Transcript Document

RECENT
COMPASS RESULTS
ON
TRANSVERSE PHYSICS
Takahiro Iwata
Yamagata University
on behalf of the COMPASS Collaboration
COMPASS presentations
L-Spin : Celso Franco
Future plans: Norihiro Doshita
Circum-Pan-Pacific Symposium on High Energy Spin Physics, Cairns, Australia, June 20-24 , 2011
OUTLINE
 Introduction to COMPASS
 The experimental setup
 Data taking history
 Transverse spin and TMD effects
 Asymmetries with a polarized proton target
 Azimuthal asymmetries in unpolarized SIDIS
 Summary
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
ＣＯＭＰＡＳＳ ａｔ CERN
Lake LEMAN
Nucleon Structure
LH C
Hadron Spectroscopy
COMPASS
Airport
SPS
(p:450GeV)
CERN
(France)
N
CERN
(Suisse)
21/07/2015
Takahiro Iwata
BEACH08 26 june 2008
3
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
THE SPECTROMETER
two stage spectrometer
• Large Angle Spectrometer (SM1)
• Small Angle Spectrometer (SM2)
tracking, calorimetry, PID
SciFi
Silicon
Micromegas
GEMs
Straws
SDC
MWPC
W45
E/HCAL
Configuration
in Muon program
MuonWall
SM2
E/HCAL
0.003 < x < 0.5
10-3 < Q2 < 10 GeV2
SM1
MuonWall
Polarised Target
RICH
Pol.
 beam
160GeV,
pol. 80%
Takahiro Iwata
• high energy beam
• broad kinematical range
• large angular acceptance
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
THE POLARIZED TARGET SYSTEM
Solid polarized target operated
in Dynamic Nuclear Polarization technique
with a dilution refrigerator
PT magnet:
+180~-180 mrad geometrical acceptance
To match larger acceptance:
3 target cells: reduction of false asymmetries
Upstream
Takahiro Iwata
Middle
Downstream
Target:
NH3 for proton , 6LiD for deuteron
 longitudinal & transverse mode available
very long relaxation time (∼ 4000 h)
magnetic field rotation without polarization loss
 Polarization of NH3 -92%, +88%, -83%
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
THE RICH DETECTOR
5m
photon
detectors
C4F10
• radiator gas: C4F10
• mirror wall: 20 m2 surface
• photon-detectors:
•outer part (75%) MWPC(pad RO) with CsI cathode
• inner part(25%) 576 MAPMTs with indiv. telescope
threshold momenta
● p = 2 GeV/c
p
● p = 9 GeV/c
K
● p =17 GeV/c
P
Takahiro Iwata
Installed in 2005,
Used in data taking from 2006
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
DATA TAKING HISTORY 2002 - 2011
 2002 Data taking started
muon program with 160 GeV polarized muon
• 2002-2006
6LiD
polarized target ( pol. deuterons)
L-mode: 80 / T-mode: 20 , DG/G measurement
2005 no data taking
• 2007 NH3 polarized target (pol. protons)
L-mode: 50 /T-mode: 50
• 2008, 2009 hadron program with hadron beam at 190 GeV
• 2010 NH3 polarized target (pol. protons) only T-mode
• 2011
Takahiro Iwata
ditto
only L-mode
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
Transverse Spin
and
TMD Effects
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TRANSVERSE SPIN &TMD EFFECTS IN COMPASS
DTq(x) = q↑↑(x) - q↑↓(x)
Transversity PDF
quark with spin parallel to the
nucleon spin in a transversely
polarized nucleon
from Collins asym. in SIDIS single hadron production,
two-hadron asym. ,transverse L polarization, …
TMD effects
angular distributions caused by the parton’s transverse momentum
related to orbital angular momentum of quark
from Sivers asym. in SIDIS, azimuthal distribution of
hadrons in unpolarized SIDIS
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
Transverse Spin Effects
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
SINGLE HADRON ASYMMETRIES IN SIDIS
SIDIS cross-section for transv. PT
Collins
Sivers
d SIDID  1 a1  sin fC  a2  sin fS  ....
Collins angle: Azim. angle of a hadron
wrt struck quark spin
FC = fh - fS’ (= fh +fS- p)
Sivers angle:Azim. angle of a hadron
wrt nucleon spin
nucleon spin (initial quark spin)
struck quark spin
FS= fh - fS
Scattering plane
fS = azim. angle of nucleon spin
(initial quark spin)
fS’ = azim. angle of struck quark spin
fS= p- fS’ （due to helicity conservation)
fh = azim. angle of leading hadron
Takahiro Iwata
hadron
quark direction
（Breit frame）
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
COLLINS ASYMMETRY
Collins Asymmetry
Modulation wrt the Collins angle
Nh fC   1  PT  Dnn  y   AColl  sin fC
± : opposite orientation of the transverse spin of the nucleon
PT is the target polarization;
DNN is the transverse spin transfer coefficient initial  struck quark, given by QED
Transvesity
AColl 
Takahiro Iwata
2
0 h
e

