The Mu3e Experiment
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Lepton Flavor and Number Conservation, and Physics Beyond the Standard Model
Lepton Flavor and Number Conservation, and Physics Beyond the Standard Model Andr´ede Gouv^ea1 and Petr Vogel2 1 Department of Physics and Astronomy, Northwestern University, Evanston, Illinois, 60208, USA 2 Kellogg Radiation Laboratory, Caltech, Pasadena, California, 91125, USA April 1, 2013 Abstract The physics responsible for neutrino masses and lepton mixing remains unknown. More ex- perimental data are needed to constrain and guide possible generalizations of the standard model of particle physics, and reveal the mechanism behind nonzero neutrino masses. Here, the physics associated with searches for the violation of lepton-flavor conservation in charged-lepton processes and the violation of lepton-number conservation in nuclear physics processes is summarized. In the first part, several aspects of charged-lepton flavor violation are discussed, especially its sensitivity to new particles and interactions beyond the standard model of particle physics. The discussion concentrates mostly on rare processes involving muons and electrons. In the second part, the sta- tus of the conservation of total lepton number is discussed. The discussion here concentrates on current and future probes of this apparent law of Nature via searches for neutrinoless double beta decay, which is also the most sensitive probe of the potential Majorana nature of neutrinos. arXiv:1303.4097v2 [hep-ph] 29 Mar 2013 1 1 Introduction In the absence of interactions that lead to nonzero neutrino masses, the Standard Model Lagrangian is invariant under global U(1)e × U(1)µ × U(1)τ rotations of the lepton fields. In other words, if neutrinos are massless, individual lepton-flavor numbers { electron-number, muon-number, and tau-number { are expected to be conserved. -
Accessible Lepton-Number-Violating Models and Negligible Neutrino Masses
PHYSICAL REVIEW D 100, 075033 (2019) Accessible lepton-number-violating models and negligible neutrino masses † ‡ Andr´e de Gouvêa ,1,* Wei-Chih Huang,2, Johannes König,2, and Manibrata Sen 1,3,§ 1Northwestern University, Department of Physics and Astronomy, 2145 Sheridan Road, Evanston, Illinois 60208, USA 2CP3-Origins, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark 3Department of Physics, University of California Berkeley, Berkeley, California 94720, USA (Received 18 July 2019; published 25 October 2019) Lepton-number violation (LNV), in general, implies nonzero Majorana masses for the Standard Model neutrinos. Since neutrino masses are very small, for generic candidate models of the physics responsible for LNV, the rates for almost all experimentally accessible LNV observables—except for neutrinoless double- beta decay—are expected to be exceedingly small. Guided by effective-operator considerations of LNV phenomena, we identify a complete family of models where lepton number is violated but the generated Majorana neutrino masses are tiny, even if the new-physics scale is below 1 TeV. We explore the phenomenology of these models, including charged-lepton flavor-violating phenomena and baryon- number-violating phenomena, identifying scenarios where the allowed rates for μ− → eþ-conversion in nuclei are potentially accessible to next-generation experiments. DOI: 10.1103/PhysRevD.100.075033 I. INTRODUCTION Experimentally, in spite of ambitious ongoing experi- Lepton number and baryon number are, at the classical mental efforts, there is no evidence for the violation of level, accidental global symmetries of the renormalizable lepton-number or baryon-number conservation [5]. There Standard Model (SM) Lagrangian.1 If one allows for are a few different potential explanations for these (neg- generic nonrenormalizable operators consistent with the ative) experimental results, assuming degrees-of-freedom SM gauge symmetries and particle content, lepton number beyond those of the SM exist. -
The Muon Guys on the Hunt for New Physics
