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Hard processes Small collision systems Other fun stu� with heavy ions Summary
Heavy Ion Physicspart II
Korinna Zapp
Lund University
ESHEP 2019
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 1 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
First lecture: summary
I heavy ion collisions: unique opportunity to study matter atextreme conditions (temperature and pressure)
I formation of new phase of QCD matter: quark-gluon plasma→ decon�nement, chiral symmetry restoration
I QGP: only strongly coupled system of Standard Modelmicroscopic degrees of freedom
I what we have learned so farI QGP created in heavy ion collisions at RHIC and LHCI �rapid hydrodynamisation�I QGP is a strongly coupled liquid
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 2 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Summary: stages of a heavy ion collision
I initial state:I geometry (→ Glauber model)I gluon saturation (→ colour glass condensate)
I pre-equilibirium dynamics:I successful descriptions at weak (kinetic theory) and strong
coupling (AdS/CFT)I leads to hydrodynamic regime on timescales O(1 fm/c)
I hydrodynamic expansion:I the QGP �ows → collective behaviourI least dissipative system known (η/s & 1/4π)
I hadronisation: phenomenological modeling
I hadronic re-scattering: hydrodynamics or transport theorymore important at lower beam energies
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 3 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Outline of today's lecture
Hard processesFactorisation and nuclear PDFsQuarkoniaElecroweak bosonsJets
Small collision systems
Other fun stu� with heavy ions
Summary
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 4 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Outline
Hard processesFactorisation and nuclear PDFsQuarkoniaElecroweak bosonsJets
Small collision systems
Other fun stu� with heavy ions
Summary
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 5 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Factorisation and nuclear PDFs
Hard processes: timescale
~-0.5 fm/c ~0.1 fm/c ~1 fm/c ~10 fm/c time
I hard processes: large momentum transfer Q
I corresponds to short time scales ∆t ∼ 1/Qdue to uncertainty principle
I �rst processes to happen in heavy ion collision
I time/length scales of production processes too short to feelnuclear environment
I produced hard particles traverse QGP
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 6 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Factorisation and nuclear PDFs
Factorisation of the cross section
I factorisation of the cross section:
σ(P1,P2) =∑i ,j
1∫0
dx1 dx2 fi (x1,Q2)fj(x2,Q
2)σ̂ij(x1P1, x2P2, αs,Q2)
I σ̂ij : partonic cross sectionI has perturbative expansion in αs
known: NNLO for di-jets, NLO for up to ∼ 5 jetsI short distance physics: insensitive to nature of incoming hadrons
i.e. no nuclear modi�cations
I fi (x ,Q2): parton distribution function
nuclear pdf �ts available
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 7 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Factorisation and nuclear PDFs
Nuclear PDFs: EPPS16
Eskola, Paakkinen, Paukkunen, Salgado, Eur. Phys. J. C 77 (2017) no.3, 163
I bound proton PDF de�ned as
fp/Ai (x ,Q2) = RA
i (x ,Q2)f pi (x ,Q2)
I bound neutron PDF from isospin symmetry
I Q2 dependence: DGLAP with2-loop splitting functions
I parametrise RAi and �t for
chosen free proton PDF (inthis case CT14NLO)
I other nPDF sets:nCTEQ15, DSSZ
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
10-4
10-3
10-2
10-1
1
antishadowing maximum
EMC minimum
small-x shadowing
xa xe
ye
ya
y0
EPPS16
x
RA i(x,Q
2 0)
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 8 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Factorisation and nuclear PDFs
Nuclear PDFs
Eskola, Paakkinen, Paukkunen, Salgado, Eur. Phys. J. C 77 (2017) no.3, 163
