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CGC and CR

CGC and CR. CGC can be applied to CR?. K. Itakura In collaboration with H.Fujii and Y.Nara Mini workshop @ ICRR October 12 th 2011 . What should be asked?. More relevant questions: Q1 “How much does “hard QCD” contribute to the extremely forward cross sections?”

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CGC and CR

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  1. CGC and CR CGC can be applied to CR? K. Itakura In collaboration with H.Fujii and Y.Nara Mini workshop @ ICRR October 12th 2011

  2. What should be asked? • More relevant questions: Q1 “How much does “hard QCD” contribute to the extremely forward cross sections?” Q2 “Which rapidity region is important for development of Air Shower?” • Answers so far: A1 “Hard QCD (alone) will not contribute a lot even after one includes the effects of saturation/CGC (which enables us to approach softer region due to the presence of “IR cutoff” Qs) ” A2 “Not clear now. Hope that relatively large rapidity will be important” • Much more relevant question: “How can one modify the hard QCD description so that it contains soft emissions too?” (cf. Sergey’s analysis) All we can do so far is to provide the BEST description of the forward physics based on (semi-)hard QCD, which must be the foundation for future improvement.

  3. “Small-x partons” are relevant x1, x2 : mom. fractions of partons (quarks+gluons) h1 Typical kinematics of hadron-hadron (hard) scattering x1 , parton a parton b outgoing particle rapidity x2 h2 pt q • Cross section • Parton distribution functionsof hadrons are necessary • High energy scattering involves very small x partons • pp @ LHC (7TeV)x1, x2 ~ 3×10-4 (h =0, pt=2GeV) , x2 ~ 7×10-7 (h =6, pt=2GeV) • pp @ cosmic ray (400TeV) x1, x2 ~ 5×10-6 (h =0, pt=2GeV) , • x2 ~ 1×10-8 (h =6, pt=2GeV) e-6~ 2.5 x 10-3

  4. Fujii,Itakura,Kitadono,Nara 2011 MC-DHJ/rcBKTowards the best “hard” description • What is MC-DHJ/rcBK? So far the best description of singlehadron spectrum in dAu (pA) collisions at forward rapidities (h <4) at RHIC energies. (Monte-Carlo Dumitru-Hayashigaki-Jalilian-Marian / running coupling Balitsky-Kovchegov) • What is good in MC-DHJ/rcBK? No free additional parameter compared with pp -- parameters are fixed in pp collision at the same energy  for initial condition, overall factor (K)

  5. MC-DHJ/rcBK Projectile as valence partons (large x) Fragment into hadrons bt • Energy evolution is imposed locally (in b space) due to BK (hard Pomeron, and Pomeron merging) • Including running-coupling effects (quark loops) Target nucleus randomly generated, and described as CGC (small-x)

  6. Provides the best description of RHIC forward data @ 200GeV • Parameter set for • the initial condition • determined for DIS • at HERA (AAMQS) Dependence on initial conditions seems to disappear with increasing rapidity Cf) pp case

  7. And if you are bold enough…. Extrapolation to LHC energy

  8. Comments • In fact, hard contribution alone is not enough to explain the very forward cross section  how to modify? Inclusion of soft emission. • Inclusive spectra is not enough for the Air Shower simulation – needs whole information of scattering  exclusive info (n-particle cross sections) in principle, n-particle Xsec can be computed …

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