Darren Price – Monte Carlo onia simulations at ATLAS QWG Workshop – 20/10/2007Page 1 Monte Carlo quarkonium simulations at A TLAS Darren Price, LANCASTER UNIVERSITY International Workshop on Heavy Quarkonium 2007

Darren Price – Monte Carlo onia simulations at ATLAS QWG Workshop – 20/10/2007Page 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 Based on hep-ph/  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/  Are updated ME values available?

Darren Price – Monte Carlo onia simulations at ATLAS QWG Workshop – 20/10/2007Page 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, k t 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 – 20/10/2007Page 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 p T, 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