1. Study of Drell-Yan processes with COMPASS
Oleg Denisov, INFN sez. Torino
Basic ideas, experimental apparatus,
feasibility, expected DY event rates
International Workshop on Structure
and Spectroscopy, Freiburg,
19-21/03/2007
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Oleg Denisov

2. Contents DY at COMPASS Basic features of the experiment:
SPS M2 secondary hadron beams
Compass polarised target
Compass spectrometer
Major limiting factors:
External (CERN safety rules)
Internal spectrometer limitations
Two possible detector layouts
Kinematical range to be covered
Spectrometer layout in the DY Monte Carlo
Very preliminary estimates of the DY event rates
Short term plans
Summary
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Oleg Denisov

3. DY at COMPASS
October 2004, CERN SPSC meeting at Villars – study of DY processes with COMPASS was at first time proposed and discussed (proposal by R.Bertini, O.Denisov and S.Paul)
– feasibility study (SPS hadron beams, Compass polarised target, CERN safety regulations (radioprotection), trigger system, spectrometer lay-out, possible ways of the background suppression, competition and complementarity, methods elaboration, two DY workshops were organized: Dubna in December 2006 and Torino in March 2007)
Summer 2007 – DY COMPASS Beam Test
December 2007 – possibly first draft of the proposal
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Oleg Denisov

4. Spectrometer to identify lepton pair
Drell-Yan Kinematics
Spectrometer to identify lepton pair
POL.Targ.
Small cross sections – high beam intensity (high secondary particles flux)
Valence quarks PDF - - or pbar
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Oleg Denisov

5. Hadron beam spin physics with COMPASS
Drell-Yan physics with transversally polarised target
Transversity and its accompanying T-odd PDF:
Sivers function
Boer-Mulders function
Get information on transversity
Drell-Yan physics with longitudinally polarised target
Pion light-cone distribution amplitude (O.Teryaev)
“Conventional” spin physics with hadron beam and polarized target
Spin asymmetries in multi-pion production (talk by Marco Radici)
Possible extension to c and  polarization
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Oleg Denisov

6. Basic features of the experiment
Intense (2x107 p/s) hadron beams
Exellent large acceptance polarised target (NH3, 6LiD)
Multipurpose running spectrometer:
Advanced and flexible triggering system with the possibility to trigger on muons, electrons and hadrons
Good hadron/electron/muon separation in the final state
Large muon/electron acceptance
High capacity DAQ system
Open structure of the spectrometer
Compass is a running experiment
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Oleg Denisov

7. SPS M2 beam line reference person - Lau Gatignon (CERN) Compass
SPS 400 GeV primary beam
Production target
Secondary beams
Magnetic lenses
Compass
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Oleg Denisov

8. Particle production at 0 mrad
Apply Atherton formula for 0 mrad (approximative only for p  60 GeV/c).
Obtain # particles per steradian per GeV/c and per 1012 interacting protons:
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Oleg Denisov

9. In present M2 line - beam ≈ 108/spill
At -100 GeV/c one may expect the following beam composition (in %):
Particle
type
Fraction
at T6
Fraction at COMPASS p
1.7
2.1 K-
5.8
1.6 p-
84.5
86.3 e-
8.0
10.0
In present M2 line - beam ≈ 108/spill
In present M2 line pbar ≤ 2 106p/spill (due to 108 limit on total beam flux for RP)
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Oleg Denisov

10. WHAT ABOUT A RF SEPARATEDp BEAM ???
First and very preliminary thoughts, guided by
recent studies for P326
CKM studies by J.Doornbos/TRIUMF, e.g.
E.g. a system with two cavities:
RF1
RF2
DUMP
DUMP L
Momentum
selection
Choose e.g. DFpp
DF = 2p (L f / c) (b1-1 – b2-1) with b1-1 – b2-1 = (m12-m22)/2p2
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Oleg Denisov

11. VERY PRELIMINARY CONCLUSION
H.W.Atherton formula tells us : 0.42 p / int.proton / GeV
Then for 1013 ppp on target one obtains:
particles per spill ≈ ppp
for a total intensity probably not exceeding 1013 ppp,
knowing that e- and p- are well filtered, but K- only partly.
Due to 108 limit on total flux, max antiproton flux remains
limited by purity (probably about 50%). Hence ≈ ppp
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Oleg Denisov

12. Compass PT for DY physics
Contact persons: W.Meyer, N.Doshita
three cells target
with opposite polarization
NH3
Polarization 90%
Dilution factor 0.18
Polarization 50%
Dilutionfactor 0.48
6LiD
180 mrad acceptance
For transversity: 1 - + + - 2
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Oleg Denisov

13. Hadron beam intensity vs beam spot
size for NH3
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Oleg Denisov

14. Acceptable heating of the cells
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Oleg Denisov

15. Compass spectrometer features
Multipurpose running spectrometer:
Advanced and flexible triggering system with the possibility to trigger on muons, electrons and hadrons
Good hadron/electron/muon separation in the final state
Large muon/electron acceptance
High capacity DAQ system
Open structure of the spectrometer
It is running spectrometer
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Oleg Denisov

