Spin Physics at

Spin Physics atSpin Physics at

Delia Hasch

(for the HERMES collaboration)

1717th th international spin physics symposiuminternational spin physics symposiumOctober 02-07, 2006; Kyoto (Japan)October 02-07, 2006; Kyoto (Japan)

talks by M.Diefenthaler, M.Contalbrigo• news on transversity & friends

gz

qzsvv

Nz ΔLΔLΔG)ΔqΔdu(

2

1

2

1S

the spin of the nucleonthe spin of the nucleon

outline:outline:• prerequisites

• final results on g1 for the proton and deuteron• flavour decomposition of q

• new result on G

• hunting L: DVCS, excl. 0

Delia Hasch spin Physics at Hermes Kyoto (Japan), 02-10-2006

• new results on polarisation (not covered) talk by K.Rith

talks by L.DeNardo, H.Jackson

talk by P. Liebing

talks by W.D.Nowak, H.Guler, E. Kinney


Hermes @ DESYHermes @ DESY

self-polarised electrons: e

<Pb>~ 53±2.5 %

27.5 GeV (e/e)

<Pb>~ 53±2.5 %

1H→ <|Pt|> ~ 85 ±3.8 %

2H→ <|Pt|> ~ 84 ±3.5 %

1H <|Pt|> ~ 74 ±4.2 %

pure nuclear-polarised atomic gas, flipped at 90s time intervals

Stern-Gerlach separation

• resolution: p/p~2%, <1 mrad

• particle ID: lepton ID with ~98%, hadron contamination <1%

RICH: , K, p ID within 2<Eh<15 GeV

kinematic range = 7 GeV:

0.2 < Q2 < 20 GeV2

0.004 < x < 0.9 for Q2 > 1 GeV2 : x > 0.02

s

polarised structure function gpolarised structure function g11


polarised structure function gpolarised structure function g11


x

[Q2>1 GeV2 data only]

assume saturation of 1d :

a0= (theory) (exp) (evol)

= 0.330 ± 0.011 ± 0.025 ± 0.028

MS

see talk by L. DeNardo

q and q and G from inclusive dataG from inclusive data])Q,(g)Qq(x,[e

2

1)Qx,( g

2qq

22q

2LO1

2NLO1 CxCegg


• uv and dv (quite) well determined: uv >0, dv <0

• q and G weakly constraint by data

how to further proceed ?how to further proceed ?• q and q and G from inclusive G from inclusive

DIS data viaDIS data via evolution evolution

equations :equations : requires wide kinematic range in Q2 and x


unpolarised DIS

only fixed target spin experiments so far …

need polarised collider

to

extend kinematic

coverage

need polarised collider

to

extend kinematic

coverage need more direct probes

OR:

polarised semi-inclusive DISpolarised semi-inclusive DIS

f

fff zDdxqz )()()(d hqh , z=Eh/

probability that struck quark

of flavour f fragments into

hadron of type h with energy fraction z

distributionfunction

fragmentationfunction


)Xe'pe( h

polarised semi-inclusive DISpolarised semi-inclusive DIS

- udK- us

flavour tagging

+ ud

f

fff zDdxqz )()()(d hqh , z=Eh/

probability that struck quark

of flavour f fragments into

hadron of type h with energy fraction z


QPA

0

s

s,

s

s,

d

d,

u

u,

d

d,

u

uQ

)Xe'pe( h

‘purities’(based on MC tuned to HERMES multiplicities)

quark/anti-quark helicity quark/anti-quark helicity distributionsdistributions

u quarks large positive polarisation

d quarks negative polarisation

[HERMES, PRL92(2004), PRD71(2005)]


0.0430.002 u -

0.0350.054 d -

0.0340.028 s

sea quarks (u, d, s ,s) compatible with 0 :in measured x-range: (0.02-0.6):

- - -

x

[HERMES, PRL92(2004), PRD71(2005)]


‘‘isoscalar’ extraction isoscalar’ extraction SS

• strange quarks carry no isospin (same in p, n)

• deuterium is isoscalar target fragmentation simplifies

all needed information extracted from HERMES data alone:

• A1d(x,Q2) , A1

K(x,Q2)

• kaon multiplicities

assumptions: isospin symmetry charge conjugation

[HERMES, PRL92(2004), PRD71(2005)]



007.0029.0006.0

)ss)(S(1

02.0

xdx

xx

• strange quarks carry no isospin (same in p, n)

• deuterium is isoscalar target fragmentation simplifies

all needed information extracted from HERMES data alone:

• A1d(x,Q2) , A1

K(x,Q2)

• kaon multiplicities

assumptions: isospin symmetry charge conjugation

[HERMES, PRL92(2004), PRD71(2005)]



007.0029.0006.0

)ss)(S(1

02.0

xdx

earlier s result confirmed with factor 2 smaller errors:

x

xS(x)/2

see talk by H. Jackson

0.0350.054 d -

0.0340.028 s

direct measurement of direct measurement of GG

hard scale is PT

• golden channel: charm productiongolden channel: charm production

• @HERMES: hadron production at high PT

(fac.)

