1 Beam Extinction and Monitoring at the Upcoming Mu2e Experiment Ryan J. Hooper on behalf of the Mu2e Collaboration DPF 2015 August 5th, 2015

The What and How The What: Looking for (Charged Lepton Flavor Violation) The How: Muon beam into a target of atoms (Aluminum) Muon transition down to 1s orbitals, where they have a lifetime of 864 ns 2  e Electrons with this energy (105 MeV) indicate signal!

3 The How: The Mu2e Experiment An Overview Production Solenoid (PS) Transport Solenoid (TS) Proton beam (used to create muon beam) Detector Solenoid (DS) Production Target Stopping Target Tracker Calorimeter For further details please see these DPF 2015 talks: Marc Buehler: “The Mu2e Experiment at Fermilab” Craig Dukes: “A Cosmic Ray Veto Detector for the Mu2e Experiment at Fermilab” Jim Popp: “A Straw Tube Tracker for the Mu2e Experiment” Daniel Ambrose: “Straw Leak Testing for the Mu2e Tracker” Tomonari Miyashita: “The Mu2e Electromagnetic Calorimeter” Yuri Oksuzian: “Studies of Beam Induced Radiation Backgrounds at the Mu2e Experiment and Implications for the Cosmic Ray Veto Detector” Single event sensitivity of 2.4× protons on target (POT) ~ 3 years of running Less than 1 background event

4 The Issue Photon energy spectrum from radiative pion capture in Mg Particles produced in the primary target (pions, neutrons, antiprotons) which interact with the stopping target just after reaching it. Radiative pion capture (RPC)  - N →  N’,  → e + e -  - N → e + e - N’ Pion/muon decays in flight These electrons can have energies close to our 105 MeV signal candidates!

5 The Pulsed Proton Beam Selection Window, defined at center plane of the tracker Shapes are schematic, for clarity Solution: Use pulsed proton beam based on muonic aluminum lifetime of 864 ns Selection window turns on late enough “prompt” backgrounds are reduced significantly!

6 The Pulsed Proton Beam Selection Window, defined at center plane of the tracker Shapes are schematic, for clarity Out-of-time tails  backgrounds leaking into selection window But, what if protons are not well localized in time!

7 The Pulsed Proton Beam Allow sufficient time between pulses to reduce backgrounds 31 Mp = 31,000,000 protons/pulse Must enforce strict beam extinction!

8 Make Extinction … Even More Extinct Beam into the M4 beamline from the Recycler + Delivery Ring will already supply an extinction of or better The g-2 Fermilab’s

9 The How: M4 Beamline Extinction Further Extinction in the M4 beamline will be achieved via 2 AC Dipoles coupled to collimators Primary harmonic = 300 kHz = (3.333  s) -1

10 The How: The AC Dipoles Half-meter prototypes already built and tested (CMD10 ferrite)  s Some measured properties at Requisite field strength

11 The How: Simulation Results Green = ESME simulation of extracted beam from Delivery ring Black = G4Beamline simulation of external AC dipole + collimators Blue = Convolution of the two 1.0E ns Better than extinction for beam outside the 230 ns transmission window!

Primary target + production solenoid Beam dump Extinction monitor Filter Pixel detector 12 Trust But Verify! Extinction Monitor: Must measure extinction to precision Good timing resolution Situated downstream and off-axis from target and production solenoid Allows for the detection of a small fraction (10-50 per in-time bunch) of scattered particles from production target Build a statistical profile for in-time and out-of-time beam Measurement done on ~ 1 hour timescale Repurposed dipole magnet Collimators Proton beam

13 The Extinction Monitor Scintillators coupled to PMTs for triggering and additional timing information Spectrometer Magnet: Repurposed dipole magnet bends out low energy elections generated by muons stopping in the upstream silicon Silicon pixels for fast, high resolution tracking

14 The Pixels FE-I4 silicon chips developed for the ATLAS B-layer upgrade Each chip = 26,880 pixels arranged into 80 columns on 250  m pitch by 336 rows on a 50  m pitch. Hits digitized on 24.9 ns cycle (24.9 ns = 1694 ns / 68 ticks) Production expertise already in place

15 Simulated Performance G4Beamline based simulation Momentum (GeV/c) Particle ID: 85% p + 1%  13%  ~0% electrons Efficiency based on hits in all 6 detector planes using protons The 0.83×10 -7 per proton on target (POT) comfortably meets requirements

16Summary  Mu2e a NEW Fermilab based experiment  Will measure muon-to-electron conversions at a level of sensitivity 10,000 times better than current state-of-the-art  To achieve this level of sensitivity the intense proton pulses must have an extinction of ~ between pulses  Extinction at this level is achievable using current plus planed Fermilab accelerator technologies  Extinction monitoring at the level will be achieved via repurposed, piggy backed and well known technologies For Further Details Home page: CDR: New (Jan. 2015) Technical Design Report (TDR):

17 Additional Slides

18 The Accelerator Complex at Fermilab The Accelerator Complex at Fermilab The Where: Fermilab South to Chicago (35 mi) Will supply intense (3×10 7 protons/pulse) pulsed proton beamWill supply intense (3×10 7 protons/pulse) pulsed proton beam

19 The How: What Happens Most of the Time Nuclear Capture (~61% for Al) Muon Decay in Orbit (DIO) (~39% for Al) 27 Al 27 Mg* p n   Hadron and photon final states  e E e (MeV) See e.g. Czarnecki et al., Phys. Rev. D 84, (2011) Notice some contribution in signal region

20 Effect on Mu2e Backgrounds Extinction and Extinction Monitoring is in place to keep the Late Arriving backgrounds low (< levels) Backgrounds based on extinction and ~3 years of running

21 Current Status Calendar Year Critical path: Solenoids Today Assemble and commission the detector We are entering a great time for students to get hands-on experiences!

22 The Device Pre-monitor highlights: Two collimators + Filter/kinematic magnet Note aperture on exit collimator increases to reduce possible interactions just before detectors. Repurposed dipole magnet to select particles with average momentum of 4.2 GeV/c.

23 An Overview of Just One Proton Bunch

24 The Trigger Counters 5 mm thick × 45 mm × 40 mm upstream; 45 mm × 55 mm downstream BC-404 scintillator readout via Hamamatsu ¾” PMT.

25 The Muon ID Range Stack Monitors muon backgrounds to the extinction monitor that were generated around the Production Solenoid Consists of several 40 cm square steel plates arranged into a 180 cm deep stack. Four scintillating planes will be used for readout BC-404 scintillator with embedded Y11 waveshifter fibers + PMT readout

26 Extinction Monitor Backgrounds Cosmic rays Interactions of late arriving particles created by the proton beam Radioactive decays in pixel sensors Electronic noise Only cosmics can produce out-of-time tracks with sufficient momenta to give 6 pixel hits (estimated to be 0.030±0.007 tracks/hour) Late arrivals estimated by MARS+GEANT4 (0.03±0.007 tracks/hour)