Heavy Ion Physics at the LHC What's new ? What's next ?

Heavy Ion Physics at the LHCWhat's new ? What's next ?

1Dec. 2013 Kyoto J. Schukraft

Selected Results from the LHC New light on old puzzles Towards precision measurements of QGP properties Discoveries

Some VERY preliminary Stuff Rocky Horror Picture Show

Dec. 2013 Kyoto J. Schukraft2

Large 'Hadron Collider' Lake GenevaDesign Energy:

14 TeV (pp) 1150 TeV (PbPb)

CMS

ATLAS

LHCb

ALICE

4 Large Experiments, all participate in HI program (pA, AA)

Collider of 'Large Hadrons'

p + pPb + Pb

What is different ? What is new ? What is different ? Same physics with ..

different 'matter:' increased energy (up to factor ~30 in √s ) QGP will be 'hotter - larger - longer living' large cross section for 'hard probes' : high pT, jets, heavy quarks,…

different experiments: new generation, large acceptance state-of-the-art detectors

Atlas, CMS, Alice, [LHCb, for pA]

Where is progress@LHC ? (very limited & personal selection)New Light on Old Problems (NLOP)hadronisation/particle productionquarkonia suppression

Towards Precision Measurements (TPM) of QGP parameterselliptic flow: viscosity h/sjet quenching: opacity q^

Discoveriesthe 'Ridge': long range correlations in pp & pA

What seems odd ?New/preliminary results which don't fit easily Dec. 2013 Kyoto J. Schukraft3

NLOP I: Particle Production Hadronisation is non-pertubative

phenomenological models ('event generators') with many parameters strings or clusters, PPAR(x), x=1,..n

Statistical ('thermal') models: particle with mass m produced in 'heat bath T' according to phase space P(m) ~ e-(m/T)

Tch Temperature (ch='chemical')mb Baryo-chemical potential (baryon conservation)gs Strangeness suppression


RHIC pp SPS Pb-Pb

Tch: 160-170 MeV gs : 0.9-1 (AA), 0.5-0.6 (pp)

strangeness enhancement = QGP signal ?

Dat

a

Model

particles created per collision

accurate to O(10%) (no 'a priori' justification)

Dynamical Origin of Thermal Ratios ? 'born into equilibrium' (e+e-, pp, AA) at the QCD phase boundary Tc ≈

Tch

yields ~ QCD x (hadronic) phase space many channels => PS dominates pp gs < 1 : QCD, ms

?: which dynamics makes strangeness enhancement in AA (gs ≈ 1) ?

'evolving into equilibrium' (AA) thermodynamics in parton/hadron phase arbitrary (eg pp-like) initial hadron ratios + inelastic reactions reach equilibrium close to phase boundary (Tch ~ Tc) A + B <=> C + D + E

?: Parton dynamics: why close to hadron rather than parton equilibrium ratios ? non-equilibrium models with additional 'unpredictable' free parameters ?: Hadron dynamics (expansion & cooling) => expect sequential freeze-out ? hadrochemistry timing miracle:

long enough to reach equilibrium, short enough for sudden, fixed T freeze-out


In this picture, statistical models work - in AA by design (thermodynamics), - in pp/e+e- by accident (dominance of PS).Conceivable, but limited direct evidence..Deviations from equilibrium would be most informative !

Particle Ratios at LHC


pp: Less well described than at lower energies ? fits 2 ratios with 2 parameters (T, mB) maybe finally 'hard QCD processes' (ME, dynamics) become visible over PS ?

RHIC pp

pp fit should be updated

better & more hadrons available now

https://aliceinfo.cern.ch/Figure/sites/aliceinfo.cern.ch.Figure/files/Figures/nsharma/2011-May-22-ThermalComp6.gif




Strangeness is enhanced +30% (K), > factor 3 (W) gs = 1, like thermal modelp/p off by factor > 1.5 from predictions !suppressed, not enhanced, compared to pp

Particle Ratios Pb-Pb


?

initially very surprising result (safest prediction for LHC !)

(Prediction, no fit)

K(s)

X(ss)

W(sss)

NLOP I: Current Explanations SM ok, but accuracy of experiment and/or model limited to 20-30% ?

