CMD-2 and SND results on the and

International Workshop «e+e- Collisions from to

»February 27 – March 2, 2006, BINP, Novosibirsk, Russia

M.N. Achasov

Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences

Cross section e+e → hadrons

Process e+e → hadrons(√s < 1,4 GeV)

V – vector meson, IG(JPC) = 1+(1 ) и 0(1 )

V = , excited states.(at √s < 1,4 GeV the vector mesons dominance model describes the

e+e → hadrons cross section with accuracy of about 1%)

Importance of the e+e → hadrons processes studies in the energy region √s < 1,4 GeV

• Determination of the parameters of the light vector mesons

• R(s)=(e+e → hadrons )/ (e+e → ) ( calculation of the hadronic contribution to the

anomalous magnetic moment of the muon (g-2)/2; …)• Check of the CVC (comparison of the isovector part of the e+e →

hadrons cross section with spectral function in → hadronsdecays)

Experimental situation in the energy region √s < 2 GeV.

• VEPP-2M (√s <1,4 ГэВ, luminosity up to 3 × 1030 cm-2s-1) finished its operation and now is

beening reconstructed as VEPP-2000 (energy region up to 2 ГэВ, luminosity up to 1032 cm-2s-1)

• factory DANE (luminosity up to 1033 cm-2s-1) nowadays produce experimental data at the meson mass (1020 MeV).

• B-factory at SLAC the e+e → hadrons cross section at low energies is measured with radiative return method :

VEPP-2M

Center of mass energy region 360 – 1400 MeV

Luminosity at 1000 MeV 3 × 1030 cm-2s-1

CRYOGENIC MAGNETIC DETECTOR - 2 (CMD-2) SPHERICAL NEUTRAL DETECTOR (SND)

1 – beam pipeline, 2 – drift chambers, 3 – scintillation counter, 4 – light guides, 5 – PMT, 6 – NaI(Tl) crystals, 7 – VPT, 8 – iron absorber, 9 – stream tubes, 10 – iron plates, 11 – scintillation counters, 12 – magnetic lens, 13 – bonding magnets.

1 – beam pipeline, 2 – drift chamber, 3 – Z-chamber, 4 – superconducting solenoid, 5 – compensating magnets, 6 – BGO end cup calorimeter, 7 – CsI(Tl,Na) calorimeter, 8 – muon system, 9 – magnet yoke.

Integrated luminosity1995 - 2000

Integrated luminosity accumulation dynamics

Integrated luminosity distribution over energy region.

Total luminosity per detector is 30 pb-1.

The cross sections e+e → hadronsmeasurement method

•The experimental data is accumulated using √s energy scan method and then analyzed ;

•The e+e → hadrons cross sections measurement:

N – number of the e+e → hadrons events;

IL – integrated luminosity (measured using e+e → e+e and );

- detection efficiency (obtained from MC simulation);

rad – radiative correction;

spr – correction due to the beam energy spread.

sprradIL

N

Analysis of the e+e → hadrons cross sections

2

,...,,

3

2/3 )()(

)()(

4)(

VX

i

V V

VVVXX

mP

e

sD

XVmmsP

ss

V

2

)()(12)(

Vm

eeVBXVBXV

In order to obtain the vector mesons V = parameters the measured cross section of the

process e+e → X is fitted with theoretical expression:

The following parameters can be obtained from the fit: mV - mass, V – width, V – phase and

Measurement of already known decays

First observation

→ →

→e+e

→ e+e → f0a0 e+e

Results of the mesons rare decays studies with CMD-2 and SND detectors at VEPP-2M.

Rare decays of (Br<103).

The e+e → cross section

The e+e→ process cross section in the VEPP-2M energy region.

The value → e+e) obtained in various

experiments. Yellow area shows the average value

For data description the mesons are required.

At √s 780 МэВ the interference is seen.

The meson parameters (mass and width)

Here are shown the m and measured in e+eexperiments in processes:

e+e →→ (SND-05, CMD-2-02, OLYA-85), e+e →→SND-05, KLOE-

03→ → (ALEPH-05, CLOE-2-00)

Yellow area shows the average value.

The e+e → cross section

The e+e →→transition dominates in this reaction. At VEPP-2M the e+e → → transition was observed. The intermediate state different from these two was observed by KLOE and CMD-2 in the -meson energy region (maybe e+e → → ).

The e+e→cross section measured by SND. Syst. error 3,4–5,4%. The

curve is the result of the fit taking into

account

The e+e → cross section

Curve is the result of the fit taking into account resonances. (Dots are SND data)

The e+e → process cross section.

Syst. error: SND - 3%, CMD-2 - 6 %.

The meson parameters (mass and width)

In measurements CMD-2-04 and SND-03 the -meson parameters were obtained using e+e →

process, while in CMD-2-05 - using e+e →reactionYellow area shows

the average value.

The meson main decays modes

Yellow area shows the average value.

The e+e → K+K and KSKL cross sections

For data description the resonances are required.

The e+e → K+K cross section in the –meson energy region. → K+K decay.

Systematic errors: SND – 7%, CMD-2 – 3-4% (preliminary) Yellow area shows the average value.

The e+e → KSKL cross section in the –meson

energy region. → KSKL decay.

The cross section measurements were based on the KS → and decays.

Systematic errors: SND – 3,3%, CMD-2 – 1,7%

Yellow area shows the average value.

The e+e → cross section

The cross section was measured using → decays. For data description the

following states are required . The systematic errors in the vicinity of the meson peak are 3-7%

The → and decays

Comparison of the SND and CMD-2 measurements with the other experimental results.

Yellow area shows the average value.

The meson parameters (mass and width)

Comparison of the SND and CMD-2 measurements with the other experimental results.

Yellow area shows the average value.

Probability of the → e+edecay.

Yellow area shows the VEPP-2M

average. Deviation from KLOE

result is 3

CMD-2-05 – using the main → hadrons decays (preliminary). KLOE-05 – using cross section and e+e forward-backward asymmetry. СНД-01 – using the main → hadrons decays and cross section.

CMD-2-95 – using the main → hadrons decays

Resonances with IG(JPC) = 1+(1 ) and 0(1 )above meson.

These resonances exist. Their parameters are not well established and nature is not clear. The number of them is unknown.

Some important results from SND and CMD-2:• The clear experimental evidence of the resonance;• Observation of the a1 dominance in the process e+e →

The e+e → cross sectionThe e+e → +-- cross section

Estimation of the /and/ / parameters

mV, MeV V , MeV (V→ 3nb

(V→ee),eV

1400 870 5 600

1770 500 5,5 860

5~)0(

)0(2

//

S

S

6,0)0(

)0(2

/

)2(

SJ

SS

The parameters of the /, / / were estimated from combined analysis of the e+e → process cross section measured by SND and

DM-2 data on the e+e → reaction

4~)0(

)0(2

/

S

S

44,0)0(

)0(2

)1(

)2(

SS

SS

The ratios of the wave functions at the origin are more then 1 :

while

Conclusions

• In the 1995-2000 the experiments with CMD-2 and SND detectors at VEPP-2M were fulfilled.

• The cross sections of the e+e annihilation in hadrons were measured in the energy region √s = 0,36 – 1,38 GeV.

• Results of these experiments determine nowadays the accuracy of the light vector mesons parameters determination. They are one of the main source of information about particle physics at low energies.