CMS results on CME and CMW in ppb and PbPb

Transcription

1 CMS results on CME and CMW in ppb and PbPb Wei Li Rice University UCLA Chirality Workshop March 27 30

2 Chiral Magnetic Effect in HI Electric current induced by magnetic field (analogous to Ohm s law ) - 2Ψ RP ) β + ϕ same γ = cos φ ' + φ ) 2Ψ -. opp. ALICE STAR s NN s NN (ALICE) same+opp. mean = 2.76 TeV = 0.2 TeV α cos(ϕ cos(ϕ + ϕ - 2ϕ ) α β c HIJING / v 2 {2} CME expectation (same charge [13]) centrality, % If discovered, evidence for Topological phase in nuclear matter Deconfinement, chiral symmetry restoration 2

3 Properties of correlations from the CME PRC81, (2010) t x x + ~ 1 unit a b O F.O. z Short-range in rapidity! # τ O τ F.O. exp% 1 2 y y a b $ & ( ' 3

4 Properties of correlations from the CME PRC81, (2010) t x x + ~ 1 unit a b O F.O. z Short-range in rapidity! # τ O τ F.O. exp% 1 2 y y a b $ & ( ' Is the CME long- or short- range? formation time of chiral quarks 3

5 Properties of correlations from the CME PRC81, (2010) When chiral quarks are formed? t x x + ~ 1 unit a b O F.O. z Short-range in rapidity! # τ O τ F.O. exp% 1 2 y y a b $ & ( ' Is the CME long- or short- range? formation time of chiral quarks 3

6 (My) status quo of the CME search in HI No doubt about the fundamental physics of CME and its potential impact However, many theoretical unknowns in HI: Lifetime of B field Formation time of quarks (long- vs short-range) Other charge-related (conservation, ordering) correlations at late time (a.k.a. BKGs) unconstrained 4

7 (My) status quo of the CME search in HI No doubt about the fundamental physics of CME and its potential impact However, many theoretical unknowns in HI: Lifetime of B field Formation time of quarks (long- vs short-range) Other charge-related (conservation, ordering) correlations at late time (a.k.a. BKGs) unconstrained How to prove or rule out the presence of CME in HI in a simple, model-independent way? 4

8 Flow-like correlations (QGP?) in small system PRL 115 (2015) Ridge 0.10 CMS PbPb s NN = 2.76 TeV 0.3 < p < 3.0 GeV/c; η < 2.4 T CMS ppb s NN = 5.02 TeV 0.3 < p < 3.0 GeV/c; η < 2.4 T v v 2 {2, η >2} v 2 {4} v 2 {6} v 2 {8} v 2 {LYZ} offline N trk offline N trk v n comparable for ppb and PbPb Long-range, collective è very little background 5

9 Flow-like correlations (QGP?) in small system PRL 115 (2015) Ridge 0.10 CMS PbPb s NN = 2.76 TeV 0.3 < p < 3.0 GeV/c; η < 2.4 T CMS ppb s NN = 5.02 TeV 0.3 < p < 3.0 GeV/c; η < 2.4 T v v 2 {2, η >2} v 2 {4} v 2 {6} v 2 {8} v 2 {LYZ} offline N trk offline N trk v n comparable for ppb and PbPb Long-range, collective è very little background Can we learn about other exotic phenomena of QGP using small systems? 5

10 B 0 New insights to the CME from pa B = 0 Problem 6.16 (D. Griffiths) 6

11 B 0 New insights to the CME from pa p Pb B = 0 Problem 6.16 (D. Griffiths) 6

12 B 0 New insights to the CME from pa p Pb B = 0 Problem 6.16 (D. Griffiths) B 0.. B 0 6

13 B 0 New insights to the CME from pa p Pb B = 0 Problem 6.16 (D. Griffiths). B ~ bφ 6

14 B 0 New insights to the CME from pa p Pb B = 0 PbPb Problem 6.16 (D. Griffiths) B. x. B ~ bz B ~ bφ 6

15 New insights to the CME from pa Charge separation signal: Δγ = B 2 cos2( Ψ B Ψ ) EP Ø B (PbPb) > B (ppb) in magnitude high-mult. ppb 7

