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First results of SND experiment at VEPP-2000

First results of SND experiment at VEPP-2000. Alexey Kharlamov. Budker Institute of Nuclear Physics (Novosibirsk, Russia) SND. Quarks in Hadrons and Nuclei, September, 2011. Outline. 1. SND and VEPP-2000 Collider complex 2. Process e + e - → ωπ 0 → π 0 π 0 γ 

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First results of SND experiment at VEPP-2000

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  1. First results of SND experiment at VEPP-2000 Alexey Kharlamov Budker Institute of Nuclear Physics (Novosibirsk, Russia) SND Quarks in Hadrons and Nuclei, September, 2011

  2. Outline • 1. SND and VEPP-2000 Collider complex • 2. Processe+e-→ ωπ0 → π0π0γ • 3. Process e+e-→ π+π-π0π0 • Process e+e-→ π+π-π0 • Process e+e-→ ηπ+π- • Process • Process • Summary

  3. CMD-3 VEPP-2000 Collider Complex • VEPP-2000 collider: 0.36-2.0 GeV in c.m., L11031 1/cm2s at 1 GeV • L11032 1/cm2s at 2 GeV • Detectors CMD-2 and SND: 60 pb-1 collected in 2010-2011 Total integrated luminosity with all detectors on VEPP-2M ~ 70 pb-1

  4. Spherical Neutral Detector 1 – VEPP-2000 vacuum chamber, 2 – tracking system, 3 – aerogel counters, 4 – electromagnetic calorimeterNaI(Tl), 5 – vacuum phototriodes, 6 – absorber, 7-9 – muon system, 10 – VEPP-2000 phocusing solenoid

  5. First experiments with SNDatVEPP-2000 Instant luminosityL > 1∙1031cm-2s-1, at 2Е = 1 GeV Round beam conception works VEPP-2000 VEPP-2М World best bunch to bunch luminosity 2011 2010

  6. Physics 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

  7. e+e- annihilation into hadrons Contributions to the Standard Model (SM) Prediction: From dispersion relations had  Dominant uncertainty from lowest order hadronic piece. Cannot be calculated from QCD (“first principles”) – but:we can use experiment  had   uncertainty

  8. Data - scan2010 Mπ0γ σ~20MeV e+e-→ ωπ0 → π0π0γcross section Cuts: - at least 5γ - no charged particles - total energy depos. > Ebeam - kinemat. reconstruction: χ25γ<30; χ2π0π0γ−χ 25γ<10; |Mπ0γ− Mω|<100 MeV Fitting: sum of ρ(770) and ρ(1450)

  9. π+ e+ V = ρρ′ρ″ π0 π0 a1 e- π- ρ e+ π+ V = ρρ′ρ″ e- π- π0 π0 e+e-→ π+π-π0π0cross section e+e-→ωπ0→π+π-π0π0 • Cuts: • - at least 2 charged • particles and 4 photons • 2 tracks are central • kinematic reconstruction: • χ2< 40; • Mπ0 in 70-200 MeV Data - scan2010 Points – Data Histogram – MC e+ π0 π0 V = ρρ′ρ″ M(π+π-π0 ) e+e-→a1π→π+π-π0π0 π+ ω e- π- ρ The bump is a sum of contributions from ρ(770), ρ(1450) and ρ(1700) decays e+e-→σV→π+π-π0π0 Only statistical errors

  10. Process e+e-→ π+π-π0 Data - scan2010 Cuts: – at least 2 central charged particles – 2 or 3 γ – Δφch.part.>10° – ΔΩch.part.>40° En.depos. of ch.part.<Ebeam Total en.depos. – (0.3-0.8)Ebeam Kinematic reconstruction: interaction point - χ2r< 40; π+π–γ γ - χ2< 30; Fittng of Mπ0 (effect+background)

  11. e+e-→ ηπ+π- cross section Data - scan2010 Cuts: – 2 central charged particles – 2 photons – θcharged (22.5°-157.5°) – θphoton (36°-144°) kinematic reconstruction (π+π–γ γ): χ2< 20

