Summary of efficiencies on measurement

Marco Incagli – 23/5/03

1. TRG, TV, TCA+LIK :• single track efficiency found with data• efficiencies combined using MC at KINE level

2. TRK :• single track efficiency found by MC and corrected with data • efficiency combined using MC at KINE level

3. VTX , MTRK :• efficiency from MC, checked with data

4. FILFO :• efficiency from data

5. geometrical acceptances (angular and Pt,Pz cuts):• efficiency from MC

1.1 – Trigger + Trigger Veto

• The single particle TRG (and TV) efficiency is first obtained, then the information are combined using MCP0±(P1) = probability that the ± fires 0(1) trigger sectors

P0R(P1R) = prob. that the Rest of the event fires 0(1) trigger sectors

PTRG = 1 P0P0P0R P1P0P0R (-) (R)

• To evaluate the single particle TRG efficiency events with TV on (with the hardware prescale factor 5) + 1/5th of the events with TV off to be independent from the TV

• TV efficiency is evaluated on triggered events, so what we find is (TRG)•(TV|TRG)

TRG + TV single track efficiency

• To get the single particle efficiency – the track is associated to one or more clusters

– the clusters are associated to trigger (TV) sectors

• The first step is performed by extrapolating the TRK to the ECAL using the newextratom procedure (developed by T.S. and C.G.) and associating to TRK all clusters within a radius R=60cm

• The second step is performed using the CTRG bank

• A check of the dependence of the procedure from the R value has been performed

1 – TR+TV efficiency

• The average efficiency starts to saturate at R60cm

• The systematic error is at the 0.2 % level

• A systematic error which is function of Q2 can be used

TRK efficiency

• Two data samples are selected: : 2 prompt photons with 0 mass + a track which extrapolates

back to IP connected to a cluster which satisfies the pion likelihood

: 1 or 2 ‘prompt’ clusters ; one is associated with a track of p=490±5 MeV which satisfies the pion likelihood

• Some cuts are applied to clean up the second sample. The following categories are selected:– monotracks

– two tracks of the same sign

– proton stars

Monotracks

Monotracks

• They are characterized by a deposit of energy in one or two cells

• Monotracks associated to clusters with 1 or 2 cells are removed from the sample

Good events

monotracks

Two tracks of Same Sign

Two tracks of Same Sign

• They are removed if the minimum distance of LH-FH is larger than 100cm

• (this is done to keep inefficiencies in which the tagging track is broken into two pieces)

Proton Stars

Proton Stars

• They are removed by cutting on the variable QTOT/Ntrk

Closing kinematically the event

• The momentum of the candidate track is evaluated using the -boost from Bhabhas, the photons after imposing the 0 mass and the tagging track extrapolated at IP

• When a vertex exists in the event, then it is possible to check the goodness of the above procedure

• The plots show that the error is symmetric and has MeV

• I take bins of p=25MeV which seems to be safe

Candidate track (TRK2) assignement

• Once the event is selected the momentum components of TRK2 are evaluated (pxe,pye,pze)

• All tracks of the events satisfying the cuts reported in the next transparency are compared with the tagging track

• The track which minimizes the 2 defined below is the candidate track

• A cut at 2 <15 (it was 2 <10) is applied

2

2222

10

)pzepz()pzepz()pxepx(

2

1

2 distribution

Definition of candidate track

A candidate track must satisfy the following cuts:

1. Charge must be opposite wrt tagging track

2. First hit must have cm

3. The point of closest approach (PCA) of backward track extrapolation must have PCAcm and |zPCA|cm

4. 2 condition must be fulfilled

TRK efficiency data() vs MC() – 5slices in btwn 40o and 90o

DATA

MC

DATA/MC

TRK efficiency

• Since the ratio data/MC is rather flat I use the MC track efficiency spectrum correcting it for the following percentage:

(98.59+99.27)/2 = 98.93%

• The systematic error of this procedure is estimated as half the maximum difference btwn the data/MC ratio:

(99.27-98.59)/2=0.34%

TCA+Likelihood eff

• The ratio data/MC is not flat , therefore MC cannot be used to measure TCA. This effect is expected, since TCA efficiency requires a detailed description of hadronic showers at low energy.

• The TCA+LIK efficiency has been obtained by B.Valeriani by tagging the event with the and looking at the and viceversa.

TCA+LIK efficiency

40o<<50o

40o<<50o

50o<<90o

50o<<90o

The single track efficiency isat the level of 98%, except forthe lowest bin which is in the intersection between BARand ECA

The OR of the likelihood hasan efficiency of ~100%, whilefor the AND the correct combination of efficiencies must be done

VTXEFF a module to select events

• VTXEFF– A prompt photon having:

• 29 < L/t < 32 cm/ns

• E>20MeV ; >100cm

– Two tracks with:

• opposite charge

• FH<50cm

• PCA<8cm

• zPCA<7cm

– Track 1 associated with a cluster which satisfies the pion likelihood

• The selected sample has a large bck from , therefore the following cuts are applied:Mass()<110MeV , >160MeV (if a second prompt photon exists)

cos()>0.9 (angle btwn photon and 2 system)

|E|<20MeV

M2 (GeV2)

Num

ber

of e

vent

s

Vertex efficiency - LA

MC

Data

vtx efficiency vs Q2 (GeV2)

vtx efficiency : (data-MC)/MC

• From the comparison data-MC at Large Angle, the systematics error on VTX is of the order of 1-2%

• Note that LA spectrum essentially dies off at Q2=0.4GeV2 (MC), while data have a sizable fraction of

• More data could improve the significance of the comparison

+2%

-2%

Vertex efficiency - SA vs LA

• Small angle events are back to back in and they are on the same side in

• This causes the different VTX efficiency for the two categories

• MC is used for SA eff.; LA used as benchmark

• Systematics ~2%

Track Mass

•The data track mass distribution has been compared with MC summing the signal + the two backgrounds and ;

•The regions above and below Q2=0.5GeV2 have been fitted separately

•.AND. of the likelihood, to suppress Bhabhas

•E(prompt)<10MeV because of

the cut in RPI stream

Before the sum the following corrections have been applied:

In the low Q2 region the following corrections have been applied:

This procedure provides also the fraction of background events wrt signal; this value is used to scale the MC shape and to estimate the number of background events

The effect of the smearing+shifting on the track mass efficiency in the region of interest (>0.35) is at the per mille level

TRKMASS final efficiency

effi

cien

cy

M2(GeV2)

FILFO efficiency

Q2 (GeV2)

• If the QQ shape does not depend upon bclde, then:

)Q()bclde,Q(k)bclde,Q( 22i

2i

bclde (MeV)

Summary of efficiencies

Systematics - preliminary

• TRG + TV : 0.2 %

• TRK : 0.34 %

• VTX : < 2 %

• FILFO : < 1%

• MTRK : 0.2 % (?)

Systematic error dominated by VTX