The complex EAS hybrid arrays in Tibet

1
The complex EAS hybrid arrays in Tibet
J. Huang for the Tibet AS? Collaboration
Institute of high energy physics,
Chinese Academy of Sciences
China, Beijing 100049

ISVHECRI2008, Paris, France, September 1-6,
(2008)
2
Outline
(1) Present status of the composition measurement
by direct observations and indirect ones. (2)
Light components around the knee energy region
obtained by Tibet ASgamma experiment. (3) Could
the present measurements be consistent with the
well-known acceleration and propagation model?
(Physics of the knee and unsolved
questions.) (4) Tibet-ASYACMD (next phase of
Tibet experiment).
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Take a look at the CR spectrum again
The change of the power index in all particle
spectrum at PeV region is clearly seen in many
air shower experiments and called knee and
possibly this steepening is related to the change
of the chemical composition, because it can be
explained as the acceleration limit by SNRs if
rigidity dependent cut off of the each chemical
component is observed.
Knee3-5 PeV dJ/dE ? E -? ?2.65?3.1
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Origin of cosmic rays (protons and nuclei) is not
confirmed yet.
There is an evidence of the acceleration of
electrons up to very high energy around 1015 eV
as revealed by ASCA observation on SN1006,
however, the origin of protons and nuclei is not
confirmed yet. If their origin is SNR too, we
will be able to observe gamma ray point source
with an energy spectrum indicating the decay of
neutral pions. Another indication of the
acceleration of the nuclear component at SNR is
related to their acceleration mechanism.
If SNR is the origin, According to the DSA
model Acceleration limit Z x 1014 eV
(Oblique acceleration may shift the limit by some
factor or an order.)
Investigate chemical composition of CRs.
Origin of the knee can be interpreted as the
acceleration limit by SNRs if rigidity dependent
cutoff of the each chemical component could be
observed.
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Present status of the study of the chemical
composition

• Direct observations(Knee is inaccessible because
  of the low flux)
• BESS,AMS (magnet) lt1TeV (high statistics)
• balloon, satellite(counter) lt several 10TeV
• balloon ECC (JACEE,RUNJOB) lt 100 TeV (low
  stat.)
• ATIC, CREAM, TRACER (Long duration flight
  at south pole)
• 
  lt 100TeV (high stat.)
• CALET (Calorimetric Electron Telescope) plan
  (ISS) lt 1000TeV
• Indirect observations ( The indirect observation
  is the unique solution to overcome the poor
  primary flux above 100 TeV)
• Xmax Fluorescence, Cherenkov,
  equi-intensity-cut
• e-µ ratio enriched muons in AS of
  nucleus origin (KASCADE)
• Lateral structure of e,µ, hadrons
• Time structure of Cherenkov (BASJE)
• Energy flux and spectrum of HE particles at
  AS cores (Tibet)
• ? From these observations, we can extract the
  information on the mass number
• of the parent particles which induce air
  showers.

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Direct Observations (P,He,Fe lt100 TeV/particle)
The break of proton spectrum is not detected yet
up to 100 TeV !
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Indirect observations

• 1. Average mass ltln Agt
• 2. Energy spectrum of individual component or
  mass groups

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Average mass
( S.Ogio et al. ApJ 612 (2004) 268 )
The results are not conclusive yet !
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Systematic errors come from

• Primary composition dependence of the AS
  development.
• This dependence can be eliminated by
  choosing the observation site at high altitude
  and also using an appropriate zenith angle cut to
  observe the shower maximum. High mountain
  altitude is suitable for the observation of the
  knee energy range.
• Interaction model dependence of the AS
  development.
• We still dont know which model is the
  best among
• QGSJET I, II, SIBYLL, DPMJET, NEXSUS,VENUS
  , EPOS and
• so on. Especially, the behavior of the most
  forward region of the multiple production is
  important to the CR propagation in the
  atmosphere. Present uncertainty of the forward
  region characteristics is estimated to be within
  30 as shown later.
• ? This situation will be improved by LHCf
  experiment .
• Further calibration is also needed on low
  energy part including Nucleus-Nucleus effect
  etc., especially for muon number and its
  fluctuation. Present uncertainty of the muon
  number is still large as seen in the result of
  e-µ size analysis.
• ? update simulation code.

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The feature of Tibet ASg experiment
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Tibet ASg Experiment

• Tibet Yangbajing (90.522oE, 30.102oN
• 4300 m above
  sea level)
• Total AS detectors 0.5 m2 x 789
• Coverage 37,000
  m2
• Angular resolution 0.2 _at_100 TeV
• Energy resolution 17 _at_1015 eV
• Total EC area 80 m2 (400 blocks of 14
  r.l thick lead plates and 6 layers of
• X-ray
  films)
• ?Tibet air shower array (AS) Primary energy and
  direction of air shower.
• ?Core detector (EC, BD) Core information ?
  Separation of primary particles.
• ? Tibet (ASECBD) (1996-1999) ? 177 gamma
  families ? P, He spectra.

