STUDY OF SPIN STRUCTURE OF NUCLEON AT COMPASS AND ITS CHALLENGES

STUDY STUDY OF OF

SPIN STRUCTURE OF NUCLEON SPIN STRUCTURE OF NUCLEON AT COMPASSAT COMPASS

ANDANDITS CHALLENGESITS CHALLENGES

Takahiro IwataYamagata University

KEK Workshop on Nucleon Structure, January 10, 2009

on behalf of the COMPASS Collaboration

COMPASS apparatus Data taking history Direct measurements of G/G

high pT hadron pairs & open charm

q from SI-DIS Transverse spin effects

asymmetries with proton target Plans and Challenges

OUTLINE

Takahiro Iwata KEK Workshop on Nucleon Structure 2009, January 10, 2009


SM1

SM2

Pol. beam

MuonWall

MuonWall

E/HCAL

E/HCAL

RICH

Polarised Target

SciFiSiliconMicromegasGEMs

StrawsSDCMWPCW45

THE SPECTROMETERtwo stages spectrometer • Large Angle Spectrometer (SM1)• Small Angle Spectrometer (SM2)

tracking, calorimetry, PID

• high energy beam• broad kinematical range• large angular acceptance

0.003 < x < 0.510-3 < Q2 < 10 GeV2

THE TARGET SYSTEM

Solid polarized target operated in Dynamic Nuclear Polarization technique with a dilution refrigerator

New COMPASS target magnet:+180~-180 mrad geometrical acceptance The world largest polarized targetTo match larger acceptance:new microwave cavity3 target cells: reduction of false asymmetries

Target: NH3 for proton , 6LiD for deuteron

longitudinal & transverse mode availablevery long relaxation time ( 4000 h)∼magnetic field rotation without polarization loss Polarization of NH3 -92%, +88%, -83%

THE RICH DETECTOR

5 m

6 m3 m

CC44FF1010

photon detectors

threshold momenta● p= 2 GeV/c● p

K = 9 GeV/c

● pP =17 GeV/c


• 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

Installed in 2005,Used in data taking from 2006

DATA TAKING HISTORY 2002 - 2008

in 2002, 2003, 2004, 2006 and 2007

COMPASS has taken data in muon program configuration

160 GeV, polarized muon

• 2002-2006 6LiD polarized target ( ~pol. deuterons)

L-mode: 80 / T-mode: 20

2005 no data taking, new target system installed

• 2007 NH3 polarized target (~ pol. protons)

L-mode: 50 /T-mode: 50

• 2008: hadron beam at 190 GeV for the hadron program



Direct Measurements Direct Measurements of of

Gluon Polarization Gluon Polarization G/GG/G

DIRECT MEASUREMENTS OF G/G

Leading order analysis in the moment..

access to G/G

Photon Gluon Fusion: g -> qq

q = u,d,s “HIGH pT HADRON PAIRS”2 hadrons with high pT

Large statistics physical background: „model” (MC) dependent

・ hard scale given by pT

q = c “OPEN CHARM”charm hadrons ( one hadron detected)

no background, less MC dependent.

small statistics

　　・　 hard scale charm mass: 2 = 4mc2



// PGF BkgPGFGA R a A

G

+PhotonGluonFusion

LeadingOrderDIS

QCD Compton

Resolved Q2 < 1 GeV2

measure

HIGH PT HADRON PAIRSextracted

Data divided into two data sets• High Q2 : Q2>1GeV2

• Low Q2 : Q2<1GeV2

PGF

totPGFR

LO

totLOR

C

totCR

PGFaLOa Ca

cross-section ratio

analyzing power

Monte Carlo


HIGH PT HADRON PAIRS : Q2>1 GeV2

/ 0 08 0 10 0 05G G . . (stat.) . (syst.)

