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., 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 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 ,  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 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   , , ,...
iV
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