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Jiangyong Jia

Publications and source records attributed to Jiangyong Jia.

At least 91 records · Page 5Linked to original sources

Study on initial geometry fluctuations via participant plane correlations in heavy ion collisions: part II

Further investigation of the participant plane correlations within a Glauber model framework is presented, focusing on correlations between three or four participant planes of different order. A strong correlation is observed for $\cos(2Φ_{2}^*+3Φ_{3}^*-5Φ_{5}^*)$ which is a reflection of the elliptic shape of the overlap region. The correlation between the corresponding experimental reaction plane angles can be easily measured. Strong correlations of similar geometric origin are also observed for $\cos(2Φ_{2}^*+4Φ_{4}^*-6Φ_{6}^*)$, $\cos(2Φ_2^*-3Φ_3^*-4Φ_4^*+5Φ_5^*)$, $\cos(6Φ_2^*+3Φ_3^*-4Φ_4^*-5Φ_5^*)$, $\cos(Φ_1^*-2Φ_2^*-3Φ_3^*+4Φ_4^*)$, $\cos(Φ_1^*+6Φ_2^*-3Φ_3^*-4Φ_4^*)$, and $\cos(Φ_1^*+2Φ_2^*+3Φ_3^*-6Φ_6^*)$, which are also measurable. Experimental measurements of the corresponding reaction plane correlators in heavy ion collisions at RHIC and the LHC may improve our understanding of the physics underlying the measured higher order flow harmonics.

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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 (Φ_n^{QP}) and the n^{th}-order participant plane (Φ_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 Φ_n^{QP} and Φ_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.

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Measurement of elliptic and higher order flow from ATLAS experiment at the LHC

We present a differential measurement of the azimuthal anisotropy of charged hadron production in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$=2.76 TeV. This azimuthal anisotropy is expanded into a Fourier series in azimuthal angle, where the coefficient for each term, $v_n$, characterizes the magnitude of the anisotropy at a particular angular scale. We extract $v_2-v_6$ via a discrete Fourier analysis of the two-particle $Δϕ-Δη$ correlation with a large $Δη$ gap ($|Δη|>2$), and via an event plane method based on the Forward Calorimeter. Significant $v_2-v_6$ values are observed over a broad range in $\pT$, $η$ and centrality, and they are found to be consistent between the two methods in the transverse momentum region $\pT<3-4$ GeV. This suggests that the measured $v_2-v_6$ obtained from two-particle correlations at low $\pT$ with a large $Δη$ gap are consistent with the collective response of the system to the initial state geometry fluctuations, and is not the result of jet fragmentation or resonance decay.

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A study of the correlations between jet quenching observables at RHIC

Focusing on four types of correlation plots, $R_{\rm AA}$ vs. $v_2$, $R_{\rm AA}$ vs. $I_{\rm AA}$, $I_{\rm AA}$ vs. $v_2^{I_{\rm AA}}$ and $v_2$ vs.\ $v_2^{I_{\rm AA}}$, we demonstrate how the centrality dependence of \emph{correlations} between multiple jet quenching observables provide valuable insight into the energy loss mechanism in a quark-gluon plasma. In particular we find that a qualitative energy loss model gives a good description of $R_{\rm AA}$ vs.\ $v_2$ only when we take $ΔE\sim l^3$ and a medium geometry generated by a model of the Color Glass Condensate. This same $ΔE\sim l^3$ model also qualitatively describes the trigger $p_T$ dependence of $R_{\rm AA}$ vs.\ $I_{\rm AA}$ data and makes novel predictions for the centrality dependence for this $R_{\rm AA}$ vs.\ $I_{\rm AA}$ correlation. Current data suggests, albeit with extremely large uncertainty, that $v_2^{I_{\rm AA}}\gg v_2$, a correlation that is difficult to reproduce in current energy loss models.

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Zeroing in on jet quenching: a PHENIX perspective

We review recent progresses on jet quenching measurements by PHENIX. With increased statistics, PHENIX has gone beyond the single hadron suppression $R_{\rm AA}$, and made measurements on multiple jet quenching observables, such as $v_2$, $I_{\rm AA}$ and $v_2^{I_{\rm AA}}$. We argue that, by combining these observables together, one can achieve a better understanding of the energy loss mechanism. We present new $γ$-hadron correlation results with associated hadrons extended to low $p_T$; an enhancement has been observed, suggesting a contribution of genuine medium response that is relatively unbiased by the initial geometry fluctuations. The status of full jet reconstruction and future perspective of PHENIX jet quenching program are discussed.

