CMS-PAS-HIN-15-008 | ||
Differential flow harmonic vn in pPb and PbPb collisions | ||
CMS Collaboration | ||
September 2015 | ||
Abstract: Previous CMS measurements have demonstrated the collective nature of multiparticle correlations in high-multiplicity pPb collisions at the LHC. This collectivity is consistent with a hydrodynamic flow origin. However, it can also be interpreted in terms of initial state effects arising from gluon saturation. The pseudorapidity dependence of the azimuthal Fourier coefficients (vn) is expected to be sensitive to the underlying mechanism with, in the hydrodynamic picture, the longer lifetime of the fireball on the Pb-going side expected to lead to a larger flow signal than found on the p-going side. To investigate the detailed properties of the observed collectivity, differential vn values in transverse momentum (pT) and pseudorapidity (η) are presented over the full range of the CMS tracker detector (−2.4<η<2.4) for pPb collisions at a nucleon-nucleon center-of mass energy of 5.02 TeV. Results based on multiparticle analyses involving four or more particles are shown. An event plane analysis is presented where the influence of recently demonstrated event-plane decorrelation is considered. Comparisons are made with peripheral PbPb collisions measured at similar mid-rapidity particle multiplicities. The results will be discussed in the context of current models of the longitudinal dependence of the multiparticle correlations. | ||
Links:
CDS record (PDF) ;
CADI line (restricted) ; Figures are also available from the CDS record. These preliminary results are superseded in this paper, PRC 98 (2018) 044902. The superseded preliminary plots can be found here. |
Figures | |
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Figure 1-a:
v2 as a function of pT in pPb (a) and PbPb (b) collisions for different Nofflinetrk ranges. v2{2,|Δη|>2} and v2{4} are extracted from Ref [26]. |
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Figure 1-b:
v2 as a function of pT in pPb (a) and PbPb (b) collisions for different Nofflinetrk ranges. v2{2,|Δη|>2} and v2{4} are extracted from Ref [26]. |
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Figure 2:
Top: Comparison of v2(pT) distributions based on HF event planes located on the p-going (vp2) and Pb-going (vPb2) sides of the tracker region, with ηC=0. Bottom: Same, but with ηC=ηPOI |
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Figure 3:
v2{EP} as a function of η in pPb collisions for different Nofflinetrk ranges with (top) ηC=0 and (bottom) ηC=ηPOI. The pseudorapidities are given in the laboratory frame. Non-flow effects are evident for points where the pseudorapidity gap between the particles of interest and the respective event plane is small. |
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Figure 4:
v2{EP} as a function of η in PbPb collisions for different Nofflinetrk ranges with (top) ηC=0 and (bottom) ηC=ηPOI. Non-flow effects are evident for points where the pseudorapidity gap between the particles of interest and the respective event plane is small. |
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Figure 5-a:
v2 corresponding to event plane, cumulant, and LYZ methods as a function of η in pPb (a) and PbPb (b) collisions for different Nofflinetrk ranges. The v2{EP} results are based on the furthest HF event plane in pseudorapidity. The pseudorapidities are given in the laboratory frame. |
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Figure 5-b:
v2 corresponding to event plane, cumulant, and LYZ methods as a function of η in pPb (a) and PbPb (b) collisions for different Nofflinetrk ranges. The v2{EP} results are based on the furthest HF event plane in pseudorapidity. The pseudorapidities are given in the laboratory frame. |
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Figure 6:
Role of fluctuations in the pPb and PbPb systems as a function of pseudorapidity for the indicated Nofflinetrk ranges. |
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Figure 7:
Comparison of event-plane (v2{EP}) and cumulant (v2{4}) results for the ratio v2(η)/v2(η=0) with the two-particle correlation results from [49] for pPb collisions at √sNN=5.02TeV and with 220≤Nofflinetrk<260. The [49] results are shown without the peripheral v2 component subtraction, a correction for non-flow effects which increases the v2 harmonics. The pseudorapidities are given in the laboratory frame. |
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Figure 8-a:
(a) Ratio p-going to Pb-going side v2 coefficients at comparable ηCM values for pPb collisions. (b) Ratio of +η to −η v2 values at comparable ηCM values for PbPb collisions. |
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Figure 8-b:
(a) Ratio p-going to Pb-going side v2 coefficients at comparable ηCM values for pPb collisions. (b) Ratio of +η to −η v2 values at comparable ηCM values for PbPb collisions. |
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Figure 9:
Triangular flow (n=3) harmonic from the event-plane method for pPb collisions at √sNN= 5.02 TeV with (top) ηC=0 and (bottom) ηC=ηPOI. The legends indicate the direction of the respective HF event planes. Non-flow effects are evident for points where the pseudorapidity gap between the particles of interest and the respective event plane is small. |
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Figure 10:
Triangular flow (n=3) harmonic from the event-plane method for PbPb collisions at √sNN= 2.76 TeV with (top) ηC=0 and (bottom) ηC=ηPOI. The legends indicate the direction of the respective HF event planes. Non-flow effects are evident for points where the pseudorapidity gap between the particles of interest and the respective event plane is small. |
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Figure 11:
Elliptic (n=2) and triangular flow (n=3) harmonics for pPb collisions at √sNN= 5.02 TeV and PbPb at √sNN= 2.76 TeV with ηC=ηPOI. The v2{EP} results are based on the furthest HF event plane in pseudorapidity. |
Tables | |
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Table 1:
Systematic uncertainty |
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Compact Muon Solenoid LHC, CERN |
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