Kuno-Group D3 Shintaro Ito - Osaka Universityosksn2.hep.sci.osaka-u.ac.jp/~s-ono/slides/SIto.pdf2...
Transcript of Kuno-Group D3 Shintaro Ito - Osaka Universityosksn2.hep.sci.osaka-u.ac.jp/~s-ono/slides/SIto.pdf2...
Precision Measurement of the π+→e+νe Branching Ratio in the PIENU Experiment
Kuno-Group D3 Shintaro Ito
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Outline
•π+→e+νe Decay
•Measurement Method
•Detector
•Analysis
•Status and Uncertainties
•Summary
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π+→e+νe Decay•π branching ratio in the SM !
!
•Previous experiment at TRIUMF REXP=[1.2265±0.0034(stat)±0.0044(syst)]×10-4
•Precise measurement of R -Electron-muon universality violation (ge≠gµ) -Helicity unsuppressed pseudoscalar interaction ➡0.1% allows access new physics up to 1000 TeV.
•The PIENU experiment (TRIUMF): aims <0.1%.
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V.Cirigliano, I.Rosell, PRL 99 231801 (2007)
π
Measurement Method
R=NPIE/NPIMU×(1+ε)
π+→µ+→e+ NPIMU/(τµ-τπ)×(e-t/τ -e-t/τ ) π+→e+νe (NPIE/τπ)e-t/τ
Raw branching ratio R’
Corrections (e.g: low energy tail)
Decay positron time (MC)
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Calorimeter
π+
μ+
e+ e+
Ee:0.5~52.8 MeV Ee:69.8 MeV
Target
Decay positron energy (MC)
π+→e+νe low energy tail
π+→µ+→e+ π+→e+νe
πµ
π
(×104)
PIENU Beam Line & Detector
WC:Wire Chamber S:Silicon Strips B1,B2,Tg,T1,T2:Plastic scintillator
48cm
48cm
TRIUMF M13 Beam line •Beam rate:~70 kHz •Beam momentum:75±1 MeV/c •π+:μ+:e+=85:14:1
PIENU detector
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Zoom up
Data taking in 2009~2012.
0.5~ 52.8MeV
V3
Analysis: Raw Branching Ratio Extraction
π+→e+νeπ+→µ+→e+
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!•Data set: November in 2010. •4.0×105 clean π+→e+νe events. • Time=tT1-tB1[ns] • Fit both time spectra simultaneously. •Raw branching ratio was blinded
52 MeV
R’=(1.1972±0.0022±0.0005)×10-4
Time window: -300<t<540 ns
Tail Correction•Low energy π→eν buried under the π→µ→e distributions.
•Estimated by 2 methods.
- Suppressed dominant π→µ→e events.
- Special data set using mono-energetic beam positron.
Tail fraction <52 MeV=3.07±0.12%
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[MeV]NaI+CsIE0 10 20 30 40 50 60 70 80 90 100
Cou
nts
1
10
210
310
410
510
Time 0.9916Energy loss 0.2947
Kink 0.1542
S3 0.1457
Pulse fit 0.1441
Tail measurement using e+ beam.
Low energy tail
Photo nuclear effect NIMA,621,188-191 (2010)
π→µ→e suppressed spectrum.
Acceptance Correction
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•The correction of acceptance difference between π+→e+νe and π+→µ+→e+. ➡ Positrons energy dependence of interactions.
•Track of positron is reconstructed by S3,WC3. •Rely on MC to study various systematic effects. - π stopping position. - Displacement of detectors. - Thickness, etc...
Acceptance correction: 0.9991 ± 0.0003
Schematic of the tracking.
NaI
CsI
CsI
Tg S3 WC3
π
e
e
μ
Branching Ratio and Uncertainties•The initial analysis was completed.
- No systematic dependence.
-R=[1.2344±0.0023(stat)±0.0019(syst)]×10-4 (0.24%) -gµ/ge=1.0004±0.0012⇨ Most precise result!!
9 Branching ratio vs Radius cut.Sliced radius at WC3[mm]
20 30 40 50 60 70 80 90 100
)-7
10×N
orm
aliz
ed b
ranc
hing
ratio
(
-120
-100
-80
-60
-40
-20
0
20
40
60
80
Raw branching ratio
DIF correctionsµTail +
DIF + Acceptance correctionsµTail +
Phys. Rev. Lett., 115, 071801 (2015)
•The dominant source was statistics. ➡×10 statistics for full data set
•Systematic uncertainty was dominated by tail correction ➡Tail depends on the statistics.
