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(Memories of) Raju as a graduate student and a Neutrino Co-conspirator. Sandip Pakvasa University of Hawaii. In january 1962, Raju showed up at Purdue……. I had been there for 4 months and with classmates was struggling to juggle a bunch of courses, get thru all the various exams….
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(Memories of)Raju as a graduate student and a Neutrino Co-conspirator Sandip Pakvasa University of Hawaii Blacksburg, Oct 20,2012
In january 1962, Raju showed up at Purdue……. • I had been there for 4 months and with classmates was struggling to juggle a bunch of courses, get thru all the various exams…. Raju was obviously different, he was already a seasoned physicist, knew exactly what he wanted to do and supremely confident. We were simply blown away by him! He had already published some well-known papers on the Mossbauer effect. We were suitably impressed… Of course, he still had to go thru the hurdles of the exams with us……
We hit it off right away, and became close friends. We shared common interests in weak interactions and nuclear/particle physics, we were lucky to have Peter Rosen for a teacher. We had a lot to discuss and argue about. Another common bond was a shared keen interest in Indian Classical Music! • We decided to share an apartment with another grad student. We agreed to take turns at preparing dinner, the most important task. After one week, we all agreed that the only viable way for this experiment to work was they would cook and I would wash dishes! This arrangement lasted one year….
As expected, Raju finished work on his thesis, with Rolf Steffen, in record time and left in 1964. During this period, Pramila was at MIT working with Grodzins • He went to Bartol and then to Munich for an extended stay. • I lost touch with him for a while until he came to Bell Labs…in 1972 • We resumed contacts mainly by my dropping in at Bell and visiting for a few days and having non-stop discussions and enjoying the hospitality of Pramila!
Grabowski, SP, Raju, Coppage1964, Steffen Lab Steffen Lab, Purdue Look ma, no beards! 1964 Grabowski, SP,Raju, Coppage
In 1973, neutral currents were discovered. Raju and I became interested in the question of the spacetime structure of neutral current and devising experimental tests to this end. We considered excitation of nuclear ground states followed by decay back to ground states with emission of a monochromatic γ ray or e+ e- pair. We calculated some cross-sections and rates, but it turned out that the spacetime structure of the neutral current was nailed down as being consistent with the Standard Model soon enuf...
Interlude: • In 1980, Barger, Philips, Whisnant and I wrote a paper extending Wolfenstein‘s work on matter effects on neutrino oscillations: “Matter effects in three neutrino oscillations” in which we had a plot of the resonance effect in the mixing angle as a function of neutrino energy. When Raju saw rhe preprint, he immediately asked,” what are the implications for solar neutrinos?” I must confess to my chagrin that I refused to think about it, and ignored his question. If we had changed the variable to density from energy we would have had the MSW effect, When the Mikheyev-Smirnov paper came out in 1985,Raju gleefully reminded me that he had asked me the very question; and he never failed to needle me on our near miss….
In 1986, Raju and I thought of using the neutral current excitation coupled with charged current excitation to study effects of MSW effect in solar neutrinos. We identified the pair of nuclei 11B and 11C as an ideal pair for this purpose, with neutral current providing flux monitor and distortion in the charged current spectrum the as a diagnostic for the MSW effect. This led to the proposal of BOREX as a detector for this purpose. A collaboration was formed and started to have regular meetings
I • In 1988 a collaboration was formed, and the studies of Boron loaded LS for a kT sized detector started. It was eventually discovered that with high radiopurity the threshold could be lowered enuf to be able to detect the 7Be line with ν-e scattering, the size requirements could be lowered by a factor of 4, and B-loading was no longer necessary. Thus BOREX became BOREXINO with NO Boron! I survived as a member of the collaboration until 1999 when it became clear that it was not possible to attend meetings in Italy or take shifts and I left… to be rescued by Atsuto and joined the “competition”! In 1987 Raju was visiting Hawaii just after the neutrinos from SN1987A were observed by Kamiokande and IMB. We deduced an obvious result about the limit on the neutrino lifetime which is still the strongest limit. During his visit, Raju and John Learned wrote a proposal for placing Borex inside a IMB style detector to provide shielding…..but there was no interest from IMB…
Raju and I continued to meet and discuss neutrino physics but less frequently, but at more congenial surroundings such as Venice and Trieste! Many late night loud sessions at the bar in the hotel in Venice…. • Raju had revived his old(1976) idea of a very low threshold solar neutrino detector using Indium 115 and after a series of metamorphoses became LENS which is still being pursued and come to fruition some day.
