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BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan Experiment A New Measurement of the Fermi Constant Berkeley, Boston University, University of Illinois, James Madison, University of Kentucky, KVI, PSI Outline: Motivate the measurement Describe the experiment Final results

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Page 1: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

BOSTONUNIVERSITY

Robert CareyMuLan CollaborationBoston University

The MuLan ExperimentA New Measurement of the Fermi Constant

Berkeley, Boston University, University of Illinois, James Madison, University of Kentucky, KVI, PSI

Outline:●Motivate the measurement●Describe the experiment●Final results

Page 2: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Precision electroweak predictions rest on three parameters

Fermi Constant

Giovanetti et al1984

±GF

GF¼ 9 ppm

Mass of the neutral weak boson

LEP EWWG2005

±MZ0

MZ0¼ 23 ppm

Fine Structure Constant

Gabrielse et al 2008

±®em

®em¼ 0:37ppb0.37 ppb

Page 3: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

The V-A theory factorizes into a pure weak contribution, and non-weak corrections, essentially uncontaminated by hadronic uncertainties.

Muon decay gives us unique access to the electroweak scale

The muon only decays via the weak interaction, which gives it a very long lifetime.

All relevant weak interaction physics confined to one easily(!) measured parameter with a clean theoretical interpretation.

Page 4: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

The Fermi constant is an implicit input to all precision electroweak studies

Contains all weak interaction loop corrections.

Page 5: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

The Fermi constant is an implicit input to all precision electroweak studies

Plot clipped from LEP Electroweak Working Group publications

Contains all weak interaction loop corrections.

Top quark mass prediction:

+

e

W t

b

W e

+

+

+

Page 6: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

±GF

GF=

1

2

sµ±¿¹

¿¹

¶2+

µ5±m¹

¶2+

µ±theory

theory

¶2

18 ppm 90 ppb 30 ppmMid 90s: 17 ppm 90 ppb

Standard Model Fermi Constant extraction used to be theory-limited

T. van Ritbergen and R. G. Stuart, Nucl. Phys. B564, 343 (2000)

Page 7: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

±GF

GF=

1

2

sµ±¿¹

¿¹

¶2+

µ5±m¹

¶2+

µ±theory

theory

¶2

van Ritbergen and Stuart: 2-loop QED corrections (massless electrons)

18 ppm 90 ppb < 0.3 ppm1999: 9 ppm 90 ppb

Lifetime error now limits the Fermi constant

Standard Model Fermi Constant extraction used to be theory-limited

T. van Ritbergen and R. G. Stuart, Nucl. Phys. B564, 343 (2000)

Page 8: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

±GF

GF=

1

2

sµ±¿¹

¿¹

¶2+

µ5±m¹

¶2+

µ±theory

theory

¶2

1 ppm < 0.3 ppmGoal: 0.5 ppmLifetime error now limits the Fermi constant

Standard Model Fermi Constant extraction used to be theory-limited

T. van Ritbergen and R. G. Stuart, Nucl. Phys. B564, 343 (2000)

Page 9: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Also ....Two muon capture experiments at PSI

Protium: MuCapDeuterium: MuSun...(where the capture rate is inferred from the difference between the positive and negative muon lifetimes) require measurements of thepositive muon lifetime to 10 ppm or better.

Page 10: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

For 1ppm, need more than 2 trillion muons ...

πE3 Beamline, Paul Scherrer Institut, Villigen, Switzerland

Page 11: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

For 1ppm, need more than 2 trillion muons ...

πE3 Beamline, Paul Scherrer Institut, Villigen, Switzerland

Page 12: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

For 1ppm, need more than 2 trillion muons ...

