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First steps to radiative return studies at Belle

B.A.Shwartz

BINP, Novosibirsk

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Plan1. Basic things

2. A sample for first study

3. What’s seen for: , , KK and

This is our first steps to see what can be done at Belle for radiative return physics.

The events with 2 charged particles were studied

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)1(ln)(

)(3

422

422

3

22

em

s

mss

msmR

sdm

dσm

)1(ln)(

)(

][

][4035.022

422

2

2

em

s

mss

ms

m

mR

GeVs

GeVnb

dm

dσ

1

0

30

e+e

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)1(ln)(πs

222

4

em

s

mss

msαm

Ldm

dl

KEKB VEPP-2000

Luminosity,

см-2 s-1

1034 1032

Integrated lum. (per 107 s)

100 fb-1 1 fb-1

Integrated in the range [1-2] GeV

0.1 fb-1 1 fb-1

Comparison to VEPP-2000project, ee up to 2 GeV

(under construction at BINP)

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A sample to study

The Tau-pair sample (skim) is used ( 2<Ntrk<8, Pch<9GeV, Eecl<9GeV)

Then the following cuts were applied:

1. Ntrk=2

2. 10<Erec<11 　 GeV

3. Ptot <0.5 GeV

4. N>0

5. Emax>3 GeV

6. 0.7<<2.6

7. Pmin >0.7 GeV (charged)

25.9 fb-1 is used study

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Erec

Ptot

Minv

P

)( 2)(2

1beam

invbeam E

ME

PR

E2<0.2 (for 2 particles modes)

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Minv(2tr), GeV

All events , (p1/, p2/ >0.5)

Two particle events

Minv(2tr), GeV

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background

calculation

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N/N ratio

By a simple separation procedure the number of and events are obtained and ratio is calculated

(just demonstration, not for usage!)

The difference 5% can be caused by the different trigger efficiency for pion and muon events. This is a measure of systematics.

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How to compare with BaBar?

N=183093

M =31061 MeV

=16.30.9 MeV

71 J/ per 1 fb-1

From BaBar J/ paper – 7800 J/ event at 88.4 fb-1 88.2 J/ per 1 fb-1

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KK 0

ECM – ( ｜ pmax ｜　 + ｜ p+ ｜　 +p ｜ )>1

GeV

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Conclusion

1. Events with radiative return can be seen at Belle with reasonable efficiency.

2. New Bhabha trigger implementation should improve the trigger efficiency at low invariant mass area