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Study of benchmark process p + p bar J/ Ψ + X l + l - + X ( l = μ , e ) (E beam = 14 GeV). A.N.Skachkova G.D.Alexeev N.B.Skachkov (JINR, Dubna). This process is of interest for the muon system from the view point of its geometrical acceptance. - PowerPoint PPT Presentation
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Study of benchmark process Study of benchmark process
pp + + ppbarbar J/J/ΨΨ + X + X l l ++l l -- + X+ X
(( ll = = μμ, e ), e ) (E (E beambeam = 14 GeV) = 14 GeV)
A.N.SkachkovaA.N.SkachkovaG.D.AlexeevG.D.Alexeev
N.B.SkachkovN.B.Skachkov(JINR, Dubna)(JINR, Dubna)
22
This process is of interest for the muon system from the view point of its geometrical
acceptance.
For this reason we have concentrated our study on kinematical, mainly angular, distributions.
To get an idea about these distributions we have used, as for the first step, PYTHIA 6.4 event
generator with its parameters adjusted for the PANDA energies.
33
J/J/ΨΨ production processes production processes
421) 421) g g g g cc¯ [ cc¯ [33S S 1 1 (1)(1) ] g ] g ll ll + X+ X
422) 422) g g g g cc¯ [ cc¯ [33S S 1 1 (8)(8) ] g ] g llll + X + X
423) 423) g g g g cc¯ [ cc¯ [33S S 0 0 (8)(8) ] g ] g ll ll + X+ X
424) 424) g g g g cc¯ [ cc¯ [33P P J J (8)(8) ] g ] g llll + X + X
425) 425) g q g q cc¯ [ cc¯ [33S S 1 1 (8)(8) ] q ] q llll + X + X
426) 426) g q g q cc¯ [ cc¯ [33P P J J (8)(8) ] q ] q ll ll + X + X
427) 427) g g g g cc¯ [ cc¯ [33S S 1 1 (1)(1) ] q ] q ll ll + X + X
428) q q428) q q¯̄ cc¯ [ cc¯ [33S S 1 1 (8)(8) ] g ] g ll ll + X+ X
429) 429) q qq q¯̄ cc¯ [ cc¯ [11S S 0 0 (8)(8) ] g ] g ll ll + X + X
430) q q430) q q¯̄ cc¯ [ cc¯ [33P P J J (8)(8) ] g ] g llll + X + X
1) q1) q i i q q i i¯̄ ̽̽ c c c c¯ ¯ J/ J/ΨΨ l l ++ll - - + X+ X
86 ) g g 86 ) g g J/ J/ΨΨ + g + g l l ++ll - - + X + X R.Baier and R.Rücke, Z.Phys. R.Baier and R.Rücke, Z.Phys. C19C19 (1983) 251(1983) 251
106) g g 106) g g J/ J/ΨΨ + + l l ++ll - - + X + X M.Drees and C.S.Kim, Z.Phys.M.Drees and C.S.Kim, Z.Phys. C53 C53 (1991) 673(1991) 673 431) g g 431) g g cc¯ [cc¯ [33P P 00 ( (11) ] g) ] g ll ll + X + X
432) g g 432) g g cc¯ [cc¯ [33P P 11 ( (11) ] g) ] g llll + X + X
433) g g 433) g g cc¯ [cc¯ [33PP 2 2 ( (11) ] g ) ] g ll ll + X+ X
434) g q 434) g q cc¯ [cc¯ [33P P 00 ( (11) ] q ) ] q ll ll + X + X
435) g q 435) g q cc¯ [cc¯ [33P P 11 ( (11) ] q) ] q llll + X + X
436) g q 436) g q cc¯ [cc¯ [33PP 2 2 ( (11) ] q ) ] q llll + X + X
437) q q 437) q q cc¯ [cc¯ [33P P 00 ( (11) ] g) ] g ll ll + X + X
438) q q¯ 438) q q¯ cc¯ [cc¯ [33P P 11 ( (11) ] g) ] g llll + X + X
439) q q¯ 439) q q¯ cc¯ [cc¯ [33PP 2 2 ( (11) ] g) ] g llll + X + X
G.T.Badwin, E.Braten and G.P.Lepage, Phys.Rev. D51 (1995) 1125
[Erratum: ibid D55 (1997) 5883];
M.Beneke, MKrämer and M.Vänttinen, Phys.Rev.D57 (1998) 4258;
B.A.Kniehl and J.Lee, Phys.Rev. D62 (2000) 114027
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PYTHIA 6 allows a proper account of the relativistic kinematics during the simulation,
but
it doesn’t give well determined cross section value for the case of J/Ψ production at the
low energies
(which is depend on some internal MCparameters, such as the limitation on the
phase space integration)
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The main contributions to the cross section give The main contributions to the cross section give the next processes:the next processes:
1)1) q qi i qqii¯ ¯ ̽̽ c c¯ c c¯ J/ J/ΨΨ ll+ + ll - - + X + X428)428) q q q q¯̄ cc¯ [ cc¯ [33S S 1 1
(8)(8) ] g ] g ll+ + ll-- + X + X430)430) q q q q¯̄ cc¯ [ cc¯ [33P P J J
(8)(8) ] g ] g ll+ + ll-- + X + X
The maximum cross section value (obtained by PYTHIA 6.4 The maximum cross section value (obtained by PYTHIA 6.4 simulation) is simulation) is
σσ = = 20.75 pb 20.75 pb that corresponds to that corresponds to
358.5 events / day 358.5 events / day
for the Efor the E beam beam = 14 GeV = 14 GeV and Luminosity = 2*10and Luminosity = 2*105 5 1/mb*sec (= 2*101/mb*sec (= 2*1032 32 cmcm-2 -2 secsec-1-1))
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Background QCD processes for the Background QCD processes for the ¯̄q q q q l l ++l l -- oneone
The generation was done with the use of more than 20 QCD subprocesses existed in PYTHIA (including The generation was done with the use of more than 20 QCD subprocesses existed in PYTHIA (including the signal one the signal one ¯̄q qq q l l ++l l -- ). ).
