1. HIGHLIGHTS FROM THE COMPASS EXPERIMENT @ CERN
F. Bradamante
University of Trieste and INFN Trieste
on behalf of the Collaboration
Sixth International Conference on Perspectives in Hadronic Physics
Trieste, May 16, 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, 6th International Confrence on Perspectives in Hadronic Physics

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, 6th International Confrence on Perspectives in Hadronic Physics

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, 6th International Confrence on Perspectives in Hadronic Physics

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, 6th International Confrence on Perspectives in Hadronic Physics

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, 6th International Confrence on Perspectives in Hadronic Physics

7. 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, 6th International Confrence on Perspectives in Hadronic Physics

8. THE COMPASS MUON PROGRAM
TWO CLASSES OF PHENOMENA:
LONGITUDINAL SPIN CASE
TRANSVERSE SPIN CASE
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

9.  SPIN CRISIS LONGITUDINAL SPIN CASE: the beginning
EMC
1988
G1p =   DS = 0.12  0.17
 SPIN CRISIS
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

10. 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, 6th International Confrence on Perspectives in Hadronic Physics

11. LONGITUDINAL SPIN CASE
physics results
ΔG/G
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

12. 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, 6th International Confrence on Perspectives in Hadronic Physics

13. 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, 6th International Confrence on Perspectives in Hadronic Physics

14. ΔG/G
from Open Charm
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

15. D mass spectra D0 → K π D0 → K π π0 nD* = 8675 nD0 = 37398
APS, 13 April 2008
G.K. Mallot 15
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

16. 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 16
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

17. ΔG/G from High-pt hadron pairs
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

18. 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, 6th International Confrence on Perspectives in Hadronic Physics

19. 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, 6th International Confrence on Perspectives in Hadronic Physics

20. 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, 6th International Confrence on Perspectives in Hadronic Physics

21. 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, 6th International Confrence on Perspectives in Hadronic Physics

22. 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, 6th International Confrence on Perspectives in Hadronic Physics

23. Summary of results new high-pT point new charm point G.K. Mallot
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

24. g1d
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

25. g1 of the deuteron ( )
Phys Lett B 612 (2005) 154
most precise measurement for < x < 0.03
new NLO QCD fit, precision of a0 improves factor 2 (Q2 = 4 GeV2)
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

26. 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, 6th International Confrence on Perspectives in Hadronic Physics

27. more on LONGITUDINAL SPIN CASE
MEASUREMENT OF
VALENCE QUARK POLARISATION
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

28. valence quark polarisation
hadron asymmetries
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

29. valence quark polarisation
comparison with other experiments
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

30. The Transverse Spin Case
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

31. Transverse Spin case Large effects observed in hadronic interactions
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

32. 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, 6th International Confrence on Perspectives in Hadronic Physics

33. 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, 6th International Confrence on Perspectives in Hadronic Physics

34. 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, 6th International Confrence on Perspectives in Hadronic Physics

35. 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, 6th International Confrence on Perspectives in Hadronic Physics

36. 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, 6th International Confrence on Perspectives in Hadronic Physics

37. 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, 6th International Confrence on Perspectives in Hadronic Physics

38. HERMES, COMPASS, BELLE
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

39. Sivers asymmetry for pions and kaons
preliminary
data
proton
(DIS07)
CERN-PH-EP/ hep-ex/ (PRL)
data
deuteron
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

40. F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

41. S.J. Brodsky and S. Gardner, PLB643 (2006) 22
Sivers asymmetry
the measured asymmetry on deuteron compatible with zero has been interpreted as
Evidence for the Absence of Gluon Orbital Angular Momentum in the Nucleon
S.J. Brodsky and S. Gardner, PLB643 (2006) 22
refs!
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

42. BIG DISCOVERY POTENTIAL
SUMMARY AND OUTLOOK
a technically challenging new experiment is IN OPERATION SINCE 2002
“LHC” technologies
detectors
read-out
data handling
a privileged situation at CERN
MANY PHYSICS RESULTS have been produced MANY MORE IN THE PIPE-LINE
COMPASS is foreseen to run up to the end of the present mid-term plan of CERN (2010)
BIG DISCOVERY POTENTIAL
with some upgrade COMPASS might be an interesting option even in the second decade of this century
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

43. F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

44. SPARE SLIDES
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

45. Transversity: two hadrons - 1
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

46. Transversity: two hadrons - 2
all +/- combinations
precise measurement of few %
systematics seems well under control
also compatible with zero
interesting to see proton in 2006
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

47. Exclusive ρ0 production
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

48. Exclusive ρ0 production (2002 data) - 1
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

49. Exclusive ρ0 production - 2
ANGULAR DISTRIBUTIONS
0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q²
0.01 < Q² < < Q² < < Q² < < Q² < < Q² < 10 GeV2
preliminary, statistical errors only, limited by MC
corrected for acceptance, smearing and efficiency (MC:DIPSI gen)
background not subtracted
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

50. Exclusive ρ0 production - 3
0.01 < Q² < < Q² < < Q² < < Q² < < Q² < 10 GeV2
measurement of r 04 00
2002
distribution :
Spin density matrix element:
Tλρ λγ are helicity amplitudes
meson photon
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

51. measurement of r and Im r
Exclusive ρ0 production
measurement of r and Im r
< Q² < < Q² < < Q² < < Q² < < Q² < 10 GeV2
0 4
1-1 3
1-1
distribution :
beam polarisation
Spin density matrix element:
if SCHC
holds
weak
violation
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

52. Pentaquark search
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

53. Φ(1860) Pentaquark search - 1
motivated by NA49 report of pentaquark candidate
COMPASS has large sample of the double-strange Ξ– baryon (18000 Ξ–, Ξ+) from data
search for Ξ– π– resonance
Φ(1860)– – → Ξ– π– → Λπ– π– → p π–π–π–
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

54. Φ(1860) Pentaquark search - 2
Ξ(1530)0
Eur Phys J C41 (2005) 469
compare to yields
opposite-sign pairs: Ξ(1530)0 → Ξ– π+ , 1700 and 920 evts
like-sign pairs: evts <79 and <89 at 99% CL
(expected ~400)
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

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57. F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

58. Transversity: Λ polarization
data
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

59. Longitudinal polarization of Λ and antiΛ in DIS
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

60. Λ POLARIZATION (2002 data) - 1- +
’+  V1 V2 q
Event selection
N()
N()
E665
750
650
NOMAD
8087
649
HERMES
10568
1687
COMPASS 2002
7919
5062
COMPASS 2003
34789
20651
The events considered were selected according to those criteria: the primary vertex has to be reconstructed, for this reason I ask for the detection of the incoming and out coming muon, then in the same event must be present a V0 secondary vertex, a marker for the lambda decay. The background to such typology are the combinatorial background, the pair production, the k0 decay, and the lambda bar decay. To reject such background several cuts were applied: the request that the primary vertex must be in the target, the distance between the primary and the secondary vertex must be greater that 400 mm, in order to reject the pair production a transversal momentum for the positive charged particle greater than 20 MeV/c was asked, also a cut on the angle theta here represented was used in order to reject the fake vertex constructed with the scattered muon. To reject this combinatorial back ground a chi square selection was applied, the vertex with best chi2 were taken, another angular cut was applied to be sure that the secondary vertex coming from the primary vertex and it is not generated by secondary interaction. All those cuts where optimized using the MC simulation.
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

61. Λ POLARIZATION
2002 data
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics

62. Λ POLARIZATION
2002 data
F. Bradamante, 6th International Confrence on Perspectives in Hadronic Physics