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Downstream PID update

Rikard Sandström

PID phone conference

2005-07-27

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Outline

• Bad news: Problem with understanding the errors in downstream time of flight.

• Good news: Small improvement to range in calorimeter.• Future plans & summary

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A large error on TOF

• An RMS on texpected – treal = 700ps was shown at last VC. Too big, why?

1. Unsatisfactory TOF1&2 reconstruction.• Added TOF Ref planes to extract truth.

2. Different phase -> different RF acceleration.

3. Different pz -> different RF acceleration.4. RMS of energy loss in absorbers.5. RMS of energy loss in trackers.6. Large rho -> high energy loss in trackers.

• Now using SciFi recon to cut on large reconstructed rho.

7. SciFi recon code was out of date.• Got the new recon from Malcolm today. Had no time to test it now,

using truth instead.

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TOF reference planes

• For all TOF detectors, a rectangular virtual detector is added to each side of the detector.

• This way, no need to compensate for where along z in detector hit was recorded.

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Study of RF acceleration, fitting

• dpz = k1+ k2 cos(phi pi + k3 + k4 betaz) + k5 pz

– k1 = -.6136,

– k2 = -12.8646

– k3 = 11.0924

– k4 = 5.2164

– k5 = 0.9991

Theory

Fit to theory

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“Quality” of fit

• Have not done any formal analysis, but picture shows adequate absolute error between theory and its fit for range of interest.

• Should be checked against G4MICE, collecting momenta and time at (flat) vacuum windows.

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Energy loss in absorbers

• For 200 MeV/c muons (on axis), static RF-field:– Flat absorbers: dE = 12.1+-1.7 MeV.

• Tof rms = 52.6 ps.

– Torispherical absorbers: dE = 12.1+-1.8 MeV.– Tiny difference!

• Non static RF-field:– Flat absorbers: 12.9+-1.8 MeV.

• Tof rms = 38.6 ps.

• The energy loss straggling cannot be predicted, hence there is an irreducible error on predicted pz,out.

– Is it useless to give an expression for RF acceleration? For predicting TOF, is the old solution using weighted mean pz (from tracker) better?

• Not part of simulation is a similar irreducible error: diffuser

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New Dt=treal-texpected

• Not using RF acceleration theoretical formula, but weighted mean of pz’s:

– Assuming 2.8 MeV loss per tracker.

– Dt = 90+-1505ps, full range.

– Dt = 334+-312 ps, for pz>180 MeV/c.

– Still rather bad…– Does not change with very

narrow pz around nominal!-> systematic and/or pt effect.

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Expected range in calorimeter• Changed to a simpler method:

– Linear approximation between T=100 and T=140 MeV, using lead data.

– Calorimeter treated as lead, but with density of composite material.

– Assume 18 MeV loss in TOF2 and Ckov2.

– Take momentum from downstream tracker, convert to energy assuming muon mass.

– Satisfactory result! (Zero is always correct value.)

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Efficiency and purity

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Future plans

• The RMS of the tof must be understood, and is possibly emittance dependent. Hence, will run with a 6 pi mm beam. – 10 pi mm scrapes, 6 pi mm does not scrape significantly.

– It is a wide beam, does it cause the statistical error? rho or p t?

• Then proceed with everything else I promised to do…– Such as see what the real tracker reconstruction gives.

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Summary

• The predicted tof still has problems, but working on it.• While it is easy to predict energy gained in a linac, it is

hard to predict energy lost in absorbers and tracker materials.– Some errors are irreducible, while others are more friendly.

• I simplified and improved the expected range in calorimeter.