Recent results from LHC-ALICE
Shingo Sakai for High energy nucl. group1

ALICE experimentn ALICE experiment --- dedicate experiment for understanding Quark-Gluon Plasma (QGP) in LHC
n Quark-Gluon plasma

Quarks are confinedin hadron by the strong force(gluon)

Quark and gluon are deconfined
under high temperature / density
Þ QGP
Þ Possibly produce byÞ heavy-ion collisions(LHC PbPb 2.76 & 5.02 TeV)
arXiv:1304.1452

n Predicted by Quantum ChromoDynamics (QCD) under extremely high temperature and density
n Test for QCD & new QCD phenomenan State of the matter in the early stage of the universe (~10 μs after Big Bang)n Add a new page in “History of the Universe”
2Results in PbPb collisions(1) Suppression of charged particles(3) Baryon-to-meson ratio(2) Azimuthal anisotropy v2

ALICE, Pb-Pb, sNN = 2.76 TeV
norm. uncertainty

charged particles, |η| < 0.81v 2{2, |∆ η|>2}

RAAdN/d(φ-ψRP) = …+ N0(1+2v2cos(2(φ-ψRP))) +…
0%π±K±p+p

ALICE Pb−Pb sNN = 5.02 TeV|y | < 0.5, 20−30%0.3

0.2

10-1
ALICE (0-5%)
CMS (0-5%)

0ALI−PUB−60550

1020HT (Chen et al.) lower density
HT (Chen et al.) higher density
HT (A.M.)
ASW (T.R.)
YaJEM-D (T.R.)
elastic (T.R.) large P esc
elastic (T.R.) small P esc
WHDG (W.H.) π0 upper limit
WHDG (W.H.) π0 lower limit

304050p (GeV/c)

0.1

100%
002

ALI−PUB−324743

Parton energy loss in QGP

468101214p (GeV/c )TT

Collective motion in QGP
Mechanism ? Origin ? Unique ?

3Quark recombination in QGP

Measurements in ALICE
pp collisions(reference)n Hadron productionn Cross sectionn Fragmentation function

pA collisions(control)n Initial staten Nuclear PDF(parton distribution in A)“Small system”
high multiplicity pp & pA eventsn Produced several partons in same timen parton-parton interaction𝑞"n Observed QGP like signals
4AA collisions(QGP)

Interaction ?

qq𝑞"n Property of QGP
n Parton dynamics in
hot & dense QCD matter(strong color filed)pp : Hadron production via heavy flavour (1)
charm

103

PHENIXSTARbeautyJHEP 05 (2021) 220
dσbb/dy |y =0 (µb)

ALICEdσcc/dy ||y |<0.5(µb)

arXiv:2105.06335

102

PHENIX pp, |y |<1.5UA1 pp, |y |<1.5
CDF pp, |y |<0.610102
1FONLL
NNLO

10−24×10−1−110 2×10

10−110−1

12 34

10s (TeV)

ALI−PUB−496403

ALICE pp

FONLL
NNLO

2×10−1b → D |y |<0.5

dielectron |ηe|<0.8b → J/ ψ |y |<0.9

fit with PYTHIA6
fit with POWHEG

b → e |y |<0.8

123 4 5 6 7 8 1020s (TeV)

ALI-PUB-488622

n Heavy flavour --- produced by initial hard scattering=> good measurements to understand particle production based on QCD
n Total heavy flavour (charm and beauty) productions are in good agreement with pQCD predictions5pp : Hadron production via heavy flavour (2)f (c → Hc)

arXiv:2105.06335

1.0

n Charm fragmentation function fractions measured including
charm baryons (Λc and Ξc) for the first time at the LHC

ALICE, pp, s = 5.02 TeV
B factories, e e−, s = 10.5 GeV+0.8LEP, e e−, s = mZ+HERA, ep, DIS

0.6

HERA, ep, PHP

0.4n Charm fragmentation fractions in pp collisions at the LHC
differ significantly from those e+e- and ep collisions

