MEG DCH Analysis MEG Review Meeting 17 February 2010 W. Molzon For the DCH Analy

MEG DCH Analysis MEG Review Meeting 17 February 2010 W. Molzon For the DCH Analy

MEG DCH Analysis MEG Review Meeting 17 February 2010 W. Molzon For the DCH Analy

Brooks, Kenneth, Freelance Columnist has reference to this Academic Journal, PHwiki organized this Journal MEG DCH Analysis MEG Review Meeting 17 February 2010 W. Molzon For the DCH Analysis Working Group Outline Goals of DC analysis Overview of calibrations in addition to analysis Low level per as long as mance: show some results, still improving resolutions Efficiency Rf resolution Z resolution High level resolutions: show some results, still improving resolutions in addition to our measurements of the resolutions Momentum Track angle at target Position at target Demonstrated per as long as mance vs. proposal per as long as mance vs. current MC Prospects as long as improvement Hardware Software Goals of DCh Analysis Optimize per as long as mance of spectrometer Best low level resolutions: R-f, Z, efficiency, noise rejection Best high level resolutions: positron energy, trajectory Determine hardware limitations in addition to possible improvements Noise, alignment, stability Characterize per as long as mance as long as purpose of physics analysis PDFs as long as likelihood analysis Optimize power of physics analysis Selection criteria vs. efficiency

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Positron Spectrometer Impact on MEG Per as long as mance Select on positron energy within interval near 52.8 MeV For fixed meg acceptance, BG/S proportional to dp (MEG prediction sRMS=180 keV/c) Select on qeg near p For fixed acceptance, BG/S proportional to df x dq (MEG prediction sRMS = 8×8 mrad2) photon position resolution ~ 4 mm sRMS ~6 mrad both f in addition to q Track fitting angle uncertainty 4-5 (7) mrad each Position of stopping target: uncertainty 0.5 mm ~6 mrad f Project to target in addition to timing counter in addition to correct te as long as propagation delay For fixed acceptance, BG/S proportional to dt (MEG prediction sRMS = 64 ps, ~2 cm) Path-length projection to target has negligible uncertainty Uncertainty in path-length projection to timing counter dominated by scattering in addition to E loss after spectrometer Improvements needed to incorporate position at timing counter in addition to material between spectrometer in addition to timing counter into trajectory fit For all effects, tails in resolution function loss of acceptance proportional to integral in tail, small increase in background because source of background is uni as long as m DC Per as long as mance 2009 vs. 2008 Significantly improved per as long as mance this year Hit in plane near track projection Hit in plane assigned to track Significant Improvements in Tracking Analysis Incorporated use of TIC time as long as track time Alternative to use of track time deduced from DCH itself Necessary last year due to inefficient chambers Track time from DC itself now much improved per as long as mance Much better algorithms as long as selecting/removing appropriate hits on track Significantly improves resolution in addition to efficiency Re-optimize this year as long as better quality data Better underst in addition to ing of merging of multi-turn tracks Developed technique as long as measuring resolutions using two-turn tracks Fit each turn of a two turn track Project each turn to common point of closest approach to spectrometer axis between two turns – one projected as long as ward, one backward Measure difference in q, f, R, z, p in addition to infer resolution in these quantities Improved fit to Michel edge to extract momentum resolution Better underst in addition to ing of chamber per as long as mance, contributions to resolution Work done on cross-checks of calibration Work on cross-check of alignment using cosmic-ray muons Better underst in addition to ing of relating measurable resolutions to kinematic resolution

DCH Alignment Primary alignment of chambers from optical survey Correct chamber displacements by minimizing mean residuals to fitted tracks using Michel data Residual chamber rotations after optical survey are negligible: no corrections Mean residuals reduced from ~100 mm to 10-20 mm Compare to typical resolutions: Position resolutions sR ~200 mm; sZ ~1000 mm; Chamber-to-chamber scattering deviation ~500 mm CR data recorded with field off as long as cross-check of alignment Different drift per as long as mance without magnetic field Possibility of getting higher momentum tracks with less scattering Remove possibility of correlated DC shifts being missed due to momentum fit Plot of rotation diagnostic Quality of Baseline Prediction Charge on anodes in addition to pads used as long as Z measurement Baseline subtracted by measuring level early in wave as long as m, subtracting average value Shown to be superior to linear, quadratic extrapolation Bin to bin pedestal fluctuations larger in 2009 data vs. 2008 data Precision of prediction of baseline in signal integration affects position resolution Histogram difference in predicted baseline in addition to average baseline in 50 ns signal region Measured on pedestal runs simultaneous with recent MEG data Contribution to Z resolution Depends on both the precision of the baseline in addition to the size of measured charge Increased HV in 2009 gives 40-50% increase in mean hit charge wrt 2008 Error in Z due to baseline fluctuation calculated as long as every hit Contribution of sz ~ 550 mm in 2009 compared to sz ~ 1 mm in 2008 Drift Per as long as mance in addition to Calibration Alignment of time offsets wire by wire Fit to leading edge of distribution of thit – ttrack as long as each end of each wire Check procedure by comparing hit time at 2 ends Typical precision of 1.5 ns Verification of time to position relationship HV in addition to B dependent drift using GARFIELD Incorporate asymmetric response at edge cells Project track from hits in planes 0,1 to common point – measure residual Alternative measurement of resolution from residual of hit to fitted track Measure dependence of residuals on track angles, drift time to verify drift model Typical single plane resolution 250 mm Some systematic effects with angle in 2008 data, being studied again in 2009 data dR Fitted track shape tied to hits

