Large Underground Xenon experiment

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The Large Underground Xenon experiment (LUX) aimed to directly detect weakly interacting massive particle (WIMP) dark matter interactions with ordinary matter on Earth. Despite the wealth of (gravitational) evidence supporting the existence of non-baryonic dark matter in the Universe, [1] dark matter particles in our galaxy have never been directly detected in an experiment. LUX utilized a 370 kg liquid xenon detection mass in a time-projection chamber (TPC) to identify individual particle interactions, searching for faint dark matter interactions with unprecedented sensitivity. [2]

Contents

The LUX experiment, which cost approximately $10 million to build, [3] was located 1,510 m (4,950 ft) underground at the Sanford Underground Laboratory (SURF, formerly the Deep Underground Science and Engineering Laboratory, or DUSEL) in the Homestake Mine (South Dakota) in Lead, South Dakota. The detector was located in the Davis campus, former site of the Nobel Prize-winning Homestake neutrino experiment led by Raymond Davis. It was operated underground to reduce the background noise signal caused by high-energy cosmic rays at the Earth's surface.

The detector was decommissioned in 2016 and is now on display at the Sanford Lab Homestake Visitor Center. [4]

The Large Underground Xenon experiment installed 1,480 m (4,850 ft) underground inside a 260 m (70,000 US gal) water tank shield. The experiment was a 370 kg liquid xenon time projection chamber that aimed to detect the faint interactions between WIMP dark matter and ordinary matter. Large Underground Xenon detector inside watertank.jpg
The Large Underground Xenon experiment installed 1,480 m (4,850 ft) underground inside a 260 m (70,000 US gal) water tank shield. The experiment was a 370 kg liquid xenon time projection chamber that aimed to detect the faint interactions between WIMP dark matter and ordinary matter.

Detector principle

The detector was isolated from background particles by a surrounding water tank and the earth above. This shielding reduced cosmic rays and radiation interacting with the xenon.

Interactions in liquid xenon generate 175 nm ultraviolet photons and electrons. These photons were immediately detected by two arrays of 61 photomultiplier tubes at the top and bottom of the detector. These prompt photons were the S1 signal. Electrons generated by the particle interactions drifted upwards towards the xenon gas by an electric field. The electrons were pulled in the gas at the surface by a stronger electric field, and produced electroluminescence photons detected as the S2 signal. The S1 and subsequent S2 signal constituted a particle interaction in the liquid xenon.

The detector was a time-projection chamber (TPC), using the time between S1 and S2 signals to find the interaction depth since electrons move at constant velocity in liquid xenon (around 1–2 km/s, depending on the electric field). The x-y coordinate of the event was inferred from electroluminescence photons at the top array by statistical methods (Monte Carlo and maximum likelihood estimation) to a resolution under 1 cm. [5]

Particle interactions inside the LUX detector produced photons and electrons. The photons ( g {\displaystyle \gamma } ), moving at the speed of light, were quickly detected by the photomultiplier tubes. This photon signal was called S1. An electric field in the liquid xenon drifted the electrons towards the liquid surface. A much higher electric field above the liquid surface pulled the electrons out of the liquid and into the gas, where they procued electroluminescence photons (in the same way that neon sign produces light). The electroluminescence photons were detected by the photomultiplier tubes as the S2 signal. A single particle interaction in the liquid xenon could be identified by the pair of an S1 and an S2 signal. LUXEvent.pdf
Particle interactions inside the LUX detector produced photons and electrons. The photons (), moving at the speed of light, were quickly detected by the photomultiplier tubes. This photon signal was called S1. An electric field in the liquid xenon drifted the electrons towards the liquid surface. A much higher electric field above the liquid surface pulled the electrons out of the liquid and into the gas, where they procued electroluminescence photons (in the same way that neon sign produces light). The electroluminescence photons were detected by the photomultiplier tubes as the S2 signal. A single particle interaction in the liquid xenon could be identified by the pair of an S1 and an S2 signal.
Schematic of the Large Underground Xenon (LUX) detector. The detector consisted of an inner cryostat filled with 370 kg of liquid xenon (300 kg in the inner region, called the "active volume") cooled to -100 degC. 122 photomultiplier tubes detected light generated inside the detector. The LUX detector had an outer cryostat that provided vacuum insulation. An 8-meter-diameter by 6-meter-high water tank shielded the detector from external radiation, such as gamma rays and neutrons. Large Underground Xenon detector diagram.png
Schematic of the Large Underground Xenon (LUX) detector. The detector consisted of an inner cryostat filled with 370 kg of liquid xenon (300 kg in the inner region, called the "active volume") cooled to −100 °C. 122 photomultiplier tubes detected light generated inside the detector. The LUX detector had an outer cryostat that provided vacuum insulation. An 8-meter-diameter by 6-meter-high water tank shielded the detector from external radiation, such as gamma rays and neutrons.

