cgc inifal$ glasma$ hadron$gas singularity$ qgp$ strongly ... filethe$glasma$ 1/qs% random typical...

The Ridge in pp and pA Collisions: CGC? Hydro?

Larry McLerran, February 2012, EMMI, Darmstadt, Germany

CGC Glasma IniFal Singularity

Thermalized QGP

Hadron Gas

Strongly Interacting QGP!

The Glasma

1/Qs

random

Typical configuration of a single event just after the collision

Highly coherent colored fields: Stringlike in longitudinal direcFon

StochasFc on scale of inverse saturaFon momentum in transverse direcFon MulFplicity fluctuates as negaFve binomial distribuFon

LHC Results

Can this be due to Hydrodynamic Flow?

These are high mulFplicity events so it is not impossible to have significant final state results

Bozek and Broniowski in pA Collisions:

Glauber Monte Carlo Model with no fluctuaFons in mulFplicity for pp colisions

“Typically, the size and life-‐Fme of the collecFve source formed in central p-‐Pb

collisions is 3-‐4 fm [31].”

FluctuaFons are generated by fluctuaFons in posiFons of nucleons in target.

What is the transverse size of region where there is ma[er produced?

In pp collisions: The proton size R < 1 Fm.

Is this reasonable?

If there are no fluctuaFons in pp interacFons, the only way one can have high mulFplicity is by interacFons with many nucleons. The highest mulFplicity events are generated by

interacFons with nucleons over the enFre nucleus. This requires either that the interacFons are at distances much larger than the range of nucleon interacFons or that all the nucleons in the nucleus fluctuate so that they sit on top of one another. The la[er is

not likely because of short distance nucleon-‐nucleon repulsion.

STAR data show that one MUST include negaFve binomial fluctuaFons in mulFplicity of pp interacFons

0.1

1

0.5 1 1.5 2 2.5 3

�Nch� P(Nch)

Nch(|d|<0.5) / �Nch�

MC-rcBK, p+Pb 3s=4.4 TeVMC-rcBK NBD off, p+Pb 3s=5 TeV

MC-rcBK, p+p 3s=0.9 TeVMC-rcBK, p+p 3s=2.36 TeV

MC-rcBK, p+p 3s=7 TeV

Understand source of fluctuaFons:

Decay of color electric and color magneFc fields. On a subatomic

size scale

Including fluctuaFons makes a big difference:

Size of region is

dN/dy ~ 30-‐50

R ⇠ 1 Fm

�r ⇠ 1/Qsat ⇠ .1� .3Fm

Physics of the flucutaFons in both pp and pA is on the subatomic scale size

When compuFng eccentriciFes, it makes a difference:

0

1

2

3

4

5

6

7

8

9

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

P(¡ 3)

¡3

CGC, loc. NBDPoisson

Glauber, glob. NBD

0

2

4

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10

12

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

P(¡ 1)

¡1


Glauber, glob. NBD

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

P(¡ 2)

¡2


Glauber, glob. NBD

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

P(¡ 4)

¡4


Glauber, glob. NBD

Physically: A high mulFplicity pp or pA collisions in hydro should have similar trends for eccentriciFes, v_N as for AA. This is born out in modeling of iniFal state where sub-‐nucleonic

substructure is included

A two parFcle correlaFon at large rapidity should include a contribuFon from a jet, which will be asymmetric in azimuthal angle and an underlying non-‐jet piece

How to subtract jet contribuFon? If we assume ma[er is hydrodynamical at transverse momentum of interest, cannot subtract an unmodified jet. Jet would be strongly modified by media. Would need to simulate jet producFon in a medium

where most jets would stop, and to model the enFre jet!

If the there are not significant final state interacFons, then

can subtract the jet component, and are lei with an underlying correlaFon.

Inconsistent to subtract jet and assume remainder arises from perfect fluid!

