µp & µ3He capture rates and

Induced pseudo-scalar couplingof proton weak interaction

A.Vorobyov

Petersburg Nuclear Physics Institute

PSI meson factory

600 MeV protons 2 mA extracted proton beam100% duty factorHigh intensity muon channelsMuon-on-request mode

• Muon catalyzed dd-and dt-fusion experiments (completed)• Muon capture on He-3 (competed)• Muon capture on proton (data taking completed, first results published)• Muon capture on deutron (experiment under preparation)

PNPI in PSI since 1986

MuCap collaboration

Petersburg Nuclear Physics Institute (PNPI), Gatchina, RussiaPaul Scherrer Institute (PSI), Villigen, Switzerland

University of California, Berkeley (UCB and LBNL), USAUniversity of Illinois at Urbana-Champaign (UIUC), USA

Université Catholique de Louvain, BelgiumTU München, Garching, Germany

University of Kentucky, Lexington, USABoston University, USA

- + p (µ-p)1S → µ+ n BR=0.16%

- + p (µ-p)1S → µ+ n BR=0.16%

MuCap goal: to measure µp-capture rate ΛS with 1% (or better) precision

Muon Capture on Proton

ΛS

µ νµ

p n

W qc2 = - 0.88 mµ

2

gv = 0.9755(5) values and q2 dependence known from EM

gM = 3.5821(25) form factors via CVC

gA = 1.245(4) gA(0)=1.2695(29) from neutron β-decay,

gP(theory) = 8.26 ±0.23 q2 dependence from neutrino scattering

gP(expt) = ?

(

(

µp-capture offers a unique probe of the nucleon’s electroweak axial structure

Theoretical predictions for gP

n

p

-

gNN

F

• Partial conservation of axial current (PCAC)• Heavy Barion chiral perturbation theory (ChPT)

W

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

PCAC pole term

ChPT leading order one loop two-loop <1%

Recent reviews:V. Bernard et al., Nucl. Part. Phys. 28 (2002), R1T. Gorringe, H. Fearing, Rev. Mod. Physics 76 (2004) 31

Theory predicts gP with ~ 3% precision

Uncertainties in other form factors set the limit : =0.45% or =3%

To approach this limit, one should measure ΛS with ~0.5% precision

Sensitivity of ΛS to form factors

Contributes 0.45% uncertainty to measured S

Examples:

10% 56%

1.0% 6.1%

0.5% 3.8%

T = 12 s-1

pμ↑↓

singlet (F=0)

S= 710 s-1

n+

triplet(F=1)

μ

pμ↑↑

ppμ

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

λop

ortho=506 s-1 para=200 s-1

ppμ ppμ ppμ

λ pp

From which muonic state the muon capture occurs ?

T = 12 s-1

pμ↑↓

singlet (F=0)

S= 710 s-1

n+

triplet(F=1)

μ

pμ↑↑

ppμ

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

λop

ortho=506 s-1 para=200 s-1

ppμ ppμ ppμ

λ pp

ppP

ppO

p

100% LH2

p

ppP

ppO

1 % LH2

time (s)

T = 12 s-1

pμ↑↓

singlet (F=0)

S= 710 s-1

n+

triplet(F=1)

μ

pμ↑↑

ppμ

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

λop

ortho=506 s-1 para=200 s-1

ppμ ppμ ppμ

λ pp

Muon capture in liquid H2 deals with uncertain muonic molecular state

The H2 gas pressure should not exceed 10 bar to provide dominant (µ-p)1S state

Status of µp-capture experiments

Year Exptl.place H2 target ΛC, s-1 Method

1962 *)

1962

1962

1963

1969

1974

1981

Chicago

Columbia

CERN

Columbia

CERN

Dubna

Saclay

liquid

liquid

liquid

liquid

gas, 8 atm

gas, 41 atm liquid

428 ± 85

515 ± 85

450 ± 50

464 ± 42

651 ± 57

686 ± 88

460 ± 20

neutron detection

- " –

- " –

- " –

- " –

- " -

Life time measurement

- + p µ+ n

Two experimental methods to measure Λ C

*) First direct observation of µp-capture

Neutron detection Life time measurement

ΛC = 1/τµ+ - 1/τµ- ΛC Nn/Nµ

µ± → e± νe νµ

CPT inv

Status of µp-capture experiments

- + p µ+ n BR = 0.16% Ordinary muon capture, OMC

- + p µ+ n + γ BR = 10-8

Radiative muon capture, RMC

RMC is more sensitive to gP (by a factor of 3) than OMCbut huge problems due to small BR.