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P, He by Tibet hybrid Experiment (Phys. Lett.
B, 632, 58 (2006))
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Primary Proton spectrum
Primary Helium spectrum
(All - (PHe)) /All
1) Our results shows that the main component
responsible for the knee structure of the all
particle spectrum is heavier than helium nuclei.
2) The absolute fluxes of protons and helium
nuclei are derived within 30 systematic errors
depending on the hadronic interaction models.
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All-particle spectrum measured by Tibet-III
array(ApJ 678, 1165-1179 (2008))
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All-particle spectrum measured by Tibet-III
array(ApJ 678, 1165-1179 (2008))
A sharp knee around 4 PeV is clearly seen.
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Comparing with cutoff model
Based on the experimental results from 1)
directly measured spectra of p, He, at energies
lower than the knee by ATIC, JACEE, RUNJOB etc
2) indirectly measured all-particle spectrum by
Tibet 3) indirectly measured (or deduced)
spectra of p and He by Tibet and Kascade well
analyse whether they could be described by the
theoretical picture of SNR acceleration and
rigidity dependent cutoff of CRs at the knee
energy region with functional form of
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Comparing with cutoff model-- Protons cutoff at
4 PeV?
Firstly, we assume the cutoff energy of protons
is at 4 PeV. Taking Ep(c)4PeV and Ez(c)ZEp(c)
and making the extrapolation of direct measured
spectra (but ATIC-1 proton spectrum is used), as
seen from the figure, the ASgamma all-particle
spectrum can essentially be obtained by their
superposition. However, the sharp knee is not
reproduced.
X component (Single Source ?)
Each component
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Comparing with cutoff model, -- Protons cutoff
at 7 PeV?(such as the Poly Gonat model proposed
by Pr. Horendel)
Secondly, we see the situation assuming
protonscutoff at 7 PeV. Taking Ep(c)7PeV and
Ez(c)ZEp(c), and making the extrapolation of
direct measured spectra (but ATIC-2 proton
spectrum is used), as seen from the figure, the
ASgamma all particle spectrum can essentially be
obtained by their superposition. The sharp knee
is also reproduced, but in this case, the main
component responsible for the knee structure of
the all particle spectrum is Proton. This
conclusion contradicted with both KASCADE and
Tibet ASgamma results.
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Comparing with cutoff model-- Protons cutoff at
7 PeV?
This conclusion contradicted with both KASCADE
and Tibet ASgamma results.
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About Kascades composition results (QGSJET)
Taking the results of individual component
spectra obtained by Kascade-QGSJET It is seen
that they are essentially consistent with the
rigidity dependent cutoff model (see the left
figure). However, 1) no good connection with
direct measured spectra at lower energies .
2) no sharp knee in the all-particle
spectrum by their superposition.
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About Kascades composition results (SIBYLL)
Taking the results of mass group spectra obtained
by Kascade (SIBYLL) it is seen that Ec
values(P4, He8, C20, Si2, Fe25 PeV)are
irregular, contradicted to the rigidity dependent
cutoff model (see the left figure). Furthermore,
no good connection with direct measured spectra
at lower energies (see the right figure) as well,
and no sharp peak in the all-particle spectrum by
their superposition.
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Short summary

• Both KASCADE and Tibet ASgamma results show the
  interaction model dependence. The difference
  between QGSJET and SIBYLL, is about a factor of 3
  in KASCADE and about 30 in Tibet.
• KASCADE-QGSJET results support the rigidity
  dependent cutoff model, but cannot be connected
  with the direct measurements. KASCADE-SIBYLL
  results do not support the rigidity dependent
  cutoff model, and cannot be connect with the
  direct measurement. Both do not show a sharp
  knee at the knee in the all particle spectrum.
• Tibet all-particle spectrum is consistent with
  the rigidity dependent cutoff model taking
  Ep(c)4PeV and the extrapolation of direct
  measurements. However, the sharp knee is not
  reproduced, unless one adds a single SNR source.
• The condition of Ep(c)7PeV gives rise to the
  best agreement with the
• Tibet all-particle spectrum, however, it
  implies proton dominance at the knee,
  contradicting with both KASCADE and Tibet
  results.

