deeply virtual compton scattering on the neutron at jlab with clas12
DESCRIPTION
e’. ~. e. t. g. H, H, E, E (x,ξ,t). g L *. (Q 2 ). x+ξ. x-ξ. INFN Frascati, INFN Genova, IPN Orsay, LPSC Grenoble SPhN Saclay University of Glasgow. ~. p’. p. Deeply Virtual Compton Scattering on the neutron at JLab with CLAS12. CLAS12 Central Detector Meeting - PowerPoint PPT PresentationTRANSCRIPT
2009/12/02– CLAS12 #1 [email protected] B. GenoliniS. Niccolai, IPN Orsay CLAS12 Workshop, Genova, 2/27/08
CLAS12 Central Detector MeetingSaclay, 12/02/09
INFN Frascati, INFN Genova,
IPN Orsay,LPSC Grenoble
SPhN Saclay University of Glasgow
Deeply Virtual Compton Scatteringon the neutron at JLab with CLAS12
e’t
(Q2)
eL*
x+ξ x-ξ
H, H, E, E (x,ξ,t)~~
p p’
2009/12/02– CLAS12 #2 [email protected] B. Genolini
nDVCS with CLAS12: kinematics
ed→e’n(p)
Detected in forward CLAS
Detected inFEC, IC
Not detected
PID (n or ?), p, angles to identify the final state
More than 80% of the neutrons have >40°→ Neutron detector in the CD is needed!
DVCS/Bethe-Heitler event generatorwith Fermi motion, Ee = 11 GeV (Grenoble)
Physics and CLAS12 acceptance cuts applied:
W > 2 GeV2, Q2 >1 GeV2, –t < 1.2 GeV2
5° < e < 40°, 5° < < 40°
<pn>~ 0.4 GeV/c
CD
In the hypothesis of absence of FSI:pμ
p = pμp’ → kinematics are complete
detecting e’, n (p,,),
pμe + pμ
n + pμp = pμ
e′ + pμn′ + pμ
p′ + pμ
FSI effects can be estimated measuringen, ep, edon deuteron in CLAS12(same experiment)
2009/12/02– CLAS12 #3 [email protected] B. Genolini
• limited space available (~10 cm thickness)→ limited neutron detection efficiency→ no space for light guides→ compact readout needed• strong magnetic field (~5 T)→ magnetic field insensitive photodetectors (APDs, SiPMs or Micro-channel plate PMTs)
CTOF can also be used for neutron detection Central Tracker can work as a veto for charged particles
CND
CTOF CentralTracker
CND: constraints & design
Detector design under study:scintillator barrel
MC simulations done for: efficiency PID angular resolutions reconstruction algorithms background studies
2009/12/02– CLAS12 #4 [email protected] B. Genolini
Simulation of the CND
Geometry:• Simulation done with Gemc (GEANT4)• Includes the full CD• 4 radial layers (or 3, if MCP-PMTs are used)• 30 azimuthal layers (can still be optimized)• each bar is a trapezoid (matches CTOF)• inner r = 28.5 cm, outer R = 38.1 cm
Reconstruction: Good hit: first with Edep > threshold
TOF = (t1+t2)/2, with
t2(1) = tofGEANT+ tsmear+ (l/2 ± z)/veff
tsmear = Gaussian with = 0/√Edep (MeV)
0 = 200 ps·MeV ½ → σ ~ 130 ps for MIPs β = L/T·c, L = √h2+z2 , h = distance betweenvertex and hit position, assuming it at mid-layer θ = acos (z/L), z = ½ veff (t1-t2) Birks effect not included (will be added in Gemc) Cut on TOF>5ns to remove events produced in the magnet and rescattering back in the CND
z
y
x
2009/12/02– CLAS12 #5 [email protected] B. Genolini
CND: efficiency, PID, resolution
pn= 0.1 - 1.0 GeV/c= 50°-90°, = 0°
Efficiency: Nrec/Ngen
Nrec= # events with Edep>Ethr.
