High-pt probes from RHIC to LHC - fisica.cab.cnea.gov.ar · Amir H. Rezaeian (USM) SILAFAE Bariloche Jan 2009 2 / 29. QCD x-Q2 phase diagram x 10-6 -5 10-4 10-3 -2 -1 1) 2 = 10 GeV

High-pt probes from RHIC to LHC

Amir H. Rezaeian

Universidad Tecnica Federico Santa Maria, Valparaiso

VII Latin American Symposium on High Energy PhysicsSILAFAE Jan 2008

Amir H. Rezaeian (USM) SILAFAE Bariloche Jan 2009 1 / 29

Outline

Direct photon production at RHIC and LHC in pp and p(A)Acollisions:

➤ The role of saturation effects on the direct photons production➤ RpA and v2 for direct photons

Hadron productions in pA collisions from SPS to LHC via RHIC:

➤ Calculating the Broadening without any fitting(parameter-free)➤ Cronin effect for pions

References:Kopeliovich, AHR and Schmidt, PRD 78, 114009 (2008)Kopeliovich, AHR and Schmidt, NPA 807, 61 (2008)Kopeliovich, Pirner, AHR. and Schmidt, PRD 77, 034011 (2008)AHR and Z. Lu, arXiv:0810.4942Kopeliovich, AHR, Pirner and Schmidt, PLB 653, 210 (2007)


QCD x-Q2 phase diagram

x-610 -510 -410 -310 -210 -110 1

)2 =

10

GeV

2xG

(x,Q

-110

1

10

210)2 = 10 GeV2gluon (Q

ZEUS-2005

H1-PDF 2000

CTEQ6.5M

Alekhin02-NLO

MRST-NLO 2001

)2 = 10 GeV2u-quark (Q MRST2001-NLO

x-610 -510 -410 -310 -210 -110 1

)2 =

10

GeV

2xG

(x,Q

-110

1

10

210

Increasing Q2: DENSITY DECREASES, PARTONS KEEP THEIR IDENTITY.

Increasing x : The density in the transverse grows, THE PARTON IDENTITY IS LOST. Evolution is nonlinear.

Saturation scale: Q2s ∼

Axg(x,Q2s )

πR2A

∼ A1/3(p

SNN )λeλy with λ ≈ 0.3 . Saturation affects the processes in

Q2 ≤ Q2s .


Parton model versus color dipole approach

σγ∗pT ,L (x ,Q2) =

∫

d2r

∫

dzΨT ,L(z, r)σ(x, r2)

The parton model:pdfs are universal.Next to leading corrections and higher twisteffects make the computation more difficult.

The color dipole model:σ(x , r2) is universal.The description by default includes thehigher order and higher twist corrections.However, it is expected to work only at verysmall Bjorken x .Golec-Biernat, Wusthoff 99

Dipole cross section (BK Eq.): GBWmodel, Itakura-Iancu-Munier model,Kharzeev-Kovchegov-Tuchin model, ....butwhat is missing in all: dipole orientation

γ* γ*

p

z

1-zr

p

H1/ZEUS

F2

Q2=1.5 GeV2 Q2=2 Q2=2.5 Q2=3.5 Q2=4.5 Q2=5

Q2=6.5 GeV2 Q2=8.5 Q2=10 Q2=12 Q2=15 Q2=18

Q2=20 GeV2 Q2=22 Q2=25 Q2=27 Q2=35 Q2=45

Q2=60 GeV2 Q2=70 Q2=90 Q2=120 Q2=150 Q2=200

Q2=250 GeV2 Q2=350 Q2=450 Q2=650 Q2=800

H1(94/95)

ZEUS(94)

0

0.5

1

1.5

0

0.5

1

1.5

0

0.5

1

1.5

0

0.5

1

1.5

0

0.5

1

1.5

10-4

10-3

10-2

10-4

10-3

10-2

10-4

10-3

10-2

10-4

10-3

10-2

10-4

10-3

10-2

10-4

10-3

10-2Amir H. Rezaeian (USM) SILAFAE Bariloche Jan 2009 4 / 29

QCD x-Q2 phase diagram

p

� ~r~b

E1� zz x x0

p0

p

� E

p0

~r~b

1� zz x x0x0xx0x

σCGCqq̄ (x, r) = σ0

8

>

<

>

:

N0

“

rQs2

”2“

γs+ 1κλY

ln 2rQs

”

: rQs ≤ 2

1 − e−A ln2(BrQs ) : rQs > 2

,

σGBW-DGLAPqq̄ (x,~r) = σ0

1 − exp

−π2r2αs (µ

2)xg(x, µ2)

3σ0

!!