•Remaining data is being analyzed.
Uncertainties
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2011 data set is about twice statistics. 2011 data set is still blinded.
Error Previous Experiment
PIENU (2010)
PIENU (2010+2011) Preliminaly
Goal of PIENU
Statistic 0.28% 0.18% 0.11% 0.05%
Time spectrum 0.19% 0.03% 0.03% 0.03%
Tail Correction 0.25% 0.12% 0.08% 0.03%
Acceptance Correction 0.11% 0.03% 0.03% 0.03%
Other 0.11% 0.05% 0.03% 0.03%
合計 0.47% 0.24% ~0.15% <0.1%
Summary•Precise π+ branching ratio measurement is sensitive to new physics beyond the SM. •PIENU aims to measure π+ branching ratio to <0.1% level. •Finished data taking in 2012. •The initial analysis was completed:0.24%. •Analyzing the remaining data. - Systematic study for 2011 data set was finished. - Precision level: ~0.15%, improved by a factor of 3.
•Final result using full data set will be finished next year.
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Thank you for your attention!!
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Backup
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Pseudoscalar Interaction
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e+u
d νe
π+W+
e+u
d νe
π+~1/Λ2+
SM New interaction
π+→e+νe Decay•π+ branching ratio R in SM !
!
!
!!
- ge=gµ: lepton universality. - π+→e+νe is disfavored (V-A). ➡ Helicity suppression.
•Experimental result
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R =Γ((π→µν)+(π→µνγ))Γ((π→eν)+(π→eνγ))
SM
=ggme (m -m )
µ m 2π
(m -m )πµ
e e
µ
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2
2
2 2
2 2
2 (1+δ)(1+ε)Radiative Correction
= (1.2352±0.0002)×10-4 (0.02%)
R = (1.230±0.004)×10-4 (0.4%)Exp
W+
e+,µ+u
d νe,νµ
π+
ge,gµ
Couplings
History of R measurement.
V.Cirigliano, I.Rosell, PRL 99 231801 (2007)Expected by New Measurement
CzapekBrittonBryman
DiCapuaAnderson
Theoretical region
Universality Test & Beyond SM
•Lepton universality violation. - π+ R is one of the most
precise measurement.
- Improve R measurement.
➡0.05% in gµ/ge.
•New pseudo-scalar interaction without helicity suppression.
- 0.1% level allows to access new physics up to 1000 TeV/c2.
- R-parity violation SUSY, leptoquarks etc...
• PIENU experiment at TRIUMF → aims at <0.1% level.
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Decay Mode g /g Yearτ→µ/τ→e 1.0018±0.0014 2010π→µ/π→e 1.0021±0.0016 1994K→µ/K→e 0.996±0.005 2011K→πµ/K→πe 1.002±0.002 2007W→µ/W→e 0.997±0.010 2008
Current experimental results of g /g
µ e
µ e
R-Parity Violation SUSY
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Current constraints
Expected by PIENU
Future measurement of proton weak charge.
λ’i1k
M.J.Ramsey-Musolf, S.Su & S.Tulin, PRD 76 095017 (2007).
Previous TRIUMF Experiment
•E248 experiment at TRIUMF in 80’s. •R=(1.2265±0.0034±0.0044)×10-4 •1.5×105 π+→e+νe events. •Dominant sources of errors - Small acceptance: ~2% ➡ Low statistics.
- Many unsuppressed π-DIF in low energy region : ~20% ➡ Largest systematic uncertainty.
E248 detector
Energy spectrum after π+→µ+→e+ suppression
Many π-DIF in low energy region
(stat) (syst)
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Experiments of Universality Test
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•Γ(K+→e+νe(γ))/Γ(K+→µ+νµ(γ)): NA62, TREK etc
➡gµ/ge=0.996±0.005
•Γ(τ-→µ-νµντ)/Γ(τ-→e-νeντ): Bhabha etc
➡gµ/ge=1.0018±0.0014
•Γ(π+→e+νe(γ))/Γ(π+→µ+νµ(γ)): PIENU(TRIUMF), PEN(PSI)
➡Ongoing. Expected to improve gµ/ge <0.05%.
•Γ(B+→K+µ+µ-)/Γ(B+→K+e+e-):LHCb
➡0.745 (stat) ± 0.036(syst) (2.6σ from SM)+0.090-0.074
PIENU Detectors & Beam Line
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NaI 1 CsI crystal Scint + Si Strip WC3
PIENU detector
π+ beam
Trigger Logic
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Analysis: Blind Technique•Need to avoid bias in precision measurement. • The procedure shown below is done before analysis. - Central value of R should be blinded. - π+→e+νe/π+→µ+→e+ events are suppressed. - Inefficiency factor is produced by random number (~1%). - R should be blinded until all systematic errors are estimated.