The main contributions come from the following partonic subprocesses:The main contributions come from the following partonic subprocesses:
q + g q + g q + g q + g (gives (gives 50%50% of events with the of events with the σσ == 4.884.88 mb); mb);
g + g g + g g + g g + g (gives (gives 30%30% of events with the of events with the σσ == 2.962.96 mb); mb);
q + q’ q + q’ q + q’ q + q’ (gives (gives 18%18% of events with the of events with the σσ == 1,75 1,75 mb);mb);
q + q bar q + q bar g + g g + g (gives (gives 0.6%0.6% of events with the of events with the σσ == 5.89 E- 02 5.89 E- 02 mb);mb);
¯̄q + q q + q l l++ + l + l-- (has (has 0.00005%0.00005% of events with the of events with the σσ == 5.02 E- 065.02 E- 06 mb);mb);
The simulation was done within approximation when particles are allowed to decay
in cylinder volume R =2500 mm , L=8000 mm
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Applied cutsApplied cuts
To separate signal leptons from thoseTo separate signal leptons from those from pion’s decaysfrom pion’s decays
We select the leptonsWe select the leptons withwith EEl l > 0.2 GeV, PT> 0.2 GeV, PTll > 0.2 GeV > 0.2 GeV We select the events with only We select the events with only 22 leptons leptons
It gives pure signal events by cost of It gives pure signal events by cost of 1.7% loss1.7% loss
ll
Muon and electron distributions (and cross sections)Muon and electron distributions (and cross sections) look the same within PYTHIA simulation look the same within PYTHIA simulation
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Signal Signal ll± : (± : (ll = = μμ,e),e)
00 ≤ E ≤ Ell ≤ ≤ 1010 GeV, GeV,
< E< Ell > = > = 4.4 4.4 GeV GeV 00 ≤ PT≤ PTll ≤ ≤ 22 GeV, GeV,
< PT< PTll > = > = 1.2 1.2 GeV GeV
PTPTll peakpeak = = 1.41.4 GeV GeV
< < ΘΘl l > = > = 27.2 27.2 °°
some some ΘΘll > > 9090°°
l l -- - left, - left, l l ++ - right: - right:
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Signal Signal ll± :± :
00 ≤ E ≤ Eslow slow ≤ ≤ 55 GeV, GeV,
44 ≤ E ≤ Efast fast ≤ ≤ 1010 GeV GeV 00 ≤ PT≤ PTslow/fast slow/fast ≤ ≤ 22 GeV, GeV, PTpeak = PTpeak = 1.41.4 GeV GeV
1515oo < < ΘΘslowslow < < 140140oo ΘΘslow slow
peak peak = = 2525oo
00oo < < ΘΘfastfast < < 2626oo
ΘΘfast fast peak peak = = 1212oo
LEFT - Less energetic (slow), RIGHT - more energetic (fast)
1111
ΘΘ ll”slow””slow” / /ΘΘ ll”fast” ”fast” correlationscorrelations
Max of cos (l+,l-) is at ≃ 0.75 that
corresponds to an angle ≃ 42 o
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ΘΘll/E/Ell distributions fordistributions for“slow” leptons (left) and “fast” leptons “slow” leptons (left) and “fast” leptons
(right)(right)
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the possible events loss due to the the possible events loss due to the muon system cuts:muon system cuts:
9090o o cutcut 5.3 %5.3 %
6060o o cutcut 18.0 %18.0 %
A special interest had been attracted to the angular distributions of muons from J/Ψ
decay,
that shows
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The interesting problem of The interesting problem of specification the value of the cross specification the value of the cross section is postponed for the future.section is postponed for the future.
It may happen that to solve this It may happen that to solve this problem another than PYTHIA problem another than PYTHIA generator should be used.generator should be used.
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SummarySummary We have studied 50000 events generated with PYTHIA for We have studied 50000 events generated with PYTHIA for
the beam energy of 14 GeVthe beam energy of 14 GeV J/J/ΨΨ output output μμ, e, e range within range within 0 <0 < ΘΘll << 140 140 °,°, 00 ≤ E ≤ Ell ≤ ≤ 10 10 GeV, GeV, 00 ≤ PT≤ PTll ≤ ≤ 22 GeV. GeV. It looks that J/It looks that J/ΨΨ decay muons do not impose any new decay muons do not impose any new
special requirements for PANDA muon systemspecial requirements for PANDA muon system compared to muons from MMT/DY processcompared to muons from MMT/DY process
The generated PYTHIA events can be available on the web The generated PYTHIA events can be available on the web (mail to Anna.Skachkova@cern.ch)(mail to Anna.Skachkova@cern.ch)
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