Transcript Q 2 - KEK

CERN NA58
COMPASS実験による核子のスピン構造測定の
最近の結果
“Recent results on Nucleon Spin Structure
at COMPASS”
Tatsuro Matsuda (University of Miyazaki)
On behalf of
山形大理A, 山形大理/Bochum大B, 中部大工C ，宮崎大工D, KEKE, CERNF
岩田高広A ，近藤薫B ，堂下典弘B，堀川直顕C，長谷川武夫D,
松田達郎D,石元茂E，堀川壮介F および
COMPASS国際共同研究グループ
Czech Republic, Finland, France, Germany, India,
Israel, Italy, Japan, Poland, Portugal, Russia
28 Institutes, 12 countries, ~230 physicists
ＫＥＫ研究会『核子の構造関数２００８』,12 Jan. 2008
The COMPASS Experiment at the
CERN-SPS
COmmon Muon and Proton Apparatus for Structure and Spectroscopy
•Nucleon structure
•Hadron structure
•Hadron spectroscopy
•Common spectrometer
•High intensity muon and hadron beams
LHC
COMPASS
NA58
1.Muon program 2002～2007
2.Hadron program 2008～
SPS
COMPASS muon program
Purpose and features
Nucleon spin
Spin sum rule
quark spin contribution
1 1
S z    q  Lq  G  Lg
2 2
0.3
?
Small? 0?
・COMPASS experiment has been studied nucleon spin structure
using 160GeV spin polarized muon beam and polarized target.
(cf. HERMES 27.6 GeV electron (positron)-beam）
COMPASS covers the kinematical region at lower x and high Q2.
・COMPASS has exploited newly developed detectors and new
data acquisition systems and softwares(LHC technologies) to
utilize 5 times stronger beam than SMC experiment, and add the
wide-angle spectrometer to detect scattered hadrons.
・COMPASS can study gluon polarization, valence quark spin
structure, transverse quark spin structure as well as quark spin
structure function.
COMPASS実験のセットアップ
ーCOMPASS spectrometerー
μ
μ’
d
Trigger-hodoscopes
Beam: 160 GeV polarised μ+
2 . 108 µ/spill
(4.8s/16.2s)
ECal & HCal
μ Filter
SM2
Polarization:
•μBeam: ~80%
MWPC
•LiD Target:<50%>
Straws
RICH
SM1
6LiD
Target
Gems
Drift chambers
Micromegas
SciFi Silicon
TWO STAGE
SPECTROMETER:
Polarized beam and target
SAT, LAT, PID
0.003 < x < 0.5
10-3 < Q2 < 10 GeV2
ーCompass 6LiD Polarized targetー
動的偏極法（DNP)
Target dilution factor: ~40%
3He
Maximum Polarization:+57%
– 4He 希釈冷凍機
Longitudinal & transverse pol.
Superconducting
solenoid (2.5 T)
Longitudinal orientation
beam
Two 60 cm long target cells
with opposite polarisation
1m
Longitudinal
Transverse
Transverse orientation
History of DATA TAKING
2002 - 2007

