Glasgow, October 25, 2007 Results on e+e- annihilation from CMD2 and SND G.V.Fedotovich and S.I.Eidelman Budker Institute of Nuclear Physics Novosibirsk On behalf of CMD-2 and SND collaborations

VEPP-2M colliderVEPP-2M collider VEPP-2M collider: GeV in c.m., L  2 * /cm 2 s at 1 GeV Integrated Luminosity collected by CMD-2 and SND:  70 pb -1 collected in compared to 6 pb -1 in Orsay and Frascati at 1.4 < 2E < 3 GeV

What can we learn?What can we learn? 1. Detail study of exclusive processes: e+e-  (2 – 7)h, h = , ,K,p,…  Test of models and input to theory (ChPT, MVD, QCD,…)  Properties of vector mesons (ρ’,  ’,  ’,…)  Search for hybrids (qqg and glueballs)  Test of CVC relations between e+e- and  -lepton  Interactions of light (u, d, s) quarks 2. High precision determination of R at low energies and fundamental quantities  (g μ – 2)/2  α (M² z )  QCD sum rules (α s, quark and gluon condensates)

CMD-2 and SND detectors 1 –vacuum chamber, 2 – drift chambers, 3 – scintillation counter, 4 – light guides, 5 – PMT, 6 – NaI(Tl) crystals, 7 – VPT, 8 – iron absorber, 9 – muon range system based on streamer tubes, 10 – iron plates, 11 – scintillation counters 1 – vacuum chamber, 2 – drift chamber, 3 – Z-chamber, 4 – superconducting solenoid, 5 – compensating magnets, 6 – BGO end cap calorimeter, 7 – CsI(Tl,Na) calorimeter, 8 – muon system, 9 – magnet yoke

Some features of experiments with CMD-2 and SND Large data sample due to high integrated luminosity and large detectors acceptance (calorimetry  0.9  4  ) Large data sample due to high integrated luminosity and large detectors acceptance (calorimetry  0.9  4  ) Multiple scan of the same energy range to avoid possible systematics: step  (2E) = 10 MeV in the continuum and 1 MeV near  and  peaks Multiple scan of the same energy range to avoid possible systematics: step  (2E) = 10 MeV in the continuum and 1 MeV near  and  peaks Absolute calibration of the beam energy using the resonance depolarization method  negligible systematic error from an uncertainty in the energy measurement Absolute calibration of the beam energy using the resonance depolarization method  negligible systematic error from an uncertainty in the energy measurement Good space and energy resolutions lead to small background Good space and energy resolutions lead to small background Redundancy – unstable particles detected via different decay modes (  º → 2 , e + e -  ;  → 2 ,  +  -  0, 3  0 ; …) Redundancy – unstable particles detected via different decay modes (  º → 2 , e + e -  ;  → 2 ,  +  -  0, 3  0 ; …) Detection efficiencies and calorimeter response are studied by using “pure” experimental data samples rather than MC events (about 20 million  and  meson decays have been used) Detection efficiencies and calorimeter response are studied by using “pure” experimental data samples rather than MC events (about 20 million  and  meson decays have been used)

How cross-sections are measured Efficiency  is calculated via Monte Carlo + corrections for imperfect detector Integrated luminosity L is measured using Bhabha scattering at large angles Radiative correction  accounts for ISR effects only Vacuum polarization effects are included in cr. sect. properties All modes except 2  Ratio N(2  )/N(ee) is measured directly  detector inefficien- cies are cancelled out in part Radiative corrections account for ISR and FSR effects Analysis does not rely on simulation Formfactor is measured to better precision than L  mode

Selection of e + e - →  +  - at CMD-2 e/  /  separation using particles momentum in DC can measure N(  )/N(e) and compare to QED  0.6 GeV    GeV N(  )/N(e) is fixed according to QED e  separation using energy deposit. in CsI calorimeter   Likelihood minimization:

Selection of e + e - →  +  - at SND Event separation is based on neural network: 1 output parameter – R e/π 2 hidden layers 20 neurons each 7 input parameters: energy deposition in each layer for both clusters and polar angles      Θ   Distribution on separation parameter

Example of CMD-2 and SND events e + e -  π + π - in CMD-2e + e -  K + K - in SND

Pion form-factor (CMD-2)   ~ 9  10 5  +  - events

Comparison of CMD-2(95) and CMD-2(98) Δ 

Pion form-factor (SND)   Systematic error ~ 8  10 5  +  - events

Compa rison of CMD-2 and SND √s<0.55 GeV 0.6<√s<1 GeV Δ(SND-CMD2)≈1.2%±3.6% Δ(SND-CMD2) ≈ -0.53%±0.34% Syst.error Systematic errors: CMD % SND % Systematic errors: CMD % SND 1.3 %

