heavy ion physics at atlas, cms and lhcb · 2018-02-27 · heavy ion physics at atlas, cms and lhcb...

Heavy Ion Physics at ATLAS, CMS and LHCbMichael Schmelling - MPI for Nuclear Physics

– on behalf of the collaborations –

Outline

IntroductionQuarkonia productionCorrelation studiesUltra-peripheral collisionsFixed target physicsSummary

XXXII Les Recontres de Physiquede la Vallée d’Aoste

Heavy Ion Physics M. Schmelling, La Thuile, February 25 – March 3, 2018 1

1 Introduction

v theoretical understanding of strong interactions:

the QCD Lagrangian is well known and tested

I good agreement between data and theory where perturbative QCD is applicable

many open questions in the non-perturbative regime, such as : : :

I properties of hadronic matter at high densities and temperatures (QGP)

I bound states, e.g. nucleon structure (vital for BSM searches)

I nuclear effects in multiparticle production (nuclear PDFs, energy loss)

I dynamics of soft processes, e.g. diffractive scattering and hadronisation

I also interesting: QED at extreme field strengths

Heavy Ion Physics - Introduction M. Schmelling, La Thuile, February 25 – March 3, 2018 2

v Experimental approach

different nucleon-nucleon centre-of-mass energies

different beam-target combinations

comparison of different systems Ü always look at the complete picture


v Angular coverage of the LHC experimentsALICEI central detectorI forward muon coverageATLAS & CMSI central tracking detectorsI forward calorimeterLHCbI forward detectorI tracking, PID and calorimetry

in the full acceptance


v rich harvest of papers and conference notes

generic topics addressed in papers:

ATLAS CMS LHCb

Flow- and correlation measurements 17 24 1

Jets and QCD 10 19 0

Quarkonia 3 10 4

Particle production 6 15 1

Electroweak gauge bosons 3 5 1

QED 1 1 0

total 40 74 7

plus > 200 papers by the ALICE collaboration (Ü next talk)many papers touch on more than a single topic

textbook results from the LHC Ü


Melting of bound states in QGP

v check the Matsui-Satz-idea regarding b�b and c�c systems

PLB

770(

2017

)357

heavy-quark bound states melt inthe hot medium of the deconfinedcolour charges of a QGP

Ü experiment: � production inpp and PbPb collisions

negligible recombinationless tightly bound statesare strongly suppressed

Ü intriguing QGP signature


Jet quenchingJ

xdNd N1

0.5

1

1.5

2

2.5

3

3.5

4

< 126 GeVT1

p100 < 0 - 10 %

Pb+Pbpp

10 - 20 %ATLAS

= 0.4 jetsR tkanti-

JxdNd

N1

0.5

1

1.5

2

2.5

3

3.5

4

20 - 30 % 30 - 40 %

Jx

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

JxdNd

N1

0.5

1

1.5

2

2.5

3

3.5

4

40 - 60 %

Jx

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

60 - 80 % = 2.76 TeVNNs

-1 data, 4.0 pbpp2013

-12011 Pb+Pb data, 0.14 nb

PLB 774 (2017) 379

v energy loss of hard partons in QGP

look at the pT -ratio for jet pairs

xJ =pT2

pT1with pT1 > pT2

preference for balanced jets

comparison of pp and PbPb

I fewer high-energy jets incentral PbPb collisions

I same behaviour for pp andperipheral PbPb collisions

Ü signature of a dense deconfined QCD medium


2 Quarkonia productionv study p-Pb collisions to probe cold nuclear matter effects

effects of energy loss in nuclear mattermodification of parton densities of bound nucleonsstudy by inclusive particle production of heavy resonances

Ü probe two x -values for given rapidity y and mass M : x1;2 � e�y Mps

Pb p bwd fwd

Heavy Ion Physics - Quarkonia production M. Schmelling, La Thuile, February 25 – March 3, 2018 8

v parametrisation of nuclear PDFs by ratios of nucleon PDFs: FN (Pb)=FN (free)

still large uncertainties - EPPS16 error band for gluons larger than EPS09suppression at small x Ü shadowingenhancement at medium x Ü anti-shadowingenhancement at large x Ü EMC effect

valence quarks gluons

arX

iv:1

704.

