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

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

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

Road map of strong interaction LO pQCD s ≈ ( A / x ) 1 / 3 increases by lowering x or/and The saturation scale Q 2 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

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 The dipole scattering amplitude is the main ingredient with 3 or 4 free parameters fixed via a fit to the reduced cross − section. 1 − z F (x, Q ) 2 2 × i γ ∗ J/ Ψ , ρ , φ , γ 2 ∗ ∗ ∗ Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i Q² (GeV²), i γ p γ p γ p γ p γ p γ p B (GeV -2 ) 14 r � HERA e p + 2 ρ ZEUS 120 pb -1 HERA e p 10 650, 27 - γ * p →ρ p γ * p →ρ p 9 2 2 ρ ZEUS 94 10 5 0 0 , 2 6 Q = 8 GeV 2 2 D σ (nb) σ (nb) 400, 25 W = 82 GeV, H1 Q = 8 GeV 12 ρ ZEUS 95 Q ∼ 1 / r 300, 24 2 2 W = 75 GeV W = 90 GeV z 8 Q = 15.5 GeV 2 2 ρ H1 95-96 10 250, 23 10 Q = 25 GeV 200, 22 2 2 10 φ ZEUS 98-00 H1 ZEUS d σ / dt (nb/GeV 2 ) Q = 25 GeV dipole amplitude 1 5 0 , 2 1 10 φ ZEUS 94 7 10 2 10 2 10 1 2 0 , 2 0 0 90, 19 10 J/ ψ ZEUS 98-00 70, 18 J/ ψ ZEUS 96-97 10 6 60, 17 σ (nb) σ (nb) 8 J/ ψ H1 96-00 4 5 , N ( x,r,b ) 1 6 1 35, 15 DVCS H1 96-00 10 1 10 1 b ∼ 1 / | t | 5 10 27, 14 22, 13 6 1 18, 12 -2 10 4 10 15, 11 0 0 small-x physics 12, 10 10 10 10, 9 4 3 0.1 10 8.5, 8 W = 82 GeV, H1 6.5, 7 4.5, 6 J/ ψ 10 2 ρ -meson 3.5, 5 2 -1 -1 φ -meson 10 10 -4 p − q 2.7, 4 10 DVCS 1 0 0.5 1 1.5 10 100 0.1 p 10 2 . 0 , 3 25 125 2 2 2 1.5, 2 0 |t| (GeV ) Q (GeV ) W(GeV) 0 5 10 15 20 25 30 35 40 45 50 1.2, 1 (c) M. Siddikov 0 10 0.85, 0 Q 2 +M 2 (GeV 2 ) 10 0 10 1 10 2 10 0 10 1 10 2 (c) M. Siddikov t = − q 2 Q 2 +M 2 ρ (GeV 2 ) Q 2 +M 2 ρ (GeV 2 ) 10 -5 10 -4 10 -3 10 -2 Q² = 2.5 GeV² Q² = 5 GeV² Q² = 7 GeV² Q² = 12 GeV² x 0.5 0.5 0.5 0.5 γ * p → J/ ψ p γ * p →φ p γ * p →ρ p σ (nb) σ (nb) σ (nb) γ * p → J/ ψ p γ * p →φ p γ * p →ρ p Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) Q² (GeV²) R= σ L / σ T R= σ L / σ T R= σ L / σ T 0.4 0.4 0.4 0.4 10 3 W = 90 GeV H1, 35<W<180 GeV H1, 35<W<180 GeV 2.4 0.3 0.3 0.3 0.3 2 0 . 