,


From Available measurements in (x , Q2) to LHC

x -610 -510 -410 -310 -210 -110 1

)2/c2

(GeV

2Q

-210

-110

1

10

210

310

410

510

x -610 -510 -410 -310 -210 -110 1

)2/c2

(GeV

2Q

-210

-110

1

10

210

310

410

510 )ηRHIC data (forw.

= 3.2)η (±BRAHMS h

= 1.8)η (±PHENIX h

Nuclear DIS & DY data:NMC (DIS)SLAC-E139 (DIS)FNAL-E665 (DIS)EMC (DIS)FNAL-E772 (DY)

perturbative

non-perturbative

y=1 (

HERA √s=32

0 GeV

)

x

Q2 (G

eV2 )

E665, SLAC

CCFR, NMC, BCDMS,

Fixed Target Experiments:

D0 Inclusive jets η<3

CDF/D0 Inclusive jets η<0.7

ZEUS

H1

10-1

1

10

10 2

10 3

10 4

10 5

10-6

10-5

10-4

10-3

10-2

10-1

1

10-5

10-4

10-3

10-2

10-1

10010

-2

10-1

100

101

102

103

104

2 /GeV

2

mc2

mb2

E772DY

DIS NMCE665

LHCpA

DY RHICpA

DYSPSDY

from HQ LHC, pAHQ

LHC, ApDY

saturation, Pb

saturation, p

y Q~0

y Q~3

η-10 -8 -6 -4 -2 0 2 4 6 8 10

)c

(G

eV/

η/d

Td

p

-110

1

10

210

310

410

AL

ICE

LH

Cb

CA

ST

OR

, T2

CA

ST

OR

, T2 HF

/FC

al, T

1

HF

/FC

al, T

1

ATLAS,CMS

)η/2 exp(-s = maxT

pp-p @ 14 TeV Z

DC

, LH

Cf

ZD

C, L

HC

f

TO

TE

M R

Ps

AL

FA

RP

sF

P42

0

TO

TE

M R

Ps

AL

FA

RP

sF

P42

0

η-10 -8 -6 -4 -2 0 2 4 6 8 10

)c

(G

eV/

η/d

Td

p

-110

1

10

210

310

410

~140m-240m-420m

~14-17 m

~11 m

D. d‘Enterria, 0708.0551, hep−ex/0610061


Direct photons productions at RHIC, CDF and LHC

Direct photons: photons not from hadron decays

A powerful proble for the initial state of matter created in Heavy-Ioncollisions, direct photon RpA, RAA, v2 and ... yet to be understood atRHIC..Sources of direct photons:

1: LO: Compton scattering process q + q̄ > q̄ + γ and annihilationprocess : q + q̄− > g + γ

3: NLO: Bremsstrahlung

4: NNLO: Jet fragmentation

5: pre-equilibrium photon, thermal-photon, jet-photon conversion inpresence of medium


The transverse momentum pT distribution of photon bremsstrahlung frominteraction of quark with a target t( nucleon: t=N, nucleus t=A)Kopeliovich, A.H.R., Schmidt, NPA 807, 61 (2008)

dσqt→γX (b, p, α)

d(lnα)d2~pTd2~b=

1

(2π)2

∑

in,f

∫

d2~r1d2~r2e

i~pT .(~r1−~r2)

× φ⋆γq(α,~r1)φγq(α,~r2)Ft(~b, α~r1, α~r2, x),

r

��

��

��

��

αγ

q

1−αg

βq

qr

β

rr

1−β

(1−β)α

β=1/(2−α)

+

where α = p+γ /p

+q and Ft(~b, α~r1, α~r2, x) which is a linear combination of q̄q

dipole partial amplitudes on a target t at impact parameter ~b,

Ft(~b, α~r1, α~r2, x) = Imf tqq̄(~b, α~r1, x) + Imf t

qq̄(~b, α~r2, x)

− Imf tqq̄(~b, α(~r1 −~r2), x),

Imf Aqq̄(b,~r) = 1 − exp[

∫

d2~s Imf Nqq̄(~s ,~r)TA(~b +~s)]

∫Amir H. Rezaeian (USM) SILAFAE Bariloche Jan 2009 8 / 29

Advantages of this approah to the parton model:

Neither K-factor (NLO corrections), nor higher twist corrections areto be added.

