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2009
Precision measurement of R (CMD2(3) and BaBar collaborations) (Prof. Evgeny Solodov, Budker INP, Novosibirsk)
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Pacific/Honolulu
Rm 112 (UHM - Watanabe Hall)
Rm 112
UHM - Watanabe Hall
2505 Correa Road
Honolulu, HI 96822
Description
The only "significant" deviation of Standard Model (SM) predictions from observables comes from a comparison of the measured anomalous magnetic moment of the muon ((g-2)_mu) with calculation. The accuracy of this calculation strongly depends on the experimental value of R - the ratio of the e+e- -> hadron cross section to that for e+e- -> mu+mu-. Almost 100% of hadronic contribution to (g-2)_mu calculation comes from the E < 2 GeV energy region and mostly from e+e- -> pi+pi-. Two groups from BINP (SND and CMD2) published consistent results for the most precise measurements of the e+e- -> pi+pi- cross section from a direct scan of the energy range at the VEPP-2M collider. Combining these results with the latest publications by BaBar for the e+e- -> hadrons cross sections, obtained using Initial State Radiation (ISR) processes, allows us to calculate the hadronic contribution to g-2 of muons with better accuracy. The current discrepancy between the BNL experimental (g-2)_mu value and SM calculation is now ~3.3 sigma. However BINP results are not in good agreement with KLOE results obtained by ISR at the phi-factory and are in disagreement with tau-decay data; this is still a puzzle. The BaBar collaboration has an intensive program to study the e+e- cross section at low energy using ISR at Upsilon(4S) energy. A number of multi-hadron processes were studied and published. After few years of hard work (a 1% precision is needed !) a current status of e+e- -> pi+pi- process study was preseneted at Tau08 conference. The ability of 1% accuracy was demonstrated, but results are still very preliminary. Final results should come out soon.
