CMS-PAS-HIN-16-022

CMS-PAS-HIN-16-022
Correlations of azimuthal anisotropy harmonics in pp, pPb, and PbPb collisions at the LHC
CMS Collaboration
February 2017

Abstract: The first measurements of anisotropy harmonics ( $v_n$ , $n=$ 2-4) in pPb collisions at $\sqrt{s_{\mathrm{NN}}} =$ 8.16 TeV is presented. In addition, measurements of event-by-event correlations of different $v_n$ in pp at $\sqrt{s} =$ 13 TeV, pPb at $\sqrt{s_{\mathrm{NN}}} =$ 5.02 and 8.16 TeV and PbPb at $\sqrt{s_{\mathrm{NN}}} =$ 5.02 TeV collision systems at the LHC are explored. New results of the $v_n$ harmonics in 8.16 TeV pPb collisions are extracted via long-range ( $\|\Delta\eta\|>$ 2) two-particle correlations as a function of event multiplicity. The current measurement is reaching a very-high-multiplicity region beyond that achieved in 5.02 TeV pPb data collected in 2013. Event-by-event correlations among $v_2$ , $v_3$ and $v_4$ harmonics are measured using the four-particle symmetric cumulant method in pp and pPb, and compared to the large system of PbPb collisions. For high-multiplicity (more than 100 tracks) pp and pPb events, the $v_2$ harmonic is found to have a negative correlation with the $v_3$ harmonic, while the $v_2$ and $v_4$ harmonics are positively correlated. Normalized by the two-particle $v_n$ harmonics, the correlation coefficients of $v_2$ and $v_3$ harmonics are quantitatively similar for pPb and PbPb data, while a strong system size dependence is observed for correlations of $v_2$ and $v_4$ harmonics. These new data provide important insights to the origin of collectivity observed in small collision systems.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRL 120 (2018) 092301. The superseded preliminary plots can be found here.

Figures & Tables	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: The $v_2$ , $v_3$ and $v_4$ harmonics from long-range two-particle correlations for 0.3 $< p_{\mathrm{T}} <$ 3 GeV/ $c$ as a function of $N_{text{trk}}^{\text{offline}}$ in pp at ${\sqrt {s}} =$ 13 TeV, pPb at ${\sqrt {s_{\mathrm{NN}}}} =$ 8.16 TeV, and PbPb at ${\sqrt {s_{\mathrm{NN}}}} =$ 5.02 TeV. The lines show the $v_{n}$ results before subtraction of low-multiplicity correlations.
png pdf	Figure 2: The SC for the second and third harmonic (red points) and the second and forth harmonic (blue points) as a function of $N_{text{trk}}^{\text{offline}}$ in pp at ${\sqrt {s}} =$ 13 TeV, pPb at ${\sqrt {s_{\mathrm{NN}}}} =$ 5.02 and 8.16 TeV, and PbPb at ${\sqrt {s_{\mathrm{NN}}}} =$ 5.02 TeV.
png pdf	Figure 3: The SC for the second and third harmonic (left) and the second and forth harmonic (right) normalized by $< v_2^{2} > \cdot < v_3^{2} >$ and $< v_2^{2} > \cdot < v_4^{2} >$ from dihardon correlations respectively. The $p_{\mathrm{T}}$ range for considered tracks is 0.3 $< p_{\mathrm{T}} <$ 3 GeV/ $c$ and the results are shown as a function of $N_{text{trk}}^{\text{offline}}$ in pp at ${\sqrt {s}} =$ 13 TeV, pPb at ${\sqrt {s_{\mathrm{NN}}}} =$ 8.16 TeV, and PbPb at ${\sqrt {s_{\mathrm{NN}}}} =$ 5.02 TeV.

Tables
png pdf	Table 1: Summary of systematic uncertainties for $v_n$ harmonics derived from two-particle correlations in pPb 8.16 TeV and PbPb 5.02 TeV.
png pdf	Table 2: Summary of systematic uncertainties for SC in pPb 8.16 TeV and PbPb 5.02 TeV.

