Mu2e

Last updated
Mu2e project logo Mu2e-logo.jpg
Mu2e project logo
A prototype of the Mu2e Transport Solenoid module Mu2e-crew-600x400.jpg
A prototype of the Mu2e Transport Solenoid module

Mu2e, or the Muon-to-Electron Conversion Experiment, is a particle physics experiment at Fermilab in the US. [1] The goal of the experiment is to identify physics beyond the Standard Model, namely, the conversion of muons to electrons without the emission of neutrinos, which occurs in a number of theoretical models. [2] [3] Former project co-spokesperson Jim Miller likens this process to neutrino oscillation, but for charged leptons. [4] The rate for this process in the Standard Model of particle physics is unobservably small, so any observation of this process would constitute a major discovery and indicate new physics beyond the standard model. [2] The experiment will be 10,000 times more sensitive than previous muon to electron conversion experiments, and probe effective energy scales up to 10,000 TeV. [2]

Contents

Timeline

Prior work

Physicists have been searching for flavor violation since the 1940s. [2] Flavor violation among neutrinos was proven in 1998 at the Super-Kamiokande experiment in Japan. [5]

In 1989, Russian physicists Vladimir Lobashev and Rashid Djilkibaev proposed an experiment to search for lepton flavor violation. The experiment, called MELC, operated from 1992 to 1995 at the Moscow Meson Factory at the Institute for Nuclear Research in Russia, before being shut down due to the political and economic crises of the time. [6]

In 1997, American physicist William Molzon proposed a similar experiment at Brookhaven National Laboratory. Research and development on the MECO experiment began in 2001, but funding was pulled in 2005. [6]

Development

Mu2e is based on the MECO experiment proposed at Brookhaven, and the earlier MELC experiment at Russia's Institute for Nuclear Research. [7] Research and development for the Mu2e experiment began in 2009, with the conceptual design complete in mid-2011. [3] In July 2012, Mu2e received Critical Decision 1 approval (the second of five critical decision levels) from the Department of Energy, about one month after initial review. [8] Project Manager Ron Ray asserted, "I know of no other project that has received sign-off that quickly after review." [8] Funding of the Mu2e experiment was recommended by the Department of Energy's Particle Physics Project Prioritization Panel, in its 2014 report. [9]

Construction and operation

Groundbreaking on the detector hall took place on April 18, 2015. [10] Originally, commissioning was anticipated in 2019 and preliminary results were expected 2020; [1] however, the project was significantly delayed, and, in 2022, the experiment was projected to begin in 2026. [11] The delivery of two magnets from General Atomics was delayed, contributing to the shift in start-date. [12] The experiment is expected to run for three years. [7]

Later improvements to the detector may increase the sensitivity of the experiment by one to two orders of magnitude, allowing a more in-depth study of any charged lepton conversion that may be discovered in the initial run. [2]

As of February 2024, construction of the two Mu2E transport solenoid was completed and moved from Fermilab's Heavy Assembly Building to the Detector hall were final assembly will be completed.

Design

Stages of the Mu2e experiment Mu2e1-600x400.png
Stages of the Mu2e experiment

The Mu2e apparatus will be 92 feet (28 m) in length, and will consist of three sections. [10] The total cost of the experiment is $271 million. [13]

Muon production

Repurposed elements from the Tevatron collider will be used to generate and deliver an 8 GeV proton beam. The protons will be extracted from Fermilab's Delivery Ring through a non-linear third-integer resonance extraction process and sent in pulses to the tungsten target. These protons will then collide with the tungsten production target in the production solenoid, producing a cascade of particles including pions, which decay into muons. Mu2e will produce between 200 [7] and 500 quadrillion (2×1017 to 5×1017) muons per year. [6] For every 300 protons hitting the production target, about one muon will enter the transport solenoid. [7]

Transport

The 4.5-Tesla magnetic field of a production solenoid will direct some of the particles produced into an S-shaped 2-Tesla evacuated transport solenoid, consisting of 50 separate superconducting electromagnets, [14] which will select muons by charge and momentum, and carry the desired slow muons to the detector after some time delay. [3]

