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Behaviour of MicroMega chambers in magnetic field : analysis of H2 June data

Behaviour of MicroMega chambers in magnetic field : analysis of H2 June data. Outline : ( 0 ) Introduction ( 1 ) Data set used and noise filtering ( 2 ) Cluster size and length ( 3 ) m TPC behaviour ( 4 ) Space resolutions and offsets. ( 0 ) Introduction.

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Behaviour of MicroMega chambers in magnetic field : analysis of H2 June data

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  1. BehaviourofMicroMegachambers in magneticfield: analysisof H2 June data Outline: (0) Introduction (1) Data set used and noisefiltering (2) Cluster size and length (3) mTPCbehaviour (4) Spaceresolutions and offsets.

  2. (0) Introduction • Effectof the magneticfield on electron drift: wherev0dis the driftvelocitywhenB = 0. IfB perp. to E(H2 data) at the nominalMMworkingpoint. a is the “Lorentz angle” In NSW B<0.3 Tl < 0.24 B term can be neglected (unless a sizeable EB is there). Displacements in the ExB direction of typical sizes: up to hundreds of micron >> typical mechanical systematics

  3. (1) Data set used and noisefiltering side view T3 – T4 T1 – T2 B field  beam: p=150 GeV/c • Magnetic field orthogonal to Electric field • Xstrip readout (vertical coordinate) • particle bending non-negligible (displacement ≈ 50mm×B(T) btw. T1 and T3) • T1, T2: 400 mm pitch, 5mm gap, HVmesh = 500(?) V; HVdrift = 300 V , Ar-CO2 93-7 • T3, T4: 400 mm pitch, 10 mm gap, HVmesh = 500(?) V; HVdrift = 600 V , Ar-CO2 93-7

  4. Full datasetused (Junetest-beam) •  Pre-filter done based on FFT recipe (see following) • Strips are selectedusing the standard selection: • (chargethreshold = 80) • Timesobtainedusingrisetimefit • (slope > 0.15) • Extended cluster definition(seefollowing) • Resolution: score(T1-T3)/√2 (not completely correct…)

  5. NoiseFilter • CGattiNoiseFilterextractsan FFT value per chamber. High FFT means “noisy” event. Typicaldistributions are shownhere (run 7453): T1 T2 T3 T4

  6. June H2 data are “more noisy” than H8 July data Junetest-beam (run 7353) T1 T2 Julytest-beam (run 7486) T1 T2

  7. FFT tails in differentchambers are correlated : cut based on T1 and T3 chambersonly:Events are acceptedif FFT(T1)<4.5 && FFT(T3)<4.5 Typical rejection ≈ 20%: 20kevts  15-16 kevts FFT(T1) FFT(T3)

  8. Dataset A: bending “track-side” -10° and -20° data DatasetB: bending “opposite-side” +10° and +20° data Mostplots in the following: |B| = 0 |B| = 0.2 T (average NSW) |B| = 0.5 T (extreme NSW) |B| = 1T (“crash” test)

  9. (2) Numberofstrips: dataset A -10° T3 T1 average#strips • “singular” configuration @ |B|=0.2 T • increase of width •  increase of “empty events” fraction • (particularly strong for T1 data) 0-strips events

  10. Numberofstrips: dataset A -20° T3 T1 average#strips • “singular” configuration • @ 0.2<|B|<0.5 T • increase of width •  increase of “empty events” fraction • but less evident than at 10o. 0-strips events

  11. Numberofstrips: datasetB +10° T3 T1 average#strips 0-strips events • No “singular” configuration • average #strips almost constant • BUT increase of width • increase of “empty events” fraction • (particularly strong for T1 data)

  12. Average cluster charge vs. |B|: Generaldecreasewithincreasing |B|. Dataset A DatasetB

  13. Cluster length and #holes: T3 –datasetB +10° cluster length Numberofholes The cluster definitionhastobechangedto include “scattered” clusters. FormTPC (seefollowing) I require 2<#strips<16 nholes<15 CONCLUSION: clusters are spread butmaintainsapproximately the same numberofstrips; the overallchargedecreases

