Документ взят из кэша поисковой машины. Адрес оригинального документа : http://nuclphys.sinp.msu.ru/conf/lpp14/210809/Pravdin.pdf Дата изменения: Wed Sep 16 16:30:19 2009 Дата индексирования: Tue Oct 2 00:40:58 2012 Кодировка: Поисковые слова: great observatories

The Cosmic Ray Spectrum at Ultrahigh Energies
M.I. Pravdin Yukutsk EAS Array
Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy SB RAS, 31 Lenin Ave., 678980 Yakutsk, Russia

Fourteenth Lomonosov Conference on Elementary Particle Physics Moscow, August 19-25, 2009


Outline
· · · · · · · Yakutsk EAS Array AGASA HiRes Auger Energy Spectrum Yakutsk Muon Data Conclusions


Yakutsk EAS array
Cerenkov light detector

10 km2 (18 km2 in 1973-1990)

55

Scintillation detector 2 m2
1.5 m

Sinchr. reciv.

to Centrer

49 surface detectors Sdet=2x2 m2; 9 surface detectors Sdet=2 m2; 31 detectors of Cerenkov light Distance between detectors ­ 500 m


Yakutsk EAS array Yakutsk EAS array

10 km2 (18 km2 in 1973-1990) 10 km2 (18 km2 in 1973-1990)

2 muons detectors Sdet=20.25 m2 and 3 ones Sdet=20 m Threshold energy of muons 1/ cos() GeV

2


Yakutsk EAS array Yakutsk EAS array

Estimation of shower energy E0 10 km2 (18 km2 in 1973-1990)

Size parameter of EAS (energy estimator) S600 - density at a distance of 600 m from the shower core S600() S600(0 ) E0 The calorimetric formula
The relation between parameters S600(0°) and primary particle energy E0 for showers close to the vertical has been determined by the calorimetric method:

E0 = Ei + Eel + E+ Ei + E + E Ei = k
by measurements of total Cerenkov light flux

h

is the energy lost by a shower over the observation level. It is estimated



Eel - the energy of cascade below the array level E - the energy of the muon component. For E0 1019 eV : Ei / E0 74%; (Ei + E + Eh) / E0 7.4% energy of muons
neutrino and nuclear reactions

losses on ionization, the


Yakutsk EAS array

Estimation of shower energy E

0

1E19 E0, eV

E0 = (4.6 + 1.2)*10 *S600
1E18

17

(0.98 + 0.03)

10 S600(0 ), m
o -2

100

Ratio between shower energy E0 and S calorimetric method

600(0є)

determined by the

EO = (4.6 ± 1.2)1017S600(0°)

0.98 ± 0.03


Yakutsk EAS array
100

Estimation of shower energy E
S1 S2 S3 S4 S5 Q1 Q2 Q3 Q4

0

S600, m

-2

10

1 1000 1200 1400 1600
-2

1800

X, g cm

Zenith angle dependence S600
S600 versus the atmospheric depth X for different energies.


Akeno Giant Air Shower Array AGASA
Area ­ 100 km2 Distance between detectors ­ 1000 m Energy estimator ­ S600 S600() S600(0 ) E0 Zenith angle dependence S600 ­ from experiment Energy formula from model simulations 11 events > 1020 eV (2003)


The High Resolution Fly's Eye - HiRes
Fluorescence Technique HiRes 1 ­ 21 mirrors HiRes 2 ­ 42 mirrors Xmax, Nmax from EAS profile Nmax E0


Pierre Auger Observatory
Surface Array 1600 detector stations 1.5 km spacing 3000 km2

Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per enclosure 24 Telescopes total


Pierre Auger Observatory
Energy estimator ­ 1000 1000() 1000(38 ) E0 Zenith angle dependence 1000 ­ from experiment Energy formula from fluorescence detector data

Fluorescence Technique Xmax, Nmax from EAS profile Nmax E0


Differential energy spectrum: Yakutsk ­ circles, AGASA ­ triangles, Auger ­ asterisks, HiRes ­ diamondsn
1E25

