1. 「COMPASSでの核子スピン構造の研究」 STUDY OF SPIN STRUCTURE OF NUCLEON IN COMPASS
Takahiro Iwata Yamagata University
on behalf of the COMPASS Collaboration
KEK Nucleon Structure 2007, January 12, 2007

2. DG/G from high pT hadron pairs & open charm
OUTLINE
COMPASS apparatus
Data taking history
DG/G from high pT hadron pairs & open charm
g1D, new COMPASS QCD fit, DG evaluation
Transverse spin effects:
single-hadron asymmetries
two-hadron asymmetries
L transverse polarization
Upgrades in 2006
Prospects
Nucleon Structure Function January
Takahiro Iwata

3. COMPASS SETUP two stages spectrometer Large Angle Spectrometer (SM1)
Small Angle Spectrometer (SM2)
tracking, calorimetry, PID
SciFi
Silicon
Micromegas
GEMs
Straws
SDC
MWPC
W45
MuonWall
SM2
E/HCAL
E/HCAL
SM1
Polarised Target
MuonWall
RICH
m beam
high energy beam (160 GeV)
broad kinematical range
large angular acceptance
X(min.)~0.002
Nucleon Structure Function January
Takahiro Iwata

4. solid target operated in frozen spin mode
THE TARGET SYSTEM
superconductive
Solenoid (2.5 T)
3He – 4He Dilution
refrigerator (T~50mK)
Dipole (0.5 T)
two 60 cm long cells
with opposite polarization (systematics)
solid target operated in frozen spin mode
Target material: 6LiD
dN/dz
2000
zvtx (mm)
-1000
1000
4000
THE RICH DETECTOR
5 m
6 m
3 m
C4F10
photon
detectors
threshold momenta
pp = 2 GeV/c
pK = 9 GeV/c
pP =17 GeV/c
Nucleon Structure Function January
Takahiro Iwata

5. 2002 160 GeV m beam & 6LiD Long./Transv. Pol. 2003 ditto (~ 80/20)
DATA TAKING HISTORY
GeV m beam & 6LiD Long./Transv. Pol.
ditto (~ 80/20)
ditto (~ 80/20)
test run with hadron beam
NO SPS beam (Several upgrades)
GeV m beam & 6LiD Long. Pol.
Nucleon Structure Function January
Takahiro Iwata

6. DIRECT MEASUREMENT OF DG/G
Photon Gluon Fusion: gg -> qq
two ways to access DG/G
q = u,d,s “HIGH pT HADRON PAIRS” 2 hadrons with high pT
 Large statistics
 physical background: „model” (MC) dependent,
q = c “OPEN CHARM”
charm production
 less background,
less MC dependent.
 small statistics
Leading order analysis in the moment..
Nucleon Structure Function January
Takahiro Iwata

7. + HIGH PT HADRON PAIRS measure extracted Monte Carlo(LO) SIGNAL
BACKGROUND +
Photon
Gluon
Fusion
Resolved g
Q2 < 1 (GeV/c)2
Leading
Order DIS
QCD compton
Nucleon Structure Function January
Takahiro Iwata

8. HIGH PT HADRON PAIRS : Q2>1 GeV2
pT1, pT2 > 0.7 GeV/c,
ΣpT2 > 2.5 (GeV/c)2
0.1 < y < 0.9
small x : small A1d
 LODIS and QCDC neglected
LEPTO Monte Carlo
low Q2
high Q2
data result:
(prelim.)
systematic error: false asymmetry mainly contributes
Nucleon Structure Function January
Takahiro Iwata

9. HIGH PT HADRON PAIRS : Q2<1 GeV2
Direct
Resolved
photon
PGF
QCDC
neglect
LO DIS
neglect
PYTHIA-Monte Carlo for low Q²
Nucleon Structure Function January
Takahiro Iwata

10. Resolved photon processes
HIGH PT HADRON PAIRS : Q2<1 GeV2
Resolved photon processes
photon PDFs : unknown
point like: perturbative(calculable)
VMD: non-pertarbative
 extream scenarios
M.Gluck et al., Eur.Phys.J. C20:272(2001)
data result:
(prelim.)
Nucleon Structure Function January
Takahiro Iwata

11. DG/G FROM OPEN CHARM Photon Gluon Fusion: gg -> cc c c
hard scale m2 = 4mc2
Theory understood c
Kaon ID with RICH c
Combinatorial background
Limited statistics
Challenging measurement.
Nucleon Structure Function January
Takahiro Iwata