Finding dark matter

WIMPs would be expected to interact exclusively with the liquid xenon nuclei, resulting in nuclear recoils that would appear very similar to neutron collisions. In order to single out WIMP interactions, neutron events must be minimized, through shielding and ultra-quiet building materials.

In order to discern WIMPs from neutrons, the number of single interactions must be compared to multiple events. Since WIMPs are expected to be so weakly interacting, most would pass through the detector unnoticed. Any WIMPs that interact will have negligible chance of repeated interaction. Neutrons, on the other hand, have a reasonably large chance of multiple collisions within the target volume, the frequency of which can be accurately predicted. Using this knowledge, if the ratio of single interactions to multiple interactions exceeds a certain value, the detection of dark matter may be reliably inferred.

Collaboration

The LUX collaboration was composed of over 100 scientists and engineers across 27 institutions in the US and Europe. LUX was composed of the majority of the US groups that collaborated in the XENON10 experiment, most of the groups in the ZEPLIN III experiment, the majority of the US component of the ZEPLIN II experiment, and groups involved in low-background rare event searches such as Super Kamiokande, SNO, IceCube, Kamland, EXO and Double Chooz.

The LUX experiment's co-spokesmen were Richard Gaitskell from Brown University (who acted as co-spokesman from 2007 on) and Daniel McKinsey from University of California, Berkeley (who acted as co-spokesman from 2012 on). Tom Shutt from Case Western Reserve University was LUX co-spokesman between 2007 and 2012.

Status

Detector assembly began in late 2009. The LUX detector was commissioned overground at SURF for a six-month run. The assembled detector was transported underground from the surface laboratory in a two-day operation in the summer of 2012 and began data taking April 2013, presenting initial results Fall 2013. It was decommissioned in 2016. [4]

The next-generation follow-up experiment, the 7-ton LUX-ZEPLIN has been approved, [6] expected to begin in 2020. [7]

Results

Initial unblinded data taken April to August 2013 were announced on October 30, 2013. In an 85 live-day run with 118 kg fiducial volume, LUX obtained 160 events passing the data analysis selection criteria, all consistent with electron recoil backgrounds. A profile likelihood statistical approach shows this result is consistent with the background-only hypothesis (no WIMP interactions) with a p-value of 0.35. This was the most sensitive dark matter direct detection result in the world, and ruled out low-mass WIMP signal hints such as from CoGeNT and CDMS-II. [8] [9] These results struck out some of the theories about WIMPs, allowing researchers to focus on fewer leads. [10]

In the final run from October 2014 to May 2016, at four times its original design sensitivity with 368 kg of liquid xenon, LUX saw no signs of dark matter candidate—WIMPs. [7] According to Ethan Siegel, the results from LUX and XENON1T have provided evidence against the supersymmetric "WIMP Miracle" strong enough to motivate theorists towards alternate models of dark matter. [11]

Related Research Articles

Weakly interacting massive particles (WIMPs) are hypothetical particles that are one of the proposed candidates for dark matter.

<span class="mw-page-title-main">Time projection chamber</span>

In physics, a time projection chamber (TPC) is a type of particle detector that uses a combination of electric fields and magnetic fields together with a sensitive volume of gas or liquid to perform a three-dimensional reconstruction of a particle trajectory or interaction.

The Cryogenic Dark Matter Search (CDMS) is a series of experiments designed to directly detect particle dark matter in the form of Weakly Interacting Massive Particles. Using an array of semiconductor detectors at millikelvin temperatures, CDMS has at times set the most sensitive limits on the interactions of WIMP dark matter with terrestrial materials. The first experiment, CDMS I, was run in a tunnel under the Stanford University campus. It was followed by CDMS II experiment in the Soudan Mine. The most recent experiment, SuperCDMS, was located deep underground in the Soudan Mine in northern Minnesota and collected data from 2011 through 2015. The series of experiments continues with SuperCDMS SNOLAB, an experiment located at the SNOLAB facility near Sudbury, Ontario in Canada that started construction in 2018 and is expected to start data taking in early 2020s.

The XENON dark matter research project, operated at the Italian Gran Sasso National Laboratory, is a deep underground detector facility featuring increasingly ambitious experiments aiming to detect hypothetical dark matter particles. The experiments aim to detect particles in the form of weakly interacting massive particles (WIMPs) by looking for rare nuclear recoil interactions in a liquid xenon target chamber. The current detector consists of a dual phase time projection chamber (TPC).

