Precision measurement of the total hadronic cross-section with CMD-2 at VEPP-2M e+e- collider

1. Precision measurement of the total hadronic cross-section with CMD-2 at VEPP-2M e+e- collider E. Solodov Budker Institure of Nuclear Physics (Novosibirsk, Russia) CMD-2 Collaboration ICHEP – 2004 Beijin, China, August 16-22, 2004

2. Outline • VEPP-2M and available data • New results on e+e-p+p- • New results on e+e- 4p • New results on f-meson parameters • Some other new measurements • Summary Preliminary

3. R, the definition R(s) is defined as: 2p >5 GeV 2-5 GeV • R(s) is one of the most fundamental quantities in high energy physics: • its global structure reflects number of quarks and their colors; used for QCD tests and as a source of QCD parameters • plays special role in precision measurements: <2 GeV w,f 2p >5 GeV 2-5 GeV <2 GeV w,f

4. Measurement of R in Novosibirsk • VEPP-2M collider: 0.36-1.4 GeV in c.m., L31030 1/cm2s at 1 GeV • Detectors CMD-2 and SND: 60 pb-1 collected in 1993-2000 • All major hadronic modes are measured: e+e-  2, 3, 4, KK, .. e+e- , ,  Still a lot of data to analyzed !

5. Measurement of R in Novosibirsk Total hadronic cross-section measured by CMD-2 and SND

6. The approach All modes except 2 2 • Luminosity L is measured using Bhabha scattering at large angles detector inefficiencies are measured • Efficiency His calculated via Monte Carlo + corrections for imperfect detector • Radiative correction  accounts for ISR effects only • Ratio N(2)/N(ee) is measured directly  detector inefficiencies are cancelled out • Virtually no background • Analysis does not rely on simulation • Radiative corrections account for ISR and FSR effects Systematic errors Formfactor is measured to better precision than L

7. What is really measured? Definition of (e+e-hadrons) depends on the application • Hadron spectroscopy: vacuum polarization (VP) is the part of the cross-section (“dressed”), final state radiation (FSR) is not • “Bare” cross-section used in R: vice versa – FSR is the part of the cross-section, VP is not • Measured number of events include VP and part of FSR allowed by the event selection • CMD-2 published 2 cross-sections e+e-2: • radiative correction take into account part of FSR, allowed by the event selection (thus remove FSR completely from the measured cross-section); VP is left untouched. • Used to get rho-meson mass, width, … • VP is removed, all FSR is added. • Used for R calculation spp FSR VP s0pp(g)

8. The radiative corrections ISR+FSR ISR+FSR+VP Vacuum polarization Initial and final state radiation • ee, ,  final states: 1  at large angle, multiple ’s along initial or final particles (0.2%) • CMD-2 results are consistent with independent calculations (BHWIDE, KKMC) • Other final states: multiple ’s along initial particles (1%) • the correction factor |1-(s)|2 is the same for all final states • R(s) itself is used for (s) evaluation  iterations

9. e+e- —> p+p- ee mm pp ee Systematic error pp, mm 1-2% 0.6-1% 1-5% >0.6 GeV <0.6 GeV |Fp|2 • e// separation using particles momentum • can measure N()/N(ee) and compare to QED • e// separa-tion using energy deposition • N()/N(ee) is fixed according • to QED 4 separate scans over 5 years, >1 million  events, 100k published

10. r-meson parameters Syst. Errors are under study published

11. e+e- —> 4 p Ready for publication Phys.Lett. B595(2004)101 Systematic error  5% CMD-2/SND discrepancy recently resolved

12. New measurements of f - meson e+e-   ppp0 e+e-   KK 363000 events 104000 events Systematic error  3%

13. -meson parameters

14. e+e-  hg  3g w,r  hg f  hg Br(w hg) = ( 4.9 +2.8-2.2  0.4)10-4 Br(r hg) = ( 2.9 +1.5-1.3  0.3)10-4 Br(f hg) = 1.355  0.014  0.063 %

15. e+e-  p0g  3g w,r  p0g e+e- w,r,f  p0g f  p0g w’ , w” ? Br(w p0g) = 9.46  0.17  0.57 % Br(r p0g) = ( 4.2 +1.0-0.9  0.4)10-4 Br(f p0g) = (1.214+0.045-0.036  0.061) 10-3

16. e+e- w,r  e+e- p0 Using data collected with CMD-2 detector in 720-840 MeV c.m. energy range the branching fraction of the conversion decay was determined:Br(w e+e-p0)=(8.160.730.63)10-4 The upper limits on the branching fractions of the following decays have been set for the first time: Br(r e+e-p0) < 2.210-5 (90% CL); Br(r e+e-h) < 1.510-5 (90% CL); Br(w e+e-h) < 2.310-5 (90% CL);

17. Future measurements at VEPP-2000 • measure 2 mode to 0.2-0.3% • measure 4 mode to 1-2% • overall improvement in R precision by factor 2-3 • Factor >10 in luminosity (round beams) • Up to 2 GeV c.m. energy • CMD-3: major upgrade of CMD-2 (new drift chamber, LXe calorimeter) Under construction. Data taking is expected to start in 2006-2007.

18. CMD-3

19. VEPP2000 construction (August 2004) Lxe calorimeter for CMD-3 CMD-3 SND

20. Conclusion • Measurement of R is still very active and important field • Important for interpretation of g-2 experiment, evaluation of (MZ), tests of QCD • Energy range 0-1.4 GeV contributes 80% (value and error) to • amhad - motivation to continue data analysis collected with CMD-2 • New data on  , 4p , precision measurements of , - have been presented • New high luminosity machine VEPP2000 is under construction • CMD-3 and SND detectors are expected data taking in 2006 • Expect to reach 0.3-2% precision in the 0-2 GeV range in few years (factor of 2 improvement)

21. New

22. Implication to a Uncertainty of the hadronic contribution to a , 10-10 VEPP-2000 BaBar Our estimation

23. Current/Future activities in R BaBar ISR VEPP-2000 VEPP-4M BES KLOE CLEO-c VEPP-2M CLEO

24. Conclusion • Measurement of R is still very active and important field • Important for interpretation of g-2 experiment, evaluation of (MZ), tests of QCD • Recent improvements: VEPP-2M, BES • Lots of data are being analyzed: VEPP-2M, KLOE, BaBar, CLEO • Many future projects: VEPP-2000, BESIII, CLEO-c • ISR experiments have demonstrated impressive potential: KLOE, BaBar. • Expect to reach 0.3-5% precision over the whole 0-10 GeV range in few years (factor of 2 improvement)