A.N.Skachkova, N.B.Skachkov (JINR, Dubna) QCD at intermediate energies: Multimuon production and double parton interactions at PANDA A.N.Skachkova, N.B.Skachkov (JINR, Dubna) 2-nd PANDA Russia workshop 26-28 April 2010, IHEP

about quark dynamics inside the hadron and proton structure in the I. Antiproton beam with Ebeam < 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 in interplay with a reach resonance physics. II. Different to electron beams, used for measurements of proton structure functions in the region of negative values of the square of transversed momentum (q^2 < 0, “space-like” region), antiproton-proton collisions allow to make measurements in the region of positive values of the square of the transverse momentum (q^2 > 0, “time-like”, region, less studied ! ). Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

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 pair and prompt photon production, done by use of PYTHIA generator, 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 Ebeam = 14 GeV (i.e., Ecm = 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. Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

low Q**2 measuremens and combination with old (97-98) results ZEUS New measuremens and combination with old (97-98) results at low Q**2 at H1 and ZEUS

Nowdays there are new measuremens at low Q**2 at JLab 

Production of lepton pair (continum Minv (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 < kT> of quark inside the proton ( Fermi motion). C. Double lepton pairs production rate gives the information about multiple parton interactions (MPI), which rate depends on the space distribution of partons, i.e. on space structure of proton.

V. A. Matveev, R. M. Muradian, A. N. Tavkhelidze (MMT) ( V. A 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 ( 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 ̅qiqi   ̽ / Z˚ l+l- σ = 5.9 E- 06 mb PYTHIA 6 simulation for the E beam = 14 GeV ( i.e., Ecm =5.3 GeV). without detector effects (“ideal detector” --> all particles are detected) allows a proper account of the relativistic kinematics during the simulation Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Signal l± : 0 ≤ El ≤ 10 GeV, <El> = 2.6 GeV, Epeak = 0.4 GeV 0 ≤ PTl ≤ 2 GeV, <PTl> = 0.7 GeV <Θl> = 27.3 ° some Θl > 90°!!! Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

In each signal l± event: El ”fast” > El ”slow” Left column 0 < El ”slow” < 5 GeV 0 < Θl ”slow” < 180° (mostly) But !!! Some of less energetic slow leptons have Θl ”slow” > 90° Right column 0.4 < El ”fast” < 10 GeV 0 < Θl ”fast” < 60° Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Fake electron distributions In approximation when particles are allowed to decay in cylinder volume R=2500 x L=8000 mm The number of events which include fake electrons is about 1 -2% of events The most of electron pairs do appear as Dalitz pairs (πºe+e-) produced in decays of neutral mesons, which appear from η, ω or more heavy mesons or barions, produced in their turn as the resonance states according to the LUND fragmentation model. The life time of these resonance states is rather short  the electron pairs are produced close to the interaction point  the vertex position information will not be efficient for the Signal / Background separation.. Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Fake muon distributions 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 Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

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, Δ0 ,Δ+ ,Λ0 muons  are string (Lund model), ρ0, ρ+, ω, Δ+ ,Δ++ ,Λ0 Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Global variable for q qbar    l +l - process - Minv l+l- Minv l+l- = √(Pl+ + Pl-)² = q2 Minv l +l- min = Minv¯qq = 1 GeV – originates from the internal PYTHIA restriction Minv¯qq = √(Pq + P¯q)² = m_hat Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Background QCD processes for 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  l+ + l- (has 0.00005% of events with the σ = 5.02 E- 06 mb); So, initially we have 1 signal event among 2.000.000 of QCD background  S/B ≃ 5.5 * 10-6 The simulation was done within approximation when particles are allowed to decay in cylinder volume R=2500 x L=8000 mm Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

QCD Muon background The shape of muon distributions, produced in these 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 QCD events (which are other than the signal one)  fake pretty good the signal events Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

QCD background electrons The shape of QCD background electron’s distributions are identical to the ones, surrounding the signal process. The most of electron pairs do appear as Dalitz pairs (πºe+e-) The electron pairs are produced close to the interaction point  the vertex position information will not be efficient for the Signal / Background separation.. Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Parents of QCD 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, Δ0 ,Δ+ muons  are strings (Lund model), ρ0, ρ+, ω Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