2002 160 GeV m beam & 6LiD Long./Transv. Pol.
 2003 ditto
(Long./Transv.= ~80%/20%)
 2004 ditto
(Long./Transv.= ~80%/20%)
 2004 test run with hadron beam
 2005 NO SPS beam (Several upgrades)
 2006 160 GeV m beam & 6LiD only Long. Pol.
(Long./Transv.= 100%/0%)
 2007 160 GeV m beam & NH3 Long. /Transv. Pol.
(Long./Transv.= ~ 50%/ ~ 50%)
Status of analyses of nucleon spin strucutre at COMPASS
Analyses based on 2002-2004 data are proceeding.
(Please wait for results based on 2006 & 2007)
Longitudinal (Helicity) distribution
G/G
G/G from high pT hadron pairs low Q2 (02-03 data, published in 2006)
(04 data, preliminary)
G/G from high pT hadron pairs high Q2 (02-03 data, preliminary)
open charm (02-04 data, preliminary)
g1D, new COMPASS QCD fit, G evaluation (02-04, published in 2007)
Quark helicity distribution
g1D at low x and low Q2 (02-03 data, published in 2007)
polarised valence quark distribution (02-04 data, submitted in 2007)
Transverse (Transversity) distribution
Quark transversity distribution
single-hadron asymmetries (02-04 data, published in 2007)
two-hadron correlation asymmetries (02-04 data, preliminary)
Kaon and Pion asymmetries (03-04 data, preliminary)
(New) Neutral Kaon asymmetries (02-04 data, preliminary)
G/G
Almost same results as
KEK 2007 meeting
DIRECT MEASUREMENT OF G/G
Photon Gluon Fusion: gg -> qq
two ways to access G/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..
HIGH PT HADRON PAIRS
measure
extracted
PGF G
A||  RPGF  aLL 

G
SIGNAL
ABkg
BACKGROUND Monte Carlo(LO)
+
Photon
Gluon
Fusion
Leading
Order DIS
QCD
compton
Resolved g
Q2 < 1 (GeV/c)2
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
2002-2003 data result:
G / G  0.06  0.31 (stat.)  0.06 (syst.)
@ x g  0.13  0.08
m 2  3 (GeV / c)2
(prelim.)
systematic error: false asymmetry mainly contributes
HIGH PT HADRON PAIRS : Q2<1 GeV2
Resolved photon processes
photon PDFs : unknown
g
g
g
g
g
g
f  fVMD  fpoint like , f  fVMD  fpoint like
f  u , d , s, u , d , s, g
point like: perturbative(calculable)
VMD: non-pertarbative
 extream scenarios
g
g
g
-fVMD
 fVMD
 fVMD
M.Gluck et al., Eur.Phys.J. C20:272(2001)
2002-2004 data result:
G
 0.016  0.058stat.  0.014exp.syst.  0.052 MC.syst.  0.013photon.
G
@ xG  0.085 00..07
035
m2  3(GeV / c )2
(prelim.)
G/G from Open charm
Photon Gluon Fusion: gg -> cc
hard scale m2 = 4mc2
Theory understood
c
D0  K  
Kaon ID with RICH
c
Combinatorial background
Limited statistics
Challenging measurement.
G/G FROM OPEN CHARM
D0  K  π
D*  D0  πs  K  π  π
BR:68%
D* tagging with slow pion
BR:4%
untagged
D0K
D0K0
D0K
G/G FROM OPEN CHARM
G
1

