Unblinding the MuCap experiment the final results of μp capture rate Λ S and of electro-weak coupling constant g P LTP Seminar April 23, 2012 Claude Petitjean

Unblinding the MuCap experimentthe final results of μp capture rate ΛS

and of electro-weak coupling constant gP

LTP Seminar

April 23, 2012

Claude PetitjeanPSI

theor. & exp. gP bands vs. Ortho-Para transition rate

MuCap homepage http://muon.npl.washington.edu/exp/MuCap/Petitjean LTP-Seminar 23.04.12

outline- goal of MuCap experiment, theory

- experimental challenges MuCap apparatus with TPC- systematics: - impurities - formation of ppμ molecules Argon doped run - interferences with electron charges - μp scattering & diffusion list of systematic corrections- unblinding of main runs 2006/07- new results on ΛS gP

Petitjean LTP-Seminar 23.04.12

1% precision measurementof singlet nuclear muon capture rate Λs

p n

- semi-leptonic weak interaction process- determines the induced pseudoscalar coupling gP to 6%- constitutes a vigorous test of low energy HBChPT

thesis works by T.I. Banks (UC Berkeley), S.M. Clayton (UI Urbana Campaign), B.E. Kiburg, S. Knaak (both UIUC, now UW Seattle)

MuCap proposal 1997


scientific case of μ capture on the protonμ 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)

prediction of heavy baryon chiral perturbation theory (V. Bernard et al. 1994): gP

theory = 8.26 0.23- gp least known of the nucleons weak form factors- solid QCD prediction by HBChPT at the 2-3% level (NNLO < 1%)- basic test of chiral symmetries and low energy QCD

- V. Bernard et al., Nucl. Part. Phys. 28 (2002), R1 - T. Gorringe, H. Fearing, Rev. Mod. Physics 76 (2004) 31 - P. Kammel, K. Kubodera, Annu. Rev. Nucl. Part. Sci. 60 (2010) 327

recent reviews:


dependence of ΛS from gA & gPgA from neutron β decay ↓ ↓ ↓

← - 1% ← ΛS

th = (711.5 ± 4.6) s-1

(incl. rad. correction)← + 1%

a 1% Λs measurementdetermines gp to ~ 6%

the QCD prediction(HBChPT) is ± 2-3%


experimental challenges of μ- in

pure hydrogen- high precision measurement of absolute capture rate

- high statistics (1010 events)

- all μ must stop in hydrogen (no wall stops!)

+ avoid formation of ppμ molecules (Ortho-Para problem)

- ultra-high gas purity avoid μp → μZ transfers to impurities - ultra-high isotopic purity avoid μp → μd transfers (diffusion problem)

solutions of MuCap experiment

lifetime method(likeSaclay)

ΛS = λ(μ-p) – λ(μ+)muon beam with kicker

hydrogen TPC operatedin low density H2 gas

Φ ~ 0.01 (lq=1)

use of UHV materialscontinuous gas circulationsystem (CHUPS)

cZ>1 ≤ 20 ppb

HD separation columnD-depletion cd < 7 ppb

log(

coun

ts)

te-t

μ+

μ –

λμ+

λμ-

ΛCAP reduces lifetime

by ~1.6x10-3

→ e


e

cut out view of MuCap detector used in 2003-07


the MuCap detector with rolled back TPC


MWPC with Ucath = -(5-6)

kVEdrift = 2 kV/cm - vdrift = 0.55 cm/μssensitive volume (12 x 15 x 30) cm3

all wires soldered on special glass frames pure metal & ceramic

structurebakeable to 130 C

the Hydrogen TPC as active muon stop targetdeveloped 2001-03 at PSI

filling 10 bar ultra-pure protium gas

UHV = -30 kV


details of the TPC 75 anode wires

35 x 4 cathode wires2-D hor. readout + vert. drift time → 3-D reconstruction of μ tracksreliable operation achieved in 2004-07

first MWPC modul

etested

in 2001

mounting the final TPC in 2003 details of wiringPetitjean LTP-Seminar 23.04.12

first TPC assembly by PSI engineers in 2002


TPC performance shown in the event displayan

odes

strip

s

TPC signals showing a clean muon stop event with nuclear recoil from Z>1 capture allows monitoring of

impuritiesPetitjean LTP-Seminar 23.04.12

precision lifetime measurementis understanding the systematics!

the major issues in MuCap:

I impurities calibration with doped gas mixtures *II formation of ppμ molecules (rate λppμ) ** ortho-para transitions (rate λop)III electron interference with muon tracks *IV μ + p scatters *V diffusion of μdVI diffusion of μp *

