1. COMPASS PLANS Stephane Platchkov
Institut de Recherche sur les lois Fondamentales de l’Univers
CEA/IRFU, Saclay, France
(for the COMPASS Collaboration)
EIC workshop
Stony Brook, June 24-27, 2014

2. COMPASS – a fixed target experiment
A very versatile setup
Several beams available: µ+, µ-, h+, h-, e- => Several physics goals
Energy: – 200 GeV
Intensity: up to 109 /spill
Large acceptance, PID detectors
Several particles in the final state
Large (1.2 m) polarized target
50 m
“Minor” changes to the setup – switch between various physics programs
S. Platchkov
EIC 2014

3. COMPASS – a fixed target experiment
A very versatile setup
Several beams available: µ+, µ-, h+, h-, e- => Several physics goals
Measurements with muon beams
Gluon polarization
Spin-flavor decomposition
Transversity
Transv. Mom. Distributions
Measurements with hadron beams
Pion polarizability
Light meson spectroscopy
Baryon spectroscopy
Search for hybrids
COMPASS - I (2002 – 2011)
COMPASS - II (2012, 2015 – 2017/2018)
DVCS and HEMP
Unpolarized SIDIS and TMDs
Drell-Yan studies
Pion and Kaon polarizabilities
S. Platchkov
EIC 2014

4. Nucleon structure studies – physics goals
from Bacchetta
from Bacchetta
PDF (x)
TMD (x,kT)
GPD (x,bT)
Drell-Yan
S. Platchkov
EIC 2014

5. DVCS and HEMP studies
S. Platchkov
EIC 2014

6. DVCS characteristics in COMPASS
Beams
100 – 200 GeV
Beam polarization: ~80%
Both m+ and m- beams
x domain: ≈ – 0.1
Q2 domain: 1 to 10 (GeV/c)2
Luminosity: 1032 cm-2s (with a 2.5 m long LH2 target)
+ EIC
Detect both outgoing photon and recoiling proton
S. Platchkov
EIC 2014

7. DVCS and BH cross section for µ+ and µ-
Cross section for µp -> µpγ :
COMPASS beams: opposite charge/spin
Charge-and-Spin Sum:
Charge-and-Spin Difference
small for COMPASS
DVCS BH
Access both Re(H) and Im(H) by measuring the Sum and the Difference
S. Platchkov
EIC 2014

8. DVCS – SUM of m+ and m- cross sections
Expected statistics in 2 x 140 days of data taking
Goal: transverse size of the nucleon as a function of xB
- Nucleon “tomography” -
S. Platchkov
EIC 2014

9. Beam Charge and Spin Difference
Expected statistics in 2 x 140 days of data taking
Kroll, Moutarde, Sabatié, EPJC 73(2013)2278
S. Platchkov
EIC 2014

10. DVCS – the COMPASS xB regions – SIMULATION
0.005 < xB < < xB < xB > 0.03
DVCS BH
DVCS BH
Large relative amplitude variation as a function of x
EIC 2014
S. Platchkov

11. DVCS – the COMPASS xB regions – REAL DATA
Test run – 4 days with a 40 cm long H2 target
2009 data
278
134 54
DVCS
BH dominance Interference DVCS dominance
Successful feasibility measurement
S. Platchkov
EIC 2014

12. DVCS run – main new equipment
ECAL0
ECAL1
ECAL2
50 m
4.0 m longTime-Of-Flight detector: 24 inner and 24 outer slabs
2x2 m2 electromagnetic calorimeter, ECAL0
2.5 m long LH target
S. Platchkov
EIC 2014

13. 2012 DVCS setup – 4 weeks data taking
ECAL2
Partially ready ECAL0
ECAL1
Full scale recoil proton detector
Liquid H2
target
S. Platchkov
EIC 2014

14. Transverse size of the nucleon
Test data taking in 2012 – 4 weeks
2012 data: expected uncertainty
Data analysis is underway
S. Platchkov
EIC 2014

15. Semi-inclusive unpolarized DIS
Features
Pure hydrogen target, 2.4 m long
High-performance particle identification for p+,p-,p0,K+,K-,K0 etc…
Measurements of:
Multiplicities
Input to global FF analysis
Strange quark pPDF
down to x=0.004
Phys. Rev. D 89 (2014)
1 week of beam
will s(x) continue to raise?
S. Platchkov
EIC 2014

16. Beyond GPD H Hard Exclusive Meson production
Vector mesons: sensitive to H, E
allows for flavour separation
Present studies at COMPASS :
Transversely polarized target
No recoil proton detection (From transversity data: 2007/2010)
First example: exclusive r production
S. Platchkov
EIC 2014

17. Exclusive r0 production
Measurement: μ + p  μ’ + 0 + p
 +-
COMPASS:
PLB 731 (2014) 19
NPB 865 (2012) 1
First possible indication for a non-vanishing HT
Access to different E and H combinations Analysis of w ongoing
S. Platchkov
EIC 2014

18. Distant future (beyond 2018)
DVCS and HEMP on a transversely polarized target
2 years of data, NH3 target, 160 GeV, global efficiency ~10%
Main challenge: development of dedicated superconducting magnet
Planned proposal/addendum
S. Platchkov
EIC 2014

19. Overview of past/planned GPD experiments
S. Platchkov
EIC 2014

20. Drell-Yan studies
S. Platchkov
EIC 2014

21. Polarized Drell-Yan measurements
Drell and Yan, PRL 25 (1970), 316, 902. .
COMPASS setup advantages
Beam energy: 100 – 200 GeV
Hadron (pion) beam
Transversely polarized NH3 target
Large muon angular acceptance
With a negative pion beam: u/u annihilation
COMPASS acceptance (MC simulation)
Dominated by valence quarks (x ≥ 0.1)
COMPASS is an ideal place for DY studies
S. Platchkov
EIC 2014

