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Febr.28-March 2, 2006N Nbar project at VEPP VEPP-2000 Complex 2E = МeV L=10 31 сm -2 s -1 at E=510 МeV L=10 32 сm -2 s -1 at E=1000 МeV Refs for VEPP In: Proc.Frascati Phys.Series,v XVI, p.393,Nov.16-19, In: Proc. 7-th Europ.Part.Accel.Conf.,EPAC 2000, p.439, Vienna,2000
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Febr.28-March 2, 2006
N Nbar project at VEPP-2000 1
The project to measure the nucleon form factors at VEPP-2000
Workshop - e+e- collisions from phi to psi ,
February 27 – March 2, 2006
Sergey Serednyakov
Budker Institute of Nuclear Physics, Novosibirsk
Updated version of the talk givenat Nucleon form factor workshop in Frascati in Octob.14-16, 2005
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 2
OUTLINE1- VEPP-2000 collider, SND and CMD-3 detectors
2- NNbar cross section and formfactor data 3- Prospects of VEPP-2000 for NNbar measurements
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 3
VEPP-2000 Complex
2E = 400 - 2000 МeV L=1031 сm-2s-1 at E=510 МeV L=1032 сm-2s-1 at E=1000 МeV
Refs for VEPP-2001. In: Proc.Frascati Phys.Series,v XVI, p.393,Nov.16-19,19992. In: Proc. 7-th Europ.Part.Accel.Conf.,EPAC 2000, p.439, Vienna,2000
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 4
VEPP-2000 e+e- collider
CMD-3
SND
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 2E=2.0 GeV
Start of VEPP-2000 project –2000 Two collider detectors: Energy range 2E=0.4-2.0 GeV SND and CMD-3
Febr.15, 2006
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 5
SND detector for VEPP-2000
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.
Ref.: NIM A449 (2000) 125-139
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 6
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
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 7
Physical program at VEPP-2000
1. Precise measurement of the quantity R=(e+e-- > hadrons)/ (e+e-->+--)2. Study of hadronic channels: e+e-- > 2h, 3h, 4h …, h= ,K, 3. Study of ‘excited’ vector mesons: ’, ’’, ’, ’,..4. CVC tests: comparison of e+e-- > hadr. (T=1) cross section with -decay spectra5. Study of nucleon-antinucleon pair production – nucleon electromagnetic form factors, search for NNbar resonances, ..6. Hadron production in ‘radiative return’ (ISR) processes7. Two photon physics8. Test of the QED high order processes 2->4,5
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 8
N Nbar production cross section
}sin|(s)G|s
M4)cos(1|(s)G{|s4βCα
dΩdσ 22
222
2
EN
M
nnppee ,
)e1/(C
For e+ep pbar:
At the threshold we have s=4MN2 and
GE=GM,
}|)s(G|s
M2|)s(G{|s3
C4 2E
N2
2M
2
nbMGMC
NEN
7.0|)4(|4
2 222
2
if GE =GM=0.5,
then
C~1 at Tkin. ~1 MeV
Rad. correction: ,TEln
mEln4n,edd
kine
n0
For T=1MeV: e-n=0.62;For T=50 MeV: e-n=0.82;
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 9
Present data – region near thresholde+e-->p pbar e+e-->n nbar
Proton FFNeutron FF
Cross sectione+e- -> N Nbar
Time likeform factor
m=5MeVIn VEPP-2000m <= 1 MeV !
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 10
Study of p pbar production at VEPP-2000 with SND
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
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
Picture of expected event
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 11
Detection of antineutrons at VEPP-2000 with SND
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
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
Picture of expected event
MC accuracy of angle measurement, ~7-10o
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 12
Detection of antineutrons at VEPP-2000 with SND,time measurements
Monte Carlo time spectraof n nbar events in SNDcalorimeter
Time-amplitude correlation
Time resolution 3 nsec
Time measurements with NaI(Tl)counter, E=30 MeV, =3 nsec,phototriode readout
Conclusion: Time resolution of the whole NaI(Tl) calorimeter<1 nsec at E~0.5 GeV is expected.
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 13
Physical background e+ e--> KSKL, 0.1 nb e+ e--> KSKL0, 1 nb e+ e--> 0->00, 0.1 nb e+ e--> , ->neutrals,10 pb e+ e--> hadrons->neutrals,<0.1 e+ e--> 4,5, (QED), 0.1 nb
For comparison e+e-->n 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.
Background in n nbar detection
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 backgroundBeam 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
3 types of background:
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 14
Example of suppression of physical background for n nbar in SND (MC)
Conclusion: effective suppression of physicalbackground by ~ 2 orders is possible using event momentum vsevent energy distribution
Even
t mom
entu
m
Event energy
e+e->n nbar
e+e->KsKL
e+e->KsKl
e+e->
cut
Febr.28-March 2, 2006
N Nbar project at VEPP-2000 15
Conclusions
1. VEPP-2000 can produce ~105 ppbar and nnbar events per year in the range 2E<2000 MeV. This exceeds by 2-3 orders the world statistics of e+en nbar process.
2. The ppbar events can be detected by pbar annihilation star in beam pipe for T<20 MeV and by “thick” tracks in DC for T>30 MeV. The GE/GM ratio can be measured with 10% accuracy. 3. SND and CMD-3 calorimeters can be used as efficient antineutron detector. Time of flight measurements will improve events selection and background suppression. The GE/GM ratio can be measured as well..