CR spectrum and composition measured by Tibet hybrid experiment (YAC+Tibet-III) J. Huang for the Tibet ASγ Collaboration Institute of high energy physics,

CR spectrum and composition measured by Tibet hybrid experiment (YAC+Tibet-III)

J. Huang for the Tibet ASγ Collaboration

Institute of high energy physics, Chinese Academy of Sciences

China, Beijing 100049

Workshop Agenda, IHEP, CAS, Beijing, October 17 - 18, (2012)

Contents

• Knee of the spectrum.

• Two Possible explanations for the sharp knee.

• New hybrid experiment (YAC+Tibet-III).

• Primary proton, helium spectra obtained by (YAC-I + Tibet-III).

• Expected results by (YAC-II + Tibet-III).

• Summary

J. Huang (Workshop Agenda, Beijing, China, (2012))

AS array at high altitude (4300m a.s.l.)Tibet-III array:37000m2 with 789 scint. YAC array: 500m2 with 124 scint. MD array: 5000m2 with 5 pools of water Cherenkov muon D.s .Measure:energy spectrum around the kneeand chemical composition using sensitivity of air showers to the primary nuclei through detection of high energy AS core.

Tibet experiment1014-1017 eV

PbIron

Scint.

Box

7 r.l.

YAC

Merit of high altitude


The merit of the Tibet experiment is that the atmospheric depth of the experimental site (4300 m above sea level) is close to the maximum development of the air showers, with energies around the knee almost independent of the masses of primary cosmic rays as shown in this figure.

Tibet-III: Energy and direction of air shower

Cosmic ray(P,He,Fe…)

Particle density & spread

Separation of particles

Tibet YAC 　 array(Yangbajing Air shower Core arary)


5

Model

Knee　Position　(PeV)

Index　of　spectrum

QGS.+HD

4.0± 0.1 R1=　-2.67±　0.01

R2=　-3.10±　0.01

QGS.+PD

3.8± 0.1 R1=　-2.65±　0.01

R2=　-3.08±　0.01

SIB.+HD

4.0± 0.1 R1=　-2.67±　0.01

R2=　-3.12±　0.01

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All-particle spectrum measured by Tibet-III array 　 from 1014 ~1017eV (ApJ 678, 1165-1179 (2008))


　　 Tibet 　　　　　　　　　　　　 KASCADE 　　　　　　　　 HEGRA

CASA/MIA 　　　　　　　　 BASJE 　　　　　　　　　　　 AkenoDICE

Energy spectrum around the knee measured by many experiments


Normalized spectrum


8

A sharp knee is clearly seen (ApJ 678, 1165-1179 (2008)) (ApJ 678, 1165-1179 (2008))

6/ 31

What is the origin of the sharp knee?There were many models: nearby source, new interaction threshold, etc.In the following, I would introduce our two analyses for the origin of the sharp knee.


9

Two possible explanations for the sharp knee

For explaining the sharp knee we proposed two composition models (called Model A and Model B)

that are based on:

1) the up-to-now available experimental results;

2) some physics (or theoretical) assumptions.

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( M. Shibata, J. Huang et al. APJ 716 (2010) 1076 )


10

For ‘the up-to-now available experimental results’, we request:

a) In the enery region lower than 100 TeV the directly measured p, He, …, iron spectra by CREAM, ATIC, JACEE, RUNJOB etc should be smoothly connected by the modeling spectra;

b) In the energy region higher than 100 TeV the modeling p and He spectra should be consistent with our indirectly measured p and He spectra;

c) The superposed spectrum of all elemental spectra in the modeling should be consistent with our measured all-particle spectrum.


11

• Diffusive shock acceleration in SNRs is assumed;

• Multiple galactic sources were considered.

• For each source there is an ‘acceleration limit’ ε(Z) which

--- is proportional to the charge Z of accelerated nuclei,--- denotes the energy the accelerated particles start to deviate

from the power law;

• εmax is introduced that denotes the ‘Maximum acceleration limit’ among multiple sources.

