Transcript Monte Carlo quarkonium simulations at ATLAS Darren Price, LANCASTER UNIVERSITY International Workshop on Heavy Quarkonium 2007 Darren Price – Monte Carlo onia simulations at.

Monte Carlo quarkonium simulations at ATLAS
Darren Price,
LANCASTER UNIVERSITY
International Workshop on Heavy Quarkonium 2007
Darren Price – Monte Carlo onia simulations at ATLAS
QWG Workshop – 20/10/2007
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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
PYTHIA
parameter
NRQCD matrix
element
Value
PARP(141)
O ( J  )[ 3 S1 (1)]
1.16
PARP(142)
O ( J  )[ 3 S1 (8)]
0.0119
PARP(143)
O ( J  )[ 1 S 0 (8)]
0.01
PARP(144)
O ( J  )[ 3 P0 (8)] m c2
0.01
PARP(145)
O (  c 0 )[ 3 P0 (1)] mc2
0.05
PARP(146)
O (  )[ 3 S1 (1)]
9.28
PARP(147)
O (  )[ 3 S1 (8)]
0.15
PARP(148)
O (  )[ 1 S 0 (8)]
PARP(149)
O (  )[ P0 (8)] m
PARP(150)
O (  b 0 )[ P0 (1)] m
3
3
 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
0.02
2
b
2
b
0.02
0.085
 Are updated ME values available?
Based on hep-ph/0003142
Darren Price – Monte Carlo onia simulations at ATLAS
QWG Workshop – 20/10/2007
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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 crosssection
 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
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Polarisation and octet evolution in Pythia
 As standard Pythia does not contain information about octet state spinalignment 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
Darren Price – Monte Carlo onia simulations at ATLAS
QWG Workshop – 20/10/2007
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