TMCBgT|| g

Δg;)p(A)p(A

)(g

Δg;)AA(A MC

sigMCBg|| x

method I:

method II:

MC: PYTHIA6.2Bg-processes: DIS, QCDC, direct+resolved


0.0350.054 d -

0.0340.028 s

hard scale is PT

• golden channel: charm production

• @HERMES: hadron production at high PT :

)p(A)p(A TMCBgT||

)AA(A MCsig

MCBg||

method I:

method II:

MC: PYTHIA6.2Bg-processes: DIS, QCDC, direct+resolved

x

g/g

direct measurement of direct measurement of GG


see talk by P. Liebing

<2>=1.35 GeV2

exp)()(2 010.0034.0071.0),(g

Δg sysstatx +0.127-0.105 (sys-model)

quark structure of the quark structure of the nucleonnucleon


nxhxgxfx T1

5151L1Tw2Corr Sγγ)(γ)(S)(

2

1)(

q1h q

1f

quark structure of the quark structure of the nucleonnucleon

transversely polarisedquarks and nucleons

h1(x): helicity flip

chiral-odd needs a chiral odd partner:

SIDIS: COLLINS-FF azimuthal asymmetry AUT

q1g

nxhxgxfx T1

5151L1Tw2Corr Sγγ)(γ)(S)(

2

1)(

unpolarised quarksand nucleons


longitudinally polarised quarks and nucleons

HERMES transverse runningHERMES transverse running2002-05 transversally polarised p (Pt = 0.78±0.04)

0.3T transverse holding field

2002: first results [PRL94(2005)]

preliminary data 2002-2004 [hep-ex/0507013]


asymmetries and momentsasymmetries and moments

),(N),(N

),(N),(N

||

1),(A

ShSh

ShSh

TS

hUT

S

)sin()sin(2)sin()sin(2 S

h

UTSS

h

UTS

[angle and moments definitions according to Trento conventions]

Collins moment)()( 11 zHxh q )()( 11 zDxf qq

T

Sivers moment

Collins and Sivers moments extracted by fitting the asymmetry with: )5(2sin)4(sin)3(sin)2(sin)1(, PPPPPA SSSSS

FitUT


Collins Collins asymmetries asymmetries

• significantly positive and

negative asymmetries

• unexpected large role of unfavoured fragmentation function?

)(1 zH )(1 zH

.1.1 )()( favunfav zHzH .1.1 )()( favunfav zHzH

)()()( 11coll zHxhA qqS

)()()( 11coll zHxhA qqS

measurement of from


see talk by M. Diefenthaler

KK

what can we learn from what can we learn from Collins Collins AAUTUT? ?

[Efremov et al. hep-ph/0603054] h1 from QSM

Collins FF:

x-dependence: Hermes data fitted to obtain parameters for ansatz for CollinsFF

z-dependence: BELLE data fitted and asymmetry for Hermes calculated


HERMES+BELLE

data in agreement

• significantly positive asymmetry

requires non-zero orbital angular momentum

first hint of naïve T-odd DFfrom DIS

DYT1DIST1 )()( xfxf DYT1DIST1 )()( xfxf

• D1 known Sivers DFcan be extracted fromHERMES data !