I consistent �t to all available data
I constraining data sparse → sizeable uncertainties
I modi�cations less important at higher momentum scales
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 9 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Factorisation and nuclear PDFs
Nuclear PDFs
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
10-4
10-3
10-2
10-1
1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
10-4
10-3
10-2
10-1
1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
10-4
10-3
10-2
10-1
1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
10-4
10-3
10-2
10-1
1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
10-4
10-3
10-2
10-1
1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
10-4
10-3
10-2
10-1
1
EPPS16nCTEQ15
EPPS16nCTEQ15
EPPS16nCTEQ15
EPPS16nCTEQ15
EPPS16nCTEQ15
EPPS16nCTEQ15
x x x
x x x
RPb
uV(x,Q
2=10
GeV
2)
RPb
dV(x,Q
2=10
GeV
2)
RPb
u(x,Q
2=10
GeV
2)
RPb
d(x,Q
2=10
GeV
2)
RPb
s(x,Q
2=10
GeV
2)
RPb
g(x,Q
2=10
GeV
2)
Eskola, Paakkinen, Paukkunen, Salgado, Eur. Phys. J. C 77 (2017) no.3, 163
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 10 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Factorisation and nuclear PDFs
Nuclear PDFsdσ
(yZ−
0.4)
/dσ
(−y Z−
0.4)
yZ − 0.4
EPPS16
No nuclear effects
60 GeV < M`+`− < 120 GeV
|η`±lab| < 2.4
pT(`±) > 20 GeV
CMS data
Z production, pPb,√s = 5.02 TeV
dσ(η−
0.465)/dσ(−η−
0.465)
η − 0.465
EPPS16
nCTEQ15
DSSZ
|ηjetlab| < 3.0
psubleadingT > 30 GeV
pleadingT > 120 GeV
CMS data
dijetspPb√s = 5.02 TeV
Eskola, Paakkinen, Paukkunen, Salgado, Eur. Phys. J. C 77 (2017) no.3, 163
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 11 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Quarkonia
Quarkonium suppression: idea
I in decon�ned medium: colour screeningI attractive force between quark and anti-quark screened
-1000
-500
0
500
1000
0 0.2 0.4 0.6 0.8 1 1.2 1.4
F(L,T)[MeV]
L[fm]
T/Tc T/Tc
1.01 1.02 1.03 1.10 1.15 1.22 1.32
1.43 1.66 1.86 2.16 2.45 2.79
Ewerz, Kaczmarek, Samberg, JHEP 1803 (2018) 088 [arXiv:1605.07181]
I should lead to dissociation of bound statesI suitable states to observe this: charmonium & bottomonium
Matsui & Satz, 1986
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 12 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Quarkonia
J/Ψ suppression
⟩ part
N ⟨0 50 100 150 200 250 300 350 400
AA
R
0
0.2
0.4
0.6
0.8
1
1.2
1.4 12%±<4 global sys.= y = 2.76 TeV), 2.5<
NNsALICE (PbPb
9.2%±|<2.2 global sys.= y = 200 GeV), 1.2<|NN
sPHENIX (AuAu
12%±|<0.35 global sys.= y = 200 GeV), |NN
sPHENIX (AuAu
ALICE, Phys. Rev. Lett. 109 (2012) 072301 [arXiv:1202.1383]
3 clear suppression of J/Ψ
7 weaker suppression at higher cms energy
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 13 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Quarkonia
J/Ψ regeneration
I charm quarks produced earlyin a hard processes
too heavy for thermal production
I quark move quasi-freely inQGP phase
picture: J. Stachel
I at phase boundary J/Ψ production by combinatorics
I J/Ψ production rate depends sensitively on charm cross section
I e�ect increases rapidly with cms energy
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 14 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Quarkonia
Sequential suppression
state J/Ψ Ψ′ Υ Υ′ Υ′′
mass [GeV] 3.10 3.68 9.46 10.02 10.36
∆E [GeV] 0.64 0.05 1.10 0.54 0.20
r [fm] 0.25 0.45 0.14 0.28 0.39
I expect dissociation at di�erent temperatures
I �QGP thermometer�
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 15 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Quarkonia
Sequential suppression
CMS, Phys. Rev. Lett. 109 (2012) 222301 [Erratum: Phys. Rev. Lett. 120 (2018) no.19, 199903]
Guillermo Breto Rangel for CMS, Quark Matter 2012
I there is a clear trend
I the story is actually much more complicatedstatic potential over-simpli�ed, quarkonia not produced at rest, . . .
