Press kit — Chacaltaya Cosmic Ray Laboratory

Key facts

Checked figures and facts, ready to copy. Each one carries its source; those marked ⚠ involve discrepancies between sources that the project has not yet resolved, and are best not published without checking with us first.

Full name. Chacaltaya Cosmic Ray Laboratory (Laboratorio de Física Cósmica de Chacaltaya), Instituto de Investigaciones Físicas (Institute of Physics Research), Universidad Mayor de San Andrés (UMSA), La Paz, Bolivia.
Altitude of the facilities. 5,200 m above sea level. The GAW station is at 5,240 m and the ALPACA experiment, on the plateau, at 4,740 m. The weather hut on the summit stood at 5,600 m. There is no single figure: it depends on the facility.
Origin. September 1942: a weather station measuring solar radiation, set up by Ismael Escobar Vallejo (1918–2009), a Spanish teacher and meteorologist in exile and founder of the Servicio Meteorológico de Bolivia (Bolivian Meteorological Service).
Founding of the Laboratory. Three acts, not one: a draft proposal in 1949, creation by the University Council in 1951, and Supreme Decree 02921 in 1952. The agreement with the Centro Brasileiro de Pesquisas Físicas was signed in December 1952.
The pi meson. In 1947, the emulsions that César Lattes exposed at Chacaltaya provided the decisive evidence for the pi meson. The mountain supplied the proof five years before the Laboratory existed.
International recognition. On 28 February 1964 the IUPAP Cosmic Ray Commission declared Chacaltaya and Kolar (India) “essential experimental sites for research in this scientific field” (translated from the Spanish). ⚠ Known through Aguirre’s quotation; the original has yet to be located.
Scientific output. Some 600 original contributions, 78 monographs and 120 undergraduate (licenciatura), master’s and doctoral theses between 1952 and 1994.
BASJE. The site’s longest-running experiment: first detectors in 1961, in operation from January 1962 and for more than half a century (⚠ the closing date, 2015 according to the script, is yet to be confirmed). A 60 m² muon detector beneath a galena and concrete shield of about 320 g/cm².
Neutrons from the Sun. Since September 1992 Nagoya University’s solar neutron telescope has operated above the Rossi hall, the highest station in a network spanning seven mountains; it detected neutrons from the solar flares of 24 November 2000 and 7 September 2005, and it is still measuring.
GAW station. Since 2011 ⚠, one of the very few high-altitude global stations of the World Meteorological Organization, operated by UMSA with partners from six or seven countries.
The glacier. It disappeared completely in 2009. It was one of the first tropical glaciers in the Central Andes to vanish, and skiing ended with it: the mountain had been home to the highest ski run in the world.
Today. ALPACA is under construction; it will be the first instrument able to observe the southern-hemisphere sky in gamma rays above 100 TeV. Its prototype, ALPAQUITA, has been observing since September 2022.

The site in one sentence

Three versions of different lengths, in case you need a news-wire item, a standfirst or a paragraph.

Headline (12 words). The Bolivian mountain that proved the pi meson still measures the universe.
Standfirst (40 words). At 5,200 metres above La Paz, the Chacaltaya Cosmic Ray Laboratory has been measuring cosmic rays and the atmosphere for eighty years. It was there that the proof of the pi meson was obtained in 1947, and it is there that the first detector to observe the southern sky above 100 TeV is being built today.
Paragraph (90 words). The Chacaltaya Cosmic Ray Laboratory, part of the Universidad Mayor de San Andrés, is the world’s oldest high-altitude cosmic-ray research centre still in operation. It grew out of a weather station set up in 1942 by a Spanish exile, provided the decisive evidence for the pi meson in 1947, and hosted the BASJE experiment for more than half a century and the Brazil–Japan Collaboration for forty years; its work gave rise to Bolivia’s nuclear energy commission, the country’s first computing centre and UMSA’s present-day Facultad de Ciencias (Faculty of Science). It is a candidate for UNESCO World Heritage status.