0436


v experimental observable sensitive to nuclear effects:

nuclear modification factor: RpA(y) =1A� d�pA=dyd�pp=dy

central detectors: simultaneous measurement of forward and backward production

forward detectors: flip beam directions to measure both hemispheres

FORWARD (p hemisphere) BACKWARD (Pb hemisphere)

p Pb


Results from prompt J= and J= from b-decays

−5 0 5y∗

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75dσ dy∗[

mb]

LHCb√

sNN = 8.16TeV

0< pT < 14GeV/c

prompt J/ψ

pPb, Pbppp rescaled

0 5 10pT [GeV/c ]

102

103

104

105

106

dσ dpT[n

b/(G

eV/c

)]

LHCb

√sNN = 8.16TeV

prompt J/ψ , Pbp−5.0< y∗ <−2.5

Pbppp rescaled

0 5 10pT [GeV/c ]

102

103

104

105

106

dσ dpT[n

b/(G

eV/c

)]

LHCb

√sNN = 8.16TeV

prompt J/ψ , pPb1.5< y∗ < 4.0

pPbpp rescaled

−5 0 5y∗

0.00

0.05

0.10

0.15

0.20

0.25

dσ dy∗[

mb]

LHCb√sNN = 8.16TeV

0< pT < 14GeV/c

J/ψ -from-b-hadrons

pPb, Pbppp rescaled

0 5 10pT [GeV/c ]

102

103

104

105

106dσ dp

T[n

b/(G

eV/c

)]LHCb

√sNN = 8.16TeV

J/ψ -from-b-hadrons, Pbp−5.0< y∗ <−2.5

Pbppp rescaled

0 5 10pT [GeV/c ]

102

103

104

105

106

dσ dpT[n

b/(G

eV/c

)]

LHCb

√sNN = 8.16TeV

J/ψ -from-b-hadrons, pPb1.5< y∗ < 4.0

pPbpp rescaled

backward forward

backward forward

prompt J= compared to208� �pp (red)

delayed J= compared to208� �pp (red)

PLB 774 (2017) 159


v nuclear modification factors in the forward/backward region

−5.0 −2.5 0.0 2.5 5.0y∗

0.0

0.5

1.0

1.5

2.0

RpP

b

0< pT < 14GeV/c

LHCb

prompt J/ψ

HELAC−Onia with EPS09LOHELAC−Onia with nCTEQ15HELAC−Onia with EPS09NLOEnergy LossCGCLHCb (5TeV)LHCb (8.16TeV)

−5.0 −2.5 0.0 2.5 5.0y∗

0.0

0.5

1.0

1.5

2.0

RpP

b

0< pT < 14GeV/c

LHCb

J/ψ -from-b-hadrons

FONLL with EPS09NLOLHCb (5TeV)LHCb (8.16TeV)

consistent results for data withp

sNN =5 and 8.16 TeVnuclear effects clearly visible in the forward regionstronger effects for prompt J= production than for J= from b-meson decaysJ= from b-meson decays described by effects of NLO nPDFsprompt J= described by NLO nPDFs plus energy loss effects

PLB

774

(201

7)15

9


v nuclear modification factors in the central region

CMy

2.5− 2− 1.5− 1− 0.5− 0 0.5 1 1.5 2

pPb

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

< 10 GeV/cT

6.5 < p

Data

EPS09 NLO (Vogt)

EPS09 NLO (Lansberg-Shao)

nCTEQ15 NLO (Lansberg-Shao)

ψPrompt J/

(5.02 TeV)-1, pp 28.0 pb-1pPb 34.6 nb

CMS

CMy

2.5− 2− 1.5− 1− 0.5− 0 0.5 1 1.5 2

pPb

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

< 30 GeV/cT

10 < p

Data

EPS09 NLO (Vogt)

EPS09 NLO (Lansberg-Shao)

nCTEQ15 NLO (Lansberg-Shao)

