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10-0317-solodov

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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
1. VEPP-2M and available data
2. New results on e+e- п‚® p+p3. New results on e+e- п‚® 4p
4. New results on f-meson parameters
5. Some other new measurements
6. Summary
R, the definition
had
R(s) is defined as:
R(s) пЂЅ
пЃі
(0)
+
-
(e e п‚® пЃ§ п‚® hadrons )
пЃі
*
+
-
+
-
(e e п‚® пЃ­ пЃ­ ) п‚ пЂ (0 )
пЃЎ пЃ­ (l.o.)
2p
>5 GeV
2-5 GeV
R(s) is one of the most fundamental quantities in
high energy physics:
<2 GeV
w,f
• 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:
2p
>5 GeV
пѓ¦пЂ пЃЎ m пЃ­ пѓ¶пЂ had
пЃЎ пЃ­ (l.o.) пЂЅ пѓ§пЂ пѓ·пЂ пѓЁпЂ 3 p пѓёпЂ 2
пЃЎ (0 ) M Z
п‚Ґ
пѓІ
пЃ„ пЃЎ had ( M ) пЂЅ-
3p
s
2
4 mp
п‚Ґ
2
2
Z
ds
K (s )
Re
пѓІ
ds
2
4 mp
2
2-5 GeV
R(s)
w,f
R (s )
s(s - M Z ) - i пЃҐ
2
<2 GeV
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- п‚® 2p,пЂ 3p,пЂ 4p,пЂ KK,пЂ ..
e+e- п‚® пЃІ,пЂ w,пЂ f
Still a lot of data to analyzed !
Measurement of R in Novosibirsk
Total hadronic cross-section measured by CMD-2 and SND
The approach
All modes except 2p
+
-
пЃі (e e п‚® H ) пЂЅ
N H - N bg
L пѓ— пЃҐ H пѓ— (1 + пЃ¤ H )
• Luminosity L is measured using
Bhabha scattering at large anglesпѓћ
detector inefficiencies are measured
п‚ пЂ вЂў Efficiency пЃҐH is calculated via Monte
Carlo + corrections for imperfect
detector
• Radiative correction  accounts for
ISR effects only
Fp
2
пЂЅ
N 2p
пѓ—
N ee
2p
пЃі ee пѓ— (1 + пЃ¤ ee )
пЃі 2 p ( po int - like ) пѓ— (1 + пЃ¤ 2 p )
• Ratio N(2p)/N(ee) is measured
directly пѓћ detector inefficiencies are
cancelled out
• Virtually no background
• Analysis does not rely on simulation
• Radiative corrections account for
ISR and FSR effects
Systematic errors
Radiative corrections
1%
Luminosity
1-2%
Efficiency
Total
Radiative corrections 0.4%
“Experimental” (event
1-5%
selection, separation,
efficiencies,…)
0.4%
1.5-7%
Total
0.6%
Formfactor is measured to better precision than L
What is really measured?
Definition of пЃі(e+e-п‚®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 crosssection, 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-п‚®2p:
пЃіpp
пЃі0pp(пЃ§)
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
пЃі
0
pp ( пЃ§ )
VP
пЂЅ пЃі pp
FSR
пѓ¦пЂ пЃЎ
пѓ¶пЂ пѓ— 1 - пЃђ ( s ) пѓ— пѓ§пЂ 1 + пЃЊ ( s ) пѓ·пЂ пѓЁпЂ p
пѓёпЂ 2
The radiative corrections
Vacuum polarization
Initial and final state radiation
ISR+FSR
пѓ¦пЂ п‚Ґ пЃі + - *
пѓ¶пЂ (s' )ds '
s
e e п‚® пЃ§ п‚® final
пѓ§пЂ P пѓІ
пЃђ (s) пЂЅ
- i pпЃі e + e - п‚® пЃ§ * п‚® final (s ) пѓ·пЂ 2
пѓ§пЂ пѓ·пЂ 4 p пЃЎ пѓЁпЂ 4 m 2
s - s'
пѓёпЂ p
• the correction factor |1-(s)|2
is the same for all final states
• R(s) itself is used for (s)
evaluation пѓћ iterations
ISR+FSR+VP
• ee, , pp final states: 1  at
large angle, multiple ’s along
initial or final particles (пЃѕ0.2%)
• CMD-2 results are consistent
with independent calculations
(BHWIDE, KKMC)
• Other final states: multiple ’s
along initial particles (пЃѕ1%)
<0.6 GeV
pp
пЃ­пЃ­
ee
e+e- —> p+p-
>0.6 GeV
|Fp|2
pp,пЂ пЃ­пЃ­
• e//p separation
using particles
momentum
• can measure
N(пЃ­пЃ­)/N(ee) and
compare to QED
1-2%
Systematic error
0.6-1%
1-5%
ee
• e//p separation using energy
deposition
• N()/N(ee) is
fixed according
to QED
4 separate scans over 5 years, >1 million pp events, 100k published
пЃІ-meson parameters
Syst. Errors are under study
published
Data 94-95
113 k events
Data 98 (пЃІ only)
520 k events
Data 94-95-98
670 k events
PDG
mпЃІ (MeV/c2)
775.69 п‚± 0.64 п‚± 0.59
776.04 п‚± 0.55
775.36 п‚± 0.43
775.8 п‚± 0.5
пЃ‡пЃІ (MeV)
143.89 п‚± 1.33 п‚± 0.80
145.64 п‚± 0.94
143.53 п‚± 1.08
150.3 п‚± 1.6
BwppпЂ (%)
пЃЄпЃІw(rad.)
