Ivan Logashenko for Mu2e Collaboration Workshop on e+e- collisions from Phi to Psi, Sep.19-22, 2011 Novosibirsk, Russia

Search for cLFV We had several talks on cLFV already – MEG, COMET, BELLE,… Why is it interesting? Charged Lepton Flavour Violation in SM is extremely small. Any detectable signal is a sign of New Physics. Why muons? Copiusly produced We are trying to measure Standard Model predicts extremely small value: e+e- collisions from Phi to Psi Novosibirsk, 2011

History of Mu2e Mu2e goal: The current best limit was obtained at SINDRUM II experiment (90’s-2000) Mu2e is the successor of two earlier proposals: MELC at Moscow, early 90’s The main ideas of the experimental design were proposed MECO at Brookhaven, early 2000’s Part of RSVP program, along with KOPIO, search for K->pinunu At lof of design work and R&D were performed before the program was terminated Mu2e goal: e+e- collisions from Phi to Psi Novosibirsk, 2011

Mu2e vs MEG μ → eγ decay and μN → eN conversion are complementary “Model-independent” lagrangian: Mu2e @ProjectX Mu2e k << 1 magnetic moment type m → eg rate ~300X mN → eN rate MEG MEG 2011 k >> 1 four-fermion interation almost no contribution to m → eg MEGA SINDRUM II e+e- collisions from Phi to Psi Novosibirsk, 2011

Overview of the technique Stop muons in aluminum Muons quickly get to 1S orbit Lifetime of muonic atom is 864 ns Look for 105 MeV electron Hydrogen-like atom Bohr radius ≈20 fm Nucleus radius ≈4 fm Use X-rays to monitor number of muons Most of the background is well below this energy e+e- collisions from Phi to Psi Novosibirsk, 2011

Background: Muon decay-in-orbit (DIO) For decay-in-orbit , the maximum energy of electron is equal to the energy of conversion electron (≈105 MeV). The high-energy tail Need good energy resolution to beat this background! Free muon In-orbit Long tail! e+e- collisions from Phi to Psi Novosibirsk, 2011

Background: Radiative muon capture (RMC) Muon capture is the source of many background particles: This background is mostly low energy, but: Radiative Muon Capture: with small BR≈10-5, γ’s from muon captures can have high energy up to source of high energy electrons, comparable with DIO at the tail: γ can convert in target to e+e- pair, and electron can get almost all energy With good energy resolution and proper choice of target (MZ-1>MZ) this source of background is under control e+e- collisions from Phi to Psi Novosibirsk, 2011

Background: Radiative pion capture (RPC) Muon are produced from pion decays, therefore there are pions in the muon beam. Radiative Pion Capture: pions stop at the target and promptly annihilate on the nucleus with BR~10-2, γ is produced with energy up to 137 MeV (for Al) source of high energy electrons: γ can convert in target to e+e- pair, and electron can enough energy to mimic conversion electron This is prompt background, it quickly dies away. Solution: pulsed beam. Time distribution of stopped pions in the target e+e- collisions from Phi to Psi Novosibirsk, 2011

Overview of the design Production Solenoid 4 m long Transport Solenoid 13 m long Detector Solenoid 12 m long e+e- collisions from Phi to Psi Novosibirsk, 2011

Historical perspective: MELC proposal (1992) e+e- collisions from Phi to Psi Novosibirsk, 2011

Production Solenoid e+e- collisions from Phi to Psi Novosibirsk, 2011

Extinction To avoid prompt background, we use pulsed beam The signal is extremely rare Need extinction factor 10-10! …and it has to be measured Use combination of techniques to achieve this factor e+e- collisions from Phi to Psi Novosibirsk, 2011

Accelerator e+e- collisions from Phi to Psi Novosibirsk, 2011

Mu2e vs NOvA vs g-2 Mu2e can operate concurrently with FNAL neutrino experiments (NOvA) we use 6 out of 18 Booster batches, which NOvA can’t use during Main Injector cycle G-2 and Mu2e use the same beam, but in a different manner cannot run concurrently, but there is effort to make it possible to switch between the experiments e+e- collisions from Phi to Psi Novosibirsk, 2011