Δ
q

Δ
 q q T TDq
2
h
e

q

D
q q
q
Collins
fragmentation
function
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
COLLINS ASYMMETRIES
proton
h+
h−
PLB 692 (2010), 240
deuteron
h+
h−
PLB 673 (2009), 127
・ large asymmetry for proton : about 10% , for both h+ and h-
・ deuteron result  opposite sign of DTu and DTd
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
NEW RESULTS FOR p & K
proton
p+-
large
asymmetry
for p
proton
K+-
Takahiro Iwata
But,
not clear
for K
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
COMPASS-HERMES COMPARISON
in good agreement
proton
p-
p+
COMPASS
HERMES
for charged pions
ΔTq  0,
Takahiro Iwata
Δ0TDpq  0
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TRANSVERSITY GLOBAL FITS
• Fitting to AColld from COMPASS, ACollp from HERMES
and Collins F.F. from BELLE (e+e- scattering)  predictions
• good agreement with the new proton data of COMPASS
・ DTu and DTd have opposite sign as expected from deuteron data
COMPASS proton 2007
Transvesity
u
d
Anselmino et al.
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TWO-HADRON ASYMMETRY
Two hadrons produced in SIDIS
Modulation wrt the angle between two-hadron plane and struck quark spin
Nhh fRS   1  f  PT  Dnn  y   ARS  sin fRS
f : target dilution facto
Two-hadron asymmetry
PT : target polarization
DNN : transverse spin transfer coefficient
initial  struck quark
f
i
fRS
h
l-l’
fS = angle of nucleon spin
(=initial quark 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
Takahiro Iwata
nucleon spin
(=initial quark spin)
quark direction
Trento conventions
see hep-ph/0407345
Breit frame
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TWO-HADRON ASYM. FOR PROTON
transversity
ARS
e D q  x  H  z, M 


 e q  x  D  z, M 
2
i i
h
T
2
i
i
i
i
2
h
i
h
i
2
h
Interference
fragmentation
function
( not well known )
Proton
Ks  p+ + p-
r  p  p-
Clear effect observed
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
COMPASS-HERMES COMPARISON
in good agreement with the HERMES results
Proton
HERMES values scaled with 1/Dnn
Global fit possible when interference fragmentation function measured (BELLE)
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TRANSVERSE L POLARIZATION
Transversity can be studied through transverse L polarization
Transversity
Λ
T,exp
P
= fPTD  y 
2
e
 q ΔTq  x  ΔTDΛ /q  z 
q
2
e
 qq  x  DΛ /q  z 
q
Polarized
fragmentation
function to L
PT : target polarization;
f : target dilution factor
D(y): transverse spin transfer coefficient
initial  struck quark, given by QED
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TRANSVERSE L POLARIZATION
L and L-bar on transversely polarized proton target

L
p
p-
two hadron events with the 2nd. vertex (v0)
e, p, K rejection from p-track candidates by RICH
Armenteros-Podolanski plot
( for V0 , after RICH selection)
After RICH selection
L
K s0
L
Polarization measured
via parity violating decay
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
L POLARIZATION ON PROTON TARGET
The measured polarizations are compatible with zero  small DTDL/q
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TMD Effects
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
SIVERS EFFECT IN SIDIS
Modulation wrt Sivers angle
Nh fS   Nh0 1  A  sin fS 
± refer to the opposite orientation of the transverse spin of the nucleon
Sivers angle: Azim. angle of a hadron wrt the nucleon spin
ASiv
A

