Super-Kamiokande. Alexandre Zeenny, Nolwenn Lévêque

Transcription

1 Super-Kamiokande Alexandre Zeenny, Nolwenn Lévêque

2 Purpose Super-Kamiokande is a neutrino observatory located in Japan. Purposes of the Super-Kamiokande experiments is to reveal the neutrino properties through the observation of solar neutrinos, atmospheric neutrinos and man-made neutrinos. 42m t of water 39m

3 Neutrinos A neutrino ν is a fermion that interacts only via the weak subatomic force and gravity (if the neutrino has a mass). It exists in three flavors, one for each charged lepton: ν e,ν μ and ν τ. It was predicted in 1930 by Wolfgang Pauli to explain the continuous spectrum of the beta decay and the non conservation of the cinematic momentum. n p + e - + ν e They can be created by several ways, they are so-called the cosmic neutrinos, the atmospheric neutrinos, and the man-made neutrinos.

4 Principle Cherenkov Effect The neutrino will interact with one nucleon of an oxygen nucleus in the water resulting into the creation of a charged particle. The charged particle going faster than light in water, it will produce a cone of light Cherenkov that will give us information about the energy, type and direction of the incident neutrino. This light will be collected by photomultiplier tubes (PMT) which will amplify this signal and transform it into an electrical signal.

5 ν μ detection vs ν e detection ν μ + p n + μ + ν e + p n + e +

6 Cherenkov Effect

7 Different parts Top of Tank Electronics Huts Water Tank Photo-Multiplier-Tubes (Outer detector) Water Purification System Control Room Photo-Multiplier-Tubes (Inner detector)

8 Water Tank

9 Photo-Multiplier Inside Detector Outside Detector Exiting particle? no yes Fully-contained Partially-contained Stopping muon Trough going muon

10 Photo-Multiplier-Tubes (Inner detector) ~50cm 11,129 photo-sensors, called photomultiplier-tubes (PMTs) are instrumented in the inner tank. The Cherenkov light emitted by charged particles running in water is detected by these sensors. The energy and direction of the charged particle is calculated by the information of the detected charge and timing. The inner PMTs are instrumented at intervals of 70cm and cover about 40% of the detector wall. The rest of the surface is covered with black polyethylene terephthalate sheet which optically separates the tank to the inner part and the outer part.

11 Photo-Multiplier-Tubes (Outer detector) Super-Kamiokande detector is optically separated into two concentric cylindrical regions by PMT support structures and pairs of opaque sheets. 1,885 outward-facing PMTs are instrumented. The OD PMT is attached to a wavelength shifter plate in order to collect photons efficiently. ~20cm ~60cm Main purpose: distinguish the neutrino events from the cosmic ray muon events. The cosmic ray muons are background sources of the neutrino observation.

12 Electronics Huts A high voltage of about 2000 volts is supplied to each PMTs. The signals from about 13,000 PMTs are sent to the electronics system in four electronics huts via 70m cables. In September 2008, the data acquisition system of Super- Kamiokande has been updated for the first time since the Super-Kamiokande started the observation. New system has recorded all the hits of each PMT which hits about 4,500 a second for analysis. The stored data size in a day becomes as much as 500GB.

13 Water Purification System Super-Kamiokande is filled with 50,000 tons of ultra-pure water. It is very important to keep the water clean to improve the detection precision.the Super-Kamiokande uses the clean groundwater. The further removal of small dusts, ions, bacteria and radon can reduce the scatter of Cherenkov light and background noise from radon decay products in the water.

14 Top of Tank The roof of the cavity is a dome shape in order to disperse the weight of the 1000m mountain above the tank. The rock in the mine contains the radioactive material (radon) whose decay products become one of the background sources to neutrino observations. To avoid contamination of the radioactive material emitted from the rock, the ceiling and the wall are sealed by the polyethylene Mineguard. Furthermore, a "radon-free" air is piped into the tank top from the outside to further hold back contaminated mine air.

15 Neutrino Oscillations If we can deduce that neutrino has its flavor changing during its life time (an important phenomena called the neutrino oscillations), we can deduce that neutrinos are massic! Acquisition of data from Super-Kamiokande gives a proof of this phenomena.

16 Types of Neutrinos Neutrinos are produced or detected in 3 flavors, one for each charged lepton: ν e,ν μ and ν τ (neutrino states). However, neutrinos propagate in form of mass eigenstates: neutrino1, neutrino2 and neutrino3 with the respective masses m 1, m 2, and m 3. In fact, neutrino eigenstates are mix of mass ones:

17 Neutrino Oscillations The flavor of a neutrino is determined as a superposition of the mass eigenstates. The type of the flavor oscillates, because the phase of the wave changes. Neutrino oscillation occurs when neutrinos have mass and non-zero mixing.

18 Study of solar neutrinos That prove the atmospheric neutrino oscillations but then, it was demonstrated for solar neutrinos (2001). Some experimental data showing that neutrinos are coming from the Sun.

19 Study of Solar Neutrinos Since neutrinos react rarely, it is possible to catch information from the center of the Sun, where the process of fusion happens. However, the experimental results are not consistent with the expected ones: : Homestake, the 1rst observation of Solar neutrino, measured 1/3 of the expected rate : Reported measured with a highest accuracy than ever before, but the flux measured is still 45% of the SSM expectation : Combined with an SNO experiment (Canada), results can be explain by the occureness of neutrino oscillations.

20 T2K Experiment Goal of the experiment : measure the oscillation of ν μ into ν e in order to measure the mixing angle θ 13 (the last parameter of the PMNS matrix). July 2013: first observation of a muon neutrino to electron neutrino: confirm man-made neutrino oscillations.

21 T2K Experiment PMNS matrix where c ij = cos θ ij & s ij = sin θ ij. That lead to the following probability Allowing to know the proportion of ν μ in ν 3

22 Thank you for your attention! Any question?