A new approach to EAS investigations A new approach to EAS investigations in energy region 10in energy region 101515 - 10 - 101919 eV eV

R.P.Kokoulin for DECOR CollaborationR.P.Kokoulin for DECOR Collaboration

Moscow Engineering Physics Institute, RussiaMoscow Engineering Physics Institute, Russia

Istituto Nazionale di Astrofisica, Sezione di TorinoIstituto Nazionale di Astrofisica, Sezione di TorinoUniversita di Torino, ItalyUniversita di Torino, Italy

ContentsContents

RICAP'07, Roma, June 21, 2007

1. Introduction2. Local muon density phenomenology3. DECOR data VS simulation4. Conclusions

IntroductionIntroduction

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

Local muon density phenomenology - 1Local muon density phenomenology - 1

For inclined EAS, dimensions of muon LDF exceed hundreds meters. The detector with sizes of tens meters 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.

Without considering fluctuations, spectrum of events in local density may be written as

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

F D N E ,D dS , r

ρ(E, r) = D.

Dimension: [F (> D) ] = events / (s sr).

For a nearly scaling LDF around some energy E0

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

and power type primary spectrum 0N E A E E ,

1) Power type spectrum of local density, a bit steeper than the

primary one ( = / ).

0F D AD E , dS r

2) Enhanced sensitivity to the central part of the shower ( 2).

Local muon density phenomenology - 2Local muon density phenomenology - 2

Contribution of different distances to total number Contribution of different distances to total number of muons in EAS and to local muon density spectrumof muons in EAS and to local muon density spectrum

1 10 100 1000 100000.0

0.5

1.0

1.5

Arb

itra

ry u

nits

Distance from shower axis, m (log scale !)

QG, 1017 eV, 60o (protons)

Contribution to local density

r2*(r), = 2.0

Contribution tonumber of muons

r2*(r)

Enhanced sensitivity to the central part of the shower (forward interaction region) !

Contribution of distances, different zenith anglesContribution of distances, different zenith angles

• Collection area increases with zenith angle.• The effect is enhanced by the EMF influence.

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

Side SM:

• 8.4 m2 each;• σx 1 cm;• σψ 1°.

A typical muon bundle event in Side DECORA typical muon bundle event in Side DECOR( 9 muons, 78 degrees)( 9 muons, 78 degrees)

3468:0 3319:1 3290:2 3094:3

0:3264

SM=0 1:3216 2:3072 3:3207

3621:0 3336:1 3270:2 3294:3

0:2987

SM=1 1:3147 2:3051 3:3146

3514:0 3384:1 3110:2 3158:3

0:3596

SM=2 1:3446 2:4148 3:3509

3649:0 3511:1 3353:2 3378:3

0:3476

SM=3 1:3205 2:3331 3:3000

7190:0 3453:1 3239:2 3388:3

0:3705

SM=4 1:3597 2:3600 3:3859

4073:0 3360:1 4413:2 3888:3

0:3405

SM=5 1:3394 2:3410 3:3626

3623:0 3554:1 3470:2 3444:3

0:3521

SM=6 1:3532 2:3429 3:3159

3564:0 3299:1 3058:2 3303:3

0:3871

SM=7 1:3568 2:3545 3:3697

01234567

01234567

Plate1:Step=25nsec

Plate2:Step=25nsec

Run 8 --- Event 219242 ----06-12-2004 23:25:26.27 Trigger(1-16):01110100 00000000 Weit_Time:109.072 msec

X-projection Y-projection

Muon bundle event (geometry reconstruction)Muon bundle event (geometry reconstruction) Nlam=40,N5=26,N6=23,NR1=0 ,NR2=0 ,Sum1=0 ,Sum2=0 ,Sob-00000001,00000000

N1=35,N3=14 nCup= 0 SumAmp=1.26e+03 01110100,00000000 NGroup2=8,n=8,n1=8,n2=9,n0=8,nx=9,ny=8,One=0N2=32,N4=13 nCdow n= 0 NPMT=143 ETel= 0.0% ERec= 60.8%

Date=06-12-04 23:25:26.027 Nevent=219242 Group: fm=53.15 tm=77.87 Recon: f i=54.41 t=80.70 F= 0.0

A “record” muon bundle event A “record” muon bundle event (~ 160 muons, θ = 80°)(~ 160 muons, θ = 80°)

