[PPT] - Photon, photon-hadron and di-photon production in the saturation PowerPoint Presentation

SLIDE 1

Photon, photon-hadron and di-photon production in the saturation approaches at the FCC

A. Rezaeian

Universidad Tecnica Federico Santa Maria, Valparaiso Workshop on the opportunities with nuclear beams at the Future Circular Collider (CERN, Geneva, Sep 2014)

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 1 / 35

SLIDE 2

Outline

Introduction to the small-x physics; and the CGC phenomenology Prompt photons, photon-hadron and di-photon production in high-energy p+A collisions from the CGC Some predictions at the LHC and the FCC

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 2 / 35

SLIDE 3

Road map of strong interaction

LO pQCD

The saturation scale Q2

s ≈ (A/x)1/3 increases by lowering x or/and

increasing A . Is the CGC perturbative approach reliable & systematic at the small-x? What are the signatures of the gluon saturation phenomenon at HERA, RHIC, LHC, LHeC, EIC and FCC?

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 3 / 35

SLIDE 4

A unified description of e+p (x < 0.01) inclusive & exclusive data in the CGC

Rezaeian, Siddikov, Van de Klundert, Venugopalan, arXiv:1212.2974; Rezaeian, Schmidt, arXiv:1307.0825

ρ ZEUS 120 pb-1 ρ ZEUS 94 ρ ZEUS 95 φ ZEUS 98-00 φ ZEUS 94 J/ψ ZEUS 98-00 J/ψ ZEUS 96-97 J/ψ H1 96-00 ρ H1 95-96 DVCS H1 96-00

Q2+M2(GeV2) B (GeV-2) 2 4 6 8 10 12 14 5 10 15 20 25 30 35 40 45 50 J/ψ ρ-meson φ-meson DVCS D 10 100 Q 2 (GeV 2 ) 0.1 1 10 σ(nb) W = 82 GeV, H1 γ ∗ p γ p 25 125

W(GeV)

0.1 1 10

σ(nb)

Q

2

= 8 GeV

2

Q

2

= 25 GeV

2

γ

∗

p γ p

0.5 1 1.5

|t| (GeV

2

)

10

4

10

2

10 10

2

dσ/dt (nb/GeV2)

Q

2

= 8 GeV

2

Q

2

= 15.5 GeV

2

Q

2

= 25 GeV

2

γ

∗

p γ p

W = 82 GeV, H1

100 101 102 10

1

10 10

1

10

2

W = 90 GeV ZEUS γ*p →ρ p σ (nb) 100 101 102 10

1

10 10

1

10

2

W = 75 GeV H1

(c) M. Siddikov

γ*p →ρ p σ (nb) Q2+M2

ρ (GeV2)

Q2+M2

ρ (GeV2) 100 200 10 10

1

10

2

10

3 2.4 Q² (GeV²) 3.3 Q² (GeV²) 6.6 Q² (GeV²) 11.9 Q² (GeV²) 1 9 . 5 Q² (GeV²)

H1 ZEUS γ*p →ρ p 100 200 10 10

1

10

2 3 . 3 Q² (GeV²) 6 . 6 Q² (GeV²) 15.8 Q² (GeV²)

H1 ZEUS γ*p →φ p σ (nb) 100 200 10 10

1

10

2 . 5 Q² (GeV²) 3 . 2 Q² (GeV²) 7.0 Q² (GeV²) 22.4 Q² (GeV²)

H1 ZEUS γ*p → J/ψ p σ (nb) σ (nb) W (GeV) W (GeV) W (GeV)

(c) M. Siddikov

10

4

10

3

10

2

0.1 0.2 0.3 0.4 0.5 Q² = 12 GeV² 10

4

10

3

10

2

0.1 0.2 0.3 0.4 0.5 H1+ZEUS mc =1.27 GeV mc =1.4 GeV 10

4

10

3

10

2

0.1 0.2 0.3 0.4 0.5 Q² = 7 GeV²

(c) M. Siddikov

10

4

10

3

10

2

0.1 0.2 0.3 0.4 0.5 Q² = 60 GeV² 10

4

10

3

10

2

0.1 0.2 0.3 0.4 0.5 Q² = 5 GeV² 10

4

10

3

10

2

0.1 0.2 0.3 0.4 0.5 Q² = 32 GeV² 10

4

10

3

10

2

0.1 0.2 0.3 0.4 0.5 Q² = 2.5 GeV² 10

4

10

3

10

2

0.1 0.2 0.3 0.4 0.5 Q² = 18 GeV²

x F

2 cc _

(c) M. Siddikov

0.5 1 10 10

1

10

2

Q² = 2.4 GeV² Q² = 3.6 GeV² Q² = 5.2 GeV² Q² = 6.9 GeV² Q² = 9.2 GeV² Q² = 12.6 GeV² Q² = 19.7 GeV²

γ*p →φ p |t| (GeV2) dσ/dt (nb/GeV2)