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Some physics (or theoretical ) assumptions for both Model A and Model B


12

(ApJ ,716:1076-1083(2010))

In this physics picture the knee is caused by the‘minimum

acceleration limit’ε(Z), (see details in the paper). Taking different

ε(Z) and εmax the obtained all particle spectrum shows a smooth structure (see the figure below). The sharp knee cannot be produced.

To explain the sharp knee we proposed two approaches, called Model A and Model B.


13

Model A: Sharp knee is due to nearby sources

Substracting the smooth spectrum from the measured all particle spectrum, a power-law spectrum with index -2 is obtained (see the dotted line in the figure). This is very consistent with the assumption of CR particles coming from nearby source(s).

(ApJ ,716: 1076-1083 (2010))

],PeV4

exp[2 EE

Extra component can be approximated by:

9/ 28J. Huang (Workshop Agenda, Beijing, China, (2012))

14

Model B: Sharp knee is due to nonlinear effectsin the defuse shock acceleration

It was suggested (Malkov & Drury 2001; Ptuskin & Zirakashvili 2006) that:

In the diffuse shock acceleration mechanism, the nonliner effect at supernova shock fronts is present that may produce a harder cosmic ray spectrum in the source.

We included this effect by introducing an additional term in our formalism that showed to produce a dip below the ‘minimum acceleration limit’ of the spectrum of each element (see the figure).


15

Their superposition can well produce the all-particle spectrum including the sharp knee. (Model B)

(ApJ ,716: 1076-1083 (2010))J. Huang (Workshop Agenda, Beijing, China, (2012))

Two possible explanations for the sharp knee

1) Model A: Sharp knee is due to nearby sources

2) Model B: Sharp knee is due to nonlinear effects in the diffusive shock acceleration (DSA)

All-particle knee = CNO?

All-particle knee = Fe knee?

( APJ 716 (2010) 1076 )


Short summary Two scenarios (model A and model B) are proposed to explain the sharpness of the knee.

In model A, an excess component is assumed to overlap the global component, and its spectrum shape suggests that it can be attributed to nearby source(s) because it is surprisingly close to the expected source spectrum of the diffuse shock acceleration. CNO dominant composition is predicted by this model at the knee.

In model B, a hard observed energy spectrum of each element from a given source is assumed. The sharp knee can be explained by a rigidity-dependent acceleration limit and hard spectrum due to nonlinear effects. Iron-dominant composition is predicted by this model at the knee and beyond.


　　　 In order to distinguish between Model A and Model B and many

other models, measurements of the chemical composition around

the knee, especially measurements of the spectra of individual

component till their knee will be essentially important.

Therefore, we planed a new experiment:1) to lower down the energy measurement of individual

component spectra to *10TeV and make connection with direct measurements;

2) to make a high precision measurement of primary p, He, …, Fe till 100 PeV region to see the rigidity cutoff effect.

15/ 31

These aims will be realized by our new experiments YAC (Yangbajing AS Core array) !


ＹＡＣ

YAC project(*10TeV -100 PeV)


New hybrid experiment (YAC+Tibet-III+MD)

Pb7 r.l.

Scint.Iron

Tibet-III (37000 m2) : Primary energy and incident direction.

YAC2 ( 500 m2 ): High energy AS core within several x 10m from the axis.

Tibet-MD ( 5000 m2 ) : Number of muon.

This hybrid experiment consists of low threshold Air shower core array (YAC) and Air Shower (AS ) array and Muon Detector ( MD ) .

16/ 31

MD

AS

YAC2

YAC2 will measure the primary energy spectrum of

4 mass groups of P, He, 4<A<40, A>40 at

50 TeV – 1016 eV range covering the knee.


Proton Iron

YAC Detector

PbIron

Scint.Box

7 r.l. Observe shower electron size under lead plate (burst size Nb) induced by high energy E.M. particles at air-shower core.

WLSF (wave length shifting fibers) is used to collect the scintillation light for the purpose of good uniformity. Two PMTs are used to cover wide dynamic range (1MIP is calibrated by single muon). For High gain PMT , Nb: 1 – 3000 MIPs For Low gain PMT , Nb: 1000- 106 MIPs

80cm

50cm

WLSf

Plastic scintillaors(4cm×50×1cm, 20pcs)

High gain PMT R4125

Low gain PMT R5325


YAC1 is well running now( data taking started from 2009.04.01)

YAC1

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Total : 16 YAC detectors

Effective area: 10 m2


Detector Calibration

1.PMT linearity,use of LED light source;

2. Linearity of PMT+scintillator,a. probe calibration;b. accelerator beam calibration.


24

1 MIP

Probe Calibration ( The　determination　of　the　burst　size　is　calibrated　　using　single　muon　peak　)

Single muon calibration

Using a probe detector, we can obtain the single particle peak for each YAC detector.


