T2K
Encyclopedia
T2K is a particle physics
experiment that is a collaboration between several countries, including Japan
, Canada
, France
, Germany
, Italy
, Korea
, Poland
, Russia
, Spain
, Switzerland
, the United States
, and the United Kingdom
. It is the second generation follow up to the K2K experiment
, a similar long baseline neutrino oscillation experiment.
The J-PARC
facility will produce an intense off-axis beam
of muon neutrino
s. The beam is directed towards the Super-Kamiokande
detector, which is 295 km away. The main goal of T2K is to measure the oscillation of to and to measure the value of θ13, one of the parameters of the Pontecorvo–Maki–Nakagawa–Sakata matrix
.
On June 15, 2011, the T2K collaboration announced the observation of six electron neutrino-like events compared to an expected background of 1.5, a significance of 2.5 standard deviation
s.
phase δ by comparing oscillations of neutrinos to those of antineutrinos.
facility is a more powerful accelerator
than the KEK facility
used in the K2K experiment
. The main synchrotron
will eventually be able to accelerate protons to 50 GeV/c. Protons colliding with the target material will produce (mostly) positive pion
s which will decay into antimuon
s and muon neutrino
s. The beam power is expected to be 0.75 MW delivering 110 times more neutrino events than K2K.
away from the Super-Kamiokande detector
. This lowers the flux of neutrinos reaching the detector but provides a more desirable neutrino energy spectrum. Off-axis the peak energy is low with higher energies being suppressed. At the distance between Tokai
and Kamioka, maximal neutrino oscillation is expected to occur at energies lower than 1 GeV.
s (TPCs) will be able to measure the momenta
of muons produced by charged current
reactions in the detector, this information will yield the neutrino energy spectrum. Also the TPCs can be used for particle identification.
The first FGD is composed of 30 layers of 192 segmented scintillating bars
, alternating between vertical and horizontal layers, while the second FGD is composed of 14 alternating layers of segmented scintillating bars and 6 water modules. Each bar has a hole down the center containing a WaveLength Shifting fiber which collects some of the light from scintillation and is read out by a MPPC
at one end. The other end of the fiber is mirrored with aluminum in order to increase overall light yield reaching the MPPC. The mirrored end also has an LED
light injection system for calibration and testing the integrity of the fibers. The second FGD is partially composed of water because the detector at Super-Kamiokande
is water-based. This water is maintained under subatmospheric pressure
to ensure that in case of a leak air will be sucked in rather than water spill out inside the FGD. Cross sections
on carbon and on water can be determined from a comparison of neutrino interactions in the two FGDs.
s produced in neutral current
interactions. The tracker and the Pi Zero detector are surrounded by an electromagnetic calorimeter and side range muon detector. Detection of Pi0s is important because they are one of the major backgrounds of detecting neutrinos at SuperK.
s. The detector was again designed as a cylindrical structure, this time 41.4 m tall and 39.3 m across. The detector was surrounded with a considerably more sophisticated outer detector which could not only act as a veto for cosmic muons but actually help in their reconstruction.
Super-Kamiokande started data taking in 1996 and has made several important measurements. These include precision measurement of the solar neutrino
flux using the elastic scattering
interactions, the first very strong evidence for neutrino oscillations, and a considerably more stringent limit on proton decay
.
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
experiment that is a collaboration between several countries, including Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...
, Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. It is the second generation follow up to the K2K experiment
K2K experiment
The K2K experiment was a neutrino experiment that ran from June 1999 to November 2004. It used muon neutrinos from a well-controlled and well-understood beam to verify the oscillations previously observed by Super-Kamiokande using atmospheric neutrinos...
, a similar long baseline neutrino oscillation experiment.
The J-PARC
J-PARC
J-PARC is a high intensity proton accelerator facility. It is a joint project between KEK and JAEA and is located at the Tokai campus of JAEA. J-PARC aims for the frontier in materials and life sciences, and nuclear and particle physics...
facility will produce an intense off-axis beam
Particle beam
A particle beam is a stream of charged or neutral particles which may be directed by magnets and focused by electrostatic lenses, although they may also be self-focusing ....
of muon neutrino
Muon neutrino
The muon neutrino is a subatomic lepton elementary particle which has the symbol and no net electric charge. Together with the muon it forms the second generation of leptons, hence its name muon neutrino. It was first hypothesized in the early 1940s by several people, and was discovered in 1962 by...
s. The beam is directed towards the Super-Kamiokande
Super-Kamiokande
Super-Kamiokande is a neutrino observatory which is under Mount Kamioka near the city of Hida, Gifu Prefecture, Japan...
detector, which is 295 km away. The main goal of T2K is to measure the oscillation of to and to measure the value of θ13, one of the parameters of the Pontecorvo–Maki–Nakagawa–Sakata matrix
Pontecorvo–Maki–Nakagawa–Sakata matrix
In particle physics, the Pontecorvo–Maki–Nakagawa–Sakata matrix , Maki–Nakagawa–Sakata matrix , lepton mixing matrix, or neutrino mixing matrix, is a unitary matrixThe PMNS matrix is not unitary in the seesaw model which contains information on the mismatch of quantum states of leptons when they...
