Glasgow, October 25, 2007

Results on e+e- annihilation from CMD2 and SND

G.V.Fedotovich and G.V.Fedotovich and S.I.EidelmanS.I.Eidelman

Budker Institute of Nuclear Budker Institute of Nuclear PhysicsPhysics

NovosibirskNovosibirsk

On behalf of CMD-2 and SND On behalf of CMD-2 and SND collaborationscollaborations

•VEPP-2M colliderVEPP-2M collider

•VEPP-2M collider: 0.36-1.4 GeV in c.m., L2*1030/cm2s at 1 GeV•Integrated Luminosity collected by CMD-2 and SND: 70 pb-1 collected in 1993-2000 compared to 6 pb-1 in Orsay and Frascatiat 1.4 < 2E < 3 GeV

•What can we learn?What can we learn?

1. Detail study of exclusive processes: e+e- (2 – 7)h, h = ,,K,p,… Test of models and input to theory (ChPT, MVD, QCD,…) Properties of vector mesons (ρ’,’,’,…) Search for hybrids (qqg and glueballs) Test of CVC relations between e+e- and -lepton Interactions of light (u, d, s) quarks

2. High precision determination of R at low energies and fundamental quantities

(gμ – 2)/2

α(M²z)

QCD sum rules (αs, quark and gluon condensates)

CMD-2 and SND detectors

1 –vacuum chamber, 2 – drift chambers, 3 – scintillation counter, 4 – light guides, 5 – PMT, 6 – NaI(Tl) crystals, 7 – VPT, 8 – iron absorber, 9 – muon range system based on streamer tubes, 10 – iron plates, 11 – scintillation counters

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

Some features of experiments Some features of experiments with CMD-2 and SNDwith CMD-2 and SND

Large data sample due to high integrated luminosity and Large data sample due to high integrated luminosity and large detectors acceptance (calorimetry large detectors acceptance (calorimetry 0.9 0.944))

Multiple scan of the same energy range to avoid possible Multiple scan of the same energy range to avoid possible systematics: step systematics: step (2E) = 10 MeV in the continuum and 1 (2E) = 10 MeV in the continuum and 1 MeV near MeV near and and peaks peaks

Absolute calibration of the beam energy using the resonance Absolute calibration of the beam energy using the resonance depolarization method depolarization method negligible systematic error from an negligible systematic error from an uncertainty in the energy measurementuncertainty in the energy measurement

Good space and energy resolutions lead to small backgroundGood space and energy resolutions lead to small background Redundancy – unstable particles detected via different decay Redundancy – unstable particles detected via different decay

modes (modes (º→2º→2, e, e++ee--; ; →2→2, , ++--00, 3, 300; …); …) Detection efficiencies and calorimeter response are studied Detection efficiencies and calorimeter response are studied

by using “pure” experimental data samples rather than MC by using “pure” experimental data samples rather than MC events (about 20 million events (about 20 million and and meson decays have been meson decays have been used)used)

How cross-sections are measuredHow cross-sections are measured

(1 )

H bgN Ne e H

L

•Efficiency is calculated via Monte Carlo + corrections for imperfect detector

• Integrated luminosity L is measured using Bhabha scattering at large angles

•Radiative correction accounts for ISR effects only

•Vacuum polarization effects are included in cr. sect. properties

All modes except 2

2 2

2 2

(1 )

(point-like ) (1 )ee ee

ee

NF

N

• Ratio N(2)/N(ee) is measured directly detector inefficien-cies are cancelled out in part

•Radiative corrections account for ISR and FSR effects

•Analysis does not rely on simulation

•Formfactor is measured to better precision than L

mode

Selection of eSelection of e++ee-- →→++-- at CMD-2 at CMD-2

ee

•e// separation using particles momentum in DC• can measure N()/N(e) and compare to QED

0.6 GeV

ee,

GeV

• N()/N(e) is fixed according to QED•e separation using energy deposit. in CsI calorimeter

ln , ,

, , , cosmic

a aevents a

L N f E E

a e e

Likelihood minimization:

Selection of eSelection of e++ee-- →→++-- at at SNDSND

Event separation is based on neural network:•1 output parameter – Re/π •2 hidden layers 20 neurons each•7 input parameters: energy deposition in each layer for both clusters and polar angles

Θ

Distribution on separation parameter

Example of CMD-2 and SND Example of CMD-2 and SND eventsevents

e+e-π+π- in CMD-2 e+e-K+K- in SND

Pion form-factor (CMD-Pion form-factor (CMD-2)2)

~ 9105 +- events

Comparison of CMD-2(95) and CMD-Comparison of CMD-2(95) and CMD-2(98)2(98)

≈

2

2

(exp) 1

( - 2 )

FFPlotted is

F F CMD fit

Pion Pion form-factor (SND)form-factor (SND)

Systematic error

~ 8105 +- events

CompaComparison of CMD-2 and SNDrison of CMD-2 and SND√s<0.55 GeV 0.6<√s<1

GeV

Δ(SND-CMD2)≈1.2%±3.6% Δ(SND-CMD2) ≈ -0.53%±0.34%

Syst.error

Systematic errors: CMD-2 0.7 % SND 3.2- 1.3%

Systematic errors: CMD-2 0.6 % SND 1.3 %

Systematic errors

Source of error CMD-2√s<1 GeV

SND CMD-2√s>1.0

GeV

Event separation 0.2-0.4% 0.5% 0.2-1.5%

Fiducial volume 0.2% 0.8% 0.2-0.5%

Energy calibration 0.1-0.3% 0.3% 0.7-1.1%

Efficiency correction 0.2%-0.5%

0.6% 0.5-2.0%

Pion losses (decay, NI) 0.2% 0.2% 0.2%

Other 0.2% 0.5% 0.6-2.2%

Radiative corrections 0.3-0.4% 0.2% 0.5-2.0%

Total 0.6-0.8%

1.3% 1.2-4.2%

ee++ee-- → → ++--

energy interval 390 – 520 MeV energy interval 600 – 960 MeV energy interval 390 – 520 MeV energy interval 600 – 960 MeV

