1. THE COMPASS EXPERIMENT @ CERN achievements and outlook
F. Bradamante
Trieste University and INFN
to Roger Hess

2. a new spectrometer with outstanding performances
COMPASS
experiment:
thought of in
April ’94
Nov. ‘94
Trento workshop
Trieste workshop
LoI
encouraged
March ’95
June ‘95
SPSLC in Cogne
Proposal
recommended
approved by RB
March ’96
Sept. ’96
Feb. ‘97
as NA58
commissioning
June
merging of two programmes:
HMC
(muon beam)
CHEOPS
(hadron beam)
will take data on the years and onwards
with
a new spectrometer with outstanding performances
from F.B. invited SPIN 2000, Osaka
University of Geneva, March 10, 2010
F. Bradamante

3. COMPASS physics case how is a nucleon made up ?
acknowledgement that it is still worthwhile to invest in
trying to answer some questions which have been with us
since 30 years
how is a nucleon made up ?
! spin structure !
are there non qqq or qq hadrons ?
! exotics !
fundamental problems of QCD
role of the axial anomaly to the spin of the proton
glueballs non abelian nature of QCD
from F.B. invited SPIN 2000, Osaka
University of Geneva, March 10, 2010
F. Bradamante

4. University of Geneva, March 10, 2010
F. Bradamante

5. from F.B. invited talk @ SPIN 2000, Osaka
University of Geneva, March 10, 2010
F. Bradamante

6. The COMPASS Collaboration
COmmon Muon and
Proton Apparatus for
Structure and Spectroscopy
Czechia, France, Germany, India, Israel, Italy, Japan,
Poland, Portugal, Russia, Switzerland
Bielefeld, Bochum, Bonn, Calcutta, CERN, Dubna, Erlangen, Freiburg, Lisbon, Mainz, Moscow, Munich, Prague, Protvino, Saclay, Tel Aviv, Torino, Trieste, Warsaw, Yamagata
29 Institutes, about 250 physicists
University of Geneva, March 10, 2010
F. Bradamante

7. COMPASS at CERN LHC SPS p up to 400 GeV
secondary hadrons (p, K, ...): 2·107/s
tertiary m (polarized): 4·107/s
University of Geneva, March 10, 2010
F. Bradamante 7

8. The COMPASS Experiment
SM1
SM2
Beam
MuonWall
E/HCAL
RICH
Target
Two-stage spectrometer
large angular acceptance
broad kinematical range
~ channels
> 800 TB/year
50 m
Dipole magnets
Tracking detectors
RICH
El.-mag. calorimeter
Hadronic calorimeter
Muon identification
[hep-ex/ , NIM A 577, 455 (2007)]
University of Geneva, March 10, 2010
F. Bradamante

9. The COMPASS Experiment
SM1
SM2
Beam
MuonWall
E/HCAL
RICH
Target
Two-stage spectrometer
large angular acceptance
broad kinematical range
~ channels
> 800 TB/year
50 m
Data taking periods:
: 160 GeV/c m+
2004: 2 weeks 190 GeV/c p-
: 160 GeV/c m+
: 190 GeV/c p, p-
[hep-ex/ , NIM A 577, 455 (2007)]
University of Geneva, March 10, 2010
F. Bradamante

10. Hadron Spectroscopy at COMPASS
Diffraction from pions
3 p
5 p hp
Central production from pions KK hh
4 p
Diffraction from protons
Baryon spectroscopy
Central production from protons
Meson spectroscopy
Primakoff
p- Polarizability, -anomaly, p0 lifetime, radiative width
from S. HADRON 2009, Tallahassee
University of Geneva, March 10, 2010
F. Bradamante

11. = + + + + ... Meson Spectroscopy Quark model: bound state of
Quantum numbers: IG (JPC)
P=(-1)l+1, C=(-1)l+s, G=(-1)I+l+s =
QCD: other color-neutral configurations
with same quantum numbers  mixing + + +
decoupling only possible for
narrow states
vanishing leading qq term
 exotic JPC:
Hybrids
Glueballs
+ ...
Dynamics
University of Geneva, March 10, 2010
F. Bradamante

