physics at the LC Giulia Pancheri INFNFrascati Where

physics at the LC Giulia Pancheri - INFN-Frascati Where e+e- collisions were born Ad. A: where e+e- collisions were born G. Pancheri - gamma at LC 1 LNF-25 th october, 2006

For same cm energy xsections are larger G. Pancheri - gamma at LC 2 LNF-25 th 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 H loop is sensitive to all charged fundamental particles of theory Direct pair production of new fermions, charged scalars, charged vectors Pair production of neutral scalars, vectors (in loop, also Measurement of parton densities of real photons (in e mode) G. Pancheri - gamma at LC 3 LNF-25 th october, 2006

photon-photon 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 at LC Photon Collider ECM ~ 0. 8 Eee. CM Lum ~ 0. 2 ee Higgs and top physics EWSB, SUSY are accessible and interesting • • 4 LNF-25 th october, 2006

G. Pancheri - gamma at LC 5 LNF-25 th october, 2006

Photon Collider • Compton Back Scattering of laser light G. Pancheri - gamma at LC Energy is transferred to the photon up to almost 80% of initial electron’s 6 LNF-25 th october, 2006

G. Pancheri - gamma at LC 7 LNF-25 th october, 2006

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QCD tests • • Pomeron? Jets Photon densities Models for total cross-section G. Pancheri - gamma at LC 10 LNF-25 th october, 2006

Models for total xsections • 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 ? G. Pancheri - gamma at LC A. de Roeck, R. Godbole, A. Grau, G. Pancheri, JHEP 2003 11 LNF-25 th october, 2006

-h s=Bs + e As + e Cs 1 • Fit 3 C≠ 0 e=0. 093 e 1=0. 418 • Fit 1 C=0 e=0. 250 • Fit 2 C=0 e=0. 093 as in pp G. Pancheri - gamma at LC 12 LNF-25 th october, 2006

se : e controls the rise • Could e be the same for all hadronic crosssections? • The total 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 L 3 data G. Pancheri - gamma at LC 13 LNF-25 th october, 2006

e s : e controls the rise • Should e be the same for all hadronic crosssections? • 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 at LC 14 LNF-25 th october, 2006

A realistic QCD model should relate the fit to QCD phenomenological inputs quantities like densities etc. G. Pancheri - gamma at LC 15 LNF-25 th 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 1. Multiple parton interactions : optical theorem and eikonal representation for Tel(s, t) 2. Hard scattering to drive the rise due to 1/x 3. Soft gluons down to zero momentum to tame the rise G. Pancheri - gamma at LC 16 LNF-25 th october, 2006

The hard cross-section • Mini-jet cross-section S∫ densities ∫dpt ds/dpt G. Pancheri - gamma at LC 17 LNF-25 th october, 2006

The hard scattering part • qq, qg and mostly gg gg Minijet cross-section depends upon • parton densities – GRV, MRST, CTEQ for protons – GRS, CJK for photons • pt cutoff ptmin=1~ 2 Ge. V G. Pancheri - gamma at LC 18 LNF-25 th october, 2006

Soft resummation Probablity of total KT from infinite # of soft gluons ∫ d 2 b ei. K b exp{-∫d 3 n(k)[1 -e-ik b]}� T t depends upon single gluon energy Ø maximum : use Kinematics Ø minimum : 0 if Bloch-Nordsieck states G. Pancheri - gamma at LC 19 LNF-25 th october, 2006

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 Ge. V) higher qmax G. Pancheri - gamma at LC 20 LNF-25 th october, 2006

Maximum soft gluon energy • q 1 and q 2 : any two partons • X : the 2 -jet final state • Q 2≥ 4 p 2 tmin • qmax depends on x 1, x 2 • We average it over densities G. Pancheri - gamma at LC 21 LNF-25 th october, 2006

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 at LC 22 LNF-25 th october, 2006

Soft gluons give bdistributions In eikonal representation stot≈2∫d 2 b [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 at LC 23 LNF-25 th october, 2006

How the model works • Choose ptmin = 1÷ 2 Ge. V 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∫d 2 b [1 -e-n(b, s)/2] G. Pancheri - gamma at LC 24 LNF-25 th october, 2006

qmax for ptmin=1. 15 ge. V G. Pancheri - gamma at LC 25 LNF-25 th october, 2006

sjet for ptmin=1. 15 Ge. V green band MRST G. Pancheri - gamma at LC 26 LNF-25 th october, 2006

b-distribution for hard collisions from soft gluon resummation for ptmin=1. 15 Ge. V for singular as G. Pancheri - gamma at LC 27 LNF-25 th october, 2006

Example of Eikonalized proton-antiproton total cross -section for ptmin=1. 15 G. Pancheri - gamma at LC 28 LNF-25 th october, 2006

Comparison with proton data R. Godbole, A. Grau B. R. Hedge C. G. Pancheri D. Y. Srivastava E. Les Houches 200 F. G. Pancheri - gamma at LC 29 GGPS PRD 2005 LNF-25 th october, 2006

photon-photon : eikonal minijet and BN model G. Pancheri - gamma at LC 30 LNF-25 th october, 2006

Conclusions in Photon Collider Mode would be very interesting for Higgs, WW, unknown resonances, etc. In regular mode, QCD and total crosssections measurements can give insight on details of low x physics complementary to LHC G. Pancheri - gamma at LC 31 LNF-25 th october, 2006