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The neutron beta decay correlation program at SNS
Dinko Pocanic
University of Virginia
NSAC Subcommittee ReviewChicago, IL,
15 April 2011
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 1 / 42
n-decay program at FnPB
The FnPB neutron decay program at SNS
I Nab: a precise measurement of
a, the electron-neutrino correlation in neutron decay, and b, the Fierz interference term (so far not measured in n decay).
I Polarized program (abBA/PANDA): precise measurements of
A, the electron asymmetry in neutron decay, B, the neutrino asymmetry in neutron decay, C , the proton asymmetry in neutron decay; also
Goal uncertainties: δa/a, δA/A, δB/B ≤ 10−3, andδb ≤ 3× 10−3.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 2 / 42
Motivation, goals
Neutron Decay Parameters (SM)
dw
dEedΩedΩν' keEe(E0 − Ee)2
×[
1 + a~ke ·~kν
EeEν+ b
m
Ee+ 〈~σn〉 ·
(A~ke
Ee+ B
~kν
Eν
)+ . . .
]where:
a =1− |λ|2
1 + 3|λ|2A = −2
|λ|2 + Re(λ)
1 + 3|λ|2
B = 2|λ|2 − Re(λ)
1 + 3|λ|2λ =
GA
GV(with τn ⇒ CKM Vud)
also:C = κ(A + B) where κ ' 0.275 .
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 3 / 42
Motivation, goals
Goals of the Nab experiment
I Measure the electron-neutrino parameter a in neutron decay
with accuracy of∆a
a' 10−3
current results:−0.1054± 0.0055 Byrne et al ’02−0.1017± 0.0051 Stratowa et al ’78−0.091± 0.039 Grigorev et al ’68
I Measure the Fierz interference term b in neutron decay
with accuracy of ∆b ' 3× 10−3
current results: none (in n decay)
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 4 / 42
CKM matrix: Vud
Status of A and λ in n decay
-0.125 -0.120 -0.115 -0.110
PERKEO II, prelim.
Δ A/A = 0.1%(abBA goal)
Average:-0.1187(8)
UCNA, 2010
PERKEO II, 2002
Liaud, 1997
PERKEO,1986
Yerozolimskii, 1997
Beta Asymmetry A
Uncertainty of the averagescaled up by factor 2.3×
Global fit χ2/dof = 27/5 !
Statistical probability forthis χ2 is 6× 10−5.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 5 / 42
CKM matrix: Vud
Status of A and λ in n decay (cont’d)
Δ λ/ = 0.03%(Nab/abBA goals)
λ
PERKEO II, prelim.
Mostovoi, 2001
Average:-1.2733(20)
UCNA, 2010
PERKEO II, 2002
Liaud, 1997
PERKEO,1986
λ = /g gA V
-1.28 -1.26 -1.25-1.27
Yerozolimskii, 1997
Goals for ∆a, ∆A:
⇒ ∆λ ' 3.5× 10−4
i.e., an order of magn.improvement.
∆λ
λ' 0.27
∆a
a' 0.24
∆A
A
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 6 / 42
Beyond Vud
n-decay correlation parameters beyond Vud
I Beta decay parameters constrain L-R symmetric, SUSY extensions tothe SM. [Reviews: Herczeg, Prog. Part. Nucl. Phys. 46, 413 (2001),N. Severijns, M. Beck, O. Naviliat-Cuncic, Rev. Mod. Phys. 78, 991 (2006),
Ramsey-Musolf, Su, Phys. Rep. 456, 1 (2008)]
I Fierz int. term, never measured for the n, along with B, offers asensitive test of non-(V − A) terms in the weak Lagrangian (S ,T ).[S. Profumo, M. J. Ramsey-Musolf, S. Tulin, PRD 75, 075017 (2007)]
I Measurement of the electron-energy dependence of a and A canseparately confirm CVC and absence of SCC.
