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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, comet II SESAPS, Fall 2016 9 Possible Physics Processes SESAPS, Fall 2016 10 The ratio: m ->e /m ->eg ~ a ~1/a (1/137) (137) SESAPS, Fall 2016 11 SESAPS, Fall 2016 12 (MEG) m -> eg SESAPS, Fall 2016 13 Difficulties Accidental background Detector resolution SESAPS, Fall 2016 14 m -> eee (Mu3e collaboration) SESAPS, Fall 2016 15 Expected run : 2018 SESAPS, Fall 2016 16 m to e experiments • What do we measure: • Goal (2015) ~ 10-16 -10-17 • How : – generate a large number of negative muons – stop & capture and they decay to e- – the momentum of the electron is ~mass of the muon (105.66 MeV). This is a very distinct signal. SESAPS, Fall 2016 17 History (m to e) 18 SINDRUM II B(μ +Au -> e +Au) < 7x1013 SESAPS, Fall 2016 19 SESAPS, Fall 2016 20 Improvements • More stopping muons (~1018m, m/p ~ 0.0016) • Reduce background from proton target – Pulsed beam and no data taking for ~700 ns 3x107p/pulse – Beam is monitored with extinct monitor detector – Curved solenoid : remove neutral and positive particles • Better tracking - momentum resolution SESAPS, Fall 2016 21 Mu2e Detector System Al target 4.6T 2.5T 2.5T 2.1T 2 T 1 T SESAPS, Fall 2016 22 MELC (1989) MECO (2005) SESAPS, Fall 2016 23 -protons hit W target -produce mostly pions p -pions decay to muons with t = 26 ns -remove photons and neutrons -negative charges are selected -Antiprotons are reduced (absorber) SESAPS, Fall 2016 24 Stopping target • Made of 21 aluminum foil (0.15 mm thick) • Stop muons via dE/dx • Form muonic atom (~ ps) and then - - -Decay in orbit (m ->e nmne) main background -Captured by nuclei - (m N(A,z) -> nmN*(A,z-1)) Our denominator in Rme -Conversion – the signal ~ 20 fm SESAPS, Fall 2016 25 Denominator in Rme - capture : m N(A,Z) -> nmN*(A,Z-1) - (m p -> nmn) N*(A,Z-1) ->N(A,Z-1)+g ALCAP SESAPS, Fall 2016 26 Main background • The maximum momentum of muons decaying in free space is 52.8 MeV - - (m ->e nmne ). e nmne • But for DIO because of nuclei the momentum spectrum changes. This dictates our detector momentum resolution requirement. e N nmne SESAPS, Fall 2016 27 Detector • Straw tracker – Inside 1 T magnetic field – Measure momentum. Designed to measure ~ 50- 100 MeV transverse momentum particles. • Cosmic ray veto (CRV) – Surround the entire detector solenoid • E&M calorimeter – Made of CsI – Identify electrons SESAPS, Fall 2016 28 Straw Tracker • Basic component – 150 mm thick 5 mm diameter tube with 25 mm anode wire • 96 straws make a panel • 12 panels make a plane panel plane 29 • There are 18 planes (144 tube layers) • Operation in vacuum with very low leak rate • Resolution ~ 150 mm • Charge division ~ 2 cm along the wire Straw Tracker SESAPS, Fall 2016 30 B 2 T 1 T 100 MeV Target 50 MeV SESAPS, Fall 2016 31 CRV 3 out of 4 coincidence • 5504 total scintillators • 50 x 20 x 900-6600 mm3 • Two 1.4-mm diam, wavelength shifting fibers • 2 x 2 mm2 SiPM SESAPS, Fall 2016 32 EM calorimeter 674 CsI 34x34x200 mm3 square crystals UV extended SiPM (14x20 mm2) CsI crystals SESAPS, Fall 2016 33 Distinguish between electrons and other particles (m, p, p ,K) Aid tracking with timing SESAPS, Fall 2016 34 Other backgrounds • m- - - – decay in flight : m ->e nmne - + - – radiative capture: m N ->nmgN -> g ->e e • p- - - – decay: p ->e ne – Radiative capture: p-N ->gN -> g ->e+e- +/- 0 +/- • 푝 interaction with target : p p K KS • cosmic muons SESAPS, Fall 2016 35 Summary of backgrounds SESAPS, Fall 2016 36 expected signal with background from simulation SESAPS, Fall 2016 37 Phase II run schedule is Similar to Mu2e (2021) Phase I is moving well. Data : 8/2018 -8/2019 ses : ~3x10-15 SESAPS, Fall 2016 38 Goal Parameter Mu2e Comet Run time 3 years 1 year Proton on target 3.6 x 1020 8.5x1020 18 18 Stopping m (Nm) 0.7x10 1.6x10 m Capture (Cm) 0.609 0.6 0.085 0.04 Acceptance (Am) SES 2.8x10-17 2.6x10-17 Total background 0.36 0.34 SES = 1/Nm CmAm SESAPS, Fall 2016 39 CFLV Limits Mu3e MEG upgrade comet I Mu2e, comet II SESAPS, Fall 2016 40 Summary • SM is complete and working beautifully • Search for BSM physics is in full swing • Mu2e starts data taking 2021 • Stay tuned SESAPS, Fall 2016 41.
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