Summary of smallsystem
関口裕子(東大CNS)

postQM＠Nagoya University,Jun 30thOutline
Strangeness —> strangeness enhancement?
• Resonances —> dynamics of hadronic medium?
• PID vn —> collectivity?
• vn vs. collision geometry —> initial conditions?
• Multi particle cumulant —> initial or final?
• Symmetric cumulant —> initial or final?
• Ridge in ee collisions —> thermalization/collectivity inee?
•2Strangeness production relative to pion

ancement at the LHC top energy
S=1
S=1
S=0
S=1
S=2

Strangeness enhancement: LHC vs RHIC

• High precision measurement at the LHC in fairagreement with STAR results at high multiplicity

Wrap up of measurements available so far: newresults from LHC-Run2 for pp collisions at 13 TeV
and Xe-Xe collisions at 5.44 TeV

Stefania Bufalino - QM2018 in Venice• Only multiplicity plays a role? neither energy nor

system dependence observed• Measurements in small system at RHIC could

10to understand the experimental hints
help

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Baryon to meson ratio• baryon-to-meson ration with large mass gap has nomultiplicity dependence.

• Strangeness enhancement due to strangeness content.
• φ?
ALI-PREL-135238

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Multiplicity dependence of particle ratio• Results of φ/K,Λ*/Λ,Σ*/Λ are ﬂat.

No re-scattering orregeneration.

• K0*/K decrease as dNch/dη increase in pp andpPb.

Re-scattering?

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Special role of Φ-meson• φ/K: Flat or slightly increasing. S＜1?
• Ξ/φ:ﬂat S~2 or slightly increasing in pp and pPb. S<2?
• According to the results, φ behaves as 1<S<2?
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PID v2 in pPb• New: v2 of φ, Ξ, Ω, D in pPb.
• Mass ordering at low pT.
• Baron/meson grouping at intermediate pT.
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PID v2 in small systems in RHIC

• Mass ordering at low pT.
Not significant in p-Au
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NCQ scaling• Light and strange hadrons follows NCQ scaling.

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D0 v2 in pPb• D0 v2 follows NCQ scaling as light hadrons in PbPb.
• Charm quark may achieve thermalization.
• D0 v2 is smaller than light hadrons in pPb.
• Less ﬂow because system size is small or other?

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Heavy flavor v2 in RHIC

• Signiﬁcant heavy ﬂavor muon v2 indAu.

• RdA: enhancement in Au going,
which suppression in d going.

• Similar magnitude to charged
hadrons.

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J/Ψ v2 in pPb• NCQ scaling v02(J/Ψ)〜v2(D0)<K S.

• What is origin?
At RHIC, J/psi v2 is 0 in Au+Au
collisions
How about J/psi v2 in p/d+Au?
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Multi particle cumulant

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v2, v3 with Multi-Particle cumulant• v2 with multi particle

decrease as multiplicity
increase in pPb. Diﬀerent
trend to PbPb.

•Non-Gaussian ﬂuctuation??
• First measurement of v3{4}in small system• Hydro calculation describe
data.(arXiv:1405.3976)

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Ratio of vn{4} and vn{2}• v2{4}/v2{2} is larger than v3{4}/v3{4} in PbPb• Global geometry dominant for v2• v3{4}/v3{4} is comparable with v2{4}/v2{2} in pPb• initial state ﬂuctuation dominant both for v2 and v3• TRENTo εn{4}/εn{2} describe pPb data
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C2{4} in RHICp+Au

d+Au• Positive c2{4} in p+Au, while negative in d+Au.
• If ﬂuctuation σv2 > mean v2, c2{4} is positive.
• non-ﬂow?
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Multi-particle correlations in d+Au
Phys. Rev. Lett. 120,062302 (2018)• Real v2{4} observed• v2{4} ≈ v2{6}, strong indication of collectivity!17Symmetric cumulant• Symmmetric cumulant• Sensitive to IS ﬂuctuation and medium transport
coeﬃcient.

•SC(2,4) is correlated and SC(2,3) is anti-correlated in PbPb
•Non-ﬂow eﬀect is large in pp and pPb.
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Sub-event multi-particle cumulant

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Sub-event Cumulant• 3sub method largely suppress non-ﬂow in pp and low
multiplicity events in pPb.

• Signiﬁcant negative c2{4} by using 3 sub method in pp.
• Update from previous QM.
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Correlation between harmonics• Non-ﬂow suppressedat low multiplicity byusing subevent
cumulant in pp andpPb.

• Sub-event results ofSC(2,3) and SC(2,4) arecomparable in pp.

• SC(2,3) to converge athigh multiplicity in pPb.

• SC(2,4) results between

standard and subeventsare diﬀerent at highmultiplicity in pPb.

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Comparison with collision systems• Normalize to compare with diﬀerent collision systems.
• Strength of the correlations between harmonics similar between all systems
except nsc2,3{4} in pp.

