The Forward Tagger facility for low Q 2 experiments at Jefferson Laboratory A. Celentano INFN-Genova MENU 2013 –Rome, 2/10/2013
Outline ● The low Q 2 electron scattering experimental technique: kinematics, polarization, and physical motivations ● The Forward Tagger Facility in Hall B at Jefferson Laboratory ● Design overview ● Foreseen performances ● Rates and backgrounds ● The Forward Tagger components: design and tests ● FT-Cal ● FT-Hodo ● FT-Trck ● The FT-Cal prototype MENU 2013 –Rome, 2/10/2013
Low Q 2 experiments with CLAS12 Photo-production program with quasi-real photons: low Q 2 electron scattering ● Final state hadrons measured with the CLAS12 detector ● Low-angle scattered electron measured with the new Forward Tagger facility Main physical motivation: Spectroscopy Forward Tagger MENU 2013 –Rome, 2/10/2013
Low Q 2 experiments with CLAS12 Meson spectroscopy: standard PWA on H target and spectroscopy on He 4 and other gas targets ● Photoproduction: exotic quantum numbers are more likely produced by S=1 probe ● Linear polarization: acts like a filter to disentangle the production mechanisms and suppress backgrounds ● Production rate: for exotics is expected to be comparable as for regular mesons Need spin-fip for exotic No spin-fip for exotic quantum numbers quantum number MENU 2013 –Rome, 2/10/2013
Low Q 2 electron scattering: kinematics Kinematic variables: Virtual photon polarization, defined event by event: Transverse linear polarization Longitudinal polarization Q 2 vs E γ ε Τ vs E γ MENU 2013 –Rome, 2/10/2013
Low Q 2 electron scattering: equivalent photon flux Equivalent photon-flux approximation: In the Forward Tagger kinematic range: ✔ Luminosity:10 35 cm -2 s -1 γ ∼ 100 µ barn ✔ σ ΤΟΤ Expected event rate: 7 kHz Equivalent photon flux: ✔ On a 40 cm long LH 2 target Low Q 2 electron scattering is competitive and complementary to real photo-production. V.M. Budnev, et al., Physics Reports, Volume 15, Issue 4, 1975 MENU 2013 –Rome, 2/10/2013
Low Q 2 electron scattering: examples ● ZEUS: <Q 2 > ~ 5 10 -5 GeV 2 HERA e - / p collider ● COMPASS: <Q 2 > ~ 10 -1 GeV 2 160 GeV/c µ - beam on 6 LiD target ● CLAS: ● 6 GeV / c electron beam on proton target ● Events with 1 proton, 4 γ , 1 missing e − at ~ 0 deg selected ● 4 γ invariant mass measured Mass spectra show evidence of low cross-section mesons expected in these photo-production channel. MENU 2013 –Rome, 2/10/2013
JLab @ 6 GeV C ontinuous E lectron B eam A ccelerator F acility ● E = 0.75 – 6 GeV ● Imax = 100 µ A - Hall A, C ● Imax = 800 nA – Hall B ● Duty Cycle ~ 100% ● σ (E)/E ~ 2.5 x 10 -5 ● Polarization ~ 80% Beam is delivered simultaneously to the 3 experimental halls. MENU 2013 –Rome, 2/10/2013
JLab @ 12 GeV MENU 2013 –Rome, 2/10/2013
The CLAS12 detector in Hall B High acceptance (~4 π ) detector, designed to work @ luminosity 10 35 cm -2 s -1 Forward Detector (5°< θ < 35°) : - Toroidal magnet (TORUS) - High threshold Cherenkov counter (HTCC) - Drift chammbers (Region 1, 2, 3) - Low threshold Cherenkov counter (LTCC) - TOF counters (FTOF) - EM calorimeter (EC) Central Detector (θ > 35°) : - Solenoidal field (SOLENOID) - Silicon vertex tracker + Micromegas tracker (SVT) - TOF counters (CTOF) - Neutron detector (CND) MENU 2013 –Rome, 2/10/2013
The Forward Tagger Facility 3 Components : PbWO 4 calorimeter: measure the energy of scattered electrons with few % resolution. Scintillation hodoscope: distinguish photons from electrons. Micromegas tracker: determine the electron scattering plane. Forward Tagger design characteristics MENU 2013 –Rome, 2/10/2013
The Forward Tagger Facility MENU 2013 –Rome, 2/10/2013
FT rates and backgrounds Signal and background rates @ CLAS12 nominal FT-Cal rad dose @ nominal luminosity 10 35 cm -2 s -1 CLAS12 luminosity ● Signal rate ~ 1 kHz ● 1 e - detected in FT in coincidence with an hadronic event in CLAS12 Rad/h ● Total background rate ~ 100 MHz ● Low energy (< MeV) particles, e - and γ ● In the FT energy range (0.5 – 4.5 GeV) ~180 kHz ● Highly suppressed by tight time coincidence with CLAS12 MENU 2013 –Rome, 2/10/2013
FT foreseen (MC) performances ● FT energy resolution has been evaluated trough detailed MC simulations, including threshold and reconstruction effects ● Crystals shape and dimensions optimized to maximize the energy resolution Virtual photon energy resolution increment due to 1/E factor, E=11 GeV Recoil Virtual electron photon MENU 2013 –Rome, 2/10/2013
