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A.N.Skachkova G.D.Alexeev N.B.Skachkov (JINR, Dubna)

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.

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A.N.Skachkova G.D.Alexeev N.B.Skachkov (JINR, Dubna)

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  1. Study of benchmark process p + pbarJ/Ψ + Xl +l -+ X(l= μ, e )(E beam = 14 GeV) A.N.Skachkova G.D.Alexeev N.B.Skachkov (JINR, Dubna)

  2. 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.

  3. J/Ψ production processes 1) q i q i¯ ̽ c c¯  J/Ψ  l +l -+ X 86 ) g g  J/Ψ + g  l +l - + X R.Baier and R.Rücke, Z.Phys. C19(1983) 251 106) g g  J/Ψ +  l +l -+ X M.Drees and C.S.Kim, Z.Phys. C53 (1991) 673 421) g g  cc¯ [3S 1 (1) ] g ll + X 422) g g  cc¯ [3S 1 (8) ] g ll + X 423) g g  cc¯ [3S 0 (8) ] g ll + X 424) g g  cc¯ [3P J (8) ] g ll + X 425) g q  cc¯ [3S 1 (8) ] q ll + X 426) g q  cc¯ [3P J (8) ] q ll + X 427) g g  cc¯ [3S 1 (1) ] q  ll + X 428) q q¯ cc¯ [3S 1 (8) ] g  ll + X 429) q q¯ cc¯ [1S 0 (8) ] g  ll + X 430) q q¯ cc¯ [3P J (8) ] g  ll + X 431) g g  cc¯ [3P 0 (1) ] g  ll + X 432) g g  cc¯ [3P 1 (1) ] g  ll + X 433) g g  cc¯ [3P 2 (1) ] g  ll + X 434) g q  cc¯ [3P 0 (1) ] q  ll + X 435) g q  cc¯ [3P 1 (1) ] q  ll + X 436) g q  cc¯ [3P 2 (1) ] q  ll + X 437) q q  cc¯ [3P 0 (1) ] g  ll + X 438) q q¯  cc¯ [3P 1 (1) ] g  ll + X 439) q q¯  cc¯ [3P 2 (1) ] g  ll + 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

  4. 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 MC parameters, such as the limitation on the phase space integration)

  5. The main contributions to the cross section give the next processes: 1) qi qi¯  ̽ c c¯  J/Ψ l+ l - + X 428) q q¯ cc¯ [3S 1 (8) ] g l+ l- + X 430) q q¯ cc¯ [3P J (8) ] g l+ l- + X The maximum cross section value (obtained by PYTHIA 6.4 simulation) is σ= 20.75 pb that corresponds to 358.5 events / day for the E beam = 14 GeV and Luminosity = 2*105 1/mb*sec (= 2*1032 cm-2 sec-1)

  6. The generation was done with the use of more than 20 QCD subprocesses existed in PYTHIA (including the signal one ¯q q   l +l - ). The main contributions come from the following partonic subprocesses: q + g  q + g(gives 50% of events with the σ=4.88 mb); g + g  g + g(gives 30% of events with the σ=2.96 mb); q + q’  q + q’(gives 18% of events with the σ=1,75 mb); q + q bar  g + g(gives 0.6% of events with the σ=5.89 E- 02 mb); ¯q + q  l+ + l-(has 0.00005% of events with the σ=5.02 E- 06mb); Background QCD processes for the ¯q q    l +l -one The simulation was done within approximation when particles are allowed to decay in cylinder volume R =2500 mm , L=8000 mm

  7. Applied cuts To separate signal leptons from those from pion’s decays • We select the leptonswith El > 0.2 GeV, PTl > 0.2 GeV • We select the events with only 2 leptons It gives pure signal events by cost of 1.7% loss l Muon and electron distributions (and cross sections) look the same within PYTHIA simulation

  8. Signal l± : (l= μ,e) l -- left, l + - right: • 0 ≤ El≤ 10 GeV, < El> = 4.4 GeV • 0≤ PTl ≤ 2 GeV, < PTl> = 1.2 GeV PTlpeak= 1.4 GeV • < Θl > = 27.2 ° some Θl >90°

  9. Signal l± : LEFT - Less energetic (slow), RIGHT - more energetic (fast) • 0 ≤ Eslow ≤ 5 GeV, 4 ≤ Efast ≤ 10 GeV • 0≤ PTslow/fast ≤ 2 GeV, PTpeak = 1.4 GeV • 15o < Θslow < 140o Θslow peak = 25o 0o < Θfast < 26o Θfast peak = 12o

  10. El”slow”/El”fast” correlations

  11. Θl”slow” /Θl”fast”correlations Max of cos (l+,l-) is at ≃ 0.75 that corresponds to an angle ≃ 42 o

  12. Θl/Eldistributions for“slow” leptons (left) and “fast” leptons (right)

  13. A special interest had been attracted to the angular distributions of muons from J/Ψ decay, that shows the possible events loss due to the muon system cuts: • 90o cut 5.3 % • 60o cut 18.0 %

  14. The interesting problem of specification the value of the cross section is postponed for the future. It may happen that to solve this problem another than PYTHIA generator should be used.

  15. Summary • We have studied 50000 events generated with PYTHIA for the beam energy of 14 GeV • J/Ψ output μ, e range within0 <Θl<140 °, 0 ≤ El≤ 10 GeV, 0≤ PTl ≤ 2 GeV. • It looks that J/Ψ decay muons do not impose any new special requirements for PANDA muon system compared to muons from MMT/DY process • The generated PYTHIA events can be available on the web (mail to Anna.Skachkova@cern.ch)

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