26/10/04 Meeting1 M. Bonesini INFN Milano MICE TOF0, TOFI, TOFII status

26/10/04 Meeting2 Outline  Introduction  Considerations on scint. thickness  Considerations for PMT choice  Tests done at LASA  Tests for R4998 conventional PMTs  Tests for Hamamatsu fine-mesh PMTs  Conclusions

26/10/04 Meeting3 The environment The beamline design puts harder and harder requests on TOF stations Higher and higher particle rates (1 -> 3 MHz) Non-uniform magnetic fields Thinner and thinner scintillators (2 ->1 inch total thickness for TOF0, TOFI)

26/10/04 Meeting4 Proposed JUNE04A Layout (from T. Roberts) Moved, Thinner, TOF0 New Iron Shiel d (TOF1 and its iron shield are symmetrical with TOF2, except for the Diffuser) Pπ = 425 MeV/c Moved, Thinner, TOF1

26/10/04 Meeting5 Comparison of JUNE04 and Proposed JUNE04A AttributeJUNE04JUNE04A π momentum (B1)350 MeV/c425 MeV/c μ momentum (B2)250 MeV/c TOF0 positionDownstream of Q4Downstream of Q6 TOF1 PositionDownstream of Q8Downstream of Q9 TOF total thickness2 inches1 inch Upstream iron shieldNoneSame as downstream TOF0 to TOF1 distance8.5 meters7.8 meters [1] TOF0 Singles9.9 MHz3.8 MHz Good μ + rate350 ev/sec512 ev/sec Design Emittance6 π mm-rad [2] g4bl/ecalc9f emittance14.8 π mm-rad11.9 π mm-rad [1] π/μ/e discrimination in TOF1-TOF0 presented below. [2] Narrow-momentum beam, no multiple-scattering from TOF0 and TOF1, horizontal emittance much larger. Reasonably consistent with ecalc9 value.

26/10/04 Meeting6 Summary of Rates (from T. Roberts) DescriptionLAHETMARSGeant4 TOF TOF Tracker Tracker TOF Good μ Values are events per millisecond of Good Target and good RF. Good μ + = TargetDet & TOF0 & TOF1 & Tracker1 & Tracker2 & TOF2 & TOF1(μ + ) & TOF2(μ + )

26/10/04 Meeting7 Considerations on scintillator thickness Shown time resolution is FWHM vs scintillator thickness L Green/red lines from BC408; blue line is BC404 (faster) Data from MEG tests at BTF Proposed thin solution:  100 ps if all goes right (perfect detector calibration,...) Actual choice :  60 ps

26/10/04 Meeting8 Considerations for PMT choice 1. Rate capability (up to some MHz) 2. Good timing properties (TTS) 3. Sustain magnetic field ( about gauss for TOF0, about.2 T for TOF2) Tests at Lasa magnet test facility (end July 04, for 15 days) with Pavia MEG group to optimize choice (M.Bonesini, F.Strati INFN Milano, G.Baccaglioni,F.Broggi, G. Volpini INFN Milano –LASA, G. Cecchet, A. DeBari, R. Nardo’, R. Rossella INFN Pavia).

26/10/04 Meeting9 Problems for high resolution scintillator based TOF (  t < 100 ps)  pl dominated by geometrical dimensions  (L/N pe )  scint  ps (mainly connected with produced number of  ’s fast and scintillator characteristics, such as risetime)  PMT dominated by PMT TTS Additional problems in harsh environments: 1.B field (-> fine mesh PMTs) 2.High particle rates (tuning of operation HV for PMTs)

26/10/04 Meeting10 Tests done at LASA Laser source to simulate MIP signal (about 300 p.e.) : fast PLP-10 laser on loan from Hamamatsu Italia Laser sync out triggers VME based acquisition (TDC + QADC) 5000 events for each data point : different PMTs (fine-mesh vs mod R4998), different B- field, different inclination vs B field axis (  ), diff laser rate to simulate incoming particle rates