Detection

On entering the detector solenoid, the muons will hit (and stop within) an aluminum target that is about 0.2 mm thick, [6] [13] entering orbitals around nuclei within the target. [3] [10] Any muons which convert into electrons without emitting neutrinos will escape these orbitals and enter the detector with a characteristic energy of 104.97 MeV (which is the muon mass minus the binding energy of about 0.5 MeV and nuclear recoil energy of about 0.2 MeV). [6] [15]

The detector itself consists of two main components: a straw tracker to measure the momentum of outgoing particles; and an electromagnetic calorimeter to identify which particle interactions to record for further study, identify what type of particle passed through the tracker, and to confirm the measurements of the tracker. [15] An electron with energy of around 105 MeV will indicate that the electron originated in a neutrinoless muon conversion. [16]

In order to disturb the path of the electrons as little as possible, the tracker uses as little material as possible. The wire chamber tracker consists of panels of 15-micron-thick straws of metalized mylar filled with argon and carbon dioxide, the thinnest such straws ever used in a particle physics experiment. Electronics at each end of the straws will record the signal produced when electrons interact with the gas in the straw, allowing the trajectory of the electrons to be reconstructed. [16]

Sensitivity

The rate of neutrinoless conversion of muons to electrons was previously constrained by the MEG experiment to less than 2.4×10−12, and further constrained to 7×10−13 by the SINDRUM II experiment at the Paul Scherrer Institute in Switzerland. [5] Mu2e has an expected sensitivity of 5×10−17, four orders of magnitude beyond SINDRUM II, meaning that it will see a signal if as few as one in 100 quadrillion muons transforms into an electron. [5] [6]

Collaboration

As of October 2018, the Mu2e collaboration included 240 people from 40 institutions in six countries. [17] The collaboration is led by co-spokespersons Bob Bernstein (Fermilab) and Stefano Miscetti (INFN Frascati). The project manager for Mu2e is Julie Whitmore; the deputy project managers are Karen Byrum and Paul Derwent.

See also

Related Research Articles

<span class="mw-page-title-main">Muon</span> Subatomic particle

A muon is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton. As with other leptons, the muon is not thought to be composed of any simpler particles.

<span class="mw-page-title-main">Neutrino</span> Elementary particle with extremely low mass

A neutrino is a fermion that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The rest mass of the neutrino is much smaller than that of the other known elementary particles. The weak force has a very short range, the gravitational interaction is extremely weak due to the very small mass of the neutrino, and neutrinos do not participate in the electromagnetic interaction or the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.

<span class="mw-page-title-main">Particle physics</span> Study of subatomic particles and forces

Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons, while the study of combination of protons and neutrons is called nuclear physics.

<span class="mw-page-title-main">Fermilab</span> High-energy particle physics laboratory in Illinois, US

Fermi National Accelerator Laboratory (Fermilab), located in Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operated by the Fermi Research Alliance (FRA), a joint venture of the University of Chicago, and the Universities Research Association (URA); although in 2023, the Department of Energy (DOE) opened bidding for a new contractor due to concerns about the FRA performance. Fermilab is a part of the Illinois Technology and Research Corridor.

<span class="mw-page-title-main">Lepton</span> Class of elementary particles

In particle physics, a lepton is an elementary particle of half-integer spin that does not undergo strong interactions. Two main classes of leptons exist: charged leptons, including the electron, muon, and tauon, and neutral leptons, better known as neutrinos. Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. The best known of all leptons is the electron.

In particle physics, lepton number is a conserved quantum number representing the difference between the number of leptons and the number of antileptons in an elementary particle reaction. Lepton number is an additive quantum number, so its sum is preserved in interactions. The lepton number is defined by

<span class="mw-page-title-main">Collider Detector at Fermilab</span> American experimental physics device (1985–2011)

The Collider Detector at Fermilab (CDF) experimental collaboration studies high energy particle collisions from the Tevatron, the world's former highest-energy particle accelerator. The goal is to discover the identity and properties of the particles that make up the universe and to understand the forces and interactions between those particles.

