Transcript Physics at Hermes Delia Hasch

Physics at Hermes
Delia Hasch
for the
collaboration
16th international spin physics symposium
October 10-16, 2004; Trieste (Italy)
2002
 spin observables:
new or final results since Spin02
2004
nucleon quark structure

Tw2
Corr


1
( x) 
f1 ( x)  SL g1 ( x) γ 5  h1 ( x) γ 5 γ1ST n 
2
f1q 
g 
q
1

h1q 

unpolarised quarks
and nucleons
longitudinally polarised
quarks and nucleons
transversely polarised
quarks and nucleons
q(x): spin averaged
Dq(x): helicity difference
dq(x): helicity flip
vector charge
axial charge
tensor charge
well known
known
unmeasured !
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
nucleon quark structure

g 
q
1
Outline:

h
q
1
Dq(x)
dq(x)
• the Hermes experiment
• final result on g1 for the proton and deuteron
• first direct flavour decomposition of Dq
• first measurement of transverse single-spin asymmetries
• single beam-spin asymmetries
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
nucleon spin structure
1 1
S    D  L q  J g
2 2
N
z
Outline:
• the Hermes experiment
• final result on g1 for the proton and deuteron
• first direct flavour decomposition of Dq
• first measurement of transverse single-spin asymmetries
• single beam-spin asymmetries
• news on exclusive meson production and DVCS
for further details: numerous Hermes talks in QCD spin session II
Delia Hasch
not covered: GDH
SSA on AUL |hyperon
Physics at|Hermes
Trieste (Italy), 12-10-2004
Hermes @ DESY
27.5 GeV (e/e)
<Pb>~ self-polarised
53±2.5 %
electrons: e
<Pb>~ 53±2.5 %
Stern-Gerlach separation
H <|P
t|> ~ 85 ±3.8 %
• resolution: dp/p~2%, dq<1
mrad
1
→
2 H→
<|Pt|> ~ 84 ±3.5 %
• particle ID: lepton ID with
e~98%, hadron contamination <1%
1
H <|Pt|> ~ 74 ±4.2 %
RICH: p, K, p ID within 2<E <15 GeV
h intervals
pure nuclear-polarised atomic gas, flipped at 90s time
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
Hermes kinematics
inclusive:
Q2 > 0.1 GeV2 :
0.002 < x < 0.9
with y<0.91
W2>3.24 GeV2
semi-inclusive:
Q2 > 1.0 GeV2 :
0.02 < x < 0.6
with y<0.85, W2>3.24 GeV2
0.2<z<0.8
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
model-independent unfolding
 detector smearing
 QED radiative effects
Sij 

σ meas
σ born
smearing within acceptance
N meas

N born
N(i, j ) ( )
N born ( j ) ( )
 kinematic migration inside
acceptance for each spin state
 j=0 bin: kinematic migration
into the acceptance
radiative effects
detector smearing
 systematic correlations between bins fully unfolded
 resulting (small) statistical correlations known
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
quark helicity distributions

1
1
2
g1 (x)  q e q Dq  Dq  q e q2 q  (x)  q  (x)  q  (x)  q  (x)
2
2
g1 (x)   1/ 2   3 / 2
Delia Hasch
 1/ 2  q  ( x)
 3 / 2  q ( x)
1
Sγ  S N 
2
3
Sγ  S N 
2

Physics at Hermes
Trieste (Italy), 12-10-2004

g1/F1 of the proton and deuteron
deuteron
proton
Q2 > 0.1 GeV2
0.002 < x < 0.9
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
structure function g1(x)
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
Dq from inclusive data
NLO
1
g
( x)  g
LO
1
s 1
2
2
2

e
[
D
q(x,
Q
)

C

D
G
(
x
,
Q
)  Cg ]

q
q q
2p 2
• Duv and Ddv well
determined:
Duv >0, Ddv <0
• Dq and DG weakly
constraint by data
• Ds <0 expected from
violation of Ellis-Jaffe SR
more, direct probes
needed
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
polarised quark distributions
 flavour separation by flavour tagging
flavour content of final state hadrons
related to flavour of struck quark via
fragmentation functions


A  PQ
2
2
h
2
2
h
2
e
q
(x,
Q
)
dz
D
(z)
h
hq
D
q
qQ

h
2
2
e
Δq
(x,
)
dz
D
(z,
Q
σ 2  σ3 2

q x, Q ))

