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)