G
aLL fPb PT S
A
SB
aLL ( zD , pTD, y)
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
D0 + D*
G/G = - 0.57 ± 0.41 (stat) ± (syst ≤0.17
stat)
 2002 – 2004 data
preliminary @ xg ~ 0.15, m2 ~ 13 GeV2
(2007)
COMPASS g1D (2002-2004)
Indirect measument of G
precise data at low x , 3~4 better than SMC
NEGATIVE
TREND NOT
OBSERVED
PLB 647 (2007) 8-17
COMPASS g1D WITH NLO QCD FIT
Indirect measument of G
Two equally possible solutions: G>0
solutions :
G > 0
 ∫G(x)dx = +0.26 +0.04,-0.06
Previous fits do not
show the trend of
the data at low x
 ∫(x)dx =
+0.28 ± 0.01
and G<0
G < 0
-0.31 +0.10,-0.14
+0.32 ± 0.01
@ Q2=3(GeV)2
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 G>0 ,
but only 1.3s away from G<0.
G/G SUMMARY
 G/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.
 G>0 and G<0
 |G| not large (0.2-0.3)
 G>0 is in better agreement to the direct
measurement.
 Large G unlikely
Valence quark distribution
Polarised valence quark distribution
from Semi-Inclusive DIS
Inclusive measurement
μ
μ’ measured
特定せず
生成されたハドロンを特定しない
－＞すべてのクォーク分布を
測定する
d
μ
d
生成されたleadingハドロンの
電荷が正か、負かを特定すること
でもとのstruck quarkのを区別する
特定する －＞バレンスクォーク分布を
導き出して測定する
Semi-Inclusive measurement
μ’
Event selection
• Kinematical cut condition
Q2>1GeV2
0.1<y<0.9
0.2<zh<0.85
• DIS事象を選ぶ
• Current fragmentation regionから
のハドロンを捕まえる
• バックグラウンド事象の混入を少
なくする
• 入射ビーム飛跡は両方のターゲ
ットセルを通る
• 生成ハドロンはvertex pointから来
る
• ハドロンの電荷以外は同定しない
中性子もあります！
h+
h-
Deuteron標的のA , A の測定
μ
d
Plus charge
μ’
hadrons
Miuus charge
断面積と
非対称度
パートン分布
との関係
パートン分布を引き出す際に、Fragmentation functionの情報が必要
Deuteron標的の
+-hh
“difference asymmetry”A
の測定
但し
N:測定数
a:アクセプタンス
パートン分布を引き出す際に、Fragmentation functionは不要
（但しLO QCDレベル）
uv+dvを掛けてやれば、Δuv+Δdvが分かる
偏極バレンスクォーク分布を
求める
•
•
•
•
非偏極パートン分布を使う
Q2=10 GeV2への発展
重陽子のD-stateの補正
Seaクォーク成分の少ない
high x領域では、inclusive
dataから借用する
Q2=10 GeV2への発展
LO DNS : D. de Florian, G.A. Navarro, . Sassot, Phys. Rev. D71(2005)094018.
バレンスクォーク分布の核子スピンへの寄与
Discussion 簡単な方程式
a0  u  u  d  d  s  s
また、
a8  u  u  d  d  2(s  s )
a0  0.35  0.05
Inclusive dataより
a8  0.59  0.03
Hyperon decay等より
1
s  s  (a0  a8 )  0.09  0.01  0.02
3
1
u  d  (s  s )  a8  (uv  d v )より
2
1
u  d  0.09  0.59  (uv  d v )
2
uv  d v を決めれば u  d が決まる
SU(3) Sea
symmetry
u  d  0.09 
今回の結果からは u
1
0.59  (uv  d v )
2
Present data
 d  0.0  0.04 となる。(u  d )
これまでしばしば仮定してきたSU(3) symmetric seaとは2σのずれ
u  d  s  s
まとめ
本日の報告はAeXiv:0707.4077v1
・準包含反応を用いて、核子（重陽子）のスピン依
存バレンスクォーク分布を求めた。
・バレンスクォークの核子スピンへの寄与として、
Σv＝0.41±0.07±0.05 at Q2=10 GeV2 を得た。
• この結果を用いると u   d が導かれる。
今後
•2006年データを用いて統計精度を上げることが可能
•K中間子を選択して、 s  s の測定も進行中。
•2007年は偏極陽子標的を用いて測定中で、これを
•用いて u と d の分離も可能。
Transverse distribution
What is Transversity？
・Nucleon structure functions
are described with 3 functions
at twist 2 and they are complete
at twist level 2.
・q(x) is different from
Tq(x) generally because
rotation does not commute with
Lorentz boost in relativity.
(q(x)＝Tq(x) in non-relativity)
longitudinal
transverse
・q(x) is a chiral even fuction, Tq(x) is a chiral odd function.
・Tq(x) does not couple with gluon structure function , then it evolves with Q2
unlike q(x).
（Soffer inquality）
（Tensor charge）
（Transverse? Spin SR）
How do we measure transversity?
•Quark helicity is conserved in totally
Inclusive Deep Inelastic Scattering（IDIS) ,
so Inclusive DIS does not access to transversity,
because transversity needs quark helicty flip
in helicity base.
•In case of Semi-Inclusive Deep Inelastic(SIDIS)
it is possible to access transversity, because SIDIS allows both flip
and non-flip cases.
Then we measure SIDIS events to study transversity.
•If we choose phenomena with chiral odd fragmentation functions,
we can access chiral odd quark distribution functions.
•We measure SIDIS including transversity in
(1) Collins asymmetry and Sivers asymmetry
(2) SSA in two hadron correlation.
TRANSVERSE SPIN EFFECTS
Transversity PDF
quark with spin parallel to the
nucleon spin in a transversely
polarized nucleon
Tq(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
SINGLE HADRON ASYMMETRIES
SIDIS cross-section for transv. PT
Collins
Sivers
dσSIDIS  1  a1  sinFC  a2  sinFS  ...
fS = azim. angle of initial quark spin
fS’ = azim. angle of struck quark spin
fS= - 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- )
Scattering plane
•Sivers angle:Azim. angle of a
hadron wrt the initial quark spin
(=nucleon spin)
FS= fh - fS
hadron
quark direction
（Breit frame）
COLLINS & SIVERS ASYMMETRIES
Collins Asymmetry
N h  FC   N h0   1  PT  DNN  y   AColl  sinF C 
± 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
A Coll 
Sivers Asymmetry
2
0 h
e