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 16 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Elecroweak bosons
Nuclear modi�cation factors
I standard procedure for quantifying QGP e�ects: divide by resultfrom p+p
I but: have to scale p+p result by number of N-N collisionshard processes scale like Ncoll
RAA({·}) =
dσXd{·}
∣∣∣AA
〈Ncoll〉 dσXd{·}
∣∣∣pp
I deviations from unity signal e�ects beyond incoherentsuperposition of nucleon-nucleon collisions
I in case of electroweak processes: have to take di�erent isospincomposition into account
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 17 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Elecroweak bosons
W & Z production
partN0 50 100 150 200 250 300 350 400
AA
R
0
0.5
1
1.5
2
2.5 = 2.76 TeV
NNsCMS
> 0 GeV/cT
, |y| < 2.0, pµµ →Z , 0-100% centralityµµ →Z
> 0 GeV/cT
ee, |y| < 1.44, p→Z ee, 0-100% centrality→Z
pp luminosity uncertainty
CMS, JHEP 1503 (2015) 022 [arXiv:1410.4825] ATLAS arXiv:1907.10414
I no signi�cant deviation from unity
I W and Z don't interact strongly → leave dense interactionregion without re-scattering
I important con�rmation of Ncoll scaling and nPDFs
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 18 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Second main discovery of heavy ion physics
Jet quenching: Hard jets are suppressed and their structure modi�ed.
I proton-proton collisions: 2 jets with balancing transversemomentum
I in heavy ion collisions: signi�cant softening of jets
→ thermalisation of a far-from-equilibrium system
→ jet quenching informs us about equilibration in QCD
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 19 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Suppression of single-inclusive jets
[GeV]T
p
AA
R
0
0.5
1
1.5
100 200 300 400 500 600 900000
0 - 10 %30 - 40 %60 - 70 %
PreliminaryATLAS = 5.02 TeVNNs = 0.4 jets, R tkanti-
| < 2.8y|
-12015 Pb+Pb data, 0.49 nb-1 data, 25 pbpp2015
ATLAS-CONF-2017-009
I suppression of jets by factor 2 relative to expectation from p+pneed to scale p+p reference by number of hard N+N collisions
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 20 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Di-jet momentum asymmetry
0 0.2 0.4 0.6 0.8 1
Eve
nt F
ract
ion
0
0.05
0.1
0.15
0.2
0.25
0.3
70-100%
CMS
0 0.2 0.4 0.6 0.8 1
Eve
nt F
ract
ion
0
0.05
0.1
0.15
0.2
0.25
0.3
20-30%
0 0.2 0.4 0.6 0.8 1E
vent
Fra
ctio
n0
0.05
0.1
0.15
0.2
0.25
0.3 = 2.76 TeVNN
sPbPb
-1bµLdt = 150 ∫
= 2.76 TeVspp -1
Ldt = 231 nb∫PYTHIA+HYDJET
50-70%
)T,2
+pT,1
)/(pT,2
-pT,1
= (pJA0 0.2 0.4 0.6 0.8 1
Eve
nt F
ract
ion
0
0.05
0.1
0.15
0.2
0.25
0.3
10-20%
(e) 0 0.2 0.4 0.6 0.8 1
Eve
nt F
ract
ion
0
0.05
0.1
0.15
0.2
0.25
0.3
30-50%
(PFlow), R = 0.3TAnti-k
> 120 GeV/cT,1
p
> 30 GeV/cT,2
p
π32 >
12φ∆
0 0.2 0.4 0.6 0.8 1E
vent
Fra
ctio
n0
0.05
0.1
0.15
0.2
0.25
0.3
0-10%
CMS, Phys. Lett. B 712 (2012) 176
I enhancement of asymmetric con�gurations
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 21 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Intra-jet energy distribution: Jet pro�le
CMS, Phys. Lett. B 730 (2014) 243
I suppression of activity at intermediate r
I increase near the edge of the jet
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 22 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Intra-jet energy distribution: fragmentation function