Summary

First measurement of azimuthal anisotropy Fourier harmonics and event-by-event correlations of different harmonics orders in pPb collisions at

$\sqrt{ s_{\mathrm{NN}} } =$ 8.16 TeV is presented with data collected by the CMS experiment at CERN. The

$v_2$ -

$v_4$ Fourier harmonics are extracted from long-range two-particle correlations as a function of event multiplicity, and found to be similar to lower energy pPb

$\sqrt{ s_{\mathrm{NN}} } =$ 5.02 TeV data. The pPb data are compared to pp

$\sqrt{ s } =$ 13 TeV and PbPb

$\sqrt{ s_{\mathrm{NN}} } =$ 5.02 TeV systems. Using four-particle cumulant technique, correlations of different harmonic orders are obtained, where an anti-correlation is observed between

$v_2$ and

$v_3$ in pPb collisions, while

$v_2$ and

$v_4$ are positively correlated. This behavior is similar between pPb and PbPb systems. Normalized correlation coefficients of the 2

$^{\rm nd}$ and 3

$^{\rm rd}$ order are found to be quantitatively similar between pPb and PbPb systems. For the 2

$^{\rm nd}$ and 4

$^{\rm th}$ order, they are slightly higher in pPb than in PbPb. This result may point to a different contribution from the initial-state correlations or different transport properties like the shear viscosity to entropy ratio (

$\eta$ /s). The pp normalized symetric cumulant result shows a similar trend at high multiplicity compared to pPb and PbPb systems but the statistical uncertainties are too large to make a quantitative statement. The results presented in this paper provide further strong evidence of a similar origin of collectivity observed in small and large hadronic collision systems, and also impose novel constraints on the theoretical calculations.

Additional Figures
png pdf	Additional Figure 1: Level-1 (L1) trigger efficiency as a function of $N_{\text{trk}}^{\text{offline}}$ for high-multiplicity event selection in pPb 8.16 TeV.
png pdf	Additional Figure 2: High Level Trigger (HLT) efficiency as a function of $N_{\text{trk}}^{\text{offline}}$ for high-multiplicity event selection in pPb 8.16 TeV.
png pdf	Additional Figure 3: L1+HLT efficiency as a function of $N_{\text{trk}}^{\text{offline}}$ for high-multiplicity event selection in pPb 8.16 TeV.
png pdf	Additional Figure 4: 2-D two-particle correlation function for 1 $< p_{\mathrm{T}}^{\text{trig}} <$ 3 GeV/ $c$ , 1 $< p_{\mathrm{T}}^{\text{assoc}} <$ 3 GeV/ $c$ in 8.16 TeV pPb data with 330 $< N_{\text{trk}}^{\text{offline}} <$ 350 for charged particles.
png pdf	Additional Figure 5: 1-D two-particle correlation function for 1 $< p_{\mathrm{T}}^{\text{trig}} <$ 3 GeV/ $c$ , 1 $< p_{\mathrm{T}}^{\text{assoc}} < 3$ GeV/ $c$ , average over $\|\Delta \eta \| >$ 2, in 8.16 TeV pPb data with 330 $< N_{\text{trk}}^{\text{offline}} <$ 350 for charged particles. 2-particle $V_n$ coefficients obtained from a Fourier fit of the distribution are also shown.
png pdf	Additional Figure 6: SC(2,3) and SC(2,4) as a function of centrality from CMS (full) compared with ALICE data (open) with the same kinematic cuts.
png pdf	Additional Figure 7: The SC for the second and third harmonic (left) and the second and forth harmonic (right) normalized by unsubtracted $< v_2^{2} >.< v_3^{2} >$ and $< v_2^{2}>.< v_4^{2}>$ from dihadron correlations respectively. The $p_{\mathrm {T}}$ range for considered tracks is 0.3 $< p_{\mathrm {T}} <$ 3 GeV/ $c$ and the results are shown as a function of $N_{\text{trk}}^{\text{offline}}$ in pp at ${\sqrt {s}}=$ 13 TeV, pPb at ${\sqrt {s_{\mathrm{NN}}}} =$ 8.16 TeV, and {\text {PbPb}} at ${\sqrt {s_{\mathrm{NN}}}} =$ 5.02 TeV.