High gain PMT

R4125

Low gain PMTR5325

1MIP

106MIPs

Input light

25

PM

T o

utp

ut

char

ge

[pC

×0.

25]

Proton

Iron

1017 eV

Primary Energy (GeV)

Nb

_top

Dynamic range and linearity

106

PMT linearity In order to record the electromagnetic showers of burst size from 1 to 10^6 particles, a wide dynamic range of PMT is required.For each PMT (high gain and low gain) used in YAC-I the linearity has been measured by using LED light source and optical filters. In the test we fixed the positions of LED, filter and PMT. By using different filters we can get light of different intensity, and then, we can check the Linearity of PMTs.


Thin IC

Thick ICYAC

The Beam

YAC

BEPC: Beijing Electron-Positron Collider

Electron beam calibration of YAC to get ADC count vs number of particles

106 MIPs

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Thin IC

Thick IC

Saturation of PMT& Saturation of

scintillator

Calibration using BEPC

The experimental sketch

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The accelerator-beam experiment shows a good linearity between the incident particle flux and YAC-ADC output below 5×106 MIPs.

the saturation effect of the plastic scintillator satisfies YAC detector’s requirement.

Number of particles (Beam)

Primary proton, helium spectra analysis


29

　　　　 = Air Shower simulation =

CORSIKA 6.204 (QGSJET2, SIBYLL2.1)

( 1 ) Primary energy: E0 >1 TeV

( 2 ) All secondary particles are traced until their energies become 300 MeV in the atmosphere.

( 3 ) Observation Site : Yangbajing (606 g/cm2 )

　　　　　　 = Detector simulation =

• Simulated air-shower events are reconstructed with the same detector configuration and structure as the YAC array using Epics (uv8.64)

- Full M.C. Simulation -

Primary composition model

• NLA (above-mentioned

Nonlinear effects model ).

• HD model

(Heavy　Dominant　model:　

see　M. Shibata, J. Huang et al. APJ 716 (2010) 1076　)

Hadronic interaction model

•CORSIKA (Ver. 6.204 )

– QGSJET2–

– SIBYLL2.1–


Primary cosmic-ray composition spectrum assumed in MC

( M. Shibata, J. Huang et al. APJ 716 (2010) 1076 )


The difference between NLA and HD model

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The proton spectrum of the two models is connected with the direct experiment in the low energy and consistent with the spectrum obtained from the Tibet (EC+AS) experiment in the high energy.

The He spectrum of HD model coincides with the results from RUNJOB and ATIC-I, we called ‘He poor’ model.

However, the He spectrum of NLA coincides with the results from JACEE, ATIC-II, CREAM, we called ‘ He rich’ model.

The sum of all single-component spectra can reproduce the sharp knee in all particle spectrum.

NLA: ‘He rich’ model HD : ‘He poor’ model


Core event selectionEvent selection condition for AS core event was studied by MC and following criteria were adopted to reject non core events whose shower axis is far from the YAC array.

Nb>200, Nhit 4, Nbtop 1500, Ne>80000≧ ≧

| AS axis by LDF – burst center| < 5 m

Statistics of core events in MC simulation and experiment

Live Time is 106.05 days.Selected Events

QGSJET+HD 216942

SIBYLL+HD 304785

QGSJET+NLA 80861

SIBYLL+NLA 64331

YAC1 5035J. Huang (Workshop Agenda, Beijing, China, (2012))

Core event selection

R< 5m

Base on the above core event selection condition, we found the AS axis estimated by LDF is within 5 m from our YAC detector array.

