Hyper-Kamiokande

Neutrino oscillations are a quantum mechanical phenomenon in which neutrinos change their flavour (neutrino flavours states: Electron neutrino, Muon neutrino, Tau neutrino) while moving, caused by the fact that the neutrino flavour states are a mixture of the neutrino mass states (ν₁, ν₂, ν₃ mass states with masses m₁, m₂, m₃, respectively). The oscillation probabilities depend on the six theoretical parameters:

• three mixing angles (θ₁₂, θ₂₃ and θ₁₃) governing the mixing between mass and flavour states,
• two mass squared differences (∆m²₂₁ and ∆m²₃₂, where ∆m²_ij = m²_i – m²_j)
• one phase (δ_CP) responsible for the matter-antimatter asymmetry (CP symmetry violation) in neutrino oscillations,

and two parameters which are chosen for a particular experiment:

• neutrino energy
• baseline – the distance travelled by neutrinos at which oscillations are measured.{{cite journal |author=Particle Data Group and Workman |title=Review of Particle Physics |journal=Progress of Theoretical and Experimental Physics |date=August 2022 |volume=2022 |issue=8 |pages=083C01 |doi=10.1093/ptep/ptac097|doi-access=free |hdl=11585/900713 |hdl-access=free }}{{rp|285–311}}{{rp|20–23}}

Continuing studies done by the T2K experiment, the HK far detector will measure the energy spectra of electron and muon neutrinos in the beam (produced at J-PARC as an almost pure muon neutrino beam) and compare it with the expectation in case of no oscillations, which is initially calculated based on neutrino flux and interaction models and improved by measurements performed by the near and intermediate detectors. For the HK/T2K neutrino beam peak energy (600 MeV) and the J-PARC – HK/SK detector distance (295 km), this corresponds to the first oscillation maximum, for oscillations driven by ∆m²₃₂. The J-PARC neutrino beam will run in both neutrino- and antineutrino-enhanced modes separately, meaning that neutrino measurements in each beam mode will provide information about muon (anti)neutrino survival probability P_{{{SubatomicParticle|Muon neutrino}} → {{SubatomicParticle|Muon neutrino}}}, P_{{{SubatomicParticle|Muon antineutrino}} → {{SubatomicParticle|Muon antineutrino}}}, and electron (anti)neutrino appearance probability P_{{{SubatomicParticle|Muon neutrino}} → {{SubatomicParticle|Electron neutrino}}}, P_{{{SubatomicParticle|Muon antineutrino}} → {{SubatomicParticle|Electron antineutrino}}} , where P_να → P_νβ is the probability that a neutrino originally of flavour α will be observed later as having flavour β.{{rp|202–224}}

File:Hk cp exclusion ability.png

Comparison of the appearance probabilities for neutrinos and antineutrinos (P_{{{SubatomicParticle|Muon neutrino}} → {{SubatomicParticle|Electron neutrino}}} versus P_{{{SubatomicParticle|Muon antineutrino}} → {{SubatomicParticle|Electron antineutrino}}}) allows measurement of the δ_CP phase. δ_CP ranges from {{math|−π}} to {{math|+π}} (from {{math|−180°}} to {{math|+180°}}), and 0 and ±π correspond to CP symmetry conservation. After 10 years of data taking, HK is expected to confirm at the 5σ confidence level or better if CP symmetry is violated in the neutrino oscillations for 57% of possible δ_CP values. CP violation is one of the conditions necessary to produce the excess of matter over antimatter at the early universe, which forms now our matter-built universe. Accelerator neutrinos will be used also to enhance the precision of the other oscillation parameters, |∆m²₃₂|, θ₂₃ and θ₁₃, as well as for neutrino interaction studies.{{rp|202–224}}

In order to determine the neutrino mass ordering (whether the ν₃ mass eigenstate is lighter or heavier than both ν₁ and ν₂), or equivalently the unknown sign of the ∆m²₃₂ parameter, neutrino oscillations must be observed in matter. With HK beam neutrinos (295 km, 600 MeV), the matter effect is small. In addition to beam neutrinos, the HK experiment studies atmospheric neutrinos, created by cosmic rays colliding with the Earth's atmosphere, producing neutrinos and other byproducts. These neutrinos are produced at all points on the globe, meaning that HK has access to neutrinos that have travelled through a wide range of distances through matter (from a few hundred metres to the Earth's diameter). These samples of neutrinos can be used to determine the neutrino mass ordering.{{rp|225–237}}

