IFAE, June 5th, 2012.  After the earthquake in Japan, T2K is still at the top of the neutrinos investigation. The T2K collaboration presented a better estimation of the oscillation measurement between muonic and electronic neutrinos at the Neutrino 2012 conference, held in Kyoto from the 3rd to 9th of June. These are the first results after the tremendous earthquake occurred in Japan in 2011, when the T2K collaboration was going to release to the scientific community the first direct observation of the third type of oscillation between neutrino families. The Institut de Física d’Altes Energies (IFAE) in Barcelona and the Instituto de Física Corpuscular (IFIC) in Valencia play a leader role inside the international collaboration T2K. This experiment is now in an advanced position in the competition to establish whether the neutrinos are good candidates to explain the universe matter-antimatter asymmetry.

In June 2011, just one year ago, the T2K Collaboration was showing the initial indication of the last type of oscillation between neutrino families, that of muonic into electronic neutrinos. That was the experimental confirmation that the three different neutrino families (electronic, muonic and tauonic) can oscillate among them.

 

After one year and the complete recovering of the J-PARC installation, which was seriously damaged by the earthquake of March 2011 in Japan, T2K is again at the leadership of neutrino physics investigation. During the international conference Neutrino 2012, the T2K collaboration will present a more precise estimation of θ13, which is the angle that describes the oscillation between muonic and electronic neutrinos.

The experiments Double Chooz in France (with the participation of the CIEMAT neutrino group from Madrid), Daya Bay in China or Reno in Korea have already measured this angle with a better precision than the new updated measurement of the Japanese experiment. These results from other experiments could undermine the new T2K measurement. But, as explained by Federico Sanchez (T2K responsible at IFAE) “The new T2K result not only represents the confirmation of the past year measurement, but it is also in perfect agreement with the reactors measurements. This is really important because it means to measure the same parameter using different detectors and experimental techniques with distinct physical processes even if related by a common theory.”

T2K is an experiment optimized to observe the oscillation between muonic and electronic neutrinos, in other words, to measure the electronic neutrinos appearance. This is fundamental to measure with high precision some of the neutrino oscillation parameters. Is it here, in these parameters, where one of the most important and better-hidden natural secret is hold: why our universe is made of matter only?

If oscillations between the three different types of neutrinos are possible, then, according to the theory, violation of the symmetry between matter and anti-matter (known as CP symmetry) is also possible. It seems that the CP asymmetry is characterized by the behavior of neutrinos and antineutrinos oscillations. If they oscillate in a slightly different way, it might be this asymmetry the one that allowed matter dominate on anti-matter.

In appearance experiments like T2K, the oscillation amplitude depends from the parameter that describes CP violation. In contrast, the reactors experiments look at the disappearance of electronic anti-neutrinos, which is independent from CP violation. Only taking into account both types of measurements, it will be possible to decouple the CP violation term and to understand whether there is an asymmetry between matter and antimatter.

The T2K experiment uses a muonic neutrino beam produced in Tokay, at the J-PARC accelerators complex in the east coast of Japan. The Super-Kamiokande detector, located 296 Km far away, on the west coast, measures how many neutrinos oscillated along this distance. T2K is an international collaboration between physics institutes from Japan, Canada, France, Germany, Italy, South Korea, Poland, Russia, Switzerland, United States, United Kingdom and Spain. IFAE and IFIC are the Spanish research centers involved in this project, supported by the Centro Nacional de Física de Partículas, Astropartículas y Nuclear (CPAN).

Short summary of the neutrino oscillations research

In 1998 the experiment Super-Kamiokande observed for the first time the neutrino oscillation phenomenon. They found a deficit in the expected number of muonic neutrinos, measuring the muonic and electronic neutrino fluxes produced by the interactions of the cosmic rays with the atmosphere, known as atmospheric neutrinos. The flux deficit was known since the ’70s, when the experiments designed to measure the electronic neutrino flux created by nuclear reactions inside the sun found less neutrinos than expected.

Oscillations can be measured using angles θ12 and θ23, already known to be different from zero, which describe the transformation probability. In order to have CP violation it is necessary that also θ13 be different from zero, implying a third type of neutrino oscillations.

T2K is an experiment specifically designed to observe directly the oscillation between muonic and electronic neutrinos. T2K released in June 2011 the first measurement of θ13 with a certain precision. In order to perform this type of measurement it is needed to know how many muonic neutrinos, created in J-PARC, oscillate into electronic neutrinos before arriving to Super-Kamiokande. It is also fundamental to know with the highest possible precision the flux of muonic neutrinos created in Tokay and the intrinsic electronic neutrino contamination of the beam that arrive to Super-Kamiokande.

Today in Kyoto, the T2K collaboration presents these two last measurements and also an estimation of the angle that describes the oscillation between these two types of neutrinos. The Instituto de Física de Altas Energías (IFAE), at the UAB played a leading role in both measurements.

The IFAE neutrino group, leaded by the researchers Enrique Fernández and Federico Sánchez, took a really active part in the most important milestones of neutrino physics during the last ten years. The work during the last months was really hard, mainly because of the uncertainty due to the earthquake in Japan. “The new results show that T2K is still playing a leading role in neutrino physics and the contribution of T2K is still really important. From the IFAE point of view, this is a success and gives a reward to the hard work of the last years. Indeed, the IFAE institute participated in the construction of one of the most important detectors of the T2K experiment, and during the last months also contributed to two different fundamental analyses of the oscillation measurements. After ten years of hard work, IFAE is now part of the elite of neutrino physics in the world,” said Federico Sánchez satisfied for the good job done.

IFAE is a research institute, located inside the Universitat Autònoma de Barcelona (UAB) campus, specialized in high energy and neutrino physics as well as astrophysics and observational cosmology. In the recent years, the IFAE institute activated a fifth research line: physics investigation applied to medicine.

 

For more information, please contact:

Sara Strauch

IFAE Press Officer

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Tel: +34 93 581 2831

www.ifae.es

 

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