december 16 20081 extraction of exclusive neutral pions electro-production cross sections in hall a...
TRANSCRIPT
December 16 2008 1
Extraction of exclusive neutral pions electro-production cross sections in
Hall A @ Jefferson Laboratory.
Eric FUCHEYPh.D Student @ Laboratoire de Physique
CorpusculaireUMR 6533 CNRS/IN2P3Université Blaise Pascal
Clermont-Ferrand
December 16 2008 2
Outline
• 1– Motivations• 2– 0 electroproduction formalismes
– Kinematical variables – Formalismes
• 3– Experimental layout• 4– Cross sections extraction
– Calibration– Extraction method– Selection cuts
• 5– Conclusion and perspectives
December 16 2008 3
Outline
• 1– Motivations• 2– 0 electroproduction formalismes
– Kinematical variables – Formalismes
• 3– Experimental layout• 4– Cross sections extraction
– Calibration– Extraction method– Selection cuts
• 5– Conclusion and perspectives
December 16 2008 4
0 interest
• DVCS is the smartest way to get access to GPD’s theoretically.
• In most of DVCS experiments, 0 production ( with ) is an important by-product (Pollution for DVCS analysis)
0epep 0
December 16 2008 5
Outline
• 1– Motivations• 2– 0 electroproduction formalismes
– Kinematical variables – Formalismes
• 3– Experimental layout• 4– Cross sections extraction
– Calibration– Extraction method– Selection cuts
• 5– Conclusion and perspectives
December 16 2008 6
Kinematic variables
• Virtuality:
• Momentum fraction:
• Quadri transfert to proton:
• *-azimuthal angle:
• *-p CM energy:
• Transverse momentum:
22 )'( kkQ
qp
QxBj
2
2
2)''( qkkt
)11
(22 Bj
p xQMW
* h
)sin( hhh pp
December 16 2008 7
Formalismes
• Drechsel-Tiator (Nucl.Part.Phys.18(1992)449-497):
with
and
• More « intuitive » formalisme
h
v
he d
d
ddEd
d
'
5
1
1'
2 22 Q
k
E
E
)2cos()cos()1(2 hh
TTLh
h
TLL
h
LL
h
T
h
v
d
d
d
d
d
d
d
d
d
d
h
TTh
h
TLL d
d
d
d
'' 1)sin()1(2
December 16 2008 8
Formalismes
• Levelt-Mulders (Phys.Rev.D.49(1994)96-113) :
• Show an explicit dependence in transverse momentum
21
2
//4
2
2
5
21
4H
E
yMxyHyx
p
E
Q
ME
ddzdydpdx
d BjBj
h
h
hhBj
42
2
32)2cos(
21
21
)cos(2
1
21
)2( H
yE
MxE
yMxy
Q
pH
yE
MxE
yMxy
yQ
ph
Bj
Bj
hh
Bj
Bj
h
December 16 2008 9
Formalismes: comparison
• Interest: Being able to get easily cross sections from Drechsel-Tiator as function of pion transverse momentum:
With :
1HM
S
dt
d T
1224
2
HMQ
SHQ
qS
dt
d L
34Hp
Q
qS
dt
dh
TL
54
' HpQ
qS
dt
dh
TL
42
4
1Hp
QS
dt
dh
TT
hCMCMEM
WkqS
116 4
December 16 2008 10
Outline
• 1– Motivations• 2– 0 electroproduction formalismes
– Kinematical variables – Formalismes
• 3- Experimental layout• 4– Extraction des section efficaces
– Calibration– Extraction method– Selection cuts
• 5– Conclusion and perspectives
December 16 2008 11
DVCS experiment
• Incident beam : E = 6 GeV, L ~ 1037cm-2s-1 during experiment– Scattered electron measured by HRS
– 2 photons issued from 0 measured by 132 PbF2 blocks calorimeter
– Recoil proton detected by proton array -> not used
December 16 2008 12
Outline
• 1– Motivations• 2– 0 electroproduction formalismes
– Kinematical variables – Formalismes
• 3– Experimental layout• 4– Cross sections extraction
– Calibration– Extraction method– Selection cuts
• 5– Conclusion and perspectives
December 16 2008 13
Calibration
• Goal : searching coefficients to apply to calorimeter blocks in order to:– bring their reconstructed missing mass
squared value to the proton missing mass squared.
– Bring then simulated missing mass mean and resolution to real ones
Mp2
December 16 2008 14
Calibration• Calibration has been performed for set of Kin3 0 data and
our set of Kin3 0 simulated.
December 16 2008 15
Extraction method
• Kinematical domains :– Kin2: xBj = 0.36, Q2 = 1.9
GeV2
– Kin3: xBj = 0.36, Q2 = 2.3 GeV2
• Analysis made according to tmin-t.
• Fitting real data with simulated to take into account of acceptance effect.
December 16 2008 16
Extraction method
Principle: compare expected number of counts for data
to expected number of counts for simulated
),( 22
dtddxdQig
dtddxdQ
dLdtN Bj
Bini Bj
iiBinR
),( 2
2
dtddxdQig
dtddxdQ
d
N
psfLdtN Bj
BiniBinBj
ii
GenBinS
No access
What we want to extract
December 16 2008 17
Selection cuts• Missing mass cut to ensure
exclusivity
• Each photon is in a calibrated block, and E > 1.0 GeV
• k’ = pHRS +/- 4.5% ; r-function > 0.005.
• -6.0 cm < zvtx < 7.5 cm.
22mMM pX
0epep Xeep
December 16 2008 18
Fit results• Fit has been performed for helicity-independent cross
section and helicity-dependent cross section
• However, still not able to extract cross sections (debugging…)
2/NDF = 2.77 2/NDF = 0.76
December 16 2008 19
Outline
• 1– Motivations• 2– 0 electroproduction formalismes
– Kinematical variables – Formalismes
• 3– Experimental layout• 4– Cross sections extraction
– Calibration– Extraction method– Selection cuts
• 5– Conclusion and perspectives
December 16 2008 20
4 – Conclusion / perspectives
• 0 electroproduction cross section extraction in Hall A is in progress.
• Calibration has been performed (see talk on calibration this afternoon)
• Once first results obtained: – Optimizing some selection cuts
– Study evolution in other variables: xBj, Q2, W