Status Report on

Status Report on

Ilaria VillellaI.N.F.N. and Universita’ di Napoli

3rd KLOE Physics WorkshopMay 24th 2003, Capri

I. Villella May 24th 2003 - 3rd KLOE Physics Workshop, Capri 2

Study of Study of

• BR measurement() PDG’02: BR() = (4.68±0.11)x10-2

• Study of theoretical model :comparison of the predicted spectra whit the corresponding experimentally determined values

¤ In MC generator (Gormley et al. P.R.D2(1970),501 7250

events)

There is a model including the effect of a final-state interaction assuming that the dipion phase shift is dominated by the meson;

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Theoretical ModelsTheoretical Models

Anomalous contribution: Contribution of the box anomaly beside the classical triangle

anomaly responsible for ’decays predicted by PCAC and by the Wess-Zumino-Witten chiral lagrangian.

Resonant contribution:• Model M2: involving the whit its subsequent decay to

a pion pair (VDM);• Model M1: existence of a small non-VDM contribution;

The anomalous and resonat contribution are indipendent processes.

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Signal and BackgroundSignal and Background

(b)

• Signal decay 1.84 x10-3

•Background decay S/B

0.44 4 x 10-3

e+e- 7.66x10-6 2.4 x 102

8.717x10-3

0.2

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Signal: Signal:

Final State:

Topological cut:• 2 prompt photons |tcl-lcl/c| < 5t;• 1 charged vertex with two associated tracks • The Vertex must be inside the following region: rxy < 4 cm; |z|< 8 cm.

Kinematic fit without mass constraint.

Filfo EVCL(RADstream) topological cut Total selection: 99% 54% 86% 46 %

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spectrum spectrum

RAD stream

efficiency

RAD stream

efficiency

E(Mev)

RA

Dst

ream

R

AD

stre

am

E(Mev

)

RPI= 11.50%

E(Mev)

RPIs

tre RPI stream

efficiencyRPI streamefficiency

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Invariant mass of two photonsInvariant mass of two photons

(MeV)

MC true

MC trueRAD

StreamMC true

RPI Stream

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RAD+RPI Stream EfficiencyRAD+RPI Stream Efficiency

Average = 66%

E(Mev)

E(Mev)

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RPI Stream cutsRPI Stream cuts

EEMeV

(E

E

) (M

eV

)(E)(Mev)

rest frame • rest frame: (Erad) =363 Mev; pp–p

• p in lab. Frame• Boost in rest frame

SIGNALSIGNAL

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RPI Stream cutsRPI Stream cuts

EEMeV(E

E

)

(MeV

)(E)(Mev)

Background

Background

Signal Background =Ncuts/NRPI 80.7%17.8%

(S/B)RPI = 3x10-3

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RAD+RPI stream RAD+RPI stream

E (MeV)

SS+B

S/B=2x10-2

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CutsCuts

Both streams:•P(2) > 10-4

•357.8 MeV< Erad <368.2 MeV

S/B =0.14

SignalSignal

Background

Background

Erad(MeV)Erad(MeV)

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Tight cutsTight cuts

•P(2) > 10-4

•357.8MeV<Erad< 368.2MeV

Only RAD stream:

S/B = 1.63

Recoil mass(MeV)

Lint = 29 pb-1

2001 datarecV13

Recoil mass > 160 MeV S/B = 4.59x 102

Bhabha

signal

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Invariant Mass Invariant Mass

RAD stream Lint = 29 pb-1

M(MeV)

357.8MeV<Erad< 368.2MeV

Recoil mass > 160 MeV

M(MeV)

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Branching Ratio AccuracyBranching Ratio Accuracy

M(MeV)

cos

We select N=18508 events our BR 3% below PDG’02 value

BR/BR = 7 x 10-3

preliminary

preliminary

There is still background

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Conclusions and OutlookConclusions and Outlook

• We will study cuts based on angular variable to reduce other background, but we need MC events from the last GEANFI version (some bugs resolved). • We plan to analyse 100pb-1

• Faisability to check different theoretical model for decay

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KLOE: 500pb-1 4.6x105 events (selection~50%)

s = E + + E - + E

Trackmass

Trackmass(MeV)

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Angular distributionAngular distribution

Expected angular distribution dN/d(cos)~sin2

cos

Corrected MC generator is now in geanfi

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