Giorgia Mila - INFN Torino 08-02-2006 1
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
Giorgia Mila - INFN Torino 08-02-2006 2
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
Giorgia Mila - INFN Torino 08-02-2006 3
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
ANALIZED SECTORS:
(wheel 1)
sector 5
sector 6
sector 8
Giorgia Mila - INFN Torino 08-02-2006 4
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 :
1. The trigger HH+HL acceptance between MB2 / MB4
2. The MB2 trigger acceptance between HH+HL / Default / Hanytheta
Giorgia Mila - INFN Torino 08-02-2006 5
FIRST STEP
This method relies only on the angular distributions of reconstructed tracks
Measured distributions (trigger HH+HL)
TRIGGER ACCEPTANCE
sector 6 sector 5 sector 8
MB4
MB2
-60° -30° 60°
-60° -30° 60°
The study has been performed only on phi SLs
Giorgia Mila - INFN Torino 08-02-2006 6
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 :
φ0N(φ, φ0)= kφo · f(φ- φ0) · acc(φ)
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 kφ0 can bedetermined only by defining the absolute cosmic flux)
• the relative fractions kφ0/ kφ0’ of tracks crossing the different chambers
TRIGGER ACCEPTANCE
acc(φ) = trigger acceptance (unknown) f(φ) = cosmics angular distribution (unknown)
with :
(the method has been carefully checked on a simulation )
Giorgia Mila - INFN Torino 08-02-2006 7
1. RESULTS – cosmics distributions
Cosmics angular distributions obtained for MB4 and MB2 (data taken with a HH+HL trigger)
PARAMETERIZATION : sincoscoscos 2 edcb
TRIGGER ACCEPTANCE
Giorgia Mila - INFN Torino 08-02-2006 8
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)
TRIGGER ACCEPTANCE
)()(
)(0
0
acck
f
N
Giorgia Mila - INFN Torino 08-02-2006 9
1. RESULTS – single chamber acceptanceAcceptances for single chambers (MB4)
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)
TRIGGER ACCEPTANCE
sector 5 sector 8
-30° 60°
sector 6
-60°
Trigger acceptan
ce
Measuredangular
distributions
Giorgia Mila - INFN Torino 08-02-2006 10
2. RESULTS – global acceptance
Angular dependence of the MB2 trigger acceptance for different trigger configurations
The HH+HL configuration has the smallest angular acceptance
TRIGGER ACCEPTANCE
Giorgia Mila - INFN Torino 08-02-2006 11
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
TRIGGER ACCEPTANCE
Giorgia Mila - INFN Torino 08-02-2006 12
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
Giorgia Mila - INFN Torino 08-02-2006 13
RESOLUTION
Residuals on hit distance from wire
|xm|-|xextr| (cm)
Without layer exclusion
|xm|-|xextr| (cm)
With layer exclusion
σ residuals = 530 μm
Big effect due to the systematic
uncertainties in ttrig for cosmics
# e
vents
|xm|-
|xextr|
|xextr|(cm)|x
m|-
|xextr|
# e
vents
|xextr|(cm)
σ residuals = 700 μm
Giorgia Mila - INFN Torino 08-02-2006 14
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
Giorgia Mila - INFN Torino 08-02-2006 15
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?
Giorgia Mila - INFN Torino 08-02-2006 16
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
Giorgia Mila - INFN Torino 08-02-2006 17
Before and after the yellow line (horizontal cosmics) we could observe twoseparate distributions corresponding to tracks with opposite directions.The bump is due to tracks crossing the chamber from the inner to the outer SL.
vertical
vertical
horizontal
horizontal
EXPLICATIONS
Bumps in angular distributions