[Gardner, Zhang, PRL 86, 5666 (2001), Gardner, hep-ph/0312124]
I A connection exists between non-SM (e.g., S ,T ) terms in d → ueνand limits on ν masses. [Ito + Prezaeu, PRL 94 (2005)]
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 7 / 42
Beyond Vud non-V − A interaction terms
Updated limits for RH S and T currents n decay
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
RS/L
V
RT/L
A
neutron and nuclear decays(survey, 95% C.L.)
Δχ2
C.L.
2.30 68.3%
90%
95.4%
4.61
6.17neutrino
mass(68% C.L.)
neutrino mass(68% C.L.)
muon decay“90% C.L.”
Present limits (n decay data)(SM values at origin of plot.)
S V
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
R /LR
T/L
A
neutron and nuclear decays(survey, 95% C.L.)
Δχ2
C.L.
2.30 68.3%
90%
95.4%
4.61
6.17
neutrino mass(68% C.L.)
neutrino mass(68% C.L.)
muon decay“90% C.L.”
Projected limits based on a = −0.1030(1),
b ≡ 0, and no improvement in A.
[G. Konrad, W. Heil, S. Baeßler, D. Pocanic, F. Gluck, arXiv 1007.3027.]
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 8 / 42
Beyond Vud non-V − A interaction terms
Limits for LH S and T currents n decay
LS/L
V
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
LT/L
A
neutron andnuclear decays(survey, 68% C.L.)
superallowed
0 →0 decays(68% C.L.)
+ +
“present limits”(68% C.L.)
muon decay“90% C.L.”
nuclear decays
( ( In), 90% C.L.)P107
Δχ2
C.L.
2.30 68.3%
90%
95.4%
4.61
6.17
Present limits (n decay data)(SM values at origin of plot.)
-0.04 -0.02 0.00 0.02 0.04
-0.04
-0.02
0.00
0.02
0.04
LS/L
V
LT/L
A
Δχ2
C.L.
2.30 68.3%
90%
95.4%
4.61
6.17
“future limits”
(68% C.L.)
superallowed
0 →0 decays(68% C.L.)
+ +
neutron andnuclear decays(survey, 68% C.L.)
nuclear decays
( ( In), 90% C.L.)P107
Projected limits assuming a = −0.1030(1);
b = 0±0.003: no new A,B measurements.
[G. Konrad, W. Heil, S. Baeßler, D. Pocanic, F. Gluck, arXiv 1007.3027.]
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 9 / 42
Beyond Vud Second class currents
Correlation parameters with recoil correction[Gardner, Zhang, PRL 86, 5666 (2001), Gardner, hep-ph/0312124]
Most general form of hardonic weak current consistent with (V-A):
〈p(pp)|Jµ|n(pn,P)〉 =
up(pp)
(f1(q2)γµ − i
f2(q2)
Mnqµ +
f3(q2)
Mnqµ + g1(q2)γµγ5
− ig2(q2)
Mnσµνγ5qν +
g3(q2)
Mnγ5qµ
)un(pn,P)
a,A,B⇒ λ =g1
f1while τn ∝ (f1)2 + 3(g1)2
However, f2 (weak magnetism) and SCC’s (g2, g3), remain unresolved inbeta decays (best tested in A=12 system). With recoil corrections,Gardner and Zhang find:
a(Ee) = func(f2) while A(Ee) = func(f2, g2)
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 10 / 42
Comparison w/other experiments Little a
Current experiments aiming to measure a
1. Nab: goal is to measure ∆a/a ∼ 10−3
I Discussed in this presentation.
2. aCORN: goal is to measure ∆a/a ∼ 0.5− 2 %I Funded, under way at NIST,I Uses only part of neutron decays.
3. aSPECT: aims to measure ∆a/a ∼ 10−3
I Funded and running; recently overcame trapping problems,I Stat. sensitivity not as good as Nab due to integration; presently∼ 2 %/day—will likely improve on publ. results, not < 1 % this yr,
I Determination of detection function relies on theoretical model ofspectrometer; if assumptions fulfilled, input param’s easy to measure.
I Singles measurement!I will become part of the PERC program with improvements.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 11 / 42
Comparison w/other experiments Polarized measurements
Current state of the art in A: PERKEO III obtained A = −0.1189(7) in 2002; −0.1198(5) current prelim.