12. DG/G FROM OPEN CHARM BR:68% BR:4% D* tagging with slow pion untagged
D0Kp
D0Kpp0
D0Kp
Nucleon Structure Function January
Takahiro Iwata

13. DG/G = - 0.57 ± 0.41 (stat) ± (syst ≤ stat)
DG/G FROM OPEN CHARM
from Neural Network (parameterization) trained with AROMA Monte Carlo (full kinematics)
f : dilution factor ~0.4
Pb : beam polarization ~0.8
Pt : target polarization ~0.5
S/(S+B): determined from fit
AROMA MC VS. Neural Network
2002 – data D0 + D*
DG/G = ± 0.41 (stat) ± (syst ≤ stat)
@ xg ~ 0.15, m2 ~ 13 GeV2
Nucleon Structure Function January
Takahiro Iwata

14. DIRECT MEASUREMENTS OF DG/G
∫G(x) = 2. 5
GRSV2000
NLO fits to g1
m2 = 3 Gev2
∫G(x) = 0.6
(GRSV stdr)
∫G(x) = 0.2
ΔG/G is small (xg ≈ 0.1)
∫DG>1　unlikely
Consistent also with RHIC ALL (p0 channel) measurements
Nucleon Structure Function January
Takahiro Iwata

15. precise data at low x , 3~4 better than SMC
COMPASS g1D ( )
precise data at low x , 3~4 better than SMC
NEGATIVE TREND NOT OBSERVED
hep-ex/060938, CERN-PH-EP/
Nucleon Structure Function January
Takahiro Iwata

16. QCD FIT OF WORLD DATA WITH COMPASS g1D
Input data
usual cut : Q2>1GeV2
MS-bar renormalization and factorization scheme in NLO
SU(3) flavor symmetry
Nucleon Structure Function January
Takahiro Iwata

17. COMPASS g1D WITH NLO QCD FIT
Two equally possible solutions: DG>0 and DG<0
Previous fits do not show the trend of
the data at low x
Nucleon Structure Function January
Takahiro Iwata

18. RESULTS OF NLO QCD FIT solutions : DG > 0 DG < 0
∫G(x)dx = , ,-0.14
∫S(x)dx = ± ± 0.01
@ Q2=3(GeV)2
Both give for the absolute value of the gluon spin contribution (∫G(x)dx)
Gluon spin contribution is not large
Nucleon Structure Function January
Takahiro Iwata

19. QCD FIT & DIRECT MEASUREMENTS
∫G(x) = 0.3
NLO fit to g1
Q2 = 3 Gev2
∫G(x) = -0.3
COMPASS high PT, Q2<1(GeV)2 data : good agreement with DG>0 ,
but only 1.3s away from DG<0.
Nucleon Structure Function January
Takahiro Iwata

20. DG>0 is in better agreement to the direct measurement.
DG/G SUMMARY
DG/G (xg ≈ 0.1) is small from the direct measurement ( high Pt hadron pairs ,Q2<1GeV2)
Global QCD fit to g1 data gives two solutions.
DG>0 and DG<0
|DG| not large ( )
DG>0 is in better agreement to the direct measurement.
Large DG unlikely
Nucleon Structure Function January
Takahiro Iwata

21. TRANSVERSE SPIN EFFECTS
Transversity PDF
quark with spin parallel to the nucleon spin in a transversely polarized nucleon
DTq(x) = q↑↑(x) - q↑↓(x)
h1q(x),
dq(x),
dTq(x)
from Collins asym. in SIDIS single hadron production
and two hadron asym. , L transverse polarization
TMD PDFs
an intrinsic asymmetry in the parton transverse momentum distribution induced by the nucleon spin
related to orbital angular momentum of quark
Sivers PDF
from Sivers asym. in SIDIS single hadron production
Nucleon Structure Function January
Takahiro Iwata

22. RUN WITH TRANSVERSE POL. TARGET
transversely polarised deuteron target ~ 20% of the running time
2002
11 days of data taking,
2 periods
2003
9 days of data taking,
1 period
2004
14 days of data taking,
Collins and Sivers asymmetries
published results 2002
prel results
with RICH PID
Two hadron asymmetries
Λ polarimetry
prel results
trigger (large x, Q2)
DAQ, on line filter
DIS
events
(106)
Nucleon Structure Function January
Takahiro Iwata

