High density aerogel for ASHIPH SND – test results

Beloborodov K.

10-th INTERNATIONAL CONFERENCEON INSTRUMENTATION

FOR COLLIDING BEAM PHYSICS

Authors

Budker Institunte of Nuclear physics, Novosibirsk:

SND team:Beloborodov K., Golubev V., Serednyakov S., Vesenev V.

KEDR team:Barnyakov A., Barnyakov M., Bobrovnikov V., Buzykaev A.,Kononov S., Kravchenko E., Onuchin A.

Boreskov Institute of Catalysis, Novosibirsk:Danilyuk A.

Outline

• VEPP-2000, SND detector• Physical program for SND at VEPP-2000• Aerogel properties• SND aerogel counter design. Construction status.• Test with cosmic muons• Misidentification• π/K – separation power.• Conclutions

VEPP-2000 complex

Main parameters: • perimeter: 24.4 m • collision time: 82 nsec • beam current: 0.2 A • bunch length: 3.3 cm • energy spread: 0.7 MeV

Luminosity:L 1•10≃ 32 cm-2s-1 at 2E = 2.0 GeV

≃1•1031 cm-2s-1 at 2E = 1.0 GeV ► Design feature: round beams (βx≃βz:

6.3cm)► Project goal: 3 fb-1 till 2011

Physical program for SND at VEPP-2000

Precise measurement of the quantity

R = (e+e- → hadrons) / (e+e- → +-) Study of hadronic channels:

e+e- → 2h, 3h, 4h …, h = , K, Study of ‘excited’ vector mesons: ’, ’’, ’, ’’, ’,.. CVC tests: comparison of e+e- → hadrons (I=1)

cross section with -decay spectra Study of nucleon-antinucleon pair production,

nucleon electromagnetic form factors, … Hadron production in ‘radiative return’ (ISR)

processes: e+e- → γ γ* , γ* → hadrons Two photon physics: e+e- → e+e- + X Test of the QED high order processes 2 → 4,5

Spherical Neutral Detector (SND)

1 – VEPP-2000 beam pipe, 2 – Tracking system, 3 – Aerogel Cherenkov counter, 4 – NaI(Tl) counters, 5 – Vacuum

phototriodes, 6 – Fe absorber, 7-9 – Muon system, 10 – VEPP-2000 s.c. focusing solenoids

SND drift chamber: π/K-separation

• sensitive length along beam axis: 230-280 mm• internal diameters of sensitive volume: 42 mm• outer diameter of sensitive volume: 200 mm• type drift cell: JET• number of measurements within drift cell: 9• number of drift cells: 24• acceptance (4 layer / 9 layers): 94 % / 75 % of 4π• entrance material budget: ≤ 1 % X0

• total material budget: 4 % X0

• number of shield wires (Ø 120 μm): 984• number of sensitive/anode wires (Ø 15-20 μm): 312• number of cathode strips: 288

spatial resolution:

- drift time in R-φ plane: σX ≈ 150 μm

- charge division along wire: σZ ≈ 1.5 mm

- cathode strips: σZ ≈ 0.5 mm

angular resolution: σφ ≈ 0.3 o

σθ ≈ 0.5 o

energy loss resolution: σ(dE/dx)/<dE/dx> ≈ 25 %

π/K separation: at p ≤ 300 MeV/c

Main parameters: Design parameters:

Aerogel refraction index: selection

Requierements on effective π/K - separation momentum region:

should overlap with DC:pmin = 300 MeV/c

K-mesons should not produce Cherenkov light:

pmax = 870 MeV/c (for K-meson in e+e- K+K-)

n = 1.13 ± 0.01

)(1)( pep

))(1()( 20 ppp thr

Dependence of the detection efficiency on particle momentum :

μ0 – average number of photoelectrons for a relativistic particle pthr – Cherenkov threshold momentum for a particle

μ0=10 ph.e.

πK

μ0=5 ph.e.

1,14 1,12nopt

Aerogel: properties

Stages of dense aerogel production:

I. Synthesis of “light” aerogel with density ρ=0.24 г/см³ (n=1.05)

II. Sintering “light” aerogel to density ρ=0.50÷0.76 г/см³ (n=1.10÷1.15) Nucl.Instrum.Meth.A494:491-494,2002

Refraction index: n=1.13±0.01 Density: ρ=0.65 g/cm3

Light scattering length: Lsc=19 mm at =400 nm Light absorbtion length: Labs=100 cm at =400 nm

Aerogel parameters:

Aerogel counters: design

• Cylindrical shape: R=105÷141 mm• Walls material: Al, 1 mm thickness• Consists of 3 segments with 3 separate counters in each • Solid angle: ~60% of 4π • Thickness: 0.09 Xo