z =p⊥,hp⊥,J
cos(∆RhJ)
z
-110 1D
(z)
R0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
0-10%/60-80%
>100 GeVjet
Tp
R=0.4Tanti-k
ATLAS=2.76 TeVNNsPb+Pb
-10.14 nb
z
-110 1
D(z
)R
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
30-40%/60-80%
ATLAS=2.76 TeVNNsPb+Pb
-10.14 nb
z
-110 1
D(z
)R
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
DataSystematic Uncertainty
10-20%/60-80%
ATLAS=2.76 TeVNNsPb+Pb
-10.14 nb
z
-110 1D
(z)
R0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
40-50%/60-80%
ATLAS=2.76 TeVNNsPb+Pb
-10.14 nb
z
-110 1
D(z
)R
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
20-30%/60-80%
ATLAS=2.76 TeVNNsPb+Pb
-10.14 nb
z
-110 1
D(z
)R
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
50-60%/60-80%
ATLAS=2.76 TeVNNsPb+Pb
-10.14 nb
ATLAS, Phys. Lett. B 739 (2014) 320
I distribution of hadrons inside jets
I suppression at intermediate & enhancement of soft momenta
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 23 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
A �rst lesson
Summary of experimental results
I jet production suppressed by factor ∼ 2 up to p⊥'s of 1 TeV
I hard structures inside jets survive largely unmodi�ed
I enhancement of soft activity far away from jet axis
A �rst lesson to be learned
I energy loss from jets driven by peeling o� ofsoft gluons
I rare, semi-hard emissions not an importante�ect
I both were equivalent in early calculations
Casalderrey-Solana, Milhano, Wiedemann, J. Phys. G 38 (2011) 035006 [arXiv:1012.0745]
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 24 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
What is unique about jet quenching
I �calibrated� probe: well understood in p+p�xed order matrix elements + resummation (parton showers)
I jet quenching allows to observe process of equilibrationsoft observables see result of equilibration
I jets give access to scale dependence of medium properties
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 25 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
What happens to jets in medium?
Scenario I: hard partons don't resolve quasi-particles
I interactions between jet & medium at large coupling
I AdS/CFT techniques
Scenario II: hard partons do resolve quasi-particles
I jet � medium interactions at weak(ish) coupling
I perturbative techniques
I thermalisation through elastic re-scattering (slow)
I parton energy loss through QCD bremsstrahlung
I destructive interference in multiple scattering LPM e�ect
relevant scale: momentum transfer q between hard parton and medium
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 26 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Jet quenching at strong coupling
Advantages:
1. exact solution of gauge theory at strong coupling
2. no uncertainty in jet-medium interaction
Fundamental problems:
1. jets are a weak-coupling phenomenon
2. QCD is not N = 4 SYM
�holographic jet�:qq̄ pair in QGP dual to classicalstring in black hole geometry
jet
hydrodynamicmodes
boundary
horizon
falling string
Chesler, Jensen, Karch, Ya�e, Phys. Rev. D 79 (2009) 125015
Chesler & Rajagopal, JHEP 1605 (2016) 098
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 27 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
How long does it take to radiate a gluon?
