First results from SND at VEPP-2000

S. SerednyakovOn behalf of SND group

VIII International Workshop on e+e- Collisionsfrom Phi to Psi, PHIPSI11, Novosibirsk

Budker Institute of Nuclear Physics

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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) L(1 y) = 1 fb-1 .

designed

Achieved (2011):L~0.8·1031cm-2c-1 ( 2E=1.0 GeV)L~2·1031cm-2c-1 ( 2E=2.0 GeV)

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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

Iron absorber

S.C. solenoid

SND control room

Drift chamber

Aerogel Cherenkov counter

NaI(Tl) calorimeter

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SND general parametersCalorimeter:1632 NaI(Tl) crystals, VPT readout, 13.5 X0, - 90% 4, x =9º x 9º

4

E

)GeV(E

%2.4=

E

σ

63.0⊕)GeV(E

82.0=

φσ

Energy resolution:Angular resolution:

Tracking system:9-layer cylindrical drift chamber, 24-jet cells,- 94% 4,90% Ar + 10% CO2

PID (dE/dX) p<300 MeV/c

Angular resolution:

0φ 55.0=σ 0

θ 2.1=σ

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Particle ID, aerogel Cherenkov counter

Cherenkov signal vspion momentum

(pions from e+e-→ π+π-π0π0 )

n=1.13, ~60% 4

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Experiments 2010 and 2011,preprint BINP 2011-21

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 ~2

SND trigger threshold ~ 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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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

VEPP-2000 Physical program

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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 2

5γ <10;|Mπ0γ − Mω|<100 MeV

Fit: sum of ρ(770) and ρ(1450)

contributions

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Mπ0γ

e+e-→ ωπ0 → π0π0γ, 2010 scan

M0

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Selections:- at least 2 charged

particles and 4 photons- kinematic fit: χ2 < 40;

Mπ0 = 70-200 MeV

Statistical errors only

e+e-→ π+π-π0π0 , 2010 scan

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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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View of data

e+e-→ π+π- π0 event

e+e-→ π+π-π0 , 2010 scan

M0

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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

m

m

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}sin|(s)G|s

M4)cos(1|(s)G{|

s4

βCα

dΩ

dσ 222

222

EN

M

nnppee ,

)e1/(C

At s=4MN2 GE=GM

}|)s(G|s

M2|)s(G{|

s3

C4 2E

N2

2M

2

C~1 at T.~1 MeV

At s->∞ GM falls as q-4

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Picture of expected event

n

n

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

n

n

e+e-→ n nbar, 2011 scan

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e+e-→ n nbar, 2011 scanSuppression of background

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,

E=1000-1800 MeV

Physical bkgd e+e-2, n,

e+e- e+e-(),

e+e-hadrons,

No tracks in DCH,

No central in EMC,

No E-P conservation,

Type of bkgd Source of bkgd Suppression cuts

Nnbar detection efficiency ~ 20-30%

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e=n1/n0

0=nc1/nc0

Nx=(1+e)(0N0-N1)/(0-e)

n1

n0

nc1

nc0

N1

N0

Nx

Cross section:

exp= Nx/L2

MC=NxMC/LMC

LMC= N0MC/MC

e+e-→ n nbar, 2011 scan, cosmic bkgd subtraction

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e+e-→ n nbar, 2011 scan

Experimental event

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After cosmic bkgd suppression using event time ( effect + phys. bkgd)

Estimated background fromphysical processes (pp +

SND test cross section

FENICE data

Physical background – 1 – e+e- → γγγ, σ ~ 0.4 nb,2 – e+e- → ppbar, σ ~ 0.03 nb

=0.78+-0.2 nb

=0.04+-0.2 nb

threshold

e+e-→ n nbar, 2011 scan

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e+e-→ p pbar, 2011 scan

Picture of expected event near threshold

p

p Events features (near threshold):

- No signal from- “star” from annihilation point at beam pipe

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

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Selections (near threshold):– 3 or more tracks with vertex at beam pipe, – energy in EMC > 650MeV

e+e-→ p pbar, 2011 scan

Experimental event

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Selections (above threshold):– 2 or more tracks,– 2 collinear tracks with large dE/dx, – EMC energy > 650MeV,

Experimental event

e+e-→ p pbar, 2011 scan

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− SND− BaBar1

e+e−→ pp cross section, SND preliminary result

Very preliminaryVery preliminary

[1] B.Aubert et al., Phys.Rev.D73 (2006) 012005

e+e-→ p pbar, 2011 scan

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Conclusions & Plans1. First data taking runs have been performed with SND at

VEPP-2000 in the range 1.0 − 2.0 GeV with ~ 30 inv. pb2. Preliminary results on hadron cross sections have been

obtained ( e+e-→ ωπ0, π+π- π0, π+π- π0 π0, η π+π-, ppbar,

nnbar)3. To analyze the full recorded statistics 4. To upgrade the SND electronics and reconstruction

procedure5. To continue data taking runs

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Thank you