12. Glueballs  COMPASS Lightest glueballs: Quenched L-QCD prediction
Experimental candidate:
f0(1500) (Crystal Barrel, WA102)
JPC = 0++  mixing with isoscalar
mesons!
Events / 0.08 GeV
M(hh) (GeV)
WA102, Phys. Lett. B479, 59 (2000)
 COMPASS
[Y. Chen et al., Phys. Rev. D 73, (2006)]
University of Geneva, March 10, 2010
F. Bradamante

13. Hybrids  COMPASS Light meson sector exotics JPC=1-+:
p1(1400) (VES, E852, Crystal Barrel)
p1 (1600) (E852, VES)
p1 (2000)
still controversial...
[A.R. Dzierba et al., PRD 73, (2006)]
20 waves
35 waves
[S.U. Chung et al., PRD 65, (2002)]
M(3p) (GeV/c2)
Events / 0.04 GeV/c2
 COMPASS
University of Geneva, March 10, 2010
F. Bradamante

14. Hadron Reactions at COMPASS
Two production mechanisms
studied in parallel using proton, pion and kaon projectiles
Central production
Rapidity gap between pslow, hfast, X
Beam particle looses ~10% of its energy
Particles at large angles from X decays
Possible source of glueballs (DPE)
Diffractive dissociation
Forward kinematics
Need to separate particles at very small angles
Study of JPC-exotic mesons
University of Geneva, March 10, 2010
F. Bradamante

15. Diffractive Reactions at COMPASS 2004
Example:
4p vertex in Pb target
Exclusivity  target stays intact
Momentum transfer pa pc
Diffraction on Pb nuclei
Diffraction on nucleons
University of Geneva, March 10, 2010
F. Bradamante

16. Invariant Mass of 3p system 2004
COMPASS: pp =190 GeV/c
4M events in 3 days (full t range)
450k events in 0.1<t’<1.0 GeV2/c2
BNL852: pp= 18 GeV/c
250k events  p1(1600)
University of Geneva, March 10, 2010
F. Bradamante

17. p1 (1600) BW parameters for p1(1600) Leakage negligible p2(1670)
arXiv:
p2(1670)
University of Geneva, March 10, 2010
F. Bradamante

18. p1 (1600) BW parameters for p1(1600) Leakage negligible a1(1260)
University of Geneva, March 10, 2010
F. Bradamante

19. COMPASS in 2008
University of Geneva, March 10, 2010
F. Bradamante

20. COMPASS in 2008 b
University of Geneva, March 10, 2010
F. Bradamante

21. COMPASS in 2008
University of Geneva, March 10, 2010
F. Bradamante

22. p-p+p- in 2008  Very Preliminary 190 GeV/c hadron beam
Target: 40cm liquid hydrogen p-p  p-p+p- p
Diffractive dissociation: 96% p-, 3.5% K-, 0.5% p
p-p  p1(1600) p, p1(1600)  3p: events exp.
>200 times statistics of 2004 data
PWA has started
First result: compare production on proton and lead 
Very Preliminary
Dalitz plot around p2(1670)
University of Geneva, March 10, 2010
F. Bradamante

23. 3p final state p-p  p-p0p0p
Isospin partner to p-p  p-p+p-p
Consistency check
University of Geneva, March 10, 2010
F. Bradamante

24. 3p final state p-p  p-p0p0p
Isospin partner to p-p  p-p+p-p
Consistency check
Different isobars in decay chain
University of Geneva, March 10, 2010
F. Bradamante

25. 3p final state p-p  p-p0p0p
Isospin partner to p-p  p-p+p-p
Consistency check
Different isobars in decay chain
Isospin information
Use a2 : normalization
Example: a1
a2 rp
a1 rp
University of Geneva, March 10, 2010
F. Bradamante

26. Strangeness in final states pp  pKKp
Search for hidden strangeness
Neutral and charged kaon channels
High mass isobars observed cleanly
Glueball search decaying into KK
Hybrids decaying into KKp
Information on nature of states
branching fraction
decay chain
PWA being prepared
K+K-p vs K+p-
K+K-p vs K+K-
University of Geneva, March 10, 2010
F. Bradamante