(c) M. Siddikov

W=75 GeV, ZEUS 0.5 1 10

1

10 10

1

10

2

10

3

Q² = 2.7 GeV² Q² = 5 GeV² Q² = 7.8 GeV² Q² = 11.9 GeV² Q² = 19.7 GeV² Q² = 41 GeV²

γ*p →ρ p dσ/dt (nb/GeV2) |t| (GeV2)

(c) M. Siddikov

W=106 GeV, ZEUS

101 102 10 10

1

10

2

W = 75 GeV H1 ZEUS γ*p →φ p 101 102 10 10

1

W = 90 GeV H1 ZEUS

(c) M. Siddikov

γ*p → J/ψ p σ (nb) σ (nb) Q2+M2

J/ψ (GeV2)

Q2+M2

φ (GeV2)

(c) M. Siddikov

0.5 1 10 10

1

10

2

Q² = 0 GeV² Q² = 3.1 GeV² Q² = 6.8 GeV² Q² = 16 GeV²

γ*p → J/ψ p dσ/dt (nb/GeV2) |t| (GeV2)

(c) M. Siddikov

W=90 GeV, ZEUS 0.5 1 10 10

1

10

2

Q² = 0.05 GeV² Q² = 3.2 GeV² Q² = 7 GeV² Q² = 22.4 GeV²

γ*p → J/ψ p |t| (GeV2) dσ/dt (nb/GeV2)

(c) M. Siddikov

W=100 GeV, H1 5 10 15 20 1 2 3 4 5 6 7 8 H1, 35<W<180 GeV ZEUS, 40<W<140 GeV

(c) M. Siddikov

γ*p →ρ p R=σL/σT Q2 (GeV2)

5 10 15 20 1 2 3 4 5 6 7 8 H1, 35<W<180 GeV ZEUS, W=90 GeV

(c) M. Siddikov

γ*p →φ p R=σL/σT Q2 (GeV2)

5 10 15 20 1 2 3 4 5 6 7 8 W = 90 GeV ZEUS

(c) M. Siddikov

γ*p → J/ψ p R=σL/σT Q2 (GeV2)

10-5 10-4 10-3 10-2 10 10

1

10

2

10

3

10

4

10

5

10

6

10

7

10

8

10

9 0.85, 0

Q² (GeV²), i

1.2, 1

Q² (GeV²), i

1.5, 2

Q² (GeV²), i

2 . , 3

Q² (GeV²), i

2.7, 4

Q² (GeV²), i

3.5, 5

Q² (GeV²), i

4.5, 6

Q² (GeV²), i

6.5, 7

Q² (GeV²), i

8.5, 8

Q² (GeV²), i

10, 9

Q² (GeV²), i

12, 10

Q² (GeV²), i

15, 11

Q² (GeV²), i

18, 12

Q² (GeV²), i

22, 13

Q² (GeV²), i

27, 14

Q² (GeV²), i

35, 15

Q² (GeV²), i

4 5 , 1 6

Q² (GeV²), i

60, 17

Q² (GeV²), i

70, 18

Q² (GeV²), i

90, 19

Q² (GeV²), i

1 2 , 2

Q² (GeV²), i

1 5 , 2 1

Q² (GeV²), i

200, 22

Q² (GeV²), i

250, 23

Q² (GeV²), i

300, 24

Q² (GeV²), i

400, 25

Q² (GeV²), i

5 , 2 6

Q² (GeV²), i

650, 27

Q² (GeV²), i HERA e p HERA e p

x F (x, Q ) 2 ×

2 2 i

+

(c) M. Siddikov

γ∗ J/Ψ,ρ,φ,γ p p − q b ∼ 1/|t|

r

t = −q2 1 − z z Q ∼ 1/r

N(x,r,b)

The dipole scattering amplitude is the main ingredient with 3 or 4 free parameters fixed via a fit to the reduced cross−section.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 4 / 35

dipole amplitude small-x physics

SLIDE 5

The impact-parameter b and x- dependence of the saturation scale for proton

2 4 6 8

b (GeV

1)

0.1 0.2 0.3 0.4 0.5

(1/σ

γ∗p)dσ γ∗p/db (GeV) Q

2 = 0.8 GeV 2

Q

2= 3 GeV 2

Q

2= 50 GeV 2

2 4 6 8 b-CGC IP-Sat x = 10

4

1 2 3 4 5

b (GeV

1)

0.5 1 1.5 2 2.5 3

QS

2 (GeV 2)

b-CGC IP-Sat 4 8 12 16 x = 10

8

x = 10

4

LHC HERA FCC x = 10

6

The typical impact-parameter probed in the total γ∗p cross-section is about b ≈ 2 ÷ 3 GeV−1 = ⇒ less constrain for b ≈ 0 (large |t| diffractive data are needed). The proton saturation scale at HERA: Qs(x, b) < 1 GeV, at the LHC: Q2

s (x, b) < 1.5 ÷ 3 GeV2 and at the FCC: Q2 s (x, b) ≤ 4 ÷ 15 GeV2.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 5 / 35

