Experimental status ofheavy-ion collisions atLHC

Tatsuya Chujo
ATHIC 2014
Aug. 5, 2014, Osaka University, Japan

Outline
1. Collectivity in p-Pb vs. PbPb
2. Energy loss (jet, γ-jet, heavy quarks)
3. Melting temperature, quark recombination
via quarkonia production
4. Summary*Note: This talk is not intend to a complete review ofLHC HI results, but rather to show selected recent
results (from QM14 w/ personal bias), try tosummarize the current understanding of LHC HIC.
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)2

1. Collectivity(pPb and PbPb)
Highest pPb multiplicity ~ 55-60% Pb-Pb.

Sep. 13, 2012 (ALICE)
p+Pb test run
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

3

PID pT spectra in p-Pb•

ALICE preliminary results of pT
spectra in p-Pb collisions at√sNN = 5.02 TeV.

•Shown here are for π, K, p, K0, Λ,Ξ, Ω•

Fitted by the blast wave
model (global fit).

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)4

Tkin vs. <βT> in blast wavep-pp-Pb
Pb-Pb
p-p (PYTHIA)•••

Coherent fit for π, K, p, K0, Λ, Ξ, Ω for different centrality (pp, pPb, PbPb)
At same Nch, <βT> larger in p-Pb than in that in Pb-Pb, but also, <βT> similarly
large in pp and p-Pb (at same Nch) with large T.
Strong correlation between T and <βT>.

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

5

HBT correlation in p-Pb

Multiplicity

kT = (pT1 + pT2)/2 [GeV/c]

Similar large radii (Rlong up to 5 fm) in pPb & PbPb at the same Nch.
Scaling with multiplicity and kT (dynamical behavior).
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)6

Di-Hadron Correlations in p-p & p-Pb
p-p (N ≧110)

p-Pb (N ≧110)• First observation ofridge structure inhigh multiplicity p-p(CMS).

• Also confirmed in p-Pb
high multiplicity
events.

• Alway side ridge

structure is observed inhigh multiplicity p-Pb.

p-Pb (ΣET Pb) < 20 GeV
T. Chujo (U. Tsukuba)

p-Pb (ΣET Pb) > 80 GeV
ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

CMS, JHEP 1009 (2010) 91
CMS, PLB 718 (2012) 795
ATLAS, PRL 110, 182302 (2013)7

Double ridge structure in p-Pb
ALICE, PLB 719 (2013) 29

0-20%

60-100%•Extract double ridge structure by subtracting p-p jet like
distribution in p-Pb (60-100%) from central p-Pb (0-20%).

•Confirmed that near and away side ridges are almost samestructure, a la “Double ridge”.

• Strong correlation between near and away sideyields, suggesting the same origin.

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)8

Multi-particle correlations (PbPb vs.pPb)

Pb-Pbp-Pb(event multiplicity)••••
T. Chujo (U. Tsukuba)

Observed non-flow effect in v2{2}.
v2 stays large when calculated with multi-particles.
v2{4}=v2{6}=v2{8}=v2{LYZ} within 10%
Suggest collectivity in p-Pb.
ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)9

v2, v3, v4 comparisons; p-Pb vs. Pb-Pb
before scaling
1.

Adjust p+Pb pT scale by 4/5 toaccount for difference in <pT>
(Teany et al.) for ATLAS data.

2.

Pb+Pb v2 and v4 multiplied by
0.66 to match p+Pb•

Compare p+Pb and Pb+Pb•

after scaling

Good agreement between pPb and Pb-Pb when
including pT and v2, v4
rescaling

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

10

PID v2 in p-Pb
PLB719 (2013) 29
PLB726 (2013) 164•• Very similar behaviour for v2 in Pb-Pb, i.e, Massv2 for π, K, p (ALICE) and Ks0, Λ (CMS)
ordering & crossing

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)11

Quark number scaling test in pPb

Quark numberscaling of v2.

• Comparison in p-Pband Pb-Pb in same Nch.

• Seems better in pPb.