Muon Beam Line Negative gradient magnetic mirrow no trapped particles Uniform field in tracker region good resolution Torroidal field in the transport solenoid separation e+e- collisions from Phi to Psi Novosibirsk, 2011

Transport Solenoid e+e- collisions from Phi to Psi Novosibirsk, 2011

Stopping target 17 Al disks, 200 mkm thickness Why Aluminum? Perfect for this experiment higher Z: larger conversion rate different contributions to the rate lower Z: larger lifetime higher conversion energy e+e- collisions from Phi to Psi Novosibirsk, 2011

T-tracker 18 stations x 12 panels x 2x50 straws =21600 straws 5 mm dia. Mylar straws, 15 μm walls, 20 μm Au-plated W wire 200 μm position resolution e+e- collisions from Phi to Psi Novosibirsk, 2011

Measuring the momentum Low energy e- pass undetected For high energy e- we detect several points on the helix e+e- collisions from Phi to Psi Novosibirsk, 2011

Calorimeter Located downstream of tracker Main purpose: to provide trigger (1 kHz for E>80 MeV) Provides redundant position, timing and energy data Possible design: 2112 LYSO crystals, 3x3x13 cm3 arranged in 4 vanes. Density 7.3g/cm3, Moliere radius 2.07 cm, Rad. Length 1.14 cm, decay time 40 ns. Light yield relative to NaI 85%. Two APDs per crystal e+e- collisions from Phi to Psi Novosibirsk, 2011

Cosmic rays can generate high energy electrons Cosmic Ray Shield Cosmic rays can generate high energy electrons Need high suppression factor – a lot of cosmic ray events over 2 year running period Combination of passive (magnetized iron + dirt) and active (scintillation counters) shielding 99.99% coverage e+e- collisions from Phi to Psi Novosibirsk, 2011

Expected sensitivity 1.8x1013 p/s Proton flux 2x107 s Running time Total protons 3.6x1020 p Stopped μ per proton 0.0025 μ capture probability 0.61 Time window 0.49 Trigger efficiency 0.80 Selection efficiency 0.19 Sensitivity (90% CL) 6x10-17 Events for Rμe=10-16 4 Estimated background 0.18 e+e- collisions from Phi to Psi Novosibirsk, 2011

What we expect to see e+e- collisions from Phi to Psi Novosibirsk, 2011

Project schedule July 2005 RSVP @BNL cancelled for financial reasons not related to MECO October 2007 Mu2e LOI submitted to Fermilab Fall 2008 Proposal submitted to Fermilab and receives Stage I approval November 2009 CD0 status granted 2010-2011 R&D and design, preparation of CDR 2012 CD1 ~2013 CD2, Start of Solenoid Construction ~2018-2020 Start of data taking e+e- collisions from Phi to Psi Novosibirsk, 2011

Project X There is proposal to replace FNAL’s Booster with new 8 GeV high-intensity linear accelerator, based on ILC technologies – “Project X” Project X would feed neutrino and rare decay/high precision experiments Potential to upgrade Mu2e by factor x100! set much stronger limits (if there is no signal) or use different target materials to study nature of new physics (if there is signal) Serious upgrade of the detector is required e+e- collisions from Phi to Psi Novosibirsk, 2011

Conclusion In May 2008 P5 (US Particle Physics Project Prioritization Panel) Report stated: “recommends pursuing the muon-to-electron conversion experiment under all budget scenarios considered by the panel.” Why? Mu2e experiment will allow to improve the current limit by 4 orders of magnitude if signal is found, it will be an undeniable proof of the New Physics and it will provide data, complementary to LHC if no signal is found, it will set constrains much stronger than LHC (up to 1000 TeV mass scale) with better muon source and other upgrades, the limits can be improved by another 2 orders of magnitude e+e- collisions from Phi to Psi Novosibirsk, 2011