πE3 Beamline, Paul Scherrer Institut, Villigen, Switzerland

Page 13: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

+12.5 kV

-12.5 kV

… with a pulsed time structure

SlitTarget Kicker

Mu

ons

in t

arg

et

Page 14: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

+12.5 kV

-12.5 kV

… with a pulsed time structure

SlitTarget Kicker

Mu

ons

in t

arg

et

5¹s

On

Nin(t) = R¹¿³1¡ e¡t=¿

´

Page 15: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

+12.5 kV

-12.5 kV

… with a pulsed time structure

SlitTarget Kicker

Mu

ons

in t

arg

et

22¹s5¹s

On Off

Nin(t) = R¹¿³1¡ e¡t=¿

´

Nout(t) = Nin(tc)e¡t=¿

Page 16: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

+12.5 kV

-12.5 kV

… with a pulsed time structure

SlitTarget Kicker

Mu

ons

in t

arg

et

22¹s5¹s

On Off

Nin(t) = R¹¿³1¡ e¡t=¿

´

Nout(t) = Nin(tc)e¡t=¿

Modulators designed, built at TRIUMF

Plates, vacuum chamber built by PSI

Page 17: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Symmetric, highlysegmented detector

Thinstopping

target

We have reached our goal by running about 20 muon decay experiments simultaneously

Polarized surfacemuon beam

Page 18: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Symmetric, highlysegmented detector

Thinstopping

target

We have reached our goal by running about 20 muon decay experiments simultaneously

+12.5 kV

-12.5 kV

Polarized surfacemuon beam

Electrostaticbeam kicker

Page 19: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Symmetric, highlysegmented detector

Thinstopping

target

We have reached our goal by running about 20 muon decay experiments simultaneously

+12.5 kV

-12.5 kV

Polarized surfacemuon beam

Electrostaticbeam kicker

Inner/Outertile pair

Page 20: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Symmetric, highlysegmented detector

Thinstopping

target

We have reached our goal by running about 20 muon decay experiments simultaneously

+12.5 kV

-12.5 kV

Polarized surfacemuon beam

Electrostaticbeam kicker

Inner/Outertile pair

500 Mhzwaveformdigitization

MHTDC(2004)

Page 21: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Symmetric, highlysegmented detector

Thinstopping

target

We have reached our goal by running about 20 muon decay experiments simultaneously

+12.5 kV

-12.5 kV

Polarized surfacemuon beam

Electrostaticbeam kicker

Inner/Outertile pair

500 Mhzwaveformdigitization

N(t) = N0e¡t=¿ +B

MHTDC(2004)

Page 22: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Data Production in 2006-7

2006: 1.16 ppm (stat.)2007: 1.7 ppm (stat.)

We collected roughly a trillion muons each year

Page 23: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

23

Time-dependent systematic errors are the principal analysis issue

Early-to-late changes:

Time in fill

log(

coun

ts)

Page 24: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

24

Time-dependent systematic errors are the principal analysis issue

Early-to-late changes:

Instrumental issuesPMT time pickoff, gainPulse shape variationsKicker voltage sag and beam dynamics effectsPileup : does detector

system performance change when pulses get

close together?

Time in fill

log(

coun

ts)

Page 25: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

25

Time-dependent systematic errors are the principal analysis issue

Early-to-late changes:

Instrumental issuesPMT time pickoff, gainPulse shape variationsKicker voltage sag and beam dynamics effectsPileup : does detector

system performance change when pulses get

close together?Physics issues

Spin (de)polarizationand precessionNon-flat background

Time in fill

log(

coun

ts)

Page 26: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

26

Time-dependent systematic errors are the principal analysis issue

Ee

threshold

time

coun

tsi

Early-to-late changes:

Instrumental issuesPMT time pickoff, gainPulse shape variationsKicker voltage sag and beam dynamics effectsPileup : does detector

system performance change when pulses get

close together?Physics issues

Spin (de)polarizationand precessionNon-flat background

Time in fill

log(

coun

ts)

1 cut data selection

Page 27: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Pileup

time

A MuLan Detector

Tile

Hidden pulses distort lifetime ~ 100 ppm, if uncorrected

PulseResolving

Time

Page 28: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Pileup

time

A MuLan Detector

Tile

Hidden pulses distort lifetime ~ 100 ppm, if uncorrected

time

coun

ts

Ppileup /

Z tr

0

P (t)P (t+ t0)dt0

/ e¡2t=¿

PulseResolving

Time

Pileup goes as Rate2

Page 29: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Don't fit for pileup losses(big statistical cost) => reconstruct!

