neutrino mass: zatsepin's time of flight estimation

7/29/2019 Neutrino Mass: Zatsepin's Time of Flight Estimation

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Translator's NoteThe following is my own translation, from the original Russian, of the

seminal 1968 JETP Letters posting, by G. T. Zatsepin, of his suggestion that

the mass of the neutrino could be measured by observation of a not-too-

distant supernova explosion. This posting was made almost twenty years

before the 1987A supernova was observed and its first application was

demonstrated.

The original JETPreference location is given at the top of the first page

below. Two other page numbers, "205" and "206", appearing at the bottoms

of the two pages, have been omitted.

After preparing this translation, I found that much ofJETP Letters has

been translated into English. The Zatsepin article below also is available

posted in PDF format at: http://www.jetpletters.ac.ru/ps/1710/article_26008.shtml,

reprint rights apparently being controlled by theAmerican Institute of

Physics. The word usage in the corresponding online translation is different,

but the meaning corresponds reasonably closely to that of the text below.

The mathematical results are identical.


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JETP Letters, 8, p. 333, 1968

Toward the Possible Determination of an Upper Bound on the

Neutrino Mass by Time of Flight

G. T. Zatsepin

Current understanding [1,2] of the data has developed into an assumption that an

upper bound on the mass of the electron neutrino may be set at mc2 eV. Inprinciple, it is possible to give an upper limit for the neutrino mass, using a distant,

impulsive neutrino source, by measuring the arrival time of a lower-energy neutrino

relative to that of a neutrino of higher energy.

As calculated in [3 - 6], a nearby supernova explosion is expected to radiate

~1057 neutrinos and antineutrinos in a broad spectral region with an average energy

of about 10 MeV over a period on the order of a few hundredths of a second. A

typical distance in our Galaxy would be L 10 kiloparsecs, or time TL/c 1012

seconds. A particle would traverse the distance L in an elapsed time oftL/cT/. For ultrarelativistic particles, , where E/(mc2). Detection ofthe arrival of two particles, emitted simultaneously, but of different energies E1 and

E2, would yield

t t tT

or, if

tT

;

whence:

mc Et

T

;

Estimating the size oftfrom observed supernova neutrino radiation, it'sdifficult to allow for a neutrino burst length substantially less than t sec.[6]; withE1 MeV, this would make mc2 2 eV. This way, it should be possibleto improve the estimated upper bound on the mass of the neutrino by two orders of

magnitude, compared with the present.

To observe the stream of antineutrinos from a supernova in our Galaxy it would be

possible to use a large quantity ( tons) of organic scintillator, s tored in aspecial underground chamber (for shielding against cosmic rays).

The antineutrinos created at a distance of 10 kiloparsecs would fall offto a stream on Earth with a density of particles cm . Given that theeffective cross-section of the interaction p n e ~ equals cm2

333


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assuming the antineutrino energy 10 MeV, with 1000 tons of a compoundof type (CH2)n, the interaction should produce approximately 50 antineutrinos.

The energy of each interacting antineutrino would cause a definite size and

direction of a flash, allowing positive identification. From these images, it is

possible, in principle, separately to obtain the average time of arrival of the

neutrino of least energy and more.

The observation of neutrinos from supernovas in our Galaxy substantially reduces the

required waiting period for bursts and provides the opportunity for repeatedly

lowering the upper limit on the mass of the neutrino (on account of inceasing T).

Observation of extragalactic neutrino bursts would require an enormous collector of

some hydrogen-containing substance (around tons). Probably, for anexperiment on something of a large scale, it makes more sense to start off using not

a scintillating organic liquid but water Cerenkov light deep in the ocean, which,

however, would require photomultipliers with very large-area photocathodes

(totalling an area m).

Physics Institute Acting Editor

P. N. Lebedev Institute 20 July 1968

Academy of Science, USSR

References[1] L. M. Langer, R. Y. D. Moffet. Phys. Rev., 88 , 689, 1952.

[2] D. R. Hamilton, W. P. Alford, L. Gross. Phys. Rev., 92 , 1521, 1953.

[3] E. M. Burbidge, G. R. Burbidge, W. A. Fowler, F. Hoyle. Revs. Mod.

Phys., 29 , 547, 1957; Astr. J., 139, 909, 1964.

[4] Y. B. Zeldovich, O. X. Gussenov, DAN, 162, 791, 1965; JETP Letters, 1(4),

11, 1965.

[5] S. A. Colgate, R. H. White. Astr. J., 143, 626, 1966.

[6] L. N. Ivanova, B. C. Imshennik, D. K. Hadejin. Prepr in ts IPM, M. ,

1967.

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neutrino mass: zatsepin's time of flight estimation

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