Ultimately, a combined beam neutrino and atmospheric neutrino analysis will provide the most sensitivity to the oscillation parameters δ_CP, |∆m²₃₂|, Sign function ∆m²₃₂, θ₂₃ and θ₁₃.{{rp|228–233}}

Core-collapse supernova explosions produce great quantities of neutrinos. For a supernova in the Andromeda Galaxy, 10 to 16 neutrino events are expected in the HK far detector. For a galactic supernova at a distance of 10 kpc about 50,000 to 94,000 neutrino interactions are expected during a few tens of seconds. For Betelgeuse at the distance 0.2 kpc, this rate could reach up to 10⁸ interactions per second and such a high event rate was taken into account in the detector electronics and data acquisition (DAQ) system design, meaning that no data would be lost. Time profiles of the number of events registered in HK and their mean energy would enable testing models of the explosion. Neutrino directional information in the HK far detector can provide an early warning for the electromagnetic supernova observation, and can be used in other multi-messenger observations.{{rp|263–280}}{{cite journal| author = the Hyper-Kamiokande collaboration| date = Jan 13, 2021| title = Supernova Model Discrimination with Hyper-Kamiokande| arxiv = 2101.05269| url = https://inspirehep.net/literature/1840585| journal = Astrophys. J.| volume = 916| number = 1| pages = 15| doi = 10.3847/1538-4357/abf7c4| bibcode = 2021ApJ...916...15A| doi-access = free}}

Neutrinos cumulatively produced by supernova explosions throughout the history of the universe are called supernova relic neutrinos (SRN) or diffuse supernova neutrino background (DSNB) and they carry information about star formation history. Because of a low flux (few tens/cm²/sec.), they have not yet been discovered. With ten years of data taking, HK is expected to detect about 40 SRN events in the energy range 16–30 MeV.{{rp|276–280}}{{cite book| last1 = Yano| first1 = Takatomi| title = Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021)| chapter = Prospects for neutrino astrophysics with Hyper-Kamiokande| year = 2021 | chapter-url = https://inspirehep.net/literature/1930815 | volume = | pages = 1193| doi = 10.22323/1.395.1193| doi-access = free| hdl = 20.500.11850/589619| hdl-access = free}}

For the solar {{SubatomicParticle|electron neutrino}}'s, the HK experiment goals are:

• Search for a day-night asymmetry in the neutrino flux – resulting from different distances travelled in matter (during the night neutrinos additionally cross the Earth before entering the detector) and thus the different oscillation probabilities caused by the matter effect.{{rp|238–244}}
• Measurement of the {{SubatomicParticle|electron neutrino}} survival probability for neutrino energies between 2 and 7 MeV – i.e. between regions dominated by oscillations in vacuum and oscillations in matter, respectively – which is sensitive to new physics models, like sterile neutrinos or non-standard interactions.{{rp|238–244}}{{cite journal| author = Maltoni, Michele and Smirnov, Alexei Yu.| date = Jul 19, 2015| title = Solar neutrinos and neutrino physics| arxiv = 1507.05287| url = https://inspirehep.net/literature/1383834| journal = Eur. Phys. J. A| volume = 52| number = 4| pages = 87| doi = 10.1140/epja/i2016-16087-0| s2cid = 254115998}}
• The first observation of neutrinos from the hep channel: $\{^3\}\backslash text\{He\}\; +\; \backslash text\{p\}\; \backslash to\; \{^4\}\backslash text\{He\}\; +\; \backslash text\{e\}^\{+\}\; +\; \backslash operatorname\{\backslash nu\}\_\backslash text\{e\}$ predicted by the standard solar model.{{rp|238–244}}
• Comparison of the neutrino flux with the solar activity (e.g. the 11-year solar cycle).{{cite web| url = https://www-sk.icrr.u-tokyo.ac.jp/en/hk/about/research/| title= Hyper-Kamiokande website: Cosmic Neutrino Observation: Solar neutrinos}}