J Eo3, m-2s-1sr-1eV2
1E24 1E17

1E18

1E19

1E20

Eo, eV


Systematic errors E0
· · · · Yakutsk AGASA HiRes ­ Auger ­ - 0° 25-26%. 60° 30%. ­ 18% 15% 22%


Energy spectrum after the energy correction: EC = K·E0 : Yakutsk ­ K = 0.75, AGASA ­ K =0.87, Auger ­ K =1.5, HiRes ­ K =1.2.
1E25

J Eo3, m-2s-1sr-1eV2
1E24 1E17

1E18

1E19

1E20

Eo, eV


Calorimetric methods of energy estimation Yakutsk ­ Cherenkov light detectors Auger ­ Fluorescence telescopes. EYakutsk / EAuger 2


Comparison of the Yakutsk array Spectrum with accounts from AGN
1E25

J Eo , m s sr eV

3

-2 -1

-1

2

Yakutsk Berezinsky et al (2006)

1E24 1E18 1E19 1E20

Eo, eV


Distribution of ratios of observed and simulated muon densities at 1000 m from the shower core for iron on models SYBILL and EPOS. E0 >1019 eV, < 45° For EPOS fraction of iron from 95 % probability is an interval 29 68 % (average value of 48 %)


EAS 7-05-89 22:03 UT =58.7 Log(E0)=20.14 B2=2.7 L2=161.5
1000

EAS 18-02-04 22:20:38 UT =47.7 Log(E0)=20.16 B2=16.3 L2=140.2
1000

100
100
-2

Density, m

Density, m

-2

10

10

Charged particles muons
1

Charged particles Muons
1

0,1 100

1000

0,1 1000

R, m

R, m


The method: event-by-event analysis D.S. Gorbunov, G.I. Rubtsov and S.V. Troitsky, Astropart. Phys. 28 (2007) 28
The idea of the method is the event-by-event comparison of observed muon densities in air showers with those in simulated gamma-ray induced showers which have the same scintillator energy deposit (S600) and the same arrival direction as the observed ones. The advantage of the method is its independence both on the energy reconstruction procedure used by experiment and on the Monte-Carlo simulation of hadronic air showers: we use simulated gamma-induced showers and we select the simulated showers by the observable scintillator signal.

S600 ­ energy estimator (E ­ observable) (300) ­ the muon density at 300 m from the shower axis ­ composition estimator (C ­ observable)


The method: event by event analysis D.S. Gorbunov, G.I. Rubtsov and S.V. Troitsky, Astropart. Phys. 28 (2007) 28

We use the sample of events satisfying the following criteria: - the event passed the selection cuts for the spectrum

reconstruction; - the reconstructed core location is inside the array boundary; - the zenith angle < 45°; - the reconstructed energy Erec > 1018 eV; - the reconstructed shower axis is within 300 m from an operating muon detector. 1647 events Exposure of 7.4·10
14

m2·s·sr


Limits (95% CL) of photons
Fraction: E > 1018 eV: < 0.4% E > 2·1018 eV: < 0.8% E > 4·1018 eV: < 4%


Limits (95% CL) of photons Flux
1

38 A 37.5 A 37 36.5 YN 36 YN 35.5 YN 18 18.5 19 19.5 Log Emin eV 20 PA PA PA

Log E2 F



eV2 km

2

yr

1

sr


Conclusions
· The discrepancy in the intensities of the energy spectra obtained in different experiments can be explained by the presence of systematic errors in the estimated shower energies. · Calorimetric estimations two experiments Yakutsk and Auger different: E
Yakutsk

/ EAuger 2

· The HiRes and Auger data indicate the GZK - cutoff of the CR spectrum · At energy >2 1019 eV the muon fraction is great (the Yakutsk data). Fraction of iron from 95 % probability is an interval 29 - 68 % (using EPOS model) ·


Conclusions
· In the most inclined showers at E0 > 2 1019 eV, the responses of the muon the same as surface detectors in a wide range of distances. These results may indicate the occurrence of new processes upon interactions of particles with such energies. If this is true, the estimated energy of the most intense showers may be incorrect for all arrays. · The analysis of the Yakutsk muon data allowed to place the strongest (up to now) upper limits on photon fraction at E > 1018 eV and E > 2·1018 eV