105 <= Ne <= 106

R <= 5 m

3464/3483=99.5%


Interaction model dependence in (YAC1+Tibet-III) experiment

Air shower size (Ne) spectra Total burst size (sum Nb) spectra

Top burst size (Nb_top)spectra Mean lateral spread (NbR)spectra

These figures shows that QGSJET and SIBYLL, both models produce distribution shapes consistent with our experimental data.

Primary proton, He spectra analysis

Identification of proton events

ANN (a feed-forward artificial neural network) is used.

Input event features:

Ne, ΣNb, Nbtop, Nhit, <Rb>, < NbRb>, θ

Classification: proton/others

Primary energy determination

E0=f(Ne,s) based on proton-like MC events


Purity – 95.2%Efficiency – 62%

Purity – 94.5%Efficiency – 63%

QGSJET

SIBYLL

Primary (P+He) separation by ANN

P+He Other Nuclei

P+He Other Nuclei


Purity – 79%Efficiency – 46%

Purity – 78%Efficiency – 40%

Primary proton separation by ANN for MC events

QGSJET

SIBYLL

P roton Other

P rotonOther


Air shower size to primary energy

The primary energy (E0 ) of each AS event is determined by the air-shower size (Ne) which is calculated by fitting the lateral particle density distribution to the modified NKG function.

Modified NKG function


Size　resolution　(MC　Data)　(based　on　QGSJET+HD　model　)(1.0 ≦ sec(Θzenith) < 1.1 )

Ne resoultion:

~7%

(Ne>105 )

QGSJET ＋HD

QGSJET+HD

( for T<=0.4 & sec(theta) <=1.1 )

(1.) Energy Resolution – Proton like events

Energy Resolution : 22% @ 500TeV

1e+05 < Ne < 1e+06

Primary energy determination

Check the systematic errors by ANN

J. Huang (ISVHECRI2012, Berlin, Germany)

P+He Proton

HeliumThe primary energy of (P+He)-like or P-like or Helium-like events is in a good agreement with the true primary energy spectrum.

Nb >= 200

Nhit >= 4

Nbtop >= 1500

Ne >= 80000

(SΩ)eff calculated by MC (1)

Primary (P+He) spectra obtained by (YAC1+Tibet-III)

preliminary


Primary proton , helium spectra obtained by (YAC1+Tibet-III)

preliminary preliminary


YAC2 is also well running now( data taking started from 2011.8.1)

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YAC-II

Total : 124 YAC detectors

Cover area: ~ 500 m2

Pb50cm80cm


46

Expected results by (YAC2+Tibet-III)

Solid lines:input Symbols:reconstructed Expected primary energy spectra

YAC2 will measure the primary energy spectrum of 4 mass groups of P, He, 4<A<40, A>40 at 1014 – 1016 eV range covering the knee.


Summary(1) YAC1 shows the ability and sensitivity in checking the hadronic

interaction models.

(2) The experimental distribution, sumNb has the shape very close to the MC predictions of QGSJET+NLA, QGSJET+HD , SIBYLL+NLA and SIBYLL+HD. Some other quantities, such as Ne, Nb_top, <R> have the same behavior as well.

(3) Some discrepancies in the absolute intensities are seen. Data normally shows a higher intensity than MC. Taking a more hard He spectrum as given by CREAM can improve this situation. A further study is going on.

(4) (YAC1+Tibet-III ) could measure protons and heliums spectra at > 50 TeV which is shown to be smoothly connected with direct observation data at lower energies and also with our previously reported results at higher energies.


(5) We obtained the primary energy spectrum of proton, helium and (P+He) spectra between 50 TeV and 1 PeV , and found that the knee of the (P+He) spectra is located around 400 TeV.

(6) The interaction model dependence in deriving the primary proton, helium and (P+He) spectra are found to be small (less than 25%

in absolute intensity, 10% in position of the knee ), and the composition model dependence is less than 10% in absolute intensity, and various systematic errors are under study now !

(7) Next phase experiment YAC2 will measure the primary energy spectrum of 4 mass groups of P, He, 4<A<40, A>40 at 1014 – 1016

eV range covering the knee.


Thank　you　for　your　attention　!!

Documents

CR spectrum and composition measured by Tibet hybrid experiment (YAC+Tibet-III) J. Huang for the Tibet ASγ Collaboration Institute of high energy physics,