Δ
q

Δ
q q T TDq
2
h
e

q

D
q q
q
Collins
fragmentation
function
Nh  FS   Nh0   1  PT  ASiv  sinFS 
Sivers PDF
A Siv 
2
T
h
e

Δ
q

D
q q 0 q
2
h
e

q

D
q q
q
COLLINS ASYMMETRIES FOR DEUTERON
2002-2004
data
Leading hadrons
z>0.25
Kinematical
condition
Q2 > 1 GeV2
W2 > 25 GeV2
0.1 < y < 0.9
All hadrons
z>0.2
• small errors (~1%)
• small asymmetries
• cancellation between p and n
pht > 0.1 GeV/c
NP B765 (2007) 31-70

0

0

AColl,
d  Δ Tu  Δ T d 4 TDu   TDd 

0

0

AColl,
d  Δ Tu  Δ T d  TDu  4 TDd 
SIVERS ASYMMETRIES FOR DEUTERON
2002-2004
data
Leading hadrons
z>0.25
All hadrons
z>0.2
• small errors (~1%)
• small asymmetries
• cancellation between p and n
NP B765 (2007) 31-70
ASiv, d  Δ 0Tu  Δ 0Td D
Partile identified Collins & Sivers asymmetrie
±, K± ASYMMETRIES
2003-2004
same DIS event selection and hadron definition as before
plus
PID based on RICH
hadrons
no RICH information
after all cuts
new
all
leading
pions
5.3 M
3.4 M
kaons
0.9 M
0.7 M
all
leading
0.26 M
0.18 M
neutral
kaons
5%
pions
77%
kaons
12%
protons
final sample positive
100%
negative
3%
all
leading
pions
4.2 M
2.8 M
kaons
0.6 M
0.4 M
±, K± Collins Asymmetries
All hadrons
again, difficult to see an effect …
2003-2004
±, K± SIVERS ASYMMETRIES 2003-2004
All hadrons
K0 Collins & Sivers Asymmetries
Leading hadrons
All hadrons
2002-2004
TRANSVERSE SPIN EFFECTS SUMMARY
New deuteron data from COMPASS are available
Collins and Sivers asymmetries
for positive and negative hadrons, ±, K±
neutral K0 (Ks)
the measured asymmetries and polarizations are very small,
compatible with zero
PRESENT PICTURE
Collins: T0D(fav.) ~ - T0D(unfav)
Td not well constrained
Sivers: 0Tu ~ - 0Td
PROSPECTS
• 2008/2009
– hadron program
– longitudinal(+transverse) polarization run ?
• 2010– DVCS measurements with muon beam & Liq.H2 target
– Polarized Drell-Yan measurements with  beam & pol.
Target
COMPASS paper list is found at the following web site.
Please hava a look at
http://wwwcompass.cern.ch/compass/publications/papers/