A MuLan Detector

Tile

Page 30: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Don't fit for pileup losses(big statistical cost) => reconstruct!

A MuLan Detector

TileArtificial

ResolvingTime

time

Fill n

ArtificialResolving

Time

Fill n+1

Page 31: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Don't fit for pileup losses(big statistical cost) => reconstruct!

Pileup Time Distribution

Normal Time Distribution

A MuLan Detector

TileArtificial

ResolvingTime

time

Fill n

ArtificialResolving

Time

Fill n+1

Adding the pileup distribution to the normal distribution corrects for what's missing ...- and is more robust than simple extrapolation to ADT = 0

Page 32: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Don't fit for pileup losses(big statistical cost) => reconstruct!

Pileup Time Distribution

Normal Time Distribution

A MuLan Detector

TileArtificial

ResolvingTime

time

Fill n

ArtificialResolving

Time

Fill n+1

Adding the pileup distribution to the normal distribution corrects for what's missing ...- and is more robust than simple extrapolation to ADT = 0

Page 33: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

How well does our method correct the pileup?

1 p

pm

There is a small (1 ppm) unexplained change in the lifetime (R) with artificial dead time

- as if 0.1 % is unaccounted for

Page 34: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Muon spins precess in magnetic fields:The component parallel to B is static...

... while the perpendicular component precesses.

Page 35: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Muon spins precess in magnetic fields:The component parallel to B is static...

... while the perpendicular component precesses.

Residual polarization of muon ensemble decays over measurement period ...

… with different lifetimes for the perpendicular (transverse) and parallel(longitudinal) components.

Page 36: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Muon spins precess in magnetic fields:The component parallel to B is static...

... while the perpendicular component precesses.

Residual polarization of muon ensemble decays over measurement period ...

… with different lifetimes for the perpendicular (transverse) and parallel(longitudinal) components.

And decay positrons are emitted preferentiallyalong spin

Page 37: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

You can fit for the precession and depolarization… but it aint easy

ND(t) = N0e¡t=¿

µ1 +

1

3

h~Pk(0) ¢ eDe

¡t=Tk + ~P?(t) ¢ eDe¡t=T?i¶

Page 38: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

You can fit for the precession and depolarization… but it aint easy

ND(t) = N0e¡t=¿

µ1 +

1

3

h~Pk(0) ¢ eDe

¡t=Tk + ~P?(t) ¢ eDe¡t=T?i¶

Exponential lifetime decay ...

... of a system with non-zero initial ensemble polarization ...

Page 39: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

You can fit for the precession and depolarization… but it aint easy

ND(t) = N0e¡t=¿

µ1 +

1

3

h~Pk(0) ¢ eDe

¡t=Tk + ~P?(t) ¢ eDe¡t=T?i¶

Exponential lifetime decay ...

... precessing in time ...

... of a system with non-zero initial ensemble polarization ...

... with orientation and material dependent lifetimes.

Page 40: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

We start with nearly 100% polarized beam ... how do we control polarization effects?

Page 41: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

We start with nearly 100% polarized beam ... how do we control polarization effects?

Detector A

Detector A'

(µ; Á)

(¼ ¡ µ; ¼ + Á)

Central Target

Apart from acceptance differences, point symmetry of the detector cancels polarization asymmetries in the sum over symmetric tile pairs

Page 42: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

We start with nearly 100% polarized beam ... how do we control polarization effects?

