Measurement of the Positive Muon Lifetime to 1 ppm David Webber Preliminary Examination March 31, 2005

Outline Basics and theory How is the muon lifetime measured? MuLan experiment’s main components Systematics and design considerations Analysis cross-checks Personal contribution Conclusion

Basics Log(counts) time

Why is the muon lifetime important?

+ … The theoretical uncertainty on G F as extracted from the muon lifetime is < 0.3 ppm.

…it is extremely difficult to predict, even in the relatively short term, the accuracy to which fundamental parameters will be determined and it is important that these be extracted to the limits that the current theoretical and experimental technology allows. (Ritbergen and Stuart, hep-ph/ ) Why is the Muon Lifetime Important? 0.06 ppm9 ppm The goal of the Muon Lifetime Analysis (MuLan) experiment is to reduce the experimental uncertainty on G F to 0.5 ppm by measuring the muon lifetime to 1 ppm.

How is the muon lifetime measured? N=1

How is the muon lifetime measured? N=10

How is the muon lifetime measured? N=100

How is the muon lifetime measured? N=100

How is the muon lifetime measured? N=10 4

How is the muon lifetime measured? N=10 6

How is the muon lifetime measured? N=10 12

How long will it take? ~10 12 events necessary for 1 ppm measurement ~ 3 weeks beam time (usable) Pulsed beam ~1.6 years beam time 20 kHzContinuous beam ~10 4 years1 / 50 cm 2 s 1 / hand s Cosmic rays Time to Muon rateSource Scint. PMT Water ++ e+e+ ++ ++ e+e+ PMT

The MuLan Experiment #4 BEAM DETECTORS DAQ DIGITIZERS ++

The MuLan Experiment - Beamline Key Beamline Elements Production target Separator Kicker Entrance muon chamber Depolarizing target

The MuLan Experiment - Detector

The Mulan Experiment – Readout 2 Analog Pulses Waveform Digitizers Plan for runs x2

Systematics Early-to-late systematics Clock stability Pileup –2 pulses appear as one Muon spin precession Others –Sneaky muons –Instrumental changes –Kicker noise The most dangerous systematic effects occur “early-to-late” “early” “late”

Clock Stability A single clock drives the waveform digitizers The clock is tunable, and the analyzers only know the 4 most significant digits (500 ppm) Rubidium Atomic Clock MuLan Agilent Clock Error 60 MHz MHz20 ppb 30 MHz MHz20 ppb

Pileup Reduction Highly segmented detector (170 detector pairs) Analog readout by waveform digitizers Depolarize the collected muons

The importance of waveform digitizers Identify false pulses No missed pulses from pileup Pileup identification Good Pulse vs. Phototube Breakdown 2 pulses become 1 large pulse Pulse Area (outer) Pulse Area (inner)

Muon Spin Precession Muons are highly polarized and can remain so when they stop in the target Muon decay violates parity Muons precess in a magnetic field. Example: the Earth’s magnetic field will change the preferred decay direction by one detector in one muon lifetime

Muon Spin Precession - Fixes Point-like symmetric detector ball Depolarizing target –Sulfur has ~8% residual polarization –Arnokrome-3 (30% chromium, 10% cobalt, 60% iron) has 0.5 T internal field Ring magnet on sulfur dephases ensemble during accumulation Front Back Silver Target

Cross-Checks Multiple identical detectors LED system –Test-fire the detector –Check for timing shifts Stable clock system Blind analysis Analysis checks –Start-time scan –Stop-time scan Plots courtesy: D. Chitwood

Personal Contribution

Ball Discriminators TDCs Gigabit Switch TDC frontend Backend LED Drivers Flight Simulators Flight Simulator frontend High Voltage frontend High Voltage Entrance Muon Chamber TDCs EMC frontend Beamline frontend CAMAC frontend RAID and TAPE: Data Storage and Offline Analysis Ethernet Online Monitor PSI Archive Kicker Programmable gate generator Programmable gate generator frontend Marker Pulses MULAN Continuous Data Acquisition ADC/SCALER # fills protons hits in detector infinite persistence scope serial port enhanced parallel port network camac Muon Production Target Waveform Digitizers Waveform Digitizer frontends Discriminators Note: Yellow – Frontend programs Green – Frontend computers fiberoptic

The MuLan Experiment - Software “Good”“2 AM Phone Call”

High-rate, Entrance Muon Chamber I helped design the green boards (above), commissioned the chamber and readout electronics (above right), and wrote the real-time online beam profiler to the right.

Conclusion Basics of muon decay The MuLan experiment Systematics Personal contribution Last muon lifetime measurements  1984 –Muon decay gives best determination of G F –Muon lifetime gives the dominant error on G F –It is time to measure the muon lifetime again

Thank you!

References Ritbergen and Stuart, hep-ph/ Chitwood, Dan. “Measuring the Positive Muon Lifetime to 1 ppm.” Preliminary Exam Paper. September 23, R. M. Carey et al. MuLan Proposal.

History of the Muon Lifetime  Lan goal  5

Positron Michel Sprectrum Positron energy Relative Intensity Michel Spectrum 53 MeV

Why is the Muon Lifetime Important?

Model-independent extraction of G F General Analysis Restricted Analysis

Other “Early-to-Late” Effects Sneaky Muons –Fix: Entrance Muon chamber Instrumental Changes –Fix: LED test-firing system Kicker Noise –Recently reduced by 10 3 –Under investigation

The Mulan Experiment – Readout 2 Analog Pulses Time to Digital Converter Waveform Digitizer Discriminator 20-bit time word Now Planned for Runs

What is the Muon Lifetime?