calorimetry for deeply virtual compton scattering in hall a
DESCRIPTION
Calorimetry for Deeply Virtual Compton Scattering in Hall A. Alexandre Camsonne Hall A Jefferson Laboratory Workshop on General Purpose High Resolution Radiation Hard Electromagnetic Calorimeter at JLab October 31 st 2008. Measurement Experimental technique Background Analysis - PowerPoint PPT PresentationTRANSCRIPT
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Calorimetry for Deeply Virtual Compton Scattering in Hall A
Alexandre Camsonne
Hall A Jefferson Laboratory
Workshop on General Purpose High Resolution Radiation Hard Electromagnetic Calorimeter at
JLab
October 31st 2008
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Outline
•Measurement
•Experimental technique
•Background
•Analysis
•New experiment
•Requirements summary
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Workshop on Calorimetry October 31, 2008
Deeply Virtual Compton Scattering
epep
Bethe and HeitlerDVCS
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Workshop on Calorimetry October 31, 2008
• High resolution and high precision on a limited kinematic range
• Study of scaling with fixed xbj and variation in Q2
– High resolution calorimeter
– Focus on cross section measurement
– Ensure exclusivity relying on calorimeter
– High luminosity
Deeply Virtual Compton Scattering in Hall A
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Workshop on Calorimetry October 31, 2008
Specificity of the experiment
electron
HR
S
PbF2
electron
p
Centralangleup to 14 degrees
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Workshop on Calorimetry October 31, 2008
Background issues
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Workshop on Calorimetry October 31, 2008
0 contamination
• Symmetric decay: minimum angle in lab of 4.4° at max o energy
• Asymmetric decay: sometimes one high energy cluster can be misindentified for a DVCS event
•Interesting : study of Deep Exclusive 0 production could access to another linear combination of GPDs
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Workshop on Calorimetry October 31, 2008
Experimental setup
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Workshop on Calorimetry October 31, 2008
Cross sections measurement
2
55
22
55
Re
)(
Im
DVCS+
DVCS)(BH+BHdd
DVCSDVCS+
(DVCS)BHdd
2
Electron helicity dependent cross sections of photon electroproduction
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Workshop on Calorimetry October 31, 2008
Background reduction
•Scattering chamber 1 cm Al as shielding
15 cm
5 cmbeam dump
Liquid H2
target110 cm
High luminosity running possible by
• reducing secondary background source
PbF2
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Workshop on Calorimetry October 31, 2008
Data analysis
0 subtraction done using the 0 sample recorded in the
calorimeter
Subtracted data fits exactly the simulation and the shape of the
exclusive events: good understanding of the detectors
Exclusivity in two arms
Cut im Mx2
Xeep
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Workshop on Calorimetry October 31, 2008
nDVCS – deuterium Data analysis
XeepXeed )',()',( Xeep )',(
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π0 electroproduction
Invariant mass of 2 photons in the calorimeter
Missing mass2 of epeπ0x 2π production
threshold
Sigma = 0.160 GeV2
Sigma = 9.5 MeV
π0
Separation of photons for 3 GeV π0 : 4.4 degrees = 8.4 cm at 110 cm
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Workshop on Calorimetry October 31, 2008
New experimental setup• Double arm experiment
– Increase acceptance
– Increase in luminosity
• Calorimeter
– Increased size of the calorimeter from 132 to 208 blocks for larger acceptance in t
– 11x12 blocks = 33 cm x 36 cm =
= 30 mrd x 32 mrd= 98 msrd
to 13x16 blocks = 39 cm x 48 cm =
= 32.5 mrd x 40 mrd = 120 msrd
Covers full acceptance of HRS at 110 cm
from target
– Improved trigger for optimal 0 detection
– Data transfer improvement to accommodate lower threshold
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Workshop on Calorimetry October 31, 2008
Kinematics 6 GeV
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Workshop on Calorimetry October 31, 2008
Kinematics 12 GeV
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Workshop on Calorimetry October 31, 2008
Radiation hardness
Curing planned every two weeks for new experiments when more than 20 % attenuation
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Workshop on Calorimetry October 31, 2008
Requirements summary
• Lead fluoride performance were sufficient• Energy resolution
– 2.4% at 4.2 GeV – 2 % + 3.2 %*E^1/2 , DVCS photons 2 to 3 GeV– Position resolution of 3 mm– 120 msrd = 32 mrd x 40.5 mrd – Radiation Hardness to preserve resolution : around 20% change for
750 kRad.• 2000 kRad for 6 GeV experiment, 8400 kRad for 12 GeV• Curing of blocks about every 2 weeks• Cerenkov to reduce hadronic background and fast to reject background
( coincidence time 0.6 ns )• Reach forward angles around centered around 14 degrees