But for fun of it, plug one’s nose and ask what results (You go*a believe):

Generically:

eccentriciFes are typical of those for central heavy ion collisions and rather weakly decrease upon increasing centrality for head on collisions

V_2 and v_3 are both large and their raFo is slowly varying funcFon of increasing

centrality for head on collisions

V_2 for pPb is 4-‐5 Fmes larger than in pp at same mulFplicity!

Alice:

In pPb: increse of v_2 with increasing centrality

v_3 is small and slowly varying

Inconsistent with expecta9ons of

perfect fluid hydro and reasonable ini9al condi9ons

Let us now go to the opposite limit: Small final state interacFons => subtracFon of jet contribuFon is sensible. Maybe

some small effects of the subtracFon which make it not quite perfect, but should be a good approximaFon

CorrelaFon seen must arise from intrinsic correlaFon of the Glasma flux lines as they decay:

RG evolu9on of two par9cle correla9ons C(p,q) expressed in terms of “unintegrated gluon distribu9ons” in the proton

Dumitru,Dusling,Gelis,Jalilian-‐Marian,Lappi,RV, arXiv:1009.5295

Contribu9on ~ αS6/Nc

2 in min. bias, High mult. -‐> 1/αS2 Nc

2

– enhancement of 1/αS8 ~ factor of 105 !

Proton 1

Proton 2

Dusling, RV: 1201.2658 1210.3890

CGC-‐Glasma DescripFon of pp angular correlaFon:

Exci9ng first results on proton lead collisions

Key observa9on: Ridge much bigger than p+p for the same mul9plicity !

CMS coll. arXiv:1210.5482, Phys. Le*. B

Previous 2 and remaining slides courtesy of R. Venugopalan

Exci9ng results on proton lead collisions

Systema9cs of p+Pb data explained Dusling, RV: 1211.3701

Q02(lead)=NPart

Pb * Q02(proton)

# of “wounded” nucleons in Lead nucleus

Glasma signal is ~ Npart * Ntrack

p+Pb data explained Dusling, RV: 1211.3701

Q02(lead)=NPart

Pb * Q02(proton)

# of “wounded” nucleons in Lead nucleus

Large “ridge” seen in Color Glass Condensate by varying satura9on scale in proton and # of wounded nucleons

CMS p+Pb data explained Dusling, RV: 1211.3701

Smoking gun for gluon satura9on and BFKL dynamics ?

ALICE data on the p+Pb ridge ALICE coll. arXiv:1212.2001

Different acceptance (|Δη| < 1.8) than CMS (2 < |η| < 4) and ATLAS (2 < |η| <5). ALICE subtracts away-‐side “jet” contribu9on at 40-‐60% centrality from most central events –this gives dipole shape of correla9on

Different analysis technique from CMS/ATLAS -‐-‐ same normaliza9on as for CMS/ATLAS Curves for Q0,proton

2 =0.336 GeV2

& NpartPb = 12 -‐ 14

ALICE data on the p+Pb ridge ALICE coll. arXiv:1212.2001

Different acceptance (|Δη| < 1.8) than CMS (2 < |η| < 4) and ATLAS (2 < |η| <5). ALICE subtracts away-‐side “jet” contribu9on at 40-‐60% centrality from most central events –this gives dipole shape of correla9on

0-‐20% : Q0,proton

2 =0.336 GeV2

& NpartPb = 12 – 14

20-‐40% : Q0,proton

2 =0.336 GeV2

& NpartPb = 4 – 6

40-‐60%: Q0,proton

2 =0.168 GeV2

& NpartPb = 3-‐4

Associated yield per Δη

Comparison to ATLAS p+Pb ridge ATLAS coll. arXiv: 1212.5198

ATLAS yields in asymmetric pT windows compared to Glasma + BFKL:

