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

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

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
sector 5
sector 6
ANALIZED SECTORS:
(wheel 1)
sector 8
Giorgia Mila - INFN Torino

4. ASSUMPTIONS & STUDIES TRIGGER ACCEPTANCE 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
Giorgia Mila - INFN Torino

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

6. N(φ, φ0)= kφo · f(φ- φ0) · acc(φ)
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) φ0
acc(φ) = trigger acceptance (unknown) f(φ) = cosmics angular distribution (unknown)
with :
With an iterative method including a combined fit of the measured angular distributions from 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 be determined 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 )
Giorgia Mila - INFN Torino

7. 1. RESULTS – cosmics distributions
TRIGGER ACCEPTANCE
1. RESULTS – cosmics distributions
Cosmics angular distributions obtained for MB4 and MB (data taken with a HH+HL trigger)
PARAMETERIZATION :
Giorgia Mila - INFN Torino

8. 1. RESULTS – global acceptance
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)
Giorgia Mila - INFN Torino

9. 1. RESULTS – single chamber acceptance
TRIGGER ACCEPTANCE
1. RESULTS – single chamber acceptance
Acceptances for single chambers (MB4)
Trigger acceptance
sector 5
sector 6
sector 8
Measured angular 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)
Giorgia Mila - INFN Torino

10. 2. RESULTS – global acceptance
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
Giorgia Mila - INFN Torino

11. 2. RESULTS – cosmics distribution
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
Giorgia Mila - INFN Torino

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

13. Without layer exclusion
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)
Giorgia Mila - INFN Torino

14. Residuals & uncertainties in ttrig
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

15. About residuals computation
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

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

17. Bumps in angular distributions
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.
Giorgia Mila - INFN Torino