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gg physics at the LC. Giulia Pancheri - INFN-Frascati. AdA: where e+e- collisions were born. Where e+e- collisions were born. For same cm energy  xsections are larger. Photon-photon processes.

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gg physics at the lc

gg physics at the LC

Giulia Pancheri - INFN-Frascati

AdA: where e+e- collisions were born

Where e+e- collisions were born

G. Pancheri - gamma gamma at LC

slide2
For same

cm energy



xsections

are

larger

G. Pancheri - gamma gamma at LC

photon photon processes
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

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

Photon Collider

ECM ~ 0.8 EeeCM

Lum ~ 0.2 ee

Higgs and top physics

EWSB, SUSY are accessible and interesting

photon-photon

G. Pancheri - gamma gamma at LC

photon collider
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

qcd tests
QCD tests
  • Pomeron?
  • Jets
  • Photon densities
  • Models for total cross-section

G. Pancheri - gamma gamma at LC

models for total x sections
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

s bs h as e cs e 1
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

s e e controls the rise
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

s e e controls the rise1
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

slide15
A realistic QCD model should relate the fit to QCD phenomenological inputs quantities like densities etc.

G. Pancheri - gamma gamma at LC

the bn eikonal minijet model includes k t resummation
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

the hard cross section
The hard cross-section
  • Mini-jet cross-section

S∫ densities ∫dpt ds/dpt

G. Pancheri - gamma gamma at LC

the hard scattering part
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

soft resummation
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

role of resummation
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

maximum soft gluon energy
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

zero momentum quanta
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

soft gluons give b distributions
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

how the model works
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

q max for ptmin 1 15 gev
qmax for ptmin=1.15 geV

G. Pancheri - gamma gamma at LC

s jet for p tmin 1 15 gev
sjet for ptmin=1.15 GeV

green band MRST

G. Pancheri - gamma gamma at LC

b distribution for hard collisions from soft gluon resummation for ptmin 1 15 gev for singular a s
b-distribution for hard collisions from soft gluon resummation for ptmin=1.15 GeV for singular as

G. Pancheri - gamma gamma at LC

example of eikonalized proton antiproton total cross section for ptmin 1 15
Example of Eikonalized proton-antiproton total cross-section for ptmin=1.15

G. Pancheri - gamma gamma at LC

comparison with proton data
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

photon photon eikonal minijet and bn model
photon-photon : eikonal minijet and BN model

G. Pancheri - gamma gamma at LC

conclusions
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

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