New Precision Determination of

gp and GF,

the MuXperiments at PSI

Bernhard LaussUniversity of California @ Berkeley

on behalf of the MuCAP and MuLAN Collaborations

EXA’05

Overview

1) MuLAN GF

2) MuCAPgp

EXA’05

MuLAN Muon Lifetime Analysis

MuLAN makes a precision measurement of the Positive Muon Lifetime

EXA’05

Positive Muon Lifetime is closely connected to the Fermi Coupling Constant GF

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Standard Model

GF is a fundamental constant of nature

The GF from Fermi Theory successfully describes all weak

processes

ee

n pee

e

e

n

p

e

e

G

2F

L L eH e

5

G

2F

V A L eH p g g n e

1F

F

G

G

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muon decay beta decay

additional higher order QED contributions

QED radiative corrections

1

GF2 m

5

192 31

2

25

4 2

e

e

e

e

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All weak radiative corrections can be incorporated in the Standard Model

e

e

W

e

e

e

e

W

Z 0g g g Re-normalize g

e

e

e

W

Z 0

2

21

82F

W

G gr

M precision EW physics precision EW physics

via quantum loops.via quantum loops. (probes particle spectrum / top (probes particle spectrum / top prediction)prediction) EXA’05

Dominant theoretical uncertainty in muon Dominant theoretical uncertainty in muon lifetime was reduced from 16 to 0.3 ppmlifetime was reduced from 16 to 0.3 ppm

(2-loop (2-loop ’99) !’99) !

EXA’05

Recent improvement in calculations of

- Hadronic Contributions to the Muon LifetimeTimo van Ritbergen, Robin G. Stuart, Phys.Lett. B437 (1998) 201-208

- Complete 2-loop Quantum Electrodynamic Contributions to the Muon Lifetime in the Fermi Model,Timo van Ritbergen, Robin G. Stuart, Phys.Rev.Lett. 82 (1999) 488-491

- Complete O(N_f alpha2) Weak Contributions to the Muon LifetimeParesh Malde, Robin G. Stuart, Nucl.Phys. B552 (1999) 41-66

- Complete Two Loop Electroweak Contributions to the Muon Lifetime in the Standard ModelM. Awramik, M. Czakon, hep-ph/0305248

- Two Loop Electroweak Bosonic Corrections to the Muon Decay LifetimeM. Awramik, M. Czakon, hep-ph/0211041

etc ........

2 5

3

11

192FG m

EXA’05

Present Experimental Situation

PDG 2004 average: = 2.19703 s (18 ppm)

GF = 1.6637 (1) GeV2 (9ppm)

single best experiment 27 ppm error

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Duclos BalandinGiovanetti Bardin

Lan 03

1973 1974 1984 1984

EXA’05

Present Experimental Situation

PDG 2004 average: = 2.19703 s (18 ppm)

GF = 1.6637 (1) GeV2 (9ppm)

single best experiment 27 ppm error

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Duclos BalandinGiovanetti Bardin

Lan

1973 1974 1984 1984 2003

EXA’05

Present Experimental Situation

PDG 2004 average: = 2.19703 s (18 ppm)

GF = 1.6637 (1) GeV2 (9ppm)

single best experiment 27 ppm error

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Duclos BalandinGiovanetti Bardin

Lan

1973 1974 1984 1984 2003 04ex

pect

ed

EXA’05EXA’05

Duclos BalandinGiovanetti Bardin

Lan

Langoal

10

Lan goal

The MuLAN experimental goal is to no longer limit the GF extraction by experiment

ppm 5.0G ppm 1τ Fμ

Need ~1012 events

5

0

EXA’05

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How to measure muon lifetime ?

The lifetime is determined by stopping muons in a target and waiting for the decay positrons.

Segmented Scintillator Detector

+

e+

log

coun

ts

time

e+

simple slope measurement

of exponential time distribution !

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Using a pulsed muon beam will allow faster accumulation of statistics.