kµ = (ω, ~k⊥, k‖)
p′µ = (E ′, ~p′⊥, p′‖)
pµ = (E , 0, 0, p‖)
= (kµ + p′µ)
θ
assume: massless quark
I virtual state: p2 = E 2 − p2 6= 0 → m2virt = p2
I uncertainty principle: 1 = ∆t ∆E = ∆t mvirt
I gluon formation time: tform = ∆t × (boost factor)
tform =1
mvirt
E
mvirt=
E
2pµkµ' E
ωEθ2' ω
k2⊥
I time for entire jet evolution: O((1− 10) fm)I (transverse) size of medium: O((1− 10) fm)
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 28 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Bremsstrahlung in medium: heuristic discussionBaier, Dokshitzer, Mueller, Peigne, Schi�, Nucl. Phys. B 483 (1997) 291
Baier, Schi�, Zakharov, Ann. Rev. Nucl. Part. Sci. 50 (2000) 37ω, k⊥
E
E � ω � k⊥, q⊥
Brownian motion of the gluon:⟨k2⊥⟩
= q̂Lformation time of the radiated gluon:
tf 'ω
k2⊥' ω
q̂tf⇒ tf =
√ω
q̂and Ncoh =
tfλ
gluon energy spectrum:
d2I coh
dωdy' 1
Ncoh
d2I incoh
dωdy∝ αs
ωλλ
√q̂
ω= αs
√q̂ ω−3/2 radiative energy
loss: ∆E =
L∫0
dy
ωc∫0
dω ωd2I
dωdy∝ αsq̂L
2
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 29 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Beyond parametric estimates
Eikonal (straight line) propagation
I interactions result in colour phase rotation
I in-medium propagator: Wilson line
W (xf +, xi+; x⊥) = P exp
ig
xf +∫xi+
dξ A−(ξ, x⊥)
path ordering medium colour �eld
Further developments
I non-eikonal propagation
I 2-gluon emission
I resummation of incoherent emissions
I . . .Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 30 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
From partons to jets: antennae
I consider colour singlet dipole in medium
I in vacuum colour coherence leads to angular ordering of radiation
I re-scattering in medium introduces new scale: q⊥I medium modi�cations depend on whether dipole is resolved
d⊥
q⊥
d⊥
q⊥
I in particular: unresolved structures remain unperturbed
Casalderrey-Solana, Mehtar-Tani, Salgado, Tywoniuk, Phys. Lett. B 725 (2013) 357
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 31 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
From partons to jets: antennae
I decoherence time scale: τd ∼(
1
q̂θ2qq̄
)1/3
I decoherence opens up phase space
I in soft limit: geometric separationMehtar-Tani, Salgado, Tywoniuk, JHEP 1204 (2012) 064 doi:10.1007/JHEP04(2012)064 [arXiv:1112.5031]
I can be generalised to jets
Casalderrey-Solana, Mehtar-Tani, Salgado, Tywoniuk,
Phys. Lett. B 725 (2013) 357 [arXiv:1210.7765]
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 32 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Medium response
I medium response: medium's reaction to energy & momentumdeposited by jet
I gives rise to additional soft activity
I momentum conservation → additional particles follow jetdirection
I correlated background
background
jetI correlated background cannot
and should not be subtracted
I rather, it is part of jet
I �uctuations matter
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 33 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Medium response
I medium response: medium's reaction to energy & momentumdeposited by jet
I gives rise to additional soft activity
I momentum conservation → additional particles follow jetdirection
I correlated background
background
jetbackground
correlated I correlated background cannotand should not be subtracted