Quark-to-photon fragmentation function is not needed.

It is not necesary to introduce a primordial transvese momentum atthe moderate pT .

Disadvantages of this approah to the parton model:

valid at small x , high energy.


Dilepton spectrum in 800− GeV pp

Kopeliovich, A.H.R, Pirner, Schmidt, PLB 653, 210 (2007)

0 1 2 3 4 5p

T(GeV)

10-4

10-3

10-2

10-1

100

Ed

3σ

/d3P

[pb/G

eV2]

E866 DataGBWGBW-DGLAPGBW-DGLAP-Primordial

xF=0.63, M=5.70 GeV

0 1 2 3 4 5p

T(GeV)

10-3

10-2

10-1

100

Ed

3σ

/d3P

[pb/G

eV2]

E866 DataGBWGBW-DGLAPGBW-DGLAP-Primordial

xF=0.63, M=4.8 GeV

constant primordial momentum 〈k20 〉 = 0.4GeV2 is incorporated within the

GBW-DGLAP dipole model (solid line)


Direct photons productions at RHIC and CDF

0 3 6 9 12 15 18 21 24 27 30p

T [GeV]

102

103

104

105

106

d2σ

/dp

Tdη

[p

b/G

eV]

CDF dataGBW-DGLAPGBW, without charmGBW, with charmb-CGC, γ

s= 0.46

CGC, γs= 0.63

NLO QCD, CTEQ5M, µ=pT

No Sat., γs = 0.43

No Sat., γs = 1

0 2 4 6 8 10 12 14 16p

T [GeV]

10-2

100

102

104

106

Ed3 σ

/d3 P

[pb

/GeV

2 ]

RHIC dataGBW-DGLAPGBW, with charmGBW, without charmCGC, γ

s = 0.63

b-CGC, γs = 0.46

No Sat., γs = 0.43

No Sat., γs = 1

x=0.01AHR et al., PreliminaryAHR et al., Preliminary


Photons productions at LHC for different rapidities in pp

0 30 60 90 120 150 180p

T [GeV]

10-2

100

102

104

106

d2σ

/dp

Tdη

[pb/G

eV]

GBW-DGLAP, √s = 14 TeV

GBW, with charm, √s = 14 TeV

GBW, with charm √s = 5.5 TeV

GBW-DGLAP, √s = 5.5 TeV

0 2 4 6 8 10 12 14 16 18 20p

T [GeV]

10-3

100

103

106

Ed

3σ

/d3P

[p

b/G

eV2]

GBW, with charmb-CGCCGCNo Sat., γ

s = 0.43

No Sat., γs = 1

√s = 14 TeV

η = 8

η = 7

η= 6

η = 0

η = 0

AHR et al., PreliminaryAHR et al., Preliminary

At η = 0 the DGLAP anamolus dimension γs = 1 is in favour (with no Sat).At very forward rapidity, BK anamolus dimension γs = 0.43 is in favour(with no Sat).


Photons productions at LHC for different rapidities in pp

0 1 2 3 4 5 6 7 8 9 10P

T [GeV]

-50

0

50

100

150

200

250

300

10

0*

(T1

-T2

)/T

2

η = 4η = 7 η = 8

T1 = GBW with charmT2 = b-CGC

0 2 4 6 8 10P

T [GeV]

0

50

100

150

200

100*

(GB

W-r

2)/r2

1×106

2×106

3×106

4×106

5×106

Ed3 σ/

d3 P [p

b/G

eV2 ]

GBW, without charmGBW. with charmCGCNo Sat., γ

s = 0.43

5.0×105

1.0×106

Ed3 σ/

d3 P [p

b/G

eV2 ]

0 1 2 3 4 5 6 7 8 9 10η

0.0

1.0×105

2.0×105

3.0×105

4.0×105

5.0×105

Ed3 σ/

d3 P [p

b/G

eV2 ]

pT = 1 GeV

pT = 2 GeV

√s = 14 TeV

pT = 3 GeV


Elliptic flow for photons

Why Azimuthal asymmetry?Observables will become azimuthally dependent if they are sensitive to thedensity and size of system → A good test of many features of QGP