Group aGroup aµµ((), 10), 10-10 -10 aaµµ((), 10), 10-10-10

Old 48.72 ± 1.45 ± 1.12 (1.83) 374.8 ± 4.1 ± 8.5 (9.4)Old 48.72 ± 1.45 ± 1.12 (1.83) 374.8 ± 4.1 ± 8.5 (9.4)CMD-2 46.17 ± 0.98 ± 0.32 (1.03) 377.1 ± 1.9 ± 2.7 (3.3)CMD-2 46.17 ± 0.98 ± 0.32 (1.03) 377.1 ± 1.9 ± 2.7 (3.3)SND 47.80 ± 1.73 ± 0.69 (1.86) 376.8 ± 1.3 ± 4.7 (4.8)SND 47.80 ± 1.73 ± 0.69 (1.86) 376.8 ± 1.3 ± 4.7 (4.8)CMD-2/SND 46.55 ± 0.85 ± 0.29 (0.90) KLOE: 375.6 ± 0.8 ± 4.9 (5.0)CMD-2/SND 46.55 ± 0.85 ± 0.29 (0.90) KLOE: 375.6 ± 0.8 ± 4.9 (5.0)Average 46.97 ± 0.73 ± 0.45 (0.86) 376.5 ± 0.6 ± 1.5 (1.7)Average 46.97 ± 0.73 ± 0.45 (0.86) 376.5 ± 0.6 ± 1.5 (1.7)

energy interval 1040 – 1380 MeVenergy interval 1040 – 1380 MeV

Group aGroup aµµ((), 10), 10-10-10

OLYA 7.49 ± 0.18 ± 0.83 (0.83)OLYA 7.49 ± 0.18 ± 0.83 (0.83) CMD-2 7.01 ± 0.10 ± 0.16 (0.19)CMD-2 7.01 ± 0.10 ± 0.16 (0.19) Average 7.03 ± 0.09 ± 0.16 (0.18)Average 7.03 ± 0.09 ± 0.16 (0.18)

Cross-section eCross-section e++ee--ππ++ππ--ππ00

CMD2

SND

BaBar

Systematic error ≈7% outside resonances,

≈2-3% around resonances

ee++ee0 0 atat (CMD-2) (CMD-2)

3=(637 23 16) nb =(4.30 0.06 0.17) MeV= 167 14 10

r(ee)Br(3) =(4.51 0.16 0.11)10-5

2E, MeV

L = 12 pb-1

Cro

ss s

ecti

on

, n

b

ee++ee0 0 from SND and BaBarfrom SND and BaBar

Good agreement with SND and BaBar.Good agreement with SND and BaBar. Points much higher than at DM2 (early conclusions of SND)Points much higher than at DM2 (early conclusions of SND)

Cross-section eCross-section e++ee--44ππ

e+e-π+π-π0π0e+e-π+π-π+π-

CMD-2 1010³ev., 6% syst.

SND 5410³ev., 8% syst

CMD-2 3810³ev., 5-7% s.

SND 4110³ev.,7% syst.

Efficiency determination gives main contribution to the systematic error

ee++ee 4 4 after BaBar after BaBar

Good agreement with Good agreement with CMD-2/SND/BaBarCMD-2/SND/BaBarError of hadronic contribution to aError of hadronic contribution to a

significantly improved significantly improved below 2 GeVbelow 2 GeV

Cross-section eCross-section e++ee-- 2K 2Ke+e-K+K- e+e-KSKL

CMD-2

SND

CMD-2 (prelim.)

SND (prelim.)

Systematic error ≈ 5-8%~ 950 events

Systematic error ≈ 5-10%~ 2000 events

Systematic error is ≈2-3% at φ resonance

Overview of the results (CMD-Overview of the results (CMD-2)2)

Physics at VEPP-2000Physics at VEPP-2000

Precise measurement of R (~0.4 % for +-)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- → hadrons with -decay spectra5. Study of nucleon-antinucleon pair production – nucleon electromagnetic form factors, search for NNbar resonances, ..6. ISR processes7. Two photon physics8. Test of the high order QED 2 4, 5

LAYOUT of VEPP-2000

CMD-3

SND

• circumference – 24.4 m• revolution time – 82 nsec• beam current – 0.2 A• beam length – 3.3 cm• energy spread – 0.7 MeV• x= z =6.3 cm• L = 1032 cm-2s-1 at 2E=2.0 GeV• L = 1031 cm-2s-1 2E=1.0 GeV

Total integrated luminosity with all detectors on VEPP-2M ~ 70 pb-1

Plan to improve hadronic contribution of aµ by a factor of 2 !!!

-1 per dete30 ctor per ye a0 r Ldt pb

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

ConclusionsConclusions Despite decades of experiments, precise studies of e+e annihilation into hadrons at low energies are still interesting and can provide a lot of important information

● Experiments at VEPP-2M with two detectors CMD-2 and SND significantly improved the accuracy of hadronic cross sections below 1.4 GeV

● Progress is particularly important for e+e-→+-, where systematic uncertainty is ≈ 1% or even better

● Based on data from VEPP-2M together with ISR data obtained at KLOE and BaBar the error of aµ was significantly decreased matching the experimental accuracy

● aµ(exp)- aµ(SM) differs from 0 by ≈ 3.3 necessitating more accurate independent measurements

In a few years new precision data from CMD-3 and SND working at VEPP-2000 are expected as well as with ISR at DAFNE and B-factories