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. Process e+e-→ ωπ0 → π0π0γ
3. Process e+e-→ π+π-π0π0
Process e+e-→ π+π-π0
Process e+e-→ ηπ+π-
Process
Summary

3. VEPP-2000 Collider Complex
CMD-3
VEPP-2000 collider: 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
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 calorimeter NaI(Tl), 5 – vacuum phototriodes, 6 – absorber, 7-9 – muon system,
10 – VEPP-2000 phocusing solenoid

5. World best bunch to bunch luminosity
First experiments with SND at VEPP-2000
Instant luminosity L > 1∙1031 cm-2s-1, at 2Е = 1 GeV
Round beam conception works
VEPP-2000
Energy Region, GeV
Energy step, MeV
Integrated luminosity, pb-1
scan2010
100 5
scan2011 25
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
a [exp ] – a [SM ] ~ 3 σ
had 
Dominant uncertainty from lowest order hadronic piece. Cannot be calculated from QCD (“first principles”) – but: we can use experiment 
had  
uncertainty

8. e+e-→ ωπ0 → π0π0γ cross section
Data - scan2010
Mπ0γ
σ~20MeV
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. e+e-→ π+π-π0π0 cross section
Points – Data
Histogram – MC
V = ρ ρ′ ρ″ π0 π+ π- ω ρ e+ e-
e+e-→ωπ0→π+π-π0π0
e+e-→a1π→π+π-π0π0 a1
e+e-→σV→π+π-π0π0
M(π+π-π0 )
Cuts:
- at least 2 charged
particles and 4 photons
2 tracks are central
kinematic reconstruction:
χ2 < 40;
Mπ0 in MeV
Data - scan2010
The bump is a sum of
contributions from ρ(770),
ρ(1450) and ρ(1700) decays
Only statistical errors

10. Process e+e-→ π+π-π0 Cuts: – at least 2 central charged particles
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. – ( )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. Picture of expected event
Process
Picture of expected event
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 GeV
– cosmic suppression using event time
Events features:
No signal from
“star” from annihilation point of in Cherenkov counters or calorimeter

13. cross section

14. Process Cuts(at the threshold): Cuts(above 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 Very preliminary 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

18. SND old version

19. NaI(Tl) calorimeter Energy resolution: Angular resolution: 0 - mass
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

20. 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 calorimeter CsI
8 – yoke
9 – VEPP-2000 solenoid

21. 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 ,  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 OZI and isospin violation.
In the cross section of the e+e  +0 process the structure near 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
,   + 

23. Data Approximation Vector Dominance Model SU(3) JPC=1– – γ* n2S+1lJKS e+
V=ρ,ω,φ,… γ* e– KL
SU(3)
JPC=1– –
n2S+1lJ
I=1
I=0
13S1
ρ(770)
φ(1020)
ω(783)
13D1
ρ(1700) –
ω(1650)
23S1
ρ(1450)
φ(1680)
ω(1420)

24. 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