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Study of muon pairs production process at PANDA and its backgrounds. A.N.Skachkova (JINR, Dubna). Obninsk 2010. Quark-antiquark annihilation and gluon - quark scattering subprocess in antiproton-proton collision, in which the energetic - PowerPoint PPT Presentation
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Study of muon pairs production process at PANDA
and its backgrounds
A.N.Skachkova
(JINR, Dubna)
Obninsk 2010Obninsk 2010
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.
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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 q q bar c cbar c cbar J/ J/ΨΨ l l+ + ll- - + X+ X
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Production of lepton pair (continuum 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. 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.
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , ObninskAnna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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
qiqi / Z˚ l+l-
σ = 5.6 * 103 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
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Signal l± distributions
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 : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Signal l± : (l = μ,e) FastSim
0 ≤ Pz ≤ 10 GeV,
< Pz > = 4.2 GeV
-2 ≤ Px, Py ≤ 2 GeV
l l -- - left- left, , l l ++ - right- right::
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Signal l± : (l = μ,e) FastSim
0 ≤ P, El, ≤ 10 GeV,
< P, El > = 4.4 GeV
0 ≤ PTl ≤ 2 GeV,
< PTl > = 1.2 GeV
PTl peak = 1.4 GeV
l l -- - left- left, , l l ++ - right- right::
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Signal l± : (l = μ) FastSim
< Θl > = 27.2 °
some Θl > 90°
0.9 < M inv < 2 GeV
l l -- - left- left, , l l ++ - right- right::
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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 : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Applied cuts for signal events
1. We select the events with only 2 leptons with El > 0.2 GeV, PTl > 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 180o
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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 : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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 mmAnna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Parents of background leptons
The most probable parents of fakeelectrons are neutral pions (πºe+e-)
muons are charged pions
The most probable grandparents of fakeelectrons are strings (Lund model),
ρ+,η, ω, Δ0 ,Δ+
muons are strings (Lund model),ρ0, ρ+, ω
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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 El > 0.2 GeV, PTl > 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. Minv (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 = √ Δη
2+Δφ2 = 0.2.
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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 eventssignal events
bottom plot Mini-bias background
Isolation criteria (R R isolationisolation = 0.2 ) = 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
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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 7x106 signal dilepton events per 1 year (107 sec.)
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Conclusion
The proposed cuts:
1. Events with only 2 leptons having El > 0.2 GeV, PTl > 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 7x106 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.
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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J/Ψ production processes (benchmark process)
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
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. C19R.Baier and R.Rücke, Z.Phys. C19 (1983) (1983) 251251
106) g g 106) g g J/ J/ΨΨ + + l l ++ll - - + X + X M.Drees and C.S.Kim, Z.Phys. C53 (1991) M.Drees and C.S.Kim, Z.Phys. C53 (1991) 673673 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];
M.Beneke, MKrämer and M.Vänttinen, Phys.Rev.D57 (1998) 4258;
B.A.Kniehl and J.Lee, Phys.Rev. D62 (2000) 114027
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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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)
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¯ [3S1(8)] g l+ l- + X
430) q q¯ cc¯ [3PJ(8)] g l+ l- + X
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Signal l± : (l = μ,e)
0 ≤ El ≤ 10 GeV, < El > = 4.4 GeV 0 ≤ PTl ≤ 2 GeV, < PTl > = 1.2 GeV PTl
peak = 1.4 GeV
< Θl > = 27.2 ° some Θl > 90° Important: The same range
of angle distributions
l l -- - left- left, , l l ++ - right- right::
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Signal l± : (l = μ,e) FastSim
0 ≤ Pz ≤ 10 GeV,
< Pz > = 4.2 GeV
-2 ≤ Px, Py ≤ 2 GeV
l l -- - left- left, , l l ++ - right- right::
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Signal l± : (l = μ,e) FastSim
0 ≤ P, El, ≤ 10 GeV,
< P, El > = 4.4 GeV
0 ≤ PTl ≤ 2 GeV,
< PTl > = 1.2 GeV
PTl peak = 1.4 GeV
l l -- - left- left, , l l ++ - right- right::
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Signal l± Fastsim
< Θl > = 27.2 °
some Θl > 90°
Important: The same range of angle distributions
l l -- - left- left, , l l ++ - right- right::
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk
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Outline
29
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 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 (q2 < 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 (q2 > 0, “time-like”, region, which is less studied ! ).
Anna Skachkova : : ““Muon pairs production at PANDA”,”, 12.12.2010 12.12.2010 , Obninsk