COSMIC RAY PHYSICS IN
BOLIVIA
4TH School on Cosmic Rays and
Astrophysics
UFABC-Santo André-SP-Brasil
August 2010
Alfonso Velarde
Cosmic Ray Laboratory
UMSA La Paz Bolivia
THE BEGINNING
• THE PION DISCOVERY
• 1946: Second war end
• Prof. Cesar Lattes from the Sao Paulo
University joint to the Prof. Cecil Powel
group in the Bristol University to work
with a new type of emulsion chambers
developed by Ilford to obtain tracks of
charged particles.
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Ones in Bristol Lattes and
Occhialini propose to expose
that new nuclear emulsions at
high altitude montains.
First they expose some plates
at Pic du Midi in the Pyrenees
and found an unusual event:
one stopping meson and,
emerging from its end, a
new meson.
Two diferent mesons
(particles with a mass
intermediate between that of
proton and electron)
To obtain more events Lattes
search in the Department of
Geography of Bristol
university for a higher altitude
place and found that there
was a meteorological station
at about 5.000 m.a.s.l. at
mount Chacaltaya very near
to La Paz (Bolivian capital).
• Lattes expose the
plates at Chacaltaya
and back in Bristol
found about 30 double
meson events.
• A fundamental process
was discovered: the
decay of pion into
muon.
• The heavier meson
(pion) was identified
with the Yukawa
particle and its
secondary (muon) with
the Carl Anderson´s
mesotron.
• A neutral particle of
small mass was needed
to balance momentum.
• Due to this discovery, Prof.
Hideki Yukawa recived the
Nobel Price in 1949, and
Cecil Powell in 1950.
• So the discovery of pion
and meson particles
related to the nuclear force
was the beginning of
Cosmic Ray Physics in
Bolivia.
• These discovery made
Mount Chacaltaya famous
for Cosmic Ray
experiments.
• In 1952 the La Paz San
Andres University
construct the Chacaltaya
Cosmic Ray Laboratory.
NOWADAYS
EXPERIMENTS
BASJE
Bolivian Air Shower Joint Experiment
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Start: 1962
Collaboration with Tokio
Technological Institute
First main researchers: B.Rossi,
Kohichi Suga, Ismael Escobar
Objective: Study of extensive air
shower generated by prikmaries
cosmic rays with energies >
1014 eV
The study of the spectrum in the
range 8x1014 - 4x1017 eV shows
that the slope of the primary
cosmic ray energy spectrum
changes.
Todays BASJE Array
•
68 scintillation detectors
installed in an area of
700m × 500m with
separations of 75 m.
• New air shower array at Mount Chacaltaya
(5,200m above sea level) to observe primary
cosmic rays with energies greater than 1015
eV.
• In BASJE previous experiments, we
measured nuclear composition of primary
cosmic rays in the knee region, and showed
that the average mass (logaritmic) of cosmic
ray nuclei increases with energies below and
above the knee, and dominated by heavier
nuclei as iron at 1016 eV.
• The new air shower array has been
constructed in order to measure cosmic ray
composition above the knee
SYS
Saitama-Yamanashi-San
Andres
• First main researcher:
• Prof. T Matano
NEUTRON MONITOR
NM64
• Sensitive to n and p
An example of a solar flare
detected with the NM64
SOLAR NEUTRONS
TELESCOPE
Colaborattion with Solar-Terrestrial Environment
Laboratory, Nagoya University, Japan
The Chacaltaya telescope
n
Anticoincidence
scintillators
p
LAGO
Large Aperture GRB Observatory
• A GRB is
a short
time flux
of
cosmic
gamma
rays.
Some examples
detected in satellites
Arrival direction of GRBs
is isotropic
Energy spectrum
slope  -2
How to detect E>1GeV
GRBs?
• LAGO search for GRBs
with energies>1 GeV
with ground level
detectors by the single
particle technique.
• This consists in the
search for significant
excesses in the
detector counting rates
due to the remainig
secondary particles
produced by the GRB in
the atmosphere.
LAGO ARRAYS
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Para alcanzar una
sensibilidad
razonable, se han
seleccionado sitios
de altura;
Sierra Negra
(4,650 m.s.n.m.),
Puebla-México
Chacaltaya, (5,230
m.s.n.m.), La PazBolivia.
Pico Espejo (4,765
m.s.n.m.), MéridaVenezuela.
Marcapomacocha
Peru, cerca a Lima
4.400(m.s.n.m.)
AUGER en
MalargüeArgentina.
Chacaltaya´s
LAGO WCDs array
Thank you