MiniBooNE

MiniBooNE is a Cherenkov detector experiment at Fermilab designed to observe neutrino oscillations (BooNE is an acronym for the Booster Neutrino Experiment). A neutrino beam consisting primarily of muon neutrinos is directed at a detector filled with 800 tons of mineral oil (ultrarefined methylene compounds) and lined with 1,280 photomultiplier tubes.^[1] An excess of electron neutrino events in the detector would support the neutrino oscillation interpretation of the LSND (Liquid Scintillator Neutrino Detector) result.

The interior of the MiniBooNE detector.

MiniBooNE started collecting data in 2002^[2] and was still running in 2017.^[3] In May 2018, physicists of the MiniBooNE experiment reported a possible signal indicating the existence of sterile neutrinos.^[4]

History and motivation

Experimental observation of solar neutrinos and atmospheric neutrinos provided evidence for neutrino oscillations, implying that neutrinos have masses. Data from the LSND experiment at Los Alamos National Laboratory are controversial since they are not compatible with the oscillation parameters measured by other neutrino experiments in the framework of the Standard Model. Either there must be an extension to the Standard Model, or one of the experimental results must have a different explanation. Moreover, the KARMEN experiment in Karlsruhe^[5] examined a [low energy] region similar to the LSND experiment, but saw no indications of neutrino oscillations. This experiment was less sensitive than LSND, and both could be right.

Cosmological data can provide an indirect but rather model-dependent bound to the mass of sterile neutrinos, such as the m_s < 0.26 eV (0.44 eV) at 95% (99.9%) confidence limit given by Dodelson et al.^[6] However, cosmological data can be accommodated within models with different assumptions, such as that by Gelmini et al.^[7]

MiniBooNE was designed to unambiguously verify or refute the LSND controversial result in a controlled environment.

2007

After the beam was turned on in 2002, the first results came in late March 2007, and showed no evidence for muon neutrino to electron neutrino oscillations in the LSND [low energy] region, refuting a simple 2-neutrino oscillation interpretation of the LSND results.^[8] More advanced analyses of their data are currently being undertaken by the MiniBooNE collaboration; early indications are pointing towards the existence of the sterile neutrino,^[9] an effect interpreted by some physicists to be hinting of the existence of the bulk^[10] or Lorentz violation.^[11]

2008

A collaboration of MiniBooNE with other scientists a new experiment, called MicroBooNE, was designed to further investigate sterile neutrinos.^[12]

2018

With a study published on arXiv,^[3] the collaboration announced that the finding of neutrino oscillations at MiniBooNE are confirmed at a 4.8 sigma level and, when combined with data at LSND, at a 6.1 sigma level. This hints at the detection of sterile neutrinos and a significant deviation from known physics.^[13] The implication of the paper is that some of the muon neutrinos are flipping to sterile neutrinos before switching identity again to electron neutrinos.^[14]

References

1. "Detector". MiniBooNE Experiment Details. Fermilab. Retrieved 2015-12-07.
2. "MiniBooNE website".
3. The MiniBooNE Collaboration (May 2018). "Significant Excess of Electronlike Events in the MiniBooNE Short-Baseline Neutrino Experiment". Physical Review Letters. 121 (22): 221801. arXiv:1805.12028. Bibcode:2018PhRvL.121v1801A. doi:10.1103/PhysRevLett.121.221801. PMID 30547637. S2CID 53999758.
4. June 2018, Rafi Letzter 01 (2018-06-01). "A Major Physics Experiment Just Detected a Particle That Shouldn't Exist". livescience.com. Retrieved 2021-09-18.{{cite web}}: CS1 maint: numeric names: authors list (link)
5. "KARMEN experiment" (Press release). 3 August 2011. Archived from the original on 5 January 2013.
6. S. Dodelson; A. Melchiorri; A. Slosar (2006). "Is cosmology compatible with sterile neutrinos?". Physical Review Letters. 97 (4): 04301. arXiv:astro-ph/0511500. Bibcode:2006PhRvL..97d1301D. doi:10.1103/PhysRevLett.97.041301. PMID 16907563. S2CID 18263443.
7. G. Gelmini; S. Palomares-Ruiz & S. Pascoli (2004). "Low reheating temperature and the visible sterile neutrino". Physical Review Letters. 93 (8): 081302. arXiv:astro-ph/0403323. Bibcode:2004PhRvL..93h1302G. doi:10.1103/PhysRevLett.93.081302. PMID 15447171. S2CID 13111683.
8. A. A. Aguilar-Arevalo; et al. (MiniBooNE Collaboration) (2007). "A Search for Electron Neutrino Appearance at the Δm² ~ 1 eV² Scale". Physical Review Letters. 98 (23): 231801. arXiv:0704.1500. Bibcode:2007PhRvL..98w1801A. doi:10.1103/PhysRevLett.98.231801. PMID 17677898. S2CID 119315296.
9. M. Alpert (August 2007). "Dimensional Shortcuts". Scientific American. Archived from the original on 2013-01-24. Retrieved 2007-07-23.
10. H. Päs; S. Pakvasa; T.J. Weiler (2007). "Shortcuts in extra dimensions and neutrino physics". AIP Conference Proceedings. 903: 315–318. arXiv:hep-ph/0611263. Bibcode:2007AIPC..903..315P. doi:10.1063/1.2735188. S2CID 6745718.
11. T. Katori; V.A. Kostelecky; R. Tayloe (2006). "Global three-parameter model for neutrino oscillations using Lorentz violation". Physical Review D. 74 (10): 105009. arXiv:hep-ph/0606154. Bibcode:2006PhRvD..74j5009K. doi:10.1103/PhysRevD.74.105009. S2CID 6459548.
12. M. Alpert (September 2008). "Fermilab Looks for Visitors from Another Dimension". Scientific American. Retrieved 2008-09-23.
13. Letzter, Rafi (1 June 2018). "A Major Physics Experiment Just Detected A Particle That Shouldn't Exist". LiveScience. Retrieved 4 June 2018.
14. Has US physics lab found a new particle?. Paul Rincon, BBC News. 6 June 2018.

External links

• MiniBooNe first results press release and arXiv:0704.1500
• MiniBooNE website
  • MiniBooNE publications
  • Experiment details
• Overview of MiniBooNE for Mineral Oil Suppliers
• An informal discussion of the experiment and initial results
• Experiment Nixes Fourth Neutrino (April 2007 Scientific American)
• Dimensional Shortcuts - evidence for sterile neutrino; (August 2007; Scientific American)

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