Z Coordinate Measurement Determined first from charge division on anode – calibrated by using know phase in addition to periodicity of cathode pads vs. Z measured by anodes Primarily used to determine correct cycle of cathode pad Does not enter directly into precision of Z determination; used when pad signals missing Precise Z determination from charge induced on pads Pattern of induced charge studied with image charge method – impact on calibration Dependence on wire-cathode distance, offsets of wire with respect to center of pattern (in the wire plane), fluctuations of mean Z coordinate of ionization sites Optimization of technique as long as measuring charge (integration time, etc.) potentially important Noise contribution to charge is largest known source of error in Z determination St in addition to ard integration in addition to charge calibration + two alternative methods studied Preliminary results of alternatives give essentially same per as long as mance Show plot of fit to sine wave Cathode Pad Calibration: Z Determination Reminder Z = n(5 cm) + 5/(2p)(arctan(Ahood/Acathode)+fh(c) A = (Qu-Qd)/(Qu+Qd); Qu(d)= a+bsin(2pz/5+fu(d)) a,b depend on pad-anode distance Precision of dependence of A on z studied with electrostatic calculation – correct to good approximation Steps in Z calibration Correctly align time offsets in pads vs. anodes: integrate same part of signal Adjust time offsets on pad signals to set the mean value of the difference in the time of the pad in addition to anode to zero Correct as long as relative upstream-downstream gains: Adjust gain to get the mean asymmetry in the cathode in addition to pad as long as each were equal to zero Correct as long as effect of chamber foil bowing Both the induced charge in addition to the asymmetry depend on the anode-cathode distance Measure Qcathode/Qanode vs. z as long as each wire – fit to quadratic dependence on Z Apply phenomenological correction to each asymmetry depending on mean induced charge as long as that wire in addition to Z Bowing correction is ~200 mm in quadrature Some Details on Chamber Bowing Distance of hood in addition to cathode from anode wire effected by bowing due to gas pressure, foil mass, possibly details of how foils are fixed to frames Electrostatic calculations show effects >10% on induced charge as long as deflections of order 0.5 mm Measure the ratio of hood to cathode asymmetry amplitude (amplitude of sine wave) by measuring RMS in each 5 cm interval in Z along the wire Measure the ratio of the hood to cathode charge vs. Z Make scatter plot of asymmetry amplitude ratio to charge ratio – agrees with linear correlation predicted by electrostatic calculation Expect biggest effects in center of chamber, where bowing is largest, some different dependence on Z, particularly as long as first in addition to last cell

Pad Crosstalk from Adjacent Anodes Effect of charge induced by hits on adjacent wires Consider hits at same Z in two adjacent wires in same plane, indicated by circles in figure below. Charge induced on pads due to anode charge in same cell will have asymmetry zero Charge induced on pads due to anode charge in other cell will have asymmetry different from zero; in the example shown, more charge on DH as long as top pads, more on UH as long as bottom pads Only relevant as long as in-time hits: short integration time helps Effect tends to cancel when 2 hits averaged, cancellation not exact, particularly when pulse heights are different Charge induced on adjacent cell is not trivial (as much as 7-15%) When Z of two hits is different ( as long as large Z), effect will be different in addition to perhaps larger Contributions to Z Coordinate Uncertainty Measuring High Level Resolutions Need PDFs as long as likelihood fits or acceptances as long as a cut in addition to count analysis For the positron, these have contributions from: Momentum response function – no fixed momentum calibration line Positron angles (q in addition to f) at the target – no fixed direction events Positron intercept at the target – contribution to the photon angle measurement Response functions not expected to be Gaussian distributions Resolutions will depend on, as long as example, track length, pitch angle, etc. For momentum, can fit to the edge of the Michel spectrum Sensitive to only the high energy side of the response function, the important one Lower energy side strongly correlated with momentum dependence of acceptance For momentum in addition to angles, can exploit tracks that have two full turns in the spectrometer, comparing momenta in addition to angles at a common point near the axis to infer the resolution For momentum, cannot determine separately the upper in addition to lower edges, must assume it is symmetrical. Complementary to fit to Michel edge For q, possible systematic differences from dependence on Z For f, technique excludes contribution from effect of uncertainty in path length in projecting back to target: 1 mm error in path length is about 7 mrad error in f All resolution functions should be measured after perfecting low level per as long as mance in addition to optimizing selection criteria (not yet done) Results are likely to improve with analysis