0.2

n Indicate additional hadronization process
D0ALI-PUB-488617

6D+D+sΛ+c

Ξ0c

D*+

pp : Hadron production via heavy flavour (3)arXiv:2０11.06079

n Λc / D0 ratio as a function of pTn Clear enhancement in lower pT w.r.t. Λc / D0 in e+e- (~0.1)
n PYTHIA8 + Color reconnection (CR)n CR --- allow reshuffle the colors before hadronizatione+en Catania --- quark coalescencen Assume free quarks form hadrons (in QGP) & thermalizaionn SHM + RQM --- statistical hadronization7

pp : Charm & strangeness hadron production vs. multiplicityn Λc / D0 ration increase with charged multiplicity
up to dN/dη ~50
n K0s, Λ, Ξ, Ω production w.r.t π
n Contain strange quarkn Also increase with multiplicity
up to dN/dη ~50
n The trend catch up withPYTHIA + color reconnectionn Indicate same hadronimzation mechanism
between light (s) and heavy (c) quarks
n color reconnection play a role8

pp : Long range correlation in high multiplicity pp events
arXiv:2101.03110

n Long range (large rapidity correlation) in near-side (Δφ ~ 0) in high multiplicity
pp collisions (0-0.1% V0M)
n Such the correlation also observed in Pb-Pb collisionsn Near-side correlation in high multiplicity events are reproduced by
n PYTHIA + color reconnectionn EPOS (include 3D+1 ideal hydro)
9

pPb : Initial state- Gluon distribution at low x
EPJ C81 (2021) 712

dσ/dy (mb)n Parton (gluon and quark) distribution in nucleus (nPDF)
n effect total particle production in heavy-ion collisions

14

ALICE Pb+Pb → Pb+Pb+J/ψ

s NN = 5.02 TeV

ALICE coherent J/ψ
Impulse approximation
STARLIGHT
EPS09 LO (GKZ)
LTA (GKZ)IIM BG (GM)
IPsat (LM)BGK-I (LS)GG-HS (CCK)b-BK (BCCM)

12108No shadowing

642

n photo production of J/Ψ give access to the shadowing ofgluon at low Bjorken-x

0−4

ALI-PUB-482756−3−2−101yModerate shadowing of 0.65 at x ~ 6x10-410(N +µ ←W+- Nµ- ← W-) / (N +µ ←W++ Nµ- ← W-)

pPb : Initial state- Quark distribution at low & high x
JHEP09(2020)076

1.2
10.8
0.60.4

ALICE preliminarysNN = 8.16 TeV

p−Pb, s NN = 8.16 TeV

MCFM + CT14
MCFM + CT14 + EPPS16

p > 10 GeV/c
T

0.20free PDF−0.2−0.4

with nPDF

−0.6
−0.8

ALI−PREL−351947−4−2024y cms
ALI-PUB-347344

n W/Z boson productionsn Predominatly via a quark – antiquark pair annihilation (Drell-Yan)n 𝑢𝑑̅ → 𝑊 ) , 𝑑𝑢" → 𝑊 * , and 𝑞𝑞" → 𝑍
n Sensitive to quark and antiquark content in nucleon / nucleus
n Difference in pp & p-Pb (Pb-Pb) --- nuclear Parton Distribution Function (nPDF)
n W charge asymmetry --- sensitive to the down / up ratio (isospin)
11

R AA

PbPb : Parton – medium interaction ; Parton energy loss (1)ALICE Preliminary

1.4

Pb-Pb, s NN = 5.02 TeV

1.2

0-10%, |y |<0.5

10Non-prompt D

0.80Prompt D

Energy loss

0.60.4Gluon shadowingn Interaction between partons and QGP
n Low pT : Elastic scattering (collisional energy loss)n High pT : Gluon bremsstrahlung in color field (radiative energy loss)n Radiative energy loss (QCD base prediction)n Smaller energy loss for heavy quark than for light quark
due to “dead cone” effectn Bremsstrahlung probability ∝ 1/(θ2 + (m/E)2)2
n Eloss(g) > Eloss(u,d,s) > Eloss(c) > Eloss(b)0.2

1ALI−PREL−345870

Prompt; c->DNon-prompt; b->c->D1210p (GeV/c)n Both charm and beauty lose energy in QGP

Tn Smaller RAA of non-prompt (from B decay) than D mesonsn Indicate smaller energy loss of beauty than charm

Q pPb

PbPb : Parton – medium interaction ; Parton energy loss (2)n RAA for full jetsn cluster of hadron made by partonn Address parton kinematic

1.8
1.6

Centrality classes (ZNA)
0-20%
20-40%
40-60%
60-80%80-100%

ALICE p-Pb sNN = 5.02 TeV
FastJet anti-k T jets, |η | < 0.5
lab
Reference: scaled pp jets 7 TeV