SLIDE 6

Saturation scale extracted from recent combined HERA data

10

2

10

3

10

4

10

5

10

6

10

7

10

8

1/x

0.04 0.1 0.3 1 3 9

QS

2 (GeV 2)

b-CGC IP-Sat IIM rcBK

b = 0 b = 2 GeV

1

b = 3 GeV

1

pp@100 TeV(FCC) 1 GeV

2

15 GeV

2

ep@HERA pA@63 TeV(FCC)

Order of magnitude discrepancies in saturation scale extracted from different models= ⇒ sizable uncertainties in predictions of various observables. Current small-x data do not put enough constrains on saturation models at x < 10−5. Q2

s (x, b) ≤ 4 ÷ 15 GeV2 at FCC kinematics.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 6 / 35

Impact-parameter dependent

SLIDE 7

CGC description of combined HERA data: uncertainties

Rezaeian, Schmidt, arXiv:1307.0825 10

7

10

6

10

5

10

4

10

3

10

2

x

10

1

10 10

1

10

2

10

3

10

4

10

5

10

6

10

7

10

8

10

9

10

F2 (x,Q

2) 2 n

H1& ZEUS

650, 27

b-CGC IP-Sat

500, 26 400, 25 300, 24 Q

2[GeV 2], n

250, 23 200, 22 150, 21 120, 20 90, 19 70, 18 60, 17 45, 16 35, 15 27, 14 22, 13 18, 12 15, 11 12, 10 10, 9 8.5, 8 6.5, 7 4.5, 6 3.5, 5 2.7, 4 2.0, 3 1.5, 2 1.2, 1 0.85, 0

10

7

10

6

10

5

10

4

10

3

10

2

x

10

3

10

2

10

1

10 10

1

10

2

10

3

F

cc 2(x, Q 2) 2 n

H1 & ZEUS

b-CGC IP-Sat

Q

2[GeV 2],n

60, 6 32, 5 18, 4 12, 3 7, 2 5, 1 2.5, 0

Fc¯

c, F2 data were not included in the fit.

The difference among models can be considered as our current theoretical uncertainties = ⇒ significant uncertainties at small-x = ⇒ Future exps with xB < 10−5 (FCC, LHeC, EIC) can constrain saturation models.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 7 / 35 FCC

SLIDE 8

Testing CGC approach: p+p@LHC

Comparing CGC predictions with 7 TeV data: Levin, Rezaeian, arXiv:1005.0631

10

2

10

3

10

4

√ ) s [GeV] 0.3 0.35 0.4 0.45 0.5 0.55 0.6 < pT > [GeV] CMS NSD E735 NSD CDF NSD UA1 NSD < z > = 0.5 < z > = 0.48 |η|< 2.4 7 TeV 1 2 3 4 pT [GeV] 10

4

10

2

10 10

2

1/(2πpT)d2Nch/dη dpT [GeV-2]

CMS, 7 TeV CMS, 2.36 TeV 14 TeV

|η|< 2.4, <z> = 0.48 20 40 60 80 nch 0.8 0.9 1 1.1 1.2 1.3 < pT > [GeV]

ATLAS data, √) s = 0.9 TeV, pT>0.5 GeV <z> = 0.5 <z> = 0.48

7 TeV 14 TeV 0.9 TeV 10

2

10

3

10

4

√ ) s [GeV] 2 3 4 5 6 7 dNch/dη

Saturation (b-CGC) KLN UA1 NSD UA5 NSD CDF NSD CMS NSD ALICE NSD ALICE INEL>0

η = 0

4
2

2 4 η 1 2 3 4 5 6 7 8 dNch/dη

CMS, 7 TeV CMS, 2.36 TeV CDF, 1.8 TeV UA5, 0.9 TeV ALICE, 0.9 TeV CMS, 0.9 TeV UA5, 546 GeV 7 TeV

mjet = 0.4 GeV

14 TeV

7 TeV

kT-factorization+ the dipole scattering amplitude constrained by DIS data.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 8 / 35

SLIDE 9

Testing CGC approach: CGC description of p+A data at the LHC

A p

Color−Glass−Condensate in pPb Collective flow in pPb collisions

20 40 60 80 Nch 0.6 0.75 0.9 1.05 1.2 < pT > [GeV] ALICE, p+p 7 TeV ALICE, p+Pb 5.02 TeV b-CGC (Saturation)

| η| < 0.3, 0.15< pT [GeV]<10 Nch in p+Pb data rescaled

4
3
2
1

1 2 3

η

10 20 30 40 50 60

dNch/dη

60-90% 40-60% 30-40% 20-30% 10-20% 5-10% 1-5%

b-CGC (Rezaeian, 1210.2385)

ATLAS Preliminary 5.02 TeV p+A , y=-0.465

2 4 6 8 10 12 14

pT[GeV]

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

R

ch pA ALICE , prelim. ALICE systematic errors CGC-rcBK, with average Q0A

5.02 TeV, η=0

Rezaeian, 1210.2385

Rezaeian, 1308.4736 Rezaeian, 1210.2385

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 9 / 35

SLIDE 10

Evidence of saturation: Geometric scaling in e+p, e+A, p+p, p+A

Rezaeian (2013)

