CMD-2 and SND results on the r, w and f.

1
CMD-2 and SND results on the r, w and f.
Budker Institute of Nuclear Physics,
Siberian Branch of the Russian
Academy of Sciences
M.N. Achasov

• International Workshop ee- Collisions from
  f to Y
  February 27 March 2, 2006,
  BINP, Novosibirsk, Russia

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Cross section ee? ? hadrons
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Process ee? ? hadrons(vs lt 1,4 GeV)
V vector meson, IG(JPC) 1(1? ?) ? 0?(1? ?) V
r, w, f , excited states. (at vs lt 1,4 GeV the
vector mesons dominance model describes the
ee? ? hadrons cross section with accuracy of
about 1)
4
Importance of the ee? ? hadrons processes
studies in the energy region vs lt 1,4 GeV

• Determination of the parameters of the light
  vector mesons r, w, f, ...
• R(s)s(ee? ? hadrons )/ s(ee? ? mm?)
• ( calculation of the hadronic contribution to
  the anomalous magnetic moment of the muon
  (g-2)/2 )
• Check of the CVC
• (comparison of the isovector part of the ee?
  ? hadrons cross section with spectral function in
  t ? n hadrons decays)

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Experimental situation in the energy region vs lt
2 GeV.

• VEPP-2M (vs lt1,4 ???, luminosity up to
• 3 1030 cm-2s-1) finished its operation and
  now is beening reconstructed as VEPP-2000 (energy
  region up to 2 ???, luminosity up to 1032
  cm-2s-1)
• f-factory DAFNE (luminosity up to 1033 cm-2s-1)
  nowadays produce experimental data at the f-meson
  mass (1020 MeV).
• B-factory at SLAC the ee? ? hadrons cross
  section at low energies is measured with
  radiative return method

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VEPP-2M
Center of mass energy region 360 1400
MeV Luminosity at 1000 MeV 3 1030
cm-2s-1
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CRYOGENIC MAGNETIC DETECTOR - 2 (CMD-2) SPHERICAL
NEUTRAL DETECTOR (SND)
1 beam pipeline, 2 drift chambers, 3
scintillation counter, 4 light guides, 5 PMT,
6 NaI(Tl) crystals, 7 VPT, 8 iron absorber,
9 stream tubes, 10 iron plates, 11
scintillation counters, 12 magnetic lens, 13
bonding magnets.
1 beam pipeline, 2 drift chamber, 3
Z-chamber, 4 superconducting solenoid, 5
compensating magnets, 6 BGO end cup
calorimeter, 7 CsI(Tl,Na) calorimeter, 8 muon
system, 9 magnet yoke.
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Integrated luminosity1995 - 2000
Total luminosity per detector is 30 pb-1.
Integrated luminosity accumulation dynamics
Integrated luminosity distribution over energy
region.
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The cross sections ee? ? hadronsmeasurement
method

• The experimental data is accumulated using vs
  energy scan method and then analyzed
• The ee? ? hadrons cross sections measurement

• N number of the ee? ? hadrons events
• IL integrated luminosity (measured using ee?
  ? ee? and gg )
• - detection efficiency (obtained from MC
  simulation)
• drad radiative correction
• dspr correction due to the beam energy spread.

