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Update – 29 jan . 2013

Update – 29 jan . 2013. T max and effective angle in B- field : comparison between data and expectations ; Study of “ doublet -mode” performance; “ Efficiency ” in magnetic field. 1. T max and effective angle in B- field : comparison between data and expectations.

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Update – 29 jan . 2013

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  1. Update – 29 jan. 2013 • Tmaxand effectiveangle in B-field: comparisonbetween data and expectations; • Study of “doublet-mode” performance; • “Efficiency” in magneticfield

  2. 1. Tmaxand effective angle in B-field: comparisonbetween data and expectations. Electrons “slow-down” in magneticfield. Ifwe compute the driftvelocity in a magneticfield |vd|using the expressions: weget Ifq =90o (as in the case of H2 data) wehave so the driftvelocitydecreaseswith the magneticfield. Thisaffects the maximumdrifttimeTmaxand the effectivemeasured angle xsincenowwehaveto take into account 2effects: --> the trajectoryislonger --> the velocity is lower

  3. New expressions: where q is the inclination angle and qL the Lorentz angle tanqL≈ 0.8 |B|. Nextslides: comparisonwith data

  4. Tmax: data (red and green points– T3) comparedto  dashed line: expectations without “slow-down” effect  solid line: expectations including “slow-down” effect Tmax(ns) N.B. T3 has: 10 mm gap HVdrift = 600 V T0max ≈ 200 ns |B| (T)

  5. x: data (red and green points– T3) comparedto  dashed line: expectations without “slow-down”effect  solid line: expectations based on “slow-down” effect x (deg.) |B| (T)

  6. 2. Studyof “doublet-mode” performance y x Measure the doubletmiddle-pointxDcorrespondingto the track intercept at the planey = 0. It can beappliedto TPC and centroid 2advantages:  B offsets self-corrected (if B variations negligible at the O(cm) scale);  t0 jitter also self-corrected.

  7. Resolution: Julydata, no magneticfield. T1 – T3 sC(xhalf), sC(xcent), sC(xcomb) (T1+T2)/2 – (T3+T4)/2  sD(xhalf), sD(xcent), sD(xcomb) For xhalf and xcombs = “score”. For xcent only 1 gaussians. Naifly I expect sD ≈ sC/√2 . But: sC(xhalf) sC(xcent) sD(xhalf) sD(xcent) sC(xcomb) sD(xcomb) Angle (deg.) Angle (deg.)

  8. Ratio of doublet / single chamberresolutionsR = sD / sC mTPC R > 1/√2 Centroid: R ≈ 1/√2

  9. Offset= averagevalues of xD(1) - xD(2): The offset shouldbereducedto the the effectof the particlebending Offsetsare reduced to tipicalslopes of 200÷250 mm/T. Ifp=150 GeV/c and l = 20 cm lowerslopes are expected (d(m) ≈ 10-3l(cm)2B(T) = 40mm/T)

  10. 3. “Efficiency” in magneticfield Doublet-modeoperation more stringentrequirements on chamber efficiency. Itisinterestingtosee the effectofB on efficiency. I havedone the following test: Select “golden” eventswith:  a goodmTPC position on T1 a good “doublet” on T3-T4: Then look at T2. Three efficiencies: e1 = at least 1 hit (whatever the charge) e2 = a good mTPC with extended cluster definition (strip>2) e3 = a good mTPC with severe cluster definition (MI recipe) “rough” space connection (can be improved) T1 T2 T3 T4 First applicationtoJuly data thentoJune data vs. B

  11. July data: angularscan in standard operation e1 e2 e3

  12. In June data the chamberswere operated at lowergain. Comparisonbtw run 7455 (July–bluelines) run 7340 (June–redlines) (bothwith B=0 and q = 10°)  inclusive strip charge  strip multiplicity Inefficiencies are higher in June data.

  13. Efficiencies vs. |B| +20° data +10° data e1 e1 e2 e2 |B| (T) |B| (T) Verylowefficiencies. Butitisdifficult to extrapolate to higher gain data Relative e1reduction: -(3 ÷ 4)% for B = 0.2 T

  14. Summary • Evidence of electron “slow-down” effect: good description of data • Doublet-mode operation is ok, but: • resolution score for mTPCdoesn’t scale as expected • in B, offsets are larger than expected • Sizeable reduction of efficiency in B (but data have low gain)

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