I rather, it is part of jet
I �uctuations matter
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 33 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Medium response
I medium response: medium's reaction to energy & momentumdeposited by jet
I gives rise to additional soft activity
I momentum conservation → additional particles follow jetdirection
I correlated background
background
jet correlatedbackground
I correlated background cannotand should not be subtracted
I rather, it is part of jet
I �uctuations matter
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 33 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Particle distribution outside jets
0 0.2 0.4 0.6 0.8 1
r∆ddNje
tN1
Y=
0
10
20
30
40 pp reference
< 1 GeVtrk
T0.7 < p
< 2 GeVtrk
T1 < p
< 3 GeVtrk
T2 < p
< 4 GeVtrk
T3 < p
< 8 GeVtrk
T4 < p
< 12 GeVtrk
T8 < p
< 16 GeVtrk
T12 < p
< 20 GeVtrk
T16 < p
< 20 GeVtrk
T0.7 < p
0 0.2 0.4 0.6 0.8 1
r∆ddNje
tN1
Y=
0
10
20
30
40 PbPb50-100%
0 0.2 0.4 0.6 0.8 1
r∆ddNje
tN1
Y=
0
10
20
30
40 PbPb30-50%
0 0.2 0.4 0.6 0.8 1
r∆ddNje
tN1
Y=
0
10
20
30
40 PbPb10-30%
0 0.2 0.4 0.6 0.8 1
r∆ddNje
tN1
Y=
0
10
20
30
40 PbPb0-10%
r∆0 0.2 0.4 0.6 0.8 1
pp -
YP
bPb
Y
0
5
10
15PbPb - pp50-100%
r∆0 0.2 0.4 0.6 0.8 1
0
5
10
15
PbPb - pp30-50%
r∆0 0.2 0.4 0.6 0.8 1
0
5
10
15
PbPb - pp10-30%
r∆0 0.2 0.4 0.6 0.8 1
0
5
10
15
PbPb - pp0-10%
CMS r∆Particle yield vs. (5.02 TeV)-1bµ (5.02 TeV) PbPb 404 -1pp 27.4 pb
|<1.6jet
η> 120 GeV, |T
R=0.4 jets, pTanti-k
0 0 0 1
CMS,CMS-HIN-16-020,arXiv:1803.00042
I enhancement of soft particles far away from jet
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 34 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Jets
Some theory results
0.0 0.1 0.2 0.3∆r
0.4
0.6
0.8
1.0
1.2
1.4
1.6
ρ(∆r)PbPb/ρ(∆r)pp
Pb-Pb @ 2.76TeV (0-10%)anti-kT R=0.3p jetT >100GeV/c, p trkT >1GeV/c0.3<|ηjet |<2.0
without recoil
with recoil (pcut=4T)
CMS 0-10%Park,Jeon,Gale,arXiv:1807.06550
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pTjet > 100�GeV/c��R= 0.3
q̂q,0= 1.7�GeV2/fm��ωcut = 1.0�GeV/c
pTtrk, hyd > 1.0�GeV/c
ρ PbPb(r)/ρpp(r)
r
�����������������������0-10 %�
Tachibana,Chang,Qin,
Phys.Rev.C95(2017)no.4,044909
b
b
b
b
b
b
0 0.05 0.1 0.15 0.2 0.25 0.30.4
0.6
0.8
1
1.2
1.4
1.6
w/o Recoils
w/ Recoils 4MomSub
CMSb
anti-k⊥ R=0.3, |ηjet| < 2
pjet⊥ > 100 GeV
JEWEL+PYTHIA (0 − 10%), Pb+Pb√s = 2.76 TeV
r from jet axis
ρ(r
)PbPb/ρ
(r)p
p
Kunnawalkam
Elayavalli,Zapp,
JHEP1707(2017)141
CMS
sNN = 2.76 TeVR = 0.3, 0.3<È Η È<2
pT > 100 GeV
centrality 0-10%
0.00 0.05 0.10 0.15 0.20 0.25 0.300.4
0.6
0.8
1.0
1.2
1.4
1.6
r
Ρ HrLPbPb
Ρ HrLpp
All effects
CNM+RAA
CNM only
Chien,Vitev,
JHEP1605(2016)023
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 35 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Outline
Hard processesFactorisation and nuclear PDFsQuarkoniaElecroweak bosonsJets
Small collision systems
Other fun stu� with heavy ions
Summary
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 36 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Third main discovery of heavy ion physics
I (partial) equilibration of �nal state in A+AI expectation: p+p qualitatively di�erent from A+A
p+p collisions too dilute to develop collectivity
I observed:
Soft particle production in high-multiplicity p+p and p+A closelyresembles A+A, but so far no jet quenching is observed.