27. CONCLUSIONS COMPASS has started spectroscopy program tools developed
more refined PWA analysis underway
larger wave set, Deck effect, parallelization
VERY high statistics (partly > 200 times previous work)
University of Geneva, March 10, 2010
F. Bradamante

28. COMPASS muon programme
THE QCD STRUCTURE of the nucleon
LONGITUDINAL
TRANSVERSE
University of Geneva, March 10, 2010
F. Bradamante

29. Deep Inelastic Scattering
key role in the study of the partonic structure of the nucleon
Q2 >> M2
W2=(P+q)2 >> M2
valence quarks
sea quarks
gluons
Inclusive DIS: only the incident and scattered leptons are measured
Semi-Inclusive DIS: the incident and scattered leptons, and at least one final state hadron are measured
Exclusive DIS: the incident and scattered leptons, and all the final state hadron are measured
NB: COMPLEMENTARY RHIC
(will not mention)
University of Geneva, March 10, 2010
F. Bradamante

30. Structure Functions and PDF: q(x)
University of Geneva, March 10, 2010
F. Bradamante

31. measured at CERN, HERA, SLAC
Structure Functions and PDF: q(x)
Inclusive DIS: unpolarised
measured at CERN, HERA, SLAC
F2(x) = 2x·F1(x) Callan-Gross
in the parton model
 q(x) from global analysis of DIS and hard scattering data (QCD fits)
University of Geneva, March 10, 2010
F. Bradamante

32. Parton Distribution Functions
three distribution functions
are necessary to describe the structure of the nucleon at LO:
q(x) : number density or unpolarised distribution
probability of finding a quark with a fraction x of the longitudinal momentum of the parent nucleon
Dq(x) = q- q: longitudinal polarization or helicity distribution
in a longitudinally polarised nucleon, probability of finding a quark with a momentum fraction x and spin parallel to that of the parent nucleon
DTq(x) = q- q: transverse polarization or transversity distribution
in a transversely polarised nucleon, probability of finding a quark with a momentum fraction x and spin parallel to that of the parent nucleon
q quark or antiquark with a specific flavor [notation: Barone, Drago, Raftcliffe 2001]
ALL OF EQUAL IMPORTANCE !
University of Geneva, March 10, 2010
F. Bradamante

33. HELICITY vs TRANSVERSITY
HELICITY and TRANSVERSITY
are different
have different properties
are measured in different ways
thus one has to deal differently the situations
when the target spins are
LONGITUDINAL
and
TRANSVERSE
University of Geneva, March 10, 2010
F. Bradamante

34. Helicity PDFs Dq’s can be extracted from a
cross-section asimmetry Δσ for
parallel
and
antiparallel
lepton and nucleon spins
University of Geneva, March 10, 2010
F. Bradamante

35. Structure Functions and Helicity PDFs
Inclusive DIS: beam and target longitudinally polarized
beam/target helicity
g1 measured at
SLAC, EMC, SMC, HERMES, COMPASS
g2 suppressed by a factor g2  0.01
at 100 GeV (SMC, SLAC)
University of Geneva, March 10, 2010
F. Bradamante

36. Structure Functions and Helicity PDFs
Inclusive DIS: beam and target longitudinally polarized
beam/target helicity
Asymmetry Analysis Collaboration, M. Hirai, S. Kumano and N. Saito, PRD (2004)
g1 measured at
SLAC, EMC, SMC, HERMES, COMPASS
g2 suppressed by a factor g2  0.01
at 100 GeV (SMC, SLAC)
in the parton model
University of Geneva, March 10, 2010
F. Bradamante

37.  SPIN CRISIS The Quark Contribution to the Nucleon Spin
in polarised DIS one measures
using complementary information from the WEAK DECAY CONSTANTS of the BARYONS
one can get Du, Dd, Ds and then DS
EMC 1988
G1p =   DS = 0.12  0.17
 SPIN CRISIS
University of Geneva, March 10, 2010
F. Bradamante

38. The Constituent Quark Model
magnetic moments:
assuming u and d Dirac particles with
spin:
University of Geneva, March 10, 2010
F. Bradamante