J overall not too bad, including d & 3HL

L spreads misery amongst many particlespoor chi2what about RHIC results ?


http://arxiv.org/abs/1311.4662

I expected that the SM could do better (<10%)

NLOP I: Current Explanations


Sequential Freeze-out ('afterburner')J improved fit (also RHIC/SPS)centrality dependence at LHCL more art than science..many unknown s (e.g. L + W -> np + mK)detailed balance (e.g. p + p <=> 5 p)centrality dependence at RHIC, X

'Parton-Equilibrium' Statistical Model JL 2 more free parameters gQ, gs

non-intuitive values, d & 3HL (gqn)?

would be a major change of paradigm

add inelastic hadronic reactions

Particle Production: What next ? Is there indeed a significant change from RHIC to LHC ?

clear sign of thermo-dynamics in hadron production !revisit early RHIC results (decay corrections, ..), reduce syst, errors @ RHIC &

LHC Hadro-modification (sequential freeze-out) of other particles ?

K*, D++, L(1520), X* , r, … everything with large width/cross section and few-particle channelsbroad resonances are usually 'excused'; but we can't we rather use them ?


- decay & rescattering ?- late freeze-out (T ~ 140 MeV) ?

Particle Production: What next ? Strangeness (gs -> 1) enhancement in pPb ? in high multiplicity pp ??

use, rather than ignore, approach to strangeness equilibrium..


Thermal Model T = 164 MeV Thermal Model T = 164 MeV

- K/p & L/p reach central PbPb - p/p stays well above !- X,W to come..

If indeed we reach (approximate) chemical equilibrium in pPb:

=> compare small (pPb) and large (PbPb) systems

=> 'finite size' (lifetime) effects

12

NLOP II: Quarkonium suppression J/Y, the HP par excellence: 'well calibrated (pQCD) smoking gun'

June 2009 India J. Schukraft

NA38~ 1986

Matsui & Satz, 1986:

Nuclear MatterEffect !!

NA50~ 1996light ions (O,S):

nomalous (CNM)

heavy ions (Pb):Anomalous (QGP?)

13

In-InPb-Pb

Onset of Deconfinement ?Onset of Deconfinement !

NA50~ 1996

J/Y @ SPS

NA60~ 2006

Including nuclear shadowing

Deset of Onconfinement ???

Nuclear absorption measured at 158 GeV

Deconfinement of Onset ??

NA60~ 2009

J/Y @ RHIC

June 2009 India J. Schukraft14

Expectation: decisive answer from RHIC. And we even got it ! (~) all predictions were wrong ! RHIC (y=0) ≈ SPS (y=0) ; RHIC(y≠0)<RHIC(y=0)!!

Two broad classes of explanations why RHIC ≈ SPS: equal by Intelligent Design: sequential melting (Y', cc suppression only) equal by miraculous Accident: suppression cancelled by recombination

Expectation: decisive answer from LHC (+ Y @ RHIC) different sensitivity to melting (Tc) and recombination (charm density)

RHIC large rapidity

SPS

RHIC midrapidity

Predictions

J/Y measured over expected

2005

arxive:1010.582arxive:1010.582

O

Déjà vu ?

Miracle or ID ?

J/Y:RHIC ≠ LHC (finally)


ALICE vs PHENIXm+m- fwd-y, all pt

ALICE vs PHENIXe+e- y=0, all pt

CMS vs STARmid-y, high pt

CMS STAR

LHC ≠ LHC

CMS high pt mm

Alice ee

ALICE mm

J/Y RAA: pt dependence RHIC ≠ LHC


ALICE mm

PHENIX mm

CMS mm

PHENIX e+e-

J/Y suppression IS different @ LHC

unless CNM plays very dirty, unexpected tricks

ALICE e+e-

LHC = LHC !

NLOP II: J/Y Regeneration


J/Y RAA:pT dependence

regeneration

melting

J/Y RAA:centrality dependence

On Recombination/Coalesence:Purist: Another dirt effect which obscures deconfinement (CNM, HotMatterRecombination)Pragmatist: Another deconfimenet signal !Deconfinement colour conductivity'partons can roam freely over large distance'That's what the primordial charm quarks have to do to recombine

All clear ?


sequential suppression <-> suppression & regeneration compelling evidence for recombination at RHIC ? is SPS/RHIC compatible with no J/Y, only Y', cc suppression ?

measure Y', cc ! (proposed at SPS)

Miracle or ID ?