SiversSivers asymmetries asymmetries

test of universality:

)()()( 1T1siv zDxfA S )()()( 1T1siv zDxfA S


see talk by M. DiefenthalerKK

needs new unknown 2hadron fragmentation function

interference arises from different partial waves of system

!collinear factorisation! relativ. momentum: R=(PP)/2

can have transv. component even when integrating over PT of the pair

)()(A 11)sinθsin(

UTSR zHxh )()(A 11)sinθsin(

UTSR zHxh

two-hadron asymmetrytwo-hadron asymmetry


M

[Jaffe etal,PRL80,1998] [Radici etal,PRD65,2002]

M


two-hadron asymmetrytwo-hadron asymmetry)()(sin)sin(AA 11S

sin)sin(UTUT zHxhR

SR

0.040±0.009 (stat) ±0.003 (sys)

positive moments for all invariant mass bins

sin)sin(UTA SR see talk by M. Contalbrigo

hunting for Lhunting for Lqq

10-30%(DIS)10-30%(DIS)

( H + E) x dx = JJqq

= = 1/2 1/2 LLzz

Q2

t

Generalised Parton Distributions

Quantum number of final state selects different GPDs:Vector mesons ( H EH E

Pseudoscalar mesons (: H E H E

DVCS () depends on H, E, H, EH, E, H, E~~ ~~

~~ ~~

hard exclusive processes:

Q2>>, t<<


missing mass (energy)techniquebackground estimated by MC

e+/e-

27.5 GeV

Pb=55%

exclusivity @HERMESexclusivity @HERMES

(detected)


MC

associated BHBethe-Heitler

+ data

no recoil detection

Deeply Virtual Compton Deeply Virtual Compton ScatteringScattering

Bethe-Heitler

DVCS-BH interference leads to non-zero azimuthal asymmetry

γpepe ''

)τττ(τ |τ||τ|dσ BH*DVCSDVCS

*BH

2DVCS

2BH

DVCS

Bethe-Heitler

BH

II

d

dd

)(d)(d

)(d)(d)(A


UT ~ sin∙Im{k(H - E) + … }

C ~ cos∙Re{ H + H +… }~

LU ~ sin∙Im{H + H + kE}~

DVCS asymmetries DVCS asymmetries )τττ(τ |τ||τ|dσ BH

*DVCSDVCS

*BH

2DVCS

2BH

UL ~ sin∙Im{H + H + …}~

polarisation observables:

UT

beam target

= xB/(2-xB ),k = t/4M2 kinematically suppressed

H

H

H, E

~

different charges: e e (only @HERA!):

H


see talk by H. Guler

DVCS: beam charge DVCS: beam charge asymmetryasymmetry

- VanderhaeghenVanderhaeghen (1999/02)(1999/02) ––

HERA: 2005/06 e beam (10x)

e+/- p → e+/- p X<1.7 GeVin HERMES acceptance

Regge, D-term

Regge, no D-term

fac., D-termfac., no D-term

γpepe ''/-

AC sensitive to GPD-models

[hep-ex/0605108, subm.to PRL]

GPD calculations:

different parametrisations for H


tiny e-p sample (L=10pb-1)

DVCS: longitudinal target-spin DVCS: longitudinal target-spin asymmetryasymmetry


sin in agreement with GPD models

unexpected large sin2 (twist-3)

DVCS: transverse target-spin DVCS: transverse target-spin asymmetryasymmetry

]Im[F 12 EFΗ

]~

F~

Im[F 12 EΗ

γpe pe ''

first model dependent constrain on Ju+Jd


[2002-2004 data]

GPD model by: [Goeke et al. (2001)] [Ellinghaus et al. (2005)]

see talk by W.D. Nowak

00 transverse target-spin transverse target-spin asymmetryasymmetry


interference of H and E:

S ~ STsin S E∙H

GPD model calculations: quark+gluon

GPDs EE related to JJqq TSA sensitive to J Jqq

[curves: Vinnikov et al. (2005)]

add 2005 data: L/T separation

(meson production: factorisation for longitudinal photons

only)

see talk by E. Kinney

summary: HERMES view at the summary: HERMES view at the nucleon nucleon structurestructurefrom unpolarised

DISfirst glimpse

directflavourdecomp.

new constrain on s

transversity isnon-zero!first T-odd DF inDIS


polarised DIS + HERMES:

signals of GPDs Ju+Jd

a0

=0.330±0.025(exp)

Backup slidesBackup slides


e+/e-

27.5 GeV

add 2005: p data

transversity+friends exclusive AUT (DVCS, )

2006-07:

dedicated measurements of hard exclusive processes with recoil

HERMES futureHERMES future June June 20072007

contribution from exclusive VM contribution from exclusive VM in sidis samplein sidis sample

basically no VM contribution for kaons

polarised gluon polarised gluon distributiondistribution

3 data samples: • ‘anti-tagged’ : e+ not in acceptance pT measured w.r.t. beamline • ‘tagged’ : e+ identified• hadron pairs

different bg contributions, different systematics

g/g

DVCS: TTSADVCS: TTSAconstrain on Jconstrain on Juu+J+Jdd

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