Imaging crystals with TKR Benoît Lott (CENBG)

Imaging the crystals The information from the TKR can help investigate the CAL response in different ways by: mapping out the response as a function of the longitudinal and transverse positions of the particle trajectory within the crystal: “images”. cross-check of the light tapering (1D instead of 2D); non uniformity in response (see next talk); possible local flaws. enabling the determination of the trigger efficiency for the CAL; checking the trajectories as determined from the CAL; determining that the particle will leave significant “direct” energy in the photodiodes; - determining valid hits for the calibration: on-orbit calibration with heavy ions.

CRYSTAL IMAGING: Plot the average measured energy as a function of trajectory position within the crystal. The trajectory determined by the TKR must be extrapolated into the CAL and only “valid” hits are kept. Trajectories must intersect the top and bottom faces of a crystal (no crossing of vertical sides). At most 1 valid hit per layer.

The real question is how accurate is the extrapolation, as two adverse effects come into play: - the finite resolution of the tracker, the effect being amplified by the lever arm between the Tkr layers and CAL; - multiple scattering within the Tkr and CAL. Tracker recon must provide the best estimate of the actual trajectory taking two important facts into account: 1) the incident particle is a muon, not a gamma-ray; The energy deposited in the CAL (~100 MeV) does not reflect the kinetic energy. jobOptions.txt: TkrInitSvc.SetMinEnergy= 2000 MeV; TkrIter.Members={};

2) the final trajectory (i 2) the final trajectory (i.e leaving the tracker) is of interest here, not the initial one. The track reconstruction algorithm was designed to determine the initial direction of photons. It makes use of the information available as close as possible to the conversion point, to avoid the adverse effect of multiple scattering. For the present purpose, it is more sensible to use the information provided by the bottom trays: end-of-track parameters (CalValTools or xxx_recon.root) Thanks to Bill and Leon for their help.

Trajectory-extrapolation algorithm Simple root macro, using modified (thanks, Anders) svac ntuple: VtxX0,…,VtxXDir,… (start of track) Tkr1EndPos[0],…, Tkr1EndDir[0],…(end of track) CsILength=326 mm

« lTkr – ltrue » distributions position evaluated at mid-height of first CsI layer blue: start of track red: end of track lTkr – ltrue (mm) ltrue= true (MC) position in firts cal layer

Multiple scattering at play (1) position evaluated at mid-height of first CsI layer for a pencil beam l_Tkr_top 4 GeV l l_Tkr_bottom ltrue position with respect to launch position (mm) ltrue= actual (MC) position

Multiple scattering at play (2) The effect of multiple scattering in the tracker can be partly corrected for by using the bottom parameters. l_asym= actual (MC) position at first calorimeter layer

Position resolution 4 GeV muon: sl=10.5 mm 500 MeV start of track end of track muon: sl=10.5 mm 500 MeV start of track end of track

Muon energy distribution The tracker can help efficiently discard low-energy muons, associated with large multiple scattering.

Position resolution start of track end of track Lattest Svac tuple

Deposited-energy distributions 4M evts: 219041 triggering evts, 303191 valid hits valid hits total <E>=13.60 MeV 0.2% of valid hits have no energy. « doubles » <E>=21.87 MeV 2.9% (8791/303191) of hits have more than 2 MeV in a neighboring log. For these hits, the deposited energy in the « selected » log is much higher than average: emission of d electrons !

Images width (mm) length (mm) width (mm) low high light tapering

“Valid events” for calibration These values correspond to a period of 4000 s (55 Hz at the trigger level). top bottom tower 8 tower 9

How is it going to look like in real data? asym lTkr – lasym (mm)

Gsi data: protons at 1.7 GeV X layers Y layers Simulation results The width of the distribution of the residues of a linear fit is proportional to the resolution s: 0.55 s for the outer layers, 0.83 s for fhe inner layers (simulations). X layers: s = 10 mm Y layers: s = 7 mm

To be continued… A note summarizing these results will be written up with David Smith (SLAC). This work will be extended with David, to apply it to real data. The GAM( Montpellier) group will join us on some particular studies (comparison between trajectories determined by Tkr and CAL) .

MIPs in Photodiodes Same pre-amps, amps, adc, daq as for Ganil, GSI, and CERN (testbeam CsI stack at left…) This is the outline of the talk: I will briefly remind you of the design of the LAT calorimeter, give its current status, show a few slides on the construction Process, the present the status of the flight manufacturing. I then present the milestones along the way towards the delivery of the subsystem. Then I talk about the identified threats to maintaining schedule and cost. Smaller (top) scintillator: 2cm x 2cm We also used: A 2cm long “CDE” A “naked” photodiode (thanks to G. Bogaert for providing the latter)

Muons in a naked photodiode -- data In the CDE we said 1 MIP ~ 12 MeV ~ 1300 dc ~ 1.3 volts For the photodiode without CsI, we see ~250 dc Zoooooom…. ( 350-100=250 )