C. Di Donato and Ilaria VillellaI.N.F.N. and Universita’ di Napoli

Radiative decay meeting

April 17th 2003

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 2

Why Why

• PDG’02: BR() = (4.68±0.11)x10-2

• KLOE: 500pb-1 5x105 events (selection~50%)

• BR measurement error: 0.2x10-4

• Study of |M|2 (Gormley et al. P.R.D2(1970),501 7250 events) :

¤ simple gauge-invariant matrix element |M|2~q2k2sin2

¤different theoretical model include the effect of a final-state interaction assuming that the dipion phase shift is dominated by the meson;

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 3

Signal and BackgroundSignal and Background

(b)

• Signal decay 1.84 x10-3

•Background decay S/B

0.44 4 x 10-3

e+e- 7.66x10-6 240

8.717x10-3

0.2

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 4

Signal: Signal:

Final State: MC Signal Production: 5x104 events

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.

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

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 5

energy energy

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

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 6

Invariant mass of two photons

Invariant mass of two photons

(MeV)

MC true

MC trueRAD

StreamMC true

RPI Stream

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 7

RAD+RPI Stream Efficiency

RAD+RPI Stream Efficiency

Average = 66%

E(Mev)

E(Mev)

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 8

RPI Stream cutsRPI Stream cuts

EEMeV

(E

E

) (M

eV

)(E)(Mev)

SIGNALSIGNAL

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

• p in lab. Frame• Boost in rest frame

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 9

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

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 10

RAD+RPI stream RAD+RPI stream

E (MeV)

SS+B

S/B=2x10-2

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 11

CutsCuts

Both stream:

•356 MeV<Egrad<368MeV

•S/B =0.14

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 12

Strong cutsStrong cuts

Only RAD stream

•P(2) > 10-4

•356MeV<Erad< 368MeV•Track mass > 200 MeV

•S/B =163

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 13

Angular distributionAngular distribution

Expected angular distribution dN/d(cos)~sin2

cos

Corrected MC generator is now in geanfi

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 14

A first look at data A first look at data

RAD stream1 pb-1

M(MeV)

M(MeV)

Mtr

ack

I. Villella April 17th 2003 - Phi Radiative Decay Meeting- Frascati 15

Conclusions and OutlookConclusions and Outlook

• Clear signal on data •Reasonable background for events in radiative stream (but more careful evaluation is in progress)

• Events in rpi stream are vital to fit the spectrum; a strategy to recover events is in development, but will be necessary only if we improve S/B in that kinematical region

• Angular variables can help