Systematic errors Source of errorCMD-2 √s<1 GeV SNDCMD-2 √s>1.0 GeV Event separation %0.5% % Fiducial volume0.2%0.8% % Energy calibration %0.3% % Efficiency correction0.2%-0.5%0.6% % Pion losses (decay, NI)0.2% Other0.2%0.5% % Radiative corrections %0.2% % Total %1.3% %

e + e - →  +  - energy interval 390 – 520 MeV energy interval 600 – 960 MeV energy interval 390 – 520 MeV energy interval 600 – 960 MeV Group a µ (  ), a µ (  ), Old ± 1.45 ± 1.12 (1.83) ± 4.1 ± 8.5 (9.4) CMD ± 0.98 ± 0.32 (1.03) ± 1.9 ± 2.7 (3.3) SND ± 1.73 ± 0.69 (1.86) ± 1.3 ± 4.7 (4.8) CMD-2/SND ± 0.85 ± 0.29 (0.90) KLOE: ± 0.8 ± 4.9 (5.0) Average ± 0.73 ± 0.45 (0.86) ± 0.6 ± 1.5 (1.7) energy interval 1040 – 1380 MeV energy interval 1040 – 1380 MeV Group a µ (  ), Group a µ (  ), OLYA 7.49 ± 0.18 ± 0.83 (0.83) OLYA 7.49 ± 0.18 ± 0.83 (0.83) CMD ± 0.10 ± 0.16 (0.19) CMD ± 0.10 ± 0.16 (0.19) Average 7.03 ± 0.09 ± 0.16 (0.18) Average 7.03 ± 0.09 ± 0.16 (0.18)

Cross-section e + e -  π + π - π 0 CMD2 SND BaBar Systematic error ≈7% outside resonances, ≈2-3% around resonances

e + e       0 at  (CMD-2)  3  =(637  23  16) nb   =(4.30  0.06  0.17) MeV   = 167   14   10   r(  ee)Br(  3  ) = (4.51  0.16  0.11)  E, MeV L = 12 pb -1 Cross section, nb

e + e       0 from SND and BaBar Good agreement with SND and BaBar. Good agreement with SND and BaBar. Points much higher than at DM2 (early conclusions of SND) Points much higher than at DM2 (early conclusions of SND)

Cross-section e + e -  4π e+e-π+π-π0π0e+e-π+π-π0π0 e+e-π+π-π+π-e+e-π+π-π+π- CMD-2 10  10³ev., 6% syst. SND 54  10³ev., 8% syst CMD-2 38  10³ev., 5-7% s. SND 41  10³ev.,7% syst. Efficiency determination gives main contribution to the systematic error

e + e   4  after BaBar e + e   4  after BaBar Good agreement with CMD-2/SND/BaBar Error of hadronic contribution to a  significantly improved below 2 GeV

Cross-section e + e -  2K e+e-K+K-e+e-K+K- e+e-KSKLe+e-KSKL CMD-2 SND CMD-2 (prelim.) SND (prelim.) Systematic error ≈ 5-8% ~ 950 events Systematic error ≈ 5-10% ~ 2000 events Systematic error is ≈2-3% at φ resonance

Overview of the results (CMD-2)

Physics at VEPP-2000  Precise measurement of R (~0.4 % for  +  - ) 2. Study of hadronic channels: e + e -  2h, 3h, 4h …, h= ,K,  3. Study of ‘excited’ vector mesons:  ’,  ’’,  ’,  ’,.. 4. CVC tests: comparison of e + e - → hadrons with  -decay spectra 5. Study of nucleon-antinucleon pair production – nucleon electromagnetic form factors, search for NNbar resonances,.. 6. ISR processes 7. Two photon physics 8. Test of the high order QED 2  4, 5

LAYOUT of VEPP-2000 CMD-3 SND  circumference – 24.4 m revolution time – 82 nsec beam current – 0.2 A beam length – 3.3 cm energy spread – 0.7 MeV  x =  z =6.3 cm L = cm -2 s -1 at 2E=2.0 GeV L = cm -2 s -1 2E=1.0 GeV Total integrated luminosity with all detectors on VEPP-2M ~ 70 pb -1 Plan to improve hadronic contribution of a µ by a factor of 2 !!!

CMD-3 detector 1 – beam pipe, 2 – drift chamber, 3 – BGO, 4 – Z – chamber, 5 – s.c. solenoid, 6 – LXe, 7 – CSI, 8 – yoke, 9 – VEPP s.c. solenoid

Conclusions  Despite decades of experiments, precise studies of e + e  annihilation into hadrons at low energies are still interesting and can provide a lot of important information ● Experiments at VEPP-2M with two detectors CMD-2 and SND significantly improved the accuracy of hadronic cross sections below 1.4 GeV ● Progress is particularly important for e + e - →  +  -, where systematic uncertainty is ≈ 1% or even better ● Based on data from VEPP-2M together with ISR data obtained at KLOE and BaBar the error of a µ was significantly decreased matching the experimental accuracy ● a µ (exp) - a µ (SM) differs from 0 by ≈ 3.3  necessitating more accurate independent measurements  In a few years new precision data from CMD-3 and SND working at VEPP-2000 are expected as well as with ISR at DAFNE and B-factories