16 New insights to the CME from pa Charge separation signal: Δγ = B 2 cos2( Ψ B Ψ ) EP Ø B (PbPb) > B (ppb) in magnitude Ø De-correlation of ψ B (~ ψ RP ) and ψ EP (~ ψ PP ) In pa, cos2( Ψ B Ψ ) EP 0 Δγ CME 0 high-mult. ppb 7

17 New insights to the CME from pa Charge separation signal: Δγ = B 2 cos2( Ψ B Ψ ) EP Ø B (PbPb) > B (ppb) in magnitude Ø De-correlation of ψ B (~ ψ RP ) and ψ EP (~ ψ PP ) In pa, cos2( Ψ B Ψ ) EP 0 Δγ CME 0 high-mult. ppb 7

18 New insights to the CME from pa Charge separation signal: Δγ = B 2 cos2( Ψ B Ψ ) EP Ø B (PbPb) > B (ppb) in magnitude Ø De-correlation of ψ B (~ ψ RP ) and ψ EP (~ ψ PP ) In pa, cos2( Ψ B Ψ ) EP 0 Δγ CME 0 high-mult. ppb 7

19 New insights to the CME from pa Charge separation signal: Δγ = B 2 cos2( Ψ B Ψ ) EP Ø B (PbPb) > B (ppb) in magnitude Ø De-correlation of ψ B (~ ψ RP ) and ψ EP (~ ψ PP ) In pa, cos2( Ψ B Ψ ) EP 0 Δγ CME 0 high-mult. ppb A CME-free environment in HM pa Ø Δγ PbPb >> Δγ ppb è support CME in AA Ø Δγ PbPb Δγ ppb è challenge to CME 7

20 HF- CME measurement at CMS Tracker HF+ C α β C γ = cos( φ α +φ β 2Ψ ) EP ( ) cos φ α +φ β 2φ c Particle c fixed at 4.4 < η < 5 (HF) Particle α, β sliced within η < 2.4 (Tracker) v 2,c v 2,c = cos2( φ HF+ HFc φ ) c (3-subevent) 8

21 HF- CME measurement at CMS Tracker HF+ C α β C η gap > 2 γ = cos( φ α +φ β 2Ψ ) EP ( ) cos φ α +φ β 2φ c To ensure factorization (well defined EP) Particle c far removed from α, β in η Multiplicity not too low Otherwise, collective correlations not dominant and obvious BKGs present v 2,c 9

22 Δη dependence of γ p Pb 3 10 (a) ppb s NN = 5.02 TeV 3 10 arxiv: (b) PbPb = 5.02 TeV s NN CMS Pb Pb 2,c 1 offline 185 Ntrk < 220 offline 185 Ntrk < 220 ) /v c -2φ +φ β α cos(φ γ = SS OS φ (Pb-going) c φ (p-going) c η SS OS PbPb η Collective v n well established for N trk >185 Clear splitting of SS and OS in ppb, similar to PbPb NOT in favor of CME interpretation? 10

23 Δγ(OS-SS) Δη dependence of Δγ Ø Clearly short-range (~ 1 unit in η) Ø Similar in ppb and PbPb Same physical origin!? Is CME long- or short-range? When are chiral quarks produced? 11

24 Large rapidity coverage is essential 2,c ) /v c -2φ +φ β α cos(φ CMS SS OS PbPb s NN Cent % = 5.02 TeV η < 2.4, 4.4 < η < 5.0 α,β c η < 0.8, 4.5 < η < 5.0 c α,β γ = η Results stable with η α,β -η c > 1 unit and beyond 12

25 Large rapidity coverage is essential 2,c ) /v c -2φ +φ β α cos(φ CMS SS OS PbPb s NN Cent % = 5.02 TeV η < 2.4, 4.4 < η < 5.0 α,β c η < 0.8, 4.5 < η < 5.0 c α,β 2,c ) /v c -2φ +φ β α cos(φ CMS SS OS PbPb s NN Cent % = 5.02 TeV η < 2.4, 4.4 < η < 5.0 α,β c η < 0.8, η < 0.8 c α,β γ = 1 γ = η η Results stable with η α,β -η c > 1 unit and beyond 12

