MCGPJ for the process e e-?? ?-?o

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MCGPJ for the process ee-???-?o
G.V.Fedotovich, E.A.Kuraev,
A.L.Sibidanov, Budker
Institute of nuclear physics
Novosibirsk, Russia



10.10.08, IHEP, Beijing
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OUTLINE

• VEPP-2000 and CMD-3 detector
• Motivation
• SF approach to describe photon jet radiation in
  collinear region
• Stability cross section vs inner parameters
• Comparison with cross section taken into account
• one photon radiation
• 5. Conclusion
  

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Physics at VEPP-2000

• Precise measurement of R
• (0.4 0.3 for ??-,??-?o)
• 2. Study of hadronic channels
• ee- ? 2h, 3h, 4h , h ?,K,?
• 3. Study of excited vector mesons
• ?, ?, ?, ?,..
• 4. CVC tests comparison of ee- gt hadrons
• with ?-decay spectra
• 5. Study of nucleon-antinucleon pair production
  
• nucleon electromagnetic form-factors,
• search for NNbar resonance near threshold
• 6. ISR processes
• 7. Two photon physics
• 8. Test of the high order QED processes 2? 4,5

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R(s) measurements at low s
Babar/Belle (ISR)
R
VEPP-2000
KLOE (ISR)
BES
VEPP-2M
At VEPP-2M the cross-sections of each final state
are measured exclusively and the same we plan to
do at VEPP-2000
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Lay-out of VEPP-2000

• revolution time 82 ns
• beam current 200 mA
• beam length 3.3 cm
• energy spread 0.7 MeV
• circumference 24.4 m
• beta function in IP ?x ?z 4.3 cm
• L 1032 cm-2s-1 at 2E2.0 GeV
• L 1031 cm-2s-1 at 2E1.0 GeV

CMD-3
SND
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3D view CMD-3 detector
Z-chamber, LXe calorimeter and eight CsI octants,
TOF, MR system are inside detector and tested
(cosmic) Super conductive solenoids of
VEPP-2000 are located in touch to DC problem
with magnetic field uniformity inside DC volume
Map of magnetic field was measured in real
conditions. SC solenoid is inside detector.
Project magnetic field 1.5 T (1.3 T was
achieved)
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How cross sections are measured to better
understand the main factors giving dominant
contributions to systematic uncertainty for
hadronic cross sections
All modes except 2?
2? mode

• RC ?ee accounts for ISR effects only
• Integrated luminosity Lee is measured using LAB
  events
• Efficiency ?ee is calculated via MC
  corrections for detector imperfections
• VP effects are included in cross section
  properties

• Ratio N(2?)/N(ee) is measured directly ?
  detection inefficiencies are cancelled out in
  part
• RC account for ISR and FSR effects
• Events separation procedure analysis dont
  rely on simulation
• Form factor is measured to better precision than
  L

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R measurement at CMD-2, SND and KLOE (for
vslt1GeV 2pi dominant channel)
Source of error CMD-2 SND KLOE-08
Event separation 0.2-0.4 0.5 -
Fiducial volume 0.2 0.8 0.1
Energy calibration 0.1-0.3 0.3 0.2
Efficiency correction 0.2-0.5 0.6 0.3 (rec.filter)
Pion losses (decay, NI) 0.2 0.2 0.2
Other 0.2 0.5 0.5
Radiative corrections 0.3-0.4 0.2 0.1
Total 0.6-0.8 1.2 0.8
CMD-3 systematic err. for 2? channel will be
push down at least by a factor of 2 Accuracy of
hadronic contrib. to the aµ value is estimated as
60ppm?0.3 ?0.2ppm Process with 3? contributes to
the value aµ at the level ?7ppm ? it leads to
the systematic error for aµ about 0.2ppm for
current systematic error ? (2 ? 3) With CMD-3
experiments we must put down this error by factor
? 2 IT MEANS that RC must be known with
uncertainty at least better than 0.5
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Two dimensional plots for energy deposition
in EMC. Momenta are measured in DC
ee
??
??
Beam energy 400 ?eV 8X0 ? 8X07X0 ? better
energy resolution in EMC. Important for ??
reconstruc.
Beam energy 195 MeV. At CMD-3 PID in DC will be
up 350 MeV
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Physical factors which must be included to keep
bare cross section calculation at the
level 0.5 (or better)

• 1. Coulomb interaction of charged pions in FS
• 2. It is necessary to include to the RC S V H
  photon
• radiation in FS in the first order of ? (it is
  done in part while)
• 3. Extract VP effects from virtual photon
  propagator
• 4. Add to bare cross section ONE photon
  radiation in FS

1
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3? event in CMD-2 detector Two
tracks in DC and two clusters in CsI calorimeter
which do not belong to
tracks
R-? plane
Plane with beam axis
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Specific selection criteria used in
CMD-2 for the process e-e? ??????