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Dissecting the role of initial collision geometry for jet quenching observables in relativistic heavy ion collisions

The observation of large azimuthal anisotropy or $v_2$ for hadrons above $p_T>5$ GeV/$c$ in Au+Au collisions at $\sqrt{s_{\rm nn}}=200$ GeV has been a longstanding challenge for jet quenching models based on perturbative QCD (pQCD). Using a simple jet absorption model, we seek to clarify the situation by exploring in detail how the calculated $v_2$ varies with choices of the collision geometry as well as choices of the path length dependence and thermalization time $τ_0$ in the energy loss formula. Besides the change of eccentricity due to distortion from gluon saturation or event-by-event fluctuation, we find that the $v_2$ is also sensitive to the centrality dependence of multiplicity and the relative size between the matter profile and the jet profile. We find that the $v_2$ calculated for the naive quadratic path length dependence of energy loss, even including eccentricity fluctuation and the gluon saturation, is not enough to describe the experimental data at high $p_T$ ($\sim$ 6 GeV/$c$) in Au+Au collisions. However, it can match the full centrality dependence of $v_2$ data if higher power path length dependence of energy loss is allowed. We also find that the calculated $v_2$ is sensitive to the assumption of the early time dynamics but generally increases with $τ_0$, opposite to what one expects for elliptic flow. This study attests to the importance of confining the initial geometry, possibly by combining jet quenching $v_2$ with elliptic flow and other jet quenching observables, for proper interpretation of the experimental data.

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Influence of the nucleon-nucleon collision geometry on the determination of the nuclear modification factor for nucleon-nucleus and nucleus-nucleus collisions

The influence of the underlying nucleon-nucleon collision geometry on evaluations of the nuclear overlap function ($T_{AB}$) and number of binary collisions ($N_{coll}$) is studied. A narrowing of the spatial distribution of the hard-partons with large light-cone fraction $x$ in nucleons leads to a downward correction for $N_{coll}$ and $T_{AB}$, which in turn, results in an upward correction for the nuclear modification factor $R_{AB}$. The size of this correction is estimated for several experimentally motivated nucleon-nucleon overlap functions for hard-partons. It is found to be significant in peripheral nucleus-nucleus and nucleon-nucleus collisions, and are much larger at the LHC energy of $\sqrt{s}=5.5$ TeV than for the RHIC energy of $\sqrt{s}$=200 GeV. The implications for experimental measurements are also discussed.

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Away-side asymmetry of jet correlation relative to reaction plane: a sensitive probe for jet in-medium modifications

We proposed a new observable based on two particle azimuth correlation to study the away-side medium response in mid-central Au+Au collisions. We argue that a left/right asymmetry may appear at the away-side by selecting triggers separately in the left and right side of the reaction plane. A simple model estimation suggests that the magnitude of such asymmetry could reach 30% with details depends on the medium response mechanisms. This asymmetry, if observed, can help to distinguish competing theoretical models.

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Understanding the Role of Jet and Underlying Event in p+p and d+Au Collisions from PHENIX at RHIC

Dihadron azimuthal correlation measurements have revealed striking modifications of the jets by the dense medium created in heavy-ion collisions at RHIC. One important question is to what extent the modification can be attributed to cold nuclear matter effects. In this analysis, we carried out a detailed mapping of the correlation patterns using high-statistics RUN8 d+Au minimum bias data. A striking scaling behavior of the jet pair yields is observed at low and intermediate $p_T$. The jet pair yields are found to be enhanced relative to $N_{\rm coll}$ scaled p+p jet pair yields. The nuclear modification factor for jet pair yields, $J_{\rm dAu}$, seems to scale with $p_T^{\rm sum}$= $p_T^a+p_T^b$ (scaler sum), and shows a characteristic Cronin-like enhancement at $p_T^{\rm sum}<$5-7GeV/c. Interestingly, the level of yield modifications is similar between the near- and away-side pairs, and the jet shapes are not modified relative to p+p collisions. The pedestal yield under the jet peak is studied in p+p and d+Au collisions. The pedestal yield in p+p collisions is found to be larger than PYTHIA calculations. In d+Au collisions, it is found to exceed a simple sum of one p+p jet event and $\rm N_{coll}-1$ minimum bias p+p events. The possible interpretation of these results and their implications for Au+Au measurements are discussed.

