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Enriched Xenon Observatory

April 09, 2024

32°22′18″N 103°47′37″W / 32.37167°N 103.79361°W / 32.37167; -103.79361

The Enriched Xenon Observatory (EXO) is a particle physics experiment searching for neutrinoless double beta decay of xenon-136 at WIPP near Carlsbad, New Mexico, U.S.

Neutrinoless double beta decay (0νββ) detection would prove the Majorana nature of neutrinos and impact the neutrino mass values and ordering. These are important open topics in particle physics.

EXO currently has a 200-kilogram xenon liquid time projection chamber (EXO-200) with R&D efforts on a ton-scale experiment (nEXO). Xenon double beta decay was detected and limits have been set for 0νββ.

Overview edit

EXO measures the rate of neutrinoless decay events above the expected background of similar signals, to find or limit the double beta decay half-life, which relates to the effective neutrino mass using nuclear matrix elements. A limit on effective neutrino mass below 0.01 eV would determine the neutrino mass order. The effective neutrino mass is dependent on the lightest neutrino mass in such a way that that bound indicates the normal mass hierarchy.[1]

The expected rate of 0νββ events is very low, so background radiation is a significant problem. WIPP has 650 metres (2,130 ft) of rock overburden—equivalent to 1,600 metres (5,200 ft) of water—to screen incoming cosmic rays. Lead shielding and a cryostat also protect the setup. The neutrinoless decays would appear as narrow spike in the energy spectrum around the xenon Q-value (Qββ = 2457.8 keV), which is fairly high and above most gamma decays.

EXO-200 edit

History edit

EXO-200 was designed with a goal of less than 40 events per year within two standard deviations of expected decay energy. This background was achieved by selecting and screening all materials for radiopurity. Originally the vessel was to be made of Teflon, but the final design of the vessel uses thin, ultra-pure copper.[2] EXO-200 was relocated from Stanford to WIPP in the summer of 2007.[3] Assembly and commissioning continued until the end of 2009 with data taking beginning in May 2011. Calibration was done using 228Th, 137Cs, and 60Co gamma sources.

Design edit

The prototype EXO-200 uses a copper cylindrical time projection chamber filled with 150 kilograms (331 lb) of pure liquid xenon. Xenon is a scintillator, so decay particles produce prompt light which is detected by avalanche photodiodes, providing the event time. A large electric field drives ionization electrons to wires for collection. The time between the light and first collection determines the z coordinate of the event, while a grid of wires determines the radial and angular coordinates.

  •  
    The EXO-200 cryostat installed underground at WIPP.
  •  
    The EXO-200 cleanrooms installed underground at WIPP.

Results edit

The background from earth radioactivity(Th/U) and 137Xe contamination led to ≈2×10−3 counts/(keV·kg·yr) in the detector. Energy resolution near Qββ of 1.53% was achieved.[4]

In August 2011, EXO-200 was the first experiment to observe double beta decay of 136Xe, with a half life of 2.11×1021 years.[5] This is the slowest directly observed process. An improved half life of 2.165 ±0.016(stat) ±0.059(sys) × 1021 years was published in 2014.[6] EXO set a limit on neutrinoless beta decay of 1.6×1025 years in 2012.[7] A revised analysis of run 2 data with 100 kg·yr exposure, reported in the June issue of Nature reduced the limits on half-life to 1.1×1025 yr, and mass to 450 meV.[4] This was used to confirm the power of the design and validate the proposed expansion.

Additional running for two years was taken.

EXO-200 has performed two scientific operations, Phase I (2011-2014) and after upgrades, Phase II (2016 - 2018) for a total exposure of 234.1 kg·yr. No evidence of neutrinoless double beta decay has been found in the combined Phase I and II data, giving the lower bound of   years for the half-life and upper mass of 239 meV.[8] Phase II was the final operation of EXO-200.

