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, I G (J PC ) = 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  → hadrons  decays )

Experimental situation in the energy region √s < 2 GeV. VEPP-2M (√s <1,4 ГэВ, luminosity up to 3 × cm -2 s -1 ) finished its operation and now is beening reconstructed as VEPP-2000 (energy region up to 2 ГэВ, luminosity up to cm -2 s -1 )  factory DA  NE (luminosity up to cm -2 s -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 × cm -2 s -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 luminosity Integrated luminosity accumulation dynamics Integrated luminosity distribution over energy region. Total luminosity per detector is 30 pb -1.

The cross sections e + e  → hadrons measurement 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.

Analysis of the e + e  → hadrons cross sections 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: m V - mass,  V – width,  V – phase and

Measurement of already known decays First observation  →    →                    →       e + e   →      e + e   → f 0  a 0                 e + e  Results of the  mesons rare decays studies with CMD-2 and SND detectors at VEPP-2M. Rare decays of  (Br<10  3 ).

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 + e  experiments 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 %.

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 using e + e  →    reaction  Yellow area shows the average value.

The  meson main decays modes Yellow area shows the average value.

The e + e  → K + K  and K S K L 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  → K S K L cross section in the  – meson energy region.  → K S K L decay. The cross section measurements were based on the K S →     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 + e  decay. 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 I G (J PC ) = 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 a 1  dominance in the process e + e  →         The e + e  →       cross sectionThe e + e  →  +  -    - cross section

Estimation of the  /  and  / /  parameters m V, MeV  V, MeV  (V→ 3  nb  (V→ee),eV    ,5860 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 The ratios of the wave functions at the origin are more then 1 : while

Conclusions In the 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.