further studies on commissioning data

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


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


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


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


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


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 )


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


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


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


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


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


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


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


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


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?


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


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

further studies on commissioning data

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