  14. DatasetB: T3 timespectraGeneral trend: increaseofdrifttime +10° data: +20° data:

  15. Maximumdrifttime: summary T3 T1 Effectofsingluaritiesevident in Dataset A data (-10° and -20°) N.B. In mTPC the vdriftisheld at itsnominalvalueof 47 mm/ns (itshouldbeadjustedaccordingly)

  16. (3) mTPCevent gallery-1: |B|=1, q=+10o

  17. mTPCevent gallery-2: |B|=1, q=+10o

  18. mTPC T1 angles: Dataset A – T1 -10° data: -20° data: “Angle inversion”: at 0.2 T @ -10° at 0.2 ÷ 0.5 T @ -20°

  19. mTPC T3 angles: Dataset A – T3 -10° data: -20° data: “Angle inversion”: at 0.2 T @ -10° at 0.2 ÷ 0.5 T @ -20°

  20. mTPC T3 angles: DatasetB– T3 +10° data: +20° data: Increaseof the angle due toLorentz angle effect

  21. Peak angle frommTPC vs. |B| (DatasetB data –previous slide). Data (redpoints) are comparedwithexpectionsbased on geometrical considerations: +20° data +10° data |B| (T) |B| (T)

  22. (4) mTPCxhalfresolution: Dataset A -10° data: -20° data: Bad xhalfresolution: @-10° |B| = 0.2 T @-20° |B| = 0.5 T

  23. mTPCxhalfresolution: DatasetB +10° data: +20° data: @20° resolution is worsening for |B|≥0.5 T

  24. Centroidresolutions: Dataset A -10° data: -20° data: Goodcentroidresolution: @-10° |B| = 0.2 T @-20° |B| = 0.5 T

  25. xhalf and centroidresolutions: summary DatasetB Dataset A

  26. Summary: a pictorialview “singularbelt” NSW operation regions “Singular belt” = Points where Lorentz Angle ≈ Track inclination

  27. Offset (T1-T3): depends on |B| due to the different gap sizeof T1 and T3 T1 sketch of a track crossing T1 and T3 bothimmersed in the sameB-field T3

  28. xhalf x0 Tryx0 in placeofxhalf xhalfisaffectedby a systematics, the effectof the magneticfield being a rotation of the trackwith x0as “pivot”. x0shouldn’tbeaffected. Since T1 and T3 have a different gap (5mm vs. 10 mm) a B-dependent offset in xhalfisexpectedbutnot in x0.

  29. mTPC: comparisonbtw x0 and xhalfmeasurements (DatasetB data) +10° data +20° data • Offset clearly reduced BUT worse resolution (as expected)

  30. mTPC: comparisonbtw x0 and xhalfmeasurements (Dataset A data) -10° data -20° data

  31. Studyofback-to-backconfiguration: mTPC on the fourchambers, than combine and check. (T1+T2)/2 vs. (T3+T4)/2 l xcomb(1) = (xhalf(T1) + xhalf(T2))/2 xcomb(2) = (xhalf(T3) + xhalf(T4))/2 then: xcomb(1) –xcomb(2) distribution resolution and offset.

  32. Look @ 0T data: resolutionimprovesforcentroid, notforxhalf. Why ? I expect that the resolution on xcomb is roughly √2 times better than resolution on xhalf red = T1 – T3 blue = T1T2 – T3T4

  33. Offsets = averagevaluesofxcomb(1) - xcomb(2): The offset shouldbereducedto the the effectof the particlebending Offset are reducedtotipicalslopesof 350 mm/T: I expectthisslopeif p=150 GeV/c and l = 60 cm. Are thesenumberscorrect ?

  34. Summary and conclusions • The operation of MM in magnetic field requires a careful knowledge of the • field map and a careful calibration procedure providing O(100 mm) corrections; • mTPC works fine with acceptable resolution in the full |B|-q plane • apart from specific “singularities” (q=-10o, |B|=0.2 T and q=-20o, |B|≈0.4T) • where the Lorentz angle “compensates” the track inclination. • In the singularities the centroid helps to recover resolution • (but the combination should be based on clusterlength rather than #strips); • Using x0ratherthanxhalfreduces the offset butspoils the resolution. • Back-to-Back doublets show no improvements on resolution but reduction • of the offset probably consistent with track bending.

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