ridge was observed in d+Au collisions with the same technique by the PHENIX experiment at RHIC. This talk reports results of the ridge in d+Au collisions with the STAR detector at RHIC. Dihadron correlations are analyzed in 200 GeV d+Au collisions classified by forward charged particle multiplicity and zero-degree neutral energy in the Au-beam direction. It is found that the jetlike correlated yield increases with the event multiplicity. After taking into account this dependence, the non-jet contribution on the away side is minimal. The long-range near-side ridge is observed on the Au-going side for high-multiplicity events. With the STAR detector's large acceptance, the near-side (\Delta\phi=0) ridge correlated yield \Delta\eta and multiplicity dependences are studied. In a Fourier decomposition of the dihadron correlations, the second Fourier coefficients are observed to be the same for low- and high-multiplicity, d- and Au-going side, despite the large multiplicity difference and near-side ridge appearance difference. This near-side ridge yield difference is found to be due to the large negative first Fourier coefficients in the low-multiplicity and d-going side. We will discuss the implications of the STAR data on the theoretical explanations for the ridge mechanism in d+Au collisions.