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
6
8
10
12
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
P(¡ 1)
¡1
CGC, loc. NBDPoisson
Glauber, glob. NBD
0
2
4
6
8
10
12
14
16
18
20
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
P(¡ 2)
¡2
CGC, loc. NBDPoisson
Glauber, glob. NBD
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
P(¡ 4)
¡4
CGC, loc. NBDPoisson
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:
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
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
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0 0.5 1 1.5 2 2.5 3
1.0 < pTtrig < 2.0 GeV; 0.5 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
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
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
ATLAS Peripheral
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
0 0.5 1 1.5 2 2.5 3
3.0 < pTtrig < 4.0 GeV; 0.5 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
ATLAS Peripheral
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
0 0.5 1 1.5 2 2.5 3
4.0 < pTtrig < 5.0 GeV; 0.5 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
ATLAS Peripheral
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0 0.5 1 1.5 2 2.5 3
1.0 < pTtrig < 2.0 GeV; 1.0 < pT
asc < 2.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
ATLAS Peripheral
-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
2.0 < pTtrig < 3.0 GeV; 1.0 < pT
asc < 2.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
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
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
ATLAS Peripheral
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
4.0 < pTtrig < 5.0 GeV; 1.0 < pT
asc < 2.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0 0.5 1 1.5 2 2.5 3
2.0 < pTtrig < 3.0 GeV; 2.0 < pT
asc < 3.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
ATLAS Peripheral
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0 0.5 1 1.5 2 2.5 3
3.0 < pTtrig < 4.0 GeV; 2.0 < pT
asc < 3.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Central
ATLAS Peripheral
0.00
0.02
0.04
0.06
0.08
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0.18
0 0.5 1 1.5 2 2.5 3
4.0 < pTtrig < 5.0 GeV; 2.0 < pT
asc < 3.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22
0.00
0.01
0.02
0.03
0.04
0.05
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0.07
0 0.5 1 1.5 2 2.5 3
3.0 < pTtrig < 4.0 GeV; 3.0 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22
0.00
0.01
0.02
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0.04
0.05
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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
Q20,proton =0.504 GeV2; NPart
Pb = 18-22
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
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 Difference
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0 0.5 1 1.5 2 2.5 3
1.0 < pTtrig < 2.0 GeV; 0.5 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0 0.5 1 1.5 2 2.5 3
2.0 < pTtrig < 3.0 GeV; 0.5 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0 0.5 1 1.5 2 2.5 3
3.0 < pTtrig < 4.0 GeV; 0.5 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0 0.5 1 1.5 2 2.5 3
4.0 < pTtrig < 5.0 GeV; 0.5 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0 0.5 1 1.5 2 2.5 3
1.0 < pTtrig < 2.0 GeV; 1.0 < pT
asc < 2.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0 0.5 1 1.5 2 2.5 3
2.0 < pTtrig < 3.0 GeV; 1.0 < pT
asc < 2.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0 0.5 1 1.5 2 2.5 3
3.0 < pTtrig < 4.0 GeV; 1.0 < pT
asc < 2.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0 0.5 1 1.5 2 2.5 3
4.0 < pTtrig < 5.0 GeV; 1.0 < pT
asc < 2.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22
-0.01
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 0.5 1 1.5 2 2.5 3
2.0 < pTtrig < 3.0 GeV; 2.0 < pT
asc < 3.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
-0.01
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 0.5 1 1.5 2 2.5 3
3.0 < pTtrig < 4.0 GeV; 2.0 < pT
asc < 3.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22ATLAS Difference
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0 0.5 1 1.5 2 2.5 3
4.0 < pTtrig < 5.0 GeV; 2.0 < pT
asc < 3.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22
0.00
0.01
0.01
0.01
0.02
0.03
0.03
0 0.5 1 1.5 2 2.5 3
3.0 < pTtrig < 4.0 GeV; 3.0 < pT
asc < 4.0 GeV
Q20,proton =0.504 GeV2; NPart
Pb = 18-22
0.00
0.01
0.01
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
Q20,proton =0.504 GeV2; NPart
Pb = 18-22
Glasma graph contribu9ons compared to ATLAS central – ATLAS peripheral