ZY

Y

X

X

ψ

φ

b

E d3N i

d3pT= 1

2πd2N i

pT dpT dy

(

1 +∑

∞

n=1 2v incos(n(φ− ψ))

)

v2 = 〈cos(2(φ − ψ))〉 φ = tan−1py/pxAmir H. Rezaeian (USM) SILAFAE Bariloche Jan 2009 14 / 29

color dipole orientation and Azimuthal asymmetry

Kopeliovich, Pirner, AHR., Schmidt, PRD 77, 034011 (2008)

2

1

1 2

( )s, rf

( )s, rf

> ( )s, rf( )s, rf

qq

qq

qq qq

1−

α

1−

αr

rα

α

s

s

The main idea: An azimuthal asymmetry appears due to dependence of theinteraction of a dipole on its orientation.


dipole orientationA toy model: two-gluon exchange

An azimuthal asymmetry appears due to dependence of the interaction ofa dipole on its orientation.

Imfqq̄q(~s ,~r) =

2

9π2

∫

d2q d2q′ αs(q2)αs(q

′2)

(q2 + µ2)(q′2 + µ2)

×[

e i~q·(~s+~r/2) − e i~q·(~s−~r/2)] [

e i~q ′·(~s+~r/2) − e i~q ′

·(~s−~r/2)]

=8α2

s

9

[

K0

(

µ

∣

∣

∣

∣

~s +~r

2

∣

∣

∣

∣

)

− K0

(

µ

∣

∣

∣

∣

~s −~r

2

∣

∣

∣

∣

)]2

This expression explicitly exposes a correlation between ~r and ~s: theamplitude vanishes when ~s ·~r = 0.


Color dipole orientation

Kopeliovich, Pirner, AHR., Schmidt, PRD 77, 034011 (2008)

Imf Nq̄q(~s,~r , β) =

1

12π

∫

d2q d2q′

q2 q′2αs F(x , ~q, ~q ′)e i~s·(~q−~q ′)

×(

e−i~q·~rβ − e i~q·~r(1−β)) (

e i~q′·~rβ − e−i~q′

·~r(1−β))

where αs =√

αs(q2)αs(q′2)

βq

qr

β

rr

1−β

(1−β)

F(x , q) = F(x , ~q, ~q = ~q ′).

σNqq̄(r) = 2

∫

d2~s Imf Nqq̄(~s ,~r)

=4π

3

∫

d2q

q4(1 − e−i~q.~r )αs(q

2)F(x , q).

Relying on the saturation shape (CGC) of the dipole cross-section σN (r)Amir H. Rezaeian (USM) SILAFAE Bariloche Jan 2009 17 / 29

σNqq̄(r) = 2

∫

d2~s Imf Nqq̄(~s,~r) = σ0

(

1 − e−r2/R20

)

0

2

4

6

-2

0

2

0

1

2

3

0

2

4

0

2

4

6

-2

0

2

3.6843.6863.6883.69

3.692

0

2

4

0

2

4

6

-2

0

2

0

0.5

1

0

2

4

0

2

4

6

-2

0

2

0

0.001

0.002

0

2

4

α = 0 (β = 1/2)

α = 1 (β = 1)

δqqN

Im f

r [fm]

s = 0 s = 2 fm

s = 0 s = 2 fm

0 1 2 3 4 5 6 7 8 9 10

r (GeV-1

)

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

σ (

mb

)


Direct photon v2 at RHIC

3 4 5 6 7 8

-0.04

-0.02

0

0.02

0.04

0.06

0.08

v2

γ

N-N + jet-frag.direct γdirect γ (no E-loss)

3 4 5 6 7 8p

T (GeV/c)

3 4 5 6 7 8

0-20 % 20-40 % 40-60 %

0.5 1 1.5 2 2.5 3 3.5p

T (GeV)

-0.0025

-0.002

-0.0015

-0.001

-0.0005

0

0.0005

0.001

v2

AA

B = 13 fm

B = 9.4 fm

B = 7 fm

4 6 8 10-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

6 8 10

Au+Au @ s1/2

NN = 200 GeV

v2

pT (GeV/c)

jet-photon conv total initial production jet fragment

30%-- 40%

pT (GeV/c)

40%-- 50%

T

T

Turbide et al, PRL 96, 032303 (2006) Kopeliovich, AHR, Schmidt, arXiv:0712.2829

Chatterjee et al, PRL 96, 202302 (2006) Liu and Fries, arXiv:0801.0453

Thermal Photons

Jet−Photons conv

Prompt Photons

bremsstrahlung

Kopeliovich, AHR, Schmidt, NPA 807,61 (2008)


Cronin effect for photons in pA collisions

What is Cronin effect?

