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-→ ωπ0 → π0π0γ

3. Process e+e-→ π+π-π0π0

4. Process e+e-→ π+π-π0

5. Process e+e-→ ηπ+π-

6. Process

7. Process

8. Summary

nn→ee -+

pp→ee+ -

• VEPP-2000 collider: 0.36-2.0 GeV in c.m., L11031 1/cm2s at 1 GeV•L11032 1/cm2s at 2 GeV• Detectors CMD-2 and SND: 60 pb-1 collected in 2010-2011

CMD-3

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

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

Spherical Neutral Detector

First experiments with SND at VEPP-2000Instant luminosity L > 1∙1031 cm-2s-1, at 2Е = 1 GeV

Round beam conception works

VEPP-2М

VEPP-2000Energy Region, GeV

Energy step, MeV

Integrated luminosity, pb-1

scan2010 1.1-1.9 100 5

scan2011 1.05-2.0 25 25

World best

bunch to bunch

luminosity

2010 2011

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 spectra5. Study of nucleon-antinucleon pair production – nucleon electromagnetic form factors, search for NNbar resonances, ..6. Hadron production in ‘radiative return’ (ISR) processes7. Two photon physics8. Test of the QED high order processes 2->4,5

7

e+e- annihilation into hadrons

had

had

From dispersion relations

Contributions to the Standard Model (SM) Prediction:

a [exp ] – a [SM ] ~ 3 σ

uncertainty

Dominant uncertainty from

lowest order hadronic piece.

Cannot be calculated from

QCD (“first principles”) – but:

we can use experiment

8

Mπ0γ

σ~20MeV

Data - scan2010

e+e-→ ωπ0 → π0π0γ cross section

Cuts:- at least 5γ- no charged particles- total energy depos. > Ebeam

- kinemat. reconstruction:χ2

5γ <30; χ2π0π0γ− χ 2

5γ <10;|Mπ0γ − Mω|<100 MeV

Fitting:sum of ρ(770) and ρ(1450)

9

Cuts:- at least 2 chargedparticles and 4 photons- 2 tracks are centralkinematic reconstruction:χ2 < 40;Mπ0 in 70-200 MeV

The bump is a sum of contributions from ρ(770), ρ(1450) and ρ(1700) decays

Data - scan2010

Only statistical errors

Points – DataHistogram – MC

V = ρ ρ′ ρ″π0

π0

π+

π-ω

ρ

e+

e-

e+e-→ωπ0→π+π-π0π0

e+e-→a1π→π+π-π0π0

V = ρ ρ′ ρ″ π0

π0

π+

π-

e+

e-ρ

a

1

e+

e-

π0 π0

π+

π-

V = ρ ρ′ ρ″

e+e-→σV→π+π-π0π0

M(π+π-π0 )

e+e-→ π+π-π0π0 cross section

10

Process e+e-→ π+π-π0

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 - χ2

r < 40;

π+π–γ γ - χ2 < 30;Fittng of Mπ0

(effect+background)

Data - scan2010

11

e+e-→ ηπ+π- cross section

Cuts:– 2 central charged particles– 2 photons– θcharged (22.5°-157.5°) – θphoton (36°-144°)kinematic reconstruction(π+π–γ γ): χ2 < 20

Data - scan2010

12

Process nn→ee+ -

Picture of expected event

n

n

Events features:- No signal from- “star” from annihilation point of in Cherenkov counters or calorimeter

n

n

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

cross sectionnn→ee -+

14

Process pp→ee+ -

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

pp→ee+ -

SND

Babar data

Data - scan2010+scan2011(part.)

Very preliminaryVery preliminaryVery preliminaryVery preliminary

Registration efficiency ~ 40%Background ~ 6 %(estimated using the same cuts below threshold)

cross section

Summary1. 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)

2. Preliminary results on different hadron cross sections were

obtained ( e+e-→ ωπ0, π+π- π0, π+π- π0 π0, η π+π-, )3. The results are in agreement with previous measurements4. 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)

5. 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

pp,nn→ee+ -

SND old version

Energy resolution: Angular resolution:

NaI(Tl) calorimeter

0 - mass

=8,6 MeV

63.0)(

82.0, GeVE4 )(

%2.4

GeVEEE

Calorimeter parameters•1680 crystals• VPT readout• 3 spherical layers• 3.5 tons• 13.5 X0 • 90% 4 • x =90 x 90

Cryogenic Magnetic Detector-3

1 – vacuum chamber 2 – drift chamber3 – electromagnetic calorimeter BGO 4 – Z – chamber 5 – CMD SC solenoid

6 – electromagnetic calorimeter LXe7 – electromagnetic calorimeter CsI8 – yoke9 – VEPP-2000 solenoid

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 and f0 .

The measured , 00 branching ratios in 3-4 times exceed VDM

predictions. The decay 00 was observed for the first time. Its branching

ratio can be explained by -meson contribution. For the 00 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 OZI and isospin violation.

In the cross section of the e+e +0 process the structure near 1200 MeV 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, +

,...,,

2

2

3

2/30 )(

)(12)(

VVVV

iVeeVKKV

simms

ems

ss

V

LSV=ρ,ω,φ,…

e+

e–

KS

KL

γ*

)()()()()()( 03 ssssssLSKKKK

)()()()()( 23 0 sssss

)()( 2 ss

)(2)()( sssLSLSLS KKKKKK

0 180 180

SU(3)SU(3)

n2S+1lJ I=1 I=0 I=0

13S1 ρ(770) φ(1020) ω(783)

13D1 ρ(1700) – ω(1650)

23S1 ρ(1450) φ(1680) ω(1420)

JPC=1– –JPC=1– –

Data ApproximationVector Dominance Model

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