10

1

1 10 10 2 10 3 10

3

10

2

10

1

1 10 10 2 10 3 E665 ZEUS+H1 high Q2 94-95 H1 low Q2 95 ZEUS BPC 95 ZEUS BPT 97 x<0.01 all Q2

τ σtotγ*p [µb]

10

2

10

1

10 10

1

10

2

10

3

10

4

τ

0.01 0.1 1 10 He (NMC) Li (NMC) C (NMC) Ca (NMC) Ca (E665) Xe (E665) Pb (E665) 5 × proton

F2

A/A scaled 50 100 150 200 250 300

Ntracks 0.3 0.6 0.9 1.2 1.5 1.8 <pT> [GeV] π Κ p Ntracks in p+Pb data rescaled by Sp/ SA

p+Pb p+p p+Pb p+Pb p+p p+p

CMS, p+p 7 TeV CMS, p+Pb 5.02 TeV 20 40 60 80

Nch 0.6 0.75 0.9 1.05 1.2 < pT > [GeV]

ALICE, p+p 7 TeV ALICE, p+Pb 5.02 TeV b-CGC (Saturation) | η| < 0.3, 0.15< pT [GeV]<10 Nch in p+Pb data rescaled

Stasto, Golec−Biernat, Kwiecinski (2000) Marquet, Schoeffel (2006) McLerran, Praszalowicz (2010) Freund, Rummukainen, Weigert, Schaefer (2002) Rezaeian,1308.4736 McLerran, Praszalowicz, Schenke (2013), Rezaeian (2013)

eA ep ep pp

pA

10

2

10

1

1

β dσ

diff γ*p/dβ (µb) H1 data (LRG) ZEUS data (Mx) *0.85 ZEUS data (LPS) *1.23 10

2

10

1

1 10

2

10

1

1 1 10 10 2

τd

1 10 10 2

τd

Geometric scaling: the observables scale as functions of the ratio Q2/Q2

s (x)

→ universality at small-x.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 10 / 35

SLIDE 11

Universality of particle production at small-x at different energies:p+p, p+A, A+A

Levin, Rezaeian, arXiv:1102.2385 ALICE collaboration, arXiv:1210.3615

10

1

10

2

10

3

10

4

√)

s [GeV] 2 4 6 8 10 12 14

UA5, pp NSD CDF, pp NSD CMS, pp NSD ALICE, pp NSD UA1, pp NSD ALICE, AA(0-5%) BRAHMS, AA(0-5%) PHENIX 1, AA(0-5%) PHENIX 2, AA(0-5%) STAR, AA(0-5%) NA50, AA(0-5%) Saturation (CGC)

dNpp/dη (2/Npar)dNAA/dη s

0.11

s

0.145

dNh dη ∝ Q2

s ∝ sλ/2 = s0.10÷0.145

b-dependence of the saturation scale is crucial for a detailed understanding of above scaling properties = ⇒ importance of exclusive diffractive processes.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 11 / 35

SLIDE 12

Testing CGC approach at the LHC and FCC: VM diffractive photo production

Armesto and Rezaeian, arXiv:1402.4831

10

1

10

2

10

3

10

4

Wγp [GeV]

10 10

1

10

2

10

3

10

4

σ(nb)

H1 data (2005) H1 data (2013) ZEUS (2002) E516, E401, E687 LHeC Simulation LHCb (2014) ALICE

γ

∗+p J/ψ +p

CGC (IP-Sat, b-CGC) MNRT (LO) MNRT (NLO)

2000

Wγp [GeV]

500 1000

σ(nb)

E516, E401, E687 H1 data (2013) ZEUS (2002) H1 data (2005) LHeC Simulation LHCb (2013) LHCb (2014) ALICE

γ

∗+p J/ψ +p IP-Sat (1-Pomeron)

mc=1.27 GeV mc=1.20 GeV

IP-Sat (Saturation)

mc=1.4 GeV mc=1.4 GeV mc=1.20 GeV mc=1.27 GeV

The LHCb 2014 data are in favour of the CGC/Saturation predictions. Tensions between the LHCb and ALICE data with the 1-Pomeron model and pQCD results (the uncertainties related to the charm mass is large). LHeC and FCC can distinguish between the different scenarios.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 12 / 35 FCC LHC HERA LHeC

SLIDE 13

Inclusive prompt photon and diphoton production In AA collisions all hadrons are strongly quenched except prompt photon → prompt photon is a good probe of initial-state (Saturation) effect. Single inclusive prompt photon and inclusive diphoton production are free from hadronization mess. Inclusive prompt photon, photon-hadron and diphoton production are better under control in the CGC approach compared to dihadron production.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 13 / 35 PHOTON Hadron