offlinetrkN
0 50 100 150
2v
0.05
0.10 = 13 TeVspp
< 3.0 GeV/cT
0.3 < p
| < 2.4η|
CMS
|>2}η∆{2, |sub2v{4}2v{6}2v{8}2v{LYZ}2v
offlinetrkN
0 100 200 300
2v0.05
0.10 = 2.76 TeVNNsPbPb
< 3.0 GeV/cT
0.3 < p
| < 2.4η|
offlinetrkN
0 100 200 300
2v
0.05
0.10 = 5 TeVNNspPb
< 3.0 GeV/cT
0.3 < p
| < 2.4η|
CMS,Phys.Lett.B
765(2017)193
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 37 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Strangeness enhancement
I strong increase of strangeparticle production withmultiplicity
I traditional view: strangenessproduction in p+p suppressiondue to s quark mass
I strangeness practicallyequilibrated in Pb+Pbcollisions at LHC
I strangeness enhancementcounted as signal forformation of hot system
ALICE, Nature Phys. 13 (2017) 535
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 38 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Unmodi�ed observables
[GeV/c]T
p30 40 50 100 200 300
pPb
R*
0.5
1
1.5 = 5.02 TeV NNs pPb
| < 0.5, R = 0.3CM
ηCMS (0-100%), |
| < 0.3, R = 0.4CM
ATLAS (0-90%), | y
[GeV]T
p
10 15 20 25 30 35 40pP
bR
0.6
0.8
1
1.2
1.4
1.6
1.8-1 = 5.02 TeV, L = 28 nbNNs+Pb, p
-1 = 5.02 TeV, L = 25 pbs, pp
ATLASψPrompt J/
-2.0 < y* < 1.5
CMS, Eur. Phys. J. C 76 (2016) no.7, 372 [arXiv:1601.02001]
ATLAS, Eur. Phys. J. C 78 (2018) no.3, 171 [arXiv:1709.03089]
I no suppression of jets and J/Ψ in p+Pb
I large suppression in Pb+Pb collisions
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 39 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Possible explanations for vn's in p+p
Final state interactions
azimuthal anisotropies due to response to initial geometry
I hydrodynamics Weller, Romatschke, Phys. Lett. B 774 (2017) 351
I kinetic theory Kurkela, Wiedemann, Wu, Phys. Lett. B 783 (2018) 274
Initial state correlations
initial state correlations imprinted on �nal state
I color-glass condensate Schenke, Schlichting, Venugopalan, Phys. Lett. B 747 (2015) 76
Alternative explanations
models inspired by p+p physics
I string shoving Bierlich, Gustafson, Lönnblad, Phys. Lett. B 779 (2018) 58 [arXiv:1710.09725]
at hadronisation densely packed strings repel each other
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 40 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
The escape mechanism
I kinetic theory set-up:Kurkela, Wiedemann, Wu, Phys. Lett. B 783 (2018) 274
I initially isotropic particle distributionI with spatial anisotropyI number of scatterings O(1)I scattering isotropises particlesI anisotropic scattering probabilityI generates vn's closely resembling hydrodynamic vn's
I also observed in transport code AMPTHe, Edmonds, Lin, Liu, Molnar, Wang, Phys. Lett. B 753 (2016) 506
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 41 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Important di�erences between small and large systems
I multiplicity generated in di�erent ways:I Pb+Pb: requiring high multiplicity biases towards central eventsI p+p/Pb: requiring high multiplicity biases towards jetty events
I not clear what multi-particle correlations measure in jetty events
dijetη
-2 -1 0 1 2 3
dije
tηd
dije
tdN
<0]
dije
tη[
dije
tN
1
0
0.2
0.4
0.6
0.8
1
1.2
-1CMS pPb 35 nb = 5.02 TeVNNs
> 120 GeV/cT,1
p > 30 GeV/c
T,2p
/3π > 21,2
φ∆
(b)< 2020 - 2525 - 3030 - 40> 40
classes (GeV): |<5.2η4<|
TE
CMS, Eur. Phys. J. C 74 (2014) no.7, 2951
I strong auto-correlations insmall systems, e.g. betweenjets and forward multiplicity
I example: rapidity shift ofdi-jets due to energyconservation
Armesto, Gülhan, Milhano, Phys. Lett. B 747 (2015)
441 [arXiv:1502.02986]
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 42 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Outline
Hard processesFactorisation and nuclear PDFsQuarkoniaElecroweak bosonsJets
Small collision systems
Other fun stu� with heavy ions
Summary
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 43 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Ultra-peripheral collisions
I relativistic ions are sources of strong electric �elds
I evidence for γγ → γγscattering
~v −c
=
Z
Zem−fields
em−fields
~
v c~~Pb
Pb
. .