1.30 п‚± 0.24 п‚± 0.05
1.58 п‚± 0.16
1.47 п‚± 0.12
1.70 п‚± 0.27
0.232 п‚± 0.064 п‚± 0.003
0.170 п‚± 0.037
0.192 п‚± 0.029
пЃ‡пЃІee (keV)
7.05 п‚± 0.11 п‚± 0.05
7.083 п‚± 0.074
7.076 п‚± 0.062
a’;’ (rad.)
0.29п‚±0.07; p(fixed)
0.30п‚±0.06;p(f)
0.34п‚±0.03;-2.20 п‚± 0.01
m’ (MeV/c2)
1467 (fixed)
1467 (fixed)
1317 п‚± 16
1465 п‚± 25
’ (MeV)
309 (fixed)
309 (fixed)
466 п‚± 30
400 п‚± 60
a”;” (rad.)
-
-
0.0035(f);-2.17(f)
m” (MeV/c2)
” (MeV)
7.02 п‚± 0.11
1733 (fixed)
1720 п‚± 20
175 (fixed)
250 п‚± 100
e+e- —> 4 p
Phys.Lett. B595(2004)101
Ready for publication
Systematic error п‚» 5%
CMD-2/SND discrepancy recently resolved
New measurements of fпЂ - meson
e+e- п‚® f п‚® p+p-p0
104000 events
e+e- п‚® f п‚® K+K-
363000 events
Systematic error п‚» 3%
f-meson parameters
CMD-2 (2004)
PDG(average)
BeeBKK
(14.46п‚±0.07п‚±0.40)п‚·10-5
(13.93п‚±0.14п‚±0.99) п‚·10-5
mf, MeV/c2
1019.448п‚±0.010п‚±0.080
1019.456п‚±0.020
пЃ‡f, MeV
4.25п‚±0.03п‚±0.03
4.26п‚±0.05
BeeB3p
(4.62п‚±0.07п‚±0.12)п‚·10-5
mf, MeV/c2
1019.22п‚±0.02п‚±0.15
пЃ‡f, MeV
4.26п‚±0.08п‚±0.05
(4.52
п‚± 0.19) п‚·10-5
w,пЃІпЂ п‚® hпЃ§
e+e- п‚® hпЃ§пЂ п‚® 3пЃ§
fпЂ п‚® hпЃ§
Br(wпЂ п‚® hпЃ§) = ( 4.9 +2.8-2.2 п‚± 0.4)пѓ—10-4
Br(пЃІпЂ п‚® hпЃ§) = ( 2.9 +1.5-1.3 п‚± 0.3)пѓ—10-4
Br(fпЂ п‚® hпЃ§) = 1.355 п‚± 0.014 п‚± 0.063 %
w,пЃІпЂ п‚® p0пЃ§
e+e- п‚® p0пЃ§пЂ п‚® 3пЃ§
e+e- п‚® w,пЃІ,fпЂ п‚® p0пЃ§
fпЂ п‚® p0пЃ§
w’ ,пЂ w” ?
Br(wпЂ п‚® p0пЃ§) = 9.46 п‚± 0.17 п‚± 0.57 %
Br(пЃІпЂ п‚® p0пЃ§) = ( 4.2 +1.0-0.9 п‚± 0.4)пѓ—10-4
Br(fпЂ п‚® p0пЃ§) = (1.214+0.045-0.036 п‚± 0.061) пѓ—10-3
e+e- п‚®w,пЃІ п‚® 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(wп‚® e+e-p0)=(8.16п‚±0.73п‚±0.63)пѓ—10-4
The upper limits on the branching fractions of the
following decays have been set for the first time:
Br(пЃІп‚® e+e-p0) < 2.2пѓ—10-5 (90% CL);
Br(пЃІп‚® e+e-h) < 1.5пѓ—10-5 (90% CL);
Br(wп‚® e+e-h) < 2.3пѓ—10-5 (90% CL);
Future measurements at VEPP-2000
• Factor >10 in luminosity (round beams)
• measure 2p mode to 0.2-0.3%
• Up to 2 GeV c.m. energy
• measure 4p mode to 1-2%
• CMD-3: major upgrade of CMD-2 (new
• overall improvement in R
precision by factor 2-3
drift chamber, LXe calorimeter)
Under construction. Data taking is expected to start in 2006-2007.
CMD-3
VEPP2000 construction
(August 2004)
Lxe calorimeter for CMD-3
CMD-3
SND
Conclusion
• Measurement of R is still very active and important field
• Important for interpretation of g-2 experiment, evaluation of
пЃЎ(MZ), tests of QCD
• Energy range 0-1.4 GeV contributes 80% (value and error) to
aпЃ­had - motivation to continue data analysis collected with CMD-2
• New data on p+p- , 4pпЂ , precision measurements of w,f - 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)
New
Implication to aпЃ­
Uncertainty of the hadronic contribution to aпЃ­ , 10-10
Final state
Today
2004
CMD-2+ISR
2005-2006
+VEPP-2000
2010
2p
5.9
<4.0
<2.0
VEPP-2000
w, пЃЄ
1.4
1.0
<0.7
Other, <2 GeV
2.3
1.5
1.0
>2 GeV
Total
BaBar
1.8
7.2
<5.0
<3.0
Our estimation
Current/Future activities in R
BaBar ISR
VEPP-2000
KLOE
VEPP-4M
BES
VEPP-2M
CLEO
CLEO-c
Conclusion
• Measurement of R is still very active and important field
• Important for interpretation of g-2 experiment, evaluation of
пЃЎ(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)
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