• Similar initial state ﬂuctuation
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System geometry

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v2 vs initial geometry

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Non-Flow subtraction methods

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LEP1 Data vs PYTHIA6 N≥35Projection

1.6<|Δη|<3.0(Long range)(ZYAM subtracted)• Hint of near-side peak in data
• Consistent with PYTHIA6 without final state effects• Contribution from multi-jet correlation• PYTHIA6 reference limited by archive MC statistics
Yen-Jie Lee (MIT)Two-Particle Correlation in!28
e+e- with ALEPH archived data26

cn{2} in e-p
Cumulants from in e-p data from ZEUS
J Onderwaaterc2c3c4

Familiar behaviour: non-flow dominates at small multiplicity and without eta-gap
No flow-like signal seen in high-multiplicity, large eta gap for c2, c3, c4cn{2} in e-p is consistent with 0 for large Nch with large η gap.
!1329

Summary•

strangeness —> strangeness enhancement?

YES!!
• Resonances —> dynamics of hadronic medium?
• We saw re-scattering effects from K*.
•

PID v2 —> collectivity?
• Mass ordering. Charm flow? What is the origin of large J/psi v2?
• vn vs. collision geometry —> initial conditions?
• strong correction with eccentricity••

Multi particle cumulant —> initial or final?
• v2{4}/v2{2} = v3{4}/v3{2} in p-Pb (not the case for A-A). Importance of initial fluctuation inv2
• c2{4}<0 with large rapidity gap (sub event cumulant)• c2{4}<0 in dAu but c2{4}>0 in pAu

Symmetric cumulant —> initial or final?
• Correlation gets weaker if rapidity gap is required. Same trend in SC(2,4) and SC(2,3)
between p-A and A-A. Different in p-p.
• Ridge in ee collisions —> thermalization/collectivity in ee?
• no ridge in ee collisions. no flow like signal in ee.
••noThank you for your attention!!

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backup

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vnv2(η) vs dNch/dη in Geometry Control Scan
Pb-Pb sNN = 2.76 TeV

0.06

0.04

5-10%
ALICE AMPT
v2{2}
v2{4}
v3{2}
v4{2}

vn

0.02

40-50%

0.08

p+Aud+Au

0.06
0.04
0.02
0−4
ALI-PUB-111778−3−2−1012345η

• d+Au scales well, but p+Au does not at
backward rapidity• 3D hydrodynamics quantitatively!33
describes the data in p+Au
The event plane is measured in -3.9 < η < -3.1

mean pT34heavy nuclei(Anti-)nuclei production in small systems
New results from LHC- Run2 at 7 TeV and 13 TeV vs multiplicity andfirst ever observation of anti-3He in pp collisions from LHC-Run1 datatd¯d¯3Het̄

3He

ALICE Coll. PRC 97 (2018) 024615-

pp spectrum shows no sign of radial ﬂow (spectra hardening is clearly seen in heavy-ion collisions)
integrated yields reduced of a factor ~1000 when adding a nucleon
it is ~ 300 and ~ 600 in Pb-Pb and p-Pb collisions, respectivelyStefania Bufalino - QM2018 in Venice35

16

which are caused by a radially expanding source [58]. A comparison of theEq. (10) is presented in Fig. 19 and shows qualitative agreement between theheavy nuclei

In a more quantitative picture, it turns out that the coalescence process is ggeneity volume which can be extracted from the HBT radii. The mathematic
B2 to HBT radii (R⊥ and R∥ ) is given bywhat about the multiplicit
The formation probability of composite nuclei canintegrated B2 trend?
3/2
be quantiﬁed through the coalescence parameter BAProduction of light (anti-)nuclei3π ⟨C⟩ and Pb–Pb collis
dppin,
B2 =23Simple
2mT R⊥ (mT )R∥ (mT )d NA

Coalescence parameters in small systems at theEA⎛ d 3N ⎞Ap⎜⎜ E p3 ⎟dp p ⎟⎠⎝B 2 (GeV2/ c 3)

BA =

dpA 3

2010−2€dALICE, Pb-Pb, sNN = 2.76 TeV

0-10%
10-20%
20-40%

experim→ evo
spectraexplain→ noscatter

40-60%
60-80%..

−310Firs-−410 0• No pT dependence as suggested

by simple coalescence models

0.5

1ALICE Coll. PRC 97 (2018)361.522.5

p / A (GeV/c )
Treev
colo
thpRe

Fig. 18: The coalescence parameters B2 (left) and B3 (right)heavynuclei
What have we understood?
• Latest results in pp at 7 TeV and 13 TeV ﬁt thetrend drawn by other energies/colliding
systems at the LHC• matching of pp and p-Pb points at similar
multiplicities• rising with multiplicity explained incoalescence models as due to an increased
proton and neutron density• In pp (and p-Pb) the results point out that the rise in the number of nucleons

dominates over the increase in the volume size
• No signiﬁcant centrality dependence in Pb-Pb collisions in agreement withThermal-statistical model
Stefania Bufalino - QM2018 in Venice37

2

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particle ratio as a function of multiplicity

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Special role of φpostQM＠Nagoya University,Jun 30th

Strangeness enhancement

ALI-PREL-135238• Strangeness enhanced from pp to PbPb.
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Comparison with collision systems• Symmetric cumulants consistent between all threesystems in the <Nch> range covered by p+p
collisions.
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