1. HIGHLIGHTS FROM THE COMPASS EXPERIMENT @ CERN
F. Bradamante
University of Trieste and INFN Trieste
on behalf of the Collaboration
WE Heraeus Seminar on Polarized Antiprotons
Bad Honneff, June 23-25, 2008

2. COmmon Muon and Proton Apparatus for Structure and Spectroscopy NA58
Czech Republic, Finland, France, Germany, India, Israel, Italy, Japan, Poland, Portugal, Russia
Bielefeld, Bochum, Bonn, Burdwan, Calcutta, CERN,
Dubna, Erlangen, Freiburg, Heidelberg, Helsinki, Lisbon,
Mainz, Miyazaky, Moscow, Munich, Nagoya, Prague, Protvino,
Saclay, Tel Aviv, Torino, Trieste, Warsaw
28 Institutes, ~230 physicists
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

3. a new spectrometer with outstanding performances
COMPASS
experiment:
thought of in
April ’94
Nov. ‘94
Trento workshop
Trieste workshop @ICTP
LoI
encouraged
March ’95
June ‘95
SPSLC in Cogne
Proposal
recommended
approved by RB
March ’96
Sept. ’96
Feb. ‘97
as NA58
Technical run
2000
Commissioning
2001
since 2002 taking data with
a new spectrometer with outstanding performances
merging of two programmes:
HMC
(muon beam)
CHEOPS
(hadron beam)
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

4. Physics program of COMPASS
Experiments with muon beam
ΔG/G g1
Transverse spin effects
Flavor decomposition of spin distribution functions
Vector meson production
Spin transfer in Λ-hyperon production
Experiments with hadron beams
Pion and Kaon polarizabilities
Diffractive production of exotic states
Search for glueballs
Light meson spectroscopy
Production of double charmed baryons
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

5. LHC SPS luminosity: ~5 . 1032 cm-2 s-1
beam intensity: m+/spill (4.8s/16.2s)
beam momentum: GeV/c
longitudinally polarised muon beam
longitudinally or transversely polarised target
calorimetry
particle identification
LHC
SPS N
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

6. The Spectrometer for the Muon Programme
Trigger-hodoscopes
μ Filter
ECal & HCal
50 m
SM1
SM2
RICH
MWPC
Straws
6LiD Target
Gems
TWO STAGE
SPECTROMETER:
160 GeV μ
Drift chambers
Polarized beam and target
Micromegas
SAT,
LAT,
PID
Silicon
SciFi
0.003 < x < 0.5
10-3 < Q2 < 10 GeV2
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

7. the target system solid state target operated in frozen spin mode
: 6LiD (polarised deuteron)
dilution factor f = 0.38
polarization PT = 50%
two 60 cm long cells
with opposite polarisation (systematics)
2006:
PTM replaced with the large acceptance COMPASS magnet (180 mrad)
2 target cells  3 target cells
2007: NH3 (polarised protons)
dilution factor f = polarization PT = 90%
during data taking with transverse polarisation,
polarisation reversal in the cells after ~ 4-5 days
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

8. WHERE ARE WE ? physics results DG/G 1. pion polarizability
in 2002, 2003, 2004, 2006 and 2007 COMPASS has taken data in the muon program configuration
160 GeV, polarized m beam LiD polarized target (~polarized deuterons)
NH3 polarized target (~polarized protons)
2000 TB ~ 5·1010 events
pilot run in 2004 for hadron program
2008: hadron beam at 190 GeV for diffractive and central production
physics results
DG/G pion polarizability
DS PWA in diffractive
Transversity scattering
Cahn asymmetry
Pentaquark
Exclusive ρ0
Λ physics
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

9. THE COMPASS MUON PROGRAM
TWO CLASSES OF PHENOMENA:
LONGITUDINAL SPIN CASE
TRANSVERSE SPIN CASE
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

10.  SPIN CRISIS LONGITUDINAL SPIN CASE: the beginning
EMC
1988
G1p =   DS = 0.12  0.17
 SPIN CRISIS
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

11. LONGITUDINAL SPIN CASE
from polarised lepton – polarised nucleon DIS
with
and
first moments:
from measurement of EMC in 1988 and using complementary
information from neutron and hyperon β–decay one obtained
at variance with naïve expectation
since
necessity for measuring
SMC, SLAC, HERMES
and in SIDIS
SMC, HERMES, COMPASS
in SIDIS
HERMES, COMPASS
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

12. A1d from COMPASS Inclusive DIS asymmetry Q2>1 (GeV/c)2
PLB 647(2007)8
good agreement with previous experiments
significantly improved statistics at low x !
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