Ah 1 (x, Q

(
q q
2 )  1
2
2
h
A1 (x, Q )  h q
qh
e
q'
(x,
Q
)
dz
D
(z)
h
2
2
2

q'
q'

q'
σ1 2 
σ 3
e
q
(x,
Q
)
dz
D
(z,
Q
)
2 
qq

q
 
Pqh ( x, z )
  Du Dd Du Dd Ds Ds

Q  
,
,
,
, ,
 0 
 u d u d s s

Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
measured asymmetries


π
π
K
A  A1,p , A1,d , A1,p , A1,d , A1,d

Just like in short dq paper: pi,K for d
K  (us)
Delia Hasch
Physics at Hermes
all sea objects
Trieste (Italy), 12-10-2004
purities @Hermes
probability that g* hit a quark of flavour q when hadron of type h was detected
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
[PRL92,2004; hep-ex/0407032, submitted to PRD]
quark polarisations
first 5-flavour fit to Dq
• no significant
q
polarisation
 results perfectly consistent
with incl. fits: c2/dof =0.6…1.6
for BB(SU3-sym) and GRSV-valence
• in measured range (0.023-0.6):
 Du  -0.002  0.043
 Dd  -0.054  0.035
 Ds   0.028  0.034
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
light sea flavour asymmetry
  Du Dd Du - Dd Dd Ds 
Q  
,
,
,
, 
u -d
d s 
 u d
• no significant breaking
of polarised SU(2)-flavour
symmetry
• cQSM asymmetric sea
disfavoured: c2/dof=17.6/7
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
single-spin asymmetries
dσ  dσUU  cos 2 dσUU
h1  H1
f1
1
1
 cos  dσUU  λ sin  dσ LU
Q
Q
e  H1  ...




1
1
 S L sin 2 dσUL  sin  dσUL   λS L dσ LL  cos  dσ LL 
Q
Q




h1  H1  f1T  D1  hL ...
g1

1 
 ST sin(   S )dσUT  sin(   S )dσUT  sin( 3  S )d UT  ...
Q 

h1  H

1

1T
f  D1
transversity
T-odd
(Collins effect)
(Sivers effect)
Delia Hasch
Physics at Hermes

1 
 ST cos(  S )  ...  ....
Q 

Trieste (Italy), 12-10-2004
single target-spin asymmetry


N
(

,

)

N
1
h
h
S
h ( , S )
A UT ( , S ) 



| S T | N h ( , S )  N h ( , S )
Sivers
 A Collins
sin(



)

A
UT
S
UT sin(   S )
angle of hadron relative
to final quark spin
amplitudes fit simultaneously
(prevents mixing effects
due to acceptance)
Delia Hasch
Physics at Hermes
angle of hadron relative
to initial quark spin
Trieste (Italy), 12-10-2004
transverse asymmetries
[hep-ex/0408013, submitted to PRL]
Acoll  h1 ( x) H1 ( z )
Asiv  f1T ( x) D1 ( z )
positive p and negative p asym.
significantly positive p asym.
unexpected large p
first hint of T-odd DF from DIS
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
weighted transverse asymmetries
A ( , S )  A
h
UT
sin(   NS)  A
Collins
UT
sin(
N  S )
Sivers
UT
1 i 1 PhT, i  i 1 PhT, i
A ( , S ) 


| ST |
N

N
h
k T P̂h  q  2 h q  2 
2
h
UT
 ... sin(   S )q e q  I 
h1 (x, p T )  H1 (z, k T )
h
Collins  M h
 )
A UT ( , S )  M π A UT sin(   S )  Mp ASivers
sin(


UT
S
2 
 p T P̂h  q  2
2
q
 ... sin(   S ) q e q  I 
f1T (x, p T )  D1 (z, k T )
 MN

see talk of G. Schnell
I […]  convolution integral over intrinsic quark
transverse momenta
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
interference fragmentation
[Jaffe etal,PRL80,1998]
 h1 ( x) H
 ) ,sp
1
( z, M ππ )
pp phase-shift
analysis
[Radici etal,PRD65,2002]
spectator model
in s-p channel
 ongoing analysis with transverse target polarisation
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
single beam-spin asymmetry


1
N
(

)