SLIDE 14

Two-particle production in high-energy p+A collisions

Dihadron Photon−hadron Diphoton

Dihadron v. photon-hadron v. diphoton production in the CGC Soft gluons are scattered out of the projectile wave function by directly scattering on a saturated target. Photons do not scatter themselves, but rather decohere from the scattered quarks. Virtual photons do not directly interact with the gluons inside target, final-state effects are absent in the diphoton production (and also no initial-final state interference, no hadronization). Universal decorrelation for back-to-back two-particle productions due to the saturation effect.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 14 / 35

Typical diagrams:

SLIDE 15

Two-particle production in p+A collisions from the CGC

Lappi, Mantysaari (2013)

Not yet measured

Kovner, Rezaeian (2014) Jalilian−Marian, Rezaeian (2012)

Photon−hadron Diphoton Dihadron

PHENIX & STAR (2011)

Not yet measured Measured at RHIC

Marquet (2007) Albacete, Marquet (2010) Stasto, Xiao, Yuan (2014) Plots: Braidot, arXiv:1008.3989

pT = 0 pT = 0 pT = 0

Back-to-back correlation gets suppressed due to the saturation scale. This is universal to all two-particle production shown above.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 15 / 35

SLIDE 16

Two-particle production in p+A collisions from the CGC

L

Dihadron Photon−hadron Diphoton

appears in F , F structure funtions Weizsacker−Williams (WW) gluon distribution (quadropole) counts the number of gluons (never measured) Color dipole gluon distribution (dipole) (measured)

2

Dihadron v. photon-hadron v. diphoton production in the CGC In contrast to dihadron production, photon-hadron and diphoton cross section depend only on the dipole amplitude (not WW gluon distribution).

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 16 / 35

SLIDE 17

Semi-inclusive prompt photon-hadron production in p+A collisions

p A h

pγ ph l

Gelis, Jalilian-Marian, hep-ph/0205037; Baier, Mueller, Schif, hep-ph/040320; Jalilian-Marian, Rezaeian, arXiv:1204.1319 dσp A→h(ph) γ(pγ) X d2bT d2pTγ d2pThdηγ dηh = e2

q αem

√ 2(4π4) 1

zmin f

dzf z2

f

dxq fq(xq, Q2)

1 + ( l−

k− )2

[p− lT − l−pTγ]2 NF (|lT + pT

γ|, xg )Dh/q(zf , Q2)

δ[xq − lT √ S eηh − pγ

T

√ S eηγ ]

2l−p− lT · pT

γ + p−(k− − p−) l2 T + l−(k− − l−) (pγ T )2

p−

(pγ

T )2√

S ∂NA(F)(r, x) ∂ ln(x0/x) =

d2r1 K run(r, r1, r2)
NA(F)(r1, x) + NA(F)(r2, x) − NA(F)(r, x) − NA(F)(r1, x) NA(F)(r2, x)
Initial condition:

N(r, Y =0) = 1 − exp  −

r2 Q0s2γ

4 ln 1 Λ r + e  

Free parameter: Q0s

For a proton: Q0p2 = 0.168GeV 2 (AAMQS, arXiv:1012.4408; Albacete and Dumitru, arXiv:1011.5161) For a nucleus: Q0A2 = N Q0p2 with 3 ≤ N ≤ 7 (Rezaeian, arXiv:1210.2385).

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 17 / 35

SLIDE 18

Inclusive prompt photon production in high-energy pA collisions

pγ k l pA ph

∆θ → 0

Jalilian-Marian, Rezaeian, arXiv:1204.1319 dσp A→γ(pγ ) X d2bTd2pTγdηγ = K (2π)2 1

xmin q

dxqfq(xq, Q2)NF (xg , pγ

T /z)

1 z Dγ/q(z, Q2) + e2

qαem

2π2(pγ

T )4

1

xmin q

dxqfq(xq, Q2)z2[1 + (1 − z)2]

l2

T <Q2 d2lT l2 T NF (¯

xg , lT )

,

xg = xq e−2 ηγ , ¯ xg = 1 xq S

(pγ

T )2

z + |lT − pγ

T |2

1 − z

z =

pγ

T

xq √ S eηγ , with xmin

q

= pγ

T

√ S eηγ .

Both fragmentation and direct photon are sensitive to saturation via NF. pA is different from dA (unlike hadron production) due to charge squared of quarks → non-trivial isospin effect.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 18 / 35

SLIDE 19

Inclusive photon production in p+A@LHC: collinear v. CGC

Arleo, Eskola, Paukkunen, Salgado, arXiv:1103.1471 0.8 0.9 1.0 1.1 1.2 1.3 20 40 60 80 100 120 140 160 180 200 20 40 60 80 100 120 140 160 180 200

proton PDF EPS09 nDS HKN

pT [GeV] R pPb

|y|<0.5 s

1/2=8.8 TeV 2 4 6 8 10 12 14 p

γ Τ [GeV]

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

R

γ pA CGC-IIM

Inclusive prompt photon, 5 TeV

CGC-rcBK

ηγ = 0

Q

2 0A(x=0.01) = NQ 2 0p

Q

2 0p = 0.168 GeV 2

N=7 6 5 4 3

To clearly discriminate between two approaches, forward rapidities measurements of Rγ

pA are needed.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 19 / 35

SLIDE 20

Direct photon production in p+A@LHC: Linear v. nonlinear

Peitzmann, arXiv:1308.2585

At very forward rapidities, two approaches give very different results → The measurement is discriminatory. Direct photons are not suppressed in QGP, but are subject to suppression in the CGC background due to gluon saturation.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 20 / 35

SLIDE 21

Inclusive direct photon v. hadron production in p+A collisions

Main input: BK evolution Eq.