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In summary, the existing KASCADE and Tibet
results have not been satisfactorily explained by
the galactic SNR acceleration and the rigidity
dependent cutoff propagation in the Galaxy of CRs
at the knee region. Therefore, we think 1)
to lower down the indirect measurement of
individual component spectra 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 have essential importance.
These aims will be realized by next phase
experiments YAC (Yangbajing AS Core array) !
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The keys are to lower threshold, making
connections with direct measurements measure
spectra up to 100 PeV
YAC
These aims will be realized by YAC (Yangbajing AS
Core array)
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New hybrid experiment (Tibet-ASYACMD)
This hybrid experiment consists of low threshold
BD grid (YAC) and AS array and muon detector
without EC, which observe energy flow of AS core
within several x 10m from the axis.
Tibet-AS (exited) Primary energy and direction
of an air shower. YAC (Yangbajing Air shower
Core array) (to be setup) This is to measure the
energy spectrum of the main component at the
knee. Tibet-MD(to be set up) Number of muon.
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- Full M.C. Simulation -

• Air Shower simulation
• CORSIKA 6.204 (QGSJET01c)
• ( 1 ) Primary energy E0 gt50 TeV, 2107 events
• ( 2 ) All secondary particles are traced until
  their energies become 1 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, Tibet-AS array and Muon
  detector array using Epics (uv8.64)
• The energy deposit of shower particles in the
  plastic scintillator was calculated using Epics
  (uv8.64).

• Hadronic interaction model
• CORSIKA (Ver. 6.204 )
• QGSJET01c

• Primary composition model
• HD (Heavy Dominant)

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Design of YAC
YAC consists of 400 burst detectors of the size
40cm x 50cm distributed in a grid with 3.75 m
spacing between detectors. The burst size
threshold is set to 100 particles which
corresponds to 30 GeV of electromagnetic
component incident upon a detector. Wide dynamic
range between 1 and 106 is covered by 2 PMTs.
Proton
Iron
Wave length shifting fiber 2 PMTs (Low gain
High gain) 1ltNblt106

• For Proton and Helium
• 1.5 m spacing
• Nbgt100 , any 5
• (gt 30 GeV)

• For Iron
• 3.75m spacing
• Nbgt100 , any 21
• ( gt 30 GeV)

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Test experiment at Tibet Yangbajing
Small test array with 4 YAC detectors has been
constructed near the center of Tibet-III air
shower array from Nov. 2004.
Measure number of particles1 106 Trigger
condition Nb gt 40 particle/any det. Trigger
rate of each detector 0.15 Hz
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Three steps of new hybrid expt.
Tibet-AS
7 r.l.
YAC array
Pb
Iron
Scint.
Box
YAC -I
YAC -II
YAC -III
0.5m
1.5m
3.75m
YAC
YAC
YAC
0.5m
1.5m
3.75m
AS
AS
AS
Total detectors 50 Spacing 0.5 m Total
area38 m2
Total detectors 100 Spacing 1.5 m Total
area160 m2
Total detector 400 Spacing 3.75 m Total
area5000 m2
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Three physical target of future plan

• (1) Step-1 ( Tibet-ASYAC-I MD ) hybrid
  experiments
• Target (1) Check of hardronic interaction
  models.
• (2) Step-2 (Tibet-ASYAC-II MD) hybrid
  experiments
• Target (2) Measurement of primary proton
  spectrum and helium spectrum covering three
  decades of energy range around the knee.
• (3) Step-3 (Tibet-ASYAC-IIIMD) hybrid
  experiments
• Target(3) Measurement of primary iron
  spectrum and other nuclei spectrum covering
  three decades of energy range around the knee.

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Expected results by YAC
Expected number of protons , heliums and irons
using HD model are Proton (gt 100 TeV) 2300
events per one year Helium (gt 200 TeV) 800
events per one year Iron (gt 1000 TeV) 4400
events per one year.
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Large High Altitude Air Shower Observatory(LHAASO
)

• We also plan to build a ground based large and
  complex?/CR observatory at high altitude (4300m
  a.s.l.) within 10 years.
• Two major components (This project is in
  discussion)
• 1 km2 complex array for?rays and CRs gt30 TeV
• ? 1 km2 scintillation detector array
• ?40 k m2µdetector array
• ?28 C-telescopes
• ?1 km2 core detector ( YAC )
• 90 k m2 water Cerenkov detector for ?gt100GeV

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Summary

• Direct observations are going to provide high
  statistics results up to
• 100 TeV in very near future (LDF ATIC,
  CREAM, TRACER).
• The composition of the knee can be studied by
  indirect measurement
• on the basis of these direct measurements and
  well tuned MC (e.g. LHCf).
• Proton and helium spectra at the knee measured by
  Tibet hybrid experiment show steep power index of
  around 3.0 and low fraction to the all particles.
  Systematic error is within 30.
• Next phase of Tibet experiment, YAC, will
  measure the heavy component at the knee towards
  to solve the problem of the
• Origin of the HE Cosmic Rays.
• We also plan to build a ground based large and
  complex?/CR observatory at high altitude (4300m
  a.s.l.) within 10 years.
• ? Complementary to CTA in ?astronomy
• ? Unique in CR measurements at Knee.