Let's wait a bit longer and see

- give TH a chance to digest - Y' & Upsilons @ RHIC/LHC- measure CNM with p-PB

J/Y RAA: √s (in)dependence

ConSequential Y suppression

HP2012 J. Schukraft19

Y(1S), ~ 50% direct complete higher state suppression ??Y(2S) (~ J/Y) up to 5 x stronger than Y(1S)Y(3S) gone Y(3S)/Y(1S) < 0.1 (95%CL)

Sequential suppression as expected from deconfinement !! Caveats:

- Feed-downs from the many bb states to be sorted out - Initial State Effects ( to be estimated from pA)

Upsilon at RHIC


Déjà vu ? J/Y: RHIC = SPS

STARRAA(1+2+3) = 0.56+0.22

-0.26

CMS RAA(1+2+3) = 0.32

RHIC -> LHC comparison is crucial- we need to raise the temperature

1 Apple & 3 Apples

STAR

CMS

CNM in pPb: J/Y CNM = Currently Not Mastered


needs PDF + DE + sabs ? pt not very well described ! Y' stronger suppressed than J/Y !

final state absorption ?? RHIC dAu data also not easily described by theory !

Double Ratio Y'/Y in pPb / pp

J/Y RAA versus pt

J/Y RAA versus y

CNM in pPb: U


RpPb: U ≈ J/Y ? (watch the errors !!)

higher states more suppressed ≈ 20-30% for Y(2,3)/Y(1,)≈ 50% for Y'/Y CNM absorption (sabs) ?

formation time => should disappear@LHC? HNM (comover) final state interaction ???

RpPb lhcB ~ PDF(LO!)

RpPb J/Y from B decay vs y

RpPb Y versus y

Double Ratio U(n)/Y in pPb / pp

Pb-Pb

Plenty of food for thought ..

and calculations..

QM 2011: The Flow Renaissance overwhelming and unambiguous evidence: complex structures from E-b-E hydro flow


v2v3

v4

v3 for p/K/p

24

The 'face' of the collision zone, (state-of-art for 20 years)

including 'warts & wrinkles' of each event

Why did it take so long to see the obvious ?could not be overlooked or mistaken at LHClarge dNch/dy => large signal, excellent resolutionlarge acceptance detectors

A most amazing Discover

y

Dec. 2013 Kyoto J. Schukraft

Ridge

Cone

Event Plane Resolutions versus centrality1 = perfect resolution

From Leading Order ..elliptic flow v2

.. to NLO …higher harmonic flows v3,…v6

.. to NNLO …correlation between harmonic symmetry planesvia geometry constraintsvia non-linear interactions in the hydro evolution

(mode mixing) leading to better limits on h/s


TPM-I: Quantum Jump in Exp. & Theory

J. Jia http://arxiv.org/pdf/1005.0645.pdf

Y2-Y4

pre-LHC4ph/s < 3-6

post-LHC4ph/s < 2-3

Better limit, but not yet good enough.Aim for measurement (<30% ?) of h/s !

h/S < 1/4p => conjectured limit is wrongh/S > 1/4p => measure s in QGPh/S ≈ 1/4p => AdS/CFT quantum corrections ? O(10-30%)h/S(RHIC) ≠ h/S(LHC) => T dependence

Fluctuations are Bessel-Gaussian

2 parameters: <v2> and v{4} = v{6} = v{8} = ….

no additional information (if BG)central events (< 5%) and (maybe) v3 are not BG !


E-b-E flow

E-b-E v2 distributions

v2{n} versus centrality

Can one use fluctuations as 'E-b-E' selection tool (like centrality) ??

s(v3)

s(v2)

E-b-E flow as tool Whatever it is that makes v2 in 3 < pt < 8 GeV: s(v2)/v2 = constant (5-30%)

trivial for hydro: s(v2)/v2 ~ s(e2)/e2 v2 ~ e2 (almost) indept. of pt

less trivial for quenching: (density weighted pathlength integral)n ~ e

Select v2 at fixed Nch: (compare large v2 & small v2 events)

azimuthal HBT, CME effect, ….f-integrated pt distribution shows modification: larger v2 => larger <pt>radial pressure fluctuations ?


s(v2)/v2

normalized pt fluctuations vs Nch

Ratio of p/K/p pt spectra: large v2 over all v2

There is no quark scaling < 0.7-1 GeV/nq. Nor should there be ! We have Hydro mass scaling !

> 1 GeV/nq: scaling not very good either..scaling violation also seen at RHICf@RHIC closer to p/K than to pnq or hadronic 'afterburner' effect ??


Quark Scaling ?

Phenix:1203.2644

v2 p/K/p/L versus pt

1 = nq scaling

Deviation from Hydro at similar pt for radial and elliptic flowlight particles follow radial/elliptic flow up to 1.5 - 2 GeVheavy particles follow up to > 3-4 GeVvery natural consequence of hydro-push !

waiting for f at LHC where will it 'decouple' in pt and v2 ?