nEXO edit

A ton-scale experiment, nEXO ("next EXO"), must overcome many backgrounds. The EXO collaboration is exploring many possibilities to do so, including barium tagging in liquid xenon. Any double beta decay event will leave behind a daughter barium ion, while backgrounds, such as radioactive impurities or neutrons, will not. Requiring a barium ion at the location of an event eliminates all backgrounds. Tagging of a single ion of barium has been demonstrated and progress has been made on a method for extracting ions out of the liquid xenon. A freezing probe method has been demonstrated, and gaseous tagging is also being developed.[9]

The 2014 EXO-200 paper indicated a 5000 kg TPC can improve the background by xenon self-shielding and better electronics. Diameter would be increased to 130 cm and a water tank would be added as shielding and muon veto. This is much larger than the attenuation length for gamma rays. Radiopure copper for nEXO has been completed. It is planned for installation in the SNOLAB "Cryopit".[10]: 17 [11]: 7 

An Oct. 2017 paper details the experiment and discusses the sensitivity and the discovery potential of nEXO for neutrinoless double beta decay.[12] Details on the ionization readout of the TPC have also been published.[13]

The pre-Conceptual Design Report (pCDR) for nEXO was published in 2018. The planned location is SNOLAB, Canada.

References edit

  1. ^ See P. Vogel, A. Piepke (2007). "Neutrinoless Double-beta decay", in W.-M. Yao et al. (Particle Data Group) (2006). "Review of Particle Physics". Journal of Physics G. 33 (1): 1–1232. arXiv:astro-ph/0601168. Bibcode:2006JPhG...33....1Y. doi:10.1088/0954-3899/33/1/001.
  2. ^ D. Leonard (2008). "Systematic study of trace radioactive impurities in candidate construction materials for EXO-200". Nuclear Instruments and Methods in Physics Research Section A. 591 (3): 490–509. arXiv:0709.4524. Bibcode:2008NIMPA.591..490L. doi:10.1016/j.nima.2008.03.001. S2CID 118334959.
  3. ^ "EXO project equipment successfully placed underground at WIPP" (PDF) (Press release). DOENews. 24 July 2007.
  4. ^ a b Albert, J. B.; Auty, D. J.; Barbeau, P. S.; Beauchamp, E.; Beck, D.; Belov, V.; Benitez-Medina, C.; Bonatt, J.; Breidenbach, M.; Brunner, T.; Burenkov, A.; Cao, G. F.; Chambers, C.; Chaves, J.; Cleveland, B.; Coon, M.; Craycraft, A.; Daniels, T.; Danilov, M.; Daugherty, S. J.; Davis, C. G.; Davis, J.; Devoe, R.; Delaquis, S.; Didberidze, T.; Dolgolenko, A.; Dolinski, M. J.; Dunford, M.; Fairbank Jr, W.; et al. (12 June 2014). "Search for Majorana neutrinos with the first two years of EXO-200 data". Nature. 510 (7504): 229–234. arXiv:1402.6956. Bibcode:2014Natur.510..229T. doi:10.1038/nature13432. PMID 24896189. S2CID 2740003.