26/10/04 Meeting11 Rate capabilities of PMTs To have a linear signal the mean average anode current (100  A for R4998, 10  A for R7761 or R5505, 100  A for R5924 fine- mesh PMTs) must not be exceeded -> damage to dynodes... shorter PMT lifetime This gives a theoretical rate capability of: 267 KHZ with R KHZ with R7761,R5505 BUT !!! Divider can be modified only for R4998 (going up to 1.67 MHZ)

26/10/04 Meeting12 Test magnet at LASA (B up to 1.2T) PMT under test 1.B field up to 1.2 T 2.Free space 12 cm in height

26/10/04 Meeting13 Used laser light source Light source: Hamamatsu fast laser (  405 nm, FWHM 60 ps, 250 mW peak power) PLP-10 Optical system: x,y,z flexure movement to inject light into a CERAM/OPTEC multimode fiber (spread 14 ps/m) PMT under test Laser light Signal ~ 300 p.e. to reproduce a MIP as measured with an OPHIR Laser powermeter

26/10/04 Meeting14 1. R4998 PMT rate studies R4998 with modified divider circuit: booster for last dynodes Nominal: up to 1.5 MHz

26/10/04 Meeting15 R4998 with modified divider (booster for last dynodes) + mu-metal shielding One specimen on loan in Jly 2004 for tests

26/10/04 Meeting16 Gain in magnetic field for R4998 Y x Z

26/10/04 Meeting17 Timimg properties of R4998 in B field

26/10/04 Meeting18 Rate effects studies for R4998 done with available R4998 with modified divider from Hamamatsu (booster on last dynodes) Light signal corresponds to ~ 300 p.e. 1 MHz

26/10/04 Meeting19 Fine Mesh Photomultiplier Tubes Secondary electrons accelerated parallel to the B-field. Gain with no field: 5 x 10 5 – 10 7 With B=1.0 Tesla: 2 x x 10 5 Prompt risetime and good TTS Manufactured by Hamamatsu Photonics R5505R7761R5924 Tube diameter1”1.5”2 “ No. Of stages1519 Q.E.at peak Gain (B=0 T)5.0 x x 10 7 Gain (B= 1 T)1.8 x x x 10 5 Risetime (ns) TTS (ns)

26/10/04 Meeting20 Gain in B field (various orientations) B (T) G(T)/G(0) 2” 1.5”1” B(T) G(B)/G(B=0T ) PMT axis B   > critical angle

26/10/04 Meeting21

26/10/04 Meeting22 Pulse height resolution in B field 1” 2”

26/10/04 Meeting23 Rate effects (as a function of HV) rate capability is limited by maximum anode mean current (tipically 0.1mA for a 2” R5924 PMT) this is the ONLY relevant point, e.g. in B field if gain is lower by a factor F rate capability increases by 1/F with very high particle rates: try to reduce mean current HV increases

26/10/04 Meeting24 Rate effect as function of B field B field increases

26/10/04 Meeting25 Rate effects as function of B field B field increases

26/10/04 Meeting26 Timing studies

26/10/04 Meeting27 Time resolution

26/10/04 Meeting28 Time resolution vs Npe A /  N pe  c The number of p.e. is deduced from the PMT measured gain directly ( Q ADC = N pe e G )

26/10/04 Meeting29 Conclusions to have good TOF resolutions with high rate and high B fields one can try to optimize PMT working point (setting a proper HV + N pe ), but we have to study  t as a function of rate in B field (this study has been done only at fixed rate) for TOF2 it is not worthwhile to reduce too much the B field (in the range.2-.5 T it is OK) inclination angle  is a critical parameter, even F.M. PMTs do not work in very small B field if  > critical value (B fields maps are an essential ingredient to design TOF !!!!)  it may imply lightguides of quite complicate design to have  <  c. for moderate B fields increase shielding for TOF0,TOF1 Thickness of TOF detectors can be optimized (but You loose N pe )