THE MUON GUYS ON THE HUNT FOR NEW PHYSICS BY Andrea MustaIN PHOTOGRAPHY BY REIDAR HAHN, FERMILAB 10 of mysterious equipment in a workroom at AMID A sprawL Fermi National Accelerator Laboratory, Gueorgui Velev and Alexander Makarov leaned over an elegant metal box the size of a single file cabinet. Suffused by a warm halo of late-afternoon sunlight, the two men, a physicist and an engineer, had the look of modern-day priests of industry gently handling a beloved reliquary. Velev lifted the box top, revealing a thin slice of dark-gray ferrite—a ceramic compound used in powerful magnets. Although the ferrite was wired up like an intensive-care patient, for the moment it felt cool and deliciously smooth to the touch. Velev and Makarov have been testing ferrites like this one for almost a year now, send- ing powerful currents through the compound, pushing the material to its limits. Far from being a relic of something dead, the ferrite is a symbol of resurrection for an experiment that could star in its own soap opera. Attempts to carry out this experiment have died two deaths on two continents over the course of two decades. Velev and Makarov, along with a host of collaborators, are once again bringing it to life. The experiment’s newest name, in its incarnation at Fermilab, is Mu2e (pronounced Mew to E), which stands for muon-to-electron conversion; and it is a testament to the strength of the science behind this experiment that physicists are still fighting to do it. Scientists plan to break ground at Fermilab in Batavia, Illinois, in 2013 and begin taking data four years later. -
Searching for Muon to Electron Conversion: the Design of the Mu2e Experiment
Searching for Muon to electron conversion: The design of the Mu2e experiment Richie Bonventre Physics 290e Lawrence Berkeley National Lab The physics of Mu2e • Mu2e will search for neutrinoless conversion of a muon to an electron in a nuclear environment: µ−N → e−N • This would violate charged lepton flavor, something that has never been seen before • Any detection of charged lepton flavor violation would be an unambiguous sign of new physics! (SM contribution is < 10−50) 1/46 Charged Lepton Flavor Violation • Neutrino oscillation shows that Lepton Flavor is NOT a fundamental symmetry. No reason new physics should conserve it • Many models of new physics predict contributions to CLFV: 2/46 History Mu2e goal is a 104 improvement! 3/46 Types of CLFV measurements Process Current Limit Next Generation exp. τ → µη BR < 6.5 E-8 10−9 - 10−10 (Belle II, LHCb) τ → µγ BR < 6.8 E-8 τ → µµµ BR < 3.2 E-8 τ → eee BR < 3.6 E-8 KL →eµ BR < 4.7 E-12 K+ → π+e−µ+ BR < 1.3 E-11 B0 →eµ BR < 7.8 E-8 B+ →K+eµ BR < 9.1 E-8 µ+ →e+γ BR < 4.2 E-13 10−14 (MEG) µ+ →e+e+e− BR < 1.0 E-12 10−16 (PSI) − − −17 µ N→e N Rµe < 7.0 E-13 10 (Mu2e, COMET) 4/46 How to search for CLFV • τ seems easiest at first • Larger mass reduces GIM suppression, most models predict larger BF • Larger mass means more possible decay modes • But lifetime is very short • Much easier to produce a lot of muons (which is good because we need 1018!) p + p/n → n + p/n + π π → µ + ν 5/46 Muon CLFV processes: µ → eγ, µ → eee, µN→ eN • µ → eγ • Signal is back-to-back monoenergetic electron, gamma at 52.8 -
Charged Lepton Flavor Violation and Mu2e Experiment .PDF
BSM : Charged lepton flavor violation & Mu2e experiment Seog Oh Duke University SESAPS, Fall 2016 1 Outline • SM and shortcomings of SM • Status of charged lepton flavor violation (CLFV) experiments • Mu2e experiment SESAPS, Fall 2016 2 Players in SM SESAPS, Fall 2016 3 Discovery of Higgs boson (2012) H0 -> gg H0 -> ZZ(*) -> 4l H0 -> gg SESAPS, Fall 2016 4 Shortcomings of SM • 19 parameters – Masses of particles, quark mixing angles, gauge couplings, vacuum expectation value – More if neutrino mixing angles are included • Hierarchy (naturalness) problem – correction to Higgs mass becomes very large (has to introduce a very fine adjustment or cutoff, new physics) • Particle and anti-particle asymmetry • No gravity • No dark matter/energy SESAPS, Fall 2016 5 disappointment/glimpse of beyond SM search • New particles : Z’, W’, t’, LQ, H+, SUSY (~50 searches) • Dark matter • Rare decays (deviation from SM) – B0 ->mm, K*0mm • g of muon : am=(g-2)/2 : ~ 3 sigma deviation • EDM • Charged lepton flavor violation (CLFV): t <->m<->e Phy 766S, Fall 2016 6 Charged lepton flavor violation(CLFV) • Quarks mix among themselves (CKM) weak eigenstate (d’,s’,b’) <- V -> mass eigenstate (d,s,b) • Neutrinos oscillate flavor eigenstate (e,m,t) <- U-> mass eigenstate (1,2,3) • ?? - Why not the charged leptons.. (e, m, t) Phy 766S, Fall 2016 7 CLFV experiments • m -> e (in Nuclear field) • m -> eg SM Rate : ~10-54 • m -> ee+e- 0 • KL -> me (mm and ee are SM allowed) • K+ -> p+me • Z0 -> me, te, tm SESAPS, Fall 2016 8 CLFV Limits Mu3e MEG upgrade comet I Mu2e, -
