Searching for the "Ridge" in d+Au collisions at RHIC by STAR

19 May 2014, 17:30
titanium (darmstadtium)



Schlossgraben 1 64283 Darmstadt Germany
Contributed Talk Initial State Physics Initial state physics


Li Yi


Long-range pseudo-rapidity ($\Delta\eta$) correlations at small azimuthal difference ($\Delta\phi$) are observed in high multiplicity p+p and p+Pb collisions at the LHC. Subtraction of the di-hadron correlation in low-multiplicity p+Pb collisions from high-multiplicity ones reveals a back-to-back double ridge structure ($\Delta\phi\approx 0$ and $\pi$). A similar double ridge is observed in high-multiplicity d+Au collisions by the PHENIX experiment in their limited acceptance. Differences between multiplicity-selected d+Au collisions (and p+p collisions) have been observed before by STAR. However, the question remains open whether the ridge in d+Au collisions is a jet-related difference between central and peripheral collisions, or a new physics phenomenon such as anisotropic flow in d+Au. STAR, with its large acceptance, can rigorously address this question. In this talk, we report di-hadron $\Delta\eta$-$\Delta\phi$ correlations in d+Au collisions at $\sqrt{s_{NN}} =$ 200 GeV. At mid-rapidity (with $|\Delta\eta|<2$), the jet-like correlation contribution in ``central$-$peripheral" method is evaluated. At large $|\Delta\eta|\approx 3$, the comparison of di-hadron correlations in central and peripheral collisions is reported in terms of the Au and deuteron beam directions. The $\Delta\phi$ correlation functions are also analyzed via a Fourier series decomposition; the $|\Delta\eta|$ and multiplicity dependencies of the Fourier coefficients are investigated. These di-hadron correlations data over the large acceptance may elucidate the existence or lack of a ridge in d+Au collisions at RHIC.
On behalf of collaboration: STAR

Primary author

Li Yi

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