Transcript Document
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+π6. Process
7. Process
8. Summary
+ -
e e → nn
+ e e → pp
CMD-3
• 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
Total integrated luminosity with all detectors on VEPP-2M ~ 70 pb-1
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
First experiments with SND at VEPP-2000
Instant luminosity L > 1∙1031 cm-2s-1, at 2Е = 1 GeV
VEPP-2000
Round beam conception works
Energy
Region,
GeV
Energy
step,
MeV
Integrated
luminosity,
pb-1
scan2010
1.1-1.9
100
5
scan2011
1.05-2.0
25
25
VEPP-2М
2010
World
best
bunch to
bunch
luminosity
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 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
+
ee
annihilation into hadrons
Contributions to the Standard
Model (SM) Prediction:
From dispersion relations
a [exp] – a [SM] ~ 3 σ
Dominant
uncertainty from
lowest order
hadronic piece.
Cannot be
calculated from
QCD (“first
principles”) – but:
we can use
experiment
h
a
d
had
uncertainty
7
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)
8
e+e-→ π+π-π0π0 cross section
e+e-→ωπ0→π+π-π0π0
Data - scan2010
M(π+π-π0 )
Points – Data
Histogram – MC
Cuts:
e+
π0
π0
ρ ρ′ ρ″
- at leastV 2= charged
π+
particles and 4 photons
ω
e- -2 tracks are central ρ
πkinematic
+e-→areconstruction:
e
π→π+π-π0π0
1
2
χ < 40;
e+ in 70-200 MeVπ+ 0
Mπ0
V = ρ ρ′ ρ″
π
π0
a
The
e- bump is a sum of
πρ
1
contributions from ρ(770),
+π-π0π0
ρ(1450)
and ρ(1700)
e+e-→σV→π
decays
e+
Only statistical errors
π+
V = ρ ρ′ ρ″
e-
ππ0
π0
9
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)
10
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
11
Process
+ -
e e → nn
Picture of expected event
n
n
Events features:
- No signal from n
- “star” from annihilation
point of n in Cherenkov
counters or calorimeter
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
12
+ -
e e → nn cross section
Process e + e- → pp
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
14
e e → pp cross section
+ -
Data - scan2010+scan2011(part.)
Very preliminary
Registration efficiency ~ 40%
Background ~ 6 %
(estimated using the same cuts
below threshold)
Babar data
SND
15
Summary
1. 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 measurements
4. New run for e +e- → nn, pp 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
SND old version
NaI(Tl) calorimeter
Energy resolution:
E
4.2%
E 4 E (GeV )
0 - mass
=8,6 MeV
Angular resolution:
,
0.82
0.63
E (GeV )
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
2
3
4
5
–
–
–
–
–
vacuum chamber
drift chamber
electromagnetic calorimeter BGO
Z – chamber
CMD SC solenoid
6
7
8
9
–
–
–
–
electromagnetic calorimeter LXe
electromagnetic calorimeter CsI
yoke
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
, +
Data Approximation
Vector Dominance Model
KS
e+
V=ρ,ω,φ,…
e–
γ*
12
0 ( s) 3 / 2
s
V K S K L ( s)V e e m e
3
V
V , , ,...
iV
2
s mV2 imV V ( s)
KL
(s) K K (s) K S K L (s) 3 (s) (s) 0 (s)
(s) 3 (s) (s) 0 (s) 2 (s)
SU(3)
KS KL (s) KS KL (s) 2 KS KL (s)
0
(s) 2 (s)
JPC=1– –
n2S+1lJ
I=1
I=0
I=0
1 3 S1
ρ(770)
φ(1020)
ω(783)
13D1
ρ(1700)
–
ω(1650)
2 3 S1
ρ(1450)
φ(1680)
ω(1420)
180
180
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