RpA =

dσpA→h+X

dyd2pT

〈Nbinary 〉dσpp→h+X

dyd2pT

,

Two very different approaches to compute the Cronin factor RpA

Initial-state effectsDue to the broadening of the parton transverse momentum in theinitial-state where the fragmentation of hard partons is assumed tooccur outside the cold medium.

Final-state effectsDue to the recombination of soft and shower partons in the final-state.


Cronin effect for direct photons, Prediction for RHIC andLHC (preliminary)

0 1 2 3 4 5 6 7p

T [GeV]

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Rγ d

Au

without charm, with shadowingwithout charm, without shadowingwith charm, with shadowingwith charm, without shadowing

√s = 200 GeV, min bias <k

T

2> = 0, GBW

0 1 2 3 4 5 6 7p

T [GeV]

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Rγ d

Au

without charm, with shadowingwithout charm, without shadowingwith charm, with shadowingWith charm, without shadowing

LHC, 5.5 TeV, min bias<k

T

2> = 0, GBW


Hadron production in PQCD+color dipole scheme

dσhpA

d2pT

= K∑

i ,j,k,l

Fi/p ⊗ Fj/A ⊗d σ̂

dt̂(ij → kl) ⊗ Dh

k

Fi/p = fi/p

(

xi ,Q2)

⊗dNi

d2kiT

(xi , b) and Fj/A = TA(b) fj/A

(

xj ,Q2)

⊗dN

(0)j

d2kjT

(xj , b)

GG

qq

AA

Johnson, Kopeliovich and Tarasov, PRC 63 (2001) 035203

dNi

d2kiT

=1

(2π)2

∫

d2r1d2r2 e i ~kT (~r1−~r2)

[

〈k2T 〉

πe−

12 (r2

1 +r22 )〈k2

T 〉

]

[

e−12 σN

q̄q(~r1−~r2,x) TA(b)]

σNq̄q(~r1 −~r2, x)TA(b) → Imf N

qq̄(~s,~r1 −~r2, x) ⊗ TA(~b +~s)


pions production in pp collisions at RHIC

AHR, Lu, arXiv:0810.4942

10-8

10-6

10-4

10-2

100

Ed

3σ

/d3P

[m

b/G

eV

2]

PHENIX, π0

AKK08Kretzer

0 2 4 6 8 10 12 14 16P

T [GeV]

-0.8

-0.4

0

0.4

0.8

(DA

TA

-Th

eo

ry)/

Th

eo

ry

√s = 200 GeV, p + p

10-6

10-4

10-2

100

102

Ed

3σ

/d3P

[m

b/G

eV

2]

STAR, π++ π−

STAR, (p + p)* 0.1

0 2 4 6 8P

T [GeV]

-0.8-0.4

00.40.8

(Data

-Th

eo

ry)/

Th

eo

ry

√s = 200 GeV, p + p

AKK08

0 1 2 3 4 5 6 7 8 9p

T[GeV]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

STAR p/π+

STAR p/π−

(p+p)/(π++π−)

√s = 200 GeV, p+p


pions production in pA collisions at RHIC

AHR, Lu, arXiv:0810.4942

0.6

0.8

1

1.2

1.4

1.6

1.8

2

RdA

u

PHENIX (min bias)HKN 07HIJING newEKS 98

0 2 4 6 8 10 12 14p

T [GeV]

0.6

0.8

1

1.2

1.4

RdA

u

PHENIX (min bias)KretzerAKK08

√s = 200 GeV, π0

HIJING new

AKK08

0.4

0.8

1.2

1.6

RdA

u

PHENIX (0-20%)

0.4

0.8

1.2

1.6

RdA

u

PHENIX (20-40%)