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Large High Altitude Air Shower Observatory
You are invited to Lhaaso at Tibet !
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END
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Observed spectrum of the burst size (Nb)
Lower gain PMT
Higher gain PMT
Simulation was done under the next
condition Corsika QGSJET Emin0.3GeV E0gt50TeV,
HD4model Zenithlt60deg. Sampling area15m
35
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Lateral Fitting of Shower Particles

• Modified NKG function

37
Resolution of AS size Ne (MC Data)
1.0 ? sec(Tzenith) lt 1.1
QGSJETHD
QGSJETHD
1.0 ? sec(Tzenith) lt 1.1
Ne resolution(Negt105) (MC Data)

Ne resoultion 7 (Negt105 )
QGSJETHD
38
Model dependence of the size spectrum of nearly
vertical air showers (1.0 ? sec(Tzenith) lt 1.1
)
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Primary composition model (1)

• Heavy dominant (HD) model the energy spectrum of
  each component in the HD model has a
  rigidity-dependent break point of the power index
  with proton's knee around 150 TeV leading to the
  dominance of the heavy component at the knee
  energy region.
• Proton dominant (PD) model light components are
  dominant up to the knee, in which every component
  has the same break point of the power index at
  the knee energy.
• In both models, the fraction and the power index
  of each component are determined by fitting to
  the fluxes of the elements obtained by direct
  observations below 100 TeV, and fitting the sum
  of the each element at higher energies to the all
  particle flux obtained by air shower experiments.
• Therefore, the difference between two models
  exists in the fraction of the elements above
  100TeV.

Ref. (M.Amenomori et.al ApJ 678 1165-1179
(2008)
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Primary composition model (2)
41
Fraction of elements
42
Detection efficiency of YAC
42
43
Correlations between the input light and the ADC
count for PMT R4125 and R5325
Proton
PMT output charge pC0.25
Iron
1017 eV
(Low gain High gain) 1 lt Nb lt 106
44
Characteristics of burst event
45
Target (2) Check of charged multiplicity
Proton
Iron
Number of muon in EPOS is more than QGSJET !
46
Charged multiplicity
47
P-Air inelastic cross section
48
Production spectrum (p-14N)
Mesons
Baryons
49
Correlations between Ne and Nu
50
Identification of primary species by ANN
Used 8 parameters Nhit, SNb, Nb(top), ltRgt by
YAC Ne, age, Zenith angle by AS Nu by MD
51
Energy of P-like events
52
Energy of PHe-like events
53
Comparison of the primary energy spectrum with
AKENO
54
Separation of individual component or mass
groupsat the knee.

• Two kinds of experiments are carried out.
• 1. Tibet hybrid experiment ASECBD at 4300m
  a.s.l.
• Select proton(helium) induced AS events
  associated by
• ?-families. ? Reject contamination by ANN
• 2. KASCADE e-µ at sea level
• proton, helium, CNO, Si, Fe
• EASTOP, GRAPES similar to KASCADE

55
Tibet Hybrid Experiment

• Tibet As? Collaboration

1996?1999 ASECBD AS array 36,900 m2 EC 80 m2
(14 r.l. thick, 400 blocks) 177 events?P,He
spectra
56
Design of Emulsion Chamber and Burst Detector
? families ? and e (gt TeV) enter to EC with
lateral spread of several cm. They develop into
cascade showers and shower spots are registered
by X-ray films which consist of 6 layers. Burst
Detector below EC records the burst size, the
position and arrival time stamp. (4 PD are
equipped at each corner of the BD.)
57
How to obtain proton spectrum?
Hybrid system
BD(burst) (x,y) time
Burst Size (below EC)
1st trigger
EC(?family) (x,y)
TAG
SE?
AS array time
Ne
(Simulation)
E0
(GUI Software)
EC-Xray film image
Scanner
family detection
Proton identification
ANN
ASfamily matching event
(Correlations)
58
Matching of EC - BD - AS
time stamp
position
angle
?x,?ydistance between ?family and burst. ??
opening angle between arrival direction of ?
family and AS.
?2c6.25 (10 rejection)
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Generation efficiency of gamma family event by
primary protons in QGSJET and SIBYLL
SIBYLL
SIBYLL
SIBYLL
SIBYLL/QGSJET 1.3
QGSJET
SIBYLL/QGSJET 1.3
QGSJET
QGSJET
1014 1015
1016
E0 eV
1014 1015
1016
E0 eV
60
Artificial Neural Network
JETNET 3.5 Parameters
for training N?, SE?, ltR?gt, ltER?gt, Ne , ?
61
Comparison of the air shower size accompanied by
g families between QGSJET and SIBYLL(for proton
like events (ANN output lt0.4))
105 106
107
Ne
62
Comparison betweenTibet and KASCADE
Proton
Helium