Analysis of the dynamics of the decay + - o Referees report Mario Antonelli, Luca Passalacqua KLOE general meeting 10-10-2002.

Analysis of the dynamics of the Analysis of the dynamics of the decay decay ++--oo

Referees reportReferees report

Mario Antonelli, Luca Passalacqua

KLOE general meeting 10-10-2002

General:• competitive results + 2000 data KLOE note soon draft

Analysis is in a good shape:• relevant detector effects taken into account• several checks DATA-MC• systematic uncertainties evaluation• robustness of the fit

Main questions:• bias on momentum measurement • ISR not taken into account

• Detailed description in the KLOE MEMO 274

Comments

Momentum bias

• difference in measured momenta between negative and positive charged particles observed in the control samples: and events

P(+

)-P

(-)

(MeV

)

NOW: main systematic for Ms mesaurements 0.5 MeV

ONLY the AVERAGE enter in (Ms)

Profiles + lab frame

Momentum biasReferees comment: find source(s) of the effect

correct measured momenta (use control sample) verify consistency with o mass systemaitcs from uncertainties on correction Closer look to the effect:

• rest of frame + use gaussian fits to slides

P(+

)-P

(-)

(MeV

)

~ 280 KeV average

slides + frame

50o<<130o

Momentum bias

• the wire droop

is not taken into account in the present track reconstruction algorithm bias on the momentum ?

X-Y view

w ~ 200m Not in scale

Sagitta (s)

pt=pt2/(0.3BLt

2)8 s

error on the wire poistion s pt

sdroop ~

R-Z view

100 m 300 keV @ p=500MeV

Momentum biasCharge dependent effect:

X-Y view

+ / –s for + / - charge

X-Y view

dependent effect

w

s

effective bias

Parallel component

to the sagitta

s=w cos

Momentum bias

R-Z viewdependent effect

Only relative positions are important

If wires have same droops w no effect at =90o

sw

X-Z view =0

sw

s

At small angle

Momentum bias

w is not a constantWIRE SAGITTA vs. LAYER #

100

150

200

250

300

350

400

450

0 20 40 60 80 100 120

LAYER #

SA

GIT

TA

(m

icro

n)

SAGW micron

SAGAl micron

effect at =90o expected (and observed)

Momentum bias

use a toy model to verify consistency with data• linear droop vs z

• evaluate average of effective s: dependencies and differences in w(0) vs R taken into account

curvature effect on effective s also considered

z

w(0)

Not negligible R~1 m

dependence (s) on the wire

Results P

(+)-

P(-

) (M

eV

)

50o<<130o

check the model at low angles (large effects are expected)

results

Use bhabha

P(+

)-P

(-)

(MeV

)

35o>>155o

A bit asymmetric…under studyTilted plates?

ISR effects?

Initial state radiation not taken into account in the fit

o E,P evaluated from missing E,P using knowledge of W

Some event witho kinetic energy outof boundaries?

Fit stability checked varying cuts on variables sensitive to ISR