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

R

ch pA

2 4 6 8 10 12 14 pT [GeV] 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

R

ch pA αs

in = 0.1

N=7 CGC-rcBK (0.2 > αs

in > 0.09)

Q

2 0A(x=0.01) = NQ 2 0p

4 3 5 6 N=7 6 Q

2 0p = 0.168 GeV 2

CGC-rcBK (αs

in = 0)

5 4 3

η = 4 η = 4 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

R

ch pA

2 4 6 8 10 12 14 pT [GeV] 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

R

ch pA αs

in = 0.1 N=7

CGC-rcBK (0.2 > αs

in > 0.09)

Q

2 0A(x=0.01) = NQ 2 0p 6 3 4 6 N=7 5

Q

2 0p = 0.168 GeV 2

CGC-rcBK (αs

in = 0)

η = 6 η = 6

5 4 3

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

R

γ pA

Direct photon, 5 TeV

2 4 6 8 10 12 14 p

γ Τ [GeV]

0.2 0.4 0.6 0.8 1 1.2 1.4

R

γ pA

ηγ = 4

CGC-rcBK

Q

2 0A(x=0.01) = NQ 2 0p 6 5 4 3 N=7

ηγ = 6

Q

2 0p = 0.168 GeV 2 N=7 6 5 4 3

2 4 6 8 10 12 14 p

γ Τ [GeV]

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 R γ pA

CGC-IIM

Inclusive prompt photon, 5 TeV

CGC-rcBK

ηγ = 0

Q

2 0A(x=0.01) = NQ 2 0p

Q

2 0p = 0.168 GeV 2

N=7 6 5 4 3 2 4 6 8 10 12 14

pT[GeV] 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 R

ch pA ALICE , prelim. ALICE systematic errors CGC-rcBK, with average Q0A

5.02 TeV, η=0

Hadron, 5 TeV Direct photon, 5 TeV Hadron photon

Inclusive photon production at LO Typical diagrams for gluon production:

The suppression of the inclusive prompt photon and inclusive hadron production in p+A collisions at the LHC are rather similar (Rezaeian, arXiv:1210.2385).

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 21 / 35

SLIDE 22

Direct photon production in p+A@FCC:

3 6 9 12 15 18 21 24 27 30

pT[ GeV]

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Direct photon, p+A@63 TeV

σ (η = 4)/σ(η=2) σ (η = 6)/σ(η=2)

Testing small-x evolution at low pT: the ratio of cross-sections in p+A collisions at two forward rapidities. At low pT the suppression is due to the saturation effect. At high pT and very forward (still small x), the kinematic limit effects also gives suppression (competition between the saturation effect and limiting the available phase space for particle production).

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 22 / 35

At high pT and very forward rapidity (still small-x), the suppression of the ratio can be due to two effects: saturation and kinematic limit on the phase-space available for particle production.

SLIDE 23

Photon-hadron correlations in high-energy pA collisions: p + A → γ + h + X

∆θc = π/2 ∆θ 1 2 3 4 5 Δ θ 0.5 1 1.5 2 2.5 3 P( Δθ)

pp, p: Q

2 0p=0.168 GeV 2

pA, A: Q0A

2=3Q0p 2

pA, A:Q0A

2= 4Q0p 2

hadron: qt = 6 GeV, ηh = 3 photon: kt = 6 GeV, ηγ = 3 4.4 TeV γ h

1 2 3 4 5 Δθ 4 8 12 16 20 P( Δθ)

0.2 TeV 4.4 TeV 8.8 TeV hadron: qt= 3 GeV, ηh = 3 photon: kt = 5 GeV, ηγ = 3

Existence of the saturation scale unbalances the back-to-back correlations. Denser nuclei or/and Higher energy or/and Lower transverse momenta (larger saturation scale) → more suppression of away-side correlations.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 23 / 35

denser higher energy

SLIDE 24

pγ k l pA ph Photon-hadron correlations have a double peak structure because:

pT σ pT pT

2 N(pT,x)

Qs

1 2 3 4 5 Δφ 0.5 1 1.5 2 2.5 3 3.5 P(Δφ) pp p

γ Τ = 5 GeV, p h T = 4 GeV N=3

ηh= ηγ=3

5

pA (Mini-Bias)

7 Q

2 0A (x0=0.01) = NQ 2 0p

N=1 Q

2 0p = 0.168 GeV 2

1

If the projectile parton does not exchange transverse momentum with target, the production rate of photon-hadron goes to zero. pT = |lT + pTγ| = 0 → σhγ (q + A → γ(pγ) + q(l) + X)=0

2

Existence of saturation scale: p2

TNF(pT, xg) in σhγ has a maximum at

pT ∼ Qs.