22. DY (polarized) cross section expansion
Tung-Mow Yan (SLAC, 1998): “The process (1970) has been so well understood that it has become a powerful tool for precision measurements and new physics”
Full formalism for two spin ½ hadrons
COMPASS: access 4 TMDs:
Boer-Mulders, Sivers, Pretzelosity, Transversity
Access 4 TMDs – asymmetry modulations:
Arnold, Metz and Schlegel, Phys. Rev. D79 (2009)
Boer-Mulders
Sivers
Pretzelosity
Transversity
Worm-Gear
All four TMDs are also measured in SIDIS
S. Platchkov
EIC 2014

23. TMDs in Drell-Yan and SIDIS
SIDIS vs TMD
SIDIS: TMD and FF
Drell-Yan: two TMDs
Factorization
TMDs (unlike PDFs) can be process dependent (“non-universality”)
Opposite sign in SIDIS and DY processes:
Collins, Soper, Sterman, Adv. Ser. High En Phys. 5, 1988.
Crucial test of the QCD factorization approach
S. Platchkov
EIC 2014

24. Sivers asymmetry (SIDIS)
Compass data on a proton target
pions
kaons
COMPASS data: PLB 692 (2010) 240
PLB 717 (2012) 383
+ preliminary
Hermes data: PRL 103 (2009)
S. Platchkov
EIC 2014

25. Drell-Yan acceptances (COMPASS vs E615)
0.04
E615
(1989)
0.4
COMPASS
(2014)
An order of magnitude improvement
S. Platchkov
EIC 2014

26. SIDIS vs Drell-Yan (x - Q2) regions
Kinematical overlap between SIDIS and Drell-Yan
S. Platchkov
EIC 2014

27. COMPASS Drell-Yan setup
Upgrade of the spectrometer
Beam telescope (Sci-Fi)
Thick hadron absorber/beam dump
Vertex detector
Polarized target moved 2.2 m upstream
S. Platchkov
EIC 2014

28. COMPASS Drell-Yan setup
Small cross sections – high intensity h beam (~109/spill of 10 sec)
Possible use of thin nuclear targets (inside the absorber)
pion beam 190 GeV
Polarized Target
Hadron absorber: Tungsten, Alumina and Stainless steel
Nominal COMPASS setup (minor modifications)
Dimuon trigger system
S. Platchkov
EIC 2014

29. Drell-Yan – test data taking
Test setup (3 days in 2009)
190 GeV negative pion beam, I ≤ 1.5x107/s (instead of 108/s)
“poor-man” hadron absorber ( concrete and steel)
two polyethylene target cells
preliminary DY trigger
Results
Count rate confirmed
Mass resolution as expected
Good vertex resolution
Low background at high masses
S. Platchkov
EIC 2014

30. Expected statistical accuracy
Assumptions:
Ibeam = 108p/s, L = 2.3x1033, P=90%, f = 0.22, t = 140 days,
spill length = 10 s, every 34 s
~ 2000 DY events/day in the mass region 4 < Mµµ < 9 GeV/c2
J/Ψ cross section: about 50 times larger
Boer-Mulders
Sivers
Pretzelosity
Transversity
S. Platchkov
EIC 2014

31. Polarized Drell-Yan – expected results
Sivers
Boer-Mulders
140 days of data
6.108 pions/spill
2 x 55 cm NH3 target
4 < Mmm< 9 GeV
Pretzelosity
Transversity
S. Platchkov
EIC 2014

32. Further Drell-Yan studies
Dutta et al., PRC83:042201,2011
DY on nuclear targets
flavour-dependent EMC effect
First glimpse from the 2015 data
S. Platchkov
EIC 2014

33. Drell-Yan: further possibilities
Medium term
DY on nuclear targets
Flavour dependent EMC, Violation of the Lam-Tung relation
Polarized deuteron ( 6LiD) target
Flavour separated TMDs
Long term
RF separated K- and p beams
Recall: at 190 GeV: p-/K-/p = 96.5%/2.5%/1%
Aim at 1 to 2 orders of magnitude improvement for K- and p
S. Platchkov
EIC 2014

34. COMPASS OUTLOOK 2014 2015 End 2015, beg. 2016 2016/2017
Preparation for DY run
Refurbished PT magnet, PT installation, hadron absorber
2 months of data taking (October-December)
2015
Drell - Yan data taking (1 “year” ≈ 140 days)
End 2015, beg. 2016
Removal of PT, Installation of LH target, CAMERA, ECAL0
2016/2017
DVCS data taking (2 “years” ≈ 2x140 days)
2018 and beyond Long Shutdown 2
Extensions of DY and DVCS programs (definition underway)
S. Platchkov
EIC 2014

35. The End
S. Platchkov
EIC 2014

36. Exclusive r0 production
Measurement: μ + p  μ’ + 0 + p
 +-
5 single-spin (UT) asymmetries double-spin (LT) asymmetries
Curves: Goloskokov and Kroll, EPJ C74(2014)2725
Data: Compass, PLB, 731(2014)19.
S. Platchkov
EIC 2014

37. Boer-Mulders asymmetry (SIDIS)
Compass data on deuteron (6LiD)
Significantly different from zero
Larger for negative hadrons
Dependence on all three variables: x, z, pT
COMPASS preprint, hep-ex:
also HERMES: PRD 87 (2013)
S. Platchkov
EIC 2014