Tunka Experiment: Towards 1км2 EAS Cherenkov Array

B.K.Lubsandorzhiev for TUNKA Collaboration

TUNKA COLLABORATION

Scobeltsyn Institute of Nuclear Physics of MSU (Moscow, Russia)

Institute of Applied Physics of ISU (Irkutsk, Russia)

Institute for Nuclear Research RAS (Moscow, Russia)

IZMIRAN (Moscow, Russia)

Universita’ Torino , Italy

DESY-Zeuthen, Germany

“…..as far as Baikal it is Siberia’s dull prose, just from Baikal Siberian delightful poetry starts….” A.P.Chekhov (Letters from Siberia)

History of Tunka Experiment

1991-1992 experiments with QUASAR-370 tubes on the Baikal ice

1991-1993 Development of QUASAR-370 modification for EAS Cherenkov arrays - QUASAR-370G

1993 Surface Mobile EAS Cherenkov Array (SMECA) for joint work with Lake Baikal

neutrino telescope NT-200

1993 - TUNKA-4 (4 QUASAR -370G)

1996 - TUNKA-13 (13 QUASAR-370G)

2000 - TUNKA-25 (25 QUASAR-370G)

200? - TUNKA-133 (1km2 Cherenkov EAS Array)

QUASAR-370G

37 cm extended bialkalilow resistance hemisphericalphotocathode

2acceptance

YSO+BaF2 scintillator

Small 6 stages high anode current PMT

QUASAR-370G

2 ns TTS (FWHM)

70-80 % SER

IAmax ~ 200 mkA

Immunity to Earth’s magnetic field

TUNKA Wide Angle EAS Cherenkov Detector

675 m a.s.l. Seff ~ 1.6 105 m2 Eth ~ 500 TeV ~ 0.5o

The Tunka-25

„Remote detector“

25 QUASAR-370G tubes - 37 cm diameter - integrating 4 EMI D668 tubes

(AIROBICC tubes) - 20 cm diameter - fiber read-out, - FADC

prototype

Cherenkov light lateral distribution

Q(R) = Qkn·exp((Rkn-R)·(1+2/R)/R0)

Q(R) = Qkn·(Rkn/R)2.2

P = Q(100)/Q(200)

R0 = 102.83-0.2·P [m]

Rkn = 200 -20·P [m]

Hmax=10.62-0.12(P+2.73)2

Hmax=X0/cos - Xmax

Differential energy spectrum of CRs around the “knee”

E0[TeV] = 370(Q175) 0.96

[photoncm-2eV-1]

Eknee ~ 31015eV

1 = -2.660.01

2 = -3.100.02

Energy spectrum of CRs in wide range

Gap between direct and ground based measurements.

Approximations of their data don’t coincide!

Chemical composition of CRs around the knee

Mass composition is measured by two methods:

1. Measurements of Cherenkov light waveform at large distancesfrom a shower core (>200 m)

R ~ 300 m

2. Analysis of LDF

Hmax=1677+1006lg(FWHM)

Chemical composition around the knee

Mean mass composition

30% p, 30% He, 20%CN, 20% Fe

WHAT NEXT?

Тunka-133

133 optical detectors covering Seff ~ 1 km2 Eth ~ 1015 eV

Expected statistics for 1 year operation ( 400 hours): > 3·1015 eV ~ 3.0•105 events > 1017 eV ~ 200 events > 1018 eV ~ 1 – 3 events

Study of energy spectrum and mass composition of primary cosmic rays from “classical” knee ~3•1015 eV to maximumenergy in SNR ~1017 • Z eV

Tunka-133: position of optical detectors

Seven optical detectors form one Cluster

Optical detector

PreamplifierHV power supply

Plexi window with heating

Phototube:20 cm PMT fromAIROBICC and MACRO

Cluster’s Electronics

Reconstruction of EAS parameters

Shower core location ~ 6 m

Primary energy measurement ~ 15%

Xmax measurement (LDF) ~ 35 – 40 g/cm2

Xmax measurement (pulse shape) ~ 25 g/cm2

CONCLUSIONS

TUNKA experiment operates for more than 10 years.

Physics results of the experiment covers primary cosmic raysstudies in the energy range 61014 - 1017eV

The «knee» of primary energy spectrum is observed around ~3 1015eV

Primary mass composition doesn’t change significantly in therange of 1015 - 1016eV gradually rising to heavier elements athigher energies.

It is necessary to decrease energy threshold down to 1014eV to compare results with direct experiments data

It is very desirable to develope new version of QUASAR phototube (~50 cm in diameter): fast (1ns TTS (fwhm)) with a few ns time response .

We are planning to construct new array with 133 hemispherical phototubes (20 cm in diameter) to study primary cosmic rays inthe energy range of 1015- 1018 eV