Dan Watts, Derek Glazier, Jamie Fleming University of Edinburgh

The hodoscope for the forward taggerFT-HODO

Outline

• Outline general requirements

• Present first prototype design

• Outline how we arrived at this – present G4 design studies

• Funding

General considerations for FT-Hodo

• Primary task – separate charged/uncharged events in the forward tagger (dominantly electron-photon)

• Charged event identification - hit in FT-HODO correlated with calorimeter → Need high efficiency for MIPs. → Sufficient spatial resolution minimise false coincidences → Desirable to have timing resolution ~FT-Cal, coincidence time, quality info for trigger decisions?

• Charged event misidentification → Need to minimise photons misidentified as electrons. g conversion in FT-HODO, splashback from calorimeter.

Preliminary design for layer of FT-Veto

• Segmented array of plastic scintillator tiles

• Light readout by embedded WLS fibres

• WLS fibres readout by SiPMTs

• 2 layers desirable

Scint tile + WLS fibres

• Will reduce size of scint tile c.f previous CLAS hodo

→ Increases the light density, more photons captured → Tighter position coincidence FT-Hodo & FT-Cal

15mmx`5mm – “P15” tile30mmx30mm – “P30” tile

• Also expoit multiple WLSF’s per tile - 2 for P15 and 4 for P30 → Increase # Photons at SiPMT

• Fibres will be UV glued into grooves in scintillator

Routing of WLSF’s

• Scintillator tiles mounted onto thin rohacell holding sheet

• Routing of WLS fibres around shaped plastic former

• Fed around the back of the calorimeter to SiPMT and readout boards.

• Alternative - locating readout boards outside FT-Cal barrel?

Area ~100mm2

Per layer

Readout boards

• Use modified version of IC boards used for inner calorimeter

• Produced by Orsay with modifications suggested by Genoa

SiPMTs

Hamamtsu - s10362-333x3mm2 active area

• Similar designs have been operated successfully. CLAS, TAPS@MAMI, ...

•

• Geant4 full simulation developed. Model light production and collection in tile+WLS fibre parameters – model earlier detectors to check of validity of simulation

• → Then use simulation to optimise tile geometry, #WLSF’s, . for new design

Other tile+WLS designs

Geant 4 simulations

• 2 separate simulations carried out

i) Simulation of single element – full response. energy deposition, light production, propagation. Use scint, WLSF parameters established in previous measurements.

ii) Full reconstruct. FT-HODO & FT-Cal – investigate joint response, develop rough analysis algorithms

Single element simulation

• Single scintillator tile wrapped in aluminium foil (reflectivity=85%)

• WLS fibre embedded in square grooves. Surrounded by optical gease

• Fibre multiclad – core of polystyrene, surrunded by inner layer of PMMA outer layer of fluoroacrylic (both 3% of polyst radius)

• Materials given realistic photon absorption and emission properties – taken from those extracted for previous detectors. No free parameters.

Geant 4 simulations • Simulate 3.8cm x 3.8cm x 1cm scintillator tile

• One straight fibre – diameter 1mm, decay time 7ns coupled to ` ` SiPMTwith QE of 50%

• Minimum ionising particle (Electron) tracked through tile – optical photons tracked to the detector.

Previous detector reported MIP gave 18 photoelectrons

Fibre bends • Preliminary design requires at least 2 bends of the WLS fibre

• Need to assess the effect of bending the fibre

For a bend radius of 3cm 90% of photons are transmitted

Previous systems indicate 3-4cm bend radius will not significantly damage the fibres

For all following results - photon yield reduced at SiPMT by factor 0.8 to account for 2 bends and additional leakage.

Relationship between tile geometry and No. g’s at SiPMT

Tile thickness cm

• Doubling # fibres gives less than factor 2 increase• Larger tile width -> smaller # photons (more than factor 2)• Halving thickness-> smaller # photons (more than factor 2)

P15 tile P30 tileP30 tile

Tile thickness cm

Timing resolutions

Main factor in determining timing resolution -># photonsSimulations with faster Bicron fibres (3.5ns rather than 7.1ns) improve by 20%Sub nanosecond resolution possible for most configurations

Tile thickness cm Tile thickness cm

P15 tile P30 tile

Geant4 simulation of Ft-HODO and FT-Cal

Transverse distance between hodo and cal hit (mm)

Transverse distance between hodo and cal hit (mm) Transverse distance between hodo and cal hit (mm)

cou

nts

cou

nts

Incident electrons Incident photons

Degree of photon misidentification for various designs

How much will it cost?

Funding available at Edinburgh

Approved funding Euro Purpose stated

STFC (UK) New Edinburgh rolling grant

20,752 Buy scintillator tiles, machining, wavelength shifting fibres

EU (hardEx2) 10,000 Forward tagger veto prototyping

Cover shortfall from STFC (UK) current Edinburgh grant

~20,000 Edinburgh polarimeter at MAMI (but common equipment requirements. ADCs,TDCs)

Appears viable to build one layer with money available. New grant also funds Edinburgh RA (Derek Glazier) through to 2015?

Potential to apply for cost of second layer (and recoup “shortfall” costs) in new Project grant proposal - submission to STFC early 2012 (joint with Glasgow)

Summary and outlook

• First prototype design for FT-Hodo produced – guided by insights from G4 simulations

• Test tiles+WLSFs assembled. Test with Orsay board+ Hamamtsu SiPMT modules in lab.

Include modules in future JLab test?

