AdA: where e+e- collisions were born gg physics at the LC Giulia Pancheri - INFN-Frascati Where e+e- collisions were born AdA: where e+e- collisions were born G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC For same cm energy  xsections are larger G. Pancheri - gamma gamma at LC LNF-25th october, 2006

Photon-photon processes Formation of neutral resonances with other quantum numbers than in e+e- , with C=+ and J=0,2 Higher mass reach since particles can be produced individually (not necessarily in pairs) The ggH loop is sensitive to all charged fundamental particles of the theory Direct pair production of new fermions, charged scalars, charged vectors Pair production of neutral scalars, vectors (in loop, also gg gg Measurement of parton densities of real real photons (in eg mode) G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC photon-photon Photon Collider ECM ~ 0.8 EeeCM Lum ~ 0.2 ee Higgs and top physics EWSB, SUSY are accessible and interesting Normal mode of operation ECM approx up to 1/2 ee Non-monochromatic Can access JP=0± QCD and some top Total cross-sections G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC Photon Collider Energy is transferred to the photon up to almost 80% of initial electron’s Compton Back Scattering of laser light G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC QCD tests Pomeron? Jets Photon densities Models for total cross-section G. Pancheri - gamma gamma at LC LNF-25th october, 2006

Models for total x-sections Interest lies in QCD role What is the Pomeron? The Reggeon? Are these concepts universal? Or do they just phenomenologically describe our ignorance? How can ILC help ? A.de Roeck, R. Godbole, A. Grau, G. Pancheri, JHEP 2003 G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC s=Bs-h + Ase+ Cse1 Fit3 C≠ 0 e=0.093 e1=0.418 Fit 1 C=0 e=0.250 Fit2 C=0 e=0.093 as in pp G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC se : e controls the rise Could e be the same for all hadronic cross-sections? The total gg x-section is extracted from data which do not include all the phase space MC simulations are based on minijets models which indeed are the best in simulating L3 data G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC se : e controls the rise Should e be the same for all hadronic cross-sections? Yes if the model is based on Regge poles and a universal Pomeron pole exchange or On Gribov factorization alone Not necessarily if The model has some connection with QCD and photon densities play a role G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC A realistic QCD model should relate the fit to QCD phenomenological inputs quantities like densities etc. G. Pancheri - gamma gamma at LC LNF-25th october, 2006

The BN Eikonal Minijet model includes kt resummation R.Godbole, A. Grau, G.Pancheri, Y.Srivastava PRD 2005 A. Corsetti, A. Grau, G.Pancheri, Y. Srivastava PLB 1996 Multiple parton interactions : optical theorem and eikonal representation for Tel(s,t) Hard scattering to drive the rise due to 1/x Soft gluons down to zero momentum to tame the rise G. Pancheri - gamma gamma at LC LNF-25th october, 2006

The hard cross-section Mini-jet cross-section S∫ densities ∫dpt ds/dpt G. Pancheri - gamma gamma at LC LNF-25th october, 2006

The hard scattering part qq,qg and mostly Minijet cross-section depends upon parton densities GRV, MRST, CTEQ for protons GRS, CJK for photons pt cutoff ptmin=1~ 2 GeV g g g g G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC Soft resummation Probablity of total KT from infinite # of soft gluons ∫ d2b eiKTb exp{-∫d3n(k)[1-e-iktb]} depends upon single gluon energy maximum : use Kinematics minimum : 0 if Bloch-Nordsieck states G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC Role of resummation An infinite number of soft quanta down to zero momentum but how? next slides Up to an energy dependent limit qmax Higher hadron energy possibility of more small x partons with “high energy” (≈1-2 GeV) higher qmax G. Pancheri - gamma gamma at LC LNF-25th october, 2006

Maximum soft gluon energy q1 and q2 : any two partons X : the 2-jet final state Q2≥4 p2tmin qmax depends on x1,x2 We average it over densities G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC Zero momentum quanta Soft gluons need to be resummed if they are indeed soft ≈1/k Resummation implies integration over dkt What matters will be ∫as(kt )dkt f(kt) and not as(0) G. Pancheri - gamma gamma at LC LNF-25th october, 2006

Soft gluons give b-distributions In eikonal representation stot≈2∫d2b [1-e-n(b,s)/2] n(b,s)=average # of collisions at distance b, at energy √s b-distribution is needed Our ansatz: b-distribution = Fourier transform of soft gluon Kt distribution G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC How the model works Choose ptmin = 1÷2 GeV for mini-jets Choose parton densities Calculate minijet x-section Calculate qmax for soft gluons Calculate A(b,s) for given qmax Calculate nhard (b,s)=A(b,s) sjet(ptmin,s) Parametrize nsoft Evaluate n(b,s)= nsoft + nhard Eikonalize stot≈2∫d2b [1-e-n(b,s)/2] G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC qmax for ptmin=1.15 geV G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC sjet for ptmin=1.15 GeV green band MRST G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC b-distribution for hard collisions from soft gluon resummation for ptmin=1.15 GeV for singular as G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC Example of Eikonalized proton-antiproton total cross-section for ptmin=1.15 G. Pancheri - gamma gamma at LC LNF-25th october, 2006

Comparison with proton data R.Godbole, Grau R. Hedge G. Pancheri Y. Srivastava Les Houches 2005 GGPS PRD 2005 G. Pancheri - gamma gamma at LC LNF-25th october, 2006

photon-photon : eikonal minijet and BN model G. Pancheri - gamma gamma at LC LNF-25th october, 2006

G. Pancheri - gamma gamma at LC Conclusions gg in Photon Collider Mode would be very interesting for Higgs, WW, unknown resonances, etc. In regular mode, QCD and total cross-sections measurements can give insight on details of low x physics complementary to LHC G. Pancheri - gamma gamma at LC LNF-25th october, 2006