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I'm working on an open-source textbook on special relativity. The text below is what I currently have on experimental searches for tachyons. There seems to have been quite a bit of work on this kind of thing in the 60's, but very little in more recent times. Does anyone know of any better empirical evidence than what I refer to below?
The most obvious experimental signature of tachyons would be propagation at speeds greater than c. Negative results were reported by Murthy and later by Clay,[9] who studied air showers generated by cosmic rays to look for precursor particles that arrived before the first photons. One could also look for particles with |p| > E. Alvager and Erman, in a 1965 experiment, studied the beta decay of 170Tm, using a spectrometer to measure momentum and a solid state detector to determine energy. An upper limit of one tachyon per 10^4 beta particles was inferred. Experimental searches are made more difficult by conflicting theoretical claims as to whether tachyons should be charged or neutral, whether they should have integral or half- integral spin, and whether the normal spin-statistics relation even applies to them.[10] Current thinking in quantum field theory is that tachyonic fields actually would not have a superluminal signal velocity, and that tachyonic fields are to be interpreted not as real physical phenomena but as unphysical features of certain field theories.[11] A brief flurry of reawakened theoretical interest in tachyons was occasioned by a 2011 debacle in which the particle-physics experiment OPERA mistakenly reported faster-than-light propagation of neutrinos; the anomaly was later found to be the result of a loose connection on a fiber-optic cable plus a miscalibrated oscillator.
[9] “A search for tachyons in cosmic ray showers,” Austr. J. Phys 41 (1988) 93, http://adsabs.harvard.edu/full/1988AuJPh..41...93C
[10] Feinberg, Feinberg, ``Possibility of Faster-Than-light Particles,'' Phys Rev 159 (1967) 1089, http://www.scribd.com/doc/144943457...r-Than-light-Particles-Phys-Rev-159-1967-1089
[11] Baez gives a good explanation at http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html
The most obvious experimental signature of tachyons would be propagation at speeds greater than c. Negative results were reported by Murthy and later by Clay,[9] who studied air showers generated by cosmic rays to look for precursor particles that arrived before the first photons. One could also look for particles with |p| > E. Alvager and Erman, in a 1965 experiment, studied the beta decay of 170Tm, using a spectrometer to measure momentum and a solid state detector to determine energy. An upper limit of one tachyon per 10^4 beta particles was inferred. Experimental searches are made more difficult by conflicting theoretical claims as to whether tachyons should be charged or neutral, whether they should have integral or half- integral spin, and whether the normal spin-statistics relation even applies to them.[10] Current thinking in quantum field theory is that tachyonic fields actually would not have a superluminal signal velocity, and that tachyonic fields are to be interpreted not as real physical phenomena but as unphysical features of certain field theories.[11] A brief flurry of reawakened theoretical interest in tachyons was occasioned by a 2011 debacle in which the particle-physics experiment OPERA mistakenly reported faster-than-light propagation of neutrinos; the anomaly was later found to be the result of a loose connection on a fiber-optic cable plus a miscalibrated oscillator.
[9] “A search for tachyons in cosmic ray showers,” Austr. J. Phys 41 (1988) 93, http://adsabs.harvard.edu/full/1988AuJPh..41...93C
[10] Feinberg, Feinberg, ``Possibility of Faster-Than-light Particles,'' Phys Rev 159 (1967) 1089, http://www.scribd.com/doc/144943457...r-Than-light-Particles-Phys-Rev-159-1967-1089
[11] Baez gives a good explanation at http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html