2002-2004 data result:

2 2g @ x 0.082 ( : 0.055 0.123) 3 ( / ) range GeV c (prelim.)

systematic error: false asymmetry mainly contributes

• Q2>1GeV2, 0.1 < y < 0.9• pT1, pT2 > 0.7 GeV, XF1,2>0, z1,2>0, z1+z2<0.95• M2

h1,h2>1.5GeV2

• Monte Carlo• LEPTO with MRST2004LO & JETSET

fragmentation• R & a for PGF, QCDC and LO determiend• Neural Network parametrization• Good agreement with the data

New result

averaged values

Reduced by 1/3from 2002-2003

New

method

In previous analysisAbkg neglected , because A1,d~0 at small x


HIGH PT HADRON PAIRS : Q2<1 GeV2

PYTHIA-Monte Carlo for low Q²

PGF

QCDC

LO DIS

Direct Resolvedphoton

neglect

neglect


HIGH PT HADRON PAIRS : Q2<1 GeV2

point like: perturbative(calculable) VMD: non-pertarbative extream scenarios

photon PDFs : unknownResolved photon processes

,

, , , , , ,

f f f f f f

f u d s u d s g

VMD VMDpoint like point like

VMD VMD VMDf f f - M.Gluck et al., Eur.Phys.J. C20:272(2001)

/ 0 016 0 058 0 055G G . . (stat.) . (syst.) 07.0035.0085.0

Gx @ 22 )c/GeV(3 (prelim.)

2002-2004 data result:

PL B 633 (2006) 25COMPASS 2002-03 data published

Stat. error reduced by 30% compared to


πKD0 * 0D D

Kslow

untaggedD* tagged by slow pion

G/G FROM OPEN CHARM

BR:4%BR:68%

nD0 = 37398 nD* = 8675

D0K

D0K0

D0K

0K DM M GeV 0K D

M M GeV


2002 – 2006 (full deuteron statistics) D0+D*

G/G = - 0.49 ± 0.27 (stat) ± 0.11(syst) @ xg ~ 0.11, m2 ~ 13 GeV2

G/G FROM OPEN CHARM

b T

1A

fP P LL

GSG a S B

• Neural network trained with AROMA Monte Carlo

• good description of data

• f : dilution factor ~0.4• Pb : beam polarization ~0.8• Pt : target polarization ~0.5• S/(S+B): determined from fit• Calculation with event weighting

False asymmetry

& S/S+B determination

New result

Kinematics not fully given in the experiment (only one charm detected)

need efficient way to determine aLL


QCD Fit to g1

COMPASS062 = 3 Gev2

RESULTS FOR G/G

ΔG/G ≈0 @ xg ≈ 0.1

new high-pT pointhigh Q2

new open charm

∫DG=+0.26

∫DG=-0.31

RECALL: charm point at larger scale (2 = 13 Gev2 )

HERMESSinglehadron

G/G SUMMARY & PROSPECTS

New preliminary results have been obtained G/G ≈0 at xg ≈ 0.1 likely

Prospects:

open charm:

including 2007 proton data, but not much improvement

high-Pt hadron pairs:

include data from 2006, 2007

use single high-Pt hadron, determine G/G in 2-3 bins of xg



Polarized PDF, Polarized PDF, qq

fromfromSemi-Inclusive Semi-Inclusive

DISDIS

q from SI-DIS


Inclusiveasymmetry

flavor dependent fragmentation functions

flavor & valence/sea decomposition for q

Semi-inclusivehadron identified asymmetries

2 2 2q 1q2

1 2 2 2q 1q

e Δq x,Q g x,QA x,Q =

e q x,Q F x,Q

2 2 2qqh 2

1 2 2 2qq

e Δq x,Q z,QA x, z, Q

e q x,Q z,Q

hq

hq

D

D

2z,QhqD

COMPASS 2002-2006 data on deuteron (full statistics on deuteron)

Evaluation of , , v vΔu +Δd Δu+Δd Δs Δs

+ - + -π π K K1,d 1,d 1,d 1,d 1,dA , A , A , A , A

at LO QCD


deuteron data 2002-2006 ( full statistics on deuteron)

ASYMMETRIES

Q2>1GeV2, 0.004<x<0.3, 10<p<50GeV, 0.2<z<0.85

Statistics: + 623 10 - 621 10 + 64.8 10 K - 63.3 10 K

Impurities corrected; although the correction is very small

New data

at small x


• Asymmetries to be independent on Q2 :• Assume• Un-polarized PDF: MRST04• Fragmentation Functions: two parameterizations

• DSS-FF • from e+e-, SI-DIS , pp collision

• EMC-FF• charge/isospin symmetry • all un-favored FFs are equal• Assume • No Q2 dependence• s-quark favored FF is large