39. DS: latest results  = 0.330 ± 0.025 ± 0.011 ± 0.028 (from 1d)
(exp) (theory) (evol.)
HERMES
 = 0.30 ± 0.01 ± (from NLO QCD fit)
COMPASS
(stat) (evol.)
LATEST RESULTS:
University of Geneva, March 10, 2010
F. Bradamante

40. THE SPIN PUZZLE: WAYS OUT
spin sum-rule
contribution from GLUON SPIN
in inclusive DIS Dq and DG mix up in g1 (DGLAP equations)
NECESSITY OF A DIRECT MEASUREMENT OF DG
→ SIDIS experiments (HERMES and COMPASS)
contribution from ORBITAL ANGULAR MOMENTUM of quarks and gluons
University of Geneva, March 10, 2010
F. Bradamante

41. THE PLAYERS
DESY pure H and D target 28 GeV CERN high energy m-beam 160 GeV JLAB Experiments very high luminosity 6 GeV
University of Geneva, March 10, 2010
F. Bradamante

42. COMPASS
University of Geneva, March 10, 2010
F. Bradamante

43. Measurements of DG/G in polarized DIS
direct: cross-section asymmetry for charm
production COMPASS cross-section asymmetry for high pT
hadron pairs
HERMES, COMPASS
cross-section asymmetry for high pT
hadron
HERMES
indirect: scale violation of g1(x,Q2) (QCD fit) SMC, SLAC Experiments, HERMES, COMPASS
University of Geneva, March 10, 2010
F. Bradamante

44. Direct Measurements of DG/G
Photon Gluon Fusion N
q = c cross section difference in charmed meson production
→ theory well understood
→ experiment challenging
COMPASS
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
COMPASS & HERMES
University of Geneva, March 10, 2010
F. Bradamante

45. QCD fit + direct measurements
conclusion:
ΔG SMALL and unlikely to account for the missing spin
note: NLO fits, LO data
same conclusion from RHIC experiments
University of Geneva, March 10, 2010
F. Bradamante

46. TRANSVERSITY DISTRIBUTION
RECENT DEVELOPMENTS
TRANSVERSITY DISTRIBUTION
DTq(x)
University of Geneva, March 10, 2010
F. Bradamante

47. TRANSVERSITY since 10 years a very active field, rapidly growing
theory
experiments HERMES, RHIC, COMPASS, JLAB
Fruitful collaboration between
Experimentalists and Theorists
University of Geneva, March 10, 2010
F. Bradamante

48. Puzzles in hadronic reactions I
in hadronic reactions like
with a transversely polarized proton,
the spin asymmetry
in leading twist perturbative QCD
Kane, Pumplin and Repko (1978)
THE DATA STRONGLY CONTRADICT THIS!
University of Geneva, March 10, 2010
F. Bradamante

49. Hope to find solutions at the quark level (DTq(x) …)
Puzzles in hadronic reactions II
Since many years intriguing evidence of large transverse spin
effects at high energy
hyperon polarization
high pt effects in hadronic interactions
asymmetries in hadron production
STAR
Hope to find solutions at the quark level (DTq(x) …)
University of Geneva, March 10, 2010
F. Bradamante

50. HOW to MEASURE DTq(x)
DTq(x) is chiral-odd  cannot be measured in inclusive DIS
it can be measured in SIDIS: the observable is the convolution of DTq(x) with another chiral-odd quantity, the “Collins” function, which describes a possible left-right asimmetry of the hadrons in the hadronization process of a transversely polarized quark
the observable is the so-called “Collins asymmetry”, an azimuthal modulation in the cross-section of the type sinFC
FC = fh + fS fh azimuthal angle of the hadron, fS azimuhtal angle of the spin of the nucleon
because helicity of quark must flip
University of Geneva, March 10, 2010
F. Bradamante 50

51. The conjecture was right !!
PROTON TARGET
DEUTERON TARGET
plus BELLE data on e+e-  hadrons
University of Geneva, March 10, 2010
F. Bradamante

52. University of Geneva, March 10, 2010 F. Bradamante
Anselmino et al., PRD75 (2007)
University of Geneva, March 10, 2010
F. Bradamante

