Study of VHE Cosmic Ray Spectrum by means of Muon Density Measurements at Ground Level

Study of VHE Cosmic Ray Spectrum Study of VHE Cosmic Ray Spectrum by means of Muon Density by means of Muon Density

Measurements at Ground LevelMeasurements at Ground Level

II..II.. Yashin Yashin

Moscow Engineering Physics InstituteMoscow Engineering Physics Institute, , IIYashin@mephi.ruIIYashin@mephi.ru

Vulcano 2008, 26th-31st May

A.G. Bogdanov, R.P. Kokoulin, G. Mannocchi, A.A. Petrukhin, A.G. Bogdanov, R.P. Kokoulin, G. Mannocchi, A.A. Petrukhin, O. Saavedra, V.V. Shutenko, G. Trinchero, I.I. YashinO. Saavedra, V.V. Shutenko, G. Trinchero, I.I. Yashin

ContentsContents

1. Motivation2. Local muon density phenomenology3. DECOR data VS simulation4. Conclusions

Moscow Engineering Physics Institute, RussiaMoscow Engineering Physics Institute, RussiaIstituto Nazionale di Astrofisica, Sezione di TorinoIstituto Nazionale di Astrofisica, Sezione di TorinoUniversita di Torino, ItalyUniversita di Torino, Italy

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MotivationMotivation

In EAS data interpretation, primary spectrum, composition, interaction characteristics, and

their energy dependence are unknown.

To solve the problem involving several unknown functions, measurements of different

EAS observables are necessary.

In this talk, phenomenology and recent data on a new EAS observable – local muon density distributions in a wide range of zenith angles – are considered.

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Local muon density phenomenologyLocal muon density phenomenology If the size of the detector is small compared to typical distances of substantial changes of muon LDF, the detector may be considered as a point-like probe. In a muon bundle event, the local muon density D (in a random point of the shower) is estimated:

D = (number of muons) / (detector area); [D] = particles / m2.

Collection area rapidly increases with zenith angle (~ 1 km2 at 80)

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Local muon density phenomenologyLocal muon density phenomenologyWithout considering fluctuations, spectrum of events in local density

may be written as [Kokoulin at al., 2005]

where N (> E) - primary spectrum, E is defined by the equation:

F D N E r ,D dS,

E,r D

[ events / (s sr)]

For a nearly scaling LDF around some energy For a nearly scaling LDF around some energy EE00

0 0 0 9E,r E E E ,r , .

and power type primary spectrum 0

N E A E E ,

0 2F D AD E ,r dS, /

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/ ( / ) / ( , ) /dF dD dN dE dS d E r dE

General view of NEVOD-DECOR complexGeneral view of NEVOD-DECOR complex

Side SM: 8.4 m2 each• σx 1 cm; σψ 1°

Coordinate-tracking detector DECOR (~115 m2)

Cherenkov water detector NEVOD (2000

m3)

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A typical muon bundle event in Side DECORA typical muon bundle event in Side DECOR

X-projectionX-projection Y-projectionY-projection

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Muon bundle event (geometry reconstruction)Muon bundle event (geometry reconstruction) Vulcano 2008, 26th-31st May

DECOR data summary DECOR data summary Muon bundle statistics 2002 - 2007Muon bundle statistics 2002 - 2007

(*) For zenith angles < 75°, only events in limited intervals of azimuth angle (with DECOR shielded by the water tank) are selected.

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m Live time (hr)

No. events

3 30 - 60 120 < 160; 200 < 240 758 18137

5 30 - 60 120 < 160; 200 < 240 1296 8864

10 30 - 60 120 < 160; 200 < 240 2680 3272

3 60 120 < 160; 200 < 240 1552 4109

5 60 120 < 160; 200 < 240 10102 6786

10 60 120 < 160; 200 < 240 19922 2013

10 75 0 < 360 19922 395

DECOR data summary DECOR data summary Distribution in multiplicityDistribution in multiplicity

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DECOR data summaryDECOR data summaryDistribution in zenith angleDistribution in zenith angle

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1 cos-( + )dF(D, )/dD = CD α ~ (4.5 - 4.8); β ~ (1.9 - 2.3)

Procedure of the analysisProcedure of the analysisMuon bundle experimental distributions Nev (m, θ, φ)

Deconvolution accounting for Seff(θ,φ), Poisson fluctuations, trigger and selection conditions

CORSIKA simulation of LDF for different A, E and θ

Convolution with primary spectrum and composition model

Local muon density spectrumdF (D, θ)/dD

(detector independent)

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Calculation details

Primary “all-particle” spectrum:

Power type spectrum with the knee at 4 PeV

Below the knee: dN/dE = 5.0 (E, GeV) 2.7 cm-2 s-1 sr-1 GeV-1 ;

After the knee: steepening to ( 1) = 3.1.

CORSIKA simulation of 2D muon LDF:

CORSIKA 6.200 – 6.600

QGSJET 01c + GHEISHA 2002; SIBYLL 2.1 + FLUKA 2003.1b

Set of fixed zenith angles, fixed primary energies

Primary protons and Iron nuclei

EMF

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Effective primary energy rangeEffective primary energy range

Lower limit ~ 1015 eV (limited by DECOR area).Upper limit ~ 1019 eV (limited by statistics).

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Low angles: around the “knee”Low angles: around the “knee”Vulcano 2008, 26th-31st May

θθ = = 5050ºº : 10 : 101616 – 10 – 101717 eV eV

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θθ = = 6565ºº : 10 : 101616 – 10 – 101818 eV eV

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Combined estimator of primary energy Vulcano 2008, 26th-31st May

Event-by-event analysis: for every event with some set of observables(m, θ, φ) it is possible to attribute a certain effective primary energy.

1.07 3.8EST 0 0 0( / )=( ) (sec / sec ) E E D/D

Densities: (0.05 - 2.0 м-2); zenith angles: (40º - 80º);

E ~ (1016 - 1018 эВ)

Combined estimator of primary energy

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Combined estimator of primary energy

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Large angles: around 10Large angles: around 101818 eV eV

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ConclusionsConclusions 1 1 LMDS methodLMDS method

1. A new approach based on local muon density spectrum phenomenology provides possibility to study PCR in a very wide energy range (from 1015 to 1019 eV) by means of a single, not large detector.

2. Local muon density spectra are sensitive to primary spectrum and composition and forward region of hadronic interactions.

3. Analysis of local muon density spectra together with data of experiments on other EAS observables will allow putting new constraints on combinations of spectrum, composition and interaction models.

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Conclusions 2Conclusions 2

DECOR data analysisDECOR data analysis

are in a reasonable agreement with expectation in the knee energy region;

favor an increase of the effective primary mass at approaching energies 1017 eV;

indicate an increase of local muon density spectrum slope at effective primary energy around 1017 eV.

Within the frame of the considered spectrumand interaction models, DECOR data:

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Thank you for the attention!

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