5 0 2 3.3 8 8 8 10 10 3 3 . ZEUS ZEUS, W=90 GeV ZEUS, 40<W<140 GeV . 2 3 0.2 0.2 0.2 0.2 7 7 7 6.6 7.0 10 2 6 . 6 cc 0.1 0.1 0.1 0.1 _ 6 6 6 11.9 2 (c) M. Siddikov 1 1 F 10 10 22.4 10 -4 10 -3 10 -2 10 -4 10 -3 10 -2 10 -4 10 -3 10 -2 10 -4 10 -3 10 -2 5 5 5 Q² = 18 GeV² Q² = 32 GeV² Q² = 60 GeV² 1 10 9 1 5 . 15.8 0.5 0.5 0.5 0.5 H1+ZEUS 4 4 4 0.4 0.4 0.4 0.4 m c =1.27 GeV =1.4 GeV 0 0 m c 10 10 3 3 3 0 0.3 0.3 0.3 0.3 10 H1 H1 H1 2 2 2 0.2 0.2 0.2 0.2 ZEUS ZEUS ZEUS (c) M. Siddikov 1 1 1 0.1 0.1 0.1 0.1 100 200 100 200 100 200 (c) M. Siddikov (c) M. Siddikov (c) M. Siddikov (c) M. Siddikov -4 -3 -2 -4 -3 -2 -4 -3 -2 -4 -3 -2 W (GeV) W (GeV) W (GeV) 10 10 10 10 10 10 10 10 10 10 10 10 5 10 15 20 5 10 15 20 5 10 15 20 x Q 2 (GeV 2 ) Q 2 (GeV 2 ) Q 2 (GeV 2 ) γ * p → J/ ψ p γ * p → J/ ψ p γ * p →ρ p γ * p →φ p γ * p → J/ ψ p γ * p →φ p d σ /dt (nb/GeV 2 ) d σ /dt (nb/GeV 2 ) d σ /dt (nb/GeV 2 ) d σ /dt (nb/GeV 2 ) σ (nb) σ (nb) Q² = 2.7 GeV² Q² = 0.05 GeV² Q² = 0 GeV² Q² = 2.4 GeV² Q² = 5 GeV² W = 90 GeV W = 75 GeV Q² = 3.6 GeV² 2 Q² = 3.2 GeV² Q² = 3.1 GeV² Q² = 7.8 GeV² 10 Q² = 5.2 GeV² H1 H1 Q² = 7 GeV² Q² = 6.8 GeV² 3 Q² = 11.9 GeV² Q² = 6.9 GeV² 10 Q² = 19.7 GeV² Q² = 9.2 GeV² Q² = 22.4 GeV² Q² = 16 GeV² Q² = 41 GeV² ZEUS ZEUS 2 2 2 Q² = 12.6 GeV² 10 10 10 Q² = 19.7 GeV² 2 10 1 10 1 10 10 1 10 1 10 1 10 1 0 10 10 0 0 10 0 0 0 10 10 10 (c) M. Siddikov 10 -1 (c) M. Siddikov (c) M. Siddikov W=100 GeV, H1 W=90 GeV, ZEUS W=106 GeV, ZEUS W=75 GeV, ZEUS (c) M. Siddikov (c) M. Siddikov 10 1 10 2 10 1 10 2 0.5 1 (c) M. Siddikov 0.5 1 0.5 1 0.5 1 |t| (GeV 2 ) |t| (GeV 2 ) |t| (GeV 2 ) |t| (GeV 2 ) Q 2 +M 2 J/ ψ (GeV 2 ) Q 2 +M 2 φ (GeV 2 ) A. Rezaeian (USM & CCTVal) CERN, 22 Sep 2014 4 / 35

