Transcript Слайд 1 - Novosibirsk

Budker Institute of Nuclear Physics
First results from SND at
VEPP-2000
S. Serednyakov
On behalf of SND group
VIII International Workshop on e+e- Collisions
from Phi to Psi, PHIPSI11, Novosibirsk
VEPP-2000 Collider
Main parameters:
collision time – 82 ns
beam current – 0.2 A
bunch length – 3.3 cm
perimeter – 24.4 m
Energy spread – 0.7 MeV
x≃ z =6.3 cm
L ≃ 1032 cm-2c-1 (2E=2.0 GeV)
L=1031cm-2c-1 (2E=1.0 GeV)
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Achieved (2011):
L~0.8·1031cm-2c-1 ( 2E=1.0 GeV)
L~2·1031cm-2c-1 ( 2E=2.0 GeV)
designed
IL(1 y) = 1 fb-1 .
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SND for VEPP-2000 (1993, VEPP-2M)
1 – beam pipe, 2 – tracking system, 3 – aerogel Cherenkov counter , 4 –
NaI(Tl) crystals, 5 – phototriodes, 6 – iron absorber, 7–9 – muon detector, 10 –
focusing solenoids.
NIM A449 (2000) 125-139
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SND at VEPP-2000
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SND at VEPP-2000
NaI(Tl) calorimeter
Drift chamber
Aerogel Cherenkov counter
SND control room
Iron absorber
S.C. solenoid
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SND general parameters
Calorimeter:
1632 NaI(Tl) crystals,
VPT readout,
13.5 X0,
W - 90% 4,
 x  =9º x 9º
Energy resolution:
σE
=
E
4
4.2%
E(GeV)
Tracking system:
9-layer cylindrical drift chamber,
24-jet cells,
W - 94% 4,
90% Ar + 10% CO2
PID (dE/dX) p<300 MeV/c
Angular resolution:
σφ = 0.550
σθ = 1.20
Angular resolution:
σ
φ
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=
0.82
⊕0.63
E (GeV )
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Particle ID, aerogel Cherenkov counter
n=1.13, W~60% 4
Cherenkov signal vs
pion momentum
(pions from e+e-→ π+π-π0π0 )
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Experiments 2010 and 2011,preprint BINP 2011-21
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Energy
Region,
GeV
Energy
step, MeV
Integrated
luminosity, pb-1
scan2010
1.1-1.9
100
5
scan2011
1.05-2.0
25
25
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Experiments 2010 and 2011,preprint BINP 2011-21
Beam currents, e+, e-, mA
~50, 50
Beam life time, hr
SND trigger threshold
~2
~ 100 MeV
Trigger rate
Ncosm=130Hz,
Nbeam ~ 100 Hz
Trigger live time
95%
DCH rate
100 kHz
Event size
~7 kbt
Luminosity monitoring
e+e->e+e-
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VEPP-2000 Physical program
1. Precise measurement of the quantity
R=(e+e– → hadrons) / (e+e– → +-)
2. Cross section measurements of the processes of e+e- annihilation
into hadrons: e+e– → 2h, 3h, 4h …, h= ,K,, …
3. Study of excited vector states: ′, , ′, , ′,..
4. CVC tests: comparison of e+e– → hadrons cross section
with
 → ν τ + hadrons decay spectra
5. Study of nucleon - antinucleon pair production
and nucleon electromagnetic form factors, search for NNbar
resonances.
6. Hadron production in radiative return (ISR) processes:
e+e– → γ*γ, γ* → hadrons
7. Two photon physics e+e– → e+e– + hadrons
8. Test of high-order QED 2→ 4, 5
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e+e-→ ωπ0 → π0π0γ, 2010 scan, preprint BINP 2011-21
Selections:
- at least 5γ,
- no charged particles,
-energy deposition -> Ebeam
-kinematic fit: χ25γ <30;
χ2π0π0γ− χ 25γ <10;
|Mπ0γ − Mω|<100 MeV
Fit: sum of
ρ(770) and ρ(1450)
contributions
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e+e-→ ωπ0 → π0π0γ, 2010 scan
Mπ0γ
M0
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e+e-→ π+π-π0π0 , 2010 scan
Selections:
- at least 2 charged
particles and 4 photons
- kinematic fit: χ2 < 40;
Mπ0 = 70-200 MeV
Statistical errors only
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e+e-→ π+π-π0π0 , 2010 scan
0 masses
m12
m34
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e+e-→ π+π-π0 , 2010 scan
Selections:
– 2 or more tracks
– 2 or 3 γ
– Δφch.part.>10°
– ΔΩch.part. >40°
Total EMC energy
– (0.3-0.8)Ebeam
Kinematic fit:
π+π–γ γ - χ2 < 30
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e+e-→ π+π-π0 ,
2010 scan
View of data
e+e-→ π+π- π0 event
M0
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e+e-→ ηπ+π- , 2010 scan
Selections:
– 2 charged particles
– 2 photons
– θcharged (22.5°-157.5°)
– θphoton (36°-144°)
kinematic fit (π+π–γ γ):
χ2 < 20
mgg
m
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e  e   pp, nn
dσ
α 2βC
4 M 2N
2
2