3

Because of convolution with fragmentation and parton distribution functions→ local minimum will not be zero but gets smeared out.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 24 / 35

SLIDE 25

γ − π0 azimuthal decorrelations in p+A collisions at 5 TeV

Rezaeian, arXiv:1209.0478

1 2 3 4 5 Δφ 0.5 1 1.5 2 2.5 3 3.5 P(Δφ) pp p

γ Τ = 5 GeV, p h T = 4 GeV N=3

ηh= ηγ=3

5

pA (Mini-Bias)

7 Q

2 0A (x0=0.01) = NQ 2 0p

N=1 Q

2 0p = 0.168 GeV 2

1 2 3 4 5 Δφ 0.4 0.8 1.2 1.6 2 P(Δφ) pp p

γ Τ = 4 GeV, p h T = 5 GeV N=1

ηh= ηγ=3

7

pA (Mini-Bias)

Q

2 0A (x0=0.01) = NQ 2 0p

3 Q

2 0p = 0.168 GeV 2

pγ pA ph

Photon-hadron correlations have a double peak structure if:

zT = ph

T

pγ

T

≤ 1 and pγ

T

(eηh + eηγ ) √ S ≤ 1

Emergence of double peak structure is an excellent probe of saturation dynamics.

Similar behaviour was found in Drell-Yan Lepton-Pair-Jet Correlations in p+A

collisions: Stasto, Xiao, Zaslavsky, arXiv:1204.4861.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 25 / 35

ZT >1 ZT <1

SLIDE 26

γ − π0 azimuthal decorrelations in p+A collisions

1 2 3 4 5 Δφ 2e-06 4e-06 6e-06 8e-06 1e-05 1.2e-05 CPh(Δφ) pp 2 < p

γ T ,L [GeV] <20

1 < p

h T, S [GeV] <2

ηh=7, ηγ=3 8.8 TeV pA (Mini-Bias)

The double peak structure becomes stronger and wider at forward rapidities.
A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 26 / 35

SLIDE 27

γ − π0 azimuthal decorrelations in p+A@63 TeV

2 2.5 3 3.5 4 4.5 Δφ 0.5 1 1.5 2 P(Δφ) p

γ Τ = 5 GeV, p h T = 4 GeV

ηh= ηγ=3 p+A γ + π0 + X

Q

2 0A (x0=0.01) = NQ 2 0p

Q

2 0p = 0.168 GeV 2

5 TeV 63 TeV 7 N=3 N=3 7

2 3 4 5 Δφ 0.8 1 1.2 1.4 1.6 P(Δφ) 15 GeV 10 GeV 5 GeV 2 GeV p

γ Τ = p h T

ηh= ηγ=3 p+A γ + π0 + X 63 TeV

Significant more decorrelation at the FCC compared to the LHC, as large as 50%. At the FCC kinematics, the nuclear saturation scale can be as big as 10 ÷ 25 GeV, the γ − π0 decorrelation due to the saturation effect is extended to higher pT.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 27 / 35

LHC FCC Lower pT

SLIDE 28

Semi-inclusive di-photon+hadron production in p+A collisions from the CGC Kovner and Rezaeian, arXiv:1404.5632

p A

q

k1 k2

q′

dσqA→h(q′)γ(k1)γ(k2)X d2bd2k1T dηγ1 d2k2T dηγ2 d2q′

T dηh

= α2

eme4 q

√ 2S 1

zmin h

dzh z2

h

dxqf (xq, µ2

I )H

k1, k2, q, ηγ1 , ηγ2 , ηh
×NF (|qT + k1T + k2T |, xg )Dh/q(zh, µ2

F)

xq = x¯

q =

1 √s

k1T eηγ1 + k2T eηγ2 +

q′

T

zh eηh

xg

= 1 √s

k1T e−ηγ1 + k2T e−ηγ2 +

q′

T

zh e−ηh

zh

= q′

T /qT

with zmin

h

= q′

T

√s    eηh 1 − k1T

√s eηγ1 − k2T √s eηγ2

  

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 28 / 35

SLIDE 29

Inclusive prompt di-photon production in high-energy p+A collisions

Direct di−photon: Single fragmentation di−photon: Double fragmentation di−photon:

dσqA→γ(k1)γ(k2)X d2k1T dηγ1 d2k2T dηγ2 = dσDirect d2k1T dηγ1 d2k2T dηγ2 + dσFragmentation d2k1T dηγ1 d2k2T dηγ2 .

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 29 / 35

does not contribute

SLIDE 30

Inclusive di-photon production in p+p collisions (pQCD:NLO)

Direct γγ production Single−photon fragmentation

+...

(a) (b) (c) (d) (e)

(f) (g) (h) (i) (j) (k) (l)

dσqA→γ(k1)γ(k2)X d2k1T dηγ1 d2k2T dηγ2 = dσDirect d2k1T dηγ1 d2k2T dηγ2 + dσFragmentation d2k1T dηγ1 d2k2T dηγ2 .

