Update on B-analysis

Introduction Towards a definition of a limited set of plots for TDR, using all available data. Based on few general questions: – Do we understand phenomenology ? data-expectaction plots already available, in general well understood; – Do we expect efficiency drops ? HV mesh scan at B = 0.5 T and  = +10° analyzed and compared to B = 0 data; – Is the resolution degraded ? summary of  TPC and centroid resolutions at B = 0.2 T (unfortunately at HV mesh = 470 V) compared to B = 0 data at same HV; also scan in HV mesh. – Can we manage the systematics: using the back-to-back configuration, residual offsets should be due only to track bending. Single chamber points can be used only if we know the magnetic field (see Mauro’s presentation). Few new plots today on some of these items. 2

Efficiency Comparison of efficiencies have to be done at the same gain: we have an HV B=0.5 T T 2 Efficiency: at least 1 centroid within ≈ 5  Data: all at  = 10°  B = 0 are July data (runs ) and June data (run 7340)  B = 0.5 T are June data (runs 7348 and )  B = 0.2 T one run for comparison (run 7345) B = 0 B = 0.5 T HV mesh (V) 3

Resolution - I B = 0, centroid (red) vs.  TPC (blue)B = 0.2 T, centroid (red) vs.  TPC (blue) Comparison between H2 data B = 0 and B = 0.2 T at different inclination angles. Resolution =  core (T1-T3)/√(3/2). All data are at HV mesh = 470 V. Notice that at B = 0.2 T  L ≈ 9° ; a clear -10° shift is observed as expected. Inclination angle (deg.) Core gaussian width (  m) Recipes for combination still to be tested on data. 4

Resolution - II HV scan: B = 0.5 T E = 0.6 kV/cm  = +10° Resolution =  core (T1-T3)/√(3/2) HV mesh (V) Resolution (  m) -20% resolution going from 470 to 500 V 5

Systematics - I Back-to-back configuration: x(T 1 T 2 ) – x(T 3 T 4 ) vs. B. If all systematics are removed I expect a residual slope uniquely due to the track bending. I observe a slope of ≈ 300  m / T However expectations are lower (≈ l 2 /2R ≈ 50  m/T). Either: larger l, lower p or other effects at work (or wrong calculation…). 6

7  TPC: comparison btw x 0 and x half measurements (Dataset B data)  Offset clearly reduced BUT worse resolution (as expected) +10° data +20° data Slope =240  m/T Slope =260  m/T

Summary and open problems Efficiency: in the “defocussing” configuration plateau is reached at slightly higher gain  situation under control; Resolution: ok but a combination algorithm still to be tested on data (next thing to do); Systematics: still not understood – comparison with other methods is useful. Apparently a linear offset with |B| of  m/T is observed in any attempt to eliminate it. 8

Backup 9

10 Try x 0 in place of x half x half is affected by a systematics, the effect of the magnetic field being a rotation of the track with x 0 as “pivot”. x 0 shouldn’t be affected. Since T1 and T3 have a different gap (5mm vs. 10 mm) a B-dependent offset in x half is expected but not in x 0. x0x0 x0x0 x half

11  TPC: comparison btw x 0 and x half measurements (Dataset B data)  Offset clearly reduced BUT worse resolution (as expected) +10° data +20° data