This source of background is 5 times harder !!! than QCD background The main source of background for the signal q qbar     l +l – are the Minimum-Bias processes: 1. Low - PT scattering (gives 68% of events with the σ = 34.25 mb); 2. Single diffractive (gives 6% of events with the σ = 3.32 mb); and other 3. ¯q + q  l+ + l- (has 0.000012% of events with the σ = 5.9 E- 06 mb); So, we have 1 signal event among 8.333.333 of Mini-bias bkgd  S/B ≃ 10-7 This source of background is 5 times harder !!! than QCD background Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Minimun-bias background electrons The shape of QCD background electron’s distributions are identical to the ones, surrounding the signal process. The most of electron pairs do appear as Dalitz pairs (πºe+e-) The electron pairs are produced close to the interaction point  the vertex position information will not be efficient for the Signal / Background separation.. Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Lepton (µ) isolation criteria The plots show the distributions over summarized energy of the final state particles in the cones of radius R isolation = √ η2+φ2 respect to the (η – pseudorapidity) upper plot  signal events bottom plot  Mini-bias background 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) Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Cuts used for separation of single lepton pairs from Minimum bias and QCD background 1. selection of events with the only 2 leptons, having; 2. these 2 leptons must have opposite charges; 3. the vertex of lepton origin lies within the R< 15mm from the interaction point; 4. Minv ( 2 leptons) ≥ 0.9 GeV; 5. leptons do satisfy the isolation criteria: the summed energy ( Esum ) of all particles within the cone of R(in eta-phi space) =0.2 is less than 0.5 GeV, i.e., Esum < 0.5 GeV.

Efficiency of cuts and S/B ratio The total loss of signal events after application of all five cuts is expected to be about 20%. So, one can expect to gain a huge sample of about 7x106 signal dilepton events per 1 year (10^7 sec.)

A.N.Skachkova (JINR, Dubna) Direct photon production in ̅pp collisions at PANDA energies (E beam = 14 GeV) A.N.Skachkova (JINR, Dubna) PANDA EM group workshop, Ferrara 2007

N. Skachkov: EM group. ITEP PANDA workshop, 22 October 2007 Previous experiments First (pp -> g + X) experiments were done at CERN: at ISR ( pp - collider, Ecm = 31, 45, 53 GeV ): R412 experiment (Darriulat et. al., 1976); R107 (Amaldi et. al., 1978); WA98 (Aggarwal et. al., 2000); and many others at higher E. Also at Fermilab and BNL: E557 (Baltrusaitis et. al. 1979, pBe, Ecm = 19.4, 23.7 GeV) E629 (McLaughlin et. al. 1983, pC, Ecm = 19.4 GeV) N. Skachkov: EM group. ITEP PANDA workshop, 22 October 2007

The proton-antiproton cross section ( ) in quark-parton model is expressed as follows: . Here f( x, Q**2) are the structure functions, is the 22 parton level ( ) cross section ; = is the square of transfered momentum, is the energy fraction carried by a quark in a proton. In our case, ,( or ) and

Nikolay Skachkov: ISHEPP XIX, Dubna, Sept.29-Oct.4, 2008 There is also another diagram that describes fragmentation into a photon. Its contribution is supressed by photon isolation criteria and drops with -growth Nikolay Skachkov: ISHEPP XIX, Dubna, Sept.29-Oct.4, 2008

Our Physical goal: To estimate the possibility of getting the information about proton structure functions f(x, Q**2) . Main interest: To estimate the size of the x-Q**2 kinematical region in which the structure functions can be measured. Physical goal: New information about proton structure functions (gluon-distrib.) in new x-Q**2 kinematical region.

