1. Drell-Yan measurements with COMPASS
Basic ideas, experimental apparatus,
feasibility, expected DY event rates
Drell-Yan workshop Torino 05/03/2007
20/08/2019
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
Spectrometer layout in the DY MC
Covered kinematical range
Preliminary estimates of the DY event rates
Short term plans
Summary
List of questions to be discussed today
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Oleg Denisov

3. DY at COMPASS
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Oleg Denisov

4. 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)
June 2007 – EoI
December 2007 – first version of the proposal
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Oleg Denisov

5. Basic features of the experiment
Intense (2x107 p/sec) hadron beams
Exellent large acceptance polarised target (NH3, 6LiD)
Universal 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

6. 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

7. 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

8. In present M2 line - beam ≈ 108
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
In present M2 hadron beam ≤ 2 106p (due to 108 limit on total beam flux for RP)
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Oleg Denisov

9. 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

10. VERY PRELIMINARY CONCLUSION
H.W.Atherton formula tells us : 0.42 p / int.proton / GeV
Assume target efficiency of 40%
Then for 1013 ppp on target one obtains:
p ppp = 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

11. Compass PT for DY physics
Contact persons: W.Meyer, N.Doshita
NH3
Polarization 90%
Dilution factor 0.18
Polarization 50%
Dilutionfactor 0.48
superconductive
two 30 cm long 3 cm cells
with opposite polarization
6LiD
For transversity: 1 - + + -
simultaneously reversed once a week 2
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Oleg Denisov

12. Compass spectrometer features
Universal 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

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

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

15. Compass comparison to old fashion DY experiments
Spectrometer, DY -detection
Target
Beam dump
Compass
Spectrometer, DY  and e detection, “traditional” hadron beam spin physics
Target
Beam Dump
Magnet
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Oleg Denisov

16. CERN safety regulations
Reference person - Heinz Vincke (CERN)
Two major limitations:
Hadron beam intensity less then 5x107 p/sec
Integrated material bugjet less then 20% of interaction length
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Oleg Denisov

17. CERN safety regulations
There are good chance to extend these limits by:
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

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

19. Compass layout for DY measurements
MW1
SOFT Hadron absorber (DUMP) EC HC PT
Beam
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Oleg Denisov

20. 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 polarised target
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Oleg Denisov

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

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

23. DY MonteCarlo with Compass
- - beam on transversely polarized NH3 target (spin along LAB +y)
- 1.0 GeV/c < PT < 10.0 GeV/c
- -1 < Xf < +1
Generated events per each file with, respectively :
1. S=100 (P- = 53 GeV /c)
a. 1.0 GeV <= M <= 9.0 GeV
b. 1.5 GeV <= M <= 2.5 GeV
c. 4 GeV <= M <= 9 GeV
2. S=200 (P = 106 GeV /c)
a. 0.0 GeV <= M <= 9.0 GeV
c. 4.0 GeV <= M <= 9.0 GeV
3. S=300 (P- = 160 GeV /c)
a. 0.0 GeV <= M <= 9.0GeV
- Processed so far, with ComGeant, events per each generated file

24. Compass DY MW1 and MW2 acceptance
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% % %

25. Compass DY acceptance
106 GeV - beam <= Mm+m- <= 2.5 

26. Compass DY acceptance 106 GeV - beam 4.0 <= Mm+m- <= 9.0
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Oleg Denisov

27. Compass DY acceptance 106 GeV - beam 0 <= Mm+m- <= 9
Acceptance S200

28. Compass DY acceptance
106 GeV - beam <= Mm+m- <= 9.0

29. Very preliminary DY event rates estimate
Target: two cells 30 g/cm2 each : LNH3=30 g/cm2
Traget material: NH3
Density of NH3: NH3 = 0.85 g/cm3
Mass of the NH3 mole: DNH3 = 17
- beam intensity: Ibeam = 2•107 p/sec
Luminosity: L = LNH3 × Ncell × NH3 × NA × 1/DNH3 × Ibeam =
4.×1031 cm-2 sec-1
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Oleg Denisov

30. Very preliminary DY event rates estimate
Compass acceptance: A ≈ 0.5
The muon tracks recontstruction efficiency: Reff =0.9
DY cross section on NH3: NH3 = Ncorr × p , where Ncorr=13 and p taken from table given below (by A.Bianconi)
Dspill = 5 sec (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 × Reff × Dspill × Nspill × ESPS × DRUN
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Oleg Denisov

31. DY Cross sections and statistics
M (+-), GeV
1.-2.5
2.5-4.
4.-9.
S, GeV2
100
5.5 nb
0.35 nb
0.1 nb
200
6. nb
0.5 nb
0.25 nb
300
6.2 nb
0.6 nb
M (+-), GeV
1.-2.5
2.5-4.
4.-9.
S, GeV2
100
120000
24000
200
170000
85000
300
200000
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Oleg Denisov

32. Short term DY plans
DY physics with Compass spectrometer – Expression of Interest: June 2007
Compass DY Beam test: July-August 2007
DY physics with Compass spectrometer – first complete version 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

33. Summary I
Compass spectrometer + SPS M2 secondary hadron beams offers a valid facility for DY physics study:
Right kinematical 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-), hadrons in the final state
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Oleg Denisov

34. Summary II
If we are lucky we can expect statistics comparable with classical E615 and NA10 experiments
Still a lot of work has to be done to prove the feasibility of the project
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Oleg Denisov

35. Proposal for discussion:
DY with longitudinally polarised target (O.Teryaev)
Next-to-leading-order V.Barone, O.Shevchenko
Optimal kinematical range
DY cross sections
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Oleg Denisov