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The project to measure the nucleon form factors at VEPP-2000

Budker Institute of Nuclear Physics, Novosibirsk. The project to measure the nucleon form factors at VEPP-2000. Sergey Serednyakov. Workshop - e+e- collisions from phi to psi , February 27 – March 2, 200 6. Updated version of the talk given at Nucleon form factor workshop

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The project to measure the nucleon form factors at VEPP-2000

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  1. Budker Institute of Nuclear Physics, Novosibirsk The project to measure the nucleon form factors at VEPP-2000 Sergey Serednyakov Workshop - e+e- collisions from phi to psi , February 27 – March 2, 2006 Updated version of the talk given at Nucleon form factor workshop in Frascati in Octob.14-16, 2005 N Nbar project at VEPP-2000

  2. 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 N Nbar project at VEPP-2000

  3. 2E= 400 - 2000МeV L=1031сm-2s-1atE=510 МeV L=1032сm-2s-1at E=1000 МeV VEPP-2000 Complex 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 N Nbar project at VEPP-2000

  4. VEPP-2000 e+e- collider CMD-3 SND Start of VEPP-2000 project –2000 Two collider detectors: Energy range 2E=0.4-2.0 GeV SND and CMD-3 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 Febr.15, 2006 N Nbar project at VEPP-2000

  5. 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. 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 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 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 N Nbar project at VEPP-2000

  8. N Nbar production cross section C~1at Tkin.~1 MeV For e+ep pbar: 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; N Nbar project at VEPP-2000

  9. Present data – region near threshold 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 ! N Nbar project at VEPP-2000

  10. Study of p pbar production at VEPP-2000 with SND Picture of expected event Goal– measurement of proton e.m. FF at threshold, 1 – significant improvement of accuracy, 2 – separation between GMand GE , 3 – confirm rise of both FFs at threshold, 4 – search of resonant structure 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 N Nbar project at VEPP-2000

  11. Detection of antineutrons at VEPP-2000 with SND Picture of expected event Goal– measurement of neutron e.m. FF at threshold, 1 – significant improvement of accuracy, 2 – separation between GMand GE , 3 – confirm rise of both FFs at threshold, 4 – search of resonant structure 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 N Nbar project at VEPP-2000

  12. Detection of antineutrons at VEPP-2000 with SND,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. N Nbar project at VEPP-2000

  13. Background in n nbar detection Physical background e+ e--> KSKL, 0.1nb e+ e--> KSKL0, 1nb   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. KLinteractions 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 N Nbar project at VEPP-2000

  14. 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 ordersis possible using event momentum vs event energy distribution e+e->KsKlp0 e+e->wp0 Event energy 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+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 GE/GMratio 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. TheGE/GMratio can be measured as well. . N Nbar project at VEPP-2000

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