The diagrams contribution The contributions of both diagrams to the total cross section “Annihilation” diagram  “QCD Compton” Cross Sections Total:  = 2.9E-03 mb; q + qbar  gluon + photon (62%):  = 1.78E-03 mb; gluon + q  q + photon (38%):  = 1.10E-03 mb N. Skachkov: EM group. ITEP PANDA workshop, 22 October 2007

Signal photons distributions 0 ≤ E γ ≤ 10 GeV, <E γ > = 2.6 GeV 0 ≤ PT γ ≤ 2 GeV, <PT γ > = 0.67 GeV 0 ≤ Θ γ ≤ 180 ° , <Θ γ > = 29.6 ° some Θ γ > 90° Anna Skachkova: EM group workshop, Ferrara, 15-16 October 2007

In pbar + p  gamma + X process (chosing pbar beam direction as the z-axis) the role of the transfered momentum Q plays the photon transverse momentum, i.e. As it shall be shown below, at E beam = 14 GeV we can expect < 2 GeV, i.e, This region is under study now at HERA and JLab but in “space- like” region of the square of the momentum transferred q^2 <0.

Structure functions distributions 0.05 < x < 0.7 0.05 < x < 0.7 The x-distribution, given by the generated structure functions, allows, together with the photon Pt spect-rum, to estimate the range of kinematical x-Q^2 region, available for the measurement at PANDA . Anna Skachkova: EM group workshop, Ferrara, 15-16 October 2007

Neutral pions distributions 0 ≤ E γ ≤ 7 GeV, <E γ > = 1.2 GeV 0 ≤ PT γ ≤ 1 GeV, <PT γ > = 0.29 GeV 0 ≤ Θ γ ≤ 180 ° , <Θ γ > = 23.5 ° some Θ γ > 90° Up to 7 neutral photons in signal event (i.e. ≤ 14 photons/event). Distribution of N_ πº / event well explains the distribut. of N_ γ / event (due to πº  2 γ). The most probable parents of πº are η, ρ+, strings and Δ0 Anna Skachkova: EM group workshop, Ferrara, 15-16 October 2007

Fake (decay) photons distributions 0 ≤ E γ ≤ 4 GeV, <E γ > = 0.6 GeV 0 ≤ PT γ ≤ 1 GeV, <PT γ > = 0.16 GeV 0 ≤ Θ γ ≤ 180 ° , <Θ γ > = 29.6 ° some Θ γ > 90° Vx, Vy, Vz distributions show mostly zero value Up to 10 background photons in a signal event (in some few events up to 14) Anna Skachkova: EM group workshop, Ferrara, 15-16 October 2007

Gamma isolation criteria The plots show the distributions over summed energy of stable particles in the cones of radius R = √ η2+φ2 respect to the upper plot  direct photon bottom plot  fake photon Isolation criteria E (of stable particles) =0 in the R=0.3 allows to separate 100% of fake photons with loss of 4.2% of signal events Anna Skachkova: EM group workshop, Ferrara, 15-16 October 2007

Conclusion. 0.05 < x < 0.7; The simulation with PYTHIA ( used as the first step approximation ) has shown that with E beam = 14 GeV : 1. PANDA can perform the measurement of proton structure functions in the time-like !!! (q2 >0) x-Q2 kinematical region: 0.05 < x < 0.7; 2. This measurement will have the advantage over DIS because it shall be more sensitive to gluon distribution. 3. To separate the contribution of fake photons, which come from the decays of pions and other neutral fake mesons in the signal and mini-bias events, a lot of work with full GEANT simulation is needed in nearest years to find a way to identify/separate by ECAL πo, η, ω and other mesons, produced in QCD and mini- bias background events (like it was done at ISR, SppS,WA98, PHENIX, and other collaborations …). . For this region PYTHIA predicts about 5 x109 !!! signal events per year.

Double parton (DP) interaction measurements at PANDA 1.The inelastic scattering of nucleons need not to occur only through a single parton-parton interaction (A) and the contribution from double parton collisions (A and B) can be significant. 2.The probability of the second parton-parton collision (B) will be larger or smaller depending on the parton spatial distribution. If partons were concentrated within small region inside the proton then the second collision (B) would be more likely to occur for a given A collision. By contrast, in a case of uniform parton density throughout the proton, the presence of A would not increase the probability of B.

