Muon Capture in Hydrogen and Deuterium

EXA08int. conference on

exotic atoms & related topics

Vienna

Sept 15-18 2008presentation by

Claude Petitjean

representing the MuCap- &the MuSun collaboration

gP vs. λop plot showing first MuCap result

collaboration homepages http://www.npl.uiuc.edu/exp/mucapture http://www.npl.uiuc.edu/exp/musun

outline

- experimental goals

- comments to theories ChPT gP - EFT L1A

- experimental challenges & strategy

- μ- kinetics in hydrogen - the ortho-para problem

- MuCap apparatus, components

- data & 1st results, final analysis

- MuSun experiment: the new challenges

- μd-kinetics

- new Cryo-TPC

- outlook

Muon Capture Experimentsin Hydrogen & Deuterium

our goal

precision measurement of muon capture rates to ±1%

1) μ- + p → (μ-p)↑↓ → n + νμ singlet capture rate ΛS

sensitive to induced pseudoscalar coupling gP

in weak interactions

first results published – full analysis in progress

2) μ- + d → (μ-d)↑↓ → n + n + νμ doublet capture rate ΛD

sensitive to the axial two-body current term L1A

in effective field theories (EFT‘s)

in full preparation – first run in Nov 2008

scientific case of μ capture on the proton

μ capture probes axial structure of nucleon

μ capture neutron β decay

hadronic vertex determined by QCD: q2 dep. form-factors (gV, gM, gA, gP)

μp-capture is the only process sensitive to the nucleon form factor gp

pn

νe

e-

n

νμ

p

μ-

W W

μ- + p νμ+ n(analogue)

heavy baryon chiral perturbation theory (Bernard et al. 1994):

gPtheory = 8.26

0.23- gp least known of the nucleons weak form factors- solid theoretical prediction by HBChPT at 2-3% level- basic test of QCD symmetries

scientific case of μ capture on the deuteron

μ + d n + n + νμ

model-independent connection via EFT & Lmodel-independent connection via EFT & L1A1A

• impact on fundamental astrophysics processes impact on fundamental astrophysics processes (SNO, pp) (SNO, pp) basic solar fusion reaction p + p d + e+ +

key reactions for SNO + d p + p + e- (CC) + d p + n + (NC)

• comparison of modern high precision calculationscomparison of modern high precision calculations (eff. field theories,standard nucl. physics (eff. field theories,standard nucl. physics

approach)approach)

EFT: axial current reactions related by single EFT: axial current reactions related by single parameter Lparameter L1A1A

• the muon capture rate on deuteron determines the muon capture rate on deuteron determines LL1A1A

MEC

EFTL1A

- only n & ν in output channel limited precision for direct measurement of absolute rates

use lifetime method

ΛS = λ(μ-p) – λ(μ+)

measure λ‘s to 10 ppm

>~ 1010 events required

- capture rate small ~ 10-3 of λ(μ+) avoid any wall stops to 10-5!

develop ultra-clean TPC

as active muon stop target

operated in hydrogen gas

log

(co

un

ts)

te-t

μ+

μ –

λ

λ

S reduces lifetime by 10-3

→ e

experimental challenges & our strategy (I)

- μ-transfer to impuries (N2,H2O,..) μp + N (O,..) → μN (μO,..) + p

distortion of lifetime curves

develop continuously circulating & cleaning system (CHUPS)

goal: cZ ~ 10-8 (10 ppb)

- μ-transfer to deuterium μp + d → μd + p & large diffusion of μd atoms

distortion of lifetime curves

develop new special isotope separation column

goal: cd < 10-7 (100 ppb)

experimental challenges & our strategy (II)

ΛPM ~213s-1

ΛT ~ 12s-1

pμ↑↓

singlet(F=0)

ΛS~710s-1

n+

triplet(F=1)

μ-

pμ↑↑

n+

ppμ ppμ

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

ΛOM ~540s-1

λOP

n+

Λppμ

n+

- pμ↑↑ depopulates quickly (<100ns)

- ppμ molecule formation with (τ ~ 0.4μs/φ) Λppμ known only to ± 20%

- ortho to para transition rate badly known λOP known only to ± 50%

- ΛS - ΛOM - ΛPM are all quite different!

τ~10ns

experimental challenges & our strategy (III)

kinetics of μ- in H2

solution:- use low gas density φ (10 bar H2) ≈ 1% of liquid

- determine Λppμ by Argon doped run – λOP from neutron spectra

e

CAD view of MuCap experimental setup

UHV = 30 kV Ucath = 5-6 kV

MWPC readout in x-z bottom planes

sensitive volume (12 x 15 x 30) cm3

wires on glass frames - pure metallic

& ceramic structures bakeable to 130C

the 10 bar Hydrogen TPC

ultra-pure protium gas el. drift field 2 kV/cmvdrift = 0.5 cm/μs

high gas purity maintained by continuous circulation- operated by cryogenic adsorption/desorption cycles in active Carbon- traps all higher Z impurities by Zeolites immersed in liquid Nitrogen

our main impurity is water vapor outgasing from walls & materials

control & calibrations of impuritiesevent display

showing impurity capture event

time axis (60 μs)

35 s

trips

75 a

nod

e w

ires

test admixing of 21 ppm N2: cleaned off to <10 ppb

humidity of TPC protium wasmonitored with PURA device

~17 ppb reached

N2

H2O

HD separation columnconstructed in Gatchina & PSI, tested & operated in

March/April 2006principle: - H2 gas circulates from bottom to top & gets liquified at the cold head - liquid droplets fall down & evaporize gas phase depleted from D - the D-enriched liquid H2 at the bottom is slowly removed

results of AMD analysis at ETHZ:

protium in 2004/5:

cd = (1.45±0.15)10-6

protium used in 2006 after HD separation:

cd < 6*10-9 (6 ppb)

final 2004 lifetime fit (1.6*109 good μ- events)

chosen impact cut 120 mm ( small μd correction!)

