# Generation of complete events containing very high pt

- Slides: 28

Generation of complete events containing very high pt jets Sarah Porteboeuf, Klaus Werner Hot Quarks, August 18 th -24 th

Summary Jet and Jet Quenching Event Generators : EPOS Hard process in a complete event Fast computation Conclusions and outlook

Jet / Jet Quenching

The Parton Model Inclusive cross section : pp -> Jet +X No way to compute X in details Jet cross section : No information about multiples interactions How to compute jets connected with the event ?

Multiples Interactions High Energies : problème !!! More than one interaction per collision => Total cross section and partial one, inclusive and exclusive cross scetion Attention : d’abitude gribov-regge pour soft, Ici, pour tout X. N. Wang, M. Gyulassy, Phys. Rev. D 45 (1992) 844 -856 One need the complete event : with multiple interactions

Multiples Interactions pp 1. 8 Te. V EPOS simulation Acosta, Darin E. and others for the CDF collaboration, Phys. Rev. D 65 (2002) 072005

WHY is it interesting … … to compute a jet in a complete event ? • To have a real event generator One event in experiment = One event from the generator • To control the underlying event : Can substract the soft part of an event from the jet signal. Energy conservation, colour conservation. • Event generator with hydrodynamics Parallel work, for the future : interaction jet-fluid

Summary Jet and Jet Quenching Event Generators : EPOS Hard process in a complete event Fast computation Conclusions and outlook

EPOS Energy conserving quantum mechanical multiple scattering approach Based on Partons, parton ladders, strings Off-shell remnants Splitting of parton ladder

EPOS MODEL Quantum mechanical multiple scattering approach based on partons and strings Cross sections and particle production calculation in the same framework with energy conservation Careful treatment of projectile and target remnants Contains nuclear effects : splitting of parton ladders (screening) High density effect : treatment of collective effects of a dense core

EPOS MODEL Parton ladders : soft or hard interaction I 1 Multiple interaction : exchange of parton ladders in parallel with care of energy conservation I 2 I 3 I 4

Summary Jet and Jet Quenching Event Generators : EPOS Hard process in a complete event Fast computation Conclusions and outlook

Parton Ladder Proba of an interaction with b (impact parameter) Moment distribution of parton (i, j) in soft part h 1 XPE + Esoft(z+) XIB h 2 σ hard Esoft(z-) XPE - Entering the ladder, proba of a parton with x+p. QCD, parton-parton crosssection (parton model)

• What we don’t want : a spectrum generator A generator of inclusive spectrum based on parton model But, in such generators, one can deal with Pt cuts • What we want : an event generator A generator of complete event with both soft and hard part at the same time But, as in experiment, if one wants a rare event, one needs a lot of simulation How to compute hard partons, in a generator with multiple interactions, with cuts ?

How to get a fast simulation … … without loosing advantages of hard partons in a complete event We need to compute rare events without doing a lot of events. We wants to work with cuts. We wants to keep the context of multiple scaterring with energy conservations. • First step : generate (XPE+, XPE-) by Monte Carlo • Second step : Generate (XIB+, XIB-) Replace the Monte Carlo procedure by a probability distribution S(x. IB, x. PE). Keep multiple scaterring and energy conservation by keeping XPE, change only the internal treatment of a ladder.

Compute events with cuts Exemple of one events with multiple scatering High Pt jets : rare events Wants to look at events with pt > cut • • • Select a standard event Select a standard ladder Take x. PE given by MC Change the procedure that give x. IB Attribute a weight to the total event

Compute events with cuts Particles production Lund string model with kinky strings The same particle production with a different weight for the total event

Exemple of Inclusive Spectrum Once one have (XPE+, XPE) given by Monte Carlo simulation. Generate (XIB+, XIB-) by a probability distribution. n semi : represents the average number of Pomeron with light cone momentum fractions of the Pomeron ends in the intervals [x+ , x+ +dx + ] and [x , x +dx ] PE PE PE S, normalised S is used as a probability distribution to generate z+, z- for a given (x. PE+, x. PE-)

Exemple of Inclusive Spectrum With : and : Omega assures normalisation.

Conclusions and Outlook Epos : goal to be a generator of complete event One experimental event = one generator event Benefits of hard process in an event Hard process in this context : rare event, cuts Fast method : cuts but in the context of multiple scatering Paralel work to have an event generator with hydrodynamics : interaction jet-fluid

Thanks

Comparison with Parton Distribution Function

Parton ladder Iterative procedure : determined each emission h 1 X+, Q 0+ first emission z 1 z 2 σhard (S, Q 1+, Q 0 -) (S, Q 2+, Q 0 -) X-, Q 0 h 2

HIC @ RHIC d. Au Cf. talk klaus Werner, “HIC at LHC, last call for prediction”

S is used as a probability distribution to generate z+, z- for a given (x. PE+, x. PE-) n semi : represents the average number of Pomeron with light cone momentum fractions of the Pomeron ends in the intervals [x+ , x+ +dx + ] and [x , x +dx ] PE Ntilde : distribution of (x. PE+/-) given by Monte Carlo PE PE PE

Analytic Computation avec