History of Measurements of Double Parton scatterings A new measurement was done by our group at D0: Phys. Rev. D 81:052012, 2010; arXiv:0912 5104 [hep-ex] 37

Outback

DP: Signal Variables Calculated for the pair that gives the minimum value of S: 42 42

Conclusion The proposed cuts: Events with only 2 leptons of the opposite sign and El > 0.2 GeV, PTl > 0.2 GeV 2. The vertex of origin lies within the distance from the interaction point < 15 mm 3. Minv (l +,l -) > 0.9 GeV 4. Isolation criteria E (R isolation = 0.2) = 0.5 GeV Allow to suppress QCD & Mini-bias bkgd to: completely for muons; S/B = 9 for electrons Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Double parton (DP) events at PANDA Signal process Backgroud process PT-balanced muon pairs PT- inbalanced lepton pairs Preliminary PYTHIA estimations (model dependent) has shown a moderate reduction of the total cross section as comparing to lepton-pair production (by ~10-2 ). 45

Double parton (DP) events at PANDA To perform the analogous measurement we need only to substitute jets and photon by leptons: e/muons; The electrons and muons with E_l > 0.8 can be used for such kind of measurement; The measurement with leptons (which are much more better measured: Energy, Vertex position, no need of jet energy calibration) can provide a much higher preci-sion.

Conclusions: 1. PANDA energy range is quite promising for studying of a large number of very interesting Deep Inelastic QCD processes. 2. The study of single lepton pair production can provide the informa- tion about valence quark distribution in a new kinematical region of the intermediate “time-like” momentum transferred q2 > 0. 3. Direct photon production shall allow to measure the gluon distribution component of proton structure function at q2 > 0 . 4. Double parton interactions can bring the information, may be the most clean one (jets are substituted by e/muons) about the spatial distribution of partons inside the proton.

Outback

Θl ”slow” / Θl ”fast” correlation Muon system geometry cuts : Θl_”slow” & Θl_”fast” ≤ 20º  14% events saved Θl_”slow” & Θl_”fast” ≤ 40º  50% events saved Θl_”slow” & Θl_”fast” ≤ 60º  72% events saved Θl_”slow” & Θl_”fast” ≤ 90º  94% events saved ( 6% of events loss ) Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

El ”slow” / El ”fast” correlation Applying the Energy cuts: El_”fast” & El_”slow” > 0.5 GeV  loss of ~25% of signal events El_”fast” & E l_”slow” > 1 GeV  loss of ~45% of signal events Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Θl/El correlation for signal l± Θl ”slow” / E l ”slow” Θl ”fast” / E l ”fast” 1. for El > 0.5 GeV “slow “ “fast” Nevent ≈ 70% Nevent ≈ 98% 2. for El > 4 GeV Nevent ≈ 2% Nevent ≈ 40% 3. for Θl < 60° Nevent ≈ 78% Nevent ≈ 99.96% Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Some first estimations were Published (2006) as PANDA Note PHY-003: and hep-ph/0506139 A.N.Skachkova, N.B.Skachkov “Monte-Carlo simulation of lepton pair production in “ppbar  l+l - + X” events at Ebeam = 14 GeV” Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Cuts efficiency for Minimum-Bias background events e+e- production N of cuts S/B ratio Efficiency 1 (exactly 2 leptons with El > 0.2 GeV, PTl > 0.2 GeV ) 5.3 * 10 - 4 1.78 * 10 - 4 2 (2 leptons are of the opposite sign) 5.4 * 10 - 4 0.98 3 (The vertex of origin lies within the R < 15 mm) 5.5 * 10 - 4 4 (Minv(l1,l2) > 0.9) 0.09 0.006 Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Efficiency of M inv (l+,l-) cut e+e- case Minv(l+,l-)> S / B Efficiency The rest of signal events 0.9 0.09 0.0057 84 % 1.0 0.15 0.0034 81 % 1.03 0.38 0.0013 73 % 1.05 0.40 0.0012 69 % 1.1 0.83 0.0005 58 % 1.2 2.00 0.0002 42 % Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

Cuts influence on signal events Applying these cuts we have loss of the signal events: N of cuts e+e- production μ+μ- production 1 14.330 % 16.525 % 1 & 2 14.340 % 16.805 % 1 & 2 & 3 14.341 % 17.108 % The rate of events with left fake leptons is negligible ! 0.008 % 0.001 % Anna Skachkova: “Lepton pair production at intermediate energies and the main backgrounds ”, 22.11.08

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