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

Tunka-133 (update 2011)

Rkn

Qkn

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

Q(R) = Qkn·(Rkn/R)2.2

R0 = 102.95-0.245·P [m]

Rkn = 109 - 24.5·(P-4) [m]

b = 4.84 - 2.83∙log10(6.5-P)

CORSIKA: Simulated lateral distributions and fitting function (LDF)

LDF has a single variable parameter

of shape - steepness:

P=Q(100)/Q(200)

0 < R < 700 m

1 - P=5.0 2 – P=4.1 3 – P=3.2 Q(R) = Q(200)·((R/200+1)/2)-

b

Q175

E0 ~ Q1750.93

An example of real shower of 16.03.2010

WDF

LDFP – analysisFWHM(400)

– analysis

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

3. The new methods of analysis for high core distances

LDF

LDF steepness 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:

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1. Pulse selection 2. Apparatus distortions correction 3. Pulse waveform fitting

EXPERIMENT:The main parameters determination – area (light flux) Qi, amplitude Ai, width FWHMi and front delay ti at 0.25Ai.(The more accurate FWHM = τeff/1.24, τeff = Qi/Ai)

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ti

FWHMi

Ai

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)-bQ steepness: bQ

bA > bQ

Accuracy of the EAS core reconstruction

For R< 450 m: ΔRcore ~ 10 mFor 450 m < R < 800 m: ΔRcore ~ 20 m for ADF methodand ΔRcore ~ 30 m for LDF method

CORSIKA: EAS Cherenkov light front

tfront = (R+200)2/SΔθ < 0.5° for Nclusters > 4

Recalculation from Cherenkov light flux Q200 to

the primary energy E0

E0 = A·Q200g

g = 0.94

CORSIKA simulation:~ 500 protons~ 500 ironZenith angles: 0°, 30°, 45°

Zenith angular distribution for E0 > 2·1016 eV

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

Example of internal event

Shower front

Example of external event

Shower front

Plan

Light distribution

Shower front

Pulse width

Plan

Light distribution

Shower front

Pulse width

Plan

Light distribution

Shower front

Pulse width

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Experimental data

3 winter seasons 2009-2010, 2010-2011 and 2011-2012165 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 Depth of EAS maximum Xmax g·cm-2

PRELIMINARY

EXPERIMENT:Mean logarithm of primary mass.PRELIMINARY

Mean logarithm of CR atomic numberBerezhko 2009

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

Yakutsk CRs from SNRs +reacceleration +Extragalactic CRs

Accurate determination of CR composition at ε = 1017- 1019 eV is neededto find transition from galactic to extragalactic CR component

CONCLUSION

1. Primary mass composition changes from light (He) at the knee to heavy at 3·1016 eV

2. The mass composition is heavy till at least 1017 eV3. More statistics is needed at the energy range 1017 – 1018 eV

PLANS

1.More statistics.2.The new simulations. 3.Xmax distribution analysis.

Thank you!