  5. ^ N. Ackerman; et al. (2011). "Observation of Two-Neutrino Double-Beta Decay in 136Xe with EXO-200". Physical Review Letters. 107 (21): 212501. arXiv:1108.4193. Bibcode:2011PhRvL.107u2501A. doi:10.1103/PhysRevLett.107.212501. PMID 22181874. S2CID 40334443.
  6. ^ Albert, J. B.; Auger, M.; Auty, D. J.; Barbeau, P. S.; Beauchamp, E.; Beck, D.; Belov, V.; Benitez-Medina, C.; Bonatt, J.; Breidenbach, M.; Brunner, T.; Burenkov, A.; Cao, G. F.; Chambers, C.; Chaves, J.; Cleveland, B.; Cook, S.; Craycraft, A.; Daniels, T.; Danilov, M.; Daugherty, S. J.; Davis, C. G.; Davis, J.; Devoe, R.; Delaquis, S.; Dobi, A.; Dolgolenko, A.; Dolinski, M. J.; Dunford, M.; et al. (2014). "An improved measurement of the 2νββ half-life of Xe-136 with EXO-200". Phys. Rev. C. 89 (1): 015502. arXiv:1306.6106. Bibcode:2014PhRvC..89a5502A. doi:10.1103/PhysRevC.89.015502.
  7. ^ M. Auger; et al. (2012). "Search for Neutrinoless Double-Beta Decay in 136Xe with EXO-200". Physical Review Letters. 109 (3): 032505. arXiv:1205.5608. Bibcode:2012PhRvL.109c2505A. doi:10.1103/PhysRevLett.109.032505. PMID 22861843. S2CID 29698686.
  8. ^ Anton, G.; et al. (18 October 2019). "Search for Neutrinoless Double-$\ensuremath{\beta}$ Decay with the Complete EXO-200 Dataset". Physical Review Letters. 123 (16): 161802. arXiv:1906.02723. doi:10.1103/PhysRevLett.123.161802. PMID 31702371. S2CID 174803277.
  9. ^ P. Fierlinger; et al. (2008). "A microfabricated sensor for thin dielectric layers". Review of Scientific Instruments. 79 (4): 045101–045101–7. arXiv:0706.0540. Bibcode:2008RScI...79d5101F. doi:10.1063/1.2906402. PMID 18447546. S2CID 2950473.
  10. ^ Yang, Liang (8 July 2016). (PDF). XXVII International Conference on Neutrino Physics and Astrophysics (presentation). London. Archived from the original (PDF) on 17 November 2016. Retrieved 16 November 2016. Video available at Neutrino Conference 2016 - Friday (part 1) on YouTube.
  11. ^ MacLellan, Ryan (25 September 2017). nEXO: a tonne-scale next-generation double-beta decay experiment. XV International Conference on Topics in Astroparticle and Underground Physics (TAUP 2017) (presentation). Sudbury, Canada.
  12. ^ Albert, J. B.; et al. (nEXO Collaboration) (2018). "Sensitivity and Discovery Potential of nEXO to Neutrinoless Double Beta Decay". Physical Review C. 97 (6): 065503. arXiv:1710.05075. Bibcode:2018PhRvC..97f5503A. doi:10.1103/PhysRevC.97.065503. S2CID 67854591. LLNL-JRNL-737682
  13. ^ Jewell, M.; et al. (nEXO Collaboration) (14 October 2017). "Characterization of an Ionization Readout Tile for nEXO". Journal of Instrumentation. 13: P01006. arXiv:1710.05109. doi:10.1088/1748-0221/13/01/P01006. S2CID 56297955.