1.4
1.2
10.8
0.6pPb

0.4PbPb

Q pPb0.21.8
1.6

Resolution parameter R = 0.4
Centrality classes (ZNA)
0-20%
20-40%
40-60%
60-80%
80-100%

ALICE p-Pb sNN = 5.02 TeV
FastJet anti-k T jets, |η | < 0.5lab
Reference: scaled pp jets 7 TeV

1.4

q/g

1.2
10.8
0.6
0.4
ALI-PREL-351715

0.2

Resolution parameter R = 0.2020

n Difficulty jet measurement in low pT in PbPbn Large contribution from Underlying events used Machine learning techniqe
n Strong suppression of full jets in PbPb => indicate parton level energy loss
n Not observed the suppression in small system (pPb)
ALI-PUB-105240

13406080100pT, ch jet120(GeV/c )PbPb : Parton – medium interaction ; modification jet shape
arXiv : 2107. 12984

n The core of jets (leading & sub-leading particles) are narrowerin Pb-Pb compared to pp
n Find first hard splitting by soft drop groomingn First direct experimental evidence for the modificationof angular scale of jets in heavy-ion collisions
14PbPb : Azimuthal anisotropy (v2)
PRL 126 (2021) 162001
π±K±p+p

ALICE Pb−Pb sNN = 5.02 TeV|y | < 0.5, 20−30%0.3v2v 2{2, |∆ η|>2}

JHEP 09 (2018) 006
0.4
0.3
0.2ALICEb (→ c) → e
MC@sHQ+EPOS2 (20−40%)
PHSD
Elliptic Blast Wave
LIDO

0.2

|y | < 0.8

0.1

0.1
0024681012140p (GeV/c )ALI−PUB−324743

n Azimuthal anisotropy

30−50% Pb−Pb, s NN = 5.02 TeV

T−0.10n dN/d(φ-ψRP) = …+ N0(1+2v2cos(2(φ-ψRP))) +…
n Low pT; collectivity, driven by pressure gradient in the systemn High pT; path-length dependence of enery lossn Non-zero v2 from light to heavy quarks
n Clear mass dependence; v2 (light) > v2 (heavy)

ALI−PUB−490995

1512345678p T (GeV/c )PbPb : Azimuthal anisotropy (v2) from pp to PbPb
n vn measurements from pp to PbPb (mult. dependence)n Similar values of vn in pp, pPb and PbPb at low multiplicity
n Both hydro & PYTHIA are not well reproduced thev2 in pp at 13 TeV
n PYTHIA + Shoving (CR base) at high multiplicity
n Reproduced the pT dependence

arXiv:2010.07595
16

PRL 123 142301 (2019)

PbPb : transport propertyn Large suppression and v2 for D mesons
n Sensitive to medium transport propertyn Several models reproduce the measurementn Models use heavy-quark diffusion coefficient ; 1.5 < 2πDT < 4.5
17

Future plan in ALICE : ALICE Run3 & Run4n 50 kHz Pb-Pb event readout raten Previously ~ 1 kHz in the central barreln Physics goaln Heavy-flavour mesons and baryons
n Charmonium
n Dileptons from QGP radiationn High-precision measurement of light and hyper nuclein FoCal --- Tsukuba-group contribution (lead by T. Chujo)
18

Future plan in ALICE : ALICE Run3 (& Run4)

19

Future plan in ALICE : ALICE beyond Run4 (ALICE 3)
n ALICE 3n A new silicon-based heavy-ion
dedicated detector for Run5+(2030~)n Physics goaln Hadron formation in QGP
n QGP transport propertyn QGP radiationn Pre-hydrodynamization phasen Chirals symmetry restoration
ALICE 3 workshop @ Oct. 18-19 2021
https://indico.cern.ch/event/1063724/

20

Summary} Goal of the ALICE experiment}

Understand Quark-Gluon plasma} Recent results}

Important to understand multi-parton interaction for the results in PbPb} v2 & baryon enhancement also observed in small system} QCD base calculation (PYTHIA + Color reconnection) reproduced both results}

Improved knowledge of the energy loss
} Flavour dependent energy loss predicted by QCD}

Experimental observation for parton medium interaction} modification of jet shape in PbPb21