ψPrompt J/

(5.02 TeV)-1, pp 28.0 pb-1pPb 34.6 nb

CMS

CMy

2.5− 2− 1.5− 1− 0.5− 0 0.5 1 1.5 2

pPb

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

< 10 GeV/cT

6.5 < p

ψNonprompt J/

(5.02 TeV)-1, pp 28.0 pb-1pPb 34.6 nb

CMS

CMy

2.5− 2− 1.5− 1− 0.5− 0 0.5 1 1.5 2

pPb

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

< 30 GeV/cT

10 < p

ψNonprompt J/

(5.02 TeV)-1, pp 28.0 pb-1pPb 34.6 nb

CMS EP

JC77

(201

7)26

9

nuclear modification factorsclose to unitytheory lower, thoughconsistent, with the datasimilar behaviour for promptand non-prompt J= mesonsindication for a slightenhancement for lower pT


v closer look at pT dependence

[GeV]T

p

10 15 20 25 30 35 40

pPb

R

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

[GeV]T

p

10 15 20 25 30 35 40

pPb

R

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

ATLASψNon-Prompt J/

-2.0 < y* < 1.5

[GeV]T

p

0 5 10 15 20 25 30 35 40

pPb

R

0

0.5

1

1.5

2-1 = 5.02 TeV, L = 28 nbNNs+Pb, p

-1 = 5.02 TeV, L = 25 pbs, pp

ATLAS(1S)ϒ

-2.0 < y* < 1.5

small nuclear effects for centrally produced J= mesonsindication for slight enhancement of prompt productionno significant pT dependence for prompt and non-prompt J= productionindication of pT dependence for � productionI open and hidden heavy flavour seem to be affected differentlyI maybe related to breakup of bound states in nuclear matter, which for

J= from b is compensated by recombination and/or anti-shadowing?

arX

iv:1

709.

0308

9


3 Correlation studiesv distribution of phase space distance between particle pairs

probing the underlying dynamics, e.g.

I dimensions of the particle emitting regions – Bose-Einstein correlations, HBT

I particle production in jets – fragmentation dynamics

I flow effects due to properties of QCD medium

example: per trigger-particle associated yield vs angular distances �� and ��

1Ntrig

d2Npair

d�� d��=

S(��;��)B(��;��)

� B(0; 0)

I 2-dim correlation functions of prompt particles in (��;��)

I select particles in fixed pT -range as “trigger”and study all pairs with the trigger

I compare associated yields per trigger, within an event (S(��;��)) and with

random combinations (B(��;��)) from mixed events

Heavy Ion Physics - Correlations studies M. Schmelling, La Thuile, February 25 – March 3, 2018 15

v example: two-particle correlations in p-Pb collisionsforward (p-Pb, p direction) backward (Pb-p, Pb direction)