The impact-parameter b and x - dependence of the saturation scale for proton 16 b-CGC IP-Sat 12 8 0.5 FCC 2 ) -8 2 = 0.8 GeV 2 x = 10 Q 2 (GeV b-CGC IP-Sat 4 γ∗ p /db (GeV) 2 = 3 GeV 2 0.4 Q 2 = 50 GeV 2 Q 3 -4 Q S x = 10 0.3 2.5 2 LHC γ∗ p )d σ -6 0.2 x = 10 1.5 (1/ σ 1 -4 x = 10 0.1 0.5 HERA 0 0 0 1 2 3 4 5 0 2 4 6 8 0 2 4 6 8 -1 ) -1 ) b (GeV b (GeV 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 | di ff ractive data are needed). The proton saturation scale at HERA: Q s ( x , b ) < 1 GeV, at the LHC: s ( x , b ) < 1 . 5 ÷ 3 GeV 2 and at the FCC: Q 2 s ( x , b ) ≤ 4 ÷ 15 GeV 2 . Q 2 A. Rezaeian (USM & CCTVal) CERN, 22 Sep 2014 5 / 35

Saturation scale extracted from recent combined HERA data 2 15 GeV b-CGC 9 Impact-parameter dependent IP-Sat IIM rcBK 3 2 ) 2 (GeV 2 1 GeV 1 0.3 b = 0 Q S -1 b = 2 GeV 0.1 -1 b = 3 GeV pA@63 TeV(FCC) pp@100 TeV(FCC) ep@HERA 0.04 2 3 4 5 6 7 8 10 10 10 10 10 10 10 1/x Order of magnitude discrepancies in saturation scale extracted from di ff erent models= ⇒ sizable uncertainties in predictions of various observables. Current small-x data do not put enough constrains on saturation models at x < 10 − 5 . s ( x , b ) ≤ 4 ÷ 15 GeV 2 at FCC kinematics. Q 2 A. Rezaeian (USM & CCTVal) CERN, 22 Sep 2014 6 / 35

CGC description of combined HERA data: uncertainties Rezaeian, Schmidt, arXiv:1307.0825 10 3 10 10 b-CGC b-CGC 9 10 IP-Sat IP-Sat 2 [GeV 2 ], n 2 8 Q 10 10 650, 27 500, 26 400, 25 2 [GeV 2 ],n 7 Q 10 300, 24 250, 23 1 200, 22 n 10 60, 6 6 n 150, 21 2 ) 2 10 2 ) 2 120, 20 32, 5 90, 19 5 70, 18 10 2 (x, Q 60, 17 18, 4 F 2 (x,Q 0 45, 16 10 4 35, 15 12, 3 10 27, 14 22, 13 18, 12 cc 3 7, 2 10 15, 11 F -1 12, 10 10 5, 1 10, 9 2 10 8.5, 8 6.5, 7 4.5, 6 H1 & ZEUS 2.5, 0 1 3.5, 5 -2 10 2.7, 4 10 2.0, 3 0 1.5, 2 10 1.2, 1 H1& ZEUS 0.85, 0 -1 -3 10 10 -7 -6 -5 -4 -3 -2 -7 -6 -5 -4 -3 -2 10 10 10 10 10 10 10 10 10 10 10 10 x x FCC c , F 2 data were not included in the fit. F c ¯ The di ff erence among models can be considered as our current theoretical uncertainties = ⇒ significant uncertainties at small-x = ⇒ Future exps with x B < 10 − 5 (FCC, LHeC, EIC) can constrain saturation models. A. Rezaeian (USM & CCTVal) CERN, 22 Sep 2014 7 / 35

Testing CGC approach: p+p@LHC Comparing CGC predictions with 7 TeV data: Levin, Rezaeian, arXiv:1005.0631 7 CMS, 7 TeV CMS, 2.36 TeV CDF, 1.8 TeV Saturation (b-CGC) UA5, 0.9 TeV KLN ALICE, 0.9 TeV 8 6 UA1 NSD CMS, 0.9 TeV 14 TeV UA5 NSD UA5, 546 GeV 7 TeV 7 CDF NSD 7 TeV CMS NSD ALICE NSD 5 6 dN ch /d η ALICE INEL>0 5 η = 0 dN ch /d η 4 4 3 3 2 m jet = 0.4 GeV 1 2 2 3 4 0 10 10 10 -4 -2 0 2 4 ) s [GeV] η √ 0.6 2 10 CMS NSD CMS, 7 TeV ATLAS data, √ ) s = 0.9 TeV, p T >0.5 GeV E735 NSD 1.3 0.55 1/(2 π p T )d 2 N ch /d η dp T [GeV -2 ] CMS, 2.36 TeV <z> = 0.5 CDF NSD 14 TeV <z> = 0.48 UA1 NSD 7 TeV 0 10 1.2 < z > = 0.5 0.5 < p T > [GeV] 7 TeV 14 TeV < z > = 0.48 | η |< 2.4, < z> = 0.48 < p T > [GeV] 1.1 0.45 -2 0.9 TeV 1 10 0.4 | η |< 2.4 0.9 0.35 -4 0.8 10 0 20 40 60 80 0.3 n ch 2 3 4 10 10 10 0 1 2 3 4 ) p T [GeV] s [GeV] √ k T -factorization+ the dipole scattering amplitude constrained by DIS data. A. Rezaeian (USM & CCTVal) CERN, 22 Sep 2014 8 / 35