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Forward Physics Prospects using FCAL in High-Energy Collisions (pp & pA) at LHC

Forward Physics Prospects using FCAL in High-Energy Collisions (pp & pA) at LHC. Bedanga Mohanty VECC, Kolkata. Two important physics issues could be addressed :. Test of pQCD predictions : p+p collisions Gluon distribution function in proton and Nuclei : p+A collisions. uds-quark. all.

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Forward Physics Prospects using FCAL in High-Energy Collisions (pp & pA) at LHC

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  1. Forward Physics Prospects using FCAL in High-Energy Collisions (pp & pA) at LHC Bedanga Mohanty VECC, Kolkata Two important physics issues could be addressed : • Test of pQCD predictions : p+p collisions • Gluon distribution function in proton and Nuclei : p+A collisions

  2. uds-quark all c-quark b-quark s=91.2 GeV OPAL How partons fragment into hadrons How partons are distributed in hadrons we collide p+p Collisions : Test pQCD What is the probability that the partons will interact Parton Distribution Functions dominantly from deep-inelastic Scattering experiments Parton Fragmentation Functions determined from e+e- annihilations Parton-Parton Cross-Section (pQCD)

  3. Test of pQCD at RHIC Midrapidity Measurements Jet production and high pT identified particle production well explained by NLO pQCD calculations at midrapidity STAR : PLB 637 (2006) 161 PHENIX : PRL 91 (2003) 241803 STAR : PRL 97 (2006) 252001

  4. Test of pQCD at Forward Rapidity Forward rapidity Measurements √s=23.3 GeV √s=52.8 GeV √s=200 GeV data / pQCD depends on  in addition to CM energy and pT q=10o q=6o Ed3s/dp3[mb/GeV3] q=15o q=53o q=22o STAR : PRL 97 (2006) 152302 Bourrely and Soffer : hep-ph/0311110

  5. Test of pQCD : Role of Forward Rapidity Deep inelastic scattering Hard scattering hadroproduction What are the Bjorken x dependence on Simple Kinematics • Assumtions : • Initial partons are collinear • Partonic interaction is elastic pT,1  pT,2  Studying pseudorapidity, =-ln(tan/2), dependence of particle production probes parton distributions at different Bjorken x values and involves different admixtures of gg, qg and qq’ subprocesses.

  6. p+p  p0+X, s = 200 GeV, h=0 Test of pQCD : Role of Forward Rapidity - An Example • Mid-rapidity particle detection • h10 and h20 •  xq  xg  xT = 2 pT / s • Large-rapidity particle detection • h1>>h2 • xq  xT eh1 xF(Feynman x) xg xF e-(h1+h2) Large rapidity : different x for quarks and gluons

  7. Deep inelastic scattering Gluon Distribution : Proton  Low-x gluon density is large and continues to increase asx0 It cannot grow forever Fundamental question - Where does saturation set in ?

  8. Gluon Distribution : Nuclei World data on nuclear DIS constrains nuclear modifications to gluon density only for xgluon > 0.02 Crucial for knowing the initial conditions in Nucleus-Nucleus Collisions M. Hirai, S. Kumano, T.-H. Nagai, Phys. Rev. C70 (2004) 044905

  9. Forward Rapidity : Saturation Mid Rapidity CTEQ6M Forward Rapidity Nuclear amplification: xGA(x) ~ A1/3xG(x), i.e. gluon density is ~6x higher in Gold than the nucleon Saturation may set in at forward rapidity when gluons start to overlap.

  10. Experimental Signature in p(d)+A Collisions - I Mid Rapidity In CGC picture, 2 soft gluons can merge to form a harder gluon. This will lead to a suppression of low pT hadrons in p(d)+A collisions compared to p+p collisions. The effect should be stronger at forward rapidities where x is smaller but gluon densities are higher Forward Rapidity

  11. dAu: forward suppression & backward enhancement Experimental Results : d+A Collisions at RHIC PHOBOS PHENIX BRAHMS STAR Hadron production suppressed at forward rapidity

  12. SHADOWING SATURATION (CGC) R. Vogt, PRC 70 (2004) 064902. Guzey, Strikman, and Vogelsang, PLB 603 (2004) 173. Jalilian-Marian, NPA 748 (2005) 664. Kharzeev, Kovchegov, and Tuchin, PLB 599 (2004) 23; PRD 68 (2003) 094013. Armesto, Salgado, and Wiedemann, PRL 94 (2005) 022002. PARTON RECOMBINATION Hwa, Yang, and Fries, PRC 71 (2005) 024902. MULTIPLE SCATTERING & Eloss IN COLD NUCLEAR MATTER Qiu and Vitev, PRL 93 (2004) 262301; hep-ph/0410218. BREAKDOWN OF FACTORIZATION Or SUDAKOV SUPPRESSION Kopeliovich, et al., hep-ph/0501260. Nikolaev and Schaefer, PRD 71 (2005) 014023. Shaowing : Models differ by factor fo 3 Armesto & Salgado, hep-ph/0308248 Explanation : Not Unique Forward rapidity at RHIC ~ Mid rapidity at LHC

  13. d+Au: Mono-jet Dilute parton system (deuteron) PT is balanced by many gluons Dense gluon field (Au) Experimental Signature……. Kharzeev, Levin, McLerran NPA748, 627 Experimental Signature in p(d)+A Collisions - II p+p: Di-jet

  14. Ep p0 p d EN qq qp p Au xgp xqp qg EN CGC and Forward Rapidity With assumptions Taking high pT0 in forward rapidity - allows probing high-x valence quark correlations with low -x gluons : A probe of low-x gluons Kharzeev, Levin, McLerran NPA748, 627 STAR : PRL 97 (2006) 152302

  15. Unique Opportunity • To find where Saturation sets in • To map a new phase diagram ? Measurements • 0 transverse momentum spectra • Nuclear Modification factor for 0 • Forward 0 triggered correlations Summary : Why FCAL Motivations • Allows us to test pQCD predictions data / pQCD depends on  in addition to CM energy and pT • Allows us to understand the gluon distribution function in p and A Forward rapidity probes low-x regime • Knowledge of initial conditions in heavy ion collisions

  16. Thanks

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