Azimuthal anisotropy in a jet absorption model with fluctuating initial geometry in heavy ion collisions

The azimuthal anisotropy due to path-length dependent jet energy loss is studied in a simple jet absorption model that include event by event fluctuating Glauber geometry. Significant anisotropy coefficients v_n are observed for n=1,2 and 3, but they are very small for n>3. These coefficients are expected to result in a "ridge" for correlations between two independently produced jets. The correlations between the orientation of the n^{th}-order anisotropy induced by jet absorption (\Phi_n^{QP}) and the n^{th}-order participant plane (\Phi_n^{PP}) responsible for harmonic flow are studied. Tight correlations are observed for n=2 in mid-central collisions, but they weaken significantly for n\neq2. The correlations are positive for n>=3, but become negative in central collisions for n>3. The dispersion between \Phi_n^{QP} and \Phi_n^{PP} is expect to break the factorization of the Fourier coefficients from two-particle correlation v_{n,n} into the single particle v_n, and has important implications for the high-pT ridge phenomena.Comment: 5 pages, 5 figure

Measurement of the distributions of event-by-event flow harmonics in Pb-Pb Collisions at sqrt(s_nn)=2.76 TeV with the ATLAS detector

The event-by-event distributions of harmonic flow coefficients v_n for n=2-4 are measured in Pb-Pb collisions at sqrt(s_nn)=2.76 TeV with the ATLAS detector, using charged particles with p_T > 0.5 GeV and |\eta|<2.5. The shape of the v_n distributions is consistent with Gaussian fluctuations in central collisions for v_2 and over the measured centrality range for v_3 and v_4. When these distributions are rescaled to have the same , the resulting shapes are nearly the same for p_T>1 GeV and 0.5<p_T<1 GeV. The v_n distributions are compared with the eccentricity distributions from two initial geometry models: Glauber and the MC-KLN model. Both fail to describe the v_2 data consistently over the full centrality rangeComment: 4 pages, 5 figures, proceedings of talk at the 23rd International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, QM2012, August 13-18, 2012, Washington D

Long-range correlations in proton-lead collisions at sqrt{s_NN} = 5.02 TeV from ATLAS

Two-particle correlations in relative azimuth $\Delta\phi$ and relative pseudorapidity $\Delta\eta$ are studied in p+Pb collisions at sqrt{s_NN}=5.02 TeV with the ATLAS detector at LHC. The correlations are studied as a function of charged particle pT and the collision E_T^fcal summed over 3.1 < eta < 4.9 in the direction of the Pb beam. After subtracting the known sources of correlations such as dijets, resonances and momentum conservation, estimated using events with low E_T^fcal, the resulting correlations exhibit a $\Delta\phi$ modulation that is flat in $\Delta\eta$ out to $|\Delta\eta|=5$. The modulation is comparable in magnitude to similar modulations observed in heavy ion collisions, and can be described by a $1+2c_2\cos2\Delta\phi+2c_3\cos3\Delta\phi$ function over 0.5<pT<7 GeV in broad ranges of E_T^fcal. The correlation analysis is repeated for event classes defined by the number of reconstructed charged particles N_ch^rec. This analysis gives nearly the same result as the analysis based on E_T^fcal for the long-range correlation at the near-side ($\Delta\phi~0$), but leads to biases in the long-range correlations at the away-side ($\Delta\phi\sim\pi$). HIJING simulation suggests that this bias is mainly associated with the contributions from dijets which are correlated strongly with the N_ch^rec.Comment: Proceedings for the 29th Winter Workshop On Nuclear Dynamics, February 3-10, 2013, Squaw Valley, California, US

From mach cone to reappeared jet: What do we learn from PHENIX results on non-identified jet correlation?

High $p_T$ jets are known to be strongly modified by the dense, strongly interacting medium created in heavy-ion collisions. The jet signal, extracted from two particle $\Delta\phi$ correlation, shows a systematic evolution of these modifications as function of $p_T$ and centrality. At intermediate $p_T$, both near side and away side correlations are modified. But the modifications are much stronger at the away side, resulting in a characteristic cone type of structure in central Au + Au collisions. The robustness of cone structure is strengthened by studying the jet shape as function of angle relative to the reaction plane. As one increase the $p_T$ for BOTH hadrons, the cone structure seems to be filled up, and a peak structure appears on the away side. However, the interpretation of these results require careful separation of medium effect and surface bias.Comment: 8 pages, 9 figures. Proceedings for "XXXV International Symposium on Multiparticle Dynamics 2005", replace the figures and fixes some typoe

Forward-backward multiplicity correlations in pp, pPb and Pb+Pb collisions with the ATLAS detector

Two-particle pseudorapidity correlations are measured in 2.76 TeV Pb+Pb, 5.02 TeV pPb and 13 TeV pp collisions. Correlation function is measured using charged particles in the pseudorapidity range $|\eta|<2.4$ with transverse momentum $p_T>0.2$ GeV, and it is measured as a function of event multiplicity, defined by number of charged particles with $|\eta|0.4$ GeV. The correlation function is decomposed into a short-range component (SRC) and a long-range component (LRC). The SRC differs significantly between the opposite-charge pairs and same-charge pairs, and between the three collision systems at similar multiplicity. The LRC is described approximately by $1+\langle a_1^2\rangle\eta_1\eta_2$ in all collision systems over the full multiplicity range. The values of $\langle a_1^2\rangle$ are consistent between the opposite-charge and same-charge pairs, and are similar for the three collision systems at similar multiplicity. The values of $\langle a_1^2\rangle$ and the magnitude of the SRC both follow a power-law dependence on the event multiplicity.Comment: 4 pages, 4 figures, to appear in the proceedings for the Quark Matter 2015 conference, Kobe, Japa