 q eq2  DT0 q  Dqh
fPT
Sivers PDF
nucleon spin
struck quark spin
Scattering plane
correlation between
transverse momentum
of the quark and the
transverse polarization
of the nucleon
Takahiro Iwata
FS= fh – fS
hadron
quark direction
（Breit frame）
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
SIVERS ASYMMETRIES
h+
h−
COMPASS proton 2007
Proton
slightly
positive
for h+
PLB 692 (2010), 240
Deuteron
compatible
with zero
PLB 673 (2009), 127
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
SIVERS ASYMMETRIES FOR p & K
Proton
HERMES data
show clear signals
for p+ & K+
p+
p-
Proton
K+
Takahiro Iwata
K-
No definite
conclusion
with the
COMPASS data
due to limited
statistics
More statistics
with 2010
COMPASS data
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
COMPARISON IN DETAIL
COMPASS results
smaller by a factor ~2
COMPASS h+ PLB 692(2010)240-246
COMPASS proton 2007
HERMES
p+
PRL 103(2009)152002
h+
Possible explanation
kinematical regions are different
between COMASS and HERMES
Inv. mass of the hadronic final state
lower energy region probed in HERMES
Takahiro Iwata
possible W dependence ?
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
Asymmeties
for
unpol. target
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
AZIMUTHAL ASYMMETRIES FOR UNPOL. TARGET
TMD effects in SIDIS for unpolarized targets
fh : azumuthal angle of hadron from scatt. plane
cos fh and cos 2f h modulations affected by
Cahn effect
Takahiro Iwata
& Boer-Mulders Effect
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
CAHN EFFECT
kinematical effect by transverse momentum of quark


 
d lpl 'hX   fq x,Q2  d lpl 'q  Dqh z,Q2
q
elementary cross-section:
d lpl ' q  sˆ2  uˆ 2
elementary Mandelstam variables:
$
s = (l + k )2
µ= (k - l ¢)2
u
Taking account of transverse momentum of quark
k: initial quark momentum
kT: initial quark transverse momentum
k’ : final quark momentum
Acosfh
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
BOER-MULDERS EFFECT
Boer-Mulders function

1
h
kT
Correlation between quark transverse momentum
and quark spin in unpolarized nucleon
Contributes to cos fh and cos 2fh moments
with convoluted Collins function
Acos f h , Acos2f h µ h Ä H
^
1
Takahiro Iwata
^
1
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
COSf h MODULATION
COMPASS 2004 6LiD
h+
Preliminary
COMPASS 2004 6LiD
h-
large
negative
signals
over all the
x range
strong
dependence
on z, PTh
different
for h+ & h-
Preliminary
( T- mode samples)
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
COS 2f h MODULATION
COMPASS 2004 6LiD
large
signals
at small-x
h+
Preliminary
COMPASS 2004 6LiD
strong
dependence
on z, x, PTh
different
for h+ & h-
hPreliminary
( T- mode samples)
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
SUMMARY
• COMPASS is a major player in the nucleon spin physics
• Transverse Spin and TMD Effects have been
intensively studied
• Collins and Sivers asymmetries for p and K on
a transversely polarized proton and a deuteron target
• two-hadron asymmetries
• small transverse Λ polarization , compatible with zero
• large azimuthal asymmetries of hadrons produced on
an unpolarized deuteron target
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
BACKUP SLIDES
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
SIVERS ASYMMETRY FOR PROTON
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
SIVERS PDF GLOBAL FIT
Global fit using AdSiv(p±) and AdSiv(K±) from COMPASS and
ApSiv(p±) and ApSiv(K±) from HERMES:
Takahiro Iwata
M. Boglione
in collaboration with
M. Anselmino, U. D’Alesio,
A. Kotzinian, S. Melis,
F. Murgia, A. Prokudin,
Circum-Pan-Pacific Symposium, Cairns, Australia,C.June
20-24 , 2011
Turk
SIVERS ASYM. DATA V.S. PREDICTION
comparison with recent M. Anselmino et al. predictions
arXiv:0805.2677
HERMES proton data
COMPASS deuteron data
marginal agreement with
COMPASS proton data
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TWO-HADRON ASYMMETRY - Deuteron-
Deuteron
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011
TRANSVERSE MOMENTUM DEPENDENT PDFs
Nucleon
long. pol.
unpol.
unpol.
f1 ( q)
number
density
Nucleon
Parton
long. pol.
Quark
trans. pol.
h1
BoerMulders
kT
trans. pol.

1T
Sivers
f
g1L ( Dq)
kT
T-odd
helicity
g1T
kT
h1 ( DT q)transversity
survive after
integration over kT
h1L
kT
h1T
kT
T-odd
Takahiro Iwata
Circum-Pan-Pacific Symposium, Cairns, Australia, June 20-24 , 2011