Decoupling from Flow ?

PbPb: p/K/p pt spectra BlastWave fit


Everything 'Flows' at LHC

CMS high pt particles

Atlas jets Alice open charm

STAR Non Photonic Electrons

J/Y

Alice direct photons

Can there be too much of a good thing ?some flow results are not easily accommodated by theory

TPM-II: Energy Loss ('Jet-quenching') high energy partons loose energy DE when traversing a medium

jet(E) → jet (E’ ) + soft particles(DE) (E’ = E-DE) energy loss DE expected to depend on: q : 'opacity ' = property of medium ('radiation length of QGP') L: size of medium (~ L (elastic) ~ L2(radiative) ~ L3(AdS/CFT)) cq: parton type (gluon > quark) f(m) : quark mass (light q > heavy Q) f(E) : jet energy (DE = constant or ~ ln(E))

May 2012 Crete J. Schukraft31

jet quenching measures‘stopping power' of QGP

DE ~ f(m) x cq x q x Ln x f(E)^

^

Main Questions:1) How much energy is lost ?measure jet imbalance E - E'2) Shows expected scaling ?vary L, m, E, .3) Where (and how) is it lost ?measure radiated energy DE..

Main Observables:1) Inclusive single particlesRAA (Nch, PID, HF)2) Two(3) particle correlationsNch, PID, HF; near/away side3) Inclusive single jetsRAA, long/transverse frag. functions4) Jet correlations (jet-jet, g(Z)-jet)

MUCW: (my understanding of conventional wisdom)

E-E': large, O(10-20 GeV@LHC), RHIC->LHC ~ as expectedjet(E'): ~ unmodified vacuum fragmentation (pt > 4 GeV, R ~ 0.4)DE: multiple soft gluons, large angle & low pt (< 3-4 GeV)

!

!?

??

Observation of Jet Quenching Observed at RHIC in 2001

via suppression of 'leading fragments' (not enough energy to see jets)qualitative clear effect, quantitative interpretation difficult & model dependent

Very striking at LHCmany unbalanced (E1 ≠ E2) jets and 'monojets'


Atlas

47 GeV

102 GeVAlice

DhDf

CMS

Energy flow in h-f plane

g-Jet :How much Energy is lost ?

JS Nov 2012 EPFL33

CMSMean xJg= pt(jet)/pt(g) g-Fraction without jet: RJg

g looses no energy

=>calibrates jet before energy

loss !

PT1

PT1

g - jet energy (im)balance

g-jet should lead, with improved statistics, to a precise determination of q ̂

Where (& how) is it lost ?

Jet Quenching = Modified Fragmentation Function

JS Nov 2012 EPFL

34

soft

RAA of 'hump-back' plateau f(x)

leading

RCP of jet fragmentation functions f(z)

leading

soft

Energy versus jet cone radius r: PbPb/pp

Very differential information to constrain Theory

^

Mass & Color Charge Dependence

May 2013 Stockholm J. Schukraft

35

- Clear mass effect (D versus B), disappears at pt/m >> 1- Where is the gluon versus quark difference ??

RAA of p, D, B RAA inclusive jets and b-jets

The first LHC Discovery (pp, Sept 2010)long range rapidity 'ridge' in 2-particle correlationsvisible in the highest multiplicity pp collisionsarguably still the most unexpected LHC discovery


Discovery

'Near Side Ridge

'Near Side JET'

'Away Side JET'

The 'Opera' defense !

Spawned a large number of different explanations mostly rather ad hoc, very speculative, or outright weird

Color Glass Condensate CGC: 'first principles' theoryclasssical FT in high density limit (small x, small Q2)'new state of cold & dense parton matter'some success describing aspects of ep, pp, eA:

geometric scaling, low-x, particle production, ..

however, no 'smoking gun' so far…

Collective flow (Hydro) ?vaguely similar correlations in nucleus-nucleus


Origin of the pp 'Ridge'

PbPb 10-20%Flow


Ridges everywhere..