  12. Events features: • No signal from • “star” from annihilation point of in Cherenkov counters or calorimeter Picture of expected event Process Cuts: – no central charged tracks – no collinear clusters in calorimeter – no signals in muon system – signals in 3 calorimeter layers – crystals in calorimeter are not located along one line – no events with main en.dep. on small angles (θ<36° or θ>144°) and full pulse in calorimeter directed into small angles – limitations on cluster quality and total pulse in calorimeter – total en.dep in the range 1.0-1.8GeV – cosmic suppression using event time

  13. cross section

  14. Process Cuts(at the threshold): – 3 or more charged particles with common point on vacuum tube – total en. deposition > 650MeV Cuts(above the threshold): – 2 or more charged particles – 2 central collinear tracks with large dE/dx in tracking system and 36°<θ<144° – total en. deposition > 650MeV – distribution of energy deposition in calorimeter is not located along one line

  15. cross section Registration efficiency~ 40% Background ~ 6 % (estimated using the same cuts below threshold) Data - scan2010+scan2011(part.) Babar data Very preliminary SND

  16. Summary • First data runs were performed on VEPP-2000 with SND detector (approximately 30 nb-1 collected at the energy range 1.05 − 2.0 GeV) • Preliminary results on different hadron cross sections were obtained ( e+e-→ ωπ0,π+π- π0,π+π- π0 π0, η π+π-, ) • The results are in agreement with previous measurements • New run for study with higher luminosity and with smaller energy step will be performed (5 points with 25 MeV step → 25 points with 5 MeV step) • VEPP-2000 upgrade plan: • Connection to positron source VEPP-5, • Smaller vacuum chamber for BEP Booster to increase B and • to inject at 1 GeV, • Compton scattering energy measurement system

  17. SND old version

  18. NaI(Tl) calorimeter Energy resolution: Angular resolution: • Calorimeter parameters • 1680 crystals • VPT readout • 3 spherical layers • 3.5 tons • 13.5 X0 • 90% 4 •  x =90 x 90 • 0 - mass =8,6 MeV

  19. Cryogenic Magnetic Detector-3 1 – vacuum chamber 2 – drift chamber 3 – electromagnetic calorimeter BGO 4 – Z–chamber 5 – CMD SC solenoid 6 – electromagnetic calorimeter LXe 7 – electromagnetic calorimeterCsI 8 – yoke 9 – VEPP-2000 solenoid

  20. Most important SND physical results • Electric dipole radiative decays (1020) f0(980) and (1020)  a0(980)  • were observed at the first time. Relatively large rate of these processes supports • the model of 4-quark structure of the lightest scalars a0 andf0 . • The measured ,00 branching ratios in 3-4 times exceed VDM • predictions. The decay 00 was observed for the first time. Its branching • ratio can be explained by -meson contribution. For the 00 decay • there is no theoretical explanation. • The branching ratios of radiative magnetic dipole decays , ,   0 ,  were measured with high accuracy - test of VDM and quark model. • The branching ratios of 0, + decays were measured. 0 decay was observed for the first time - study of OZIand isospin violation. • In the cross section of the e+e+0 process the structure near 1200MeV was observed, which is direct manifestation of  (1400) resonance. • The e+e4,0 cross sections were measured with highest accuracy – (g-2) and CVC test. Work in progress: • e+e+ • e+eKSKL, K+K simultaneous fit • e+ee+e • e+e+ 2E > 1GeV • ,   +

  21. Data Approximation Vector Dominance Model KS e+ V=ρ,ω,φ,… γ* e– KL SU(3) JPC=1––

  22. SND subsystems • NaI(Tl) calorimeter - ~50% new phototriodes • Тracking system – new • Аerogel cherenkov detector – new subsystem • Electronics – ~50% new • Data acquisition system – 90% new • Data processing – 90% new • Antineutron detector –new subsystem

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