Aerogel System Design

1 - PMT, 2 – aerogel with n=1.13, 3 - WLS

• Scheme: Aerogel + Wavelength shifter (WLS) + PMT (Nucl.Instrum.Meth.A315:517-520,1992 )• WLS position: displaced by ~5° from counter center• Aerogel cover: teflonwith a refractivity of R ~98%• Aerogel thickness: ~31 mm

Aerogel counter Design

1

32

SND aerogel counter: construction

SND aerogel counter: 27.02.2008

Test with cosmic muons

Measurements with cosmic rays:• Signal amplitude• Inhomogeneity of light collection• Time dependence of amplitude• Time resolution

Time resolutionTime resolution

Signal amplitudeSignal amplitudepμ>500 MeV/c

pμ>1000 MeV/c

Pb

Amplitude. Inhomogeneity of light collection

Map of mean amplitudes in units of photoelectrons. Boxes indicate the locations of trigger counters. The errors are statitical.

point amplitute

a 8,2±0,2

b 10,7±0,2

c 10,4±0,3

d 9,4±0,2

e 8,9±0,3

bb

Time dependence of amplitude

1 year

A. Barnyakov. Influence of water absorbed in aerogel on light (poster) absorption length

ACC counter time resolution

FWHM/2.36 ≈ 2.0 ns

Contributions into the time resolution :• cherencov light collection time < 0.5 ns• time spread of trigger counters ~ 0.7 ns• time spread of the photon propagation in the WLS < 0.1 ns• decay time of BBQ + number of photo electrons ~ τBBQ/Nph.e.≈15/7.5≈2 ns

Time resolution vs Nph.e: ΔT= τ/Nph.e.Time resolution vs Nph.e: ΔT= τ/Nph.e.

τ = 15.7 ± 0.6 ns

),;(),0()( 0 ttSGtf trig

Time resolution of the counter mostly depends on decay time of BBQτBBQ=15 ns

KEDR aerogel counter: tests with π/p-beams

ee

Lpx

Ce

p

p ea

e dpdxdx

dEx

dx

dnMpp

dp

dnIpI

ee

ethr

C

);(),;()(

),(

0

max

maxmax

)()()()( pIpIpIpI bkgeCC

2

max 1)( ppIpI thr

C

bkgbkg IpI )(

─ Cherenkov light of the initial particle (π, p)

─ Cherenkov light of δ-electrons

─ Cherenkov light from the teflon, scintillations, …

Parameters Fit

Imax, ph.e. ─

Ibkg, ph.e. ─

nopt 1.05

dE/dx, MeV/(g/cm2) -1.72

L, cm 7 const

ρ, g/cm3 0.24 const

M, MeV/c2 Mπ, Mp const

Parameters Fit

Imax, ph.e. ─ 10.6 ± 0.4

Ibkg, ph.e. ─ 0.0243 ± 0.0003

nopt 1.05 1.045 ± 0.006

dE/dx, MeV/(g/cm2) -1.72 -1.57 ± 0.48

L, cm 7 const

ρ, g/cm3 0.24 const

M, MeV/c2 Mπ, Mp const

Cherenkov light of δ-electron with pe

δ-electron spectra

pionspions protonsprotons

Nucl.Instrum.Meth.A494:424-429,2002

Misidentification calculation

thrp

thrKpK P

PPP

,

,

Parameters Value

Imax, ph.e. 10

Ibkg, ph.e. 0.025

nopt 1.13

dE/dx, MeV/(g/cm2) -1.57

L, cm 3

ρ, g/cm3 0.65

M, MeV/c2 Mπ, MK

KEDR

SND

pK I

III

max

max

kaonskaonspions

kaons kaons pions

IK=0.18 ph.e.

Iπ=9.48 ph.e.

1. Equality of misidentifications:Mis-n: ~1% (2.6σ)

2. ε(K)=90%:Mis-n of π: ~8·10-2 % (3.3σ)

3. ε(π)=90%:Mis-n of K: ~7·10-3 % (3.9σ)

kaons

pions2 3

1

2

3

1

Separation power: DC + ACC

εK = 90%, Imax = 8 ph.e.εK = 90%, Imax = 8 ph.e.

K meson separation

K meson separation

εK = 90%, Imax = 10 ph.e.εK = 90%, Imax = 10 ph.e.

επ = 90%, Imax = 8 ph.e.επ = 90%, Imax = 8 ph.e.

επ = 90%, Imax = 10 ph.e.επ = 90%, Imax = 10 ph.e.

π meson separation

π meson separation

Conclusions

1. First time high density aerogel is used for PID2. Aerogel counters designed and constructed for

SND3. Tests with cosmics muons was perform:

• Average amplitude is around 10 ph.e.• Inhomogeneity of light collection is not more

than 20% over the counter• Maximum amplitude decrease with time

τ≈725 days and aerogel should be repaired time to time

• Time resolution is σt~15/Nph.e4. Calculation of underthreshold effects was done5. Estimated π/K-separation power for SND

detector