1. Study of muon pairs production process at PANDA and its backgrounds A.N.Skachkova (JINR, Dubna) Obninsk 2010

2. 2 Quark-antiquark annihilation and gluon - quark scattering subprocess in antiproton-proton collision, in which the energetic electromagentic particles (e, muon, photon) are produced, planned to be the subject of our study at PANDA experiment. The results of Monte Carlo simulation of processes with lepton pairs done by use of PYTHIA generator and PANDARoot fast simulaion tool, are presented here. They allowed to work out the cuts needed for background separation and to make reasonable estimations of expected selection rates for these processes. In this talk we base on the results obtained for a case of E beam = 14 GeV (i.e., E cm = 5.3 GeV). The corrections for the final estimations are planned to be done in the nearest years on the basis of the existing detector simulation tools. : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

3. 3 The considered processes. We present the results of study: 1. Production of lepton pairs with the continuum invariant mass. 2. “Resonance” production of lepton pair in J/Ψ decay: q q bar   ̽  c cbar  J/Ψ  l + l - + X : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

4. 4 Production of lepton pair (continuum M inv ( l + l - ) case) The process of lepton pair production q qbar   ̽ / Z˚  l + l - is of big physical interest because: A. The spectrum of final state leptons (e and muons) obviously depends on the form of parton distributions inside colliding protons. B. The transverse momentum of lepton pair PT ( l + l - ) provides the information about intrinsic transverse momentum of quark inside the proton (Fermi motion). C. The results of study of leptons angle and energy spectra distributions, based on Monte-Carlo simulation, was used for a proper “geometrical” design of such important component of PANDA detector as muon system. : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

5. 5 V.A. Matveev, R.M. Muradian, A.N. Tavkhelidze (MMT) ( V.A. Matveev, R.M. Muradian, A.N Tavkhelidze, JINR P2-4543, JINR, Dubna, 1969; SLAC-TRANS-0098, JINR R2-4543, Jun 1069; 27p. ) process, called also as “Drell-Yan process” ( S.D. Drell, T.M. Yan, SLAC-PUB-0755, Jun 1970,12p.; Phys.Rev.Lett. 25(1970)316-320, 1970 ) The dominant mechanism of the l + l - production is the perturbative QED/QCD partonic 2  2 subprocess ̅ q i q i   ̽ / Z˚  l + l - σ = 5.6 * 10 3 pb PYTHIA 6 simulation for the E beam = 14 GeV ( i.e., E cm =5.3 GeV) without detector effects (“ideal detector” --> all particles are detected) allows a proper account of the relativistic kinematics during the simulation : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

6. 6 Signal l ± distributions 0 ≤ E l ≤ 10 GeV, = 2.6 GeV, E peak = 0.4 GeV 0 ≤ PT l ≤ 2 GeV, = 0.7 GeV = 27.3 ° some Θ l > 90° !!! : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

7. 7 Signal l ± : ( l = μ,e) FastSim 0 ≤ Pz ≤ 10 GeV, = 4.2 GeV -2 ≤ Px, Py ≤ 2 GeV l - - left, l + - right : : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

8. 8 Signal l ± : ( l = μ,e) FastSim 0 ≤ P, E l, ≤ 10 GeV, = 4.4 GeV 0 ≤ PT l ≤ 2 GeV, = 1.2 GeV PT l peak = 1.4 GeV l - - left, l + - right : : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

9. 9 Signal l ± : ( l = μ) FastSim = 27.2 ° some Θ l > 90° 0.9 < M inv < 2 GeV l - - left, l + - right : : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

10. 10 Fake muons distributions in signal events 1. The part of signal events which include fake muons is about 16%. 2. Up to 4 fake muons in the final state. 3. Fake muons production vertices are distributed within detector volume  Vertex position information will be useful for Signal / Background separation : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

11. 11 Parents of fake leptons The most probable parents of fake electrons  are neutral pions (Dalits decay) muons  are charged pions The most probable grandparents of fake electrons  are string (Lund model), ρ +,η, ω, Δ 0,Δ +,Λ 0 muons  are string (Lund model), ρ 0, ρ +, ω, Δ +,Δ ++,Λ 0 : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

12. 12 Applied cuts for signal events 1. We select the events with only 2 leptons with E l > 0.2 GeV, PT l > 0.2 GeV 2. These 2 leptons must be of the opposite sign 3. The vertex of origin lies within the R < 15 mm from the interaction point Up to now we supposed the ideal muon system and EM calorimeter covering 180 o : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