High-resolution images

Credit is mandatory and is given on each image. The historical photographs are subject to third-party rights: journalistic use requires citing the institution that holds them, and any other use requires prior permission. Images marked “to be produced” do not exist yet.

General view of the Laboratory at 5,200 m

The Laboratory from the summit Mandatory credit: IIF–UMSA Archive · reproduced in Aguirre (1996). A present-day photograph of the Laboratory is still to be produced. Available

“The three figures of BASJE”: Ismael Escobar, Bruno Rossi and Koichi Suga

The three figures of BASJE Mandatory credit: IIF–UMSA Archive · reproduced in Aguirre (1996). Available

Construction of the muon detector, 1960s

Sixty square metres beneath the lead Mandatory credit: IIF–UMSA Archive · reproduced in Aguirre (1996). Available

Photographic collection of former workers — Carlos Ormachea’s archive

The Laboratory’s workers Mandatory credit: Carlos Ormachea Archive. 17 photographs catalogued. Available

The glacier before and after — same framing

The vanished glacier Historical: Club Andino Boliviano ⚠. Present-day: IIF–UMSA. To be produced

The ALPACA array under construction, November 2025

ALPACA being built Mandatory credit: Kazumasa Kawata · ALPACA Collaboration. ⚠ The author’s express permission must be requested before distribution. The aerial view of ALPAQUITA is still to be produced. Available

The solar neutron telescope, 1992–1994

Neutrons from the Sun above the Rossi hall Mandatory credit: Nagoya University · provided by Yasushi Muraki to the IIF–UMSA for dissemination. Available

Combined download

Once the kit is complete, all authorised images will also be offered as a single ZIP file including a credits file, so that none of them is published without attribution.

Coverage

What has already been published about the candidacy, starting with the launch of the campaign at the Laboratory on 26 September 2026. The links lead to the original stories; the texts and images belong to each outlet.

El Diario · 27 Sept 2026 · Front page“Buscan postular al laboratorio de Chacaltaya como patrimonio mundial”
El Diario · 27 Sept 2026 · National“Trabajan en nominación del laboratorio de Chacaltaya como patrimonio humano”
ABI · Agencia Boliviana de Información · 27 Sept 2026 · Central newsroom“La UMSA abre el camino de Chacaltaya hacia la Unesco con el respaldo de Brasil y Japón”Also: Facebook post · eju.tv · La Voz de Tarija · Infodiez
Red Uno · 27 Sept 2026 · Juan Marcelo Gonzáles“UMSA impulsa reconocimiento de Chacaltaya como Patrimonio ante la UNESCO”
Red Uno · 28 Sept 2026 · Greyss Nery Pinaya Acarapi“UMSA busca que el Laboratorio de Física Cósmica de Chacaltaya sea Patrimonio de la Humanidad”
El Deber · 28 Sept 2026 · Mauricio Quiroz Terán“Chacaltaya, la montaña nevada que vio Felipe de Edimburgo, y que busca llegar a la Unesco”
El Diario · social mediaFacebook post
Levántate Bolivia · social mediaFacebook post
Facebook · social mediaVideo (reel)

Have you published a story about the Laboratory or the candidacy? Send us the link through the contact page and it will be added to this list.

How to name it correctly

Common mistakes worth avoiding.

Yes: “Chacaltaya Cosmic Ray Laboratory” (in Spanish, “Laboratorio de Física Cósmica de Chacaltaya”). No: “Chacaltaya Observatory”, nor plain “Chacaltaya Laboratory” on first mention.
Yes: “Ismael Escobar Vallejo”. Careful: some sources reverse the surnames and write “Vallejos Escobar”. ⚠
Yes: “pi meson” or “pion”. No: “mu meson”, which is a different particle — and precisely the confusion that the 1947 discovery cleared up.
Yes: “5,200 metres” for the Laboratory. No: using a single altitude for the whole site — see the key facts.
Yes: “a candidate for UNESCO World Heritage status”. No: “declared a World Heritage Site”. The candidacy is still being prepared.