+

TimeAccum.Period

in target

20x faster than dc mode

Kicker2x 75 cm plates

E=0kV

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5s

Using a pulsed muon beam will allow faster accumulation of statistics.

+

Time

in target

Accum.Period

MeasurementPeriod

e+ 20x faster than dc mode

KickerE=25kV

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5s 22 s 45 ns rise/fall time

new M

uLAN beamline

developed

Kicker

@ TRIUMF

EXA’05

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Simple slope measurement at 1ppmis not so simple anymore:

The MuLAN experiment has been designed to

reduce systematic errors.

EXA’05

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The impact of muon spin rotation (SR)

N

SFront

Back

front-back symmetry

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.

fit (F+B)monitor (F-B)

FrontBack

Silver Target

EXA’05

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The impact of muon spin rotation (SR)

•Silver - preserves muon polarization (100%)

•Sulfur - muon 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.

EXA’05

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Double-Pulse Resolution - Hit Pileup

detector modularity: new electronics: 174 tile pairs 500 MHz wave form digitizers

EXA’05

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“Sneaky Muons” during beam-off period

lead to time dependent backgroundhigh rate (MHz), thin, fast (30 ns FWHM) wire chamber

beambeam

~100 Gauss magnet ring to avoid influence on systematics

due to muon stops in the chamber

EXA’05

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Online fit of 10 min of 2004 data

The time scale has a secret offset - blind analysis

all tile pairs

different start times

2004:- Setup and Test of final beam line with kicker - Finalized Detector- Accumulated 1010 decay positrons in both targets, sulfur and AK3 - sensitive systematics comparison - used multi-hit TDCs- analysis goal: 5 ppm error

2005 - finalize and test run with WFD electronics

2006- full 1012 statistics for 1ppm error

MuLAN Achievements and Plans

EXA’05

MuCAPmeasures: μ- capture rate in ultrapure hydrogen

Precision Measurement of the Singlet Muon Capture Rate on the Proton

EXA’05

g

W-

νμd

uμ–

gVud

ee

n pee

e

e

n

p

e

e

G

2F

L L eH e

5

G

2F

V A L eH p g g n e

(1 5) 1, 1.26V Ag g

1F

F

G

G

EXA’05EXA’05

muon decay beta decay

The GF from Fermi Theory successfully describes all weak

processes

Beta Decay (involves nucleons at low

momentum)

(V-A)

gv = 1gA = -1

n pee

n

p

e

e

5

G

2F

V A L eH p g g n e

1, 1.26V Ag g EXA’05

-decay

modified axial coupling

Muon Captureat higher momentum q2 = -0.88

m

p n

p

n

the simple(V-A) formbecomes more complicated

VgV(q2) + igM(q2)/2M q + gS(q2)/m q

AgA(q2) + gP(q2) q/m + igT(q2)/2M q Muon capture involves nucleons rather than isolated quarks. The strongly-interacting substructure of the proton and neutron complicates the weak interaction physics. These complicating effects are encapsulated in the nucleonic charged-current’s four “induced form factors”:

G-symmetry

no second class currents

EXA’05

nucleon charged current

Muon Capture

p n

• Vector current in SM determined via CVC gV(0) = 1, gV(q2)=1+q2 r2/6, rV

2=0.59 fm2

• gM(0) = p-n+1=-3.70589 q2 dependence from e scatt.

• Axial vector FF from n decay experimentgA(0)=-1.2670(35)

q2 dependence from quasi-elastic neutrino- nucleon scattering, e-production

• 2nd class FF gS, gT forbidden by G symmetry e.g. gT/gA=-0.15 ±0.15 (exp), -0.0152 ±0.0053(QCD sum rule, up-down mass difference)