One RMC experiment in TRIUMPH (1996)

Precise Theory vs. of Exp. Efforts

20 40 60 80 100 120

2.5

5

7.5

10

12.5

15

17.5

20

ChPT

OP (ms-1)

gP

- + p + n + @ TRIUMF

Cap precision goal

exp theory TRIUMF 2006

- + p + n @ Saclay

Emilio Zavattini 1927-2007

1969 Bologna-Pisa-CERN

1973 Dubna group

H2 –target 8 atm

Pioneers of muon capture experiments

H2 –target 41 atm

gp ≈ 11 ± 5

Expt. Problems• Wall effects• Background • Neutron detection efficiency

Δgp = ± 7

Strategy of MuCap experiment

• H2 gas target at 10 atm

(µ-p)1S

Strategy of MuCap experiment

• H2 gas target at 10 atm

(µ-p)1S

• Lifetime method ΛS = 1/τµ+ - 1/τµ-

10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1%

Strategy of MuCap experiment

• H2 gas target at 10 atm

(µ-p)1S

• Lifetime method ΛS = 1/τµ+ - 1/τµ-

10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1%

>1010 muon decay events High data taking rate

Strategy of MuCap experiment

• H2 gas target at 10 atm

(µ-p)1S

• Lifetime method ΛS = 1/τµ+ - 1/τµ-

10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1%

>1010 muon decay events High data taking rate

• Ultra clean protium impurities with Z>1 less than 10 ppb (1 ppb = 10-9) deuterium concentration less than 100 ppb

Strategy of MuCap experiment

• H2 gas target at 10 atm

(µ-p)1S

• Lifetime method ΛS = 1/τµ+ - 1/τµ-

10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1%

>1010 muon decay events High data taking rate

• Ultra clean protium - impurities with Z>1 less than 10 ppb (1 ppb = 10-9) - deuterium concentration less than 100 ppb

• Clean muon stop selection No wall effects

Strategy of MuCap experiment

• H2 gas target at 10 atm

(µ-p)1S

• Lifetime method ΛS = 1/τµ+ - 1/τµ-

10 ppm precision both in µ- and µ+ life times → δΛS/ΛS = 1%

>1010 muon decay events High data taking rate

• Ultra clean protium impurities with Z>1 less than 10 ppb (1 ppb = 10-9) deuterium concentration less than 100 ppb

• Clean muon stop selection No wall effects

• Low background < 10-4

…………………. . . . . . . . . . . .

E

-40kV

µ

G +5kVG

Time projection chamber, TPC

z

Y

x

Cathode stripsAnode wires

3D detection of muon trackX- cathode stripsY- drift timeZ- anode wires

y

x

z

Sensitive volume 15 x 12 x 28 cm3

Muon stop selection inside the sensitive volume far enough from all chamber materials

…………………. . . . . . . . . . . .

E

-40kV

µ

G +5kVG

Cathode stripsAnode wires

e ePC1

ePC2

eSC hodoscope

µSC

e-µ space correlation eliminates background

tµ = t eSC – t µSC

Display of a µ→eνν event detected in TPC

Chemical purity control of hydrogen gas

• Self-control for Z>1 contaminations by recoil detection in TPC. Sensitivity 10 ppb.• Chromotography CN2, CO2. Sensitivity 10 ppb• Humidity control device. Sensitivity 3 ppb