T. Chujo (U. Tsukuba)

Pb-Pb

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

p-Pb

12

v3 in Pb-Pb vs. p-Pb

Event multiplicity

Remarkable similarity in v3 as a function ofmultiplicity in p-Pb and Pb-Pb
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)13

Now on PbPb;
towards precession
measurements of identified
particle v2
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)14

PID v2 in Pb-Pb
arXiv:1405.4632• ALICE data of v

2measured forπ, K, K0, p, φ, Λ, Ξ, Ω• Mass ordering (p < 2.5TGeV/c).

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)15

PID v2 in Pb-Pb
arXiv:1405.4632•

Number of quark
constituent scaling
violated by ~20% in
particular in central
collisions(pT/nq > 1 GeV/c)

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)16

Closer look at φ meson v2 (Pb-Pb)••

v2 at low pT follows mass orderingv2 at high pT close to p in central, andclose to π in mid-central

v2 vs pT

• In central collisions p and φ pT spectra

have similar shape up to ~4 GeV/c, as
expected from radial flow.

• Indicated that mass (and not number ofconstituent quarks) is main driver of v2
and spectra in central only?

π p φ# 10-20%
π p φ#Pb-Pb: p/φ ratio vs pT
80-90%

30-40%

0-10%

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)17

2. Energy loss

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)18

Di-jet energy imbalance
CMS, PRC 84, 024906 (2011)

1) Large energy imbalance isobserved in central Pb-Pb.

ATLAS, PRL, 105 (2010) 252303

pT,1: leading jet
pT,2: sub-leading jet2) Large AJ : low momentum
particle (< 4 GeV/c) emitted
at large angle on away side.
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)19

γ-jet: jet tomography
RJγ : fraction of photons with jetpartner

CMS, Phys. Lett. B 718 (2013) 773• γ as a calibrated probe of jet energy.
• significant change in R , <x > compared to PYTHIA and pp. 20
Jγ

T. Chujo (U. Tsukuba)

Jγ

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

γ-jet in pPb, PbPbpPb

PbPb 30-100%

PbPb 0-30%

RJγ•RJγ = fraction of photons with a jet of pT, jet > 30 GeV•

Jet energy is essentially unmodified in pPb.

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)21

Jet spectra in Pb-Pb, p-p
pp 2.76 TeV

Pb-Pb 2.76 TeV• ATLAS: in different y and centrality, up to p < 400 GeV
TT. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)22

Jet RAA: centrality and y dep.

•••

| y | < 2.1

Jet RAA vs pT and y.
Factor of ~2 suppression upto jet pT of 400 GeVSlow increase withincreasing jet pT, may varywith centrality

0.3 < | y | < 0.8

1.2 < | y | < 2.1T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)23

Jet RAA: centrality and y dep.
Centrality dep.

•RAA monotonically decreasesvs Npart•••

RAA ~0.8 in 60-80%,
RAA ~0.4 in 0-1% at lower jet pT

No significant dependence on
rapidity observed•

Even though both spectrum
shape and q/g fractions varywith yT. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

y dep.

24

Jet Fragmentation in PbPb
centralR= 0.4••

Ratios of D(z) vs centrality, using baseline peripheral (60-80%)

peripheral

In addition to features previously seen (modification of small z (low pT)),
indication of an enhancement at large z

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)25

Jet Fragmentation in PbPb
R= 0.2R= 0.3• Enhancement

at large z (orpT )clearer forsmaller jet radii(R = 0.2, 0.3).

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)26

D meson RAA and v2
arXiv:1405.2001• D mesons are also strongly suppressed.
• significant non-zero v2 for D.
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)27

Charm vs. Bottom• R for charmed
AAmeson (D) vs.
bottom meson(J/ψ from B
decay).

• First indicationof a flavor
dependence ofRAA.

•R
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

B > R
DAAAA

28

Now on pPb;
Jet/heavy q in pPb

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

29

RAA for h± and jet in p-Pb
Charged hadron

Jet (charged)• Unmodified for charged hadron and jet in pPb.
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

30

RpA & RAA for jets and b jetspPb

inclusive jetPbPb 0-5%•••
T. Chujo (U. Tsukuba)b-JetpPb

PbPb 0-5%

Jets coming from b (second vertex)
As suppressed as incl. jets (RAA ≈ 0.5)
Not suppressed in pPb (RpA ≈ 1)
ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)31

Jet in pPb, RAA, y dep.

