Low-momentum direct photon measurement in Cu++Cu collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV

International audienceWe measured direct photons for pT<5GeV/c in minimum bias and 0%–40% most-central events at midrapidity for Cu+Cu collisions at sNN=200GeV. The e+e− contribution from quasireal direct virtual photons has been determined as an excess over the known hadronic contributions in the e+e− mass distribution. A clear enhancement of photons over the binary scaled p+p fit is observed for pT<4GeV/c in Cu+Cu data. The pT spectra are consistent with the Au+Au data covering a similar number of participants. The inverse slopes of the exponential fits to the excess after subtraction of the p+p baseline are 285±53(stat)±57(syst)MeV/c and 333±72(stat)±45(syst)MeV/c for minimum bias and 0%–40% most-central events, respectively. The rapidity density, dN/dy, of photons demonstrates the same power law as a function of dNch/dη observed in Au+Au at the same collision energy

Measurement of emission angle anisotropy via long-range angular correlations with high pTp_T hadrons in d+d+Au and p+pp+p collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV

International audienceWe present measurements of two-particle angular correlations between high-transverse-momentum (2<pT<11 GeV/c) π0 observed at midrapidity (|η|<0.35) and particles produced either at forward (3.1<η<3.9) or backward (−3.7<η<−3.1) rapidity in d+Au and p+p collisions at sNN=200 GeV. The azimuthal angle correlations for particle pairs with this large rapidity gap in the Au-going direction exhibit a characteristic structure that persists up to pT≈6 GeV/c and which strongly depends on collision centrality, which is a similar characteristic to the hydrodynamical particle flow in A+A collisions. The structure is absent in the d-going direction as well as in p+p collisions, in the transverse-momentum range studied. The results indicate that the structure is shifted in the Au-going direction toward more central collisions, similar to the charged-particle pseudorapidity distributions