53. HOPE TO GET INFORMATION ON Lq FROM THE SIVERS ASYMMETRY
RECENT DEVELOPMENTS
when taking into account the intrinsic transverse momentum of the quarks several azimuthal modulations are possible
sin 2fh
sin (fh + fS)
sin (fh - fS)
sin (3fh - fS) …
 Transversity PDF x Collins FF
 Sivers PDF
the amplitudes are convolutions of different Transverse Momentum Dependent (TMD) PDFs e FFs:
all these amplitudes can be extracted from the SIDIS data
HOPE TO GET INFORMATION ON Lq FROM THE SIVERS ASYMMETRY
University of Geneva, March 10, 2010
F. Bradamante

54. AN ELECTRON-NUCLEON COLLIDER
CONCLUSIONS
The relative size of DG and L not clearly assessed
TRANSVERSE SPIN PHENOMENA:
NEW Properties of matter have been unveiled
Collins effect Sivers effect
OTHER correlations are still possible (Boer-Mulders)
More precise measurements are needed to compare with calculations (pQCD and Lattice)
COMPASS two years of run: T (2010), L JLab RHIC GSI
and in the long run
AN ELECTRON-NUCLEON COLLIDER
University of Geneva, March 10, 2010
F. Bradamante

55. TRANSVERSITY and TMDs TODAY
Transversity, Network7 Integrated Infrastructure Initiative in Hadronic Physics (I3HP) project, funded by the European Community FP6 ( )
TMD-Net, WorkPackage3 Hadron Physics 2 project FP7 ( )
PRIN2003, 2006, 2008 MIUR, Italy Transversity 2005 (Como), 2008 (Ferrara), 2011 (Trieste)
dedicated workshops at ECT* (~1 each year)
Beijing (2008)
Yerevan (2009) ....
a dedicated session at the International Spin Symposium in 2006, 2008, 2010
University of Geneva, March 10, 2010
F. Bradamante

56. … and COMPASS proposal in preparation GPDs, polarised DY, Primakov
to know more:
University of Geneva, March 10, 2010
F. Bradamante

57. SPARE SLIDES
University of Geneva, March 10, 2010
F. Bradamante

58. g1 and F1 in Quark Parton Model
s = 1
s = - 1/2
definitions:
University of Geneva, March 10, 2010
F. Bradamante

59. Measurement of g1 in inclusive DIS
0.15
~0.2
target ~0.8
beam ~0.8
D, h kinematical quantities
A1 and A2 are the asymmetries in g*p (n) scattering
University of Geneva, March 10, 2010
F. Bradamante

60. recently much interest !
TRANSVERSITY
DTq(x), h1q(x), dq(x), dTq(x) , q=uv, dv, qsea
recently much interest !
properties:
DTq(x)  Dq(x)
probes the relativistic nature of quark dynamics
no contribution from the gluons  simple Q2 evolution
positivity (Soffer) bound
first moments: tensor charge
sum rule for transverse spin in Parton Model framework
it is related to GPD’s
is chiral-odd: decouples from inclusive DIS
because helicity of quark must flip
Bakker, Leader, Trueman, PRD 70 (04)
University of Geneva, March 10, 2010
F. Bradamante 60

61. Transversity and TMD PDFs
Three parton distributions describing quark’s transverse momentum and/or transverse spin
1) Transversity
2) Sivers function
3) Boer-Mulders function
University of Geneva, March 10, 2010
F. Bradamante

62. PWA Technique high s: t-channel Reggeon exchange
reflectivity basis in G-J frame
e = h of Regge trajectory
isobar model
1. Mass-independent PWA of angular distributions in 40 MeV mass bins
Tire production amplitudes - determined by fit
42 partial waves i = JPCMe[...]L
[...] = isobar: (pp)S, f0(980), r(770), f2(1270), r3(1690)
University of Geneva, March 10, 2010
F. Bradamante 62

63. PWA Technique high s: t-channel Reggeon exchange
reflectivity basis in G-J frame
e = h of Regge trajectory
isobar model
1. Mass-independent PWA of angular distributions in 40 MeV mass bins
2. Mass-dependent c2 fit to results of step 1
6 waves
parameterized by BW ( incl. barrier factors and G (m) )
coherent background for some waves
University of Geneva, March 10, 2010
F. Bradamante 63