Febr.28-March 2, 2006N Nbar project at VEPP 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 given at Nucleon form factor workshop in Frascati in Octob.14-16, 2005

Febr.28-March 2, 2006N Nbar project at VEPP OUTLINE 1- 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, 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

Febr.28-March 2, 2006N Nbar project at VEPP 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 ≃ at 2E=2.0 GeV Start of VEPP-2000 project –2000 Two collider detectors: Energy range 2E= GeV SND and CMD-3 Febr.15, 2006

Febr.28-March 2, 2006N Nbar project at VEPP SND detector for VEPP – 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)

Febr.28-March 2, 2006N Nbar project at VEPP 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, 2006N Nbar project at VEPP Physical program at VEPP 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 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->4,5

Febr.28-March 2, 2006N Nbar project at VEPP N Nbar production cross section For e+e  p pbar: At the threshold we have s=4M N 2 and G E =G M, if G E =G M =0.5, then C~1 at T kin. ~1 MeV Rad. correction: For T=1MeV: e -n =0.62; For T=50 MeV: e -n =0.82;

Febr.28-March 2, 2006N Nbar project at VEPP Present data – region near threshold e + e - ->p pbar e + e - ->n nbar Proton FF Neutron FF Cross section e + e - -> N Nbar Time like form factor  m=5MeV In VEPP-2000  m <= 1 MeV !

Febr.28-March 2, 2006N Nbar project at VEPP Study of p pbar production at VEPP-2000 with SND Estimates of statistics at threshold : Instant luminosity – - 0.1/(nb.sec) Time – 10 7 sec Integrated luminosity - 1/fb Cross section nb Detection efficiency – 0.15 Number of events: 10 5 G E /G M – with 5% of statistical accuracy, 10 bins Goal – measurement of proton e.m. FF at threshold, 1 – significant improvement of accuracy, 2 – separation between G M and G E, 3 – confirm rise of both FFs at threshold, 4 – search of resonant structure Picture of expected event

Febr.28-March 2, 2006N Nbar project at VEPP Detection of antineutrons at VEPP-2000 with SND Estimates of statistics at threshold : Instant luminosity – - 0.1/(nb.sec) Time – 10 7 sec Integrated luminosity - 1/fb Cross section nb Detection efficiency – 0.15 Number of events: 10 5 G E /G M – 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,  ~7-10 o

Febr.28-March 2, 2006N Nbar project at VEPP Detection of antineutrons at VEPP-2000 with SND, time measurements Monte Carlo time spectra of n nbar events in SND calorimeter 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, 2006N Nbar project at VEPP Physical background e + e - -> K S K L,  0.1 nb e + e - -> K S K L  0,  1 nb e + e - ->  0 ->  0  0 ,  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 K L. K L 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 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 3 types of background:

Febr.28-March 2, 2006N Nbar project at VEPP Example of suppression of physical background for n nbar in SND (MC) Conclusion: effective suppression of physical background by ~ 2 orders is possible using event momentum vs event energy distribution Event momentum Event energy e+e->n nbar e+e->KsKL e+e->KsKl   e+e->   cut

Febr.28-March 2, 2006N Nbar project at VEPP Conclusions 1. VEPP-2000 can produce ~10 5 ppbar and nnbar events per year in the range 2E<2000 MeV. This exceeds by  2-3 orders the world statistics of e+e  n 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 G E /G M 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 G E /G M ratio can be measured as well..