I data acquisition finished,
I data analysis of last (3rd) run completed; result not yet published,
I symmetric setup on cold n beam, similar to original abBA design,
Electron Detector (Plastic Scintillator)
Polarized Neutrons
Split Pair Magnet
Decay Electrons
Magnetic Field PERKEO II
I singles e detection
I benchmark design forall comparisons,
I major uncertainties:I statistics,I neutron beam
polarization,I background,I electron detection.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 12 / 42
Comparison w/other experiments Polarized measurements
1. abBA: aim δA/A ' 1× 10−3; (discussed in this talk)I uses magnetic filter,I expected improvements: background (coincidences), electron detection
(Si detector), sensitivity to field inhomogeneities,I measurements of C (B) planned
2. PERKEO III: aim δA/A ' 2× 10−3 in AI data analysis of second run ongoing, aim to measure A and f2I expected improvements: pulsed wide beam (statistics, background)
3. UCNA: aim δA/A ' 2× 10−3 (discussed at this meeting)I achieved −0.11966+152
−166 in 2010,I uses (so far, dedicated) UCN source,I major uncertainties: statistics, Pn (so far: > 99.5%, viz. 99.7(1)% in
PERKEO II), E loss in foil, muon veto bgd,I further measurements of B, b planned,
4. PERC: aim δA/A ' 3× 10−4; (funded, being designed)I uses magnetic filter behind a pulsed beam in a neutron guide,I main expected improvements: counting statistics, background (singles
det’n, but w/pulsed beam), sensitivity to field inhomogeneities;I future measurements of a, C, et al., in planning.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 13 / 42
Measurement principles
Nab Measurement principles: Proton phase space
Ee (MeV)
p p2 (
MeV
2 /c2 )
cos θeν = -1
cos θeν = 1
cos θeν = 0
proton phase spaceprobability (arb. units)
Ee =
75 keV
236 keV
450 keV
700 keV
0
0.5
1
1.5
0 0.2 0.4 0.6 0.8
NB: For a given Ee , cos θeν is a function of p2p only. Slope = a
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 14 / 42
Measurement principles Detection function
Measurement principles: Detection function (I)
Proton time of flight in B field:
tp =f (cos θp,0)
ppwhere cos θp,0 =
~pp0 · ~Bpp0B
∣∣∣∣∣decay pt.
.
For an adiabatically expanding field prior to acceleration,
f (cos θp,0) =
∫ l
z0
mp dz
cos θp(z)=
∫ l
z0
mp dz√1− B(z)
B0sin2 θp,0
.
To this we add effects of magnetic reflections and, later, of electric fieldacceleration.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 15 / 42
Measurement principles Detection function
Measurement principles: Detection function (II)
The proton momentum distribution within the phase space bounds is givenby
Pp(p2p) = 1 + aβe cos θeν , [recall: cos θeν = f (p2
p)]
while
Pt
(1
t2p
)=
∫Pp(p2
p) Φ
(1
t2p
, p2p
)dp2
p .
Detection function Φ relates the proton momentum and time-of-flightdistributions! To extract a reliably:
I Φ must be as narrow as possible,
I Φ must be understood very precisely.
Two methods (“A” and “B”) pursued to specify Φ.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 16 / 42
Measurement principles Detection function
Measurement principles: Detection function (II)
The proton momentum distribution within the phase space bounds is givenby
Pp(p2p) = 1 + aβe cos θeν , [recall: cos θeν = f (p2
p)]
while
Pt
(1
t2p
)=
∫Pp(p2
p) Φ
(1
t2p
, p2p
)dp2
p .
Detection function Φ relates the proton momentum and time-of-flightdistributions! To extract a reliably:
I Φ must be as narrow as possible,
I Φ must be understood very precisely.