Pb
Pb
. .
Pb
Pb
. .
Pb82+
Pb82+
Pb82+
Pb82+
X
γ
γ
acoplanarityγγ0 0.01 0.02 0.03 0.04 0.05 0.06
Eve
nts
/ 0.0
05
0
2
4
6
8
10
12
14 ATLAS
= 5.02 TeVNNsPb+Pb
Signal selectionno Aco requirement
-1bµData, 480 MC γγ→γγ
MC -e+e→γγ MC γγCEP
ATLAS, Nature Phys. 13 (2017) no.9, 852 [arXiv:1702.01625]
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 44 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Search for the chiral magnetic e�ect
I spectator protons generate strong B �eld (1018 − 1020 G)I quark interactions with topological gluon con�gurations can
induce chirality imbalance and local parity violationI leads to electric charge separation along direction of magnetic
�eld → chiral magnetic e�ectI leads to charge dependent elliptic �ow
Belmont, Nucl. Phys. A 931 (2014) 981 [arXiv:1408.1043]
ALICE, Phys. Rev. C 93 (2016) no.4, 044903 [arXiv:1512.05739]
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 45 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Outline
Hard processesFactorisation and nuclear PDFsQuarkoniaElecroweak bosonsJets
Small collision systems
Other fun stu� with heavy ions
Summary
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 46 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Wrap-up
I heavy ion collisions allow to study fundamental questions instrong interaction physics
I three main discoveries of heavy ion physics:1. hydrodynamic behaviour
I QGP behaves as an almost perfect liquidI lowest η/s observed, close to theoretical lower bound of 1/4π
2. jet quenchingI partial thermalisation of a far-from-equilibrium systemI informs us about how the QGP came into beingI gives access to scale dependence of QGP properties
3. similarity between p+p/p+A and A+A collisionsI exciting, but no �rm conclusions yet
I many more exciting phenomenasome of which I discussed, others I had to leave out
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 47 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Wrap-up
I heavy ion physics is new physics
I rich and diverse phenomenology
I have to develop new theoretical tools usingI classical �eld theoryI AdS/CFTI thermal �eld theoryI kinetic theory/transport theoryI relativistic hydrodynamicsI e�ective �eld theoriesI zero-temperature �eld theory (in particular perturbation theory)I phenomenological models
I also new experimental techniques needede.g. variety of correlations, background subtraction for jets, . . .
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 48 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Wrap-up
I heavy ion physics is��new unexplored physics
I rich and diverse phenomenology
I have to develop new theoretical tools usingI classical �eld theoryI AdS/CFTI thermal �eld theoryI kinetic theory/transport theoryI relativistic hydrodynamicsI e�ective �eld theoriesI zero-temperature �eld theory (in particular perturbation theory)I phenomenological models
I also new experimental techniques needede.g. variety of correlations, background subtraction for jets, . . .
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 48 / 48
Hard processes Small collision systems Other fun stu� with heavy ions Summary
Wrap-up
I heavy ion physics is��new unexplored physics
I rich and diverse phenomenology
I have to develop new theoretical tools usingI classical �eld theoryI AdS/CFTI thermal �eld theoryI kinetic theory/transport theoryI relativistic hydrodynamicsI e�ective �eld theoriesI zero-temperature �eld theory (in particular perturbation theory)I phenomenological models
I also new experimental techniques needede.g. variety of correlations, background subtraction for jets, . . .
I heavy ion physics is a broad, multifaceted and exciting �eld
Korinna Zapp (Lund University) Heavy Ion Physics ESHEP 2019 48 / 48