Spin transfer coefficient K LL’ in photoproduction at HERMES D. Veretennikov On behalf of the...
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Transcript of Spin transfer coefficient K LL’ in photoproduction at HERMES D. Veretennikov On behalf of the...
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