Measurements of e + e hadrons at VEPP-2M

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1 Measurements of e + e hadrons at VEPP-2M B.Khazin Budker Institute of Nuclear Physics Novosibirsk Centerville, Cape Cod, MA June 2006

2 Cross-section section e + e - hadrons VEPP-2M energy range : π + π - production threshold 1.4 GeV c.m. energy parameters of light vector mesons: ρ, ω, φ, ρ, ρ, ω, ω measurement of R(s) Rs () = σ ( + e e γ hadrons) (0) ( + + ee μ μ ) (0) * σ comparison with spectral functions of the hadronic tau decays

3 VEPP-2M collider VEPP-2M collider: GeV in c.m., L /cm 2 s at 1 GeV Latest detector generation - CMD2 and SND: 75 pb -1 collected through operation years

4 CMD2 and SND detectors e - e cm 1 vacuum chamber, 2 drift chamber, 3 Z-chamber, 4 superconducting solenoid, 5 compensating magnets, 6 BGO end cap calorimeter, 7 CsI(Tl,Na) calorimeter, 8 muon system, 9 magnet yoke 1 vacuum chamber, 2 drift chambers, 3 scintillation counter, 4 light guides, 5 PMT, 6 NaI(Tl) crystals, 7 VPT, 8 iron absorber, 9 streamer tubes, 10 iron plates, 11 scintillation counters

5 Example of CMD2 and SND events e + e - π + π - in CMD2 e + e - K + K - in SND

6 How cross-sections sections are measured All modes except 2π σ NH Nbg = L ε (1 + δ ) ( ee H) + Luminosity L is measured using Bhabha scattering at large angles Efficiency ε is calculated via Monte Carlo and corrections for detector imperfections are applied F N σ ee (1 + δee) = σ ( π) (1 + δ ) 2 2π π Nee 2π mode 2π point-like 2π Ratio N(2π)/N(ee) is measured directly detector inefficiencies are cancelled out Virtually no background Analysis does not rely on simulation Formfactor is measured to better precision than L Radiative corrections δ accounts for ISR and FSR (except bare case required for R)

7 Μομεντυμ < 0.6 GeV ππ μμ ee Event separation (CMD2) >0.6 GeV Ενεργψ μμ, ππ ee Ενεργψ Μομεντυμ e/μ/π separation using particles momentum can measure N(μμ)/N(ee) and compare to QED Likelihood minimization: L= ln Na fa( E+, E ), events a a= e e, μμ, ππ,cosmic e/μ/π separation using energy deposition N(μμ)/N(ee) is fixed according to QED

8 Event separation (SND) Event separation is based on neural network: 7 input parameters: energy deposition in each layer for both clusters and polar angle 2 hidden layers 20 neurons each 1 output parameter R e/π Ε 1 (1,2,3), Ε 2 (1,2,3),Θ Ρ ε/π Distribution by separation parameter

9 Pion formfactor (CMD2) Systematic error 0.7% 0.6% (95)/ 0.8% (98) %

10 Pion formfactor (CMD2) Systematic error 0.7% 0.6% (95)/ 0.8% (98) %

11 Pion formfactor (SND) Systematic error 3.2% 1.3%

12 Comparison of CMD2(95) and CMD2(98) Δ(95 98) 0.7%±0.5% Plotted is π F 2 Fπ CMD 2 Δ F F (exp) = 1 ( -2 fit)

13 Comparison of CMD2 and SND s<0.55 GeV 0.6< s<1 GeV Syst.error Δ(SND-CMD2) 1.2%±3.6% Systematic errors: CMD2 0.7 % SND % Δ(SND-CMD2) -0.53%±0.34% Systematic errors: CMD % SND 1.3 %

14 Comparison with KLOE Systematic errors: CLOE 0.9 %

15 Comparison with tau data ALEPH vs e+e BELLE vs ALEPH and CLEO

16 Comparison with tau data BELLE vs ALEPH and CLEO ALEPH vs e+e ALEPH vs BELL and e+e

17 Cross-section section e + e - π + π - π 0 CMD2 (prelim.) SND Systematic error 7% (outside resonances), 2-3% (resonances)