Display of a µp → µZ→ n + recoil event detected by TPC

µZ-capture rate measured in TPCCZ increases by 0.1 ppm per day

Cryogenic circulation-purification hydrogen gas system

TT1 LT1H1 H2 H3 H4TT2 TT3 TT4

T1

MF

C-1

MF

C-2

MF

C-3

Co

lum

n1

Co

lum

n2

Co

lum

n3

L-

nit

rog

en t

ank

Vacuumline

Vacuumline

Membranepump

HV pumping system

Compressed air

Oil-free vacuum line

Relief

Refilling ports

Gas/Liquidseparator

Ref

illin

g p

ort

FA1 FA2

Lower L-nitrogen

tank

Upper L-nitrogen

tank

Radiation shielding

PT2

PT1

PT4 PT3

TPC

F8

F11

F12

F11

F9

F10

SV1

V12V11

V21

V35 V19

V10

MFC-4MFC-5

Sa

mp

le

T2

T3

LT1

V14

Sampling valve

V13CV12

F12

F21

F22

F31

F32

CV31 CV32

F5

F4

CV22CV21CV11

F11

F6F7

FromDewar

Oil freevacuumline

Releasevolume

Compressor

Co

mpr

esso

r un

it

Pur

ifica

tion

unit

Control Gas Panel

Reserve volume

Vacuum system

Purifier

CHUPS

V6

RV2

RV1V1V2

V26

V27

V30

HS

V29

V24

V28

V31

V3

4

V37 V38

V9

V25V5 V4

G - getter

PT - pressure sensorTT - temperature sensor

LT - level meter- hydrogen line

- nitrogen line

- compressed air line

- electronic signal

- pumping lineSV - operating valve

V manual valve - F - filter

H - heaterM - manometer

T - thrermalizerEF - electrostatic filterHS - humidity sensor

LT - level detector

MFC - mass-flow controller

F - filter adsorber-

SV3

SV2

G

V32

V33

V3

V36

T5

T4

V15

V23

V16

V17

Oil freevacuumline

TT10H10 TT6DAC_24 TT5

N2 less than 10 ppbO2 less than 10 ppbH2O about 10 ppb

Gas purification system

-5 0 5 10 15 2010

100

1000

Nitr

ogen

con

cent

ratio

n, p

pb

Time from CHUPS start, hours

Run 2006H

2 flow: 3 slpm

Isotopic purity of protium

Deuterium concentration in hydrogen gas

Natural gas 140 ppmBest on market 2 ppmProduced for MuCap ≤ 6 ppb

Cryogenic isotopic exchange column

Accelerator mass spectrometryat ETH in Zurich

Reached sensitivity 6 ppb

Gas purification system Hydrogen isotopes separation column

PSI muon channel can provide ~ 70 kHz muons

MuCap could use only ~ 7kHz (to prevent pile up)

New beam system (Muon-on-demand) constructed in 2005 allowed to increase

the usable beam intensity up to 20 kHz

-

+12.5 kV -12.5 kV

Kicker Plates

50 ns switching time

detector

TPC ~3 times higher rate

Data taking rate

Muon-on-demand system

run2006

Beam at TPC entrance 20 kHzRate of selected µ→eνν events 4kHzStatistics of selected events 3·108 /day 1010 events ~ for a two month run Fast (dead time free) read out system

µ e

Reduction of background by µ-e vertex cut

The impact cut can reduce the background to a level of 10-4-10-5

Statistics of selected events

2004 2005 2006 2007 total

µ- 1.6 x 109 3.5 x 109 8 x 109 6.2 x 109 2 x 1010

µ+ 0.5 x 109 1.4 x 109 4 x 109 4 x 109 5.5 x 109

Only 2004 data are analyzed at present (~10% of total statistics)

The results are published in PRL 99,032002(2007)

MuCap World average

events =1/ (s-1) 1/(s-1)

- 1.6 x 109 455851 12.5 8.5

+ 0.5 x 109 455164 28 455160 4.4 *)

µ- and µ+ disappearence rates from 2004 data

*) including last MuLan data

λµ- = (λµ+ + ∆λµp) + ΛS + ∆Λpµp

∆λµp = -12.3 s-1 bound state correction∆Λpµp = - 23.5 ± 4.3 ± 3.9 s-1 µ- captures from pµp molecules

ΛS = 725.0 ± 13.7 ± 10.7 s-1

Average of HBChPT calculations of S:

MuCap 2007

gP = 7.3 ± 1.1gP = 7.3 ± 1.1

Apply new rad. correction (2.8%):A.Czarnecki, W.J.Marciano,A.Sirlin , PRL 2007

ΛS = 725.0 ± 13.7 ± 10.7 s-1MuCap

Comparison with theory

gp = gp + δgp/δΛS( ΛS - ΛS ) = 7.3 ± 1.1 MuCap Th MuCap Th

δgp/δΛS = - 0.065 s

gP = 8.2 ± 0.2HBChP theory

- + p + n +

MuCap agrees within 1σ with the Heavy Barion Chiral Perturbation Theory

Further analysis of the MuCap data should decrease the experimental error by a factor of three

“That agreement would seem to close a confusing chapter in nuclear physics which has seen decades of disagreement regarding the value of gp

expt. It would be interesting to watch continuing improvements in the MuCap results.”

A.Czarnecki, W.J.Marciano,A.Sirlin , PRL 2007

An extract from an article commenting the MuCap results

Muon Capture on He-3

µ- + 3He → 3H + νµ Et = 1.9 MeV

TPC operating in ionization modeat 120 bar of clean 3He

Λstat = 1496 ± 4 s-1 Physics Letters B417,224 1998)

The precision of previous data was improved by a factor of 50

Since then, this result was a subject of various analyseswith the goal to obtain the value of gp

Muon Capture on He-3

Elementary particle model (Kim,Primakoff,1965)

FV(qC2)) = 0.834 (11)

FM(qC2) = -13.969 (52)

FA(qC2) = 1.052 (10)

extrapolated from FA(0) = 1.212(5), tritium beta-dacay

FP PCAC = 20.7FP (expt) = 20.8 ± 2.8

qC2 = -0.954 mµ

2

Surprisingly good agreement with PCAC

Impulse approximation model

Three body wave function Meson Exchange Currents

Latest analysis A.Czarnecki, W.J.Marciano,A.Sirlin , PRL 2007

gPexpt(µ3He) = 8.7 ± 0.6

Muon Capture on He-3

This value agrees with our result from the µp-capture experiment

gPexpt(µp) = 7.3 ± 1.1

This agreement may be considered as an indication of validity of the theoretical approach used to treat the µ3He capture process

Future Complete analysis of the MuCap data. Expectations: δΛS/ΛS ≤1.0 % ΔgP ≤ 6 %

Prepare new experiment to measure muon capture rate on deuterium µ + d n + n + ν with ~ 1% precision.

Similar to basic solar fusion reactionsp + p d + e+ + + d p + p + e- + d p + n +

1.

2.