23. SINGLE HADRON ASYMMETRIES
SIDIS cross-section for transv. PT
Collins
Sivers
fS = azim. angle of initial quark spin
fS’ = azim. angle of struck quark spin
fS= p- fS’ （due to helicity conservation)
fh = azim. angle of leading hadron
initial quark spin (nucleon spin)
struck quark spin
Collins angle: Azim. angle of a hadron wrt the struck quark spin
FC = fh - fS’ (= fh +fS- p)
Sivers angle:Azim. angle of a hadron wrt the initial quark spin (=nucleon spin)
FS= fh - fS
Scattering plane
quark direction
hadron
（Breit frame）
Nucleon Structure Function January
Takahiro Iwata

24. COLLINS & SIVERS ASYMMETRIES
Collins Asymmetry
± refer to the opposite orientation of the transverse spin of the nucleon
PT is the target polarisation;
DNN is the transverse spin transfer coefficient initial  struck quark, given by QED
Transvesity
Collins fragmentation
function
Sivers Asymmetry
Sivers PDF
Nucleon Structure Function January
Takahiro Iwata

25. EVENT SELECTION DIS events Q2 > 1 GeV2 W2 > 25 GeV2
0.1 < y < 0.9
hadrons
pht > 0.1 GeV/c
z > (all h)
z > (leading h)
Q2 = 2.4 (GeV/c)2
W = 9.4 GeV/c2
xBj  0.035
2002 data
Nucleon Structure Function January
Takahiro Iwata

26. COLLINS ASYMMETRIES FOR DEUTERON
DIS2006
DIS2006
small errors (~1%)
small asymmetries
CERN-PH-EP/
cancellation between p and n
(lh and ah)
Nucleon Structure Function January
Takahiro Iwata

27. COLLINS ASYMMETRY & GLOBAL FIT
SIDIS(deuteron COMPASS/ proton HERMES) & Belle data
Belle(e+e-  hh’X )
Anselmino et al.,
hep-ph/ v1
PRESENT PICTURE
DT0D(fav.) ~ - DT0D(unfav)
DTd not well constrained from the global fit
RICH + AGS annual Users’ Meeting June 6,
2006, ags/users meetings/workshops/basp , and paper in
preparation.
Nucleon Structure Function January
Takahiro Iwata

28. SIVERS ASYMMETRIES FOR DEUTERON
DIS2006
DIS2006
small errors (~1%)
small asymmetries
CERN-PH-EP/
cancellation between p and n
(lh and ah)
Nucleon Structure Function January
Takahiro Iwata

29. SIVERS ASYMMETRIES & MODELS
model calculations　consistent with HERMES proton DATA
to be compared with the COMPASS data
preliminary COMPASS
preliminary COMPASS
Collins et al
Vogelsang and Yuan
preliminary COMPASS
PRESENT PICTURE
RICH + AGS annual Users’ Meeting June 6,
2006, ags/users meetings/workshops/basp , and paper in
preparation.
Anselmino et al
Nucleon Structure Function January
Takahiro Iwata

30. p±, K± ASYMMETRIES
same DIS event selection and hadron definition as before
plus
PID based on RICH 3%
protons
12%
kaons
77%
pions 5%
no RICH information
100%
hadrons
after all cuts
final sample
positive
all
leading
pions
5.3 M
3.4 M
kaons
0.9 M
0.7 M
negative
all
leading
pions
4.2 M
2.8 M
kaons
0.6 M
0.4 M
Nucleon Structure Function January
Takahiro Iwata

31. p±, K± Collins Asymmetries 2003-2004
again, difficult to see an effect …
Nucleon Structure Function January
Takahiro Iwata

32. p±, K± SIVERS ASYMMETRIES 2003-2004
Nucleon Structure Function January
Takahiro Iwata

33. TWO HADRON ASYMMETRIES
modulation of the number of events in fRS
fS = angle of initial quark spin (=target spin)
fS’ = angle of final (struck) quark spin
fS= p - fS’ （due to helicity conservation)
fR = angle of two-hadron plane
fRS =fR –fS’ = fR +fS- p i f h
l-l’
transversity
: interference fragmentation function( presently unknown)
initial quark spin
quark direction
Trento conventions
see hep-ph/
Breit frame
Nucleon Structure Function January
Takahiro Iwata