η∆2

0

2

φ∆

10

12

34

φ∆

dη

∆d

N2

d

trig

N1

0.35

0.4

0.45

= 5 TeVNNs p+PbLHCb

Event class 50100%

< 2.0 GeV/cT

1.0 < p

η∆2

0

2

φ∆

10

12

34

φ∆

dη

∆d

N2

d

trig

N1

0.4

0.45

0.5

= 5 TeVNNs Pb+pLHCb

Event class 50100%

< 2.0 GeV/cT

1.0 < p

η∆2

0

2

φ∆

10

12

34

φ∆

dη

∆d

N2

d

trig

N1 1.35

1.4

1.45

= 5 TeVNNs p+PbLHCb

Event class 03%

< 2.0 GeV/cT

1.0 < p

η∆2

0

2

φ∆

10

12

34

φ∆

dη

∆d

N2

d

trig

N1 2.05

2.1

2.15

2.2

= 5 TeVNNs Pb+pLHCb

Event class 03%

< 2.0 GeV/cT

1.0 < p

low activity

high activity

PLB

762(

2016

)473


v ��-integrated yields in p-Pb/Pb-p outside of the jet peak vs ��

φ∆ φ∆ φ∆ φ∆

< 1.0 GeV/cT

0.15 < p < 2.0 GeV/cT

1.0 < p < 3.0 GeV/cT

2.0 < p

50-1

00%

30-5

0%

10-3

0%

0-1

0%

0-3

%

ZY

AM

)-C

φ∆

Y(

0.00

0.05

0.10

0.15=1.61 (p+Pb)ZYAMC

=2.06 (Pb+p)ZYAMC

=0.32 (p+Pb)ZYAMC

=0.37 (Pb+p)ZYAMC

φ∆

LHCb

= 5 TeVNN

s

data p+Pb

data Pb+p

ZY

AM

)-C

φ∆

Y(

0.00

0.05

0.10

0.15=2.83 (p+Pb)ZYAMC

=4.01 (Pb+p)ZYAMC

=0.56 (p+Pb)ZYAMC

=0.70 (Pb+p)ZYAMC

=0.18 (p+Pb)ZYAMC

=0.21 (Pb+p)ZYAMC

ZY

AM

)-C

φ∆

Y(

0.00

0.05

0.10

0.15=3.74 (p+Pb)ZYAMC

=5.78 (Pb+p)ZYAMC

=0.81 (p+Pb)ZYAMC

=1.14 (Pb+p)ZYAMC

=0.23 (p+Pb)ZYAMC

=0.26 (Pb+p)ZYAMC

ZY

AM

)-C

φ∆

Y(

0.00

0.05

0.10

0.15=5.03 (p+Pb)ZYAMC

=7.81 (Pb+p)ZYAMC

=1.19 (p+Pb)ZYAMC

=1.78 (Pb+p)ZYAMC

=0.29 (p+Pb)ZYAMC

=0.36 (Pb+p)ZYAMC

φ∆0 2 4

ZY

AM

)-C

φ∆

Y(

0.00

0.05

0.10

0.15=5.67 (p+Pb)ZYAMC

=8.63 (Pb+p)ZYAMC

φ∆0 2 4

=1.39 (p+Pb)ZYAMC

=2.07 (Pb+p)ZYAMC

φ∆0 2 4

=0.32 (p+Pb)ZYAMC

=0.40 (Pb+p)ZYAMC

after offset subtraction (Zero-Yield-At-Minimum):

I near-side ridge largest at 1<pT <2 GeV/c

I fixed relative activity (left):

ridge of the 3% most active Pb-p events stronger

than the ridge of the 3% most active p-Pb events

I fixed absolute activity in the LHCb acceptance:

similar ridges in p-Pb and Pb-p events

φ∆0 2 4

ZY

AM

)C

φ∆

Y(

0.00

0.05

0.10

0.15

φ∆0 2 4

0.00

0.05

0.10

0.15

Activity bin I

)p+Pb=1.21 (ZYAMC

)Pb+p=1.04 (ZYAMC

= 5 TeVNN

sLHCb

φ∆0 2 4

0.00

0.05

0.10

0.15

Activity bin II

)p+Pb=1.32 (ZYAMC

)Pb+p=1.16 (ZYAMC

< 2.0 GeV/cT

1.0 < p

φ∆0 2 4

0.00

0.05

0.10

0.15

Activity bin III

)p+Pb=1.42 (ZYAMC

)Pb+p=1.27 (ZYAMC

φ∆0 2 4

0.00

0.05

0.10

0.15

Activity bin IV

)p+Pb=1.51 (ZYAMC

)Pb+p=1.38 (ZYAMC

φ∆0 2 4

0.00

0.05

0.10

0.15

Activity bin V

)p+Pb=1.64 (ZYAMC

)Pb+p=1.54 (ZYAMC

PLB

762(

2016

)473


v results from central measurements

(radians)φ∆0 2 4

]η∆ [p

er u

nit o

f φ∆d

pair

dN tr

igN

1

0

0.5

1 =5.02 TeVNNsCMS pPb

<3 GeV/cT

0.3 < p

Pb-side trigger

< 0.2η∆0 <

(radians)φ∆0 2 4

]η∆ [p

er u

nit o

f φ∆d

pair

dN tr

igN

1

0

0.5

1

< 3.0η∆2.8 <

(radians)φ∆0 2 4

]η∆ [p

er u

nit o

f φ∆d

pair

dN tr

igN

1

0

0.5

1 < 260offlinetrk N≤220

< 20trkN

p-side trigger

< 0η∆- 0.2<

(radians)φ∆0 2 4

]η∆ [p

er u

nit o

f φ∆d

pair

dN tr

igN

1

0

0.5

1

< - 2.8η∆- 3.0 <

I outside the jet peak (bottom) the ridge

appears in high-multiplicity events (red)

I similar strengths for p-side and Pb-side

I ridge also in high multiplicity pp events

I universal feature when many QCD

degrees of freedom are present?P

RC

96(2

017)

0149

15

PR

C96

(201

7)02

4908


4 Ultra-peripheral collisionsv exploit the high-intensity photon flux from relativistic Pb nuclei

~v −c

=

Z

Zem−fields

em−fields

~

v c~~Pb

Pb

. .

