Observations of cosmic neutrinos in the Kamiokande II detector
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Presentation about researches that won the Nobel Prize as a part of the seminar class of the School of Physics, Suranaree University of Technology.
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Observations of cosmic neutrinos in the Kamiokande II detector
- 1. OBSERVATIONS OF COSMIC NEUTRINOS IN THE KAMIOKANDE II DETECTOR THE NOBEL PRIZE IN PHYSICS, 2002 Wathan Pratumwan
- 2. 2 The Nobel Prize in Physics, 2002 was concerned about new windows for astronomical observation. “for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources” “for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos” Masatoshi KoshibaRaymond Davis Jr.Ricardo Giacconi <http://www.nobelprize.org/nobel_prizes/physics/laureates/2002/>
- 3. II. Cosmic neutrino sources ‣ The Sun ‣ Supernovae III. Kamiokande II detectorI. Neutrinos IV. Observation results ‣ Supernova neutrinos ‣ Solar neutrinos V. The outlook COSMIC NEUTRINOS IN THE KAMIOKANDE II DETECTOR
- 4. INTRODUCTION | NEUTRINOS Neutrinos are rarely interact with other matter. 4 <https://commons.wikimedia.org/wiki/File:Standard_Model_of_Elementary_Particles.svg> ` Relative strength (two protons in nucleus) EM interaction = 1 weak interaction = 10-7 strong interaction = 20
- 5. THE SUN & SUPERNOVAE COSMIC NEUTRINO SOURCES <http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=ssc2005-14c>
- 6. INTRODUCTION | THE SUN Nuclear fusions in the core energise the Sun and produce neutrinos. 6 the standard solar model (SSM) proton-proton chain 1H + 1H → 2H + e+ + νe 1H + e- + 1H → 2H + νe 3He + 1H → 4He + e+ + νe 2H + 1H → 3He + γ 3He + 4He → 7Be + γ 7Be + e- → 7Li + νe 3He + 3He → 4He + 21H 7Li + 1H → 4He + 4He 7Be + 1H → 8B + γ 8B → 8Be* + e+ + νe 8Be* → 4He + 4He pp pep hep 8B 7Be ppI ppII ppIII 99.77% 0.23% 84.92% 25.08% 99.9% 0.1% 10-5 %
- 7. TEXT 7
- 8. INTRODUCTION | SUPERNOVAE Core-collapse supernovae produce neutrinos which ignite the explosions. 8 Neutrino burst (left) and accretion (right) stage of stellar core collapse <http://dx.doi.org/10.1016/j.physrep.2007.02.002> electron capture electron capture pair creation In a supernova, a star releases >99% of its gravitational binding energy as neutrinos. ~ 1044 J
- 9. INTRODUCTION | SUPERNOVAE Q: Which of the following would be brighter, in terms of the amount of energy delivered to your retina? 9 <https://what-if.xkcd.com/73/> a. A supernova, seen from as far away as the Sun is from the Earth b. The detonation of a hydrogen bomb pressed against your eyeball? Ans: a. is brighter by nine orders of magnitude! Hint: However big you think supernovae are, they're bigger than that.
- 10. INTRODUCTION | NEUTRINOS AS A PROBE Neutrino could travel undisturbedly. 10 The structure of the Sun <https://commons.wikimedia.org/wiki/File:Sun_poster.svg> Neutrinos Visible light
- 11. KAMIOKANDE II DETECTOR NEUTRINO DETECTION
- 12. KAMIOKANDE EXPERIMENT | ORIGINAL KAMIOKANDE KamiokaNDE aimed to search for proton decay. 12 <http://www-sk.icrr.u-tokyo.ac.jp/uploads/slide-08.jpg> ‣ KamiokaNDE = Kamioka Nucleon Decay Experiment ‣ It was first designed to search for proton decay by measuring the water Cherenkov radiation. ‣ The experiment was located in a mine under a mountain to reduce backgrounds.