ALICE pPb 5 TeV

Double Ridge

CMS pPb 5 TeV

Stronger NSR

2 particles4 particlesATLAS pPb 5 TeV Ridge is much stronger in pPb (end 2012)!

and is, in fact, a 'double ridge'even and odd components (v2, v3)collective multiparticle v2{4} (i.e., not 'jet' like)mass dependent v2(m,pt)now also seen in dAu at RHIC ! (tbc)strength ≈ as predicted by some hydro model

It looks like a rose …

More on the Ridge


ALICE v2 for p, K, p

ATLAS v2 v3

CMS v2{2}, v2{4}, v3

Hydro predictions

e{2}/e{4} ≈ 1.7 Npart = 25 e{2}/e{4} ≈ 1.5 Npart = 12 e{4} ≈ e{6}

v{2}/v{4} ≈ 1.4


(Mis)Use PbPb Glauber MC for pPb

It smells like a rose …

Where there is elliptic Flow..


.. there MUST be radial flowCMS <pt> versus Nch for p, K, p 'Baryon Anomaly' L/K0

S BlastWave Fit p, K, p

Combined BW fit to pt and v2

It pricks like a rose …

Another prediction come true ..


BW fit (b,T) pPb and PbPbb versus Nch in pPb, PbPb

T versus Nch in pPb, PbPb

smaller fireball, larger gradient, more radial flow ?as predicted (e.g.by Shuryak) ??

arXiv:1301.4470 [hep-ph]

A. Ortez et al http://arxiv.org/abs/1303.6326v2

http://arxiv.org/abs/1301.4470

.. or too much of a good thing ?


BW fit (b,T) pPb and PbPb and ppBW fit to high multiplicity pp

Where are all the roses gone ...

?

All Options look bad:- Hydro everywhere (incl. low mult. pp)- Hydro nowhere (incl. central PbPb)- Looks like flow in pp but isn't (pPb ??)

We can not (longer) afford to ignore small systems:- similarity in particle ratios (smooth evolution of gs)- similarity in flow patterns (radial & azimuthal)

??? Where is the onset ???

CGC ?some results come natural, others need additional 'ad hoc' explanations odd harmonics (v3), cumulants v2{4}, PID v2,

Collective 'Hydro-like' flow in pA (& pp) ??most results are 'natural' (at least within factor 2) if one assumes hydro..energy/particle density quiet comparable to AA (eg high Nch pp@LHC ≈ Cu-Cu mid-central

@RHIC)

system size only few fm3 ?? (presumably << 10 compared to >> 1000)

however, hydro has no intrinsic size, only ratio's: l/r, and l ≈ 0 ! (from h/s)a proton@LHC is more like a small nucleus (dozens of partons, MPI,..) !

what other measurements are needed ?? In either case, more than a curiosity

CGCdiscovered a 'new state of matter'smoking gun for new 'first principle' limit of QCD

Hydro stunning: a system the size of a single hadron behaves like 'macroscopic matter'

'extra dimension' for QGP study: size !finite size effects => correlation & coherence length, time scales, ….


pPb (pp): Panta Rhei ?

RHIC Scientists found "Colorful Glass" to serve the Perfect Liquid

New State of Matter created at CERN which features many of the characteristics of the

theoretically predicted Colour Glass Condensate.

Rewrite the textbooks at least change the title from 'Heavy Ion physics' to ..


The rocky Horror Picture Show A random collection of recent results (Hard Probes Conferences 2012/2013)

which don't fit easily anywhere

will fade away with a whimper or disappear with a bang

or stay and have a big impact ?


Weird !

CMS: RpPb at high pt

CMS charged particles vs ALICE/ATLAS jets

ATLAS jets pt x 0.5ALICE jets pt x 0.5

ALICE charged

' Anti-shadowing on steroids'Anti-doping squad is investigating; so far

just about compatible with competition (Atlas/Alice)

Weirder !! "RAA" ; i.e. double ratio Y'/Y(Pb) / Y'/Y(pp) high pt: "RAA"< 1 (Y' suppression stronger), small indication rising with Npart ?? lower pt: "RAA" > 1!!! (Y' suppression less strong !), rising with Npart !!


high pt Y'lower pt Y'

CMS has discovered the'anomalous Y' un-suppression'implications totally unknown, but

definitely profound (one way or another)Some tension with ALICE


Weirdest !!!ATLAS has discovered 'Super jet-quenching'in central pPb collisions

jet RCP in p-Pb as function of centrality & y

which however turns out to be 'Hyper-jet un-quenching'

in peripheral pPb collisions !

jet RpA(Phythia) in p-Pb as function of centrality & y

jet RpA(Phythia) inMinBiasSpectra biased by centrality selection ?as seen by ALICE in pt spectra

http://www.costumeshut.com/files/productsimages/BS_C/7169.jpg

Weirdissimo !!!!


