Spin transfer coefficient KLL’ in photoproduction at HERMES

D. VeretennikovOn behalf of the HERMES collaboration

DIS08, London

Λ decay and spin transfer coefficient is “self-analyzing” particle due to its parity violation p - decay

''

LLL LP S P

Spin transfer coefficient SLL’

KLL’ from longitudinally polarized target

KNN’ from transversely polarized target

DLL’ from longitudinally polarized beam

DNN’ from transversely polarized beam

L is primary axis along target or beam polarizationL’ is secondary axis along momentum

Unpolarized cross-section

angle between proton momentum in the rest frame and the spin

decay constant, 0.642 (), -0.642 ()

0'(1 cos )pL

p p

d dP

d d

Angular distribution of protons (in rest frame)

Study of Λ polarization at HERMES

DIS, e + p e’ + + X

DLL’ spin transfer from longitudinally polarized e+/e- beam in semi-

inclusive reaction / Published P.R. D 64 (2001), P.R. D 74 (2006) /

Quasi-real photoproduction, e + p → Λ+ X

KLL’ spin transfer from longitudinally polarized target

DLL’ spin transfer from longitudinally polarized e+/e- beam

KNN’ spin transfer from transversely polarized target

Pn transverse (spontaneous) Λ polarization / Publish P.R. D 76 (2007) /

e’ + * ( Q2 0 GeV2 )

Λ photoproduction mechanism in PYTHIA

According to PYTHIA is produced due to

diquark fragmentation or due to quark

fragmentation0.0 0.1 0.2 0.3 0.4 0.5

102

103

104

105

N e

ven

ts

Q2 ( GeV2 )

Most of events are within photoproduction peak (for 80% events Q2 < 0.05 GeV2, 15 GeV)

Such that photon is quasi-real

p

ud

uu squarkd

hadrons, ,u d s

, ,u d s

hadrons

p

ud

u

( )dudiquark

s

hadrons, ,u d s

, ,u d s

hadrons

HERMES experiment

Polarized lepton (e-/e+) beam Ee = 27.5 GeV , monthly spin flip ( DLL’ )

Long. / trans. polarized gas targets (H, D) , spin flip every 90 s ( KLL’ ,

KNN’ )

Detector is up / down symmetric ( Pn )

1

0

2

�1

�2

m

LUMINOSITY

CHAMBERSDRIFT

FC 1/2

TARGETCELL

DVC

MC 1�3

HODOSCOPE H0

MONITOR

BC 1/2

BC 3/4 TRD

PROP.CHAMBERS

FIELD CLAMPS

PRESHOWER (H2)

STEEL PLATE CALORIMETER

DRIFT CHAMBERS

TRIGGER HODOSCOPE H1

012345678910

RICH270 mrad

270 mrad

MUON HODOSCOPEWIDE ANGLE

FRONTMUONHODO

MAGNET

m

IRON WALL

e+

27.5 GeV

140 mrad

170 mrad

170 mrad

140 mrad

MUON HODOSCOPES

Background suppression cuts forleading rejection (in HERMES acceptance proton is always leading) :

Threshold Cherenkov det. 1996-1997

Ring imaging Cherenkov 1999-2000

h+h- pair background rejection :

Vertex separation d(V1,V2) > 15 cm

() event reconstruction

3 3126 10 , 25 10N N

Data sample for longitudinally polarized target ( 1996 - 2000 )

T ,12 2 2 2

1

cos cos1 1

cos cos

N ipL T i pLi

LL N iT pL T pLi

P PK

P P

1LL bgr LL LL bgr bgrK K K N N N

Formalism extraction of KLL’

No MC simulation needed

0' '(1 cos )LL T pL

p p

d dK P

d d

2 2

'

02 2' ' '0 0

'

' ' 0

' 0

cos coscos

1 coscos

TT pL LL T pL

T pL

LL T pL

LL T pL

PP K

PK

P

KPP

2 3' ' '2 0 0

'

' '

2' 0

0

0

cos coscos

1 coscos

TpL LL T pL

pL

LL T p

p

P

L

L

K P

K P

10T TP P dL

L Helicity balanced data sample

Moment method

Background subtraction

target polarization

luminosityTP

L

1 2 3 4 5 60

200

400

600

800

1000

1200

1400

1600

t GeV

-0.2 0.0 0.2 0.4 0.6 0.8 1.00

200

400

600

800

1000

1200 totalquarkdiquark

xF

Photoproduction kinematics

max

2 2z t x

F z

yp p

p

p

x p p

p

not measuredin rest frame

Only reconstructed are and

2

pt p p

Mandelstam invariant

Better separate production channels

Value of t allows for easy comparison with other experiments

1 2 3 4 5 6 7-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

t GeV

p

X

t

' 0.026 0.009 0.005LL stat systK KLL’ seems to be increasing at small t (diquark fragmentation?)KLL’ is pt independent (0 < pt < 1.2 GeV)

Kinematical dependences of KLL’ for

2.0 2.5 3.0 3.5 4.0 4.5-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

HERMES p

relim

inary

t GeV

'LLK

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

HERMES p

relim

inary

'LLK

GeVtp

Statistics for is not enough to see dependences on t or pt

' 0.002 0.022 0.008LL stat systK

Kinematical dependences of KLL’ for

2.0 2.5 3.0 3.5 4.0 4.5-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

HERMES p

relim

inary

'LLK

t GeV

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

HERMES p

relim

inary

'LLK

GeVtp

Spin transfer for and , world data

FNAL, E704pp collisions with transversely

polarized beam

RICH, STARpp collisions with

longitudinally polarized beam

200GeV, 1.0GeV/c

, ,

p t

p F t

E p

E x p t

1200GeV, tanh

,

zs p p

s t

World data compilation for spin transfer

1 2 4 8 16

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

t GeV

FNAL result confirms a trend to increase spin transfer at small t

Conclusion

Longitudinal spin transfer from polarized target to the is measured for the first time in quasi-real photoproduction

KLL’ = 0.026 ± 0.009stat ± 0.005syst

Spin transfer is increasing at small t

KLL’ is pt independent

Longitudinal spin transfer to is compatible with zero for available statistics

KLL’ = 0.002 ± 0.022stat ± 0.008syst