- 13. KAMIOKANDE EXPERIMENT | KAMIOKANDE II DETECTOR Upgraded Kamiokande II aimed to detect solar neutrinos. 13 Schematic outline of the Kamiokande II detector <http://dx.doi.org/10.1103/PhysRevD.38.448> fiducial volume 2140-ton water photomultiplier tube (PMT) ~20% of total surface of the fiducial volume anticounter ‣ shielding against gamma rays and neutrons ‣ muon “veto” ‣ Real-time detection ‣ Directional sensitive ‣ Energy threshold of 8.8 MeV
- 14. KAMIOKANDE EXPERIMENT | NEUTRINO DETECTION A neutrino generates a charged particle emitting the Cherenkov radiation. 14 left <http://www-sk.icrr.u-tokyo.ac.jp/sk/detector/howtodetect-e.html> right <http://www.ps.uci.edu/~tomba/sk/tscan/compare_mu_e/> ν + e- → ν + e-ν̅e + p → n + e+ Neutrino… ‣ arrival time ‣ direction ‣ energy The Cherenkov ring emitted by an electron and detected by PMTs
- 16. 10 days afterBefore Australian Astronomical Observatory KAMIOKANDE EXPERIMENT | SUPERNOVA NEUTRINOS Supernova 1987A was discovered on 24 Feb. 1987. 16 SN 1987A ‣ Type ‣ Host galaxy ‣ Distance ‣ Discovery Type II (peculiar) Large Magellanic Cloud 167,885 light-years 24 Feb. 1987 (23:00 UTC)
- 17. KAMIOKANDE EXPERIMENT | SUPERNOVA NEUTRINOS A neutrino burst was detected on 23 Feb. 1987, 7:35:35 UTC 17 A time sequence of events in a 45-sec interval entered on 23 February 1987, 7:35:35 UTC. <http://dx.doi.org/10.1103/PhysRevLett.58.1490>
- 19. KAMIOKANDE EXPERIMENT | SOLAR NEUTRINOS The 450-days sample showed an enhancement in the direction of the Sun. 19 Distribution in the cosine of the angle between the electron trajectory and the direction of the Sun <http://dx.doi.org/10.1103/PhysRevLett.63.16>
- 20. KAMIOKANDE EXPERIMENT | SOLAR NEUTRINOS The measured 8B neutrino flux is lower than the prediction by the standard solar model. 20 KAM-II data SSM = 0.46 ± 0.13(stat.) ± 0.08(syst.) Energy distribution of the solar neutrino signal. The histogram is the distribution predicted by SSM. <http://dx.doi.org/10.1103/PhysRevLett.63.16> The deficiency was consistent with the result from Davis’ experiment.
- 21. THE OUTLOOK IMPACTS OF THE KAMIOKANDE II
- 22. THE OUTLOOK Impacts of the Kamiokande II experiment on astronomy, astrophysics and particle physics 22 ‣ Cherenkov detectors for neutrinos ‣ Neutrino telescopes for neutrino astronomy ‣ Core-collapse mechanism of supernova ‣ Supernova Early Warning System (SNEWS) ‣ The solar neutrino problem ▶︎ neutrino oscillations
- 23. SUMMARY Observations of cosmic neutrinos in the Kamiokande II detector 23 a) Solar neutrinos ‣ enhanced in the direction of the Sun ‣ lower than prediction b) Supernova neutrinos ‣ high-flux burst signal ‣ arrived before light detect neutrinos with the water Cherenkov radiation
- 24. EXTRA
- 25. EXTRA Stellar evolution http://www.jpl.nasa.gov/infographics/uploads/infographics/full/10737.jpg
- 26. EXTRA Core-collapse mechanism of supernovae <http://dx.doi.org/10.1016/j.physrep.2007.02.002>
- 27. EXTRA Supernova neutrino signal modeling <ArXiv:1507.05613>
- 28. EXTRA Supernova neutrinos Scatter plot of the detected electron energy and the cosine of the angle between the measured electron direction and the direction of the Large Magellanic Cloud. <http://dx.doi.org/10.1103/PhysRevD.38.448>
Editor's Notes
- The Nobel Prize in Physics, 2002 was concerned about discoveries of new windows for astronomical observation. A half of the prize went to Ricardo Giacconi for the discovery of cosmic x-ray sources. The other half was jointly awarded to Raymond Davis Jr. of the Homestake experiment and Masatoshi Koshiba of the Kamiokande experiment for the detection of cosmic neutrinos. Today, I will present you the observations of cosmic neutrinos in the Kamiokande II detector which was led by Prof. Koshiba.
- I organise the talk as follows. Firstly, I will give you an introduction about neutrinos and cosmic neutrino sources including the Sun and supernovae. Next, I will tell you about the Kamiokande II detector. This will be followed by observation results of supernova and solar neutrinos. Last is the outlook, how the experiment affected various fields.
- Neutrinos are elementary particles which rarely interact with other matter. Since they are leptons without electric charges, they can only interact via weak interaction. The weak interaction, like its name suggests, is… weak. How weak is it? Let’s consider interactions between two protons in nucleus. If we take the strength of electromagnetic interaction as 1, the strength of the weak interaction will be 10^-7, one of ten millions. This makes neutrinos rarely interact. They have even been called the ghost particles.
- Today we are interested in two sources of cosmic neutrinos, the Sun and supernovae.