Theory Challenges and Opportunities of Mu2e-II: Letter of Interest for Snowmass 2021
Theory challenges and opportunities of Mu2e-II: Letter of Interest for Snowmass 2021 Robert H. Bernstein,1 Leo Borrel,2 Lorenzo Calibbi,3, ∗ Andrzej Czarnecki,4 Sacha Davidson,5 Bertrand Echenard,2 Julian Heeck,6, y David G. Hitlin,2 William Marciano,7 Sophie C. Middleton,2 Vitaly S. Pronskikh,1 and Robert Szafron8 1Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA 2California Institute of Technology, Pasadena, California 91125, USA 3School of Physics, Nankai University, Tianjin 300071, China 4Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada 5LUPM, CNRS, Universit´eMontpellier, Place Eugene Bataillon, F-34095 Montpellier, Cedex 5, France 6Department of Physics, University of Virginia, Charlottesville, Virginia 22904, USA 7Department of Physics, Brookhaven National Laboratory, Upton, New York 11973, USA 8Theoretical Physics Department, CERN, 1211 Geneva 23, Switzerland Searches for lepton flavor violation are extremely sensitive to physics beyond the Standard Model. Several experiments are going to probe uncharted parameter space in the near future; notably, the Mu2e experiment is aiming to improve sensitivity to µ− ! e− conversion in nuclei by several orders of magnitude over existing limits. Mu2e-II marks a potential upgrade of Mu2e with another order-of-magnitude increase in sensitivity. This remarkable reach will make Mu2e(-II) an important experiment to probe new physics, not only via µ− ! e− conversion, but potentially also via µ− ! e+ conversion or µ− ! e−X decays involving a light new boson X. Theory challenges of this project include comparing the sensitivity of different experiments to a given model, evaluating possible stopping targets to maximize complementarity, and understanding the unavoidable muon-decay-in- orbit background at this unprecedented precision. -
The Mu2e Experiment at Fermilab⇤
NuFact15 - Rio de Janeiro, Brazil - August 2015 The Mu2e Experiment at Fermilab⇤ 1, 2, Kevin R. Lynch † , (The Fermilab Mu2e Collaboration) ‡ 1Department of Earth and Physical Sciences, York College, City University of New York, 94-20 Guy R. Brewer Blvd, Jamaica, NY 11451 USA 2The Graduate Center, City University of New York, 365 Fifth Avenue New York, NY 10016 USA (Dated: April 18, 2016) 449 NuFact15 - Rio de Janeiro, Brazil - August 2015 Abstract The Mu2e Experiment at Fermilab will search for the coherent, neutrinoless conversion of a muon to an electron in the field of an atomic nucleus. Such charged lepton flavor violating events have never been observed, but are predicted to occur in many Beyond the Standard Model scenarios at rates accessible to our experiment. I outline the physics and key issues for the experiment, our progress on design and construction to date, and prospects for the future. INTRODUCTION The Mu2e e↵ort holds a prominent place in the near term future of the U.S. High Energy Physics program. In fact, the recent report of the Particle Physics Project Prioritization Panel (P5) - which advises the U.S. Government on HEP community priorities - advises completion of the Mu2e Experiment under all budget scenarios considered [1]. With a project baseline cost of $270 million, this involves a significant investment of available resources; why, then, this level of interest? Although charged lepton flavor violation (CLFV) has never been observed experimentally, we know that it must occur: neutrino flavor oscillations coupled with loops guarantees the existence of CLFV; see Figure 1. However, even with the most optimistic parameter values in the PMNS neutrino mixing matrix U, the Standard Model rate prediction is tiny 2 2 3↵ ∆m1k 54 Br(µ eγ)= Uµk⇤ Uek 2 < 10− . -
The Mu3e Ultra-Low-Mass Tracker
