Accidentals et al.

MC meeting 1-Dec-2004

• MC study of Early-Time window • Calibration of P1A, P2A in MC• Accidental rate and spectra:

- comparison MC vs Data

• Identification of a problem ...

S.Miscetti

S.Miscetti

Ks in 2pi0 with 4, 5, 6 gamma in TW.• Only drawback is the impossibility to test the probability of stoling theT0 (work already done with Ks to pippim ..). If this method gives satisfactory results it can be then done also with other samples.• Aside the small correction for the T0 losses this is a powerfull sample to look to the early timing window and compare with the MC accidentals in time window• We define 2 categories: Nacci Early (T-R/C between –68ns,-13.6ns ) Nacci Early in acceptance ( E>7 costhe <0.915) but application of TW..

Then ... Compare with events with Kine=0 Count accidentals in acceptance and in TW after rephasing to 2*Trf

and then divide by the number of peaks in early tw (10)

SAMPLEs used for the MC calibration

Timing spectrum in the MC

• Accidental clusters are IN with a flat rate vs T-R/C • in the MC they can be identified accurately

Nacci early vs Early in acceptance

Let’s check the rates:• we have measured the P1A,P2A, P(>=1A) in early TW w and w/o acceptance cut( excluding the timing)

• the time spectra looks wider in MC than in data

• the rates look different! (Table in a while)

Data vs MC energy and costhe spectra

The energy and angular spectraare well reproduced!

MC calib: rephased events from ETW vs acci in TW

We also tried to quantify,using MC, how well wecan calibrate the expectedEvents in TW from earlyTW.

P1A in TW expected by ETWcompared with 1A in Ng=5

P2A in TW expected by ETWCompared with 2A in Ng=6

Not too bad .. expecially for 1A Precision 10-20%

- Acci in TW MC (Ng=6)• 2 Acc exp by ETW

- Acci in TW MC (Ng=5)• 1Acc exp by ETW

Accidental Rates: Data vs MC 2001

MC DATA MC x 0.7

P(ge1) 100% 70.3%

P1A 64.8% 38.2% 45.3%

P2A 25.6% 16.7% 17.9%

P(ge1) Early Acc

54.7% 33.2% 38.2%

P1A

Early Acc42.9% 25.4% 30.0%

P2a Early ACC

9.3% 5.9% 6.5%

P1A TW 1.01 % 0.66 % 0.70%

P2A TW 0.11% 0.11% 0.077%

Accidental Rates: Data vs MC 2002MC DATA MC x 0.46

P(ge1) 93% 43.0%

P1A 58.2% 26.2% 26.7

P2A 20.4% 9.0% 9.4

P(ge1) Early Acc

47.8% 19.0% 22.0

P1A

Early Acc38.4% 15.0% 17.4

P2a Early ACC

7.1% 3.1% 3.3%

P1A TW

extrapol0.86 0.37 0.39

P2A TW

extrapol0.094 0.068 0.044

Rate EarlyTW ( Data vs MC) 2001

- ev 1Acc in ETW scaled to TW (DATA)• ec 1Acc in ETW scaled to TW (MC)Normalization by number of Ks2pi0 xP1A(data)/P1A(MC)

- ev 2Acc in ETW scaled to TW (DATA)• ev 2Acc in ETW scaled to TW (MC)Normalization by number of Ks2pi0 xP2A(data)/P2A(MC)

Rate EarlyTW ( Data vs MC) 2002

- ev 1Acc in ETW scaled to TW (DATA)• ev 1Acc in ETW scaled to TW (MC)Normalization by number of Ks2pi0 xP1A(data)/P1A(MC)

- ev 2Acc in ETW scaled to TW (DATA)• ev 2Acc in ETW scaled to TW (MC)Normalization by number of Ks2pi0 xP2A(data)/P2A(MC)

Summary of the calibration ...

S.Miscetti

Using Ks2pi0 sample with 4 gamma and studying the Early TW we have calibrated how to quantify the P1A, P2A in TW

(with a precision of 10-20%) and compared data and MC:

• Energy and angular distributions OK• T-R/C spectra are slightly wider in MC events• Rate comparison There is a large DATA-MC difference both in P1A ,P2A.

The difference remains “almost” constant with and without acceptance requirements.

P2A in TW slightly larger in data even after a scale correction.

This difference is much larger in 2002

Identification of the rate problem ??

S.Miscetti

The problem of P1A is related to the fact that in BGG files there is always at least one accidental hit which is a condition mostly satisfied in 2001 (testing sample) Not at all in 2002!

The rate problem can be partially fixed by measuring P1A for the whole 2001-2002 period and scaling it whenever P1A < 100%