16. COMPASS Universal spectrometer Polarized target
(longitudinal or transversely)
Have the possibility to operate with
muon or hadron beams.
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Oleg Denisov

17. Compass layout for DY measurements
MW1 EC HC PT
Beam
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Oleg Denisov

18. Compass comparison to old fashion DY experiments
Spectrometer, DY -detection
Target
Beam dump
≈108 p/s
COMPASS
Spectrometer, DY  and e detection, “traditional” hadron beam spin physics
Pol.T
Beam Dump
Magnet
≈107 p/s
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Oleg Denisov

19. CERN safety regulations
Reference person - Heinz Vincke (CERN)
Two major limitations:
Hadron beam intensity less then 2x107 p/s
Integrated material budget less then 20% of one interaction length
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Oleg Denisov

20. CERN safety regulations
There were some chances to extend these limits by:
Extremely IMPORTANT
(last week news) :
We have very good chances to be approved for running with 50% of interaction length polarized target and 2x107 /s
NOT OFFICIAL
Improving the Compass area shielding
Taking into account all Compass detector “heavy” components like magnets, polarised target, calorimeters, hadron absorbers etc
Doing additional measurements of charged particle fluxes in the experimantal hall
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Oleg Denisov

21. Internal Compass limiting factors
High charged particles flux
+- DY channel - high background from pion decays (soft hadrons absorber?)
e+e- DY channel - thick target,-conversion and Dalitz-pair production
Very selective trigger because of the small cross section
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Oleg Denisov

22. COMPASS DY layout I PT Advantages:
Possibility to measure both (+ - ) and (e+ e-) channel
Higher statistics + better systematics control ?
(Semi)Exclusive DY processes
Possibility to use in the DY trigger Hadron Calorimetry
Traditional hadron beam spin physics ( asym., c etc.)
Disadvantages:
High secondary particles flux though set-up
Higher background for + - from   decays
MW1 EC HC PT
Beam
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Oleg Denisov

23. SOFT Hadron absorber (DUMP)
COMPASS DY layout II
MW1
Advantages:
Lower irradiation degree of the spectrometer
Background suppression for + - channel by factor of 102
Disadvantages:
One only channel of DY and nothing else apart of DY  - channel
No use of the hadron calorimetry in trigger
SOFT Hadron absorber (DUMP) EC HC PT
Beam
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Oleg Denisov

24. Compass DY program beam test
The only reliable way to study the DY feasibility is to run Compass DY beam test in the real Compass environment with high intensity hadron beam and Compass polarized target
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Oleg Denisov

25. VERY IMPORTANT!!! Compass DY beam test in 2007 Conditions:
Hadron beam intencity (-) – 107 p/sec
Compass polarised target NH3 polarized transversaly
Muon program spectrometer layout
VERY IMPORTANT!!!
Goals:
Compass polarized target test with intense hadron beam
Compass spectrometer test with intense beam and thick polarized target
Test for the radioactive conditions in the experimental hall with intense hadron beam and Compass polarized target
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Oleg Denisov

26. Spectrometer layout in the DY MC
MW1 PT
Beam
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Oleg Denisov

27. Torino DY Workshop recomendations
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Oleg Denisov

28. DY Monte Carlo with COMPASS
Michela Chiosso
External DY generator (A.Bianconi) -> COMGeant -> CORAL ->PHAST
- beam on transversely polarized NH3 target
Various energies of the incoming beam (s= GeV2)
Different intervals of M
0.1 GeV/c < PT < 10.0 GeV/c
-1 < Xf < +1
FOR DETAILS, Please, follow the reference on the COMPASS
WEB page (analysis).
The best compromise of the beam energy is ≈ 160 GeV (s=300 GeV2):
better statistics in high dilepton mass region
in the interesting Muu mass region the dominant contribution is coming from valence quarks annihilation
(x1, x2 ) > 0.1

29. Compass DY MW1 and MW2 acceptance
MW1 and MW2 acceptance 160 GeV pion beam
Total acceptance = m+m- in MW1 + m+m- in MW2 + m+(-) in MW1 and m-(+) in MW2
generated m+m- in MW m+m- in MW m+(-) in MW1, m-(+) in MW2 Q2 Pt Xf
67.5% % %

30. Compass DY acceptance
s = 200 GeV - beam GeV < Mm+m- < 9 GeV 

31. Compass DY acceptance
s = 300 GeV - beam GeV < Mm+m- < 9 GeV 

32. Compass DY acceptance
s = 375 GeV2 - beam GeV < Mm+m- < 9.0 GeV
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Oleg Denisov

33. Compass DY acceptance
s = 300 GeV2 - beam GeV < Mm+m- < 3.5 GeV
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Oleg Denisov

34. Compass DY vs E615 acceptance
106 GeV - beam <= Mm+m- <= 9.0
E615

35. DY background simulation (just started)
L.Colantoni,
S.Petrochenkov, ..
Reconstruction MC
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Oleg Denisov