Two methods (“A” and “B”) pursued to specify Φ.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 16 / 42
Measurement principles Detection function
Measurement principles: Detection function (III)
kine-maticinput
pp2 (MeV2/c2)
Yie
ld (
arb.
uni
ts)
Ee = 500 keV
0
0.1
0.2
0.3
0.4
0 0.2 0.4 0.6 0.8 1 1.2 1.4
mean: 0.00394 s
RMS: 0.00015
μ-2
μs-2
0.000 0.001 0.002 0.003 0.004
1/tp
2[1/µs
2]
101
102
103
104
Sp
ectr
om
eter
resp
on
sefu
nct
ion
Φ(⋅
,p
p
2)
mean
Ep =500 eV
analyt.calcul’n
0.00 0.02 0.04 0.06 0.08
1/tp
2[1/µs
2]
103
104
105
106
107
Sim
ula
ted
cou
nt
rate
Ee = 300 keV
Ee = 500 keV
Ee = 700 keV
1/tp
2[1/µs
2]
Sim
ula
ted
co
un
ts [
A.U
.]
0.002 0.004 0.0060
Ee = 300 keV
Ee = 500 keV
Ee = 700 keV
MCGEANTsimul’n
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 17 / 42
Measurement principles Apparatus
Nab principle of operation
I Collect and detectboth electron andproton from neutronbeta decay (magneticfield, detectors at bothends)
I Measure electronenergy and protonTOF and reconstructdecay kinematics(Magnetic field shape,silicon detectors atboth ends).
SegmentedSi detector
SegmentedSi detector
TOF region(field ∙ )r BB 0
Uup (upper HV)
Udown (lower HV)
magnetic filterregion (field )B0
decay volume(field ∙ )r BB,DV 0
Neutronbeam
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 18 / 42
Measurement principles Apparatus
abBA/PANDAconfiguration:
I A: detect electronsin upper, protonsin lower detector;
I B/C: detectprotons in upper,electrons in lowerdetector;
SegmentedSi detector
TOF region(field ∙ )r BB 0
Uup (upper HV)
Udown (lower HV)
magnetic filterregion (field )B0
decay volume(field ∙ )r BB,DV 0
Polarizer withspin-reversal
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 19 / 42
Measurement principles Apparatus
The spectrometer: coil design and magnetic field profile
466.25
0.03
5.00
25.28 43.81
37.50
0.50
481.25
14.7525.90
67.09
0.47
41.66
14.7725.90
4.34
4.34
10.5220.5838.16
3.13
3.13
29.94
16.4130.24
3.19
3.28
4.9312.92
8.00
16.77
c1i
z
r
c6i
c4i
c5i
c3ic2i
c1o
c6o
c4o
c5o
c3oc2o
Mag
net
ic f
ield
[T]
B
z [m]
z [cm]
00
0
1
20
-1 2
-20
3
10
4
-10
5
-30
1
2
3
4
5
Bz(on axis)
Bz(on axis)
Bz(off axis)
Mag
net
ic f
ield
[T]
B
0
1
2
3
4
5
Decayvolume
Decayvolume
Si detector
Filter
4 m flight path is omitted here
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 20 / 42
Hardware and installation Detectors
Si detector prototypes (15 cm diameter)
LANL group has full-size prototypes from Micron Corp.Full thickness t = 2 mm; dead layer thickness td ≤ 100 nm.Detailed testing currently under way at LANL.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 21 / 42
Hardware and installation Detectors
Spectrometerinstallationin FnPB:
Beam shutter
Beam stop
Spectrometer magnet
Passive Antimagnetic Shield
Neutron guide
Beam pipe
200cm
200cm
300cm
Spectrometer magnet
Magnet Pit
Detector housing
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 22 / 42
Overview of uncertainties Event statistics, rates, running time
Statistical uncertainties for a and b
Statistical uncertainties for a
Ee,min 0 100 keV 100 keV 300 keVtp,max – – 100µs 40µs
σa 2.4/√N 2.5/
√N 2.5/
√N 2.5/
√N
σa† 2.5/
√N 2.6/
√N 2.6/
√N 2.7/
√N
σa§ 4.1/
√N 4.1/
√N 4.1/
√N 4.1/
√N
† with Ecalib and LTOF variable; § using inner 70% of p2p data.
