KAMIOKANDE

Super-Kamiokande light-water experiment reveals atmospheric neutrino oscillations. 

Among electronic neutrino detectors is the great KAMIOKANDE experiment and its extension SUPERKAMIOKANDE. Spread out at the bottom of a mine in Japan, this device has directional sensitivity and it can thus be checked whether captured neutrinos do actually come from the Sun. 

Five experiments have so far detected solar neutrinos. These are Homestake (USA), GALLEX, SAGE, KAMIOKANDE and SUPERKAMIOKANDE, all set up down mines or tunnels. Detected fluxes agree qualitatively with theoretical predictions, both in numbers and energies. We may say that we have basically understood how the Sun shines. The same set of nuclear reactions invoked to explain the solar luminosity does give rise to neutrinos. 

Figure 1. Spectra of SN1987a on a relative flux scale. The numbers indicate days since the Kamiokande-II neutrino event. 

A neutrino burst was observed in the KAMIOKANDE-II detector on 23 February, 7 35 35 UT ( 1 minute) during a time interval of 13 seconds. The signal consisted of 11 electron events of energy 7.5 to 36 MeV, of which the first 2 point back to the Large Magellanic Cloud (LMC) with angles 18 18 and 15° 27 °. 

A new analysis of the special low threshold trigger counts strongly indicates that KAMIOKANDE did not observe any signals at 2 52 36 which is the time claimed by the Mont Blanc group. 

Following the optical sighting on 24 February 1987 of the supernova [1], now called SN1987a, a search was made of the data taken in the detector KAMIOKANDE-II during the period from 1609h, 21 February 1987 to 0731h, 24 February 1987. The results of that search has been published elsewhere. [2]... 

We present here the other argument against the consistency between Mont Blanc and KAMIOKANDE. The KAMIOKANDE trigger system possesses a special low level discriminator output, the rate of which is counted with an online scaler. The low level discriminator has a threshold of approximately 6.4 MeV at 50% efficiency. The scaler count is read out at every event occurrence. The result is shown in Fig.6. The count rates between 2 52 UT and 2 54 UT are compared with the average rate of 9.96 Hz. They are all consistent with background. Since the threshold level is similar with Mont Blanc, one can easily calculate the event rate inferred from the Mont Blanc result ... 

If we plot the Kamiokande and IHB data together as in Figure 3, we see that for the first two seconds a fairly high luminosity is followed for 10 seconds by a much lower luminosity. We infer from this fact that there may have been a 2 second period of accretion, followed by the explosion and subsequent Kelvin-Helmholtz cooling of the proto-neutron star. 

Figure 3. The stair step curve is the detected sample cumulative distribution function (CDF) for the combined detectors. We have weighted the two detectors equally so that the height of an IMB detection is 12/8 the height of a Kamiokande detection (note we have included the count at. 686 seconds rejected by the Kamiokande group as being too close to their threshold). If millions of counts had been seen, the CDF would be smooth and directly proportional to the number luminosity emitted by the supernova.

In conclusion, we mention the following statistically weak observational oddities the 7 sec time gap in Kamiokande data, the lack of late time events in IM8, the occurrence of two possible electron scattering events very early in time, and the discrepancy of the Kamiokande and IMB average neutrino energies. The work on particle models is being pursued with G. Fuller, R. Mayle, K. Olive, D. Schramm. 

Finally, I turn to the question of limits on neutrino masses. One can obtain a good limit on mp. by examination of Table II, constructed by mapping the Kamiokande data back to its source at the supernova, after imposition of a finite mass. The KII data itself corresponds to mDe = 0 I... 

Fig. 4 - Visual light curve during the first two days. Time zero is defined by the Kamiokande - IMB neutrino signal. Light curves from four models (Table 1) are shown as solid lines. A distance modulus of 18.5 and visual extinction of 0.5m have been adopted. Shown for comparison axe observational data points.

The two nearly simultaneous neutrino detections, the Kamiokande II and the IMB data are analyzed. The energy range of the IMB experiment is from 20 to 40 MeV, and the experimental dead time is 0.1 sec. The lower limit for detectability of a mass energy is at least 5 eV. The energy range of the Kamiokande II experiment is from 7.5 MeV to 35 MeV, and the dead time is 50 nano-sec, so that the lower limit of the detectable mass is well below 1 eV ... 

Neutrino Temperature Assuming the neutrino spectrum to be Fermi-Dirac distribution with the vanishing chemical potential, we got the Fe temperature, T [3,4]. For the Kamiokande data, T is 2.6 3.lMeV, for IMB 3.9 5.3 MeV. These values are a little close to the values by those who insist the late time neutrino heating mechanism of the explosion. 

Bunched Structure of the Data Kamiokande and IMB data show some bunched structure. We calculate the neutrino temperature and the the radius of the neutrinosphere for each bunch[5]. The first 8 events of Kamiokande and the first 6 events of IMB can be well understood in the scenario of the protoneutron star contraction. That is, the protoneutron star bom with the radius of several times 10km contracts to the normal neutron star whose radius is about 10km in a few seconds and in this stage neutrino temperature once increases with the reduction of the volume. 

The Last 3 Events As described above, whole feature of the neutrino burst is well explained by the standard model. But the last 3 events of Kamiokande which occurred after the 7sec gap is mysterious. For example, the corresponding energy is large and the radius of the neutrinosphere of several times 10km is necessary for this energy[5]. 

The concept that neutrinos diffuse out of the supernova core carrying out its thermal energy is confirmed by the observation of the neutrino burst from SN1987A for the first time. But we must keep in mind that there are some puzzles such as the last 3 events of Kamiokande. There may exist some unknown mechanism of neutrino emission at the late time. 

Probability of 7 Seconds Gap before 3 Events Using the above models of the neutrino fiux, we have done Monte Carlo simulations for the Kamiokande detector. Then we investigate the... 

N is the expected number of events in the Kamiokande detector and Et is the total energy emitted as... 

The neutrino burst from SN1987A were detected by KAMIOKANDE and also IMB in February this year. The neutrino events detected by KAMIOKANDE were clustered into three bunches event number 1-5, 7-9, 10-12. The first two bunches of the neutrino events can be understood by the standard scenario of supernova explosions. 

However, as is seen in Fig. 1, the absolute value of JE depends sensitively on the normal EOS the stiffer EOS can release larger energy. If we adopt BJ, the releases energy is too small to explain the last three events. However, the enough energy is released for the very stiff EOS of CLRC. Therefore, we conclude that, if the normal EOS is sufficiently stiff, JE is large enough to explain the last three events detected by KAMIOKANDE by this mechanism. 

It is shown that the bunch structure of the Kamiokande neutrino events associated with SN1987a can be naturally understood, if one assumes that the core of the progenitor star was rotating moderately with q(= Jc/GM2) 3 with J the total angular momentum and M the gravitational mass of the core. 

The direct observational evidence for the occurrence of neutrino oscillations came from observations with the Cerenkov detectors. The SNO detector found one-third the expected number of electron neutrinos coming from the sun in agreement with previous work with the radiochemical detectors. The Super Kamiokande detector, which is primarily sensitive to electron neutrinos, but has some sensitivity to other neutrino types found about one-half the neutrino flux predicted by the standard... 

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