26 Centrality dependence of γ in AA Integrated over η α -η β <1.6 2,c ) /v 10 3 SS OS 0.5 CMS ( η <2.4) PbPb CMS ( η <0.8) PbPb ALICE ( η <0.8) PbPb STAR ( η <1.0) AuAu s NN s NN s NN s NN CMS = 5.02 TeV = 5.02 TeV = 2.76 TeV = 200 GeV c -2φ β +φ 0 α cos(φ γ = 0.5 CMS η η < 1.6 α β η ALICE η α < 1.6 β STAR η η < 2.0 α β Centrality (%) arxiv: Little energy dependence from 0.2 to 5 TeV 13

27 Comparing Δγ in ppb vs PbPb 2,c ) /v c -2φ β +φ s NN = 5.02 TeV SS OS PbPb centrality(%) ppb, φ (Pb-going) c PbPb CMS α cos(φ 0.5 η α -η β < 1.6 arxiv: offline Ntrk Similarity between ppb and PbPb extends over a wide range of N trk or centrality

28 Comparing Δγ in ppb vs PbPb Almost all BKG in ppb and PbPb OR CME+BKG in PbPb BKG only in ppb 15

29 Some personal thoughts Experimental facts: Δγ (OS-SS) agrees well for ppb and PbPb at 5 TeV in both Δη and multiplicity As CME not expected in ppb, little room for CME in AA at 5 TeV? Is expected as B lifetime is too short at higher s 11? 3 Au+Au 30-60% Pb+Pb ) - γ (γ SS 10 4 OS 2 1 STAR preliminary Experimental data No dramatic s 11 dependence of γ 0 BES II error projection s NN (GeV)

30 Some personal thoughts If all BKGs, what are they? Should they be same in ppb and PbPb? γ = cos φ ' + φ ) 2Ψ -. = cos φ ' φ ) + 2φ ) 2Ψ -. ~γ 5 + cos φ ' φ ) cos 2 φ ) Ψ -. δ*v 2 17

31 Some personal thoughts If all BKGs, what are they? Should they be same in ppb and PbPb? γ = cos φ ' + φ ) 2Ψ -. = cos φ ' φ ) + 2φ ) 2Ψ -. ~γ 5 + cos φ ' φ ) cos 2 φ ) Ψ -. δ*v 2 Can we find new observables insensitive to BKGs? Maybe not if CME is short-range and non-collective 17

32 Some personal thoughts If all BKGs, what are they? Should they be same in ppb and PbPb? γ = cos φ ' + φ ) 2Ψ -. = cos φ ' φ ) + 2φ ) 2Ψ -. ~γ 5 + cos φ ' φ ) cos 2 φ ) Ψ -. δ*v 2 Can we find new observables insensitive to BKGs? Maybe not if CME is short-range and non-collective In general, pa is a litmus test for any effect related to OR B (CME, CMW) J (CVE, Λ polarization) A search in pa must yield zero signal 17

33 Chiral Magnetic Wave Coupling of electric and axial charge densities and currents 18

34 Chiral Magnetic Wave Coupling of electric and axial charge densities and currents Ach. ch 18

35 Chiral Magnetic Wave Evidence of the CMW in AA STAR PRL 114 (2015)

36 Chiral Magnetic Wave slope parameter r Evidence of the CMW in AA ALICE, PRC 93 (2016) STAR PRL 114 (2015) ch 19

37 Chiral Magnetic Wave Does it stand the test of pa? How about higher-order harmonics, v 3? r(v 3 ) slope from CMW expected to be zero Ψ 3 and B direction uncorrelated 20

38 CMW results in ppb and PbPb p Pb CMS Preliminary 185 N 0.3 p T η > 1 offline trk < 220 < 3.0 GeV/c ppb 5.02 TeV h+ h CMS Preliminary 185 N 0.3 p T η > 1 offline trk < 220 < 3.0 GeV/c ppb 5.02 TeV v v v 2 - v 2 - v Corrected A ch r norm (v ) = ± Corrected A ch Pb Pb CMS Preliminary 185 N 0.3 p T η > 1 offline trk < 220 < 3.0 GeV/c PbPb 5.02 TeV h+ h CMS Preliminary 185 N 0.3 p T η > 1 offline trk < 220 < 3.0 GeV/c PbPb 5.02 TeV v v v 2 - v 2 - v r norm (v ) = ± Corrected A ch Corrected A ch Significant nonzero slope in ppb: unexpected by CMW! 21