Papers Raju and I wrote together: • New Tools for solving the Solar Neutrino Problem, 1986 • Probing the Nature of the Neutrino: The Boron Solar Neutrino Experiment, 1988 • MSW Catalysed Neutrino Decay, 1988. • Galactic Supernova signal in BOREX and the measurement of νμand ντmasses, 1990 • Direct Tests for Neutrino mass, mixing and Majorana Magnetic Moment, 1991 • Discussion on a possible neutrino detector located in India, 2000
Back to Mossbauer! • The basic idea of a neutrino Mossbauer experiment had been considered in 1959 and in the ’60s and again later as a speculative possibility. Raju returned to it in 2006-7 and showed that it is feasible, even if technically extremely challenging and if succesful can lead to a variety of neutrino oscillation table-top experiments and open up a whole new field. His papers were very provocative and stimulating and generated a lot of heated debate….
SrinivasaRaghavan (A man of thousand ideas) -------------------------------------------- • I knew him as SrinivasaRaghavan from 1958 when he joined TIFR, Bombay. Although i did not keep continuous contact with him for many years, he started visiting me in Madras University regularly in late 70's. He used to tell me about his ambition of mapping out the complete spectrum of the solar neutrinos including the lowest energies. He had a hunch that a lot of physics (of the Sun as well as of the neutrino) is hidden in the low- energy part. He continued to visit me at the Institute of Mathematical Sciences (Madras, now Chennai) and talked to us about his newest ideas in neutrino physics which were always very stimulating. He was a staunch supporter of India-based Neutrino Observatory (INO) and became one of the prime movers of the project. But here I will restrict myself to two of his recent interests. One is the recoilless emission and recoilless resonant absorption of neutrinos (Mossbauer effect on neutrinos). I still remember vividly a hectic week at Chennai when Raghavan visited us and goaded by him we feverishly argued and worked on one of his ideas, namely a monochromatic directed beam of neutrinos by combining recoilless emission with the idea of neutrino helicity. Ultimately it did not work, although, in the process i learnt the correct way of characterizing the neutrino helicity in general (it is recorded elsewhere). However the Mossbauer neutrinos was dear to his heart and we had discussions with many experimental physicists on how to push it. This idea of Raghavan's is bound to revolutionize neutrino physics one day. The other dream of Raghavan was the Indo-US LENS Project and we worked ceaselessly in the last two years to initiate this project. I took him to meet leaders of science establishments in India to discuss it with them. Their response was very positive and the LENS Collaboration was being formed. Raghavan was scheduled to address many meetings in India in December 2011 and January 2012 but he was snatched away just at that critical juncture. This is a very serious loss to Science in India. But we must push on with his dream. Realization of the Indo-US LENS project will be the best tribute that his friends and colleagues in USA and India can pay to his memory. G Rajasekaran (Institute of Mathematical Sciences, Chennai,India)
In the last few years, Raju got very interested in trying to use radioactive nuclei as targets for zero threshold detectors…..and the use of sources placed inside detectors for short baseline oscillation experiments. Kamland is now considering these proposals seriosly. We continued to argue about many ideas and many of our arguments were ongoing and our discussions were incomplete….. • John Learned’s reaction…….
SP, Raju, John Learned, Divakaran Chennai 2000 when INO was proposed!