Geoneutrinos are produced in decays of radionuclides inside the Earth. Hyper-Kamiokande geoneutrino studies will help assess the Earth's core chemical composition, which is connected with the generation of the geomagnetic field.{{rp|292–293}}

The decay of a free proton into lighter subatomic particles has never been observed, but it is predicted by some grand unified theories (GUT) and results from baryon number (B) violation. B violation is one of the conditions needed to explain the predominance of matter over antimatter in the universe. The main channels studied by HK are {{SubatomicParticle|Proton+}} → {{SubatomicParticle|link=yes|Positron}} + {{SubatomicParticle|link=yes|Pion0}} which is favoured by many GUT models and {{SubatomicParticle|Proton+}} → {{SubatomicParticle|link=yes|Antineutrino}} + {{SubatomicParticle|link=yes|Kaon+}} predicted by theories including supersymmetry.

{{cite journal

|last1 = Mine |first1 = Shunichi

|year = 2023

|title = Nucleon decay: theory and experimental overview

|journal = Zenodo

|doi = 10.5281/zenodo.10493165

}}

After ten years of data taking, (in case no decay will be observed) HK is expected to increase the lower limit of the proton mean lifetime from 1.6 · 10³⁴ to 6.3 · 10³⁴ years for its most sensitive decay channel ({{SubatomicParticle|Proton+}} → {{SubatomicParticle|Positron}} + {{SubatomicParticle|Pion0}}) and from 0.7 · 10³⁴ to 2.0 · 10³⁴ years for the {{SubatomicParticle|Proton+}} → {{SubatomicParticle|Antineutrino}} + {{SubatomicParticle|Kaon+}} channel.

{{Cite journal |author1 = K. S. Babu | author2 = E. Kearns |author3 = U. Al-Binni | display-authors=2 |title = Baryon Number Violation |journal = Proceedings, 2013 Community Summer Study on the Future of U.S. Particle Physics: Snowmass on the Mississippi (CSS2013) |date = 2013-11-20 |location = Minneapolis, MN, USA |arxiv = 1311.5285}}

Dark matter is a hypothetical, non-luminous form of matter proposed to explain numerous astronomical observations suggesting the existence of additional invisible mass in galaxies. If the dark matter particles interact weakly, they may produce neutrinos through annihilation or decay. Those neutrinos could be visible in the HK detector as an excess of neutrinos from the direction of large gravitational potentials such as the galactic centre, the Sun or the Earth, over an isotropic atmospheric neutrino background.{{rp|281–286}}

The Hyper-Kamiokande experiment consists of an accelerator neutrino beamline, a set of near detectors, the intermediate detector and the far detector (also called Hyper-Kamiokande).

The far detector by itself will be used for proton decay searches and studies of neutrinos from natural sources. All the above elements will serve for the accelerator neutrino oscillation studies. Before launching the HK experiment, the T2K experiment will finish data taking and HK will take over its neutrino beamline and set of near detectors, while the intermediate and the far detectors have to be constructed anew.{{cite web |last1=Vilela |first1=Cristovao |title=The status of T2K and Hyper-Kamiokande experiments |url=https://indico.lip.pt/event/592/contributions/3550/ |website=PANIC 2021 Conference |date=September 5–10, 2021 |access-date=2021-09-29 |archive-date=2021-09-29 |archive-url=https://web.archive.org/web/20210929161023/https://indico.lip.pt/event/592/contributions/3550/ |url-status=live }}

{{multiple image

| align = right

| perrow = 2 / 1

| total_width = 460

| image1 = Numu flux iwcd.png

| caption1 = The muon neutrino flux at the IWCD detector for different off-axis angles

| image2 = Nue flux iwcd.png

| caption2 = The electron neutrino flux at the IWCD detector for different off-axis angles

}}

{{main|T2K experiment#Neutrino beam}}

{{main|T2K experiment#Beam upgrade}}

{{main|T2K experiment#Near detectors}}

{{main|T2K experiment#ND280 Upgrade}}

The Intermediate Water Cherenkov Detector (IWCD) will be located at a distance of around {{convert|750|m}} from the neutrino production place. It will be a cylinder filled with water of {{convert|10|m}} diameter and {{convert|50|m}} height with a {{convert|10|m}} tall structure instrumented with around 400 multi-PMT modules (mPMTs), each consisting of nineteen {{convert|8|cm}} diameter PhotoMultiplier Tubes (PMTs) encapsulated in a water-proof vessel. The structure will be moved in a vertical direction by a crane system, providing measurements of neutrino interactions at different off-axis angles (angles to the neutrino beam centre), spanning from 1° at the bottom to 4° at the top, and thus for different neutrino energy spectra.The average energy of neutrinos decreases with the deviation from the beam axis.