- According to the standard solar model, the Sun is energised by chain reactions of nuclear fusions in the core. Some of these reactions produce neutrinos. This diagram shows the proton-proton chain which dominates in stars the size of the Sun and smaller. In this chain, 3 hydrogens turn into 1 helium. 5 reactions produce neutrinos. The ones that are relevant today are called B-8 neutrinos from the beta decay of boron-8. Fusions of heavier nuclei can occur in larger stars. The larger the star, the heavier the nuclei. These chain reactions continue until all nuclei in the core become iron. Then, the core will collapse under its own gravity.
- This is where a core-collapse supernova happens. The star explodes while its core forms a neutron star.
- During a core-collapse supernova, neutrinos are produced. These neutrinos play an important role in igniting the explosion of the supernova. I show you here two stages in the core-collapse mechanism. On the right diagram, neutrinos are produced from electron capture by protons in the outer core. On the left hand side, when the inner core is cooling down to form proto-neutron star, neutrinos and antineutrinos produced by the pair creation in addition to the electron capture. In a core-collapse supernova, a star releases more than 99% of its gravitational binding energy as neutrinos. This energy is enormous.
- Here’s a question to give you a sense of scale. Which would be brighter, in terms of the amount of energy delivered to your retina? A supernova, seen from as far away as the Sun is from the Earth. or The detonation of a hydrogen bomb pressed against your eyeball. The answer is…. a. The supernova is brighter by nine orders of magnitude. And recall that photons carry less than 1% of all energy in the supernova compared with 99% carried by neutrinos.
- Although these neutrinos are difficult to detect, the plus side is that they could travel for a very long distance without being disturbed. We can use neutrinos to probe environments which other radiations such as photon cannot penetrate. For example, shown here are the structure of the Sun. At the centre is the core where the nuclear fusions occur and neutrinos are produced. There are also photons released in the core. However it takes more than a hundred thousands years for these photons to reach the outer edge of radiative zone. Almost all of observed light is from the outer shell called the photosphere.
- In the next section, I will tell you how the kamiokande II detector detected these ghost particles.
- Originally, the kamiokande experiment led by Prof. Koshiba aimed to search for proton decay, as its name stands for Kamioka Nucleon Decay Experiment. It planed to use the Cherenkov radiation to detect the decay. I will tell you about the Cherenkov radiation later. To reduce backgrounds signal, the experiment was located in a mine under a mountain. After a year without any decay signal, their thought may be like, O.K. let’s just make the bound of the proton lifetime and do something else.
- Inspired by Davis’ solar neutrino experiment, Prof. Koshiba upgraded the detector into Kamiokande II aiming to detect solar neutrinos. It was the first Cherenkov detector for neutrinos. The target detector was a water tank containing 2 ton water. Installed on the inner surface of the tank are newly developed photomultiplier tubes. These covered about 20% of total surface of the fiducial volume. Outside of the tank is the anticounter composed of water to shield against gamma rays and neutrons, and also photomultiplier tubes for muon veto. With this configuration, the detector was able to detect neutrinos in real-time with directional data. It had the energy threshold of 8.8 MeV.
- When a neutrino enters the detector, it may interact with nuclei or electrons. The product is a charged particle travelling faster than the speed of the light in the water and emitting a cone of light known as Cherenkov radiation, equivalent to a sonic boom. The Cherenkov radiation is then detected as a ring by PMTs. From this ring, we could reconstruct the neutrino arrival time, its direction and energy.
- On 24 February 1987 a supernova was discovery. It’s located in Large Magellanic Cloud about 170,000 light-years away. After the discovery, scientists at the Kamiokande experiment searched for a possible neutrino signal from the supernova in measured data.
- They found that they detected a neutrino burst on 23 February at 7:35 UTC. It was hours before the first optical indication of the supernova. This plot shows a time sequence of events in a 45-second interval centred at the burst time. They detected 12 neutrinos from the supernova. The signal was concentrated within the first 2 second.
- From the 450-days sample, we can see an enhancement of neutrino flux in the direction of the Sun over the isotropic background. This demonstrates that the detected neutrinos were indeed from the Sun. According to the standard solar model, spectral of neutrinos from pp chain are like this. Note that with the threshold of 8.8 MeV, the Kamiokande II was able to detected only the B8 neutrinos from the beta decay of boron-8. The histogram is the prediction by the standard solar model. We can see that the measured solar neutrino flux was lower than the prediction.
- Again this energy distribution shows that the detected signal was lower than the prediction by the standard solar model. The ratio of the measured data and the prediction was 0.46. This deficiency was consistent with earlier results from Davis’ experiment.