0 2 4 6 8 10p

T [GeV]

0.4

0.8

1.2

1.6

RdA

uPHENIX (40-60 %)

√s = 200 GeV, π0

0

0.4

0.8

1.2

1.6

2

2.4

2.8

RdA

u

STAR (min bias), p+ pHKN 07HIJING newEKS 98

0 1 2 3 4 5 6 7 8 9p

T [GeV]

0

0.4

0.8

1.2

1.6

2

2.4

2.8

RdA

u

STAR (min bias), π++π−

AKK08

The observed Cronin ratio for pions in d + Au collisions can be fairlydescribed by transverse momentum broadening due to initial partonsmulti-scatterings. But the same mechanism seems to underestimatethe observed Cronin ratio for protons in d + Au collisions.


Our choices:

1: Initial state-effects might not be totally accountable for the observedCronin effect for baryons in p + A collisions and the separation of partonsinto two non-interacting components, soft and hard, might be anoversimplification.


Our choices:


2: Baryons productions mechanism in cold nuclear medium is different frompions productions.


Our choices:



3: Both 1 and 2 are correct!


Our choices:



3: Both 1 and 2 are correct!

4: None of 1,2,3


Pions v2 in pp and pA collisions (predictions)

Kopeliovich, AHR and Schmidt, PRD 78, 114009 (2008)

1 1.5 2 2.5 3 3.5p

T [GeV]

0

0.01

0.02

0.03

v2

π

b = 0.2 fmb = 0.4 fmb = 0.6 fm

√s = 200 GeV, pp π0

X

GBW model

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6p

T [GeV]

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

v2

π

b = 7 fmb = 6 fm

E lab

= 400 GeV, pAu π0X

KST model

Azimuthal asymmetry of pions in both pp and pA collisions is rather small. This

indicates that the contribution of the initial state effects, which is present in cold

nuclear matter in the observed azimuthal asymmetry v2 of the produced hadrons

in AA collisions at RHIC, is very small.Amir H. Rezaeian (USM) SILAFAE Bariloche Jan 2009 26 / 29

Cronin effect for pions, prediction for LHC at η = 0

1: PQCD factorization+color dipole

2: Color dipole factorization

3: Color Glass condensate senario

Predictions are based on:

2 4 6 8 10p

T [GeV]

0.6

0.8

1

1.2

1.4

1.6R

dA

uRHIC Data (min bias)RHIC, √

s = 200 GeV

LHC, √s = 5.5 TeV

dAu π0X

EKS, <kT

2> = 3 GeV

2

0.8

0.9

1

1.1

1.2

0.8

0.9

1

1.1

1.2

0 2 4 6 8 10 12 14 16

pT (GeV/c)

RA(p

T)

√s−=200 GeV

√s−=5.5 TeV

pT (GeV)

R d+A

u

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6

Kopeliovich, et al, PRL 88 (2002) 232303

Kharzeev, et al, PLB 599 (2004) 23

AHR, et al, (Preliminary)


Summary and outlook

Direct photons: A global picture is emerging where the physics ofQCD jets and electromagnetic probe in nuclear collisions need to betreated systematically in order to understand the underlying dynamics.


Summary and outlook


LHC is expected to become a laboratory for gluo-dynamics, whichshould settle many of controversies in our understanding the small-xphysics, e.g the saturation effects.


Summary and outlook



The inclusive direct photons production is not very sensitive to thesaturation effects even at very forward rapidities at LHC, while itstrongly depends on the anamolous dimension.


Summary and outlook




One can measure anamolous dimension (coming either from DGLAP,BFKL, BK or etc) by LHC.


Summary and outlook




One can measure anamolous dimension (coming either from DGLAP,BFKL, BK or etc) by LHC.

LHC data with nuclear beams will reveal the gluonic structure ofnuclei. They should resolve the controversy about the magnitude ofgluon shadowing. The saturation scale in nuclei is expected to reachvalues of few GeV, leading to strong observable effects.


Looking forward to the first real collision


Documents

High-pt probes from RHIC to LHC - fisica.cab.cnea.gov.ar · Amir H. Rezaeian (USM) SILAFAE Bariloche Jan 2009 2 / 29. QCD x-Q2 phase diagram x 10-6 -5 10-4 10-3 -2 -1 1) 2 = 10 GeV