The Forward Tagger facility for low Q 2 experiments at Jefferson - - PowerPoint PPT Presentation

MENU 2013 –Rome, 2/10/2013

The Forward Tagger facility for low Q2 experiments at Jefferson Laboratory

• A. Celentano

INFN-Genova

MENU 2013 –Rome, 2/10/2013

Outline

• The low Q2 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

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Photo-production program with quasi-real photons: low Q2 electron scattering

• Final state hadrons measured with the

CLAS12 detector

• Low-angle scattered electron measured with the

new Forward Tagger facility

Forward Tagger

Low Q2 experiments with CLAS12

Main physical motivation: Spectroscopy

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Low Q2 experiments with CLAS12

Meson spectroscopy: standard PWA on H target and spectroscopy on He4 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 quantum numbers No spin-fip for exotic quantum number

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Low Q2 electron scattering: kinematics

Kinematic variables: Virtual photon polarization, defined event by event: Q2 vs Eγ εΤ vs Eγ

Transverse linear polarization Longitudinal polarization

MENU 2013 –Rome, 2/10/2013 V.M. Budnev, et al., Physics Reports, Volume 15, Issue 4, 1975

Low Q2 electron scattering is competitive and complementary to real photo-production. Equivalent photon-flux approximation: In the Forward Tagger kinematic range:

✔ Luminosity:1035 cm-2 s-1 ✔ σΤΟΤ

γ ∼ 100 µbarn

Expected event rate: 7 kHz Equivalent photon flux:

✔ On a 40 cm long LH2 target

Low Q2 electron scattering: equivalent photon flux

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Low Q2 electron scattering: examples

• ZEUS:

<Q2> ~ 5 10-5 GeV2 HERA e- / p collider

• COMPASS:

<Q2> ~ 10-1 GeV2 160 GeV/c µ- beam on 6LiD 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.

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Continuous Electron Beam Accelerator Facility

• E = 0.75 – 6 GeV
• Imax = 100 µA - 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.

JLab @ 6 GeV

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JLab @ 12 GeV

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The CLAS12 detector in Hall B

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)

High acceptance (~4π) detector, designed to work @ luminosity 1035 cm-2 s-1

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The Forward Tagger Facility

Forward Tagger design characteristics

3 Components :

PbWO4 calorimeter: measure the energy of scattered electrons with few % resolution. Scintillation hodoscope: distinguish photons from electrons. Micromegas tracker: determine the electron scattering plane.

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The Forward Tagger Facility

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FT rates and backgrounds

FT-Cal rad dose @ nominal CLAS12 luminosity Rad/h

• Signal rate ~ 1 kHz
• 1 e- detected in FT in coincidence with an hadronic event

in CLAS12

• 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 Signal and background rates @ CLAS12 nominal luminosity 1035 cm-2 s-1

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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

Recoil electron Virtual photon Virtual photon energy resolution increment due to 1/E factor, E=11 GeV

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The FT-Cal

Foreseen energy resolution

Design:

• 332 channels
• PbWO4 crystals, 15x15x200 mm3
• Large Area APD readout (10x10 mm2)
• Custom FEE
• 0° operating temperature

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

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FT-Cal crystals

FT-Cal crystals properties measured with ACCOS facility @ CERN

• Dimensions
• Light yield
• Optical transmission
• Radiation hardness

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FT-Cal APDs

G=1

FT-Cal APDs characterized with a custom- designed facility, in the temperature range 0° – 25°

• Gain vs Vb and T
• Dark current vs Vb and T
• Stability

Gain measured with “DC-technique”: measure I vs Vb under constant illumination, subtract dark current, and re-normalize to G=1 (Vb < 50 V)

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FT-Cal FEE and REO

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

FEE electronics: custom amplifier circuit

• Gain ~ 1800
• Noise RMS ~ 5 mV (ENE ~ 5 MeV)
• Input impedance matched to

APD capacitance

• Bandwidth ~ 20 MHz

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The FT-Hodo

Design:

• Plastic Scintillator tiles: 2 layers with 116

elements each, 30x30 and 15x15 mm2

• Readout based on WLS fibers

coupled to Hamamatsu 3x3 mm2 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

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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

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Amplitude Charge

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

Nominal gain

dG / G ~ 10

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Amplitude Charge

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

Nominal gain

dG / G ~ 10

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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

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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 PbWO4 matrix, each

15x15x200 mm3

• Large Area APD readout (10x10mm2)
• Copper shield for thermal stabilization
• Custom motherboard for signal, LV,

HV distribution

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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
• Cal. constants ratio

Cosmic rays 500 MeV e- beam

The measure was aimed to:

• Demonstrate operational principles
• Test the detector performances
• Provided a first estimate of cal. Constants
• Tune MC simulations

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FT-Cal prototype test @ LNF BTF

DAΦNE LINAC BTF

The BTF test beam is obtained attenuating the primary LINAC electron beam delivered to the DAFNE machine.

• Variable intensity:

1 - 105 e-/bunch

• Variable electron energy: 25 – 500 MeV

BTF beam properties:

MENU 2013 –Rome, 2/10/2013

FT-Cal prototype test @ LNF BTF

DAΦNE LINAC BTF

The BTF test beam is obtained attenuating the primary LINAC electron beam delivered to the DAFNE machine.

• Variable intensity:

1 - 105 e-/bunch

• Variable electron energy: 25 – 500 MeV

BTF beam properties:

DETECTOR BEAM

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FT-Cal prototype test @ LNF BTF

FT-CAL BTF test results

• Excellent linearity up to 4 GeV
• Good

agreement

• f

the experimental energy resolution with MC results for Ee>1.5 GeV

• Low-energy MC-underestimated

noise contribution Measure @0°C

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Conclusions

• Low Q2 electron scattering provides a high-flux of linearly polarized, quasi-real

photons: competitive and complementary to “real” photo-production experiments.

• The Forward Tagger Facility in Hall B at Jefferson Laboratory is designed to

perform quasi-real photo-production experiments. Main physical motivation: spectroscopy

• The Forward Tagger is made of 3 sub-detectors: FT-Cal, FT-Hodo, FT-Trck
• Detector R&D completed
• Design finalized
• Construction in progress
• Ready to take data with the first CLAS12 beam!
• Tests from 16-channel FT-Cal prototype, both with cosmic rays and e- beam,

confirmed the detector operational principles, provided a first measure of the foreseen performances, and was used to tune MC parameters.

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Backup slides

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Neglect q-dependent terms due to EM current conservation:

Resulting amplitude is the product of two terms:

• Emission of a quasi-real photon (m ~ 0) by the electron
• Photoproduction on the proton of the final state pX

Photo-production amplitudes in the low Q2 framework

Reaction amplitude in the OPE approximation: Completeness relation for virtual-photon polarization:

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CLAS12 design specifications

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Forward Tagger integration in CLAS12