18 Cross-section section e + e - 4π e + e - π + π - π + π - e + e - π + π - π 0 π 0 CMD2 SND CMD2 (prelim.) SND Systematic error 5% Systematic error 8% Efficiency determination gives main contribution to the systematic error

19 Cross-section section e + e - 2K e + e - K + K - e + e - K S K L CMD2 (prelim.) SND (prelim.) CMD2 SND Systematic error 5-8% Systematic error 5-10% Systematic error is 2-3% at φ resonance

20 Overview of the results (CMD2)

21 VEPP-2000 circumference 24.4 m revolution time 82 nsec beam current 0.2 A beam length 3.3 cm energy spread 0.7 MeV β x = β z =6.3 cm L = cm -2 s -1 at 2E=2.0 GeV L = cm -2 s -1 2E=1.0 GeV CMD-3-1 Ldt 500 pb per detector per year SND Total integrated luminosity with all detectors on VEPP-2M ~ 70 pb -1

22 Physics at VEPP Precise measurement of R (~0.4 % for π + π - ) 2. Study of hadronic channels: e + e - 2h, 3h, 4h, h= π,k,η 3. Study of excited vector mesons: ρ, ρ, ω, φ,.. 4. Search for hybrids and exotics 5. CVC tests: comparison of e + e - hadrons (T=1) with τ-decay spectra 6. Study of nucleon-antinucleon pair production nucleon electromagnetic form factors, search for NNbar resonances,.. 7. ISR processes 8. Two photon physics 9. Test of the higher order QED 2 4, 5

23 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

24 Systematic errors Source of error CMD-2 s<1 GeV SND CMD-2 s>1.0 GeV Event separation % 0.5% % Fiducial volume 0.2% 0.8% % Energy calibration % 0.3% % Efficiency correction 0.2%-0.5% 0.6% % Pion losses (decay, NI) 0.2% 0.2% 0.2% Other 0.2% 0.5% % Radiative corrections % 0.2% % Total % 1.3% %

25 Conclusions Despite decades of experiments, precise studies of e + e annihilation into hadrons at low energies are still interesting and provides a lot of important information In a few years new high precision data from CMD-3 and SND working at VEPP-2000 are expected

26 Backup slides

27 e + e π + π π 0 at φ (CMD2) Λ = 12 pb -1 Cross section, nb Β ee Β 3π =(4.35 ± 0.27 ± 0.08) E, MeV σ 3π =(637 ± 23 ± 16) nb Γ φ =(4.30 ± 0.06 ± 0.17) MeV ϕ ωφ = 167 ±14 ±10

28 e + e π + π π 0 at φ (CMD2) th r r N dxdy p p A ae + A k k + 2 iϕ 2 n ρπ CMD-2 a = ± ± ϕ = ± 0.14 ± 0.07 KLOE a = ± ± ϕ = ± 0.08 ± 0.08 but addition of ρ (1450)π provides equally good description with a = g g g φρ π ρ ππ φρπ g ρππ a =0.215±0.092±0.036 ϕ =0.177±0.132±0.051

29 Cross-section section e + e - ηγ (SND) Λ = 27.8 pb -1 Β(ρ ηγ)=(2.53±0.29±0.07) 10-4 Β(ω ηγ)=(4.70±0.47±0.13) 10-4 Β(φ ηγ)=(1.354±0.016±0.035) 10-2 ϕ ω = (12.0 ± 7.9 ± 0.3) ϕ φ = (170 ± 13 ± 4)

30 Why + ee NN 2 2 4m 2 dσ α βc = G ( s) ( 1+cos θ ) + N G (s) sin θ dο 4s M s E 2παmp y= βs -y C=y/(1-e ), pp ee + e + e pp ee + pp At VEPP-2000 energies: σ 0.7 nb L = cm -2 с events/day (BaBar from threshold to 2 GeV 874 events )