Elliptic Flow Signal Research Articles

Elliptic flow in Pb+Pb Collision at (s_NN )=5.02 TeV

Elliptic flow signal, v_2, is widely studied in heavy ion collisions. Researches have been done to obtain the pseudorapidity dependence of v_2, while the measurement of transverse momentum dependence is relatively few. This paper presents the transverse momentum dependence of v_2 in Pb+Pb collision at(s_NN )=5.02 TeV. The measurement is performed in the region with pseudorapidity ||<2.8 and transverse momentum 0.2 < p_T<6.0GeV. In this work, we use sub-event method to measure elliptic flow for the collisions in different ranges of transverse momentum. The result shows a polynomial relation between elliptic flow signal and transverse momentum. In Section 4, the limitation of our measurement is also discussed.

Recent heavy-flavour results from ATLAS

The ATLAS heavy-ion program utilizes heavy-flavour hadrons to probe the hot, dense matter formed at the LHC. Quarkonium measurements have been performed in pp, p+Pb and Pb+Pb systems to study medium effects. The Pb+Pb results show a strong suppression of charmonium productions in more central events. Proton-lead interactions show little modification of the 1S charmonium state, but seem to indicate a centrality dependence of the 2S state. Upsilons have been studied in p+Pb and are found to show decreasing behaviour in more central collisions. Inclusive muons with pT above 4 GeV have been studied to provide insight on open-flavour production, and are found to be strongly suppressed in Pb+Pb collisions with a substantial and significant elliptic flow signal. Muon-hadron correlations have also been studied in the 2016 [see formula in PDF] = 8.16 TeV p+Pb data. There are clear indications of a near-side ridge, suggesting that similar mechanisms may be relevant for both the small and large systems.

Elliptic Flow of Charged Particles in Pb-Pb Collisions atsNN=2.76 TeV

We report the first measurement of charged particle elliptic flow in Pb-Pb collisions at sqrt[S(NN)] =2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurement is performed in the central pseudorapidity region (|η|<0.8) and transverse momentum range 0.2<p t<5.0 GeV/c. The elliptic flow signal v₂, measured using the 4-particle correlation method, averaged over transverse momentum and pseudorapidity is 0.087 ± 0.002(stat) ± 0.003(syst) in the 40%-50% centrality class. The differential elliptic flow v₂ p t reaches a maximum of 0.2 near p t =3 GeV/c. Compared to RHIC Au-Au collisions at sqrt[S(NN)] 200 GeV, the elliptic flow increases by about 30%. Some hydrodynamic model predictions which include viscous corrections are in agreement with the observed increase.

Eccentricity Fluctuations Make Flow Measurable in High Multiplicityp−pCollisions

Elliptic flow is a hallmark of collectivity in hadronic collisions. Its measurement relies on analysis techniques which require high event multiplicity and so far can only be applied to heavy ion collisions. Here, we delineate the conditions under which elliptic flow becomes measurable in the samples of high-multiplicity (dN(ch)/dy > or = 50) p-p collisions, which will soon be collected at the LHC. We observe that fluctuations in the p-p interaction region can result in a sizable spatial eccentricity even for the most central p-p collisions. Under relatively mild assumptions on the nature of such fluctuations and on the eccentricity scaling of elliptic flow, we find that the resulting elliptic flow signal in high-multiplicity p-p collisions at the LHC becomes measurable with standard techniques.

Elliptic flow in Au+Au collisions at [formula omitted] GeV

We report the elliptic flow of charged and identified particles at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{NN}}}=130$ GeV using the STAR TPC at RHIC. The integrated elliptic flow signal, $v_2$, for charged particles reaches values of about 0.06, indicating a higher degree of thermalization than at lower energies. The differential elliptic flow signal, $v_2$($p_t$) up to 1.5 GeV/$c$, shows a behavior expected from hydrodynamic model calculations. Above 1.5 GeV/$c$, the data deviate from the hydro predictions; however the $v_2$($p_t$) is still large, suggesting finite asymmetry for the products of hard scattering. For the identified particles, elliptic flow as a function of $p_t$ and centrality differ significantly for particles of different masses. This dependence can be accounted for in hydrodynamic models, indicating that the system created shows a behavior consistent with collective hydrodynamical flow.

Results from the PHOBOS Experiment at RHIC

Au+Au collisions have been studied at center-of-mass energies of $$\sqrt {s_{NN} } = 56$$ and 130 GeV using the PHOBOS detector at RHIC. Charged particle multiplicites have been measured as a function of center-of-mass energy, centrality and pseudo-rapidity, η. A total of 4100±400 charged particles are observed in the pseudo-rapidity range −5.4 < η < 5.4 for the most central collisions. A strong elliptic flow signal is seen in peripheral collisions at η = 0. The measurement of an antiprotons to protons ratio of $$\bar p/p = 0.60 \pm 0.04(stat) \pm 0.06(syst)$$ indicates that a nearly baryon-free region is created at midrapidity.

Elliptic flow in Au+Au collisions at square root(S)NN = 130 GeV.

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at square root(S)NN = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.

Elliptic flow of ν ands π 0 mesons in heavy-ion collisions at 2 A GeVmesons in heavy-ion collisions at 2 A GeV

Elliptic flow of ν and π 0 mesons emitted at midrapidity are studied in collisions of 1.9 A GeV 58Ni+58Ni and 2 A GeV 40Ca+natCa. The observed anisotropy corresponds to a negative elliptic flow signal for ν mesons, indicating a preferred emission perpendicular to the reaction plane. In contrast, only small azimuthal anisotropies are observed for π 0 mesons. This may indicate that ν mesons freeze out earlier from the central interaction region than pions.