.
On June 15, 2011, the T2K collaboration announced the observation of six electron neutrino-like events compared to an expected background of 1.5, a significance of 2.5 standard deviation
Standard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...
s.
Physics goals
The goal of the T2K experiment is to gain a more complete understanding of neutrino oscillation parameters. Previous neutrino experiments have observed the disappearance of muon neutrinos in a beam as they oscillate to tau neutrinos, but oscillation from to has not been observed. The reason for this that the mixing angle θ13, that controls the probability for this oscillation, is very small. T2K hopes to be the first experiment to measure the appearance of electron neutrinos in a muon neutrino beam. Precise measurements of the other neutrino mixing parameter Δm and θ23 are another aim of the experiment. Future upgrades to T2K could yield measurement of the CP violationCP violation
In particle physics, CP violation is a violation of the postulated CP-symmetry: the combination of C-symmetry and P-symmetry . CP-symmetry states that the laws of physics should be the same if a particle were interchanged with its antiparticle , and left and right were swapped...
phase δ by comparing oscillations of neutrinos to those of antineutrinos.
J-PARC
The J-PARCJ-PARC
J-PARC is a high intensity proton accelerator facility. It is a joint project between KEK and JAEA and is located at the Tokai campus of JAEA. J-PARC aims for the frontier in materials and life sciences, and nuclear and particle physics...
facility is a more powerful accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
than the KEK facility
KEK
, known as KEK, is a national organization whose purpose is to operate the largest particle physics laboratory in Japan, which is situated in Tsukuba of Ibaraki prefecture. Established in 1997. The term "KEK" is also used to refer to the laboratory itself, which employs approximately 900 employees...
used in the K2K experiment
K2K experiment
The K2K experiment was a neutrino experiment that ran from June 1999 to November 2004. It used muon neutrinos from a well-controlled and well-understood beam to verify the oscillations previously observed by Super-Kamiokande using atmospheric neutrinos...
. The main synchrotron
Synchrotron
A synchrotron is a particular type of cyclic particle accelerator in which the magnetic field and the electric field are carefully synchronised with the travelling particle beam. The proton synchrotron was originally conceived by Sir Marcus Oliphant...
will eventually be able to accelerate protons to 50 GeV/c. Protons colliding with the target material will produce (mostly) positive pion
Pion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
s which will decay into antimuon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
s and muon neutrino
Muon neutrino
The muon neutrino is a subatomic lepton elementary particle which has the symbol and no net electric charge. Together with the muon it forms the second generation of leptons, hence its name muon neutrino. It was first hypothesized in the early 1940s by several people, and was discovered in 1962 by...
s. The beam power is expected to be 0.75 MW delivering 110 times more neutrino events than K2K.
Off-axis
The neutrino beam at J-PARC is designed so that it is directed 2 to 3 degreesDegree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
away from the Super-Kamiokande detector
Super-Kamiokande
Super-Kamiokande is a neutrino observatory which is under Mount Kamioka near the city of Hida, Gifu Prefecture, Japan...
. This lowers the flux of neutrinos reaching the detector but provides a more desirable neutrino energy spectrum. Off-axis the peak energy is low with higher energies being suppressed. At the distance between Tokai
Tokai, Ibaraki
is a village located in Naka District, Ibaraki, Japan. It is approximately 120 km north of Tokyo, Japan on the Pacific coast.As of 1 January 2005, the village has an estimated population of 35,467 and a population density of 946.29 persons per km²...
and Kamioka, maximal neutrino oscillation is expected to occur at energies lower than 1 GeV.
Near detector
The near detector 280 meters (ND280) from the graphite target is a segmented detector composed of neutrino targets inside a tracking system surrounded by a magnet taken from the UA1 experiment. ND280 will be able to measure the neutrino beam's energy spectrum, flux, flavor contents, and interaction cross-sections before the neutrino oscillation. The detector is located 280 m from the target in the off-axis direction.Time projection chambers
Three time projection chamberTime projection chamber
In physics, a time projection chamber is a particle detector invented by David R. Nygren, an American physicist, at Lawrence Berkeley Laboratory in the late 1970s...
s (TPCs) will be able to measure the momenta
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
of muons produced by charged current
Charged current
The Charged current interaction is one of the ways in which subatomic particles can interact by means of the weak force. It is mediated by the and bosons....
reactions in the detector, this information will yield the neutrino energy spectrum. Also the TPCs can be used for particle identification.
