arXiv:physics/0211026v1 [physics.ed-ph] 6 Nov 2002 ro tm ocletdb ai a ytmtclylwrta what pr than lower neutrino systematically “solar was The Davis by sun. collected the so of atoms models argon fac the in from neutrinos solar prediction that the o established met of efficacy thus a the He used demonstrate produced. to He so able atoms. atoms was He argon 2 of these gas. noble order out the another flush of helium, to was technique month a a of devise run to a in during neutrinos, products reaction solar of the inge number to realized the using that was however, of and noted, idea Pontecorvo be The must Bruno argon. physicist gas Soviet nobel born the neutrino Italian of the isotope of radioactive products tetrachloroeth a the were liquid, and cleaning experiment, common underground a the in in su present construct atoms to was chlorine achievement of small Davis’ between this targets. (distance by of unit number astronomial induced large 1 events of observable distance the have interaction at to neutrinos small order very In the th to during particles. due sun unhindered, produce the are practically in neutrinos outwards the numbers low-energy copious suggests, of number in name large produced the extraordinarily are As that USA. dee those Dakota, a are in South observations in painstaking Mine, of Homestake decades through observed he 4’ n h a etni h 7’,haircuiso h lcrn t electron, the neutrinos. of type tau cousins and heavier type ’70’s, muon the the in in intera lepton strong tau the the of and charge ’40’s color conservatio so-called momentum the angular and and charge energy electric for account ne to type inte electron order weak Ma the in the of with in existence prize only The the participate interactions. shared tygravitational that particles who electron are Jr.), the Neutrinos Cowan, of L. lepton. discovery Clyde the deceased for typ then Reines muon Frederick by the to of 1995 discovery in the and for experime Steinberger controlled Jack from On and neutrinos Schwartz of neutrinos. discovery cosmic for of awarded observations been their for Koshiba Masatoshi presented. re ecito ftewr o hc h rthl fteN the of half first the which for work the of description brief A h rthl fteNblPiei hsc o 02hsbe shared been has 2002 for physics in Prize Nobel the of half first The h aeo a ai salgnayoeadi soitdwt h “so the with associated is and one legendary a is Davis Ray of name The h oe rz nPyis20 o h bevto fcosmic of observation the for 2002 Physics in Prize Nobel The etefrTertclSuis ninIsiueo Science of Institute Indian Studies, Theoretical for Centre aglr 6 1,India 012, 560 Bangalore .Ananthanarayan B. Abstract tiowspsue n13 yWlgn Pauli Wolfgang by 1930 in postuled was utrino tos ihtedsoeyo h uni the in muon the of discovery the With ctions. ha xeiet h agt eetenuclei the were targets the experiment: an ch h vr65tne ffli htwr exposed were that fluid of tonnes 615 over the h at n h u) n uthv very a have must one sun), the and earth the hc r rdcdi h oeadtravel and core the in produced are which d xs,tefis xeietldemonstration experimental first the exist, t t:i 98t enM eemn Melvin Lederman, M. Leon to 1988 in nts: etioadtenurn emmethod, beam neutrino the and neutrino e blpiefrpyisfrteya 02is 2002 year the for physics for prize obel atr ytence fteclrn atoms chlorine the of nuclei the by capture nncerbt ea.Te ontcarry not do They decay. beta nuclear in n ro tm.Teigniyo ai was Davis of ingenuity The atoms. argon 0 negon xeietlctdi the in located experiment underground p hsmto oatal olc h argon the collect actually to method this f be”hwvr a httenmesof numbers the that was however, oblem” w ale cain,Nblpie have prizes Nobel occasions, earlier two enurn dsoee onl ihthe with jointly (discovered neutrino pe hoience streswsdet the to due was targets as nuclei chlorine o ywihtetn a uhdwith flushed was tank the which by hod atos pr rmpriiaigi the in participating from apart ractions, a rdce ytemdl,b smuch as by models, the by predicted was rs-eto fteewal inteacting weakly these of cross-section eul yteeprmn fDvs It Davis. of experiment the by neously eeeto yenurn on cousins found neutrino type electron he rs-eto,dsietelreflxof flux large the despite cross-section, ln,wihh trdi ag tank large a in stored he which ylene, aypoessta oe t An it. power that processes many e tnPr o i icvr ftetau the of discovery his for Perl rtin etio hth ogtt observe to sought he that neutrinos yRyodDvs r and Jr. Davis, Raymond by neutrinos a etio”which neutrinos” lar as a factor of a third or a fourth. Through dedicated experiments, he was able to show that none of the argon atoms produced were being lost during the procedure of extraction, and that the problem was to stay for many decades. The existence of the solar neutrino problem was confirmed by the experiment Kamiokande, located in the Mozumi mine in Kamioka-cho, Gifu, in Japan (Kamiokande: Kamioka Nucleon Decay Experiment) and with which the person sharing the prize with Davis, M. Koshiba is identified. The experiment was established to search for nucleon decay, predicted by grand unified theories of the fundamental interactions. The experiment proved to be versatile enough to serve as a “neutrino telescope.” The experiment uses the principle that neutrinos coming from cosmic sources when entering a large tank of water would interact with the electrons in the water and scatter elastically off the electrons. These ultra-relativistic electrons emit characteristic Cerenkovˇ radiation which is detected by photomultiplier tubes on the periphery of the container of the water. At Kamiokande, 3000 tonnes of water were surrounded with 1000 photomultiplier tubes. Unlike the Davis experiment, the measurements here were “real time” and also had information of the direction from which the observed neutrino was coming. These experiments were able to spectacularly confirm the existence of the solar neutrino problem. Another unexpected and brilliant observation of the Kamiokande experiment was that of 11 neutrino events in the year 1987 associated with the collapse of the neutrino-sphere of the supernova 1987A. The supernova which exploded in the Large Magellenic cloud, one of the two companions of the Milky Way galaxy, was also observed optically and in other regions of the electromagnetic spectrum, and its light curve was carefully monitored. This was the first ever supernova to be explored in this remarkable manner. The standard picture of the supernova explosion requires that a significant fraction of the energy transport out of the supernova be in the form of that transported by neutrinos in a spectacular burst. The event rates calculated for Kamiokande proved to be in agreement with what was observed. Supernova neutrinos were also observed by the experiments IMB (Irvine-Michigan-Brookhaven) and the Baksan mine experiments, which confirmed that the neutrinos observed by Kamiokande were indeed supernova neutrinos. The direct observation of the neutrino oscillations by the Sudbury Neutrino Observatory has re- cently resolved the solar neutrino problem in favor of a particle physics scenario whereby the electron type neutrino that is produced at the core of the sun has a finite probability of oscillating into a muon or tau type neutrino. Furthermore, no modification of the standard solar model based on which the fluxes of neutrinos are calculated is necessary (see article in Resonance, Vol. 7, No. 10, pp. 79 (2002)). The award of the Nobel prize to Davis is one that would do the prize proud. During the 30 or years of the running of his experiment, around 2000 argon atoms were collected! At age 87, he stands as an example of the rare dedication and perseverence that is required to make a truly outstanding contribution to science. A chemist by training, Davis is Professor Emeritus at the University of Pennsylvania. The award to Koshiba is no less deserving; the courage to design outstanding and brilliant ex- periments to search for the unusual and to prove the versatility of experiments. At the age of 76, Koshiba is Professor Emeritus at the University of Tokyo.

For recent articles in Resonance of related interested, see

1. B. Ananthanarayan and Ritesh K. Singh, Vol. 7, No. 10, pp. 79 (2002).

2. S. M. Chitre, Resonance, Vol. 7, No. 8, pp. 67 (2002).