<span class="mw-page-title-main">MINOS</span> Particle physics experiment

Main injector neutrino oscillation search (MINOS) was a particle physics experiment designed to study the phenomena of neutrino oscillations, first discovered by a Super-Kamiokande (Super-K) experiment in 1998. Neutrinos produced by the NuMI beamline at Fermilab near Chicago are observed at two detectors, one very close to where the beam is produced, and another much larger detector 735 km away in northern Minnesota.

<span class="mw-page-title-main">DØ experiment</span> Particle physics research project (1983–2011)

The DØ experiment was a worldwide collaboration of scientists conducting research on the fundamental nature of matter. DØ was one of two major experiments located at the Tevatron Collider at Fermilab in Batavia, Illinois. The Tevatron was the world's highest-energy accelerator from 1983 until 2009, when its energy was surpassed by the Large Hadron Collider. The DØ experiment stopped taking data in 2011, when the Tevatron shut down, but data analysis is still ongoing. The DØ detector is preserved in Fermilab's DØ Assembly Building as part of a historical exhibit for public tours.

<span class="mw-page-title-main">Neutrino detector</span> Physics apparatus which is designed to study neutrinos

A neutrino detector is a physics apparatus which is designed to study neutrinos. Because neutrinos only weakly interact with other particles of matter, neutrino detectors must be very large to detect a significant number of neutrinos. Neutrino detectors are often built underground, to isolate the detector from cosmic rays and other background radiation. The field of neutrino astronomy is still very much in its infancy – the only confirmed extraterrestrial sources as of 2018 are the Sun and the supernova 1987A in the nearby Large Magellanic Cloud. Another likely source is the blazar TXS 0506+056 about 3.7 billion light years away. Neutrino observatories will "give astronomers fresh eyes with which to study the universe".

T2K is a particle physics experiment studying the oscillations of the accelerator neutrinos. The experiment is conducted in Japan by the international cooperation of about 500 physicists and engineers with over 60 research institutions from several countries from Europe, Asia and North America and it is a recognized CERN experiment (RE13). T2K collected data within its first phase of operation from 2010 till 2021. The second phase of data taking is expected to start in 2023 and last until commencement of the successor of T2K – the Hyper-Kamiokande experiment in 2027.

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

The NOνA experiment is a particle physics experiment designed to detect neutrinos in Fermilab's NuMI beam. Intended to be the successor to MINOS, NOνA consists of two detectors, one at Fermilab, and one in northern Minnesota. Neutrinos from NuMI pass through 810 km of Earth to reach the far detector. NOνA's main goal is to observe the oscillation of muon neutrinos to electron neutrinos. The primary physics goals of NOvA are:

The timeline of particle physics lists the sequence of particle physics theories and discoveries in chronological order. The most modern developments follow the scientific development of the discipline of particle physics.

A Muon Collider is a proposed particle accelerator facility in its conceptual design stage that collides muon beams for precision studies of the Standard Model and for direct searches of new physics. Muons belong to the second generation of leptons, they are typically produced in high-energy collisions either naturally or artificially. The main challenge of such a collider is the short lifetime of muons.

<span class="mw-page-title-main">CUORE</span> Cryogenic Underground Observatory for Rare Events

The Cryogenic Underground Observatory for Rare Events (CUORE) – also cuore (Italian for 'heart'; ) – is a particle physics facility located underground at the Laboratori Nazionali del Gran Sasso in Assergi, Italy. CUORE was designed primarily as a search for neutrinoless double beta decay in 130Te, a process that has never been observed. It uses tellurium dioxide (TeO2) crystals as both the source of the decay and as bolometers to detect the resulting electrons. CUORE searches for the characteristic signal of neutrinoless double beta decay, a small peak in the observed energy spectrum around the known decay energy; for 130Te, this is Q = 2527.518 ± 0.013 keV. CUORE can also search for signals from dark matter candidates, such as axions and WIMPs.