Fine-grained detectors
Two fine-grained detectors (FGDs) are placed after the first and second TPCs. Together the FGDs and TPCs make up the tracker portion of ND280. The FGDs provide the active target mass for the neutrino interactions and are able to measure the short tracks of proton recoil.The first FGD is composed of 30 layers of 192 segmented scintillating bars
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
, alternating between vertical and horizontal layers, while the second FGD is composed of 14 alternating layers of segmented scintillating bars and 6 water modules. Each bar has a hole down the center containing a WaveLength Shifting fiber which collects some of the light from scintillation and is read out by a MPPC
Silicon photomultiplier
Silicon photomultipliers, often called "SiPM" in the literature, are Silicon single photon sensitive devices built from an avalanche photodiode array on common Si substrate. The idea behind this device is the detection of single photon events in sequentially connected Si APDs...
at one end. The other end of the fiber is mirrored with aluminum in order to increase overall light yield reaching the MPPC. The mirrored end also has an LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
light injection system for calibration and testing the integrity of the fibers. The second FGD is partially composed of water because the detector at Super-Kamiokande
Super-Kamiokande
Super-Kamiokande is a neutrino observatory which is under Mount Kamioka near the city of Hida, Gifu Prefecture, Japan...
is water-based. This water is maintained under subatmospheric pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
to ensure that in case of a leak air will be sucked in rather than water spill out inside the FGD. Cross sections
Cross section (physics)
A cross section is the effective area which governs the probability of some scattering or absorption event. Together with particle density and path length, it can be used to predict the total scattering probability via the Beer-Lambert law....
on carbon and on water can be determined from a comparison of neutrino interactions in the two FGDs.
Pi Zero detector
The Pi Zero detector is composed of layers of triangular scintillating plastic bars with embeded wavelength shifting fibers to channel light. Thousands of Multi-Pixel Photon Counters(MPPCs) are used to receive photon counts synchronously to detect particle events. These particle events are correlated to proton beam spill timings and are reconstructed using geometric and intensity data of photon counts. The P0D is used to measure neutral pionPion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
s produced in neutral current
Neutral current
Weak neutral current interactions are one of the ways in which subatomic particles can interact by means of the weak force. These interactions are mediated by the boson...
interactions. The tracker and the Pi Zero detector are surrounded by an electromagnetic calorimeter and side range muon detector. Detection of Pi0s is important because they are one of the major backgrounds of detecting neutrinos at SuperK.
Side Muon Range Detector
The Side Muon Range Detector (SMRD) consists of scintillator modules which are inserted into the gaps in the magnet. The SMRD records muons escaping the inner parts of the detector at large angles with respect to the beam direction. It can also act as a trigger for cosmic rays. Finally it can help identify beam interactions in the surrounding walls and in the magnet itself.Electromagnetic Calorimeter
The Electromagnetic Calorimeter (ECAL) surrounds the inner detectors (P0D,TPCs,FGDs) and consists of scintillator bars and lead absorber sheets between layers of scintillators. The ECAL has 13 modules: 1 downstream of the last TPC, six surrounding the P0D and six surrounding the tracker.Super-Kamiokande
The Super-Kamiokande detector is massive, even by particle physics standards. It consists of 50,000 tons of pure water surrounded by about 11,200 photomultiplier tubePhotomultiplier
Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...
s. The detector was again designed as a cylindrical structure, this time 41.4 m tall and 39.3 m across. The detector was surrounded with a considerably more sophisticated outer detector which could not only act as a veto for cosmic muons but actually help in their reconstruction.
Super-Kamiokande started data taking in 1996 and has made several important measurements. These include precision measurement of the solar neutrino
Solar neutrino
Electron neutrinos are produced in the Sun as a product of nuclear fusion. By far the largest fraction of neutrinos passing through the Earth are Solar neutrinos....
flux using the elastic scattering
Elastic scattering
In scattering theory and in particular in particle physics, elastic scattering is one of the specific forms of scattering. In this process, the kinetic energy of the incident particles is conserved, only their direction of propagation is modified .-Electron elastic scattering:When an alpha particle...
interactions, the first very strong evidence for neutrino oscillations, and a considerably more stringent limit on proton decay
Proton decay
In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...
.