Combining the results from different off-axis angles, it is possible to extract the results for nearly monoenergetic neutrino spectrum without relying on theoretical models of neutrino interactions to reconstruct neutrino energy. Usage of the same type of detector as the far detector with almost the same angular and momentum acceptance allows comparison of results from these two detectors without relying on detector response simulations. These two facts, independence from the neutrino interaction and detector response models, will enable HK to minimise systematic error in the oscillation analysis. Additional advantages of such a design of the detector is the possibility to search for sterile oscillation patterns for different off-axis angles and to obtain a cleaner sample of electron neutrino interactions, whose fraction is larger for larger off-axis angles.{{rp|47–50}}{{cite arXiv |author=nuPRISM Collaboration |title=Letter of Intent to Construct a nuPRISM Detector in the J-PARC Neutrino Beamline |date=13 December 2014 |class=physics.ins-det |eprint=1412.3086}}{{cite web |author=nuPRISM Collaboration |title=Proposal for the NuPRISM Experiment in the J-PARC Neutrino Beamline |url=https://j-parc.jp/researcher/Hadron/en/pac_1607/pdf/P61_2016-17.pdf |date=7 July 2016 |access-date=1 April 2020 |archive-date=2 December 2020 |archive-url=https://web.archive.org/web/20201202213200/https://j-parc.jp/researcher/Hadron/en/pac_1607/pdf/P61_2016-17.pdf |url-status=live }}{{cite web |author1=Mark Hartz |title= Near Detectors for the Hyper-K Neutrino Experiment |url=https://indico.cern.ch/event/868940/contributions/3817119/ |website=40th International Conference on High Energy Physics (ICHEP 2020) |date=2020-07-29}}{{cite web |author1=Umut Kose (on behalf of the Hyper-Kamiokande Collaboration) |title=The Hyper-Kamiokande Experiment: Status and Prospect |url=https://indico.cern.ch/event/1303630/contributions/5620874/ |website=The 17th International Workshop on Tau Lepton Physics (TAU2023) |date=2023-12-07 |access-date=2024-02-08}}

File:Hyper-Kamiokande scheme.png

The Hyper-Kamiokande detector will be built {{convert|650|m}} under the peak of Nijuugo Mountain in the Tochibora mine, {{convert|8|km}} south from the Super-Kamiokande (SK) detector. Both detectors will be at the same off-axis angle (2.5°) to the neutrino beam centre and at the same distance ({{convert|295|km}}) from the beam production place in J-PARC.The Super-Kamiokande detector serves as a far detector for the neutrino oscillation analysis by the T2K experiment. However, Super-Kamiokande is also a separate experiment in the matter of proton decay searches and studies of neutrinos from natural sources.{{rp|35}}{{cite web| url = https://www-sk.icrr.u-tokyo.ac.jp/en/hk/about/detector/| title=Hyper-Kamiokande website: Hyper-Kamiokande Detector}}

File:HK ID PMT.jpg

{{multiple image

| align = right

| perrow = 2

| total_width = 330

| image3 = Prototipo completo piccola.jpg

| caption3 = A prototype of a mPMT for the Hyper-Kamiokande Far Detector Inner Detector

| image4 = HK mPMT scheme.jpg

| caption4 = A schematic of a mPMT for the Hyper-Kamiokande Far Detector Inner Detector

| image5 = HK OD PMT.jpg

| caption5 = 3-inch PMT (Photomultiplier) and WLS (Wavelength-Shifting Fiber) plate for Hyper-Kamiokande Far Detector Outer Detector

| image1 =

}}

HK will be a water Cherenkov detector, 5 times larger (258 kton of water) than the SK detector. It will be a cylindrical tank of {{convert|68|m}} diameter and {{convert|71|m}} height. The tank volume will be divided into the Inner Detector (ID) and the Outer Detector (OD) by a 60 cm-wide inactive cylindrical structure, with its outer edge positioned 1 meter away from vertical and 2 meters away from horizontal tank walls. The structure will optically separate ID from OD and will hold PhotoMultiplier Tubes (PMTs) looking both inwards to the ID and outwards to the OD.