• error fromVud = 0.16 %

nucleon weak form factors gV,gM ,gA,gP

• determined by SM symmetries and data

• contribute <0.4% uncertainty to S

gV = 0.9755(5)

gM = -3.5821(25)

gA = -1.245(3)

remains induced pseudo-scalar

gP = ?known at best only to ~ 20%

EXA’05

Pseudoscalar Form Factor gP in

TheoryPCAC: gP=8.7

heavy baryon chiral perturbation theory:

gP=(8.74 0.23) – (0.48 0.02) = 8.26 0.23

n

p

-

gNN

F

EXA’05

- fundamental but least known weak nucleon FF - solid theoretical prediction at few percent level- basic test of chiral QCD symmetriesCalculations NNLO show

good convergence: 100 % 25 % 3 % delta effect small LO NLO NNLO

Calculation by Fearing, Meißner et al.

Ordinary muon capture on the proton can be considered an excellent testing ground for our understanding of spontaneous and explicit chiral symmetry breaking in QCD.

Meißner, nucl-th/0001052

existing precise

calculations

are a

strong motivation

for a precision experim

ent

Experimental Informationon gp comes from nuclear Muon Capture Rate s

EXA’05

p n

Ordinary Muon Capture

Radiative Muon Capture

p n

Yield = 10-3

Yield = 10-8

EPH>60MeV

μ–, muon capture competes with muon decay:

(99.85%)

( ) (0.15%)

ee

p n

1 1

( )' ( )'s

Lifetime method

avoids absolute neutron counting

MuCAP Experimental PrincipleComparison of Lifetimes

log

coun

ts

time

e+

e –

μ+ lifetime = 2.19703 s

+ e+ + e+ ~

Experimental goal: measure + and - to 10-5 Experimental goal: measure + and - to 10-5

EXA’05

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Present Experimental Situation

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20

g p(-0

.88

m2 )

OP

(ms-1)

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20update from Gorringe & Fearing

ChPT

EXA’05

g p(-0

.88m

2 )

μ– Kinetics in Hydrogen -> Experimental Challenges

T = 12 s-1

n+

pμ↑↓

singlet(F=0)

S= 664 s-1

n+

triplet(F=1)

μ

pμ↑↑

EXA’05

strong spin dependence of V-A interaction

EXA’05

Present Experimental Situation

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20

g p(-0

.88

m2 )

OP

(ms-1)

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20update from Gorringe & Fearing

ChPT

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g p(-0

.88m

2 )

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Present Experimental Situation

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20

OP

g p(-0

.88

m2 )

OP

(ms-1)

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20update from Gorringe & Fearing

ChPT

Saclay 1981 Theory

TRIUMF 2004

EXA’05

with recent TRIUMF result

on op

situation even more puzzling !g p(

-0.8

8m2

)

EXA’05

Present Experimental Situation

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20

OP

g p(-0

.88

m2 )

OP

(ms-1)

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

20update from Gorringe & Fearing

ChPT

Saclay 1981 Theory

TRIUMF 2004

MuCAP - PSI: precision goal

need for a new,

unambiguous

precision determination

EXA’05

g p(-0

.88m

2 )

Mark & Dimitarplease check calculation

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negative muons in hydrogen pose additional problems in

comparison to positive stopped muons

EXA’05

μ– Kinetics in Hydrogen -> Experimental Challenges

T = 12 s-1

n+

ZμBackground: Wall stops and diffusion Transfer to impurities p+Z Z +p

pμ↑↓

singlet(F=0)

S= 664 s-1

n+

triplet(F=1)

μ

pμ↑↑

EXA’05

strong spin dependence of V-A interaction

ppμ ppμ

para (J=0)ortho (J=1)

λop

ortho=506 s-1

para=200 s-1

molecular disturbances

experimental strategyPhysics

• Unambigous interpretation At low density (1% LH2) mostly capture from p(F=0) atomic state.