<span class="mw-page-title-main">Vladimir Lobashev</span> Russian particle physicist

Vladimir Mikhailovich Lobashev was a Soviet and Russian physicist and expert in nuclear physics and particle physics. He authored over 200 papers, of which 25 were considered groundbreaking.

<span class="mw-page-title-main">David B. Cline</span> American particle physicist

]

The Enhanced NeUtrino BEams from kaon Tagging or ENUBET is an ERC funded project that aims at producing an artificial neutrino beam in which the flavor, flux and energy of the produced neutrinos are known with unprecedented precision.

An accelerator neutrino is a human-generated neutrino or antineutrino obtained using particle accelerators, in which beam of protons is accelerated and collided with a fixed target, producing mesons which then decay into neutrinos. Depending on the energy of the accelerated protons and whether mesons decay in flight or at rest it is possible to generate neutrinos of a different flavour, energy and angular distribution. Accelerator neutrinos are used to study neutrino interactions and neutrino oscillations taking advantage of high intensity of neutrino beams, as well as a possibility to control and understand their type and kinematic properties to a much greater extent than for neutrinos from other sources.

Karol Sylwester Lang is an experimental particle physicist and the Jane and Roland Blumberg Professor of Physics at the University of Texas at Austin.

References

  1. 1 2 "Mu2e: muon-to-electron-conversion experiment". Fermilab. April 21, 2015. Retrieved 30 April 2015.
  2. 1 2 3 4 5 "Research Goals". Fermilab. March 17, 2015. Retrieved 1 May 2015.
  3. 1 2 3 4 Glenzinski, Doug (February 2011). "The Mu2e Experiment at Fermilab" (PDF). University of Pennsylvania. Retrieved 1 May 2015.
  4. ↑ Piergrossi, Joseph (January 10, 2013). "Midwest muon experiments carry on East Coast legacy". Symmetry Magazine. Retrieved 4 May 2015.
  5. 1 2 3 Dorigo, Tommaso (December 3, 2012). "Mu2E: Exploring Lepton Flavour Violation At Fermilab". Science 2.0. Retrieved 4 May 2015.
  6. 1 2 3 4 5 6 Mustain, Andrea (June 2010). "The muon guys: On the hunt for new physics". Symmetry Magazine. Retrieved 4 May 2015.
  7. 1 2 3 4 "How does it work?". Fermilab. March 17, 2015. Retrieved 30 April 2015.
  8. 1 2 Piergrossi, Joseph (July 20, 2012). "Department of Energy advances Fermilab's Mu2e experiment". Symmetry Magazine. Retrieved 4 May 2015.
  9. ↑ Jepsen, Kathryn (May 22, 2014). "Proposed plan for the future of US particle physics: The Particle Physics Project Prioritization Panel's report recommends a strategic path forward for US particle physics" . Retrieved 4 May 2015.
  10. 1 2 3 Kwon, Diana (April 21, 2015). "Mu2e breaks ground on experiment seeking new physics". Fermilab Today.
  11. ↑ Bernstein, Maxwell (March 24, 2022). "Straws, crystals and the quest for new subatomic physics". Fermilab News.
  12. ↑ "HEP Project Status, Mike Procario" (PDF). High Energy Physics Advisory Panel November 1–2, 2021 Agenda.
  13. 1 2 "Mu2e-doc-4299-v15: Mu2e Technical Design Report (TDR)". mu2e-docdb.fnal.gov. Retrieved 2017-01-18.
  14. ↑ Salles, Andre (December 16, 2013). "Mu2e attracts magnet experts". Symmetry Magazine. Retrieved 4 May 2015.
  15. 1 2 "Mu2e-doc-8084-v1: The Mu2e Experiment at Fermilab". mu2e-docdb.fnal.gov. Retrieved 2017-01-18.
  16. 1 2 "How to Detect a Rare Particle Decay with a Detector Made of (Almost) Nothing". Newswise. March 3, 2015. Retrieved 4 May 2015.
  17. ↑ "Collaboration". Fermilab. 26 October 2018. Retrieved 7 December 2018.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.