In the ID, there will be at least 20,000 {{convert|50|cm}} diameter PhotoMultiplier Tubes (PMT) of R12860 type by Hamamatsu Photonics and approximately 800 multi-PMT modules (mPMTs). Each mPMT module consists of nineteen {{convert|8|cm}} diameter photomultiplier tubes encapsulated in a water-proof vessel. The OD will be instrumented with at least 3,600 {{convert|8|cm}} diameter PMTs coupled with 0.6×30×30 cm³ wavelength shifting (WLS) plates (plates will collect incident photons and transport them to their coupled PMT) and will serve as a vetoVeto is part of a detector where no activity should be registered to accept an event. Such a requirement allows constraining the number of background events in a selected sample. to distinguish interactions occurring inside from particles entering from the outside of the detector (mainly cosmic-ray muons).{{cite journal | author = Jan Kisiel (Silesia U.) for the Hyper-Kamiokande collaboration | date = Jun 28, 2023 | title = Photodetection and electronic system for the Hyper-Kamiokande Water Cherenkov detectors | url = https://inspirehep.net/literature/2675891 | journal = Nucl. Instrum. Meth. A | volume = 1055 | pages = 168482 | doi = 10.1016/j.nima.2023.168482| bibcode = 2023NIMPA105568482K | doi-access = free }}

File:J-PARC neutrino beam Japan to Korea.png

HK detector construction began in 2020 and the start of data collection is expected in 2027.{{rp|24}} Studies have also been undertaken on the feasibility and physics benefits of building a second, identical water-Cherenkov tank in South Korea around 1100 km from J-PARC, which would be operational 6 years after the first tank.{{cite journal| author = Francesca Di Lodovico (Queen Mary, U. of London) for the Hyper-Kamiokande collaboration| date = Sep 20, 2017| title = The Hyper-Kamiokande Experiment| url = https://inspirehep.net/literature/1625581| journal = J. Phys. Conf. Ser.| volume = 888| number = 1| pages = 012020| doi = 10.1088/1742-6596/888/1/012020|bibcode=2017JPhCS.888a2020D|doi-access=free}}{{cite journal| author=Hyper-Kamiokande Proto-Collaboration| date = June 20, 2019 | title = Physics potentials with the second Hyper-Kamiokande detector in Korea | url = https://academic.oup.com/ptep/article/2018/6/063C01/5041972 | journal = Progress of Theoretical and Experimental Physics | volume = 2018 | issue = 6 | pages = 063C01 | arxiv =1611.06118 | doi = 10.1093/ptep/pty044}}

File:Hyper-Kamiokande detector construction schedule.png

A history of large water Cherenkov detectors in Japan, and long-baseline neutrino oscillation experiments associated with them, excluding HK:

• 1983-1996: Kamiokande (Kamioka Nucleon Decay Experiment), which main goal was proton decay searches (the Nobel Prize in Physics 2002 for Masatoshi Koshiba) – the predecessor of Super-Kamiokande
• 1996–present: Super-Kamiokande experiment – the predecessor of the Hyper-Kamiokande experiment, studying neutrinos from natural sources and searching for proton decay (the Nobel Prize in Physics 2015 for Takaaki Kajita)
• 1999–2004: K2K experiment – the predecessor of the T2K experiment
• 2010–present: T2K experiment – the predecessor of the Hyper-Kamiokande experiment, studying accelerator neutrino oscillations

A history of the Hyper-Kamiokande experiment:

• September 1999: First ideas of the new experiment presented{{cite conference|last=Shiozawa|first=M.|title=Study of 1-Megaton water Cherenkov detectors for the future proton decay search|date=23–25 September 1999|book-title=AIP Conf.Proc. 533 (2000) 1, 21–24|doi=10.1063/1.1361719|location= Stony Brook, NY, United States|conference=International Workshop on Next Generation Nucleon Decay and Neutrino Detector (NNN99)}}
• 2000: The name "Hyper-Kamiokande" used for the first time{{cite journal |last=Nakamura|first=K.|title=HYPER-KAMIOKANDE: A next generation water Cherenkov detector for a nucleon decay experiment |url=https://inspirehep.net/literature/550304 |journal =Part of Neutrino Oscillations and Their Origin. Proceedings, 1st Workshop, Fujiyoshida, Japan, February 11–13|pages =359–363 |year =2000}}
• September 2011: Submitting LOI{{cite arXiv |author1=K. Abe|author2=T. Abe|author3=H Aihara|author4=Y. Fukuda| author5=Y. Hayato|display-authors=1 |title=Letter of Intent: The Hyper-Kamiokande Experiment --- Detector Design and Physics Potential --- |date=15 September 2011 |class=hep-ex |eprint=1109.3262}}
• January 2015: MoU for cooperation in the Hyper-Kamiokande project signed by two host institutions: ICRR and KEK. Formation of the Hyper-Kamiokande proto-collaboration{{cite web| url = https://www-sk.icrr.u-tokyo.ac.jp/en/hk/news/detail/449| date= February 5, 2015| title=Hyper-Kamiokande website: The Inaugural Symposium of the Hyper-K Proto-Collaboration| location = Kashiwa, Japan}}{{cite news| publisher= CERN Courier | date= 9 April 2015 | title= Proto-collaboration formed to promote Hyper-Kamiokande| url= https://cerncourier.com/a/proto-collaboration-formed-to-promote-hyper-kamiokande/}}
• May 2018: Hyper-Kamiokande Design Report
• September 2018: Seed funding from MEXT allocated in 2019{{cite news| publisher= CERN Courier | date= 28 September 2018 | title= Hyper-Kamiokande construction to start in 2020| url= https://cerncourier.com/a/hyper-kamiokande-construction-to-start-in-2020/}}
• February 2020: The project officially approved by the Japanese Diet
• June 2020: Formation of the Hyper-Kamiokande collaboration
• May 2021: Start of the HK detector access tunnel excavation{{cite news| publisher= The University of Tokyo | date= 28 May 2021 | title= Groundbreaking ceremony for Hyper-Kamiokande held in Hida, Japan | url= https://www.u-tokyo.ac.jp/focus/en/articles/z0208_00113.html}}
• 2021: Beginning of the photomultiplier tubes mass production{{cite book |last1=Itow, on behalf of the Hyper-Kamiokande Collaboration |first1=Y. |title=Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021) |chapter=Construction status and prospects of the Hyper-Kamiokande project |year=2021 |page=1192 |publisher=Proceedings of Science|doi=10.22323/1.395.1192 |s2cid=199687331 |doi-access=free }}
• February 2022: Completion of the access tunnel construction{{cite web |title=Hyper-Kamiokande experiment; Excavation of the gigantic underground cavern has finally begun |url=https://www-sk.icrr.u-tokyo.ac.jp/en/news/detail/684}}
• October 2023: Completion of the HK detector main cavern dome section{{cite web| url = https://www-sk.icrr.u-tokyo.ac.jp/en/news/detail/738| date= 11 October 2023| title=Kamioka Observatory website: Completion of the main cavern dome section of the Hyper-Kamiokande experiment}}
• 2027: The expected beginning of data-taking

{{reflist|group=note}}

• Super-Kamiokande, predecessor
• T2K experiment, Japan
• Deep Underground Neutrino Experiment, South Dakota

• {{cite journal|doi=10.1126/science.347.6222.598 |pmid=25657225|year = 2015|last1 = Normile|first1 = D|title = Particle physics. Japanese neutrino physicists think really big|journal=Science|volume=347|issue=6222|pages=598|doi-access=free}}

{{reflist}}

{{Commons|T2K}}

• [https://www-sk.icrr.u-tokyo.ac.jp/en/hk/ Hyper-Kamiokande website]

{{Neutrino detectors}}{{University of Tokyo}}{{Proton decay experiments}}

Category:Neutrino observatories

Category:Astronomical observatories in Japan