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Analysis of the ee? ? hadrons cross sections
In order to obtain the vector mesons V
r,w,f,... parameters the measured cross section
of the process ee? ? X is fitted with
theoretical expression
The following parameters can be obtained from the
fit mV - mass, GV width, fV phase and
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Rare decays of r, w, f (Brlt10?3).
Measurement of already known decays First observation
r ? p0g, hg r ? p0p0g, pp-pp-, pp-p0
w ? hg, p0p0g, p0ee?
f ? pp-, hee? f ? f0g, a0g, h/g, wp0, pp-pp-, p0ee?
Results of the r, w, f mesons rare decays
studies with CMD-2 and SND detectors at VEPP-2M.
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The ee? ? pp- cross section
The value G (r ? ee?) obtained in various
experiments. Yellow area shows the average value
The ee??pp- process cross section in the
VEPP-2M energy region.
For data description the r, w, r/ mesons are
required. At vs 780 ??? the r - w
interference is seen.
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The r-meson parameters (mass and width)
Here are shown the mr and Gr measured in ee-
experiments in processes
ee? ? r0 ? pp-
(SND-05, CMD-2-02, OLYA-85),
ee? ?rp ? pp- p0 (SND-05, KLOE-03),
t ? r n ? p p0n
(ALEPH-05, CLOE-2-00) Yellow area shows the
average value.
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The ee? ? pp-p0 cross section
The ee?? pp?p0 cross section measured by SND.
Syst. error 3,45,4. The curve is the
result of the fit taking into account w, r, f,
w/, w//.
The ee? ?rp ? pp-p0 transition dominates in
this reaction. At VEPP-2M the ee? ? wp ? pp-p0
transition was observed. The intermediate state
different from these two was observed by KLOE and
CMD-2 in the f-meson energy region (maybe ee? ?
r/ p ? pp-p0 ).
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The ee? ? p0g cross section
Curve is the result of the fit taking into
account r, w, f resonances. (Dots are SND
data)
The ee? ? p0g process cross section.
Syst. error SND - 3, CMD-2 -
6 .
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The w-meson parameters (mass and width)
In measurements CMD-2-04 and SND-03 the w-meson
parameters were obtained using ee? ? pp-p0
process, while in CMD-2-05
- using ee? ? p0g reaction.

Yellow area shows the average value.
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The w-meson main decays modes
Yellow area shows the average value.
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The ee? ? KK? and KSKL cross sections
For data description the f, r, w, f/ resonances
are required.
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The ee? ? KK? cross section in the f meson
energy region. f ? KK? decay.
Systematic errors SND 7, CMD-2 3-4
(preliminary) Yellow area
shows the average value.
20
The ee? ? KSKL cross section in the f meson
energy region. f ? KSKL decay.
The cross section measurements were based on the
KS ? p0p0 and pp- decays.
Systematic errors SND 3,3, CMD-2
1,7 Yellow area shows the average value.
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The ee? ? hg cross section

• The cross section was measured using h ?
  p0p0p0, pp-p0, gg decays. For data description
  the following states are required f, r, w, r/.
  The systematic errors in the vicinity of the
  f-meson peak are 3-7

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The f ? pp-p0 and hg decays.
Comparison of the SND and CMD-2 measurements
with the other experimental results.
Yellow
area shows the average value.
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The f-meson parameters (mass and width)
Comparison of the SND and CMD-2 measurements
with the other experimental results.
Yellow
area shows the average value.
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Probability of the f ? ee- decay.
Yellow area shows the VEPP-2M average. Deviation
from KLOE result is 3 s.
CMD-2-05 using the main f ? hadrons decays
(preliminary). KLOE-05 using
mm- cross section and ee- forward-backward
asymmetry. ???-01 using the main
f ? hadrons decays and mm- cross section.
CMD-2-95 using the main f ? hadrons
decays
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Resonances with IG(JPC) 1(1? ?) and 0?(1?
?)above f meson.
The ee? ? pp-p0 cross section
The ee? ? pp-pp- cross section

• These resonances exist. Their parameters are not
  well established and
• nature is not clear. The number of them is
  unknown.
• Some important results from SND
  and CMD-2
• The clear experimental evidence of the w/
  resonance
• Observation of the a1p dominance in the process
  ee? ? pp-pp-

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Estimation of the w/ and w/ / parameters
The parameters of the w/, w/ / were estimated
from combined analysis of the ee? ? pp-p0
process cross section measured by SND and DM-2
data on the ee? ? wpp reaction
mV, MeV GV , MeV s(V? 3p), nb G(V?ee),eV
w/ 1400 870 5 600
w// 1770 500 5,5 860
The ratios of the wave functions at the origin
are more then 1
while
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Conclusions

• In the 1995-2000 the experiments with CMD-2 and
  SND detectors at VEPP-2M were fulfilled.
• The cross sections of the ee? annihilation in
  hadrons were measured in the energy region vs
  0,36 1,38 GeV.
• Results of these experiments determine nowadays
  the accuracy of the light vector mesons
  parameters determination. They are one of the
  main source of information about particle physics
  at low energies.