External links edit

  • EXO web site
  • nEXO web site
  • EXO experiment record on INSPIRE-HEP

April 09, 2024
enriched, xenon, observatory, 37167, 79361, 37167, 79361the, particle, physics, experiment, searching, neutrinoless, double, beta, decay, xenon, wipp, near, carlsbad, mexico, neutrinoless, double, beta, decay, 0νββ, detection, would, prove, majorana, nature, n. 32 22 18 N 103 47 37 W 32 37167 N 103 79361 W 32 37167 103 79361The Enriched Xenon Observatory EXO is a particle physics experiment searching for neutrinoless double beta decay of xenon 136 at WIPP near Carlsbad New Mexico U S Neutrinoless double beta decay 0nbb detection would prove the Majorana nature of neutrinos and impact the neutrino mass values and ordering These are important open topics in particle physics EXO currently has a 200 kilogram xenon liquid time projection chamber EXO 200 with R amp D efforts on a ton scale experiment nEXO Xenon double beta decay was detected and limits have been set for 0nbb Contents 1 Overview 2 EXO 200 2 1 History 2 2 Design 2 3 Results 3 nEXO 4 References 5 External linksOverview editEXO measures the rate of neutrinoless decay events above the expected background of similar signals to find or limit the double beta decay half life which relates to the effective neutrino mass using nuclear matrix elements A limit on effective neutrino mass below 0 01 eV would determine the neutrino mass order The effective neutrino mass is dependent on the lightest neutrino mass in such a way that that bound indicates the normal mass hierarchy 1 The expected rate of 0nbb events is very low so background radiation is a significant problem WIPP has 650 metres 2 130 ft of rock overburden equivalent to 1 600 metres 5 200 ft of water to screen incoming cosmic rays Lead shielding and a cryostat also protect the setup The neutrinoless decays would appear as narrow spike in the energy spectrum around the xenon Q value Qbb 2457 8 keV which is fairly high and above most gamma decays EXO 200 editHistory edit EXO 200 was designed with a goal of less than 40 events per year within two standard deviations of expected decay energy This background was achieved by selecting and screening all materials for radiopurity Originally the vessel was to be made of Teflon but the final design of the vessel uses thin ultra pure copper 2 EXO 200 was relocated from Stanford to WIPP in the summer of 2007 3 Assembly and commissioning continued until the end of 2009 with data taking beginning in May 2011 Calibration was done using 228Th 137Cs and 60Co gamma sources Design edit The prototype EXO 200 uses a copper cylindrical time projection chamber filled with 150 kilograms 331 lb of pure liquid xenon Xenon is a scintillator so decay particles produce prompt light which is detected by avalanche photodiodes providing the event time A large electric field drives ionization electrons to wires for collection The time between the light and first collection determines the z coordinate of the event while a grid of wires determines the radial and angular coordinates nbsp The EXO 200 cryostat installed underground at WIPP nbsp The EXO 200 cleanrooms installed underground at WIPP Results edit The background from earth radioactivity Th U and 137Xe contamination led to 2 10 3 counts keV kg yr in the detector Energy resolution near Qbb of 1 53 was achieved 4 In August 2011 EXO 200 was the first experiment to observe double beta decay of 136Xe with a half life of 2 11 1021 years 5 This is the slowest directly observed process An improved half life of 2 165 0 016 stat 0 059 sys 1021 years was published in 2014 6 EXO set a limit on neutrinoless beta decay of 1 6 1025 years in 2012 7 A revised analysis of run 2 data with 100 kg yr exposure reported in the June issue of Nature reduced the limits on half life to 1 1 1025 yr and mass to 450 meV 4 This was used to confirm the power of the design and validate the proposed expansion Additional running for two years was taken EXO 200 has performed two scientific operations Phase I 2011 2014 and after upgrades Phase II 2016 2018 for a total exposure of 234 1 kg yr No evidence of neutrinoless double beta decay has been found in the combined Phase I and II data giving the lower bound of 3 5 1025 displaystyle 3 5 cdot 10 25 nbsp years for the half life and upper mass of 239 meV 8 Phase II was the final operation of EXO 200 nEXO editA ton scale experiment nEXO next EXO must overcome many backgrounds The EXO collaboration is exploring many possibilities to do so including barium tagging in liquid xenon Any double beta decay event will leave behind a daughter barium ion while backgrounds such as radioactive impurities or neutrons will not Requiring a barium ion at the location of an event eliminates all backgrounds