36. DY background.vs.signal (not normalized to cross sections)
DY 3. GeV < M < 9. GeV, s = 300 GeV
Minimum bias
107 bkg events at least 2 charged outcoming pions
500 events caused “DY” trigger
500 bkg events caused DY trigger
Q2 trig. big
Big
Sig.
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Oleg Denisov

37. DY background.vs.signal (not normalized to cross sections)
DY 3. GeV < M < 9. GeV, s = 300 GeV
Bkg, 2 out coming pions
Bkg
Signal
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Oleg Denisov

38. DY background.vs.signal (not normalized to cross sections)
DY 1. GeV < M < 2.5 GeV, s = 300 GeV
Bkg minimum bias
Signal
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Oleg Denisov

39. Very preliminary DY event rates estimate
Target: two cells 30 cm each : NH3 cm
Target material: NH3
Density of NH3: NH3 = 0.85 g/cm3
Mass of the NH3 mole: ANH3 = 17
- beam intensity: Ibeam = 2107 p/s
Luminosity: L = LNH3 × Ncell × NH3 × NA × 1/ANH3 × Ibeam ≈
4.×1031 cm-2 s-1
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Oleg Denisov

40. Very preliminary DY event rates estimate
Compass DY pairs reconstruction efficiency (acceptance included) : A ≈ 0.5
DY cross section on NH3: NH3 = Ncorr × p , where Ncorr=17 and p taken from table given below (by A.Bianconi)
Dspill = 5 s (duration of spill), Nspill =4000 (number of spills per day), Esps= 80% (efficiency of the machine)
Duration of the Run 100 days: DRUN=100
R = L × Ncorr × p × A × Dspill × Nspill × ESPS × DRUN
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Oleg Denisov

41. DY cross sections and statistics estimate (very preliminary, 100 days of running)
M (+-), GeV
2.5-4.
4.-9.
S, GeV2
100
0.35 nb
0.03 nb
200
0.65 nb
0.10 nb
300
0.78 nb
0.15 nb
M (+-), GeV
2.5-4.
4.-9.
S, GeV2
100
140000
12000
200
320000
35000
300
370000
58000
VERY PRELIMINARY
Cross section values were taken from AB_5 A.Bianconi generator crosschecked with PYTHIA data (A.Nagaytsev, Dubna), without J/ contribution
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Oleg Denisov

42. Competition and complementarity I
SPIN Physics at GSI:
Two LoI submitted:
ASSIA (Collider mode)
PAX polarized antiproton beam and proton polarized internal target
L = 2.71031 cm-2 s-1
S = 30 GeV2
e+e-, alternative +-
Not yet approved
L = cm-2 s-1
S = 30 GeV2
+ - , alternative e+e-
YEAR 201?
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Oleg Denisov

43. Competition and complementarity II
J-PARK,
The DY measurement is under discussion, no detailed information is available yet
L ≈ 1031 cm-2s-1 (polarized pp)
s = 200 GeV
small x, pp collision
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Oleg Denisov

44. MISSED HARDWARE
Muon Trigger in LAS I
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Oleg Denisov

45. Muon Trigger in LAS II
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Oleg Denisov

46. Short term DY plans
DY physics with Compass spectrometer – Expression of Interest: possibly June 2007
Compass DY Beam test: July-August 2007
DY physics with Compass spectrometer – possibly first draft of the technical proposal: December 2007
Proposal merging with the proposal on GPDs measurements with Compass: beginning of 2008
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Oleg Denisov

47. Summary I
Compass spectrometer + SPS M2 secondary hadron beams represents a valid facility for DY physics study:
Right kinematicat range
Compass polarised target
Very universal and flexible spectrometer
Two spectrometer schemes has to be examined (2007 beam test is decisive):
Pure DY (+-) set-up with hadron absorber in the first spectrometer
Universal spectrometer scheme, DY (+-), (e+e-), pions, charmed hyperons in the final state
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Oleg Denisov

48. Summary II
Right now we have no any show stopper buu still a lot of work has to be done to prove the feasibility of the project
According to optimistic and very preliminary estimates in a one year of data taking we can expect statistics comparable with classical E615 and NA10 experiments
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Oleg Denisov

49. spares
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50. h1 in Drell-Yan process
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Oleg Denisov

51. Lam-Tung sum rule violation E615
1 -  - 2 = 0
J.S.Conway et al., Phys.Rev. D, 1989, Vol.39, p.92
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Oleg Denisov

52. E615 The approach to angular distribution analysis was taken from
J.S. Conway et al ., Phys. Rev. D39 (1989) 92
NA10 Collab., Z. Phys. C31 (1986) 513
NA10 Collab.,Z. Phys. C37 (1988) 545.
The DY events from PYTHIA are weighted with parameterizations on n versus x1 and qT from
J.S. Conway et al ., Phys. Rev. D39 (1989) 92.
The parameters l and m were taken equal to 1 and 0 respectively
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Oleg Denisov

53. Charged pions asymmetry
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Oleg Denisov

54. J/ region angular distributions
G.E.Hogan et al., Phys.Rev.Lett. 1979, V42, p.948
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Oleg Denisov

55. DY Cross sections taken from PYTHIA
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Oleg Denisov

56. +- Invariant mass 450 GeV
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Oleg Denisov