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Case1: π+→e+νe suppression. Case2: π+→µ+→e+ suppression.
Initial Analysis: Event Selection Cuts•Data set: taken in Nov~Dec 2010. ➡~10% of full data.
• Event selection cuts. - Beam profile by WC1,2. - Pion selection by dE/dx in B1,B2. - Single hit requirement in B1,B2,T1,T2 - Acceptance cut.
23Beam profile by WC1 dE/dx in B2 Reconstructed radius
at WC3.
0.5~ 52.8MeV
V3
Tail Analysis
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πDIF
Analysis: Tail Correction1•π+→e+νe low energy tail due to shower leakage buried under π+→µ+→e+.
• Suppress π+→µ+→e+ by time window, target energy, beam angle, etc ➡π+→µ+→e+ were suppressed by a factor of ~105. ➡Estimated tail fraction: N<52MeV/NAll=1.48±0.10%.
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π+→µ+→e+π+→e+νe
π+→µ+→e+ suppression
Target energy
π μ eπDIF
πDAR
θ
Beam angle
Time window: 5<t<35 ns
Analysis: Tail Correction•Assume that all events below i(0~52 MeV) are coming from remaining unsuppressed π+→µ+→e+ backgrounds. • The amount of tail is estimated by shapes of suppressed spectrum and Michel spectrum from data. !
•This procedure gives only lower bound of tail. N<52MeV/NAll = (2.95 ± 0.12)%
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The amount of π+→e+νe tail = A - a[i]×B/b[i]
π+→µ+→e+ suppressed spectrum
A
a[i]
iMichel spectrum from data
b[i]
B
i
Tail Analysis
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Zoom
Analysis: Tail Correction1•Some π+→e+νe events were removed by target energy cut. •Most events with large Target energy events are due to Bhabha scattering in Target. •MC correction was studied.
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π+→e+νe events with/without Target cut by MC study.
•Tail fraction before correction. N<52MeV/NAll=1.48±0.10%.
•After correction of lower bound N<52MeV/NAll=2.95±0.12%.
Analysis: Tail Correction2•Tail measurement using mono-energetic positron beam.
•Rotate the crystals for different entrance angle measurement.
•Possibility of low momentum positron beam contamination.
➡Upper bound: N<52MeV/NAll = (3.19 ± 0.09)%
29Positron beam measurement. Rotation of crystals Tail measurement at 0 degrees.
Low energy tail
Photo nuclear effect NIMA,621,188-191 (2010)
Tail Analysis -NaI Response-
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MC without hadronic interactionMC with hadronic interactionData
•First observation of photo-nuclear effect.
•Peaks are consistent with neutrons escaping.
•Good agreement between data and MC
A.Aguilar-Arevalo et al Nucl. Inst. and Methods A (2010)
Tail Analysis
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Analysis: Combination of Tail Correction•Lower bound: 2.95±0.12% Upper bound: 3.19±0.09%
•Assume both distribute Gaussian functions (Left).
•Combine the 2 error functions and get combined value (Right).
Combined tail fraction:3.07±0.12%
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Lower bound Upper bound
Acceptance Correction
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Example of MC study: Pion beam stopping position.
Radius at WC3[mm]20 30 40 50 60 70 80 90 100
Rat
io o
f acc
epta
nce
0.995
0.996
0.997
0.998
0.999
1
1.001
Usual+0.1mm-0.1mm+0.2mm-0.2mm
Radius at WC3[mm]58.5 59 59.5 60 60.5 61 61.5
Rat
io o
f acc
epta
nce
0.998
0.9982
0.9984
0.9986
0.9988
0.999
0.9992
0.9994
Energy Dependence in T1
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B1
B3
T1
e+: 0.5~52.8 MeVµ+
Energy Dependence in T1
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Energy in NaI+CsI[MeV]0 10 20 30 40 50
t0 ti
me[
ns]
1.46
1.48
1.5
1.52
1.54
1.56
/ ndf 2χ 12.72 / 8Intercept 0.01013± 1.514 Slope 0.0003104± -0.0002794
/ ndf 2χ 12.72 / 8Intercept 0.01013± 1.514 Slope 0.0003104± -0.0002794
Correction value: 1.0004±0.0005