• Kinematics cuts (some examples)
• Accolinearity angle between two tracks in R-?
  plane
• ?1- ?2-? gt 0.25 radian to eliminate
  collinear events
• 2. Average momentum of two charged pions should
  be inside gap
• 0.35 lt (P1P2)/2Ebeam lt 0.8 to put down
  collinear events
• 3. Invariant mass of two charged pions ?inv lt
  1.66 Ebeam - this condition also suppress
  collinear events
• 4. To provide good reconstruction efficiency in
  DC only the part of the acceptance was used 0.85
  lt ?1,2 lt ? - 0.85 radian for polar angles
• 5. EMC is needed to put down cosmic background
  and to eliminate events ee-? ee- ?, ???? ?,
  ???? ? which
• have very similar signature in detector (in
  one plane).
• Angle between missing momentum direction of
  the two
• charged pions and two photon directions is
  grater than
• 0.1 radian

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Selection criteria used in CMD-2
for the process e-e? ??????
Distribution of the missing mass squared as a
function of the maximal energy deposition in
EMC among two charged particles
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Selection criteria used in CMD-2
for the process e-e? ??????
Dependence of the mass squared of two charged
particles as a function of the accollinearity
angle in R-? plane
?1- ?2-? gt 0.25 rad.
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e?e? ? ???? ? total cross section
Contribution of FSR, . CMD-2 selection criteria
were used (to feel a scale of the
effect for 3? channel)
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e?e? ? ????? total cross section
Contribution of FSR, . CMD-2 selection
criteria were used (to feel a scale of the
effect for 3? channel, Ebeam 400MeV)
CMD-2 cut for 3? channel
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Shift Born cross section for the process
ee-???-?0
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Cross-section for one photon radiation
?
?(cuts)

?
, C0 cos(?0)

where
First term describes one photon radiation in
collinear region (inside narrow cones) Second
term describes one hard photon radiation out of
narrow cones. Last term represents Soft and
Virtual parts of the cross section Cross section
does not depend on inner parameters ?, ?0
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Master formula for the process ee-???-?0 n?
?(cuts)



x ?/E - photon energy fraction in
relative units
First term describes photon jet radiation in
collinear region (enhance contributions
proportional to (???)L) Second term represents
compensators Third term describes one hard photon
radiation out of narrow Cones. Cross section
does not depend on inner parameters ?,
?0 Systematic accuracy is estimated as 0.5
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Cross section stability ee-???-?0 n? vs inner
parameter ?0
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Cross section stability ee-???-?0 n? vs inner
parameter ?E
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RC for the process ee-???-?0 n?
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Cross sections comparison when one photon is
radiated
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Coulomb factor Exchange by virtual photon
between charged pions in FS
?c averaged with Born cr.sect.
?c averaged with SF
?3? ? 1nb
?3? ? 1nb
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Variation of the geometrical efficiency vs
energy (CMD-2 selection criteria)
One photon in CsI EMC ?? variation ? 0.25
Two photon in CsI EMC ?? variation ? 1.5
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Conclusion
1. MCGPJ for the process ee- ? ??-?0 is
constructed 2. Theoretical accuracy is estimated
as 0.5 (or better) 3. MCGPJ simulates photon
jets in collinear regions and one hard photon out
of narrow cones. The same approach as we used for
others channels 4. Very important geometrical
efficiency must be determined with RC 5. Coulomb
interaction in FS very similar to that as we have
for two pion channel 6. Firstly correction with
FSR for this channel is calculated (E.Kuraev) and
numerical evaluation is done 7. Bare cross
section can be determined now with accuracy
better than 0.5 (for (g-2)/2 calculation)
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???-
???-
51
?????
2
18
5
????-?
14
???-? ?-
10
?
???-?0 ?0
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????? ????????? ???????? ?????????? ????????
??????? ????? 0.2 0.3 ? ??????? ??????
??????? ?
R(s) ?bare ?ee- ?hadrons?/??ee- ? ??-?,
??? ??ee- ? ??-? (4???)(?²?s)
?bare?hadr? ?dress (hadr)1-P(s)²
70 ppm
70 ppm ? 0.5 ? ? 0.35 ppm (??? 0.5 ppm) ?
????? ???????????? ??? (?969) ???????????
???????? ???????? ????????? ???????????
?????????? ??????? ????? ?? ??????? ???? ? ???
??? ???? ? ?????????? 0.2 0.3 ppm ? ?????????
??????? ????? ????? ???????? ????? 0.2
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SND only
CMD2 only
CMD2 0.7 0.6 (95)/ 0.8
(98) 1.2-4.2
SND 3.2 1.3
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Cross-section ee- ? 3p
Fit with ?, ?, ?, ?? and ???
Systematic error 2 on omega, 2.5 on phi, 6
(gt1GeV)
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Dress cross section
Dependence of the dress cross section vs energy
is determined by strong interaction. Then VP
effects in photon propagator MUST be attached to
the vertex of the hadrons production
e
?-
?
?0
------?
?
e-
?-
e
Dress cross section ALSO contains correction due
to photon radiation in FS to provide the
systematical accuracy better than 0.5
?
?0
------?
?
e-
?
?-
Coulomb interaction of pions (electro- magnetic
corrections ) MUST be excluded from dress cross
section. They are taken into account in radiative
corrections
e
?
?0
------?
?
e-
?
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