N
h
h
h ( )
A LU ( ) 
| Pb | N h ( )  N h ( )
M
2 2
 λ e sin(  ) y 1  y
e
x

q q
Q

 eq ( x) H1q ( z)  h1q ( x) E q ( z)

 QdQ-model prediction of
z-dependence [Gamberg,Hwang,Oganessyan,PLB584]
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
hunting for Lq
factorisation theorem for hard exclusive processes:
- Műller (1994) - Ji & Radyushkin (1996) -
Generalised Parton Distributions

( H + E) x dx = Jq
= 1/2 D  Lz
10-30%(DIS)
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
Generalised Parton Distributions
2>>, t<<
Q
2
Q >>, t<<
GPDs @twist-2:
g, r0L, p ...
H, E
g *L
xx
xx
N’
N
~ ~
H, E
quantum number of final state
selects different GPDs:
 DVCS 
t
vector mesons
Delia Hasch
Physics at Hermes
pseudoscalar mesons
Trieste (Italy), 12-10-2004
exclusivity for ep  e’p(n)
Missing Mass2 = (gpp)2
g, r0L, p ...
use p yield (ep  e’pn) to subtract non-exclusive background


e p  e' π X
Delia Hasch
N
Physics at Hermes
e p  e' π n
N’
Trieste (Italy), 12-10-2004
cross section for ep  e’pn
no L/T separation but T suppressed by 1/Q2 and e > 0.8
[Vanderhaeghen, Guichon &
Guidal (1999) ]
p production:
~
H pseudovector contrib.
~
E pseudoscalar contrib.
(pion pole related to Fp)
asymptotically
1

LO
calculations
underestimate
the data
L
6
for fixed xB and
 evaluation
of ttheQpower
correction appears too large
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
exclusive meson production: AUT
 quadratic combination of GPDs appear in
unpolarised crosss section
 polarisation provides new observables:
*
L

γ p ρ p
0
target spin asymmetry
γ pπ n
*
L
 ongoing analyses with transversely polarised target
x
particulary sensitive to E
pion pole contribution
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
exclusive pp production

e p (d)  e' p (d) π π
[PLB599,2004]
 evidence for interference of pp
in different wave states
GPD model predictions:
w/o 2-gluon exchange
with 2-gluon exchange
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
deeply virtual Compton scattering
e p  e' p' γ Bethe-Heitler
@HERMES kinematics:
DVCS << Bethe-Heitler
dσ | τ BH |2  | τ DVCS |2  (τ*BH τ DVCS  τ*DVCS τ BH )
DVCS-BH interference leads to
non-zero azimuthal asymmetry
A C, LU ( ) 
Delia Hasch
Physics at Hermes
N  ( )  N  ( )
N  ( )  N  ( )
Trieste (Italy), 12-10-2004
DVCS asymmetries
Beam Spin Asymmetry

e p  e' p' γ
e /- p  e' p' γ
BSA ~ Im(τ BH τ DVCS )
Delia Hasch
Beam Charge Asymmetry
Physics at Hermes
BCA ~ Re(τ BH τ DVCS )
Trieste (Italy), 12-10-2004
latest news: BCA vs t
GPD calculations:
- Vanderhaeghen (1999/02) –
different parametrisations for H
 t-dependence of BCA: high
sensitivity to model assumptions
tiny ep sample (L~10pb-1)
…BUT…
HERA: >2004 e
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
improvement of exclusivity
> mid 2005:
full reconstruction of exclusive events
with recoiling proton
• DVCS: HERA switches to e !
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
conclusion
• longitudinally polarised protons and deuterons:
 final data on g1 for proton and deuteron
 final data on Dq five flavour separation
• transversely polarised protons:
 first results for Collins and Sivers effect
 ongoing analyses on transversity and friends (ALU, IFF,…)
• exclusive processes:
 meson production: cross section, pp production
ongoing analyses on transverse asym.
Stay
 DVCS: single-spin
andtuned
charge…
asymmetries
New exiting results will come soon !
HERMES >mid 2005 : recoil detector
Delia Hasch
Physics at Hermes
Trieste (Italy), 12-10-2004
Power correction
-Vanderhaeghen, Guichon & Guidal (1999) -
intrinsic transverse momentum of the active quark (kperp)
(Q2>>) → 0
soft overlap contribution → no gluon exchange