1. The Mu2e experiment at Fermilab Finding a needle in a trillion haystacks Bertrand Echenard California Institute of Technology APS Meeting – April 2013 - Denver

2. Bertrand Echenard - APS Meeting - April 2013 - p.2 The Mu2e experiment will study muon-to-electron conversion in the coulomb field of a nucleus:  → e   (more on that later). Muon-to-electron conversion is a charged lepton flavor violating process (CLFV). These reactions are strongly suppressed in the Standard Model. For example, BR(  → e  ) < 10 -50 in the SM, effectively zero!!! New Physics can enhance CLFV rates to observable values Observation of CLFV is New Physics Mu2e and charged lepton flavor violation  00 ~ lili ~  e ljlj ~ qq  - q → e - q

3. Bertrand Echenard - APS Meeting - April 2013 - p.3 Already a long history… Many people have searched for CLFV in many different channels! I’ll discuss muon-to-electron conversion and the Mu2e experiment

4. Bertrand Echenard - APS Meeting - April 2013 - p.4 Muon-to-electron conversion Neutrinoless conversion of a muon to an electron in the field of a nucleus  - N → e - N Neutrinoless conversion of a muon to an electron in the field of a nucleus  - N → e - N Experimental signature: One single mono-energetic electron For N=Al, electron energy = 105 MeV Coherent process, the nucleus remains intact  e

5. Bertrand Echenard - APS Meeting - April 2013 - p.5 Complementary to other CLFV searches (e.g.  → e  and direct searches at the LHC Can probe mass scales way beyond direct reach of LHC New Physics can enhance rate to observable values, either through loops or exchange of heavy intermediates particles “Loop”“Contact” A. De Gouvea   (TeV)  Probing New Physics

6. Bertrand Echenard - APS Meeting - April 2013 - p.6 Antusch et al.,hep-ph/0610439 CMSSM - seesaw BR(  →  ) BR(  → e  MEG B A B AR Belle Mu2e current SUSY GUT in an SO(10) framework (tan  =10) Project X M 1/2 (GeV) L. Calibbi et al., hep-ph/0605139 Complementary with the LHC experiments, provide model discrimination Minimal Flavor Violation (CKM) Neutrino-Matrix Like (PMNS) CR(  → e) x 10 12 Probing New Physics

7. Bertrand Echenard - APS Meeting - April 2013 - p.7 The Mu2e collaboration Boston University Brookhaven National Laboratory University of California, Berkeley University of California, Irvine California Institute of Technology City University of New York Duke University Fermilab University of Houston University of Illinois, Urbana-Champaign University of Massachusetts, Amherst Lawrence Berkeley National Laboratory Lewis University Los Alamos National Laboratory Northern Illinois University Northwestern University Rice University University of Virginia University of Washington, Seattle Boston University Brookhaven National Laboratory University of California, Berkeley University of California, Irvine California Institute of Technology City University of New York Duke University Fermilab University of Houston University of Illinois, Urbana-Champaign University of Massachusetts, Amherst Lawrence Berkeley National Laboratory Lewis University Los Alamos National Laboratory Northern Illinois University Northwestern University Rice University University of Virginia University of Washington, Seattle ~130 collaborators and growing… Istituto G. Marconi Roma Laboratori Nazionale di Frascati Università di Pisa, Pisa INFN Lecce and Università del Salento Gruppo Collegato di Udine Istituto G. Marconi Roma Laboratori Nazionale di Frascati Università di Pisa, Pisa INFN Lecce and Università del Salento Gruppo Collegato di Udine Institute for Nuclear Research, Moscow, Russia JINR, Dubna, Russia Institute for Nuclear Research, Moscow, Russia JINR, Dubna, Russia

8. Bertrand Echenard - APS Meeting - April 2013 - p.8 Fermilab muon campus Mu2e g-2 Small changes to existing accelerator complex, reuse as much as possible Mu2e and g-2 can run this decade (8 GeV muon program) Run in parallel with the Nova experiment (neutrino experiment) And you’re close to the cafeteria…

9. Bertrand Echenard - APS Meeting - April 2013 - p.9 Mu2e overview Production Target / Solenoid Proton beam strikes target, producing mostly pions Graded magnetic field contains backwards pions/muons and reflects slow forward pions/muons Transport Solenoid Selects low momentum, negative muons Antiproton absorber in the mid-section Target, Detector and Solenoid Capture muons on Al target Measure momentum in tracker and energy in calorimeter Graded field “reflects” downstream conversion electrons emitted upstream (isotropic process) protons 2T 1T 2.5T 4.6T

10. Bertrand Echenard - APS Meeting - April 2013 - p.10 Pulsed beam and delayed search window Beam hits target Prompt background Mainly Decay In Orbit (DIO) background Next bunch Pulsed beam with beam extinction between bunches and delayed search window reduces prompt backgrounds like  - N →  N*,  → e + e - and  - N → e + e - N*.

11. Bertrand Echenard - APS Meeting - April 2013 - p.11 Expected sensitivity 3 years running period with 1.2x10 20 protons on target per year Bottom line: Single event sensitivity: R  e =2x10 -17 90% C.L. (if no signal) : R  e <6x10 -17 Typical SUSY Signal:~50 events or more for rate 10 -15 p MeV/c Reconstructed momentum assuming conversion rate 10 -15 Expected backgrounds

12. Bertrand Echenard - APS Meeting - April 2013 - p.12 Mu2e schedule The schedule is technically limited, driven by the solenoid construction Start construction in ~ two years and start taking data (cosmic rays) by ~ 2019. Interesting project for students, plenty of things for to do on many aspects of the experiment before taking the data.

13. Bertrand Echenard - APS Meeting - April 2013 - p.13 Conclusion We will measure muon-to-electron conversion with a single event sensitivity R  e ~2x10 -17. Mu2e is complementary to the LHC, and will either improve the current limit on R  e by four orders of magnitude, probing New Physics up to 10 4 TeV OR provide unambiguous evidence of Physics beyond the Standard Model, and help elucidate the nature of New Physics. The sensitivity of Mu2e at Project X will further improve by two orders of magnitude, either studying the signal in detail or improving limits. In this one…