Detector A

Detector A'

(µ; Á)

(¼ ¡ µ; ¼ + Á)

Central Target

Apart from acceptance differences, point symmetry of the detector cancels polarization asymmetries in the sum over symmetric tile pairs

Uniform 3-pi coverage!

Page 43: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

We also minimize the remnant polarization itself, by choice of target environment

A polarization destroying ferromagnetic target, AK3, with high internal field (2004,2006)

Page 44: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

We also minimize the remnant polarization itself, by choice of target environment

A polarization destroying ferromagnetic target, AK3, with high internal field (2004,2006) Or dephasing alone...

Polarization preserving and muonium forming target, crystalline quartz, with an applied external field (2007)

Page 45: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

We also minimize the remnant polarization itself, by choice of target environment

A polarization destroying ferromagnetic target, AK3, with high internal field (2004,2006) Or dephasing alone...

Polarization preserving and muonium forming target, crystalline quartz, with an applied external field (2007)

We also minimize muon stops outside the controlled target region with a vacuum beam corridor directly to the target (2006, 2007)

Page 46: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

In 2006 data, spin polarization was not an issue...

Page 47: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

In 2006 data, spin polarization was not an issue...

… but in 2007 data, it was.

Page 48: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Dozens of systematic runs taken in 2007 are consistent

Can sum all detectors and fit or fit individualdetectors and then average : same result

In 2006 data, spin polarization was not an issue...

… but in 2007 data, it was.

Page 49: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Blindanalysis

Final 2006-7 Error Table

Page 50: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

0.3 ppm difference!

Blindanalysis

Final 2006-7 Error Table

Page 51: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

11ppm 16ppm

The old world average was driven by two recent measurements

FAST Collaboration, Phys.Lett.B663:172-180,2008

Page 52: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Final results: D.M. Webber et al., Physical Review Letters 106, 041803 (Jan. 2011)PRD in progress

Page 53: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Conclusions

1. Using two very different techniques, we have made two consistent measurements of themuon lifetime and thus of the Fermi constant.

Page 54: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Conclusions

1. Using two very different techniques, we have made two consistent measurements of themuon lifetime and thus of the Fermi constant.

2. Both measurements are consistent with our 2004 result and those of other groups.

Page 55: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Conclusions

1. Using two very different techniques, we have made two consistent measurements of themuon lifetime and thus of the Fermi constant.

2. Both measurements are consistent with our 2004 result and those of other groups.

3. Statistical errors are slightly larger thansystematic errors, which are, in turn, slightly largerthan current theoretical uncertainties.

Page 56: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Conclusions

1. Using two very different techniques, we have made two consistent measurements of themuon lifetime and thus of the Fermi constant.

2. Both measurements are consistent with our 2004 result and those of other groups.

3. Statistical errors are slightly larger thansystematic errors, which are, in turn, slightly largerthan current theoretical uncertainties.

Muon lifetime: 2196981.3 +/- 2.3 ps

Page 57: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

(Most of)The MuLan Collaboration

Page 58: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Backup Slides

Page 59: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Page 60: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Where's the bucket?

There's the bucket!

MuLan: “The world's largest research-grade soccer ball”

Page 61: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Result is consistent across analysis conditions

Page 62: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Consistency over data set: 2006

Page 63: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Residual polarization (along z) is a is a very small effect

upstream downstream

Slope in R: 13 ppm/detector half

Page 64: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Our analyzers do not know the size of a clock tick

And neither do the rest of us!

Time in clock ticks

Counts

Page 65: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

It doesn't matter when you start the fit

Page 66: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Page 67: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Treating each detector as a separate experiment

Page 68: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Many-at-onceNeed time structured (AC) beam, not a continuous (DC) beam

Electron timeline

Muon timeline

Wrong assignments

Right assignmentsMuch higher rates, but much harder experiment R&D and construction

BeamOff

BeamOff

BeamOn

BeamOn

time

coun

ts

Page 69: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

One-at-a-time

Can't really do one-at-a-time, the next best thing is a low rate, DC beam.