{| G M (s)| (1  cos  ) 
| G E (s)|2 si n2  }
dΩ
4s
s


42 C
2M 2 N
2
2


{| G M (s) | 
| G E (s ) | } C 
/(1  e  )
3s
s

At s=4MN2 GE=GM
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C~1 at T.~1 MeV
At s->∞ GM falls as q-4
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e+e-→ n nbar, 2011 scan
Picture of expected event
n
n
Events features:
- no signal from n
- “star” from annihilation
point of n in Cherenkov
counters or calorimeter
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e+e-→ n nbar, 2011 scan
Suppression of background
Type of bkgd
Source of bkgd
Suppression cuts
Cosmic bkgd
Muon tracks in
EMC, showers
In EMC
Muon system veto, r.f.
time,
Signature in EMC
Beam bkgd
Beam scattering
on residial gas,
Toushek effect
High EMC threshold,
Signature in EMC,
Physical bkgd e+e-2g, ng,
e+e- e+e-(g),
e+e-hadrons,
E=1000-1800 MeV
No tracks in DCH,
No central g in EMC,
No E-P conservation,
Nnbar detection efficiency ~ 20-30%
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e+e-→ n nbar, 2011 scan, cosmic bkgd subtraction
e=n1/n0
0=nc1/nc0
n0
n1
Nx=(1+e)(0N0-N1)/(0-e)
nc1
nc0
Cross section:
Nx
MC=NxMC/LMC ed
N1
N0
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exp= Nx/L2g ed
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LMC= N0MC/MC
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e+e-→ n nbar,
2011 scan
Experimental event
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e+e-→ n nbar, 2011 scan
After cosmic bkgd suppression using
event time ( effect + phys. bkgd)
Estimated background from
physical processes (pp + ggg)
SND test cross section
=0.04+-0.2 nb
FENICE data
=0.78+-0.2 nb
Physical background –
1 – e+e- → γγγ, σ ~ 0.4 nb,
2 – e+e- → ppbar, σ ~ 0.03 nb
threshold
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e+e-→ p pbar, 2011 scan
Events features (near threshold):
- No signal from
- “star” from annihilation point
at beam pipe
p
p
p
Events features (above the threshold):
- charged track and no energy
deposition for
- charged track and “star” from
annihilation point in Cherenkov
counter for p
p
p
Picture of expected event near threshold
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e+e-→ p pbar, 2011 scan
Selections (near threshold):
– 3 or more tracks with vertex at
beam pipe,
– energy in EMC > 650MeV
Experimental event
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e+e-→ p pbar, 2011 scan
Selections (above
threshold):
– 2 or more tracks,
– 2 collinear tracks with large
dE/dx,
– EMC energy > 650MeV,
Experimental event
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e+e-→ p pbar, 2011 scan
− SND
− BaBar1
Very preliminary
e+e−→ pp cross section, SND preliminary result
[1] B.Aubert et al., Phys.Rev.D73 (2006) 012005
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Conclusions & Plans
1.
2.
3.
4.
5.
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First data taking runs have been performed with SND at
VEPP-2000 in the range 1.0 − 2.0 GeV with ~ 30 inv. pb
Preliminary results on hadron cross sections have been
obtained ( e+e-→ ωπ0, π+π- π0, π+π- π0 π0, η π+π-, ppbar,
nnbar)
To analyze the full recorded statistics
To upgrade the SND electronics and reconstruction
procedure
To continue data taking runs
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Thank you
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