U(2S)/U(1S) versus Nch

More likely a totally obvious & trivial effectleft as an easy exercise to the reader

hint: little/no dependence on Et(|h|)>4 in pp..

After hadrochemistry & hydro-flow The final proof:

'Y suppression in pp'

U(2S)/U(1S) versus ET(|h|>4)

Abrupt End !

50

CMS versus Alice: LHC ≠ LHC ??


1) How much Energy is lost ? Di-Jet energy balance Aj Aj = (PT1-PT2)/(PT1+PT2)


<DE> ≈ 20 GeV (wide distribution)

Medium is VERY stronglyinteracting ('opaque')(but within expectations)

PT1

PT1

jet quenching DE ~ .....

2) Energy dependenceroughly as expected (weak dep. on Energy)(CMS PLB 712 (2012) 176)

jet quenching DE ~ f(m) x cq x q x Ln x f(E)^

Quenching Model

PT1 ≈ PT2

PT1 >> PT2

g looses no energy


loss !

OLD

g-Jet (The Holy Grail of jet-quenching)

JS Nov 2012 EPFL53

CMSMean xJg= pt(jet)/pt(g) g-Fraction without jet: RJg

g looses no energy


loss !

PT1

PT1

NEW

Df12

3) Where (& how) is it lost ?


Di-jet angular correlation Df12

back-to-back Df12=1800

pp

Unexpected Result : - jets remain back-to-back (little additional broadening)- radiated energy appears in low energy hadrons, far away from the jet (CMS PRC 84 (2011) 024906)

?

E → E’ + DESimulation

PbPb

Energy versus jet cone radius r: PbPb/pp

OLD

Jet Quenching = Modified Fragmentation Jet(E) → jet (E’ = E-DE) + soft particles(DE)

Energy is conserved but redistributed into more low energy (soft) gluons

JS Nov 2012 EPFL55

soft

RCP of jet fragmentation functions f(z) RAA of 'hump-back' plateau f(x)

leadingleading soft

NEW

Charm Mesons(p+ + p-) RAA

B Meson

4) Mass & Color Charge Dependence


Measure Heavy Quarks (c,b) versus p (gluon fragmentation dominates p at LHC)

jet quenching DE ~ f(m) x cq x q x Ln x f(E)^RAA = measured/expected ~ AA/pp

Expectation:DE(p) > DE(D) > DE(B) - qluon ↔ quark- light ↔ heavy

hints for the expected hierarchyless strong than naively expected

OLD

Flavour Dependence

May 2013 Stockholm J. Schukraft

57

- Clear mass effect (D versus B), disappears at pt/m >> 1- Where is the gluon versus quark difference ??

NEW

3) Energy dependence

Ratio of energies between jets: <pT2/pT1> versus pT1 ("1" = leading jet)

JS Nov 2012 EPFL58

Simulationpp

PbPb

~ 10%

~ 10%

Difference in <pT2/pT1> between data and MC of O(10%)~ independent of leading jet pT

=> DE ~ E ?? comparison with full calculation shows DE ~ constant!!

jet quenching DE ~ f(m) x cq x q x Ln x f(E)^

59

60

61/16

QpPb

0-5%5-10%10-20%20-40%40-60%60-80%80-100%

Dec. 2013 Kyoto J. Schukraft

CL1

V0M V0A

clear indication of jet-veto bias in most peripheral bin selected using CL1

no jet-veto bias in V0A

QpPb spread between centrality classes reduced increasing the rapidity gap

Dec. 2013 Kyoto J. Schukraft 62

Dec. 2013 Kyoto J. Schukraft 63/16

QpPb normalized to high pT

CL1

V0M ZNA

V0A

shape only

ZN selects more similar event classes

0-5%5-10%10-20%20-40%40-60%60-80%80-100%

Dec. 2013 Kyoto J. Schukraft 64/16

<QpPb> at high pT

Glauber MC

<QpPb> for pT>10 GeV/c vs. centrality

same centrality dependence as seen for multiplicity bias from Glauber MC

n hard

/Nco

ll

TOY MC:Pythia6 (Perugia 2011)+ Glauber MC

TOY MC p-Pb collision = Ncoll p-p collisions superimposed with Ncoll distributed according to Glauber MC

number of hard scatterings per collision shows strong deviations from Ncoll scaling

high pT particle production seems to scale as the incoherent superposition of N-N collisions

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Heavy Ion Physics at the LHC What's new ? What's next ?

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