λμ- = 455‘851.4 ± 12.5stat ± 8.5syst s-1 (main MuCap result)

λμ+ = 455‘162.2 ± 4.4 s-1 (new world average incl. μLAN)

455’164 ± 28 (MuCap result with 0.6*109 μ+ events) μ- lifetime curves

2004 data

resulting μp capture rate:

ΛS = 725.0 17.4 s-1

theory (+ radiative corr.):

ΛS = 710.6 3 s-1

gP vs λOP plot with first unambiguous MuCAP result

our result is gP = 7.3±1.1 (HBChPT: 8.26±0.23)

gP

λop

TRIUMF

SACLAY

final MuCap analysis

data statistics result / errors: stat. syst. total

2004 1.6 * 109 ΛS = 725.0 ± 13.7 ± 10.7 ± 17.4 s-1

(2.4%)

(published) gP = 7.3 ± 1.1 (15%)

2005-07 1.8 * 1010 expect δΛS to ± 3.7 ± 4 ± 5.5 s-1

(0.8%)

(analysis in progress) δgP to ± 0.35 (5%) (HBChPT: 8.26±0.23)

***************************

list of systematic errors [s-1]:

topic 2004 2005-07 method of improvement

Z>1 impurities 5.2 2 improved CHUPS-system, FADC

μd diffusion 1.6 <0.1 isotope separator (cd < 6 ppb)

analysis methods 6.6 3 improved analysis programs, MC

ppμ form. rate (Λppμ) 5 0.5 measurement (Argon doped run)

ortho-para rate (λOP) 3.5 2 measurement of neutron spectra

---------------------------------------------------------sum of syst. errors 10.7 s-1 4 s-1

completion of final analysis in 2009

Argon doped run for Λppμ measurement

e- time spectrum yields λe neutron time spectrum Ar capture time spectrum

- protium run with 20 ppm Argon doping- electron spectrum 5.5*108 events- neutrons from μAr capture 3*105 events- tpc data from μ-Ar capture 4*106 evts

combined analysis of time spectra yields

λcaptAr , λ

transferpAr , λppμ to ~2%

reduces error of ΛS to 0.5 s-1 !

(analysis in progress at Urbana)

V.A. Andreev, T.I. Banks, T.A. Case, D. Chitwood, S.M. Clayton, K.M. Crowe, J. Deutsch, J. Egger,S.J. Freedman, V.A. Ganzha, T. Gorringe, F.E. Gray, D.W. Hertzog, M. Hildebrandt, P. Kammel, B.

Kiburg,S. Knaak, P. Kravtsov, A.G. Krivshich, B. Lauss, K.L. Lynch, E.M. Maev, O.E. Maev, F. Mulhauser,C.S. Özben, C. Petitjean, G.E. Petrov, R. Prieels, G.N. Schapkin, G.G. Semenchuk, M. Soroka, V.

Tichenko,A. Vasilyev, A.A. Vorobyov, M. Vznuzdaev, P. Winter

authors of first μp capture results published in

Phys. Rev. Letters 99, 032002 (2007)

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, BelgiumUniversity of Kentucky, Lexington, USA

Boston University, USA

parts of the collaboration during parts of the collaboration during the main run in 2006 at PSIthe main run in 2006 at PSI

(graduate students in red)

the MuSun experiment

nuclear muon capture on the deuteron

there are new challenges compared to μp capture:

- at room temperature the μd spin state is badly known due to slow spin flip rate and strong ddμ formation + fusion (see kinetics)

- transfer rates to impurities are significantly larger

technical solution: go to low temperatures (~30 K)And higher gas density (5-10% of liquid, up from 1%)

Λ(μd3/2 μd1/2) ~ 3x106s-1

impurities (H2O, etc) freeze out

μd kineticsslow spin flip and resonant dμd fusion cycles

μ

μd↑↑

μd↑↓

dμd

μZΛD

n + n + ν

μ3He + n

μ + 3He + n

μ + t + p

effect of ddμ kinetics

time (s)

30K, 5%

d()

d()

He

1% LD2

300 K

10% LD2

30 K

at low density φ=1%, 300K(as μp capture experiment):

- spin flip very slow- rate not precisely known (±15%)

no precise interpretation of observed capture rate possible

at higher density (φ=5-10%), 30K(proposed for μd capture experiment):

- strong depopulation of quartet state- observable in dμd fusion time spectrum

pure μd(F=1/2) state capture rate highest (~400s-1)

conclusion: develop cryo-tpc

for μd experiment

setup of MuSun detector

PC

SC

ePC2

ePC1

eSC

Cryo-TPC

e

technical design of the cryo-system

liquid Neon cooling circuit (vibration free)

continuous cleaning by CHUPS

CAD view of cryo tpc, vacuum & cooling system

outlook

- Nov 2008 first test run using still the MuCap setup (300K) 10 bar high purity deuterium charge collection on 8x10 cm2 pad plane studies of:

- impurity events, controls, cleaning - ddμ fusion events - measure μ transfer rate to impurities - neutron spectra

- fall 2009 commissioning run with new cryo tpc at 30K

- 2010-11 main statistics runs ~2*1010 events