• Clean muon stop definition: Wall stops and diffusion eliminated by 3-D muon tracking

• In situ gas impurity control

(goal: cZ<10-8, cd<10-6 /reached in 2004: cZ=7x10-8, cd= ~2x10-6) hydrogen chambers bakeable to 150º C, continuous purification TPC monitors capture on impurity and transfer to deuterium 10-8 sensitivity with gas chromatograph

• +SR: calibrated with tranverse field 70 G (saddle coil magnet around the TPC vessel)

Statistics

• 1010 statistics

ppP

ppO

p

pp

ppP

ppP

ppO

ppO

time (s)

100% LH2 1 % LH2 10% LH2

Experimental Challenges / MuCAP’s Solutions

EXA’05

The Time Projection Chamber

tracks muon stops in 3D.

- dT

active Target = TPC

- operates in proportional mode (gain ~104) - 5 - 6 kV- bakeable- quartz glass with very low thermal expansion- operates in 10 bar protium

EXA’05

horiz

onta

l

beam

dire

ctio

n

Anodes

Strips

Stop

vertical (drift time)

Anodes

Cathod

es

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Mucap Setup Fall 2004

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ePCs

TPC+magnet

eSC

hydrogen system

MuCap Achievements

Fall 2004: - full experiment ran stably for several weeks- collected 2.5 109 statistics => s 2-3%

EXA’05

(ns)

Impact Parameter Cutsno cut60 mm30mm

huge BG reduction

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Careful data selectionand online monitoring

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Mucap Data 2004

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Mucap Data 2004

ONLINE:continuous monitoring

of muon stopping

anddetector performance

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Drift Time

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Mucap Data 2004

continuous monitoring

of beam quality

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entering beam spot

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continuous high Z cleaning systemfor hydrogen based on Zeoliteafter filling through Pd filter

EXA’05

obtained 70 pbb

over several weeks

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We achieved gas impurity levels of 7x10–8, as determined from real-time software analysis of impurity events, and post-run chromatography analysis.

high Z purity monitoring (mainly Nitrogen, H2O)

EXA’05

MuCap Achievements

Fall 2004: - 70 ppb high-Z contamination over 5 weeks maintained- 1-2 ppm deuterium

EXA’05

A trickier impurity: deuterium transfer to deuterium, diffusion, CF

cd = 1ppm -> change in lifetime ~ 1ppm

p+d d + p

Ramsauer Townsend minimum in d + p scattering at 1.6 eV

Check by comparing + and

Diffusion

-catalyzed pd fusion (Alvarez)

monitors deuterium concentration

d + p pd (5.3MeV)+3He(0.2KeV)

EXA’05

MuCAP plans to add components to directly

monitor the deuterium concentration

to ± 0.1ppm in liquid hydrogen,

via fusion ’s and Alvarez muons

MuCap TimetableSummer 2005:

- additional development of the online impurity monitoring system- improvement of high-Z cleaning capacity- TPC overhaul to reach stable 5.4 kV running conditions - FADC implementation on all TPC channels- additional neutron counter for -kinetics control (pd, op)

Fall 2005/Spring 2006: - Planned 18 weeks of production data taking towards the final goal: s 1% - muon on request beamline (using the MuLAN kicker)

EXA’05

muon capture on deuteron

- + d + n +n

to 1 %

muon capture on deuteron

- + d + n +n

to 1 %

Basic EW two nucleon reaction

tests effective theories and serves to

calibrate v-d reactions via L1a (SNO)

Future (<2007)

D project

EXA’05

Paul Scherrer Institute (PSI), Villigen, Switzerland

University of California, Berkeley (UCB and LBNL), USA

University of Illinois at Urbana-Champaign (UIUC), USA,

University of Kentucky, Lexington, USA

Boston University, USA

James Madison University, USA

KVI Groningen, Netherlands

Istanbul Technical University

MuLAN Collaborating Institutions MuCap

EXA’05

Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia

Paul Scherrer Institute (PSI), Villigen, Switzerland

University of California, Berkeley (UCB and LBNL), USA

University of Illinois at Urbana-Champaign (UIUC), USA

Université Catholique de Louvain, Belgium

TU München, Garching, Germany

University of Kentucky, Lexington, USA

Boston University, USA

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