• Least square fit in each x bin

+ +K πus

D =D

BASES OF EVALUATION

Δs=Δs h

1,dA x, z

+ -

+ -

K Ks s

SF

u u

D DR = 3.4

D D

K K

SFR 6.6

main differencein favored FF of strange quark

:

:

Ku

K

s

u uDK

s sD

:

:

K

u

Ks

D u uK

s sD


Similar results with different FFs;agreement with LO DNS-PDF

RESULTS OF FIT

Compatible with 0;Not sensitive to FFs

EMC-FF gives larger stat. errors

DNS-PDF: global fit to e+e-, SIDIS & pp Phys.Rev.D71:094018,2005(comparable to typical QCD fits to g1)

0.3

0.0040.035 sdx DNS-PDF:

0.3

0.004

0.01 0.01 0.01(DSS-FF)

0.05 0.03 0.01(EMC-FF)

sdx

valence

sea

strange

1 0.3

0.3 0.0040.002 s dx sdx

small contribution from large x


agreement between two evaluations

s FROM CHARGED KAON ASYMMETRY

well constrained

by K+ and K- cross-

section data

+ -K +K1,d 1,d 1,d

Δs Q/s+α=A + A -A

s α-0.8

DNS-FF

+

+

Kd

UF Ku

D z dzR = 0.14

D z dz

Q=u+u+d+d

+

+

K

sSF K

u

D z dzR =

D z dz

UF SF

UF

2R 2R=

3R 2

UF

SF

R =0.14

R =6.6

=3.4

6.6 EMC-FF

DNS-FF

=2.1 KRE-FF

not constrained !

Alternative way to access s


• 1st moment strongly depends on RSF

• With a large RSFs<0 expected in unmeasured lower x region

• Comparison between SI-DIS and inclusive DIS is limited by the errors

s V.S. RSF

from SI-DIS0.3

0.004 sdx

UFR =0.14

1

0 sdx from inclusive DIS

COMPASS,QCD-fits to g1

Phys.Lett. B 660 (2008) 458

1 0.3

0.3 0.0040.002 s dx sdx

only 2 difference


q FROM SI-DIS SUMMARY

SI-DIS asymmetries from full deuteron data shown

Evaluation of valence, sea, strange polarized PDFs

Valence component is consistent with inclusive DIS data

Sea polarization is 0 over the measured range

Strange component strongly depends on s-quark FF (RSF )

Comparison between SI-DIS and incl. DIS is limited by errors

Prospects:

analysis of 2007 proton data

extraction of RUF and RSF form COMPASS


Transverse Spin EffectsTransverse Spin Effects

TRANSVERSE SPIN EFFECTS IN COMPASS

Tq(x) = q↑↑(x) - q↑↓(x)

h1q(x),

q(x), Tq(x)

Transversity PDF quark with spin parallel to the nucleon spin in a transversely polarized nucleon

from Collins asym. in SIDIS single hadron production transverse polarization, two hadron asym. , ,,,

related to orbital angular momentum of quark

TMD PDF an intrinsic asymmetry in the parton transverse momentum distribution induced by the nucleon spin

from Sivers asym. in SIDIS single hadron production


New COMPASS data for Collins & Sivers Asymmetries on Proton

SINGLE HADRON ASYMMETRIES

S = azim. angle of initial quark spin

S’ = azim. angle of struck quark spin

S= - S’ （ due to helicity conservation)

h = azim. angle of leading hadron initial quark spin (nucleon spin)struck quark spin

hadron （ Breit frame ）quark direction

•Collins angle: Azim. angle of a hadron wrt the struck quark spin

C = h - S’ (= h +S- )

•Sivers angle:Azim. angle of a

hadron wrt the initial quark spin

(=nucleon spin)

S= h - S

Scattering plane

SIDIS cross-section for transv. PT

1 ... C SSIDIS 1 2dσ a sin a sin

Collins Sivers


COLLINS & SIVERS ASYMMETRIES

Collins Asymmetry

± refer to the opposite orientation of the transverse spin of the nucleonPT is the target polarisation; DNN is the transverse spin transfer coefficient initial struck quark, given by QED

y 0

h C h T NN Coll CN N 1 P D A sin

2 0 hq T T qq

Coll 2 hq qq

e Δ q Δ DA

e q D

0h S h T Siv SN N 1 P A sin

2 T hq 0 qq

Siv 2 hq qq

e Δ q DA

e q D

Sivers Asymmetry

Transvesity

Sivers PDF

Collins fragmentation

function


PROTON DATA EVENT SELECTION


DIS cuts:

