VEPP-2000 plans for the study of the nucleon form factors Budker Institute of Nuclear Physics, Novosibirsk VEPP-2000 plans for the study of the nucleon form factors Sergey Serednyakov Nucleon 05 Workshop 12-14 October, 2005 12-14 October, 2005 N Nbar at VEPP-2000

NNbar cross section and formfactor data OUTLINE VEPP-2000 collider SND and CMD-3 detectors NNbar cross section and formfactor data Prospects of VEPP-2000 for NNbar measurements Conclusions 12-14 October, 2005 N Nbar at VEPP-2000

VEPP-2000 Complex 2Emax=2000 МeV L=1031сm-2s-1 at E=510 МeV 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 12-14 October, 2005 N Nbar at VEPP-2000

VEPP-2000 e+e- collider CMD-3 Start of VEPP-2000 project –2000 SND Start of VEPP-2000 project –2000 Two collider detectors: Energy range 2E=0.4-2.0 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 2E=2.0 GeV 12-14 October, 2005 N Nbar at VEPP-2000

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. 12-14 October, 2005 N Nbar at VEPP-2000

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 12-14 October, 2005 N Nbar at VEPP-2000

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 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 12-14 October, 2005 N Nbar at VEPP-2000

N Nbar production cross section For e+ep pbar: C~1 at Tkin. ~1 MeV At the threshold we have s=4MN2 and GE=GM, if GE =GM=0.5, then Rad. correction: For T=1MeV: e-n=0.62; For T=50 MeV: e-n=0.82; 12-14 October, 2005 N Nbar at VEPP-2000

Present data Cross section e+e- -> N Nbar Time like form factor e+e-->p pbar e+e-->n nbar Cross section e+e- -> N Nbar Neutron FF Proton FF Time like form factor Dm=5MeV In VEPP-2000 Dm <= 1 MeV ! 12-14 October, 2005 N Nbar at VEPP-2000

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 12-14 October, 2005 N Nbar at VEPP-2000

Detection of antineutrons at VEPP-2000 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, s~7-10o 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 12-14 October, 2005 N Nbar at VEPP-2000

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 T=10 MeV:  0.3 - 0.4 12-14 October, 2005 N Nbar at VEPP-2000

e+e- -> n nbar, MC distribution over cos q. Extraction of GM , GE GM gives (1+ cos 2q ), GE gives (1- cos 2q ). With T =10MeV, N=3000 ev., ratio GE /GM is measured with 8% accuracy 12-14 October, 2005 N Nbar at VEPP-2000

Detection of antineutrons at VEPP-2000, time measurements Time-amplitude correlation Time resolution s=3 nsec Monte Carlo time spectra of n nbar events in SND calorimeter Time measurements with NaI(Tl) counter, DE=30 MeV, s=3 nsec, phototriode readout Conclusion: Time resolution of the whole NaI(Tl) calorimeter s<1 nsec at DE~0.5 GeV is expected. 12-14 October, 2005 N Nbar at VEPP-2000

Background in n nbar process Physical background e+ e--> KSKL, 0.1 nb e+ e--> KSKL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 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 12-14 October, 2005 N Nbar at VEPP-2000

Example of suppression of physical background for n nbar in SND (MC) e+e->n nbar Event momentum cut e+e->KsKL Conclusion: effective suppression of physical background by ~ 2 orders is possible using event momentum vs event energy distribution e+e->KsKlp0 e+e->wp0 Event energy 12-14 October, 2005 N Nbar at VEPP-2000

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 12-14 October, 2005 N Nbar at VEPP-2000

Conclusions 1. VEPP-2000 can produce ~105 ppbar and nnbar events per year at the threshold region 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. 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) . 12-14 October, 2005 N Nbar at VEPP-2000