VEPP-2000 plans for the study of the nucleon form factors

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VEPP-2000 plans for the study of the nucleon
form factors
Budker Institute of Nuclear Physics, Novosibirsk
Sergey Serednyakov

• Nucleon 05 Workshop
• 12-14 October, 2005

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OUTLINE VEPP-2000 collider
SND and CMD-3 detectors NNbar cross
section and formfactor data Prospects of
VEPP-2000 for NNbar measurements
Conclusions
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VEPP-2000 Complex

• 2Emax2000 ?eV
• L1031?m-2s-1 at E510 ?eV
• L1032?m-2s-1 at E1000 ?eV

Refs for VEPP-200 1. In Proc.Frascati
Phys.Series,v XVI, p.393,Nov.16-19,1999 2. In
Proc. 7-th Europ.Part.Accel.Conf.,EPAC 2000,
p.439, Vienna,2000
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VEPP-2000 ee- collider
CMD-3
SND
Start of VEPP-2000 project 2000 Two collider
detectors Energy range 2E0.4-2.0 GeV SND
and CMD-3
14.06.2005
VEPP-2000 parameters perimeter 24.4 m
collision time 82 nsec beam current 0.2 A
bunch length 3.3 cm energy spread 0.7 MeV
?x? ?z 6.3 cm L ? 1032 at 2E2.0 GeV
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SND detector for VEPP-2000
Ref. NIM A449 (2000) 125-139
1 VEPP-2000 beam pipe, 2 tracking system, 3
aerogel cherenkov counter, 4 NaI(Tl) counters,
5 vacuum phototriodes, 6 absorber, 7-9 muon
system, 10 VEPP-2000 s.c focusing solenoids.
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CMD-3 detector
1 beam pipe, 2 drift chamber, 3 BGO, 4
Z chamber, 5 s.c. solenoid, 6 LXe, 7
CSI, 8 yoke , 9 VEPP s.c. solenoid
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Physical program at VEPP-2000
1. Precise measurement of the quantity
R?(ee-- gt hadrons)/ ?(ee--gt??--) 2. Study of
hadronic channels ee-- gt 2h, 3h, 4h , h
?,K,? 3. Study of excited vector mesons ?,
?, ?, ?,.. 4. CVC tests comparison of ee--
gt hadr. (T1) cross section with ?-decay
spectra 5. Study of nucleon-antinucleon pair
production nucleon electromagnetic form
factors, search for NNbar resonances, .. 6.
Hadron production in radiative return
(ISR) processes 7. Two photon physics 8. Test of
the QED high order processes 2-gt4,5
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N Nbar production cross section
C1 at Tkin. 1 MeV
For ee?p pbar
At the threshold we have s4MN2 and GEGM,
if GE GM0.5, then
Rad. correction
For T1MeV e-n0.62 For T50 MeV e-n0.82
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Present data
ee--gtp pbar
ee--gtn nbar
Cross section ee- -gt N Nbar
Neutron FF
Proton FF
Time like form factor
Dm5MeV
In VEPP-2000 Dm lt 1 MeV !
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Study of p pbar production at VEPP-2000
Picture of expected event
Goal measurement of proton e.m. FF at
threshold, 1 significant improvement of
accuracy, 2 separation between GM and GE , 3
confirm rise of both FFs at threshold, 4
search of resonant structure
GEANT p pbar DC trigger efficiency
P pbar z-distribution (MC)
Estimates of statistics at threshold Instant
luminosity - 0.1/(nb.sec) Time 107 sec
Integrated luminosity - 1/fb Cross section - 0.7
nb Detection efficiency 0.15 Number of
events 105 GE /GM with 5 of statistical
accuracy, 10 bins
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Detection of antineutrons at VEPP-2000
Picture of expected event
Goal measurement of neutron e.m. FF at
threshold, 1 significant improvement of
accuracy, 2 separation between GM and GE , 3
confirm rise of both FFs at threshold, 4
search of resonant structure
MC accuracy of angle measurement, s7-10o
Estimates of statistics at threshold Instant
luminosity - 0.1/(nb.sec) Time 107 sec
Integrated luminosity - 1/fb Cross section - 0.7
nb Detection efficiency 0.15 Number of
events 105 GE /GM with 5 of statistical
accuracy, 10 bins
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Antineutron interaction with detector material
General comments - the antineutron
annihilation length 15 cm is
calorimeter thickness 35 cm - neutrons and
antineutrons have similar interaction length
the detection efficiency of n nbar events is
close to 100
Detection efficiency ??a ?Tr ?Rec , where ?a
annihilation probability, ?Tr trigger
efficiency ?0.8 ?Rec reconstruction eff.
? 0.5 The detection efficiency at T10 MeV
? ?0.3 - 0.4
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ee- -gt n nbar, MC distribution over cos q.
Extraction of GM , GE
GM gives (1 cos 2q ), GE gives (1- cos 2q ).
With T 10MeV, N3000 ev., ratio GE /GM is
measured with 8 accuracy
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Detection of antineutrons at VEPP-2000,time
measurements
Time-amplitude correlation
Time resolution s3 nsec
Monte Carlo time spectra of n nbar events in
SND calorimeter
Time measurements with NaI(Tl) counter, DE30
MeV, s3 nsec, phototriode readout
Conclusion Time resolution of the whole NaI(Tl)
calorimeter slt1 nsec at DE0.5 GeV is expected.
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Background in n nbar process
Physical background e e--gt
KSKL, ??0.1 nb e e--gt KSKL?0,
??1 nb   e e--gt ??0-gt?0?0?, ??0.1 nb   e
e--gt ??,?? -gtneutrals,??10 pb   e e--gt
hadrons-gtneutrals,?lt0.1   e e--gt 4?,5?, (QED),
??0.1 nb For comparison ee--gtn nbar
cross section ??1 nb The most physical
background comes from the reactions with
production of KL. KL interactions and decays in
flight look similar to nbar because they give
stars outside the detector center.
3 types of background

• Cosmic background
• - they are suppressed by cosmic
• veto system
• the survived events can fake
• the n nbar events
• time measurements can separate
• the effect from cosmic background

• Beam background
• is inverse proportional to the beam
• life time
• can be monitored by measurements
• with one beam in the ring
• can be suppressed by nbar
• annihilation time measurements

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Example of suppression of physical background for
n nbar in SND (MC)
ee-gtn nbar
Event momentum
cut
ee-gtKsKL
Conclusion effective suppression of
physical background by 2 orders is possible
using event momentum vs event energy distribution
ee-gtKsKlp0
ee-gtwp0
Event energy
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Schedule

• VEPP-2000 -- beam -- 2006
• -- luminosity -- 2006
• -- running -- 2007--2012

SND -- upgrade -- 2004-2006
-- nbar trigger -- 2006 --
data taking -- 2007-2012 -- FF
results -- 2008-2010
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Conclusions
1. VEPP-2000 can produce 105 ppbar and nnbar
events per year at the threshold region
2Elt2000 MeV. This exceeds by ?2-3 orders
the world statistics of ee?n nbar process. 2.
The ppbar events can be detected by pbar
annihilation star in beam pipe. The GE/GM
ratio can be obtained from the star
z-coordinate distribution 3. SND calorimeter
can be used as efficient antineutron detector.
Time measurements in NaI(Tl) option is
considered to improve events selection and
suppress background (physical, beam and
cosmic)
.