Physics with low energy recoil detector and options for instrumentation for the CLAS12

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Physics with low energy recoil detector and
options for instrumentation for the CLAS12

• S. Stepanyan (JLAB)
• CLAS12 European Workshop 
• February 25-28, 2009, Genova, Italy

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• Few physics topics with low energy recoil (
  ) detector
• neutron structure
• nuclear structure (see also K. Joos talk)
• meson spectroscopy
• Options for a recoil detector
• RTPC
• LPMWPCSSD

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Neutron target and accessible physics

• Free neutrons decay in 15 min
• Can we explore the structure of the neutron if
  all we have are neutrons bound in nuclei?
  nuclear model uncertainties
• Low energy spectator tagging can be a solution
  for a neutron target

• PDF at large x
• d/u at large x
• quark-hadron duality on neutron
• neutron elastic scattering
• neutron DVCS
• S. Bueltman et al., E12-06-113

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d/u ratio at x ? 1
F2n/F2p F2d/F2p -1???
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Modifications to Simple Spectator Picture
Binding Effects
BoNuS
Final State Interactions
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Spectator Tagging with BoNuS RTPC
E 4.223 GeV
ltQ2gt 1.19 (GeV/c)2

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DVCS on nuclei

• Coherent DVCS
• Nuclear GPDs - partonic structure of nuclei,
• momentum and spatial distribution of quarks in
  nuclei, generalized EMC effect
• Incoherent DVCS
• bound nucleon GPDs nuclear medium effects,
  modification with respect to free nucleon ones

Both will require low energy recoil detector
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Nuclear DVCS
Coherent and incoherent were not cleanly
separated.
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CLAS experiment E08-024 (K. Hafidi et al.)

• For nucleon DVCS

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Meson spectroscopy
Production on hydrogen - physics background
from associated baryon resonance production
CLAS/g6 gpnppp-
D(1232)
N(1520)
N(1680)
D, N
a2(1320)
Strong kinematical cuts and a complex PWA are
required
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Spectroscopy in coherent production on nuclei
Method to eliminate the baryon background
All three charged modes can be studied using gas
targets 3H, 3He, and 4He
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Example coherent production on 4He
Scattering off a spin and isospin zero target
works as a spin and parity filter
with
JLAB experiment E07-009, Stepanyan et al.
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Coherent production of p0h and p0h off 4He
Only C-1 w-exchanges is allowed, Natural Parity
Exchange (NPE)
The helicity of the produced state will be that
of the incoming photon, llg, production of p0h
(p0h) in S-wave is forbidden
Test for above assumptions
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CLAS12 central detector
5T SC Solenoid Magnet
Silicon Vertex Tracker
Scintillator Counters, dt50ps
Low (200 MeV/c) energy protons in CLAS12 CD (M.
Ungaro, GEMC)
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CLAS12 Central detector
Protons
Deuterons
Specialized detector is needed for a broad
physics program requiring low energy recoil
detection
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BoNuS RTPC
Helium/DME at 80/20 ratio
7 atm D2 gas
Drift Region
Gas Electron Multiplier
Readout pads and electronics
BoNuS Barely off-shell Nucleon
Scattering RTPC Radial Time Projection Chamber
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Performance and limitations of BoNuS RTPC
e- reconstructed in CLAS RTPC
dE/dx from charge along the track
Reasonable 3-vector reconstruction Reasonable PID
for a proton Low rate of DAQ - 500Hz Poor PID
for high mass fragments gain uniformity of GEM
pads
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BoNuS-II (for EG6 run in October)
Lightweight (carbon-foam composite structure)
rungs for stress-free, self support of GEMs to
avoid wrinkles
Ground and cathode foils, each 6mm thick
Target region - new cell ID 4mm, 30mm thick wall
Open, 2p geometry only 80 is accessible due to
the GEM and readout pad sizes
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Expected performance of BoNuS-II

• Better gain uniformity better PID
• new GEM foils
• stress free support
• calibration system (a-source and elastic
  scattering)
• Lower momentum threshold (250 MeV for as)
• thinner target walls
• Increased DAQ rate - 0.5 kHz to 5 kHz
• new RCUs, crate, backplane work is done at INFN
  Genova (R. De Vita, M. Battaglieri, S. Minutoli)