T. Chujo (U. Tsukuba)• Inclusive jet in pPb, no y dependence seen
ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)32

Jet RCP for pPb (centrality and y dep.)• ATLAS observes astrong variation in jet
yield with centrality
at high pT or forward
rapidities.

T. Chujo (U. Tsukuba)

Rcp

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

pT (GeV)33

Jet RpPb (centrality dep.)•If inclusive RpPb ~ 1 and RCP showssuch effects, necessarily;••

Peripheral enhancement
Central suppression

RpPb

Some explanations:•Geometrical effect (proton special
configuration, protons with larger x
partons have a reduced soft crosssection)•It is still unclear for this effect...

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)34

B meson in p-Pb
RpA
B+B0

Bs

pT (GeV/c)

B+ à J/ψ K+, B0 à J/ψ K*, BS à J/ψ φ• Showing no modification (large uncertainty, incl. the FONLL ref)T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

35

RpPb for heavy quarkDb→µb(→c)→e•Showing no modification

for D, b(→c)→e, c,b →µT. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)36

3. Melting temperaturefor quarkonia, andrecombination

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)37

Dissociation temperature
CMS, PRL 109(2012) 222301

Melting excited ϒ states• Suppression of ground state Y(1s), and excited states Y(2S) and Y(3S).
• Consistent with the sequential melting scenario, Y(3S) > Y (2S) > Y (1S).
T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)38

Y in pPb

pPb
pPb

PbPb

ppMid-rapidity activity••Excited states in pPb: less suppressed than in PbPb
Excited/ground state ratio appears to vary w.r.t. the pPb and pp
event multiplicity (at mid-rapidity)

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)39

J/ψ (color screening vs. regeneration)
mid-rapidity RAA for J/ψ

• J/ψ measured at

mid-rapidity |y|<0.9, by e+e- atLHC.

• Compared toRHIC midrapidity data.

• Significant

larger RAA thanthose at RHIC.

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)40J/ψ (color screening vs. regeneration)
forward-rapidity RAA for J/ψ

• J/ψ measured atforward-rapidity
2.5 < y < 4, by μ+μat LHC.

• Compared to

RHIC forwarddata.

• Significant larger

RAA than those atRHIC.

• Suppression isT. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

stronger than thatat mid-rap.
41

J/ψ (color screening vs. regeneration)
Low pT: RAA at forward y, J/ψ→μ+μ-High pT: RAA at forward y, J/ψ→μ+μ-• J/ψ R is enhanced at low p .
• Compatible with models including
AAvs.

Tregeneration.

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)42

J/ψ v2
ALICE: arXiv:1303.5880• J/ψ produced via regeneration of thermal de-confined cquarks should show a non zero v2.

• Data: Hint of non‐zero v .
• Consistent with the transport model with regeneration.
2

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

43

•

p-Pb

Summary• High multi. events: collectivity, similar to those in Pb-Pb,
but not same.

• Inclusive hard probes (jet, γ-jet, heavy q) do not show
modification.

• Indication of centrality dep. of jet yields in high pT(ATLAS).

• Pb-Pb• φ: mass effect dominant in central only?
• Stronger suppression for D than that for B.
• J/psi: importance of regeneration of cc-bar, non-zero v . 44
2

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)

Questions to be answered in Run-1/2
MMyy  ppeerrssoonnaall  vviieeww!!

1. What is the driving force of collectivity in pPb and p-p high multiplicity events?

• Multi-parton int. is the only cause?
• Role of CGC?
2. Medium response to jet.

• Measurements of hard + soft interaction, i.e. soft
observables w/ jet axis.

3. Jet tomography.

• di-jet, γ-jet, h(π0)-jet, correlations etc. w.r.t. reaction
plane.

T. Chujo (U. Tsukuba)

ATHIC 2014, Osaka Univ. ( Aug. 5, 2014)45

Thank you for yourattentions!