1. for meson spectroscopy
New detectors
for meson spectroscopy
in Hall B at JLab
Baryons2013, June
Gabriel Charles

2. Gabriel.Charles@cea.fr CEA Saclay Baryons2013, 06/27/2013 1
New detectors for meson spectroscopy in hall-B at Jefferson Lab
1) Meson spectroscopy at CLAS12
2) Feasibility
3) Detector development and time schedule
De Marco :
CEA Saclay Baryons2013, 06/27/

3. Gabriel.Charles@cea.fr CEA Saclay Baryons2013, 06/27/2013 2
Why meson spectroscopy ?
Meson spectroscopy at CLAS12
In the quark model, quantum numbers of mesons are constrained :
Total angular momentum J : |L-S|<J<L+S
Parity P = (−1) 𝐿+1
Charge conjugation C = (−1) 𝐿+𝑆
where L and S are respectively the orbital angular momentum and the spin
States for L=0,1,2
Forbidden states ( 𝟎 −− , 𝟎 +− , 𝟏 −+ ...) are called exotic mesons. They can be glueballs, tetraquarks, a meson composed of two quarks and one gluon ...
The discovery of one these states would give a strong proof of the existence of other quark-gluon configurations.
The MesonEx collaboration has proposed to perform meson spectroscopy at CLAS12.
CEA Saclay Baryons2013, 06/27/

4. Gabriel.Charles@cea.fr CEA Saclay Baryons2013, 06/27/2013 3
Jefferson Lab, Newport News, Virginia
Meson spectroscopy at CLAS12
About the Hall B :
Started to take data in 1996
Around 160 collaborators in 12 countries from more than 40 different institutions
Focused on understanding nucleon structure
Hall A
Hall B
Hall C
Main physics focus of the Hall B :
What is the longitudinal and transverse structure of the hadron ?
What is the 3D structure of the hadrons ?
What is the hadronic spectra ?
Hadrons and cold nuclear matter
About the accelerator :
Two linear accelerators connected by recirculation arcs
Continuous electron beam
Upgraded very soon to deliver a 12 GeV electron beam at a luminosity of 𝑐𝑚 −2 𝑠 −1
CEA Saclay Baryons2013, 06/27/

5. Meson spectroscopy at CLAS12
Fixed target experiment
11 GeV continuous electron beam
liquid hydrogen target
4𝜋 detectors
good particule identification and energy resolution
Spectropscopy will use quasi-real photons as a probe.
Something different than pions for complementarity. For the moment kaons can be detected only by CLAS12, Hall D they have recently proposed something but it’s tricky.
As 𝑄 2 = 4EE’ 𝑠𝑖𝑛 2 (θ/2), electron at low angles must be detected.
new detectors at low angles are required
Example of studied reactions
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6. Gabriel.Charles@cea.fr CEA Saclay Baryons2013, 06/27/2013 5
Forward Tagger
Meson spectroscopy at CLAS12
Electromagnetic calorimeter
The Forward Tagger is 1.8 m away from the target. It aims to reconstruct the scattered electron between 2.5° and 4.5°.
Hodoscope
Micromegas tracker
Three new detectors will be added to the Hall B :
Electromagnetic calorimeter to reconstruct the energy of the electron
Hodoscope to differenciate photons and electrons
Micromegas tracker to determine the space variables of the electron
The Forward Tagger has been implemented to Gemc and a full analysis performed.
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7. Missing mass reconstruction
Simulations
Feasibility
Full reconstruction of a 3𝜋 reaction with the software framework of CLAS12 has been performed.
Acceptance
Missing mass reconstruction
Fast MC simulations
Gemc
Good agreement between fast Monte Carlo and realistic simulations
Excellent differenciation of 3𝜋 from 4𝜋 events
X mass resolution is around 10 MeV/c².
+ PWA to determine the quantum numbers
Experiment has been approved with 118 days of beam time.
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8. Detector developpment
Calorimeter
Detector developpment
APD
LED
The main elements of the calorimeter are :
a matrix of 332 crystals
each crstal is made of 𝑃𝑏𝑊𝑂 4 and has a rectangular shape of 15 x 15 x 200 𝑐𝑚 3
cooling system
APDs and pre-amplifiers
amplifier
crystal
downstream peek support
Momentum resolution from simulations
Tooling for crystal assembly
lead tungstate
Resolution is about 3.5 % from 2 to 4.5 GeV/c and 2 % at 0.5 GeV/c
CEA Saclay Baryons2013, 06/27/

9. Photon misidentification
Hodoscope
Detector developpment
The main elements of the hodoscope are :
two layers of plastic scintillators (Eljen-204) to minimise photon mis-ID
The first layer is 7 mm thick and the second 15 mm thick
WLS fibers
silicon PM
Time resolution
(from simulations)
Photon misidentification
(from simulations)
Recent and on-going work :
design of the fiber holder
fiber protection
fiber connector to the SiPM
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10. Gabriel.Charles@cea.fr CEA Saclay Baryons2013, 06/27/2013 9
Micromegas tracker
Detector developpment
The main elements of the tracker are :
two layers of two Micromegas detectors
each detector has an internal radius of 67 mm and an external radius of 142 mm
a dedicated electronics for the 3,600 channels
signal cables of about 1 m
Angular resolutions
(from simulations)
The detector is very similar to the Micromegas developped by the CEA Saclay for the Forward Micromegas Tracker (FMT). Prototypes for the FMT have already been succefully tested and a prototype for the Forward Tagger will be tested during the summer.
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11. Gabriel.Charles@cea.fr CEA Saclay Baryons2013, 06/27/2013 10
Mechanical design
Detector developpment
95 %
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12. Gabriel.Charles@cea.fr CEA Saclay Baryons2013, 06/27/2013 11
Time schedule
Detector developpment
Installation maybe be delayed due to funding issues.
CEA Saclay Baryons2013, 06/27/