Expected PID with fully calibrated RTPC
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DAQ with new Readout Control Unit board
Rx - PASA - ALTRO
Max event rate 7 kHz
FEC 128 ch
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Front-end bus ( 200 MB / s )
FEC 128 ch
2
RCU
FEC 128 ch
1
Data Proc. and Memory
Tx
DDL ( 200 MB/s )
Bus controller ( conf. R/O )
DETECTOR
DAQ int. (DDL-SIU)
DCS ( 1 MB/s )
FEC 128 ch
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BOARD Controller
DCS int. (Ethernet)
Local Monitor and Control
TTC optical Link (Clock, L1 and L2 )
Trigger and Timing circuit
Trigger int. (TTC-RX)
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FEC 128 ch
Control Network (I2C-serial link)
FEC 128 ch
1
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LPACSSD (NIKHEF NIM A409, 1998)
MeV
H 3.2
2H 4.2
3H 4.9
3He 11
4He 13
Sci E
SiY DE or E, y
H 2H 3H 3He 4He
8.8 12 14 31 35 MeV
SiX DE or E, x
Isobutane_at_ 7 mbar
AC DE, t(dt100ps), y
Entrance foil 1mm
Low-pressure avalanche chamber and silicon
strip detectors
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LPMWPC (JLAB FF detector NIM A426, 1999)
Detector was developed by YerPhI group for
detection of fission fragments for studies of the
absolute photofission cross sections at MAX-lab
(Lund, Sweden) and for hypernuclear experiments
in Hall C at JLAB
Two windowless gas proportional counters with
three electrodes, operating as a parallel plate
(wire planes) avalanche counter Silicon strip
detectors to measure full energy Options for
running the chamber with helium, helium/heptane
(99/1), or helium/hydrogen (86/15) are under
studies (YerPhI/Idaho)
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Test of LPMWPC in Hall B
Two symmetric arms placed on top and bottom of
the beam centerline The inner chambers active
area - 10.5 x 21cm2 Distance of the anode plane
from the beam line - 3 cm. The outer chambers -
21 x 21 cm2 Target - 209Bi with a thickness of 2
mg/cm2.
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RTPC and LPMWPC
BoNuS RTPC LPMWPCSSD
Rate High High
Background Insensitive to MIP Insensitive to MIP
Momentum resolution Dp/p20, full trajectory fitting Two point position recopnstruction
Minimum energy 6 MeV for a Defined by target, can be 1 MeV for a
Efficiency 100 100
Time resolution None 200ps
Use in the trigger No Yes
Solid targets No, high accidental rates, long drift time Yes, good for heavier fragments
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Summary
Broad physics program, ranging from nucleon and
nuclear structure to meson spectroscopy, can be
accessed with CLAS12 and a low energy recoil
detector Exploration of some of these physics
topics is started with CLAS and BoNuS RTPC 2nd
generation RTPC will have much improved
characteristics for PID and data rate (3rd
generation detector for CLAS12 can have 2p
azimuthal coverage) Option with LPMWPC must be
carefully studied, specially for the detection of
a-s and the heavier fragments from solid targets
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Backup slides
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CLAS12
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Low Threshold Cherenkov Counters
Pre-shower calorimeters
CLAS12 Solenoid
Electromagnetic calorimeters
Central Detector
Drift Chambers
High Threshold Cherenkov Counter (HTCC)
TOF Counters
CLAS12 Torus
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EMC effect
?4He/?D
Gomez et al., PRD49, 1994
Medium Modification
S. Liuti S. K. Taneja PRC72, 2005
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Electroproduction at 0 degrees photoproduction
Reaction eppggggX at 5.76 GeV (e1-6 and e1-DVCS
experiments)
Missing transverse momentum distribution for
MX2lt0.1 GeV
Invariant mass of 2 photon pairs in the reaction
eppgggg(e)
Data were taken with loosely defined electron
trigger
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Reaction eppp0p0(e) and eppp0h(e)
CLAS DVCS
CLAS e1-6
Note - data were taken with unfavorable trigger
conditions - transferred momentum squared,
tgt0.2 (GeV/c)2 (proton momentum gt0.4 GeV/c) -
spectra contain the baryon background
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Event display of RTPC BoNuS data on D2 and 4He
2xQD lt QHe
Deuterium Target
Helium Target