Pb

Pb

. .

Pb

Pb

. .

Pb82+

Pb82+

Pb82+

Pb82+

X

γ

γ

distinguish two photon-processes (depicted above) and photoproduction (not shown)

common characteristic: low transverse momentum of the final state systemexisting/upcoming results also from LHCb

field strength amplified by

em-coupling amplified by Z 2

strong coupling regime of QED

Heavy Ion Physics - Ultra-peripheral collisions M. Schmelling, La Thuile, February 25 – March 3, 2018 19

Coherent production of J= mesons in PbPb collisions

) [GeV]-µ+µm(2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5

Eve

nts

/ (0.

045

GeV

)

0

20

40

60

80

100

120

140

160

180CMS

(2.76 TeV)-1bµ) 159 n0n

(Xψ Pb+Pb+J/→Pb+Pb

) < 1.0 GeV-µ+µ(T

p

)| < 2.3-µ+µ1.8 < |y(CMS data

-µ+µ → γγTotal

) [GeV]-µ+µ(T

p0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Eve

nts

/ (0.

05 G

eV)

0

20

40

60

80

100

120

140

160

CMS data

ψCoherent J/

ψIncoherent J/-µ+µ → γγ

Total

CMS

(2.76 TeV)-1bµ) 159 n0n

(Xψ Pb+Pb+J/→Pb+Pb

)| < 2.3-µ+µ1.8 < |y() < 3.5 GeV-µ+µ2.6 < m(

y0.5− 0 0.5 1 1.5 2 2.5 3 3.5

/ dy

[mb]

coh

σd

0

1

2

3

4

5

6

7

8

9CMS dataALICE dataImpulse approximationLeading twist approximation

(2.76 TeV)-1bµ 159 ψ Pb+Pb+J/→Pb+Pb

CMS

experimental selections with a breakup neutron accepts coherent (on the entirenucleus) and incoherent (on a single nucleon) productionclean signal on top of a small and well understood backgroundmeasurement of the photoproduction cross-section probes the gluon densitycross-section consistent with nuclear effects as expected from gluon shadowing

PLB

772(

2017

)489


Evidence for light-by-light scattering

X X X

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

Nat

ure

Phy

sics

13(2

017)

379

back-to-back photons transverse to the beam

13 candidates in 480�b�1

expected background 2.6�0.7 events

cross-section consistent with SM


5 Fixed target physicsv exploit the LHCb SMOG “System for Measuring Overlap with Gas”

inject noble gases (10�7 mbar) into the interaction region: He, Ne, Armotivation: beam-profile measurements with beam-gas interactionsplus: full charm and (soft) QCD fixed-target physics program with p and Pb beams

Heavy Ion Physics - Fixed target physics M. Schmelling, La Thuile, February 25 – March 3, 2018 22

v links to cosmic ray and astroparticle physics: antiproton/proton ratio

I indication of antiproton excessI dark-matter annihilation?I large cross-section uncertainties for pH! pXI predictions vary within a factor 2

Ü LHCb: measure pHe! pX atp

sNN =110 GeV 7% uncertaintydata compared to EPOS-LHC

JCA

P09

(201

5)02

3

LHCb-CONF-2017-002

Heavy Ion Physics - Fixed target physics M. Schmelling, La Thuile, February 25 – March 3, 2018 23

6 Summaryv extremely rich (heavy) ions physics portfolio and results at the LHC

simultaneous views are the key to the understanding of non-perturbative QCDI study of the same observables in pp, p-Pb and Pb-Pb collisionsI central and forward measurementsunderstanding QGP signatures requires understanding of nuclear effectsheavy flavour measurements probe nuclear PDFs and properties of the mediumcorrelation measurements probe collective effects in the final stateI hints of universality when sufficiently many degrees of freedom are excitedfixed target physics radiates also into neighbouring fieldsultra-peripheral collisions test soft QCD and QED under extreme conditions

Stay tuned for more from the and collaborations!

Heavy Ion Physics - Summary M. Schmelling, La Thuile, February 25 – March 3, 2018 24

heavy ion physics at atlas, cms and lhcb · 2018-02-27 · heavy ion physics at atlas, cms and lhcb...

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