Muon timeline

Electron timeline

time

coun

ts

Wrong assignments

Right assignments S

B/N

N2=

1

N

30 kHz! 385 d for 1012¹+

Page 70: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

The muon lifetime is similarly crucial for nucleon weak structure functions

V® = gV (q2)°® +

igM(q2)

2MN

¾®¯q¯

A® = gA(q2)°®°5 +

gP (q2)

q®°5

iM =GFVudp

2hºj °®(1 ¡ °5) j¹i hnj V® ¡ A® jpi

gV ; gM ; gA Well known from other experiments

¤S

Page 71: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

The muon capture rate is determined by a lifetime difference technique

! ¤S =1

¿¹¡¡

1

¿¹+

log

(co

un

ts)

time

μ+μ –

¢¿ ¼ 0:146%±gP

gP¼ 5

±¤S

¤S

5% 1%

±¿¡¿¡

! 10¡5

¤¹¡ = ¤¹free +¤S

Andreev, et.al. Phys. Rev. Lett. 99, 032002 (2007)

Page 72: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

A brief history...

Before 2007, the best measurements were over 20 years old, and until 1999, G

F

was theory limited.

G. Bardin et al., Phys. Lett. B 137, 135 (1984)K. Giovanetti et al., Phys. Rev. D 29, 343 (1984)

Page 73: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

QED Theory Uncertainties

● Hadronic uncertainties give 10–8 ● Dominant errors come from uncalculated

effects:● Three loop estimates give 1.4 × 10–7 ● Two loop logs give 1.7 × 10–7

● Overall, theory errors are a “few 10–7”

Page 74: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Definitions: PDG vs vRS

Conventional, but really a weak interaction correction. Van Ritbergen and Stuart leave this out as inconsistent with principle, while Erler and Langacker leave it in (PDG review)

Massive part of the phase space integration

1-loop QED corrections

Page 75: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Standard Electroweak Model

● All 1-loop corrections known (Sirlin)● Most (all?) two loop corrections known● Important class of contributions related to

oblique corrections (vector boson self-energies)

Page 76: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

The Fermi constant beyond the Standard Model

Non-zeroneutrino mass

Non-standardMichel parameters

Heavy weakgauge bosons

< 3 ppm

< 70 ppm

Page 77: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

Extra Slides

Page 78: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Watching the bucket empty

This gives about 40 MB/s of data that has to be stored!

The PMTs feed the WFDs

Page 79: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

We have made much progress in proving that our results are consistent across various conditions

Fit start time scans show no evidence of missing long time scale components

The lifetimes measured by individual detector pairs are statistically consistent

Page 80: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

FAST @ PSI: 2 ppm goal■ Basic idea: Take many events “at once” using an imaging

detector ■ Locate stops, π + → µ + decays, and µ + → e+ decays

and track them■ Advantage: No beam structure to worry about

π +

First result reported in July 2007: δτ µ = 16 ppm

Page 81: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

RMC, PANIC, July 2011

MuCap Experiment

Page 82: The MuLan Experiment - MITweb.mit.edu/.../6-1510/carey/496-0-MuLanPANIC2011.pdf · 2011. 7. 24. · BOSTON UNIVERSITY Robert Carey MuLan Collaboration Boston University The MuLan

Stop µ - in 10 atm pure hydrogen … and image stop location

ΛTΛS

µ

ppµ

ppµ

pµpµ

Λortho

Λpara

F=0 F=1

J=1

J=0

λOP

λOP (ms-1)

gP

20 40 60 80 100 120

2.5

5

7.5

10

12.5

15

17.5

20

µ - + p → νµ + n + γ @ TRIUMF

Saclay exp theory TRIUMF 2005

µ- + p →

νµ + n @ Saclay ChP

T

Previous experiments cannot be interpreted due to muon molecular chemistry ambiguities

TPC stopping volume