Precision muon lifetime at PSI

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Swiss Physical Society Annual Meeting Bern July 14 2005 p.

1 Swiss Physical Society Annual Meeting Bern July p. 1/23 Precision muon lifetime at PSI MuLan Experiment Françoise Mulhauser, University of Illinois at Urbana Champaign (USA) and Paul Scherrer Institute (Switzerland) On behalf of the MuLan Collaboration

2 Outline Swiss Physical Society Annual Meeting Bern July p. 2/23 Motivation: Theory and actual experimental situation Experimental Principle: How will we reach 1 ppm precision Kicker: Principle and results Detectors: Scintillators and Wire chamber First Results: Run December 2004 Future: This year and the next ones

3 Scientific Questions Swiss Physical Society Annual Meeting Bern July p. 3/23 What are the fundamental electroweak parameters? G F, α(z), m Z Precision µ + lifetime

4 Scientific Questions Swiss Physical Society Annual Meeting Bern July p. 3/23 What are the fundamental electroweak parameters? G F, α(z), m Z Precision µ + lifetime µ + e + + ν e + ν µ Current World average τ µ + = ±0.04 ns (18ppm) ±0.002 ns (1ppm)

5 Muon Lifetime Swiss Physical Society Annual Meeting Bern July p. 4/23 The muon lifetime τ µ is closely related to the Fermi coupling constant GF, which sets the basic strength of the weak interaction: 1 τ µ = G2 F m5 µ 192π 3 (1 + δq ) QED radiative corrections: Two-loop diagrams finished in 1999 by Stuart and van Ritbergen ; now known to < ± 0.3 ppm (previously ± 30 ppm) Extraction of G F is now limited by the muon lifetime a truly fundamental parameter of the standard model that should be measured as precisely as possible with today s technology. T. van Ritbergen and R.G. Stuart, Phys. Rev. Lett. 82, 488 (1999); and Phys. Rev. D 437, 201 (1998).

6 Experimental status Swiss Physical Society Annual Meeting Bern July p. 5/23 Lifetime [µs] µ Duclos 73 Balandin 74 Bardin 84 Giovanetti 84 Experiments mostly statistics limited PDG: τµ = ± µs (18 ppm) Our goal: 1 ppm uncertainty in τµ (0.5 ppm in G F ) δg F G F = 4 m2 ν µ m 2 µ (< 25 ppb) 5 2 δm µ m µ (75 ppb) 1 2 δτ µ τ µ (9 ppm)

7 10 12 Statistics: more than one muon at a time Swiss Physical Society Annual Meeting Bern July p. 6/23 1 ppm measurement at least stopped muons. Each muon (or pion) enters target individually with pre and post quiet periods. Watch for decay positron and record its time. For muon, one need about s... several years! To be practical, we need to observe several muons at once:

8 10 12 Statistics: more than one muon at a time Swiss Physical Society Annual Meeting Bern July p. 6/23 1 ppm measurement at least stopped muons. Each muon (or pion) enters target individually with pre and post quiet periods. Watch for decay positron and record its time. For muon, one need about s... several years! To be practical, we need to observe several muons at once: Spatial separation: FAST π arrive continuously into highly segmented timer/tracker; several events can overlap

9 10 12 Statistics: more than one muon at a time Swiss Physical Society Annual Meeting Bern July p. 6/23 1 ppm measurement at least stopped muons. Each muon (or pion) enters target individually with pre and post quiet periods. Watch for decay positron and record its time. For muon, one need about s... several years! To be practical, we need to observe several muons at once: Spatial separation: FAST π arrive continuously into highly segmented timer/tracker; several events can overlap Bunched muons: MuLan Many muons arrive at once and decay into segmented detector

10 Muon Lifetime Techniques Swiss Physical Society Annual Meeting Bern July p. 7/23 Burst of N muons arrives during accumulation period Tacc Observe muon decays during measuring period of length T meas No other muons arrive during this time Get another burst Ideally: A small N = Reduces pileup T acc + T meas 32µs = Cycles fast Counts 10 6 Accumulation Period Measurement Period Kicker On Background Time Relative to Kicker [ns]

11 Swiss Physical Society Annual Meeting Bern July p. 8/23 Pulsed Muon Beam Collect handful of muons in a few µs Accumulation Period

12 Swiss Physical Society Annual Meeting Bern July p. 8/23 Pulsed Muon Beam Turn off beam and watch them decay Measurement Period

13 πe3: Adequate flux but high complexity Swiss Physical Society Annual Meeting Bern July p. 9/23 A Beam Rate > 12 MHz; Spot at target, only few cm 2. Separator leaves about 5 10% positron background. Many elements to tune. Tricky to have a straight beam. Extinction fraction looks reasonable. The Final transport through helium.