13. COMPASS QCD fit using these results plus the same asymmetries
on p and n from the
other experiments
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

14. LONGITUDINAL SPIN CASE
direct measurement of
ΔG/G:
main objective of the
longitudinal run
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

15. MEASUREMENTS OF THE GLUON POLARIZATION
FOUR LINES OF ATTACK:
Double spin asymmetry of the OPEN CHARM cross-section in high energy µD scattering
Double spin asymmetry of the HIGH-pt HADRON PAIRS in high energy µD DIS (Q2 > 1 GeV2)
Double spin asymmetry of the high-pt hadron pairs in high energy µD scattering (Q2 < 1 GeV2)
Measurement of g1 of the deuteron and QCD fit of all the world data
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

16. DG/G at COMPASS Photon Gluon Fusion N
q = c cross section difference in charmed meson production
→ theory well understood
→ experiment challenging
q = u,d,s cross section difference in 2+1 jet production in COMPASS: events with 2 hadrons with high-pt
→ experiment easy
→ theory more difficult
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

17. ΔG/G
from Open Charm
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

18. D mass spectra D0 → K π D0 → K π π0 nD* = 8675 nD0 = 37398
APS, 13 April 2008
G.K. Mallot 18
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

19. ΔG/G = -0.49 ± 0.27 (stat) ± 0.11 (syst)
DG/G from open charm
2002 – data D0 + D*
ΔG/G = ± 0.27 (stat) ± 0.11 (syst)
@ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2
preliminary 19
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

20. ΔG/G from High-pt hadron pairs
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

21. ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2
PGF and background
PGF
QCD-
Compton
LO DIS
Anreicherung von PGF mit high pt Schnitten
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

22. ΔG/G from High-pt hadrons, Q2 > 1 (GeV/c)2
2002 – 2004 data: High pT, Q2 > 1 GeV/c2
ΔG/G = 0.08 ± 0.10 (stat) ± 0.05(syst)
@ <xg> = (range: – 0.123), m2 ~ 3 (GeV/c)2
Anreicherung von PGF mit high pt Schnitten
preliminary
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

23. ΔG/G from High-pt hadrons
PGF
low Q2
all Q2
LO DIS
resolved photon
QCD-
Compton
Anreicherung von PGF mit high pt Schnitten
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

24. ΔG/G from High-pt hadrons, Q2 < 1 (GeV/c)2
2002 – 2004 data: High pT, Q2 < 1 GeV/c2
ΔG/G = ± (stat) ± (syst)
@ <xg> = 0.085, m2 = 3 GeV2
Anreicherung von PGF mit high pt Schnitten
preliminary
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

25. Gluon Polarization COMPASS preliminary results
high-pT pairs, Q2>1GeV2 :
2002–2004
ΔG/G = 0.08 ± 0.10 (stat) ± 0.05(syst)
@ <xg> = (range: – 0.123), m2 ~ 3 (GeV/c)2
high-pt pairs, Q2< 1GeV2 :
2002–2004
ΔG/G = ± (stat) ± (syst)
@ <xg> = 0.085, m2 = 3 GeV2
open charm:
2002–2006
ΔG/G = ± 0.27 (stat) ± 0.11 (syst)
@ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

26. Summary of results new high-pT point new charm point G.K. Mallot
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

27. CONCLUSION from ΔG MEASUREMENTS:
ΔG SMALL
more precise measurements will come soon
COMPASS 2006
RHIC RUN6 ….
interest in
orbital angular momentum
GPD’s
because helicity of quark must flip
Ji’s SUM RULE
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

28. The Transverse Spin Case
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

29. Transverse Spin case Large effects observed in hadronic interactions
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

30. Transverse Spin case Large effects observed in hadronic interactions
at leading order a third PDF is necessary for a complete description of the structure of the nucleon
Theoretical developments:
q(x) Dq(x) DTq(x)
DTq(x) being chiral-odd, it can be measured only in conjunction
with another chiral-odd partner:
Collins function DY
SIDIS
measurable in
e+e- hadrons
relevance of transverse momentum dependent (TMD) PDF and FF
Sivers function
Many Workshops in recent years on Transverse Momentum, spin, and position distributions of partons in hadrons
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

31. Collins and Sivers angles
Transversity – single hadron - 1
Collins and Sivers angles
C = h - S’
 S = h - S
S ’ azimuthal angle of spin vector of fragmenting quark (S’’ = p - S)
h azimuthal angle of hadron momentum
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