4873:0 3644:1 3754:2 3814:3

0:3923

SM=0 1:3332 2:3387 3:3266

3859:0 4199:1 3877:2 5106:3

0:3054

SM=1 1:3101 2:3351 3:3591

3562:0 3149:1 3376:2 3672:3

0:3570

SM=2 1:3435 2:3511 3:3948

4000:0 4098:1 4109:2 4255:3

0:3619

SM=3 1:3601 2:3894 3:3760

3786:0 3732:1 3712:2 4030:3

0:3750

SM=4 1:3582 2:3655 3:3992

4000:0 3388:1 3477:2 4119:3

0:3641

SM=5 1:3639 2:3849 3:4104

4050:0 4120:1 4164:2 5038:3

0:3609

SM=6 1:3508 2:3684 3:3647

3961:0 3769:1 3844:2 4323:3

0:4245

SM=7 1:3814 2:4037 3:4338

3352:0 3438:1 3922:2 4134:3

0:4850

SM=8 1:4191 2:3898 3:5122

3181:0 3942:1 5269:2 5326:3

0:3347

SM=9 1:3879 2:3924 3:4615

3820:0 4458:1 4688:2 4870:3

0:475

SM=10 1:5515 2:5367 3:6392

3239:0 3452:1 4038:2 4575:3

0:3800

SM=11 1:5594 2:4104 3:4670

01234567

01234567

Plate1:Step=25nsec

Plate2:Step=25nsec

Run 242 --- Event 847205 ----05-05-2003 06:11:04.43 Trigger(1-16):01110101 00111100 Weit_Time:30.065 msec

X-projection Y-projection

DECOR data summary - 1. DECOR data summary - 1. Muon bundle statisticsMuon bundle statistics

Muon multiplicity

Zenith angle range (*)

Live time, (hours)

Number of events

3 30 – 40 524.7 4754

3 40 – 60 524.7 7945

3 60 1552 4114

5 60 6848 4531

10 60 16668 1651

10 75 16668 332

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

DECOR data summary - 2. DECOR data summary - 2. Distribution in multiplicityDistribution in multiplicity

DECOR data summary - 3. DECOR data summary - 3. Distribution in zenith angleDistribution in zenith angle

Procedure of the analysisProcedure of the analysis

Calculation detailsCalculation details

Reference 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; steepening to ( 1) = 3.1 after the knee.

Close to MSU “all-particle” spectrum as given by PDG (T. Gaisser, T. Stanev); not much different from most of other data around the knee; close to Fly’s Eye “stereo” at 1018 eV.

CORSIKA simulation of 2D muon LDF:CORSIKA 6.502; two combinations of interaction models QGSJET01c + GHEISHA2002, SIBYLL2.1 + FLUKA2003.1.b.

Set of fixed zenith angles and of primary energies.Primary protons and Fe nuclei; with and without EMF.

Effective primary energy rangeEffective primary energy range

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

Differential local muon density spectrum - 35°Differential local muon density spectrum - 35°

0.01 0.1 1 10

10-4

10-3

D

3 d

F/d

D, 1

/ (

s sr

m 4

)

D, m - 2

solid: QGSJET01dashed: SIBYLL

DifStar35 23.05.2007

1015 eV 1016 eV 1017 eV

Fe

p

35 o

Differential local muon density spectrum - 65°Differential local muon density spectrum - 65°

PCR intensity around 10PCR intensity around 101818 eV: two models eV: two models

HiRes Collaboration: astro-ph/0703099v1 (March 2007)

PCR intensity around 10PCR intensity around 101818 eV: two models eV: two models

ConclusionsConclusions - 1- 1

1. Local muon density spectra are sensitive to primary spectrum and composition, and have an enhanced sensitivity to forward region of hadronic interactions.

2. 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, relatively small-size detector.

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.

ConclusionsConclusions - 2- 2

1. DECOR data at moderate zenith angles are in a reasonable agreement with simulations based on a usual picture of PCR spectrum and interaction around the knee.

2. Within the frame of the considered spectrum model (with γ 2.1 after the knee), DECOR data favor an increase of the effective primary mass up to energies 1017 eV.

3. There is an indication (at 2σ-level) for an increase of local muon density spectrum slope at effective primary energy around 1017 eV.

4. Within the considered interaction models, DECOR data at large zenith angles (E0 ~ 1018 eV) are not compatible in absolute intensity with spectrum model based on HiRes data, and are in agreement with AGASA-based intensity.

Thank you !Thank you !