Tagging of a single ion of barium has been demonstrated and progress has been made on a method for extracting ions out of the liquid xenon A freezing probe method has been demonstrated and gaseous tagging is also being developed 9 The 2014 EXO 200 paper indicated a 5000 kg TPC can improve the background by xenon self shielding and better electronics Diameter would be increased to 130 cm and a water tank would be added as shielding and muon veto This is much larger than the attenuation length for gamma rays Radiopure copper for nEXO has been completed It is planned for installation in the SNOLAB Cryopit 10 17 11 7 An Oct 2017 paper details the experiment and discusses the sensitivity and the discovery potential of nEXO for neutrinoless double beta decay 12 Details on the ionization readout of the TPC have also been published 13 The pre Conceptual Design Report pCDR for nEXO was published in 2018 The planned location is SNOLAB Canada References edit See P Vogel A Piepke 2007 Neutrinoless Double beta decay in W M Yao et al Particle Data Group 2006 Review of Particle Physics Journal of Physics G 33 1 1 1232 arXiv astro ph 0601168 Bibcode 2006JPhG 33 1Y doi 10 1088 0954 3899 33 1 001 D Leonard 2008 Systematic study of trace radioactive impurities in candidate construction materials for EXO 200 Nuclear Instruments and Methods in Physics Research Section A 591 3 490 509 arXiv 0709 4524 Bibcode 2008NIMPA 591 490L doi 10 1016 j nima 2008 03 001 S2CID 118334959 EXO project equipment successfully placed underground at WIPP PDF Press release DOENews 24 July 2007 a b Albert J B Auty D J Barbeau P S Beauchamp E Beck D Belov V Benitez Medina C Bonatt J Breidenbach M Brunner T Burenkov A Cao G F Chambers C Chaves J Cleveland B Coon M Craycraft A Daniels T Danilov M Daugherty S J Davis C G Davis J Devoe R Delaquis S Didberidze T Dolgolenko A Dolinski M J Dunford M Fairbank Jr W et al 12 June 2014 Search for Majorana neutrinos with the first two years of EXO 200 data Nature 510 7504 229 234 arXiv 1402 6956 Bibcode 2014Natur 510 229T doi 10 1038 nature13432 PMID 24896189 S2CID 2740003 N Ackerman et al 2011 Observation of Two Neutrino Double Beta Decay in 136Xe with EXO 200 Physical Review Letters 107 21 212501 arXiv 1108 4193 Bibcode 2011PhRvL 107u2501A doi 10 1103 PhysRevLett 107 212501 PMID 22181874 S2CID 40334443 Albert J B Auger M Auty D J Barbeau P S Beauchamp E Beck D Belov V Benitez Medina C Bonatt J Breidenbach M Brunner T Burenkov A Cao G F Chambers C Chaves J Cleveland B Cook S Craycraft A Daniels T Danilov M Daugherty S J Davis C G Davis J Devoe R Delaquis S Dobi A Dolgolenko A Dolinski M J Dunford M et al 2014 An improved measurement of the 2nbb half life of Xe 136 with EXO 200 Phys Rev C 89 1 015502 arXiv 1306 6106 Bibcode 2014PhRvC 89a5502A doi 10 1103 PhysRevC 89 015502 M Auger et al 2012 Search for Neutrinoless Double Beta Decay in 136Xe with EXO 200 Physical Review Letters 109 3 032505 arXiv 1205 5608 Bibcode 2012PhRvL 109c2505A doi 10 1103 PhysRevLett 109 032505 PMID 22861843 S2CID 29698686 Anton G et al 18 October 2019 Search for Neutrinoless Double ensuremath beta Decay with the Complete EXO 200 Dataset Physical Review Letters 123 16 161802 arXiv 1906 02723 doi 10 1103 PhysRevLett 123 161802 PMID 31702371 S2CID 174803277 P Fierlinger et al 2008 A microfabricated sensor for thin dielectric layers Review of Scientific Instruments 79 4 045101 045101 7 arXiv 0706 0540 Bibcode 2008RScI 79d5101F doi 10 1063 1 2906402 PMID 18447546 S2CID 2950473 Yang Liang 8 July 2016 Status and Prospects for the EXO 200 and nEXO Experiments PDF XXVII International Conference on Neutrino Physics and Astrophysics presentation London Archived from the original PDF on 17 November 2016 Retrieved 16 November 2016 Video available at Neutrino Conference 2016 Friday part 1 on YouTube MacLellan Ryan 25 September 2017 nEXO a tonne scale next generation double beta decay experiment XV International Conference on Topics in Astroparticle and Underground Physics TAUP 2017 presentation Sudbury Canada Albert J B et al nEXO Collaboration 2018 Sensitivity and Discovery Potential of nEXO to Neutrinoless Double Beta Decay Physical Review C 97 6 065503 arXiv 1710 05075 Bibcode 2018PhRvC 97f5503A doi 10 1103 PhysRevC 97 065503 S2CID 67854591 LLNL JRNL 737682 Jewell M et al nEXO Collaboration 14 October 2017 Characterization of an Ionization Readout Tile for nEXO Journal of Instrumentation 13 P01006 arXiv 1710 05109 doi 10 1088 1748 0221 13 01 P01006 S2CID 56297955 External links editEXO web site nEXO web site EXO experiment record on INSPIRE HEP Retrieved from https en wikipedia org w index php title Enriched Xenon Observatory amp oldid 1212918923, wikipedia, wiki, book, books, library,

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