34. TWO HADRON ASYMMETRIES
Event selection
z1> 0.1 & z2>0.1　
xf1>0.1 & xf2>0.1
z=z1+z2<0.9
diffractive
r production
6.1x106 combinations
Nucleon Structure Function January
Takahiro Iwata

35. TWO HADRON ASYMMETRIES
DNN : transverse spin transfer
coefficient initial  struck quark
f : target dilution factor
PT : target polarization;
Nucleon Structure Function January
Takahiro Iwata

36. TWO HADRON ASYMMETRIES
z ordered pairs
Nucleon Structure Function January
Takahiro Iwata

37. L TRANSVERSE POLARIZATION
Transversity
PT : target polarization;
f : target dilution factor
D(y): transverse spin transfer
coefficient initial  struck quark,
given by QED
Nucleon Structure Function January
Takahiro Iwata

38. L TRANSVERSE POLARIZATION
systematic errors not larger than statistical errors
RICH ID not used yet
Nucleon Structure Function January
Takahiro Iwata

39. TRANSVERSE SPIN EFFECTS SUMMARY
New deuteron data from COMPASS are available
the measured asymmetries and polarizations are very small, compatible with zero
Collins and Sivers asymmetries
for positive and negative hadrons, p±, K±
Two hadron asymmetries
L transverse polarization
PRESENT PICTURE
Collins: DT0D(fav.) ~ - DT0D(unfav)
DTd not well constrained
Sivers: D0Tu ~ - D0Td
Nucleon Structure Function January
Takahiro Iwata

40. UPGRADES IN 2006 upgrade of polarized target New magnet
Old SMC
Magnet
New magnet
with a large aperture
60 cm
30 cm
hadron acceptance increased
Nucleon Structure Function January
Takahiro Iwata

41. UPGRADES IN 2006 RICH upgrade field lenses ¼ of inner part
concentrator
3 m
6 m
MAPMT
photon
detectors
5 m
¼ of inner part
C4F10
mass spectrum
upgrade of RICH p K
previous system
upgraded RICH
inner part :
576 MAPMTs with indiv. Telescope
HAMAMATSU R7600-M16-03, 16 ch
PID performance raised up
Nucleon Structure Function January
Takahiro Iwata

42. PROSPECTS
2007
Transverse polarization run with pol. proton target
Hadron program with p/p beam + Liq.H2 target
2008/2009
longitudinal(+transverse) polarization run & hadron program
2010-
DVCS measurements with muon beam & Liq.H2 target
Polarized Drell-Yan measurements with p- beam & pol. target
Nucleon Structure Function January
Takahiro Iwata

43. Nucleon Structure Function 2007 @KEK, January 11-12 2007
BACKUP SLIDES
Takahiro Iwata
Nucleon Structure Function January

44. HERMES DG/G from single hadron
P.Liebing
(HERMES)
SPIN2006, Kyoto
RICH + AGS annual Users’ Meeting June 6,
2006, ags/users meetings/workshops/basp , and paper in
preparation.
Takahiro Iwata
Nucleon Structure Function January

45. TRANSVERSE MOMENTUM DEPENDENT PDFs
Nucleon
unpol.
long. pol.
trans. pol.
number
density
Sivers
unpol.
Nucleon
Parton
T-odd
helicity
long. pol.
Quark
transversity
Boer-Mulders
survive after integration over kT
RICH + AGS annual Users’ Meeting June 6,
2006, ags/users meetings/workshops/basp , and paper in
preparation.
trans. pol.
T-odd
Takahiro Iwata
Nucleon Structure Function January

46. SINGLE HADRON ASYMMETRIES
unpol B and T
transvely polarised
target
SIDIS cross-section
long pol B and/or T
h azimuthal angle of the hadron
s’ azimuthal angle of the transverse spin of the struck quark
s azimuthal angle of the transverse
spin of the initial quark
s’ = p - s FS
at leading order
Collins
Sivers
beam polarization
independent angles  independent extraction of
the asymmetries
Nucleon Structure Function January
Takahiro Iwata

47. increase in statistics by a factor of 7!
ASYMMETRIES vs 2002
data released in April 2006 (DIS2006)
comparison with the published 2002 data
PRL 94 (2005)
increase in statistics by a factor of 7!
Nucleon Structure Function January
Takahiro Iwata