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Tunka-133: Cosmic Ray Mass Composition at 10 16 – 10 18 eV

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Tunka-133: Cosmic Ray Mass Composition at 1016 – 1018 eV

Vasily Prosin (SINP MSU)

For the Tunka Collaboration

Tunka Collaboration

S.F. Beregnev, S.N. Epimakhov, N.N.Kalmykov, E.E.Korosteleva, N.I. Karpov, V.A.Kozhin, L.A.Kuzmichev, M.I.Panasyuk, E.G. Popova, V.V.Prosin, A.A.Silaev, A.A.Silaev(ju),

A.V.Skurikhin, L.G. Sveshnikova, I.V.Yashin

–Skobeltsyn Inst. of Nucl. Phys.of Lomonosov Moscow State Univ., Moscow, Russia;

N.M.Budnev, A.V. Dyachok, O.A. Chvalaev, O.A.Gress, A.V. Korobchenko,R.R. Mirgazov, L.V.Pan’kov, Yu.A.Semeney,A.V. Zagorodnikov

–Inst. of Applied Phys. of Irkutsk State Univ., Irkutsk, Russia;

B.K.Lubsandorzhiev, B.A. Shaibonov(ju)

–Inst. for Nucl. Res. of Russian Academy of Sciences, Moscow, Russia;

V.S.Ptuskin

–IZMIRAN, Troitsk, Moscow Region, Russia;

Ch.Spiering, R.Wischnewski

–DESY-Zeuthen, Zeuthen, Germany;

A. Chiavassa

–Dip. di Fisica Generale Universita\' di Torino and INFN, Torino, Italy.

D. Besson, J. Snyder, M. Stockham

– Department of Physics and Astronomy, University of Kansas, USA

CORSIKA: Simulated lateral distributions and fitting function (LDF)

E0 ~ Q1750.93

LDF has a single variable parameter of shape - steepness: P=Q(100)/Q(200)

0 < R < 700 m

Q(R) = Qkn·exp((Rkn-R)·(1+3/(R+3))/R0)

Q(R) = Qkn·(Rkn/R)2.2

Qkn

R0 = 102.95-0.245·P [m]

Rkn = 109 - 24.5·(P-4) [m]

b = 4.84 - 2.83∙log10(6.5-P)

Rkn

1 - P=5.0 2 – P=4.1 3 – P=3.2

Q175

Q(R) = Q(200)·((R/200+1)/2)-b

An example of real shower of 16.03.2010

The limits for distances used now to unify Xmax analysis for all energy range:

WDF

FWHM(400) – analysis

LDF

P – analysis

EXPERIMENT:Every event = 7 – 133 pairs of records:

The primary data record for each Cherenkov light detector containes 1024 points of amplitude vs. time with the 5 ns time step:

- Pulse selection
- Apparatus distortions correction
- Pulse waveform fitting

anode

dynode

EXPERIMENT:

The main parameters determination – area (light flux)Qi, amplitudeAi, width FWHMiand front delay ti at 0.25Ai.

(The more accurate FWHM = τeff/1.24, τeff = Qi/Ai)

ti

FWHMi

anode

Ai

dynode

CORSIKA: Core location – LDF and ADF

Core location: Amplitude – Distance Function (ADF),

ADF tail fit: A(R) = A(400)·((R/400+1)/2)-bA steepness: bA

LDF tail fit: Q(R) = Q(300)·((R/300+1)/2)-bQsteepness: bQ

bA > bQ

Accuracy of the EAS core reconstruction

For R< 450 m: ΔRcore ~ 10 m

For 450 m < R < 800 m: ΔRcore ~ 20 m for ADF method

and ΔRcore ~ 30 m for LDF method

Recalculation from Cherenkov light flux Q200tothe primary energy E0

E0 = A·Q200g

g = 0.94

CORSIKA simulation:

~ 500 protons

~ 500 iron

Zenith angles: 0°, 30°, 45°

CORSIKA: Xmax reconstruction

∆Xmax = 2767 - 3437∙log10(bA-2), g∙cm-2

PHENOMENOLOGICAL APPROACH:Experimental LDF steepness vs. zenith angle for E0 = 3·1016 eV

~3500 events: 16.4 < log10(E0/eV) < 16.5

cosθ ΔXmax = X0/cosθ – Xmax

X0 = 965 g·cm-2

<Xmax> = 570 g·cm-2 for E0 = 3·1016 eV

PHENOMENOLOGY: Xmax reconstruction

∆Xmax = 2870 – 3520∙log10(bA-2), g∙cm-2

dynode

dynode

dinode

Experimental data

3 winter seasons 2009-2010, 2010-2011 and 2011-2012

165 clean moonless nights

~ 980 h of data acquisition with trigger rate ~ 2-3 Hz

~7 000 000 events

Zenith angle θ≤ 45°, Rcore < 450 m:

~ 170 000 events with E0 > 6·1015 eV – 100% efficiency

~ 62 000 events with E0 > 1016 eV

~ 590 events with E0 >1017 eV

Zenith angle θ≤ 45°, Rcore < 800 m:

~ 1800 events with E0 >1017 eV – 100% efficiency

~ 150 events with E0 > 3·1017 eV

~ 8 events with E0 >1018 eV

Mean logarithm of CR atomic number

Berezhko 2009

CRs from SNRs +

reacceleration +

Extragalactic CRs

Yakutsk

Experiment:

ATIC-2 (Panov et al. 2006)

JACEE (Asakimori et al. 1998)

KASKADE (QGSJET, SIBYLL)

(Hörandel 2005)

HiRes (QGSJET, SIBYLL)

(Abbasi et al. 2005)

CRs from SNRs +CRs from AGNs

Accurate determination of CR composition at ε= 1017- 1019 eV is needed

to find transition from galactic to extragalactic CR component

CONCLUSION

- Primary mass composition changes from light (He) at the knee to heavy at 3·1016 eV
- The mass composition is heavy till at least 1017 eV
- More statistics is needed at the energy range 1017 – 1018 eV

- PLANS
- More statistics.
- The new simulations.
- Xmaxdistribution analysis.

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