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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. Outline. VEPP-2M and available data

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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

outline
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

r the definition
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

measurement of r in novosibirsk
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 !

measurement of r in novosibirsk1
Measurement of R in Novosibirsk

Total hadronic cross-section measured by CMD-2 and SND

the approach
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

what is really measured
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)

the radiative corrections
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
e e p p
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

r meson parameters
r-meson parameters

Syst. Errors are under study

published

e e 4 p
e+e- —> 4 p

Ready for publication

Phys.Lett. B595(2004)101

Systematic error  5%

CMD-2/SND discrepancy recently resolved

new measurements of f meson
New measurements of f - meson

e+e-   ppp0

e+e-   KK

363000 events

104000 events

Systematic error  3%

e e hg 3g
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 %

e e p 0 g 3g
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

e e w r e e p 0
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);

future measurements at vepp 2000
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.

vepp2000 construction august 2004
VEPP2000 construction (August 2004)

Lxe calorimeter for CMD-3

CMD-3

SND

conclusion
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)
implication to a
Implication to a

Uncertainty of the hadronic contribution to a , 10-10

VEPP-2000

BaBar

Our estimation

current future activities in r
Current/Future activities in R

BaBar ISR

VEPP-2000

VEPP-4M

BES

KLOE

CLEO-c

VEPP-2M

CLEO

conclusion1
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)