• Q2>1 (GeV/c)2, 0.1<y<0.9, W>5 GeV/c2

Cut for hadrons

Track Length<10 X0

Energy Deposit in HCALs

pT>0.1 GeV/c

Z>0.2

Statistics h+ : 5.7M h-: 4.5M

Proton data in 2007, ~20% analyzed

COLLINS ASYMMETRY ON PROTON


at small x, the asymmetries are compatible with zero in the valence region the asymmetries are different from zero,opposite sign for positive and negative hadrons, and the same strength and sign as HERMES

systematic errors ~ 0.3 stat

20% statistics


COLLINS ASYM. DATA V.S. PREDICTIONcomparison with M. Anselmino et al. predictions

arXiv:0805.2677

good agreement

SIVERS ASYMMETRY FOR PROTON


the measured asymmetries are small, compatible with zero

systematic errors ~ 0.5 stat


SIVERS ASYM. DATA V.S. PREDICTION

comparison with recent M. Anselmino et al. predictionsarXiv:0805.2677

marginal agreement with COMPASS proton data

HERMES proton data

COMPASS deuteron data

TRANSVERSEPOLARIZATION

2q

qT 2

q Λ /qq

T Λ /ΛT,ex

T

p

qΔ q xe

= fP D ye q x D

D

P

Δ z

z

PT : target polarization;

f : target dilution factor D(y): transverse spin transfer coefficient initial struck quark, given by QED

Transversity


2002-2004 deuteron data (no RICH ID) already reported Small tendency seen for anti-Λ

Another way to access Transversity

NEW DATA ON PROTON TARGET

p


• Secondary vertex downstream of primary vertex.• PT > 23 MeV/c to exclude e+e− pairs• Proton and pion momenta > 1 GeV/c• Q2 > 1 (GeV/c)2, 0.1 < y < 0.9• Λ decay distance DΛ > 7 σD

• Collinearity < 10 mrad

0sK

0sK

• Pid by RICH• 60% higher statistics

w.r.t. deuteron data

POLARIZATION ON PROTON TARGET


• Systematic errors have been estimated to be smaller than statistical errors from false polarization.

• No dependence on x.

TRANSVERSE SPIN EFFECTS SUMMARY

New preliminary results of 2007 proton transverse run:

• Collins Asymmetry:• different from zero• Agreement with predictions of Anselmino et al.

(consistent with HERMES, Belle)• Sivers Asymmetry:

• Small and compatible with zero within present statistical errors

• Marginal agreement with the prediction • Transverse polarization:

• small and compatible with zero within present statistics



Plans and Challenges Plans and Challenges in in

COMPASSCOMPASS

PLANS & CHALLENGES IN COMPASS

2009 Run for Hadron program 190 GeV hadron beam & Liq.H2 target (partly test with the muon beam)2010~ Run for Muon program(with pol. proton target)?

Challenges• Polarized Drell-Yan program

• 200 GeV - Beam & Polarized Target• TMD PDFs(Boer-Mulders, Sivers) • Transversity

• GPD program• 100GeV polarized Beam & Liq.H2 Target(+ Pol.T)

• DVCS(Deeply Virtual Compton Scattering)• HEMP(Hard Exclusive Meson Production)



BACKUP SLIDES

EVENT SELECTION

DIS events

Q2 > 1 GeV2

W2 > 25 GeV2

0.1 < y < 0.9

hadrons

pht > 0.1 GeV/c

z > 0.2 (all h)

z > 0.25 (leading h)

Q2 = 2.4 (GeV/c)2

xBj 0.035

W = 9.4 GeV/c2

2002 dataTakahiro Iwata KEK Workshop on Nucleon Structure 2009, January 10, 2009

ASYMMETRIES 2003-2004 vs 2002

2003-2004 data released in April 2006 (DIS2006)

comparison with the published 2002 data PRL 94 (2005) 202002

increase in statistics by a factor of 7!