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 30 / 35

SLIDE 31

Di-photon decorrelation in p+A collisions at the LHC 8.8 TeV

2 3 4 5 Δφ 1 2 3 4 5 6 7 8 9 C

Fragmentation di-photon Direct di-photon Prompt (Frag.+direct) di-photon k1T=1 GeV, k2T=2 GeV

p+A

ηγ1 = ηγ2 = 2

FF scale: µ = (k1T+k2T)/2

2 3 4 5 Δφ 2 4 6 8 10 12 14 C ηγ = 1 ηγ = 2 ηγ = 3 ηγ = 4

Fragmentation di-photon correlation

k1T=1 GeV, k2T=2 GeV

p+A

ηγ1 = ηγ2 = ηγ 2 3 4 5 Δφ 0.5 1 1.5 2 2.5 3 C ηγ = 1 ηγ = 2 ηγ = 3 ηγ = 4

Prompt di-photon correlation

k1T=1 GeV, k2T=2 GeV

p+A

ηγ1 = ηγ2 = ηγ

De-correlations of prompt, direct and fragmentation diphoton production at forward rapidities due to saturation effect. if Qs → 0, the photon collinear to the outgoing quark, and the photon emerging from the initial photon-quark state will have

pposite transverse momenta, leading to back-to-back correlation →

back-to-back (de)-correlations in prompt diphoton production are stronger in fragmentation part than in the direct one.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 31 / 35

Forward Forward

SLIDE 32

Di-photon decorrelation in p+A collisions at the FCC 63 TeV

2 2.5 3 3.5 4 4.5 Δφ 2 4 6 8 10 12 14 C

k1T = K2T =15 GeV k1T = k2T = 10 GeV k1T = k2T = 4 GeV k1T = K2T = 2 GeV

p+Pb, 63 TeV ηγ1 = ηγ2 = 2 1.5 2 2.5 3 3.5 4 4.5 Δφ 2 4 6 8 10 C 8.8 TeV 63 TeV

p+Pb

ηγ1 = ηγ2 = 2 k1T = k2T= 4 GeV

Back-to-back de-correlations of fragmentation diphoton production by increasing saturation scale (increasing density or rapidity/energy or decreasing transverse momenta).

At the FCC kinematics, the saturation scale can be as big as 10 ÷ 25 GeV, the γ − γ decorrelation due to the saturation effect is extended to higher pT compared to the LHC.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 32 / 35

SLIDE 33

Dijet production in p+A collisions at the FCC 63 TeV

A. van Hameren, Kotko, Kutak, Marquet, Sapeta, arXiv:1402.5065

0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 0.5 1 1.5 2 2.5 3 RpA Δ Φ pt1>pt2>20 GeV 3.2<y1,y2<4.9 KS gluon √s = 5 TeV √s = 63 TeV 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 20 30 40 50 60 70 80 90 100 RpA pt, leading [GeV] pt1>pt2>20 GeV 3.2<y1,y2<4.9 KS gluon √s = 5 TeV √s = 63 TeV 0.60 0.65 0.70 0.75 0.80 20 30 40 RpA pt, subleading [GeV] pt1>pt2>20 GeV 3.2<y1,y2<4.9 KS gluon √s = 5 TeV √s = 63 TeV

Dijet production in p+A collisions at the FCC is a good probe of the small-x dynamics.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 33 / 35

SLIDE 34

Conclusion:

The CGC picture at RHIC and HERA is consistent with LHC data (p+p, p+A) at small-x so far: the future p+A run at the FCC provides a systematic test of gluon saturation/CGC physics.

Await to be verified in p+A collisions at the LHC and FCC: ➤ Suppression of inclusive charged hadron, and direct photon production at very forward rapidities. ➤ Suppression of away-side photon-hadron and diphoton correlations at forward rapidities. Standard DGLAP-like QCD calculations are not yet available for γ − h and γ − γ production in p+A collisions.

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 34 / 35

SLIDE 35

backup: Di-photon decorrelation in p+A collisions at the LHC 8.8 TeV

2 3 4 5 Δφ 2 4 6 8 10 12 14 C

k1T = k2T = 4 GeV k1T = k2T = 2 GeV k1T = k2T = 1 GeV k1T = k2T = 0.5 GeV

p+A

ηγ1 = ηγ2 = 2 2 3 4 5 Δφ 4 8 12 16 20 24 28 C k2T = 3 GeV k2T = 2 GeV k2T = 0.5 GeV

p+A

ηγ1 = ηγ2 = 2 k1T = 1 GeV 2 3 4 5 Δφ 4 8 12 16 20 C p+A p+p k1T=1 GeV, k2T=2 GeV ηγ1 = ηγ2 = 2

Back-to-back de-correlations of fragmentation diphoton production by increasing saturation scale (increasing density or rapidity/energy or decreasing transverse momenta).

A. Rezaeian (USM & CCTVal)

CERN, 22 Sep 2014 35 / 35