32. Transversity – single hadron - 2
first measurements of transverse spin asymmetries in DIS of high energy
muons on a transversely polarized deuteron target
published single hadron asymmetries from runs
Collins: related to transverse quark distributions
Sivers: related to intrinsic kT
Phys Rev Lett 94 (2005)
Nucl Phys B765 (2007) 31
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

33. Collins asymmetry for pions and kaons
preliminary
data
proton
(virtual photon asymm)
(lepton beam  DIS07)
final CERN-PH-EP/ hep-ex/ (PRL)
data
deuteron
(virtual photon asymm)
COMPASS
sign convention
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

34. Independent Measurement of the Collins FF
measurable in e+e– annihilation
first attempts to measured it from the correlation between the azimuthal angles of p‘s from e+e– annihilation using LEP data
last years: great news from BELLE
the Collins FF is being measured in
e+e– annihilation, and it is different from zero!
measurement of the correlation between the azimuthal angles of p‘s in the near jet and in the far jet from e+e– annihilation
547 fb-1 charm corrected data sample,
UL and UC double ratios
spin2004
ref?
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

35. Collins asymmetries: SUMMARY
The facts:
HERMES has measured on a proton target non-zero Collins asymmetries for π+ and π-
COMPASS has measured on a deuteron target Collins asymmetries compatible with zero
BELLE has produced the first results on Collins FF
Conclusion:
Collins mechanism is a real phenomenon
universality of Collins FF
transversity can be measured in SIDIS
Present picture
Collins: DTu ~ - DTd DT0D(fav.) ~ - DT0D(unfav)
To extract TMD DF and FF GLOBAL ANALISYS are necessary
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

36. HERMES, COMPASS, BELLE
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

37. Sivers asymmetry for pions and kaons
preliminary
data
proton
(DIS07)
CERN-PH-EP/ hep-ex/ (PRL)
data
deuteron
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

38. F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

39. conclusions from COMPASS deuteron data
the unpolarised azimuthal asymmetries are different from zero and different for positive and negative hadrons
all the transverse spin asymmetries have been measured to be compatible with zero
HERMES, COMPASS, BELLE data:
consistent picture
first fits, extractions of the new DFs, and predictions for other experiments
still, a lot of expectation for the higher energy COMPASS proton data
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

40. 2007 Transverse data statistics
2007 run: May to November equally shared between transverse and longitudinal Transverse polarization data taking:
Period
“Weeks”
Target Polarization 1
25 / 26 / 2
27 / 28 3
30 / 31
+ - + / 4
39 / 40 5
41 / 42a 6
42b / 43
Period
“Weeks”
Target Polarization 1
25 / 26 / 2
27 / 28 3
30 / 31
+ - + / 4
39 / 40 5
41 / 42a 6
42b / 43
Data used for these results
several stability tests have been performed
detectors and triggers performances
event reconstruction
K0 reconstruction
distributions of kinematical variables:
( zvtx, Em’, fm’, xBj Q2,y, W, Ehad, fhadLab , qhadLab , fhadGNS , qhadGNS , pt)
~20% of the total collected data has been used for this analysis
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

41. Collins asymmetry – proton data
integrated over x and z
statistical errors only; systematic errors ~ 0.3 sstat
at small x, the asymmetries are compatible with zero
in the valence region the asymmetries are different from zero,
of opposite sign for positive and negative hadrons, and have the same strength and sign as HERMES
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

42. Collins asymmetry – proton data
comparison with M. Anselmino et al. predictions
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

43. Sivers asymmetry – proton data
integrated over x and z
statistical errors only; systematic errors ~ 0.5 sstat
the measured symmetries are small, compatible with zero
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

44. Sivers asymmetry– proton data
comparison with the most recent predictions from M. Anselmino et al.
arXiv:
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

45. Results: Sivers asymmetry
comparison with predictions from
S.Arnold, A.V.Efremov, K.Goeke, M.Schlegel and P.Schweitzer, arXiv:
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons

46. conclusions COMPASS preliminary results on
unpolarised hadron asymmetries on deuteron for positive and negative hadrons
Collins and Sivers asymmetries on protons
Collins asymmetry different from zero the effect is there at COMPASS energies
Sivers asymmetry: smaller, compatible with zero to be understood
near future: analysis of the whole 2007 proton data sample
longer term: transverse spin physics is one of the items being spelled out for the future COMPASS program
the study of transverse spin effects needs further precise measurements and the COMPASS facility is the only place where SIDIS can be measured at high energy
F. Bradamante, WE Heraeus Seminar on Polarized Antiprotons