The Mu3e ultra-low-mass tracker Frank Meier Universit¨at Heidelberg for the Mu3e collaboration 25 June 2018 1 / 52 Introduction to Mu3e Mu3e is an experiment to search for + + + µ e e−e ! A very rare decay. We're in an unusual regime, hence allow for some physics background. 2 / 52 Introduction to Mu3e µ eee in the standard model. ! e+ + W γ∗ e− + + µ ν¯µ ν¯e e 3 / 52 Introduction to Mu3e µ eee in the standard model. ! SM: < 1 10 54 × − The suppression comes from the + neutrino masses. e 12 Current best limit: < 1 10− + × W γ∗ (SINDRUM 1988) e− Alternative models predict BR within 16 reach of Mu3e (< 1 10− ). + + × µ ν¯µ ν¯e e 3 / 52 Introduction to Mu3e {{ Signal in rφ-view e– e+ e+ Signal SM: < 1 10 54 × − 4 / 52 Introduction to Mu3e {{ Signal in rφ-view e– e+ e+ Signal SM: < 1 10 54 × − P pi = 0 4 / 52 Introduction to Mu3e {{ Signal in rφ-view e– e+ e+ Signal SM: < 1 10 54 × − P pi = 0 minv = mµ 4 / 52 Introduction to Mu3e {{ Signal in rφ-view e– e+ e+ Signal SM: < 1 10 54 × − P pi = 0 minv = mµ t = t i; j i j 8 4 / 52 Introduction to Mu3e {{ Signal in rφ-view e– e+ e+ Signal SM: < 1 10 54 × − P pi = 0 minv = mµ t = t i; j i j 8 common vertex 4 / 52 Introduction to Mu3e {{ Signal in rφ-view e– ν e– e+ e+ ν + e+ e Signal Radiative decay SM: < 1 10 54 SM: 3:4 10 5 × − × − P p = 0 P p = 0 i i 6 minv = mµ minv < mµ t = t i; j t = t i j 8 i j common vertex common vertex 4 / 52 Introduction to Mu3e {{ Signal in rφ-view – e– ν e– e e+ e+ e+ ν + e+ e e+ Signal Radiative decay Accidental SM: < 1 10 54 SM: 3:4 10 5 background × − × − P p = 0 -
Department of Physics and Astronomy
Department of Physics and Astronomy University of Heidelberg Master thesis in Physics submitted by Lennart Huth born in Buchen 2014 Development of a Tracking Telescope for Low Momentum Particles and High Rates consisting of HV-MAPS This Master thesis has been carried out by Lennart Huth at the Physikalisches Institut under the supervision of Herrn Prof. Dr. André Schöning Development of a Tracking Telescope for Low Momentum Particles and High Rates consist- ing of High-Voltage Monolithic Active Pixel Sensors Physics beyond the Standard Model (SM) of particle physics motivates the search for the charged lepton flavor violating decay m+ ! e+e−e+ by the Mu3e experiment. This decay is suppressed with a branching ratio below 10−54 within the SM. Detecting this decay would be a clear sign for new physics beyond the SM. Reaching the aimed sensitivity of better than one in 1016 m+− decays in a reasonable time requires excellent momentum and vertex resolution for background suppression at high decay rates O(109µ/s). The maximum energy of 53 MeV of the decay particles results in a multiple scattering limited vertex and momentum resolution requiring a detector with little material. These requirements will be fulfilled by a pixel detector consisting of 50 µm thin High-Voltage Monolithic Active Pixel Sensors (HV-MAPS) with a time resolution of better than 20 ns. A low momentum particle tracking telescope was developed to test the detector components and the data acquisition (DAQ) to perform a first integration test of the Mu3e detector and to use it at the Paul-Scherrer-Institue (PSI). -
Status of the Mu2e Experiment at Fermilab
EPJ Web of Conferences 234, 01010 (2020) https://doi.org/10.1051/epjconf/202023401010 FCCP2019 Status of the Mu2e experiment at Fermilab Stefano Miscetti1;a on behalf of the Mu2e Collaboration 1Laboratori Nazionali di Frascati dell’INFN, Via Enrico Fermi 40, 00044, Frascati, Italy Abstract. The Mu2e experiment aims to improve, by four orders of magnitude, current sensitivity in the search for the charged-lepton flavor violating (cLFV) neutrino-less conversion of a negative muon into an electron. The conversion process will be identified by a distinctive signature of a mono-energetic electron with energy slightly below the muon rest mass. In the Standard Model this process has a negligible rate. However, in many Beyond the Standard Model scenarios its rate is within the reach of Mu2e sensitivity. In this paper, we explain the Mu2e design guidelines and summarize the status of the experiment. 