39 CMW results in ppb and PbPb p Pb v CMS Preliminary 185 N 0.3 p T η > 1 offline trk < 220 < 3.0 GeV/c ppb 5.02 TeV h+ h- - v v 2 v 2 - v CMS Preliminary 0.01 CMS Preliminary offline trk 185 N < 220 offline 0.3 p 185 < 3.0 GeV/c N T trk η > p T η > 1 < 220 ppb 5.02 TeV < 3.0 GeV/c PbPb ppb v v v 2 - v 2 0 r norm (v ) = ± Corrected A ch Corrected A ch Pb Pb CMS Preliminary 185 N 0.3 p T η > 1 offline trk < 220 < 3.0 GeV/c PbPb 5.02 TeV h+ h CMS Preliminary 185 N 0.3 p T η > 1 offline trk < 220 < 3.0 GeV/c PbPb 5.02 TeV norm PbPb r (v ) = ± norm ppb r (v ) = ± v v v 2 v 2 - v Corrected A ch absolute r(v 2 ) ) = ± for rnorm (v both ppb and PbPb Corrected A ch Corrected A ch Significant nonzero slope in ppb: unexpected by CMW! 21

40 CMW results in ppb and PbPb Significant nonzero slope in ppb: unexpected by CMW! 22

41 Local charge conservation in cluster decay + A. Bzdak, P. Bozek. PLB726 (2013) 239 High p T cluster Low p T cluster + Not Detected! èa ch Correlation between A ch and p T of detected particles A ch : <p T >(h + ), <p T >(h - ) 23

42 Local charge conservation in cluster decay v n {2, η >2} ppb = 5.02 TeV ALICE: (0 20%) (60 100%) v2 v3 s NN ALICE, sub. ATLAS, sub. CMS (ATLAS): 185 (180) -5-4 (~10 10 N trk < 220 centrality) CMS, sub. CMS v 2 v p T (GeV/c) v n ~ p T at low p T LCC + finite detector acceptance Ø Δ<p T > (h - -h + ) ~ A ch Ø p T -averaged Δv 2, Δv 3 ~ A ch Ø Δv 3 /Δv 2 ~ v 3 /v 2 24

43 Local charge conservation in cluster decay v n {2, η >2} ppb = 5.02 TeV ALICE: (0 20%) (60 100%) v2 v3 s NN ALICE, sub. ATLAS, sub. CMS (ATLAS): 185 (180) -5-4 (~10 10 N trk < 220 centrality) CMS, sub. CMS v 2 v p T (GeV/c) v n ~ p T at low p T LCC + finite detector acceptance Ø Δ<p T > (h - -h + ) ~ A ch Ø p T -averaged Δv 2, Δv 3 ~ A ch Ø Δv 3 /Δv 2 ~ v 3 /v 2 24

44 <p T > slopes in ppb and PbPb p Pb Pb Pb Qualitatively in line with LCC mechanism 25

45 <p T > slopes in ppb and PbPb r norm (v 2 ) r norm (<p T >) v Similar normalized p T slopes of ppb and PbPb 26

46 v 3 slopes in ppb and PbPb r norm (v 2 ) and r norm (v 3 ) in PbPb are nearly identical Unexpected by CMW but in line with LCC! 27

47 v 3 slopes in ppb and PbPb r norm (v 2 ) and r norm (v 3 ) in PbPb are nearly identical Unexpected by CMW but in line with LCC! 28

48 Summary and outlook CMS search of CME and CMW in ppb at 5 TeV Ø CME/CMW not expected in ppb Ø Observed signal similar between ppb and PbPb, a challenge to the CME/CMW? Ø CMW results in line with LCC mechanism 29