Efficiency ~ 10-16% for a threshold of 5 MeVand pn = 0.2 - 1 GeV/c
Layer 1 Layer 2
Layer 3 Layer 4
distributions (for each layer) for:• neutrons with pn = 0.4 GeV/c• neutrons with pn = 0.6 GeV/c• neutrons with pn = 1 GeV/c• photons with E = 1 GeV/c (assuming equal yields for n and )
n/ misidentificationfor pn ≥ 1 GeV/c
“Spectator” cut
p/p ~ 5%~ 1.5°
2009/12/02– CLAS12 #6 [email protected] B. Genolini
CLAS 12
B. Genolini, T. Nguyen Trung, J. Pouthas
http://ipnweb.in2p3.fr/~detect
Recent measurements at OrsayCEA – Orme des Merisiers
Dec. 2-3, 2009
2009/12/02 – CLAS12 #7 http://ipnweb.in2p3.fr/~detect - B. Genolini
Main issues
• Requested time resolution < 200 ps RMS– Plastic scintillator (best ≈ 2.5 ns
FWHM) Large number of photoelectrons:
> 100
• High magnetic field (5T): no PMT SiPM (MPPC, GAPD, etc.)
APD MCP PMT
• 60-cm long scintillator:– Important light losses
(wrapping, absorption) – Spread of the photon time
distribution
w
h
l = 60 cm
Plastic scintillator (BC408)
2009/12/02 – CLAS12 #8 http://ipnweb.in2p3.fr/~detect - B. Genolini
The test bench at Orsay
• Scintillator: 60×3×3 cm^3, BC408• Trigger: the time reference is taken from
the thickest scintillator, validated by the coincidence of the two others
• Mobile support to scan the scintillator• Test readout: PMT as the reference, or
SiPM (in a box, for shielding)
Reference readout PMT
(XP20D0) Coincidence scintillators
Trigger scintillator
Test readout:
PMT orSiPM
Mobile support
TestRef
Trig
2009/12/02 – CLAS12 #9 http://ipnweb.in2p3.fr/~detect - B. Genolini
Results
Single pe
σ2test =1/2 (σ2
test,trig + σ2test,ref − σ2
ref,trig) TestRef
Trig
Test = 1 SiPM Hamamatsu (MPPC 1x1 mm2)• TOF ~ 1.8 ns • rise time ~ 1 ns• nphe ~1
Test = 1 SiPM Hamamatsu (MPPC 3x3mm2)• rise time ~5 ns (> capacitance)• more noise than 1x1 mm2
Test = 1 APD Hamamatsu (10x10 mm2 ) • TOF ~ 1.4 ns• high noise, high rise time
Test = 1 MCP-PMT Photonis/DEP (two MCPs)• TOF ~ 130 ps•tested in B field at Saclay(end of November)
Test = PMT• TOF < 90 ps• nphe ~1600
Thi Nguyen TrungBernard Genolini
S. PisanoJ. Pouthas
2009/12/02 – CLAS12 #10 http://ipnweb.in2p3.fr/~detect - B. Genolini
Extruded scint. + WLS fiber
• Extruded scintillator made at Triumph
• Wavelength shifting fiber (best results with multi cladding): > 10 pe
• Measurement with a 1×1 m2 MPPC (Hamamatsu SiPM) and a PMT (Photonis XP20D0)
• Time resolution: 1.4 ns RMS
100 ns
Typical signals
PMT averaged signal
20 ns
2009/12/02 – CLAS12 #11 http://ipnweb.in2p3.fr/~detect - B. Genolini
MCP-PMT
• Double-stage MCP (Photonis-DEP)• Time resolution without magnetic field = 130 ps• Test at CEA under magnetic field: not working at
5 T (amplitude ratio = 10-4)
2-stage MCP
1
10
100
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5
Magnetic field (T)
Am
pli
tud
e (m
V)
2600V
2800V
2009/12/02 – CLAS12 #12 http://ipnweb.in2p3.fr/~detect - B. Genolini
Simulation of the light collection
Adjusted on thePrototype measurements
w
h
l
Scintillator (BC408)
z
y
x
Readout (MCP PMT)
Readout (MCP PMT)
Prototype (0 layer)
2 layers
Scint. 1
Scint. 2
3 layersScint. 2Scint. 1
Scint. 3
Simulations with Litrani
Pulse shapesRelative light yields
Time resolution along the scintillator length
2009/12/02 – CLAS12 #13 http://ipnweb.in2p3.fr/~detect - B. Genolini
Issues
1/Can we obtain ~150 ps time resolution give the existing constraints ? (B-field,
space, photodetector lifetime,…) ? (3 MCP-PMTs, APDs, SiPMs,…)
2/If not, can we afford to give up on the TOF measurement ?
TOF measurement has three purposes:
A/ n/ separation
B/ pn measurement
C/ measurement
Energy deposition profile (1cm2 scintillator trapezoids) ?
Preshower ? Pulse shape analysis ?
Could measuring only (pe,e,e), (p,), (n,n)
be enough ?
Additional segmentation in
3/Measuring the recoil proton instead ?