References
1	STAR Collaboration	Distributions of charged hadrons associated with high transverse momentum particles in pp and Au + Au collisions at $\sqrt{ s_{\mathrm{NN}} } =$ 200 GeV	PRL 95 (2005) 152301	nucl-ex/0501016
2	STAR Collaboration	Long range rapidity correlations and jet production in high energy nuclear collisions	PRC 80 (2009) 064912	0909.0191
3	PHOBOS Collaboration	System size dependence of cluster properties from two- particle angular correlations in Cu+Cu and Au+Au collisions at $\sqrt{ s_{\mathrm{NN}} } =$ 200 GeV	PRC 81 (2010) 024904	0812.1172
4	PHOBOS Collaboration	High transverse momentum triggered correlations over a large pseudorapidity acceptance in Au+Au collisions at $\sqrt{ s_{\mathrm{NN}} } =$ 200 GeV	PRL 104 (2010) 062301	0903.2811
5	STAR Collaboration	Three-particle coincidence of the long range pseudorapidity correlation in high energy nucleus-nucleus collisions	PRL 105 (2010) 022301	0912.3977
6	CMS Collaboration	Long-range and short-range dihadron angular correlations in central PbPb collisions at a nucleon-nucleon center of mass energy of 2.76 TeV	JHEP 07 (2011) 076	CMS-HIN-11-001 1105.2438
7	CMS Collaboration	Centrality dependence of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at $\sqrt{ s_{\mathrm{NN}} }$ = 2.76 TeV	EPJC 72 (2012) 2012	CMS-HIN-11-006 1201.3158
8	ALICE Collaboration	Harmonic decomposition of two-particle angular correlations in Pb-Pb collisions at $\sqrt{ s_{\mathrm{NN}} } =$ 2.76 TeV	PLB 708 (2012) 249	1109.2501
9	ATLAS Collaboration	Measurement of the azimuthal anisotropy for charged particle production in $\sqrt{ s_{\mathrm{NN}} } =$ 2.76 TeV lead-lead collisions with the ATLAS detector	PRC 86 (2012) 014907	1203.3087
10	CMS Collaboration	Studies of azimuthal dihadron correlations in ultra-central PbPb collisions at $\sqrt{ s_{\mathrm{NN}} } =$ 2.76 TeV	JHEP 02 (2014) 088	CMS-HIN-12-011 1312.1845
11	J.-Y. Ollitrault	Anisotropy as a signature of transverse collective flow	PRD 46 (1992) 229
12	B. Alver and G. Roland	Collision geometry fluctuations and triangular flow in heavy-ion collisions	PRC 81 (2010) 054905, , Erratum: \DOI10.1103/PhysRevC.82.039903	1003.0194
13	S. Voloshin and Y. Zhang	Flow study in relativistic nuclear collisions by Fourier expansion of azimuthal particle distributions	Z. Phys. C 70 (1996) 665	hep-ph/9407282
14	B. H. Alver, C. Gombeaud, M. Luzum, and J.-Y. Ollitrault	Triangular flow in hydrodynamics and transport theory	PRC 82 (2010) 034913	1007.5469
15	B. Schenke, S. Jeon, and C. Gale	Elliptic and triangular flow in event-by-event D=3+1 viscous hydrodynamics	PRL 106 (2011) 042301	1009.3244
16	Z. Qiu, C. Shen, and U. Heinz	Hydrodynamic elliptic and triangular flow in Pb-Pb collisions at $\sqrt{ s_{\mathrm{NN}} } =$ 2.76 TeV	PLB 707 (2012) 151	1110.3033
17	ATLAS Collaboration	Measurement of the correlation between flow harmonics of different order in lead-lead collisions at $\sqrt{s_{NN}} =$ 2.76 TeV with the ATLAS detector	PRC 92 (2015) 034903	1504.01289
18	ALICE Collaboration	Correlated event-by-event fluctuations of flow harmonics in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}} =$ 2.76 TeV	PRL 117 (2016) 182301	1604.07663
19	A. Bilandzic et al.	Generic framework for anisotropic flow analyses with multiparticle azimuthal correlations	PRC 89 (2014) 064904	1312.3572
20	G. Giacalone, L. Yan, J. Noronha-Hostler, and J.-Y. Ollitrault	Symmetric cumulants and event-plane correlations in Pb + Pb collisions	PRC 94 (2016) 014906	1605.08303
