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

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

How to Make Sense of the Jet Correlations Results at RHIC?

We review the di-hadron correlation results from RHIC. A consistent physical picture was constructed based on the correlation landscape in $p_T$, $\Delta\phi$, $\Delta\eta$ and particle species. We show that the data are consistent with competition between fragmentation of survived jets and response of the medium to quenched jets. At intermediate $p_T$ where the medium response are important, a large fraction of trigger hadrons do not come from jet fragmentation. We argue that these hadrons can strongly influence the interpretation of the low $p_T$ correlation data. We demonstrate this point through a simple geometrical jet absorption model simulation. The model shows that the correlation between medium response hadrons dominates the pair yield and mimics the double hump structure of the away-side $\Delta\phi$ distribution at low $p_T$. This correlation was also shown to lead to complications in interpreting the results on reaction plane dependence and three particle correlations. Finally, we briefly discuss several experimental issues which are important for proper interpretations of the experimental data.Comment: 9 pages, 12 figures, proceedings for Hot Quarks in Estes Park, Colorad

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

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