FURTHER STUDIES ON COMMISSIONING DATA

FURTHER STUDIES ON COMMISSIONING DATA MAIN TOPICS : • study of trigger acceptance ( combined fit ) • first look at residuals (for resolution and alignment studies) Giorgia Mila,Vincenzo Monaco Gianluca Cerminara 08-02-2006

Study of the trigger angular acceptance The initial problem : We observed a regular pattern of distorted time boxes and drops in MB4 occupancy plots We supposed that this was due to a trigger acceptance asymmetry : the TRACO connects the BTIs of two phi SLs without taking into account the correct staggering 08-02-2006

Study of the trigger angular acceptance OUR GOAL : extract the trigger acceptance for each type of chamber and for different trigger configurations in order to check possible asymmetries for MB4 trigger sector 5 sector 6 ANALIZED SECTORS: (wheel 1) sector 8 08-02-2006

TRIGGER ACCEPTANCE ASSUMPTIONS & STUDIES • The method requires that : • the cosmics angular distribution is the same for all the chambers (symmetric with respect to the vertical direction) • trigger acceptances have the same angular dependence for all the chambers (it has the same angular dependence for all the chambers in a half-wheel – same staggering between SLs) • We have compared : • The trigger HH+HL acceptance between MB2 / MB4 • The MB2 trigger acceptance between HH+HL / Default / Hanytheta 08-02-2006

MB4 -60° -30° 60° sector 8 sector 6 sector 5 MB2 60° -60° -30° TRIGGER ACCEPTANCE FIRST STEP This method relies only on the angular distributions of reconstructed tracks Measured distributions (trigger HH+HL) The study has been performed only on phi SLs 08-02-2006

φ0 TRIGGER ACCEPTANCE SECOND STEP The measured angular distributions of reconstructed tracks N(φ)for a chamber with an angle φo with respect to the vertical direction are : N(φ, φ0)= kφo· f(φ- φ0) · acc(φ) acc(φ) = trigger acceptance (unknown) f(φ) = cosmics angular distribution (unknown) with : • With an iterative method including a combined fit of the measured angular distributionsfrom chambers with the same internal geometry (equal angular dependence of the trigger acceptance) it is possible to extract: • the cosmics angular distribution f(φ) (parameterized) • kφ0· acc(φ)= trigger acceptance (the normalization factor kφ0can bedetermined only by defining the absolute cosmic flux) • the relative fractions kφ0/ kφ0’of tracks crossing the different chambers (the method has been carefully checked on a simulation ) 08-02-2006

TRIGGER ACCEPTANCE 1. RESULTS – cosmics distributions Cosmics angular distributions obtained for MB4 and MB2 (data taken with a HH+HL trigger) PARAMETERIZATION : 08-02-2006

TRIGGER ACCEPTANCE 1. RESULTS – global acceptance Angular dependence of the global HH+HL trigger acceptances obtained for MB4 and MB2 The HH+HL trigger acceptance of a MB4 chamber is more asymmetric than a MB2 one (in MB2 chambers the staggering between SLs is of only 1 cell) 08-02-2006

TRIGGER ACCEPTANCE 1. RESULTS – single chamber acceptance Acceptances for single chambers (MB4) Trigger acceptance sector 6 sector 8 sector 5 Measuredangular distributions -30° -60° 60° Each single chamber has an acceptance very similar to the global one Note that the points with a big error are correlated to very inclined tracks(at angles of about 90 degrees respect to the vertical) 08-02-2006

TRIGGER ACCEPTANCE 2. RESULTS – global acceptance Angular dependence of the MB2 trigger acceptance for different trigger configurations The HH+HL configuration has the smallest angular acceptance 08-02-2006

TRIGGER ACCEPTANCE 2. RESULTS – cosmics distribution Cosmics angular distributions obtained with the 3 different trigger configurations (data taken with on a MB2 chamber) Although the 3 triggers have different angular acceptance they give very similar cosmics angular distributions 08-02-2006

RESOLUTION • We have implemented the possibility to exclude one layer at a time from the segment fit to obtain an unbiased resolution measurement • It is important to study the plots of residuals on the distance from the wire and on the position because they give different information • distance info about ttrig and vdrift • position info about possible misalignments inside the SL • NOTE : • We didn’t use t0 correction event by event • Drift velocity not perfectly calibrated 08-02-2006

RESOLUTION Residuals on hit distance from wire Without layer exclusion # events |xm|-|xextr| σ residuals = 530 μm |xm|-|xextr| (cm) |xextr|(cm) With layer exclusion # events |xm|-|xextr| σ residuals = 700 μm Big effect due to the systematic uncertainties in ttrig for cosmics |xm|-|xextr| (cm) |xextr|(cm) 08-02-2006

RESOLUTION Residuals & uncertainties in ttrig Ideal event with correct ttrig Event where there is a systematic uncertainty on ttrig (real case for cosmics data since not bunched) If we remove one hit from the fit, the residual increases more than in the ideal case where ttrig is perfectly known 08-02-2006

RESOLUTION About residuals computation • it would be useful to use Anna’s routine for event by event t0 corrections • we need to tune calibration parameters ( ttrig and vdrift ). Needed tools are already implemented in ORCA (see Sara & Gianluca’s talk of tomorrow session) but: • how to define the recipe for the ttrig definition independently from drift velocity • what is the effect of cosmics ttrig uncertainties on the Mean Timers : is it still possible to calibrate the vdrift from Mean Timers? 08-02-2006

OVERVIEW TO DO : Add in our analysis the t0 correction event by event routine(plans to have it public/committed?) Study misalignments between the SLs inside a single chamber Study misalignments inside a SL 08-02-2006

EXPLICATIONS Bumps in angular distributions vertical vertical horizontal horizontal Before and after the yellow line (horizontal cosmics) we could observe two separate distributions corresponding to tracks with opposite directions. The bump is due to tracks crossing the chamber from the inner to the outer SL. 08-02-2006

FURTHER STUDIES ON COMMISSIONING DATA