21	CMS Collaboration	Observation of Long-Range Near-Side Angular Correlations in Proton-Proton Collisions at the LHC	JHEP 09 (2010) 091	CMS-QCD-10-002 1009.4122
22	ATLAS Collaboration	Observation of Long-Range Elliptic Azimuthal Anisotropies in $\sqrt{s}=$ 13 and 2.76 TeV pp Collisions with the ATLAS Detector	PRL 116 (2016) 172301	1509.04776
23	CMS Collaboration	Measurement of long-range near-side two-particle angular correlations in pp collisions at $\sqrt s =$ 13 TeV	PRL 116 (2016) 172302	CMS-FSQ-15-002 1510.03068
24	CMS Collaboration	Evidence for collectivity in pp collisions at the LHC	Submitted to PLB	CMS-HIN-16-010 1606.06198
25	CMS Collaboration	Observation of long-range near-side angular correlations in proton-lead collisions at the LHC	PLB 718 (2013) 795	CMS-HIN-12-015 1210.5482
26	ALICE Collaboration	Long-range angular correlations on the near and away side in pPb collisions at $\sqrt{ s_{\mathrm{NN}} } =$ 5.02 TeV	PLB 719 (2013) 29	1212.2001
27	ATLAS Collaboration	Observation of Associated Near-side and Away-side Long-range Correlations in $\sqrt{ s_{\mathrm{NN}} } =$ 5.02 TeV Proton-lead Collisions with the ATLAS Detector	PRL 110 (2013) 182302	1212.5198
28	LHCb Collaboration	Measurements of long-range near-side angular correlations in $\sqrt{s_{\text{NN}}}=$ 5 TeV proton-lead collisions in the forward region	PLB762 (2016) 473--483	1512.00439
29	CMS Collaboration	Long-range two-particle correlations of strange hadrons with charged particles in pPb and PbPb collisions at LHC energies	PLB 742 (2015) 200	CMS-HIN-14-002 1409.3392
30	ALICE Collaboration	Long-range angular correlations of pi, K and p in p--Pb collisions at $\sqrt{ s_{\mathrm{NN}} } =$ 5.02 TeV	PLB 726 (2013) 164	1307.3237
31	CMS Collaboration	Multiplicity and transverse momentum dependence of two- and four-particle correlations in pPb and PbPb collisions	PLB 724 (2013) 213	CMS-HIN-13-002 1305.0609
32	ATLAS Collaboration	Measurement of long-range pseudorapidity correlations and azimuthal harmonics in $\sqrt{s_{NN}}=$ 5.02 TeV proton-lead collisions with the ATLAS detector	PRC 90 (2014) 044906	1409.1792
33	CMS Collaboration	Evidence for collective multi-particle correlations in pPb collisions	PRL 115 (2015) 012301	CMS-HIN-14-006 1502.05382
34	K. Dusling, W. Li, and B. Schenke	Novel collective phenomena in high-energy proton-proton and proton-nucleus collisions	Int. J. Mod. Phys. E 25 (2016) 1630002	1509.07939
35	S. Schlichting and B. Schenke	The shape of the proton at high energies	PLB739 (2014) 313--319	1407.8458
36	P. Bożek, W. Broniowski, and M. Rybczyński	Wounded quarks in A+A, p+A, and p+p collisions	PRC 94 (2016) 014902	1604.07697
37	J. Qian and U. Heinz	Hydrodynamic flow amplitude correlations in event-by-event fluctuating heavy-ion collisions	PRC 94 (2016) 024910	1607.01732
38	CMS Collaboration	Description and performance of track and primary-vertex reconstruction with the CMS tracker	JINST 9 (2014) P10009	CMS-TRK-11-001 1405.6569
39	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
40	CMS Collaboration	Observation of charge-dependent azimuthal correlations in pPb collisions and its implication for the search for the chiral magnetic effect	Submitted to: PRLett (2016)	CMS-HIN-16-009 1610.00263
41	CMS Collaboration	Differential flow harmonic vn in pPb and PbPb collisions	CMS-PAS-HIN-15-008	CMS-PAS-HIN-15-008
42	ALICE Collaboration	Multiparticle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider	PRC 90 (2014) 054901	1406.2474
43	A. Bilandzic, R. Snellings, and S. Voloshin	Flow analysis with cumulants: Direct calculations	PRC 83 (2011) 044913	1010.0233