* thesis Brendan Kyburg** thesis Sara Knaack


I. impurities: removal with CHUPS (Cont. H2 Ultra-Purification System, developed in Gatchina)- cryogenic adsorption/desorption cycles in active Carbon- Zeolite in liquid nitrogen absorbs all Z>2 impurities: cN2 <5ppb, cH2O

~17ppb

CHUPS duringmain runs

our main impurity source was water vapor

from walls & materials

H2O

N2

gas chromatography

humidity sensorPetitjean LTP-Seminar 23.04.12

cleaning effect of CHUPS gas circulation

thesis B. Kiburg

calibration

calibration run with 11 ppm N2


effect on μ lifetime determined with extrapolation method

ppm impurity admixtures correction to ΛS: -7.8 ± 1.87 (2006); -4.54 ± 0.93 (2007) [s-1] (-1.1%) (-0.6%) thesis B. Kiburg

syst. error due to badly known ratio

α = YN/Yall

we include: 0<α<1


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+

φλppμ

n+

- ppμ formation rate λppμ was known to ± 30% only- ortho para transition λop known to ± 50% only

- capture rates ΛS - ΛOM - ΛPM very different

τ~10ns

- our observed capture rate is not pure ΛS- at our gas density (10 bar) φ = 1.13% of lq H2 gives to ΛS a 3% correction with large error bar

- determine φλppμ by a special Argon doped run– remeasure λop from n-time spectra (to be done!)

II. ppμ molecule formation – the ortho-para problem

problem:

solution:Petitjean LTP-Seminar 23.04.12

ppP

ppO

p

100% lq. H2

p

ppP

ppO

1% lq. H2

→ time (μs)

development of atomic & molecular states of μ in H2

(a) liquid hydrogen, φ = 1 (b) hydrogen gas at φ = 0.01 pμ depopulated in 1-2 μs pμ remains dominant

~ 81% ppμ formation ~ 5% ppμ formation badly known ortho-para ratio! small effects from op transitions!


20 40 60 80 100 120

2.5

5

7.5

10

12.5

15

17.5

20

op (ms-1)

- + p + n + @ TRIUMF

MuCap precision goal

Saclay 1981 theory TRIUMF 2006

- + p + n @ Saclay

experimental situation on gP before MuCap

experiments & op rates are inconsistent Saclay experiment (in lq. H2) cannot be interpreted!

gP

HBChPT (8.26)


new ppμ measurement using 18.5 ppm Argon admixture

μp

ppμ

Λppμ = ppμ2.30x10-2s-1

ΛpAr = cAr pAr 4.46 x10-2 s-1

μAr

μ+ArCl+n+

ΛAr 1.3 s-1

kinetics scheme with rates Λppμ, ΛpAr, ΛAr

new result measured at MuCap conditions:

ppμ = 1.99 ± 0.058stat μs-1

(prelim.)(thesis Sara Knaack, to be published)correction to observed ΛS: ΔΛppμ = (18.2±2.5) s-1

(2.5%)

5x108 eventsΧ2/NDF = 0.98


(c) decay electron deposits energy (d) can generate or

augment pixels

(a) μ enters TPC & ionizes gas(b) charge drifts towards

MWPC

III. electron interference with muon tracks:charge deposition from decay electrons can generate or modify

pixelsof a muon track acceptance of events may become time

dependent!

thesis B. KiburgPetitjean LTP-Seminar 23.04.12

• EL Pixel• separated from track • added near the track

• EH Pixel• EL pixel “upgraded”• this modifies NCEH in

a complicated way

example of an interference between a muon trackand the decay electron producing blue pixels

crucial parameter is NCEH (# of EH pixels)


μ + p scattersgenerates EH pixel on one anode cut NCEH = 1

events

IV. μ + p scatters: can fake a μ stop, but actually stops in

surrounding high Z material & distorts the lifetime


fast neutron time component in NCEH=1 eventsdue to μ + p scatters leaving the TPC


thesis B. Kiburg

lifetime fits vs. NCEH

upper e-detector: no μ-e interference,but effect from μ-e scatters

lower e-detector: μ-e interference withμ track is time and space dependent


• match NCEH =2+ • determine

NCEH =1 distortion

• allows μ + p scatter estimate

correction of μ + p scatter effects: the μ+ data has NCEH interference, but no μ + p scatter distortion in NCEH = 1

thesis B. Kiburg

correction to ΛS: -12.4 ± 3.2 (2006); -7.20 ± 1.25 (2007) [s-1] (-1.7%) (-1.0%)