1 Introduction A solid international program continues nowadays with the upgrade of MEG [7, 8], the proposed Mu3e search Since flavor violation has been established in quarks and at PSI [7, 9] as well as the searches for muon to electron neutrinos, it is natural to expect flavor violating processes conversion with Mu2e at Fermilab [10] and COMET at J- also among the charged leptons. Albeit in the Standard PARC [7, 11]. These experiments plan to extend the cur- Model (SM) there is not any global symmetry requiring rent sensitivity of one or more orders of magnitude pro- lepton flavor violation, when massive neutrinos are in- viding access to new physics mass scales in the 103 -104 troduced, the SM provides a mechanism for cLFV via GeV range, well beyond what can be directly probed at neutrino-mixing in loops. -
The Mu2e Experiment at Fermilab: a Search for Charged Lepton Flavor Violation
The Mu2e Experiment at Fermilab: a Search for Charged Lepton Flavor Violation James Miller, Boston University, R. Bernstein, FNAL, on behalf of the Mu2e Collaboration. A new experiment, Mu2e, is being developed at Fermilab to measure the ratio of the rate of the neutrinoless, coherent conversion of muons into electrons in the field of a nucleus, relative to the rate of ordinary muon capture on the nucleus, P oA(,Z N )e A (,Z N ) RPe PQoA(,Z N )P A (Z 1,)N Mu2e expects a four orders of magnitude improvement on the experimental uncertainty in this ratio, providing a stringent test of the SM with an energy scale on the order of thousands of TeV. The conversion process is an example of charged lepton flavor violation (cLFV), where muon and electron numbers change by -1 and 1, respectively. Until the discovery of neutrino oscillations, lepton numbers in each generation were strictly conserved in the Standard Model (SM) for any interaction. In a simple extension of the SM that includes neutrino oscillations, an extremely small rate of muon to electron conversion is predicted, far below any foreseeable experimental sensitivity. Therefore a non-vanishing signal would be a definite sign of new physics. In most of the proposed models of physics beyond the SM, cLFV is allowed. Better experimental limits on cLFV processes produce ever tighter limits on the available parameters in these models. Although the existence of lepton generations and conservation of lepton numbers plays a central role in the SM, there is no understanding of the underlying symmetry that causes it. -
Physicists Raid Tevatron for Parts Fermilab Icon Plundered Amid Tight Budgets and Shifting Scientific Aims
IN FOCUS NEWS HIGH-ENERGY PHYSICS Physicists raid Tevatron for parts Fermilab icon plundered amid tight budgets and shifting scientific aims. BY EUGENIE SAMUEL REICH CANNIBALIZING THE TEVATRON Parts at the Tevatron and its two main experiments, the CDF and D0, are being t is a 4,000-tonne edifice that stands three considered for recycling in the wake of the collider’s closure in September 2011. stories high, chock full of particle detectors, Antiproton power supplies, electronics and photo source Imultiplier tubes, all layered like a giant onion Possibly open around a cylindrical magnet. During 26 years Booster of operation at the Fermi National Accelerator to visitors Laboratory in Batavia, Illinois, this behemoth, Main injector the Collider Detector at Fermilab (CDF), and recycler helped to find the top quark and chased the • Photomultiplier tubes for Higgs boson. But since the lab’s flagship parti- nuclear-structure experiment CDF cle collider, the Tevatron, was switched off in • Electronics for the Large September 2011, the detector has been surplus Hadron Collider in Europe • Central magnet for a stock — and it is now slowly being cannibal- possible particle-decay ized for parts. Beams repurposed experiment When the Tevatron closed, Fermilab for neutrino and • Possible educational display announced that the CDF would become an other experiments educational display. Along with its companion experiment, D0, the detector was supposed to form the centrepiece of a tour through simu- Tevatron lated control rooms and decommissioned Possible educational display accelerator tunnels. But tight budgets for experimental particle physicists — combined 500 m with their tendency to tinker and recycle — are pushing the outcome in a different direction, D0 at least for the CDF.