49 Summary and outlook CMS search of CME and CMW in ppb at 5 TeV Ø CME/CMW not expected in ppb Ø Observed signal similar between ppb and PbPb, a challenge to the CME/CMW? Ø CMW results in line with LCC mechanism However, a key question still remains: What are the backgrounds? (is it δ*v 2?) ESE, mixed harmonics 29

50 Summary and outlook CMS search of CME and CMW in ppb at 5 TeV Ø CME/CMW not expected in ppb Ø Observed signal similar between ppb and PbPb, a challenge to the CME/CMW? Ø CMW results in line with LCC mechanism However, a key question still remains: What are the backgrounds? (is it δ*v 2?) ESE, mixed harmonics With a large (CXX-free) ppb data sample in 2016, great opportunity to Ø Nail down the nature of backgrounds Ø Hopefully, a convincing hint of the signal in AA 29

51 Backups

52 Associated Yield / (GeV/c) (a) η >2 0.6 CMS ppb CGC Q Q Q PbPb ppb ppb pp (proton)=0.336 GeV (proton)=1.008 GeV (proton)=1.680 GeV s NN = 2.76 TeV s NN = 5.02 TeV, 2013 s NN = 5.02 TeV, 2012 s = 7 TeV offline N trk (b) η <1 minus η >2 1 < p 1 < p trig T assoc T < 2 GeV/c < 2 GeV/c offline N trk

53 The CMS experiment at the LHC EM Calorimeter (ECAL) Hadron Calorimeter (HCAL) Beam Scintillator Counters (BSC) Forward Calorimeter (HF) Tracker (Pixels and Strips) Wide kinematic range and acceptance Muon System

54 Apple-to-apple comparison with ALICE CMS Preliminary 0.02 Cent % 0.2 p T η < 0.8 < 5.0 GeV/c CMS, PbPb 5.02 TeV ALICE, PbPb 2.76 TeV - v + n + v + n v - n - v n norm r (ALICE) = ± norm r (CMS) = ± Corrected A ch

55 CMS Preliminary ppb 5.02 TeV CMS Preliminary ppb 5.02 TeV offline 185 Ntrk 0.3 p T η > 1 < 220 < 3.0 GeV/c h+ h offline 185 Ntrk 0.3 p T η > 1 < 220 < 3.0 GeV/c v v v 2 - v 2 - v Corrected A ch r norm (v ) = ± Corrected A ch CMS Preliminary PbPb 5.02 TeV CMS Preliminary PbPb 5.02 TeV offline 185 Ntrk 0.3 p T η > 1 < 220 < 3.0 GeV/c h+ h offline 185 Ntrk T p 0.3 η > 1 < 220 < 3.0 GeV/c v v v 2 - v 2 - v r norm (v ) = ± Corrected A ch Corrected A ch

56 Backup 2,c ) /v c s NN = 5.02 TeV η η < 1.6 α β 65 SS OS PbPb centrality (%) ppb, φ (Pb-going) c PbPb CMS η < 2.4, 4.4 < η < 5.0 α,β c 2,c ) /v -2φ β +φ α cos(φ 2 c SS OS CMS ( η <2.4) PbPb ALICE ( η <0.8) PbPb STAR ( η <1.0) AuAu s NN s NN s NN CMS = 5.02 TeV = 2.76 TeV = 200 GeV -2φ β +φ α cos(φ 2 CMS η η < 1.6 α β ALICE η η < 1.6 α β STAR η η < 2.0 α β offline Ntrk Centrality (%)

57 Backup 2,c ) /v c -2φ β +φ α cos(φ s NN = 5.02 TeV SS OS PbPb centrality(%) ppb, φ (Pb-going) c ppb, φ (p-going) c PbPb CMS 2 10 offline Ntrk 3 10

58 Backup 2,c ) /v c -2φ +φ β α cos(φ CMS SS OS PbPb s NN Cent % η = 5.02 TeV η < 2.4, 4.4 < η < 5.0 α,β c η < 0.8, η < 0.8 c α,β (OS-SS) 2,c ) /v c -2φ +φ β α cos(φ CMS η η α,β α,β PbPb s NN Cent % < 2.4, 4.4 < η < 5.0 c < 0.8, η < 0.8 c η = 5.02 TeV