COLLINS ASYMMETRIES 2002-2004

DIS2006DIS2006

• small errors (~1%)• small asymmetries

d0Tu

0TTTd Coll, DD4dΔuΔA• cancellation between p and n

(lh and ah) d0Tu

0TTTd Coll, DDdΔuΔA 4

CERN-PH-EP/2006-036


• SIDIS(deuteron COMPASS/ proton HERMES) & Belle data

Anselmino et al., hep-ph/0701006v1

COLLINS ASYMMETRY & GLOBAL FIT

PRESENT PICTURE

T0D(fav.) ~ - T

0D(unfav)

Td not well constrained

from the global fit


SIVERS ASYMMETRIES 2002-2004

DIS2006DIS2006

DdΔuΔA T0

T0d Siv,

• small errors (~1%)• small asymmetries

• cancellation between p and n (lh and ah)

CERN-PH-EP/2006-036


model calculations to be compared with the COMPASS 2002-04 data

Vogelsang and Yuan

Anselmino et al

preliminary COMPASS 2002-2004


Collins et al


SIVERS ASYMMETRIES & MODELS

T T0 0Δ u - Δ d

PRESENT PICTURE


again, difficult to see an effect …

±, K± Collins Asymmetries 2003-2004


±, K± SIVERS ASYMMETRIES 2003-2004


TWO HADRON ASYMMETRIES

modulation of the number of events in RS

initial quark spin quark direction

S = angle of initial quark spin (=target spin)

S’ = angle of final (struck) quark spin

S= - S’ （ due to helicity conservation)

R = angle of two-hadron plane

RS =R –S’ = R +S-

Breit framesee hep-ph/0407345

Trento conventions

( ) / ( ) /( )

( ) / ( ) /RS tot RS tot

UT RS

RS tot RS tot

N N N NA

N N N N

RSsinUT RSA sin( )

2 2

2 2

,

,RS

hi T i i hsin i

UT hi i i hi

e q x H z MA

e q x D z M

2,hi hH z M : interference

fragmentation function( presently unknown)

transversityRSi

f

h

l-l’



Event selectionz1> 0.1 & z2>0.1　xf1>0.1 & xf2>0.1z=z1+z2<0.9

2002-2004

6.1x106 combinations

diffractive production



RSsin

RSUT

NN T

=D P

AA

f

DNN : transverse spin transfer

coefficient initial struck quark

f : target dilution factor




z ordered pairs



TRANSVERSE MOMENTUM DEPENDENT PDFs

1( )f qNucleon

Parton

numberdensity

Nucleonunpol. long. pol. trans. pol.

unpol.long. pol.

trans. pol.Q

uark

1Tf

Tk

Sivers

1 ( )Lg q helicity 1Tg

1h

Tk

1( )Th q transversity

1ThTk1Lh

Tk

T-odd

Tk

survive after integration over kT

T-odd

Boer-Mulders

RESULTS OF NLO QCD FIT

solutions : G > 0 G < 0

∫G(x)dx = +0.26 +0.04,-0.06 -0.31 +0.10,-0.14

∫(x)dx = +0.28 ± 0.01 +0.32 ± 0.01

@ Q2=3(GeV)2

Both give 0.2-0.3 for the absolute value of the gluon spin contribution (∫G(x)dx)

Gluon spin contribution is not large


TRANSVERSEPOLARIZATION

L L

L L

P P

P P

2q

qT 2

q Λ /qq

T Λ /ΛT,ex

T

p

qΔ q xe

= fP D ye q x D

D

P

Δ z

z

p


f : target dilution factor D(y): transverse spin transfer coefficient initial struck quark, given by QED

Transversity


systematic errors not larger than statistical errors

RICH ID not used yet

POLARIZATION ON DEUTERON TARGET


SIVERS ASYMMETRY ON PROTON


x>0.05 x>0.05

H.Wollny, SPIN 2008

hard scale: 2 = 4mc2

Theory understood

Combinatorial background

Limited statistics

Challenging measurement

c

c

Photon Gluon Fusion: g -> c c

G/G FROM OPEN CHARM

0

0( )

D K

D K

Kaon ID with RICH


c

c

q from SI-DIS, Impurity studies


STUDY OF SPIN STRUCTURE OF NUCLEON AT COMPASS AND ITS CHALLENGES

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