• Funding for one layer seems coverable from current Edinburgh funds. Future UK funding request (early 2012) for 2nd layer

Environment of FT-Hodo

• High magnetic field

• Constrained space

Environment

• High magnetic field – need resistant light readout devices

• Space constrained

Decay gamma detection with electron scattering - Illinois

Decay gamma detection with electron scattering - Illinois

Decay gamma detection with electron scattering - Illinois

Decay gamma detection with electron scattering - Illinois

Decay gamma detection with electron scattering - Illinois

Decay gamma detection with electron scattering - Illinois

Decay gamma detection with electron scattering - Illinois

Decay gamma detection with electron scattering - Illinois

The simulation WITH the Moller shield (not yet optimized) gives the following distributions: top left: the total energy deposited is reduce by a factor 3.8 with respect to the condition without Moller shield. This corresponds to about 14 rad/h on the whole calorimeter. bottom right: the maximum energy deposited in a single crystal is now about 0.6 MeV/ns. This occurs now for the second circle of crystals since the first is partially shielded by the Moller cone. This value corresponds to a dose of about 0.98 rad/h. The third circle of crystals has a dose of about 0.15-0.3 rad/h and the rest of the crystals have a dose of 0.02-0.1 rad/h

Possible crystals for CLAS12

• Phoswich design - good timing properties of LaBr to be combined with high stopping power, lower cost scintillators

• Being developed for Spiral – set up collaboration to share costs of crystals for use at JLAB

Count rate estimates: t-channel h production

N = ds/dW x dW x Luminosity x emeson x edgam

N = (1000x10-9)(10-24) x 0.015 x 4x1031 x 0.3 x 0.1

dW = 2p(1-cos(q))Take q =4: d =0.015W

Average cross section in range q=0-4 Is ~1000 nb/sr

Assuming decay gammaDetector coverage of Q=120-160o (20% of 4p)With 50% eff

Tagged rateN = ~1.5k day-1

Untagged rateN = ~15k day-1

~tagged virtual photon fluxassuming CLAS12 luminosity(1035 cm-2s-1

Prelim. calculations : Sherif , Hedayatipoor incl. t-channel amplitudes of Donnachie

Count rate estimates: t-channel f0 production

N = ds/dW x dW x Luminosity x emeson x edgam

N = (150x10-9)(10-24) x 0.015 x 4x1031 x 0.15 x 0.1

dW = 2p(1-cos(q))Take q =4: d =0.015W

Average cross section in range q=0-4 Is ~150 nb/sr

Assuming decay gammaDetector coverage of Q=120-160o

With 50% eff

Tagged rateN = ~120 day-1

Untagged rateN = ~1.2k day-1

~tagged virtual photon fluxassuming CLAS12 luminosity(1035 cm-2s-1

Expect low cross section. f0 production dominantly t-channel r exchange (T=1)Isoscalar transition suppresses dominant mechanism e.g A. Donnachie arXiv:0806.3698

Next steps:

Physics case will be further developed – more theoretical calculations

Full simulations with realistic event generator and background

Summary

First tests of LaBr/CsI phoswich

• Investigate phoswich: particle ID capabilities, timing etc. (In collaboration with Univ. York (UK). Plans for portable array for use at SPIRAL - shared use at JLAB ?

• Explore LaBr / hybrid modules alongside other crystal possibilities for forward calorimeter

• Grant request (approved but pending) - additional RA support and further money for prototype crystals

Future plans

12C12C(2+;4.4MeV)

• Coherent proposal 4He at JLAB: virtual photon tagger with TPC estimate ~60k hybrid mesons produced

• Incoherent

→ Rate not limited by TPC ~102 increase in g flux

→ No minimum limit on t

→ Will lose factor ~10 in cross section due to loss of coherence in amplitudes, form factor effects

Incoherent hybrid meson production

A. Donnachie arXiv. 0806. 3698(2008)

p1(1600)

p1(1400)

a2(1320)TPC detection limit

0.30.20.1 t(GeV/c2)

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100

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12C( ,g J/Y)12C

CoherentSum incoherentIncoherent 2+ level

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• As well as the Jp of the nuclear state the angular distribution of the nuclear decay photons tells you about the alignment of the residual nucleus

• Polar distribution wrt mom transfer gives sensitivity to the spin dependence of the production amplitude (next slide) (Tryasuchev and Kolchin Phys. At. Nuc. 70 827 (2007))

• Azimuthal distribution allows information on meson-nucleon interaction to be extracted. e.g. J/Y photoproduction from 12C (V.L. Korotkikh and N.I. Strakov, Yad. Phys. 37 1030 (1983)

Nuclear decay photons

• t-channel amplitudes of (Sandy Donnachie, Univ. Manchester, UK) being incorporated into model of nuclear photoproduction (Helmy Sherif, Univ. Alberta, Canada)

• First step - Plane wave calculations for t-channel eta production. Calculations for further channels e.g. ao, fo in progress

New calculations in progress

Detector issues – next steps

• Can LaBr readout be in a region where conventional PMTS could be used? – Depend on necessary solenoid, shielding etc

• Edinburgh group applied for R&D funds for LaBr and SenSL avalanche PMT readout and 1 year RA

•

Device would need upwards of ~60 crystals

Crystals should be ~10cm depth to give~80% photopeak efficiency up to 10 MeVSOLENOID

Nuclear decay Photon calorimeter

Detector issues – next steps

• Can LaBr readout be in a region where conventional PMTS could be used? – Depend on necessary solenoid, shielding etc

• Edinburgh group applied for R&D funds for LaBr and SenSL avalanche PMT readout and 1 year RA

•

Device would need upwards of ~60 crystals

Crystals should be ~10cm depth to give~80% photopeak efficiency up to 10 MeVSOLENOID

SOLENOID