Darren Price – Monte Carlo onia simulations at ATLAS QWG Workshop – 20/10/2007 Page 1

Monte Carlo quarkonium simulations at AMonte Carlo quarkonium simulations at ATLASTLAS

Darren PriceDarren Price,,LANCASTER UNIVERSITYLANCASTER UNIVERSITY

International Workshop on Heavy Quarkonium 2007

Darren Price – Monte Carlo onia simulations at ATLAS QWG Workshop – 20/10/2007 Page 2

Monte Carlo onia samples at ATLAS

Official high statistics production samples at ATLAS currently use NRQCD octet processes only. Originally written by S. Wolf, now incorporated into Pythia.

Colour octet NRQCD matrix elements describe non-perturbative onia evolution Matrix elements set to values derived from Tevatron data

P Y T H I A

p a r a m e t e rN R Q C D m a t r i x

e l e m e n tV a l u e

P A R P ( 1 4 1 ) )]1()[( 13 SJO 1 . 1 6

P A R P ( 1 4 2 ) )]8()[( 13 SJO 0 . 0 1 1 9

P A R P ( 1 4 3 ) )]8()[( 01 SJO 0 . 0 1

P A R P ( 1 4 4 ) 20

3 )]8()[( cmPJO 0 . 0 1

P A R P ( 1 4 5 ) 20

30 )]1()[( cc mPO 0 . 0 5

P A R P ( 1 4 6 ) )]1()[( 13 SO 9 . 2 8

P A R P ( 1 4 7 ) )]8()[( 13 SO 0 . 1 5

P A R P ( 1 4 8 ) )]8()[( 01 SO 0 . 0 2

P A R P ( 1 4 9 ) 20

3 )]8()[( bmPO 0 . 0 2

P A R P ( 1 5 0 ) 20

30 )]1()[( bb mPO 0 . 0 8 5

Based on hep-ph/0003142

Much interest at ATLAS in producing samples of 2S and 3S states.

In Pythia, requires separate production runs so this has not been done yet

Currently ME’s for these higher states have not been added into ATLAS Pythia tuning but should be possible based on hep-ph/0003142

Are updated ME values available?

Darren Price – Monte Carlo onia simulations at ATLAS QWG Workshop – 20/10/2007 Page 3

Extending processes available in Pythia

Only LO order NRQCD processes are implemented in Pythia (as of 6.413)

Desirable to extend range of processes we are able to study at ATLAS

Pythia can handle showering/hadronisation if provided with short distance cross-section

NNLO calculations should be added, MadOnia interfaced, kt factorisation approach?

Theoretical cross-sections and distributions for various processes need to be run through detector simulation and reconstruction software to see if we can really see what we hope to see!

Can investigate feasibility of excluding or proving various production models at the LHC if we have these processes simulated sooner rather than later

After discussions with Lansberg, considering associated charm/beauty production Will be able to look for J/ produced with , but need processes in Pythia!

Would like to be able to compare different MC generators, such as Herwig++

Darren Price – Monte Carlo onia simulations at ATLAS QWG Workshop – 20/10/2007 Page 4

Polarisation and octet evolution in Pythia

As standard Pythia does not contain information about octet state spin-alignment so this cannot be determined in the final analysis Would be useful to be able to include and keep track of this polarisation information

throughout the evolution Would allow us to run normal simulations through the detector and see effect of

detector acceptance with pT, h etc. Reducing dependence on MC templates important, can reduce any unknown

systematics and correlations that may be otherwise present

Octet states in Pythia currently very simplistic -- states have correct quantum numbers but are assumed to all evolve as either:

J/(8)->g+J/(1) or (8)->g+(1)with the emitted gluon taking away colour having 4 MeV phase space!

By changing the mass of the octet quarkonia, can give this gluon a better chance of doing something (anything!) Would like to know if there are any predictions for what values would be sensible, or upper limits?

This effects how likely we are to see associated hadronic activity If gluon has ~O(MeV) phase space, have no chance of differentiating octet/singlet

evolution based on associated hadronic activity near onia direction after reconstruction