<span class="mw-page-title-main">UK Dark Matter Collaboration</span> 1987–2007 particle physics experiment

The UK Dark Matter Collaboration (UKDMC) (1987–2007) was an experiment to search for Weakly interacting massive particles (WIMPs). The consortium consisted of astrophysicists and particle physicists from the United Kingdom, who conducted experiments with the ultimate goal of detecting rare scattering events which would occur if galactic dark matter consists largely of a new heavy neutral particle. Detectors were set up 1,100 m (3,600 ft) underground in a halite seam at the Boulby Mine in North Yorkshire.

The ArDM Experiment was a particle physics experiment based on a liquid argon detector, aiming at measuring signals from WIMPs, which may constitute the Dark Matter in the universe. Elastic scattering of WIMPs from argon nuclei is measurable by observing free electrons from ionization and photons from scintillation, which are produced by the recoiling nucleus interacting with neighbouring atoms. The ionization and scintillation signals can be measured with dedicated readout techniques, which constituted a fundamental part of the detector.

<span class="mw-page-title-main">DEAP</span> Dark matter search experiment

DEAP is a direct dark matter search experiment which uses liquid argon as a target material. DEAP utilizes background discrimination based on the characteristic scintillation pulse-shape of argon. A first-generation detector (DEAP-1) with a 7 kg target mass was operated at Queen's University to test the performance of pulse-shape discrimination at low recoil energies in liquid argon. DEAP-1 was then moved to SNOLAB, 2 km below Earth's surface, in October 2007 and collected data into 2011.

<span class="mw-page-title-main">Sanford Underground Research Facility</span> Underground laboratory in Lead, South Dakota

The Sanford Underground Research Facility (SURF), or Sanford Lab, is an underground laboratory in Lead, South Dakota. The deepest underground laboratory in the United States, it houses multiple experiments in areas such as dark matter and neutrino physics research, biology, geology and engineering. There are currently 28 active research projects housed within the facility.

<span class="mw-page-title-main">European Underground Rare Event Calorimeter Array</span> Planned dark matter search experiment

The European Underground Rare Event Calorimeter Array (EURECA) is a planned dark matter search experiment using cryogenic detectors and an absorber mass of up to 1 tonne. The project will be built in the Modane Underground Laboratory and will bring together researchers working on the CRESST and EDELWEISS experiments.

<span class="mw-page-title-main">EDELWEISS</span>

EDELWEISS is a dark matter search experiment located at the Modane Underground Laboratory in France. The experiment uses cryogenic detectors, measuring both the phonon and ionization signals produced by particle interactions in germanium crystals. This technique allows nuclear recoils events to be distinguished from electron recoil events.

The DarkSide collaboration is an international affiliation of universities and labs seeking to directly detect dark matter in the form of weakly interacting massive particles (WIMPs). The collaboration is planning, building and operating a series of liquid argon time projection chambers (TPCs) that are employed at the Gran Sasso National Laboratory in Assergi, Italy. The detectors are filled with liquid argon from underground sources in order to exclude the radioactive isotope 39
Ar, which makes up one in every 1015 (quadrillion) atoms in atmospheric argon. The Darkside-10 (DS-10) prototype was tested in 2012, and the Darkside-50 (DS-50) experiment has been operating since 2013. Darkside-20k (DS-20k) with 20 tonnes of liquid argon is being planned as of 2019.

<span class="mw-page-title-main">ZEPLIN-III</span> 2006–2011 dark matter experiment in England

The ZEPLIN-III dark matter experiment attempted to detect galactic WIMPs using a 12 kg liquid xenon target. It operated from 2006 to 2011 at the Boulby Underground Laboratory in Loftus, North Yorkshire. This was the last in a series of xenon-based experiments in the ZEPLIN programme pursued originally by the UK Dark Matter Collaboration (UKDMC). The ZEPLIN-III project was led by Imperial College London and also included the Rutherford Appleton Laboratory and the University of Edinburgh in the UK, as well as LIP-Coimbra in Portugal and ITEP-Moscow in Russia. It ruled out cross-sections for elastic scattering of WIMPs off nucleons above 3.9 × 10−8 pb from the two science runs conducted at Boulby.

Richard Jeremy Gaitskell is a physicist and professor at Brown University and a leading scientist in the search for particle dark matter. He is co-founder, a principal investigator, and co-spokesperson of the Large Underground Xenon (LUX) experiment, which announced world-leading first results on October 30, 2013. He is also a leading investigator in the new LUX-Zeplin (LZ) dark matter experiment.

The Particle and Astrophysical Xenon Detector, or PandaX, is a dark matter detection experiment at China Jinping Underground Laboratory (CJPL) in Sichuan, China. The experiment occupies the deepest underground laboratory in the world, and is among the largest of its kind.