14 Kicker Time-line Swiss Physical Society Annual Meeting Bern July p. 10/23

15 Fast Kicker Swiss Physical Society Annual Meeting Bern July p. 11/23 TRIUMF-built kicker

16 Swiss Physical Society Annual Meeting Bern July p. 11/23 Fast Kicker TRIUMF-built kicker 45 ns rise/fall time, ± 25 kv swing, two 75 cm plates

17 Swiss Physical Society Annual Meeting Bern July p. 11/23 Fast Kicker TRIUMF-built kicker 45 ns rise/fall time, ± 25 kv swing, two 75 cm plates Extinction factor is quite subtle (seems momentum dependent) 300 during Run 2004 > 1000 in during Beam test in 2005.

18 Swiss Physical Society Annual Meeting Bern July p. 11/23 Fast Kicker TRIUMF-built kicker 45 ns rise/fall time, ± 25 kv swing, two 75 cm plates Extinction factor is quite subtle (seems momentum dependent) 300 during Run 2004 > 1000 in during Beam test in Some bad news too... We killed many MOSFETS in We ran with half of them, at lower voltage.

19 Scintillators: 32 sided, soccer ball geometry Swiss Physical Society Annual Meeting Bern July p. 12/23 The complete detector has 30 active houses, with 170 tile pairs

20 The Crew Swiss Physical Society Annual Meeting Bern July p. 13/23

21 The Detector in Area Swiss Physical Society Annual Meeting Bern July p. 14/23

22 Impact of muon spin rotation (µsr) Swiss Physical Society Annual Meeting Bern July p. 15/23 The muon beam is polarized = muon precesses in magnetic field Decay e + s are preferentially emitted in the direction of the µ + spin. Residual polarization effects will produce direction-dependent distortions in the µ + lifetime histograms. Pointlike symmetric geometry Fit F + B Monitor F B

23 Impact of muon spin rotation (µsr) Swiss Physical Society Annual Meeting Bern July p. 15/23 The muon beam is polarized = muon precesses in magnetic field Decay e + s are preferentially emitted in the direction of the µ + spin. Residual polarization effects will produce direction-dependent distortions in the µ + lifetime histograms. Pointlike symmetric geometry Fit F + B Monitor F B

24 Swiss Physical Society Annual Meeting Bern July p. 16/23 Impact of muon spin rotation (µsr) Silver preserves muon polarization (100%) Sulfur residual polarization (8%) Arnokrome-3 (AK3) (30% chromium, 10% cobalt, 60% iron) Internal Field 1 T No observable precession frequency up to 320 MHz or < B >= 2.4 T

Double-Pulse Resolution - Hit Pileup Swiss Physical Society Annual Meeting Bern July 14

25 Double-Pulse Resolution - Hit Pileup Swiss Physical Society Annual Meeting Bern July p. 17/23 detector modularity: 170 tile pairs new electronics: 500 MHz wave form digitizers

Sneaky Muons Swiss Physical Society Annual Meeting Bern July 14 2005 p.

26 Sneaky Muons Swiss Physical Society Annual Meeting Bern July p. 18/23 During beam-off period sneaky muons lead to time dependent background high rate (MHz), thin, fast (30 ns FWHM) wire chamber Efficiency >95%, stable within 5% Active Area mm

27 Beam Profile Swiss Physical Society Annual Meeting Bern July p. 19/23 y raw x and y hits rawxy Entries e+07 Mean x Mean y RMS x RMS y raw x and y hits rawxy Entries e+07 Mean x Mean y RMS x RMS y x y x rawx counts vs channel rawx Entries e+07 Mean RMS identifier rawy counts vs channel rawy Entries e+07 Mean RMS identifier

28 First physics fits Swiss Physical Society Annual Meeting Bern July p. 20/23 (the clock timescale is only approx in ns... and they don t know the offset) All kicked data summed up without too much screening N(t) = N 0 e t τ + B Better than 10 ppm and good, stable fits (so far)

29 Fit Stability Swiss Physical Society Annual Meeting Bern July p. 21/23 Stability of fit parameters versus fit start time is a good barometer of fit quality

30 Fit Stability Swiss Physical Society Annual Meeting Bern July p. 21/23 Also important, behavior of different detectors...

31 Fit Stability Swiss Physical Society Annual Meeting Bern July p. 21/23... and by run number, but...

32 Fit Stability Swiss Physical Society Annual Meeting Bern July p. 21/23... These fits started about 1.8 µs after kicker off because of a nasty ripple in the data, probably from the kicker, but we are not sure yet... we will figure it out Conclusion on data: We are hoping for a 5 10 ppm result by the end of the summer

33 MuLan Future plans Swiss Physical Society Annual Meeting Bern July p. 22/23 June 2005: Beam Tuning: Improve Rate Improve Extinction Factor Many combinations were studied. Improvement achieved. Fall 2005: First Run with waveform digitizers New Run with the improved kicker 2006: Major production run with waveform digitizers Full proposed O(10 12 ) statistics

34 Swiss Physical Society Annual Meeting Bern July p. 23/23 MuLan Collaboration University of Illinois at Urbana-Champaign, USA (UIUC) Boston University, USA (BU) University of California, Berkeley, USA (UCB and LBNL) University of Kentucky, Lexington, USA James Madison University, USA (JMU) KVI Groningen, Netherlands Istanbul Technical University, Turkey Paul Scherrer Institute, Villigen, Switzerland (PSI)

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