Report

TRACKER choice: Comparison of tracking capability and systematics 1. Not all information is available – only one group gave results (bravo!) and they are not complete – I use yesterdays results. 2. For this reason the ‘critical comparison’ will be critical of them – which is unfair. 3. Conclusion will be that we may have one device that is good enough, but we are not *sure*. We need thorough documentation and discussion of results before final endorsement of any device. Alain Blondel Quantities to be measured in a cooling experiment cooling effect at nominal input emittance ~10% equilibrium emittance = 0.25 cm curves for 23 MV, 3 full absorbers, particles on crest Alain Blondel Emittance measurement Each spectrometer measures 6 parameters per particle x y t x’ = dx/dz = Px/Pz y’ = dy/dz = Py/Pz t’ = dt/dz =E/Pz Determines, for an ensemble (sample) of N particles, the moments: Averages <x> <y> etc… Second moments: variance(x) sx2 = < x2 - <x>2 > etc… covariance(x) sxy = < x.y - <x><y> > Covariance matrix s 2x ... M = ... ... ... ... s xy s xt s xx' s xy ' s 2y ... ... ... ... ... ... ... s t2 ... ... ... ... s 2x' ... ... ... ... s 2y ' ... s xt' s yt ' s tt ' s x't ' s y 't ' s t2' 6D de t(M xytx 'y 't ' ) Evaluate emittance with: 4 D de t(M xyx 'y ' ) 2 Getting at e.g. sx’t’ is essentially impossible with multiparticle bunch measurements Compare in with out Alain Blondel requirements on spectrometer system: 1. must be sure particles considered are muons throughout 1.a reject incoming e, p, p => TOF 2 stations 10 m flight with 70 ps resolution 1.b reject outgoing e => Cerenkov + Calorimeter 2. measure 6 particle parameters i.e. x,y,t, px/pz , py/pz , E/pz => 3. measure widths and correlations … resolution in all parameters must be better than 10% of width at equilibrium emittance (correction less than 1%) s2meas = s2true+ s2res = s2true [ 1+ (sres/ strue)2 ] (n.b. these are r.m.s.!) 4. robust against noise from RF cavities Alain Blondel b 30 cm in the detector solenoid Beam size at eq. emittance is sigmax= sqrt ( 30. 0.25) = 2.7 cm Transverse angle is sigma x’ = sqrt(0.25/30) = 0.09 radians i.e. Pt = 18 MeV resolution in all parameters must be better than 10% of width at equilibrium emittance (correction less than 1%) requires resolution better than 1.8 MeV/c in Pt. THIS MUST BE THE RESOLUTION ON THE PREDICTION OF THE PARTICLE ENTERING/EXITING THE COOLING CHANNEL (not what it was in the tracking device) This situation is quite usual in HE experiment (e.g. track extrapolation to muon chambers) Alain Blondel TRANSVERSE MOMENTUM RESOLUTION spt = 110 keV RESULTS From proposal: PL= 200 MeV/c Pz resolution degrades at low pt : resolution in E/Pz is much better behaved measurement rms is 4% of beam rms Alain Blondel Limit to precision: multiple scattering in the last plane of detector: e.g. 1.9 mm of plastic (sci-fi) or 0.2 mm of mylar (TPG end window – to be verified) Sci fi: qMS= 15MeV/c / bp L/X0 ~ 0.09 L/X0 =0.006 Or Pt = 1.25 MeV/c (rms will be somewhat worse) There is no way this can be 110 KeV/c…. There must have been a mistake TPG same calculation gives 0.41 MeV/c .. *Not* 0.035…. 1.4 Safety factor What is the loss performance in the spectrometers which will compromise the measurement? How large is the safety factor? recalled the requirement in the LOI (1/10 of the beam size at equilibrium emittance) beam size in transverse momentum is about 10 MeV at equilibrium emittance we have 110 keV Pt resolution with sci-fi 270keV multiplexed. 35 keV for TPG Safety factor is large, but systematic errors (alignment!) have not been taken into account. This was wrong. Alain Blondel No Multiple Scattering Sci-Fi (M. Ellis) • Point resolution determined exclusively by d/12 •Ganging times 7 makes resolution 7 times worse •This is the configuration that had been (accidentally) presented at previous meetings. Alain Blondel No Ganging Multiple scattering is now on in all future plots Point resolution is dominated by effect of m/s with no ganging Momentum resolution is still good enough for a cooling measurement Tails come from MS… and are real! •Sigma (Pt) of 1.13 matches the b.o.e. calculation that gives 1.25 (but please use rms -- and careful with tails?) Alain Blondel 7 Fibre Ganging Position and momentum resolution have degraded slightly, but no longer by factor of 7 Use of “projector” in Kalman package will allow improvement in resolution per plane ? Alain Blondel iii. Tracking performance: The detector response and point resolution must be based on experimental demonstration. […] A viable scenario for alignment and calibration must be described. Alain Blondel Nominal Configuration Dead Channels (0.25%) based on D0 experience Official background source equivalent to estimate of rate based on Lab G tests. All relevant physics processes simulated 7 times Ganging Full simulation, digitisation, pattern recognition and track fitting/extrapolation Main worry (and deep reason for TPG preference) is that traking with only 5 points makes it delicate to estimate precisely the efficiency (which will NOT be 100%) and to be certain that it is not a biasing factor. My wish: I would like a prototype that shows that we can really achieve the ‘nominal conditions’: 100% hit efficiency(?), 0.25% dead channels in the MICE tracker, and that a tracking algorithm is able to recover from the resulting inefficiency. Alain Blondel Pattern Recognition Efficiency What would be this result if the efficiency and dead channel were those achieved in the prototype ? Number of space points in fitted track (or zero if no track fitted) Most of the time 5 space points are made and fitted in track With no dead channels or background: 99.9 ± 0.1 % Overall tracking efficiency in nominal situation: 99.0 ± 0.5 % Alain Blondel Why do we bother with a TPG? Results Strip number up&down stream, 1 muon, 1 graph = 1 layer Sampling number Alain Blondel Why do we bother with a TPG? 5 points per track: a little noise and inefficiency and you are lost. Alain Blondel Typical cosmic-ray event By M.Ellis This is very nice, but we need an analysis of Cosmic ray results => eficiency etc… Alain Blondel TPG Alain Blondel At first sight TPG looks like a killer: ----- better momentum reconstruction (factor 3) less X0 many points and unbeatable pattern reconstruction capability. it is also less expensive. -- only design default: long integration time ~50 microsecond during which background accumulates, this is compensated by lower Xo and higher number of time slices. Alain Blondel However, the TPG is a more delicate object as we could see very clearly: 1. Construction of GEMs and hexaboard is new technology. How many prototypes will be needed to reach acceptable performance? 2. Aligment and control of distortions is a notoriously difficult problem. Existing ideas are based on deposition of permanent radioactive sources on the field membrane, followed by measurements with B field on/off/reversed. (It is not possible to align the chamber with B-off tracks as will be done in Sci-fi.) This also can be done in the foreseen test, but has not been done as of today. These ideas have not been worked out and have not been demonstrated experimentally. Demonstration of alignment procedure is essential. Alain Blondel Conclusions The Sci-fi group has carried out many of the requirements ! There remain several serious questions related to Efficiency, light yield, dead-channels and their effect on resolution & efficiency The Pt resolution is not far from the upper limit that we fixed ourselves and we must make sure that no unwanted effect will push it over the edge. => Document work and have cross-checks performed! The TPG is clearly very promising but has encountered difficulties in the construction and the situation of MICE in Italy did not help. Alain Blondel