The Cryogenic Low-Energy Astrophysics with Noble liquids (CLEAN) experiment by the DEAP/CLEAN collaboration is searching for dark matter using noble gases at the SNOLAB underground facility. CLEAN has studied neon and argon in the MicroCLEAN prototype, and running the MiniCLEAN detector to test a multi-ton design.

<span class="mw-page-title-main">LZ experiment</span> Experiment in South Dakota, United States

The LUX-ZEPLIN (LZ) Experiment is a next-generation dark matter direct detection experiment hoping to observe weakly interacting massive particles (WIMP) scatters on nuclei. It was formed in 2012 by combining the LUX and ZEPLIN groups. It is currently a collaboration of 30 institutes in the US, UK, Portugal and South Korea. The experiment is located at the Sanford Underground Research Facility (SURF) in South Dakota, and is managed by the United States Department of Energy's (DOE) Lawrence Berkeley National Lab.

Daniel Nicholas McKinsey is an American experimental physicist. McKinsey is a leader in the field of direct searches for dark matter interactions, and serves as Co-Spokesperson of the Large Underground Xenon experiment. and is an executive committee member of the LUX-ZEPLIN experiment. He serves as Director and Principal Investigator of the TESSERACT Project, and is also The Georgia Lee Distinguished Professor of Physics at the University of California, Berkeley.

Direct detection of dark matter is the science of attempting to directly measure dark matter collisions in Earth-based experiments. Modern astrophysical measurements, such as from the Cosmic Microwave Background, strongly indicate that 85% of the matter content of the universe is unaccounted for. Although the existence of dark matter is widely believed, what form it takes or its precise properties has never been determined. There are three main avenues of research to detect dark matter: attempts to make dark matter in accelerators, indirect detection of dark matter annihilation, and direct detection of dark matter in terrestrial labs. The founding principle of direct dark matter detection is that since dark matter is known to exist in the local universe, as the Earth, Solar System, and the Milky Way Galaxy carve out a path through the universe they must intercept dark matter, regardless of what form it takes.

Daniel S. Akerib is an American particle physicist and astrophysicist. He was elected in 2008 a fellow of the American Physical Society (APS).

Alvine Kamaha is a Cameroonian-born assistant professor of physics at the University of California, Los Angeles (UCLA).

References

  1. ↑ Beringer, J.; et al. (2012). "2012 Review of Particle Physics" (PDF). Phys. Rev. D. 86 (10001). Bibcode:2012PhRvD..86a0001B. doi: 10.1103/PhysRevD.86.010001 .
  2. ↑ Akerib, D.; et al. (March 2013). "The Large Underground Xenon (LUX) experiment". Nuclear Instruments and Methods in Physics Research A. 704: 111–126. arXiv: 1211.3788 . Bibcode:2013NIMPA.704..111A. doi:10.1016/j.nima.2012.11.135. S2CID   67768071.
  3. ↑ Reich, E. Dark-matter hunt gets deep Nature 21 Feb 2013
  4. 1 2 Van Zee, Al (July 20, 2017). "LUX dark matter detector now part of new exhibit at Sanford Lab". Black Hills Pioneer . Lead, South Dakota. Retrieved June 21, 2019.
  5. ↑ Akerib; et al. (May 2013). "Technical results from the surface run of the LUX dark matter experiment". Astroparticle Physics. 45: 34–43. arXiv: 1210.4569 . Bibcode:2013APh....45...34A. doi:10.1016/j.astropartphys.2013.02.001. S2CID   118422051.
  6. ↑ "Dark-matter searches get US government approval". Physics World. July 15, 2014. Retrieved February 13, 2020.
  7. 1 2 "World's most sensitive dark-matter search comes up empty handed". Hamish Johnston. physicsworld.com (IOP). 22 July 2016. Retrieved February 13, 2020.
  8. ↑ Akerib, D. (2014). "First results from the LUX dark matter experiment at the Sanford Underground Research Facility" (PDF). Physical Review Letters. 112 (9): 091303. arXiv: 1310.8214 . Bibcode:2014PhRvL.112i1303A. doi:10.1103/PhysRevLett.112.091303. hdl:1969.1/185324. PMID   24655239. S2CID   2161650 . Retrieved 30 October 2013.
  9. ↑ Dark Matter Search Comes Up Empty Fox News, 2013 October 30
  10. ↑ Dark matter experiment finds nothing, makes news The Conversation, 01 November 2013
  11. ↑ Siegel, Ethan (February 22, 2019). "The 'WIMP Miracle' Hope For Dark Matter Is Dead". Starts With A Bang. Forbes . Archived from the original on February 22, 2019. Retrieved June 21, 2019.

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