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 HowThe 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
m
e
Electrons with this energy (105 MeV) indicate signal!
The How: The Mu2e ExperimentAn Overview
Production Solenoid (PS)
Transport Solenoid (TS)
Proton beam (used to create muon beam)
Detector Solenoid (DS)
Production TargetStopping Target
TrackerCalorimeter
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 2.4×10-17
1020 protons on target (POT) ~ 3 years of runningLess than 1 background event
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) p- N → g N’, g → e+e-
p- N → e+e- N’
• Pion/muon decays in flight
These electrons can have energies close to our 105 MeV signal candidates!
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!
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!
The Pulsed Proton Beam
Allow sufficient time between pulses to reduce backgrounds
31 Mp = 31,000,000 protons/pulse
Must enforce strict beam extinction!
Make Extinction … Even More Extinct
Beam into the M4 beamline from the Recycler + Delivery Ring will already supply an extinction of 10-4 or better
The g-2
Fermilab’s
The How: M4 Beamline ExtinctionFurther Extinction in the M4 beamline will be achieved via 2 AC Dipoles coupled to collimators
Primary harmonic = 300 kHz = (3.333 ms)-1
The How: The AC DipolesHalf-meter prototypes already built and tested (CMD10 ferrite).
3.33 ms
Some measured properties at
Requisite field strength
The How: Simulation ResultsGreen = ESME simulation of extracted beam from Delivery ringBlack = G4Beamline simulation of external AC dipole + collimatorsBlue = Convolution of the two
1.0E-11
115 ns
Better than 10-11 extinction for beam outside the 230 ns transmission window!
Primary target + production solenoid
Beam dump
Extinction monitor
Filter Pixel detector
Trust But Verify!Extinction Monitor:• Must measure extinction to 10-10 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
Prot
on b
eam
The Extinction MonitorScintillators 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
The Pixels• FE-I4 silicon chips developed for the ATLAS B-layer
upgrade• Each chip = 26,880 pixels arranged into 80 columns on 250
mm pitch by 336 rows on a 50 mm pitch.
• Hits digitized on 24.9 ns cycle (24.9 ns = 1694 ns / 68 ticks)• Production expertise already in place
Simulated PerformanceG4Beamline based simulation
Momentum (GeV/c)
Particle ID:85% p+
1% m13% p
~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
Summary 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 ~10-10 between pulses
Extinction at this level is achievable using current plus planed Fermilab accelerator technologies
Extinction monitoring at the 10-10 level will be achieved via repurposed, piggy backed and well known technologies
For Further DetailsHome page: http://mu2e.fnal.govCDR: http://arxiv.org/abs/1211.7019New (Jan. 2015) Technical Design Report (TDR): http://arxiv.org/abs/1501.05241
Additional Slides
• The Accelerator Complex at FermilabThe Where: Fermilab
South
to Chicago(35 mi)
• Will supply intense (3×107 protons/pulse) pulsed proton beam
The How: What Happens Most of the TimeNuclear Capture (~61% for Al)
Muon Decay in Orbit (DIO) (~39% for Al)
27Al 27Mg* pn
nm
m
Hadron and photon final states
nm
e
Ee (MeV)
See e.g. Czarnecki et al., Phys. Rev. D 84, 013006 (2011)
Notice some contribution in signal region
Effect on Mu2e BackgroundsExtinction and Extinction Monitoring is in place to keep the Late
Arriving backgrounds low (< 0.023 levels)
Backgrounds based on 10-10 extinction and ~3 years of running
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!
The DevicePre-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.
An Overview of Just One Proton Bunch
The Trigger Counters
5 mm thick ×45 mm × 40 mm upstream;45 mm × 55 mm downstream
BC-404 scintillator readout via Hamamatsu ¾” PMT.
The Muon ID Range StackMonitors 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)