13. 13 Cuts influence on signal events Applying these cuts we have loss of the signal events: N of cutse + e - productionμ + μ - production 114.330 %16.525 % 1 & 214.340 %16.805 % 1 & 2 & 314.341 %17.108 % The rate of events with left fake leptons is negligible ! 0.008 % 0.001 % : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

14. 14 Background QCD processes to the q q     l + l - one 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 bar  l + + l - (signal process gives 0.00005% of bkgd events, due to σ = 5.02 E- 06 mb); So, initially there is 1 signal event among 2.000.000 of QCD background i.e., initially  S/B ≃ 5.5 * 10 -6 The simulation was done with approximation when particles are allowed to decay within cylinder volume of R=2500 and L=8000 mm : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

15. 15 The main source of background for q qbar     l + l – are the Minimum-Bias processes: Some examples : Low - PT scattering (gives 68% of events with the σ = 34.25 mb); Single diffractive (gives 6% of events with the σ = 3. 32 mb); qbar + q  l + + l - (gives 0.000012% of events, σ = 5.9 E- 06 mb); So, we have 1 signal event aginst 8.333.333 of Mini-bias bkgd  S/B ≃ 10 -7 Mini-bias background is 5 times harder than QCD background : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

16. 16 Muon’s distributions from background events The shape of muon distributions, produced in background events do not differ from those of fake “decay” muons, produced in the signal process  a rather high probability of appearing the muon pair with the different signs of their charges in Minimum-bias events (which are other than the signal one)  fake pretty well the signal events : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

17. 17 Parents of background leptons The most probable parents of fake electrons  are neutral pions (πº  e + e -  ) muons  are charged pions The most probable grandparents of fake electrons  are strings (Lund model), ρ +,η, ω, Δ 0,Δ + muons  are strings (Lund model), ρ 0, ρ +, ω : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

18. 18 Cuts for mini-bias and QCD processes (including the signal one) The following cuts were applied to the minimum bias and QCD sample: 1. selection of events with the only 2 leptons, having E l > 0.2 GeV, PT l > 0.2 GeV ; 2. these 2 leptons have charges of the opposite charge; 3. the vertex of lepton origin lies within the R< 15mm from the interaction point; 4. M inv ( l + l - ) ≥ 0.9 GeV; 5. leptons have to satisfy the isolation criteria: the summed energy of particles E sum < 0.5 GeV within the cone of R isolation = √ Δ η 2 +Δ φ 2 = 0.2. : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

19. 19 The plots show the distributions over summarized energy of the final state particles in the cones of radius R isolation = √ η 2 +φ 2 respect to the (η – pseudorapidity) signal events upper plot  signal events bottom plot  Mini-bias background R isolation = 0.2 ) Isolation criteria (R isolation = 0.2 ) E (of particles) = 0.5 GeV allows to separate 100% of Mini-bias bkg leptons with the loss of 8% of signal events (after applied 3 cuts discussed above + cut M inv (l +,l - ) > 0.9) Lepton (µ) isolation criteria : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

20. 20 Efficiency of cuts in the presence of mini-bias and QCD bkgd & S/B ratio The total loss of signal events after application of all five cuts is expected to be about 20%. So, we can expect to gain a huge sample of about 7x10 6 signal dilepton events per 1 year (10 7 sec.) : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

21. 21 Conclusion The proposed cuts: 1. Events with only 2 leptons having E l > 0.2 GeV, PT l > 0.2 GeV; 2. The charges of these 2 leptons have opposite sign; 3. The vertex of origin lies within the distance < 15 mm from the interaction point 4. M inv (l +,l - ) > 0.9 GeV 5. Isolation criteria E (R isolation = 0.2) = 0.5 GeV allow: I. To gain about 7x10 6 signal dilepton events per 1 year; II. To suppress QCD & Mini-bias bkgd: completely for muons and to S/B = 9 for electrons; III. Next step: full detector MC simulation. : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