The FT-Cal Forward Tagger Facility “core” component. Requirements: ● Strong radiation hardness ● Good Energy and Timing resolution ● Small radiation length and Moliere Radius ● Compatible with high magnetic field Foreseen energy resolution Design: ● 332 channels ● PbWO 4 crystals, 15x15x200 mm 3 ● Large Area APD readout (10x10 mm 2) ● Custom FEE ● 0° operating temperature MENU 2013 –Rome, 2/10/2013
FT-Cal crystals FT-Cal crystals properties measured with ACCOS facility @ CERN ● Dimensions ● Light yield ● Optical transmission ● Radiation hardness MENU 2013 –Rome, 2/10/2013
FT-Cal APDs FT-Cal APDs characterized with a custom- designed facility, in the temperature range 0° – 25° ● Gain vs V b and T G=1 ● Dark current vs V b and T ● Stability Gain measured with “DC-technique”: measure I vs V b under constant illumination, subtract dark current, and re-normalize to G=1 (V b < 50 V) MENU 2013 –Rome, 2/10/2013
FT-Cal FEE and REO FEE electronics: custom amplifier circuit ● Gain ~ 1800 ● Noise RMS ~ 5 mV (ENE ~ 5 MeV) ● Input impedance matched to APD capacitance ● Bandwidth ~ 20 MHz Readout board: JLab-made FADC ● Employed for CLAS12 fast detectors ● 250 Msamples/s ● 12 bit resolution ● 2 Volts maximum input signal ● 16 channels ● VXS extension ● Online signal elaboration trough on-board FPGA ● Energy ● Timing ● Evolute trigger capabilities MENU 2013 –Rome, 2/10/2013
The FT-Hodo Design: ● Plastic Scintillator tiles: 2 layers with 116 elements each, 30x30 and 15x15 mm 2 ● Readout based on WLS fibers coupled to Hamamatsu 3x3 mm 2 SiPMs ● Custom FEE with single-channel tunable gain ● 1 ns foreseen timing resolution for precise coincidence with FT-Cal Detector design supported by dedicated GEANT4 simulations of its optical response 20 detected photons expected for MIP MENU 2013 –Rome, 2/10/2013
FT-Hodo FEE Custom electronics developed for FT-Hodo SiPM readout ● Modular design ● 16 channels mezzanine cards connected to 2 8-channels amplifier boards ● Up to 15 mezzanines in the same system (240 channels) ● 1 controller card ● Custom crate, VME-9U mechanical compliant ● Single channel amplifier: transimpedance configuration ● 2 stage amplifier ● Gain ~ 660 ● ENC ~ 0.5 phe ● Common SiPM HV for groups of 8 ● Individual HV tunable within + 2 V for fine gain tuning MENU 2013 –Rome, 2/10/2013
FT-Hodo FEE Results obtained with a laser test-bench setup: ● 200 ps width laser bunches, with variable intensity and frequency ● Signal acquired with digital oscilloscope ● Trigger from the laser sync signal ✔ Single phe peaks well resolved and separated from background ✔ SiPM gain tunable within factor ~10 wrt nominal working point dG / G ~ 10 Nominal gain Amplitude Charge MENU 2013 –Rome, 2/10/2013
FT-Hodo FEE Results obtained with a laser test-bench setup: ● 200 ps width laser bunches, with variable intensity and frequency ● Signal acquired with digital oscilloscope ● Trigger from the laser sync signal ✔ Single phe peaks well resolved and separated from background ✔ SiPM gain tunable within factor ~10 wrt nominal working point dG / G ~ 10 Nominal gain Amplitude Charge MENU 2013 –Rome, 2/10/2013
The FT-Tracker Design: ● Two double layers of bi-face bulk Micromegas with 500 μm strip readout ● Custom FE electronics: 3392 channels, based on DREAM ASIC ● Same technology adopted for CLAS12 central tracker MENU 2013 –Rome, 2/10/2013
FT-Cal prototype 16 channel FT-Cal prototype: ● Measure energy resolution and linearity between few MeV (cosmic rays) to 4 GeV (e - beam test) ● Measure the energy resolution temperature dependence ● Measure the electronic noise in realistic conditions ● Validate MonteCarlo simulations Design: ● 4x4 matrix of PbWO 4 matrix, each 15x15x200 mm 3 ● Large Area APD readout (10x10mm 2 ) ● Copper shield for thermal stabilization ● Custom motherboard for signal, LV, HV distribution MENU 2013 –Rome, 2/10/2013
FT-Cal prototype test with cosmics ray First FT-proto tests performed with cosmic- rays setup ● Detector placed in between 3 plastic scintillators counters ● Scintillators hits positions provide cosmic track ● Trigger given by the 3 counters coincidence The measure was aimed to: ● Demonstrate operational principles ● Test the detector performances ● Provided a first estimate of cal. Constants ● Tune MC simulations Cal. constants ratio Cosmic rays 500 MeV e - beam MENU 2013 –Rome, 2/10/2013
FT-Cal prototype test @ LNF BTF The BTF test beam is obtained attenuating the primary LINAC electron beam delivered to the DA Φ NE DAFNE machine. ● Variable intensity: 1 - 10 5 e - /bunch BTF ● Variable electron energy: 25 – 500 MeV LINAC BTF beam properties: MENU 2013 –Rome, 2/10/2013
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