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Influence of quenched jets on di-hadron correlations

A simple jet absorption model is used to study the influence of hadron pairs produced by quenched jets, on di-hadron angular correlations at intermediate transverse momentum ($p_T$). We demonstrate that such pairs can dominate both the yield and the shape of angular correlations, and may account for the similar properties between the near-side "ridge" and the away-side "double-humped" structure seen in recent data. These hadron pairs also show azimuthal anisotropy which is sensitive to the emission angle of hadrons relative to that of the jet. Measurement of this anisotropy may provide a constraint for elucidating the production mechanism for near- and away-side hadron pairs at intermediate $p_T$.

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Hard Probes of the ATLAS Heavy Ion Physics Program

We review the physics performance of the ATLAS detector for hard probes in heavy ion collisions, focusing on three topics: jet reconstruction, direct photon measurement, and heavy flavor jet tagging.

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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 $p_T$, $Δϕ$, $Δη$ 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 $Δϕ$ 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.

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Understanding jet quenching and medium response with di-hadron correlation

A brief review of the $p_T$ dependence of the dihadron correlations from RHIC is presented. We attempt to construct a consistent picture that can describe the data as a whole, focusing on the following important aspects, 1) the relation between jet fragmentation of survived jet and medium response to quenched jets, 2) the possible origin of the medium response and its relation to intermediate $p_T$ physics for single hadron production, 3) the connection between the near-side ridge and away-side cone, 4) and their relations to low energy results.

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Probe the QGP via dihadron correlations: Jet quenching and Medium-response

We summarize the di-hadron correlation results from RHIC, focusing on the high $p_T$ region and lower $p_T$ region for the away-side. The former is consistent with fragmentation of jets that surviving the medium, while the latter suggests the redistribution of the energy from the quenched jets. We also discuss the role of the jet in the intermediate $p_T$.

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Mapping out the Jet correlation landscape: Jet quenching and Medium response

A selected set of di-hadron correlation results from PHENIX are discussed. These results provide evidences for four distinct contributions concentrated at various $Δϕ$ ranges. The $p_T$, particle species and energy dependence of these contributions reflect detailed interplay between jet quenching and response of the partonic matter to the lost energy.

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$π^0$-h correlation in Cu+Cu at $\sqrt{s_{NN}}$=200 GeV

We present the results of the two-particle $Δϕ$ correlation between high $p_T$ $π^0$ and charged hadrons in Cu+Cu collisions at $\sqrt{s_{NN}} = 200$ GeV. Clear away-side jet signals are seen in central Cu+Cu collisions at all associated hadron $p_T$, albeit suppressed by factor of 2 above 2 GeV/$c$. This level is similar to the suppression seen for inclusive hadrons at high $p_T$ ($>7$ GeV/$c$). However, this agreement is argued to be the result of a cancellation between a flatter away-side parton spectra due to the requirement of high $p_T$ triggers and a bigger energy loss due to a longer path length traversed by the away-side jet.

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Mapping out the jet correlation landscape: a perspective from PHENIX experiment

This is a status report on where PHENIX stands in terms of mapping out the landscape of jet correlation in $p_T$, hadron species, $\sqrt{s}$. We discuss separately high $p_T$ correlation results and low and intermediate $p_T$ correlation results. The former is sensitive to the quenching of the jet by medium, the later allows detailed study of the medium response to the (di-)jet.

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Quark number scaling of $v_2$ in transverse kinetic energy and it's implications for coalescence models

We find that a simple extension of the coalescence model is sufficient to incorporate the perfect quark number scaling behavior of the elliptic flow in transverse kinetic energy, recently discovered by the PHENIX Collaboration. The flavor dependence of the elliptic flow can be consistently described in the low and intermediate $p_T$ if the transverse kinetic energy is conserved in the $2\to1$ or $3\to1$ parton coalescence process at the hadronization. Thus suggesting the quark coalescence as a possible hadronization mechanism at low $p_T$ as well.

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