Momentum Resolution Fit to Michel edge Fit function is sum of offset Gaussians Fit results depend on acceptance function in addition to dataset: Michel, low intensity, MEG sideb in addition to s Sample fit to 2009 data be as long as e DRS correction: RMS as long as -1.5< dE <1.5 = 0.580 MeV Alternative measurement from 2 turn comparison Single Gaussian fit: RMS = 0.490 MeV Fit to convolution of sum of 2 Gaussians: RMS in region -1.5 < dE < 1.5 = 0.447 MeV Third possibility to use Mott scattering of mono-energetic electron beam scattered into spectrometer to characterize momentum resolution De-convolve energy spread in beam, energy loss dispersion in thick scattering target Angle in addition to Vertex Position Resolutions Use technique of two-turn tracks to project to common point near spectrometer axis Theta angle resolution Reasonably well fit by Gaussian: sRMS of q = 12.7 mrad Z position resolution Well fit by Gaussian: sRMS of z = 3.1 mm Roughly consistent with contribution from scattering Phi angle resolution Well fit by Gaussian: sRMS of f = 8.1 mrad Error is correlated with momentum error R position resolution Well fit by Gaussian: sRMS of R = 2.4 mm Correspondence Between Resolutions at Target in addition to 2-Turn Comparison Can use MC to get correspondence between z position resolution in addition to positron q resolution For perfect z resolution, q resolution is 7 mrad Expect ~9 mrad resolution as long as current Z resolution Can also use MC to calculate correspondence between resolutions inferred from comparisons of 2 turns to the resolution at the target Plot s(q1 - q2)/2 vs. s(qmeas-qtrue) parametric in sz Current resolution in q1 - q2 corresponds to about 10.5 mrad q resolution Two avenues as long as improvement Improve Z resolution Underst in addition to in addition to fix lack of agreement between measured q resolution in addition to that predicted as long as current Z resolution MC dq vs. dZ MC dq2turn vs. dqtgt Correlation of Momentum in addition to Quality Measures Events with p>52.8 MeV/c represent poorly measured tracks; is there a correlation with track properties Width of central part of momentum resolution function most important as long as physics background estimate Tails in positron momentum resolution function less important; few low momentum positrons satisfy trigger, hence few low momentum positrons can contribute to accidental background. Can We Estimate Tracking Efficiency from Data Use highly pre-scaled timing counter trigger data ~ 520 C total live protons on target 1.31 x 107 m/s/mA (assume livetime same as long as MEG, other triggers) Implies ~ 683 x 1010 total muon stops Nmenn = 1935 muons satisfying selection criteria counted = 6.83×1012 muon stops calculated ( few percent uncertainty ) X 10-7 prescale factor known X 0.35 TIC acceptance x efficiency as long as Michel measured X 0.101 fraction of Michel spectrum > 50 MeV calculated X (0.92-1.0) conditional trigger efficiency as long as TIC measured X 0.091 Michel geometric acceptance X eDCH drift chamber reconstruction & cuts unknown eDCH = 1935 x 107 / 0.35 / 0.101 / 0.96 / 0.091 / (6.83×1012) = 0.92 Need to redo TIC efficiency measurement as long as 2009 Conclusions Tracking efficiency in 2009 data is much better due to improved chamber per as long as mance. Intrinsic resolutions are improved wrt last year’s data Current status is really a lower limit on per as long as mance Central part of Rf resolution is close to expectations, but tails are more than originally anticipated Z resolution worse than planned in addition to not fully understood from calculated contributions, but now not a dominant contribution to angular resolution Angle resolutions better understood, still work to be done Should get better agreement with MC when measured low-level resolutions are used Incorporate cell dependences in resolutions Underst in addition to contribution to f resolution from momentum error resulting in error in path-length to target

Conclusions Prospects as long as improvement Still early in optimization of even low level per as long as mance Fitting as long as improved baseline subtraction (noise filtering – some indications of possible improvements) Drift time-distance model verification Anode to adjacent pad crosstalk corrections Re-optimization of integration time with fully calibrated system Correction of edge effects (near wire ends) in Z determination Some possible software improvements ( preliminary results show little improvement ) Alternative alignment Alternative integration scheme High level improvements Incorporating partial turns in fitting Improved projection to TIC using TIC signal Incorporating track time as parameter in fitting Underst in addition to ing of 1-2 mm offset in magnet vs. spectrometer Hardware changes Reduction of noise at hardware level Additional measurements of resolution with Mott scattering

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Brooks, Kenneth Freelance Columnist

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