22. 22 J/Ψ production processes (benchmark process) 421) g g  cc¯ [ 3 S 1 (1) ] g  ll + X 422) g g  cc¯ [ 3 S 1 (8) ] g  ll + X 423) g g  cc¯ [ 3 S 0 (8) ] g  ll + X 424) g g  cc¯ [ 3 P J (8) ] g  ll + X 425) g q  cc¯ [ 3 S 1 (8) ] q  ll + X 426) g q  cc¯ [ 3 P J (8) ] q  ll + X 427) g g  cc¯ [ 3 S 1 (1) ] q  ll + X 428) q q¯  cc¯ [ 3 S 1 (8) ] g  ll + X 429) q q¯  cc¯ [ 1 S 0 (8) ] g  ll + X 430) q q¯  cc¯ [ 3 P J (8) ] g  ll + X 1) q i q i ¯   ̽  c c¯  J/Ψ  l + l - + X 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 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) 673 106) g g  J/Ψ +   l + l - + X M.Drees and C.S.Kim, Z.Phys. C53 (1991) 673 431) g g  cc¯ [ 3 P 0 ( 1 ) ] g  ll + X 431) g g  cc¯ [ 3 P 0 ( 1 ) ] g  ll + X 432) g g  cc¯ [ 3 P 1 ( 1 ) ] g  ll + X 432) g g  cc¯ [ 3 P 1 ( 1 ) ] g  ll + X 433) g g  cc¯ [ 3 P 2 ( 1 ) ] g  ll + X 434) g q  cc¯ [ 3 P 0 ( 1 ) ] q  ll + X 434) g q  cc¯ [ 3 P 0 ( 1 ) ] q  ll + X 435) g q  cc¯ [ 3 P 1 ( 1 ) ] q  ll + X 435) g q  cc¯ [ 3 P 1 ( 1 ) ] q  ll + X 436) g q  cc¯ [ 3 P 2 ( 1 ) ] q  ll + X 436) g q  cc¯ [ 3 P 2 ( 1 ) ] q  ll + X 437) q q  cc¯ [ 3 P 0 ( 1 ) ] g  ll + X 437) q q  cc¯ [ 3 P 0 ( 1 ) ] g  ll + X 438) q q¯  cc¯ [ 3 P 1 ( 1 ) ] g  ll + X 438) q q¯  cc¯ [ 3 P 1 ( 1 ) ] g  ll + X 439) q q¯  cc¯ [ 3 P 2 ( 1 ) ] g  ll + X 439) q q¯  cc¯ [ 3 P 2 ( 1 ) ] g  ll + X G.T.Badwin, E.Braten and G.P.Lepage, Phys.Rev. D51 (1995) 1125]; M.Beneke, MKrämer and M.Vänttinen, Phys.Rev. D57 (1998) 4258; B.A.Kniehl and J.Lee, Phys.Rev. D62 (2000) 114027 : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

23. 23 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*10 5 1/mb*sec (= 2*10 32 cm -2 sec -1 ) J/ Ψ production The main contributions to the cross section give the following 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 : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

24. 24 Signal l ± : ( l = μ,e) 0 ≤ E l ≤ 10 GeV, = 4.4 GeV 0 ≤ PT l ≤ 2 GeV, = 1.2 GeV PT l peak = 1.4 GeV = 27.2 ° some Θ l > 90° Important: The same range of angle distributions l - - left, l + - right : : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

25. 25 Signal l ± : ( l = μ,e) FastSim 0 ≤ Pz ≤ 10 GeV, = 4.2 GeV -2 ≤ Px, Py ≤ 2 GeV l - - left, l + - right : : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

26. 26 Signal l ± : ( l = μ,e) FastSim 0 ≤ P, E l, ≤ 10 GeV, = 4.4 GeV 0 ≤ PT l ≤ 2 GeV, = 1.2 GeV PT l peak = 1.4 GeV l - - left, l + - right : : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

27. 27 Signal l ± Fastsim = 27.2 ° some Θ l > 90° Important: The same range of angle distributions l - - left, l + - right : : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk

28. 28 Outline

29. 29 I. Antiproton beam with E beam < 15 GeV may provide an interesting information about quark dynamics inside the hadron and proton structure in the energy region where the Perturbative QCD comes into interplay with a reach resonance ( i.e. Nonperturbative ) physics. II. Different to electron beams, used for measurements of proton structure functions in the region of !negative! values of the square of transferred momentum (q 2 < 0, “space-like” region), antiproton-proton collisions allow to make measurements of proton structure functions in the region of !positive! values of the square of the transferred momentum (q 2 > 0, “time-like”, region, which is less studied ! ). : “”, 12.12.2010 Anna Skachkova : “Muon pairs production at PANDA”, 12.12.2010, Obninsk