detector alignment Stefania and Bepo Martellotti 20/12/10

Detector misalignment / Trigger inefficiency - We know that hardware alignment is already good at the order of 1 mm. Is some further improvement possible ? - Check alignment using trigger unbiased muons matched to high momentum tracks with a stand alone method independent of the tracking system alignment and independent of the geometry data base We concentrate on misalignments affecting Trigger efficiency. Main effect is given by y misalignment of stations M1 M2 M3 (Y FOI is only 1 pad while for M4 M5 is 3 pads) The effect of eventual x misalignments is less relevant and strongly “analysis/channel dependent”

Trigger efficiency - Y misalignments Stefania muon meeting In the Y intercept of fitted track with plane Z=0 we see a spike of tracks with all Y pads perfectly aligned and many tracks with not aligned pads  trigger inefficiency 1 m Trigger inefficiency for Multiple scattering Punch through Decays with large kink & Detector misalignments

FOLLOWED PROCEDURE: # Min Bias events # Muon ID with a) Neural Network algorithm b) “alessia algorithm” (starting from M5)  same results have been obtained # Select muon tracks with hits in ≥ 4 stations # Select muons matched to high momentum long tracks (different cuts on momentum have been tested) # Consider only events having one cluster per station associated to the track. The cluster must be composed of ( ≤ 4) hits having the same Y # Start from the hit pad of station M2 # Consider the projective track IP-hitM2 (do not fit θ YZ ) and find the extrapolation in M1, M3

# Look in Mi at the difference between the Y of the cluster and the extrapolation from M2 Δ Mi = Y Mi – Y MiM2 # For tracks crossing the same region in the 3 stations Δ Mi = 0  good alignment Δ Mi = ± 1 pad  physical misalignment (Mult Scatt…) or detector misalignment If Δ ≠ 0 for 1 station  no L0mu trigger The purpose is to maximize trigger efficiency

Example YM2-YM3 DY = ± ½ pad When tracks change region DY = ± 1 pad Mult Scatt or misalignment Stefania R1 R2R3R4

R1R2R3 R4 Y X M3 M1 WITH MAGNET ON, TRACKS OFTEN CHANGE REGION A track in M1R3 can easily go in M3R4 rarely in M3R2n X Z M3 M1 R3R4R2 YM1-YM3 = ± 1/4pad ± 1/2pad rare frequent Y station alignment w.r.t. M3 when track change region M3 M1

R2 R3 Count the Number of DY = ± 1 pad  Mult Scatt or misalignment YM1-YM3 n +1 Misalignment can be measured by (n +1 - n -1 ) Stefania R2R3 n -1

Supposing a uniform track distribution in the detector, we can assume that physical effects (MS, K decay kink, secondary interactions) smear symmetrically the distribution equally populating n +1 and n -1  Asymmetries can only be generated by detector misalignment that can be measured in each region multiplying the pad length by (n +1 - n -1 ) / (n 0 + n +1 + n -1 ) The hit distributions in Y are not at all uniform and generate systematic effects. Nevertheless the distributions are symmetric up and down  considering side A/C as a whole the asymmetry (n +1 - n -1 ) should correctly measure the misalignment

No significant effects were detected eliminating border pads in regions R1 R2 Viceversa systematic effects due to the non uniform muon/hit distributions have been observed looking at Up and Down quadrants separately: Significant systematic asymmetries are observed which do not correspond to real misalignments from the perfect projectivity. The relevance of these effects increases with low momenta (larger MS smearing) and for larger pad size. Such effects have been studied with MC We have measured misalignments considering sides A-C as a whole. But also checked separately different regions and different quadrants and eventually considered only tracks crossing M3 in the inner pads of the chambers in regions R1, R2 to check possible systematic effects at chamber edges

R1 +R2 R1 25mm R2 50mm ΔYΔY

St//ReA-side(y 0)/2C-side(y 0)/2 M1R1 25mm 1.21±0.13 (0.97) 0.889±0.13 (1.5) M1R2 50mm 1.21±0.19 (2.9)0.543±0.19 (2.5) M3R1 34mm 0.414±0.095 (-0.93) 0.37±0.095 (-0.68) M3R2 68mm 0.526±0.11 (-2.1) 0.673±0.11 (-2.1) Misalignments found (for MB data) in mm ± statistical error (systematic difference Up/Down) Residuals for y>0 and y<0 have opposite signs - The effect is due to non uniformity of the hit distribution, Multiple scattering & large pad size - The effecrt increase with the region, decrease with high momentum tracks - The average (y>0 + y<0) should measure the deviation from projectivity due to relative misalignments. - The pattern on M1 is reversed respect M3 since M2 is taken as reference for projectivity - The results obtained for R1 and R2 are averaged

SHIFTS TO BE APPLIED To correct misalignment (mm) ± statistical error M1 M2M3 A1.2 ± ±0.08 C0.75 ± ±0.08 Alternatively we can shift M2 and M3 Y C A

Station/R egion A-sideSystematicsC-sideSystematics M1R1 25mm 0.437± mm 1.14± mm M1R2 50mm 0.398± mm 1.2± mm M3R1 34mm 0.379± mm0.136± mm M3R2 68mm 0.302± mm 0.109± mm MC2010 MBias Nnet track selection Applied the same cuts of the real data In the table are counts for pad Misalignments MCarlo MBias

MC shows same pattern as real data. The mean value (y>0 + y<0) should return the simulated deviations from projectivity that was in the DDDB+LHCBCOND DDDB: head > Survey (see DATA BASE INFORMATION) values respect “nominal” (TDR) positions NB: C side is rotated by 180º respect Aside: Dz >0 means more downstream for A But more upstream for C-side Dx >0 means far from beam pipe for Aside BUT closer to the beam pipe for C-side DDDBC-sideA-side [mm]TxTyTzRy [ o ]TxTyTzRy [ o ] M M M M M

Station/ Region A-sidesystematicsC-sidesystematics M1R1 25mm 0.302± ± M1R2 50mm 0.859± ± M3R1 34mm ± ± M3R2 68mm 0.015± ± Mcarlo Jpsi Systematics are much smaller than for Mbias ==> they are due to multiple scattering

Conclusion The method is robust – Independent of eventual misalignments of tracking system and of Data Base  There are still misalignments of the order of 1 mm in the detector # Shall we (can we) correct them ? MC studies confirm that we understand systematics - Summing quadrants Up and Down, systematic effects are almost cancelled (possible residual systematic effect on the result are certainly small) Some further check could be done in the next days in particular increasing the statistic of real data and selecting higher momenta. General comment: Trigger : too small YFOI in M1 M2  we loose significantly efficiency

SPARES

RealData MBias Apr2010 Mbias data Nnet track selection Applied the same cuts of the real data In the table are counts for pad

RealData MBias

Mcarlo MBias MC2010 MBias Nnet track selection Applied the same cuts of the real data In the table are counts for pad

Trigger algorithm in few words: Starting from each M3 seed, look for hits in the other stations - Search in projective XY FOI in M4, M5 (± 1 pad Y allowed) - Search in projective FOI in M2 (only one pad Y allowed) - Make the straight line M3M2 (seed – hit found) From here on two possibilities with or without M1 M1 yes: open FOI in M1 around M3M2 extrap. (only one pad Y) find the nearest hit to the extrapolation make the straight line M2M1 M1 no: use directly the M3 M2 straight line calculate pT  cut

Alessia 19/05/2010 Monte Carlo