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0.60

0 0.5 1 1.5 2 2.5 3

0.5 < pTtrig < 1.0 GeV; 0.5 < pT

asc < 4.0 GeV

Q20,proton =0.504 GeV2; NPart

Pb = 18-22ATLAS Central

ATLAS Peripheral

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0.60

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0.80

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1.0 < pTtrig < 2.0 GeV; 0.5 < pT

asc < 4.0 GeV



ATLAS Peripheral

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 0.5 1 1.5 2 2.5 3

2.0 < pTtrig < 3.0 GeV; 0.5 < pT

asc < 4.0 GeV



ATLAS Peripheral

-0.20

0.00

0.20

0.40

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0.80

1.00

1.20

1.40

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3.0 < pTtrig < 4.0 GeV; 0.5 < pT

asc < 4.0 GeV



ATLAS Peripheral

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1.40

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4.0 < pTtrig < 5.0 GeV; 0.5 < pT

asc < 4.0 GeV



ATLAS Peripheral

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1.0 < pTtrig < 2.0 GeV; 1.0 < pT

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ATLAS Peripheral

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2.0 < pTtrig < 3.0 GeV; 1.0 < pT

asc < 2.0 GeV



ATLAS Peripheral

-0.10 -0.05 0.00 0.05 0.10 0.15

0.20 0.25 0.30 0.35 0.40 0.45

0 0.5 1 1.5 2 2.5 3

3.0 < pTtrig < 4.0 GeV; 1.0 < pT

asc < 2.0 GeV



ATLAS Peripheral

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0 0.5 1 1.5 2 2.5 3

4.0 < pTtrig < 5.0 GeV; 1.0 < pT

asc < 2.0 GeV


Pb = 18-22

-0.02

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0.02

0.04

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0 0.5 1 1.5 2 2.5 3

2.0 < pTtrig < 3.0 GeV; 2.0 < pT

asc < 3.0 GeV



ATLAS Peripheral

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3.0 < pTtrig < 4.0 GeV; 2.0 < pT

asc < 3.0 GeV



ATLAS Peripheral

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4.0 < pTtrig < 5.0 GeV; 2.0 < pT

asc < 3.0 GeV


Pb = 18-22

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3.0 < pTtrig < 4.0 GeV; 3.0 < pT

asc < 4.0 GeV


Pb = 18-22

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Pb = 18-22

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Pb = 18-22ATLAS Difference

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asc < 4.0 GeV



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0 0.5 1 1.5 2 2.5 3

4.0 < pTtrig < 5.0 GeV; 0.5 < pT

asc < 4.0 GeV



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0 0.5 1 1.5 2 2.5 3

1.0 < pTtrig < 2.0 GeV; 1.0 < pT

asc < 2.0 GeV



-0.05

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2.0 < pTtrig < 3.0 GeV; 1.0 < pT

asc < 2.0 GeV



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3.0 < pTtrig < 4.0 GeV; 1.0 < pT

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0 0.5 1 1.5 2 2.5 3

4.0 < pTtrig < 5.0 GeV; 1.0 < pT

asc < 2.0 GeV


Pb = 18-22

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0 0.5 1 1.5 2 2.5 3

2.0 < pTtrig < 3.0 GeV; 2.0 < pT

asc < 3.0 GeV



-0.01

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0 0.5 1 1.5 2 2.5 3

3.0 < pTtrig < 4.0 GeV; 2.0 < pT

asc < 3.0 GeV



0.00

0.01

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0.03

0.04

0.05

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0 0.5 1 1.5 2 2.5 3

4.0 < pTtrig < 5.0 GeV; 2.0 < pT

asc < 3.0 GeV


Pb = 18-22

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0.01

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0 0.5 1 1.5 2 2.5 3

3.0 < pTtrig < 4.0 GeV; 3.0 < pT

asc < 4.0 GeV


Pb = 18-22

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0.01

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0 0.5 1 1.5 2 2.5 3

4.0 < pTtrig < 5.0 GeV; 3.0 < pT

asc < 4.0 GeV


Pb = 18-22

Glasma graph contribu9ons compared to ATLAS central – ATLAS peripheral

cgc inifal$ glasma$ hadron$gas singularity$ qgp$ strongly ... filethe$glasma$ 1/qs% random typical...

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