V. diffusion of μd: remove all deuterium by a H-D isotope separation

column (developed by Gatchina & PSI 2006/07)principle: - H2 gas circulates from bottom to cold head at top & gets liquefied

- liquid droplets fall down & evaporize gas phase gets depleted from D - the D-enriched liquid H2 at the bottom is slowly removed

AMS protium analysis at ETHZ:in 2004: cd = (1.45±0.15)10-6

in 2006-07: cd < 6*10-9

World Record: cd < 6 ppbPetitjean LTP-Seminar 23.04.12

VI. μp diffusion: it distorts the lifetime slope!

impact parameter

our choice of impact parameter is 120 mm resulting in a correction due to μp

diffusion of

ΔΛS = -3.0 ± 0.1 s-1 (0.4% of ΛS)


source old run8 (2004)

Phys. Rev. Lett. 99,032002 (2007)

new run10 (2006)

P. Winter et al.

new run11 (2007)

B. Kiburg et al.

remarks

unit s-1 s-1 s-1

μ+p scatter 0 ± 3.0 -12.40 ± 3.22* -7.20 ± 1.25* err. prelim.

μ+p diffusion -2.7 ± 0.5 -3.1 ± 0.1 -3.0 ± 0.1μ+d diffusion -10.2 ± 1.6 0 0 cd < 7

ppbHigh-Z impurities -19.2 ± 5.0 -7.80 ± 1.87 -4.54 ± 0.93entrance counter

inefficiencies 0 ± 3.0 0 ± 0.5 0 ± 0.5

e det. - definition 0 ± 5.0 0 ± 1.8* 0 ± 1.8* err. prelim.

fiducial volume cut

- 0 ± 3.0 0 ± 3.0

total correction -32.1 ± 8.5 -23.3 ± 5.1* -14.7 ± 3.9* *error correlated

systematic corrections to μ and errors [s-1]


lifetime fit of full run11 statistics


MuCap‘s new physics resultsfrom unblinding the 2006 & 2007 data

at UW Seattle, Dec 16, 2011

(preliminary)


lifetime fit results in blinded mode(with unknown offset of master clock)


final lifetime results after unblinding Dec 16, 2011


old run8 (2004)Phys. Rev. Lett. 99,

032002 (2007)

new run10 (2006)

evaluated byP. Winter et al.

new run11 (2007)

evaluated byB. Kiburg et al.

remarks

statistics 1.6 x 109 5.5 x 109 5.0 x 109 events after cuts

μ- fit 455‘883.5 ± 12.5

455‘880.4 ± 7.0 455‘867.0 ± 7.6 2/NDF ~1.15±0.1

syst. corr. -32.1 ± 8.5 -23.3 ± 5.1 -14.7 ± 3.9 systematical errorμ- corr. 455‘851.4 ±

12.5455‘857.1 ± 7.7 455‘852.3 ± 8.3 stat. error inflated

μ- average all

runs

455‘854.2 ± 7.2

stat.+sys. errors combined

μ+ 455‘170.2 ± 0.5 Phys. Rev. Lett. 106,041803 (2011)

final MuLan result

Δμp +12.3 Phys. Rev. 119(1),365 (1960)

bound state effect

ΔΛpμp +18.2 ± 2.5 pμp formation

ΛS= μ- - μ+

+Δμp +ΔΛpμp

714.5 ± 7.6 (±5.4stat±5.4sys

) preliminary

(within < 0.5s-1)final MuCap

result

ΛS 711.5 ± 4.6 theory

μp lifetimes & evaluation of capture rate ΛS [s-1]


the induced pseudoscalar coupling constant gP

δΛS/ΛS = -0.197 δgP/gP δgPMuCap = -0.021 gP

ChPT

gPChPT = 8.26 ± 0.23 gP

MuCap = 8.1 ± 0.5 (preliminairy!)

excellentagreementwith chiralperturbationtheory!


gP (MuCap prelim.) = 8.1 ± 0.5gP (theory) = 8.26 ± 0.23

precise & unambiguous MuCap result solves longstanding puzzle


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.E.

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

MuCap collaboration & authors of P.R. Lett. 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*

*now University of Washington (UW), Seattle, USAUniversité Catholique de Louvain, Belgium

University of Kentucky, Lexington, USABoston 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)


Documents

Unblinding the MuCap experiment the final results of μp capture rate Λ S and of electro-weak coupling constant g P LTP Seminar April 23, 2012 Claude Petitjean