Statistical uncertainties for b
Ee,min 0 100 keV 200 keV 300 keV
σb 7.5/√N 10.1/
√N 15.6/
√N 26.3/
√N
σb†† 7.7/
√N 10.3/
√N 16.3/
√N 27.7/
√N
†† with Ecalib variable.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 23 / 42
Overview of uncertainties Event statistics, rates, running time
Statistical uncertainties for a and b
Statistical uncertainties for a
Ee,min 0 100 keV 100 keV 300 keVtp,max – – 100µs 40µs
σa 2.4/√N 2.5/
√N 2.5/
√N 2.5/
√N
σa† 2.5/
√N 2.6/
√N 2.6/
√N 2.7/
√N
σa§ 4.1/
√N 4.1/
√N 4.1/
√N 4.1/
√N
† with Ecalib and LTOF variable; § using inner 70% of p2p data.
Statistical uncertainties for b
Ee,min 0 100 keV 200 keV 300 keV
σb 7.5/√N 10.1/
√N 15.6/
√N 26.3/
√N
σb†† 7.7/
√N 10.3/
√N 16.3/
√N 27.7/
√N
†† with Ecalib variable.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 23 / 42
Overview of uncertainties Event statistics, rates, running time
Nab event rates, statistics and running timesNab expects data rates of about 300 evts./s.In a typical ∼ 10-day run of 7× 105 s of net beam time we would achieve
σa
a' 2× 10−3 and σb ' 6× 10−4
We plan to collect samples of 1− 2× 109 events in several 6–8-week runs.
Overall accuracy will not be statistics-limited.
Analysis methods to be used:
A. parametrize edges and width of Φ(pp, 1/tp) by fitting; use central partof Φ (∼ 70%) to extract a in a multiparameter fit, and
B. specify all possible parameters of Φ by direct measurement; ⇒treat a, µ = 1/t2
p(pp), and Ndecays as free parameters in a two-stepfitting procedure,
as well as a hybrid of the two.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 24 / 42
Overview of uncertainties Event statistics, rates, running time
Nab event rates, statistics and running timesNab expects data rates of about 300 evts./s.In a typical ∼ 10-day run of 7× 105 s of net beam time we would achieve
σa
a' 2× 10−3 and σb ' 6× 10−4
We plan to collect samples of 1− 2× 109 events in several 6–8-week runs.
Overall accuracy will not be statistics-limited.
Analysis methods to be used:
A. parametrize edges and width of Φ(pp, 1/tp) by fitting; use central partof Φ (∼ 70%) to extract a in a multiparameter fit, and
B. specify all possible parameters of Φ by direct measurement; ⇒treat a, µ = 1/t2
p(pp), and Ndecays as free parameters in a two-stepfitting procedure,
as well as a hybrid of the two.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 24 / 42
Overview of uncertainties Systematic uncertainties
Nab systematic uncertainties
Experimental parameter (∆a/a)SYST
Magnetic field: curvature at pinch 5× 10−4
ratio rB = BTOF/B0 2.5× 10−4
ratio rB,DV = BDV/B0 3× 10−4
LTOF, length of TOF region (*)U inhomogeneity: in decay / filter region 5× 10−4
in TOF region 1× 10−4
Neutron Beam: position 4× 10−4
width 2.5× 10−4
Doppler effect smallunwanted beam polarization small
Adiabaticity of proton motion 1× 10−4
Detector effects: Ee calibration (*)Ee resolution 5× 10−4
Proton trigger efficiency 2.5× 10−4
Accidental coincidences smallResidual gas smallBackground small
Sum 1× 10−3
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 25 / 42
Overview of uncertainties Systematic uncertainties
abBA/PANDA rates and statistical uncertainties
Additions to Nab apparatus:
(supermirror) polarizers,
polarization analyzers,yield these rates:
decays in DV: nd =dNd
dt' 250 s−1 , and
e’s in UD: neU =dNeU
dt' 30 s−1 .
(He-3 polarizers may give higher rates.)
Ee lower cutoff (keV) none 100 200 250
σA (symm., 2 det’s) 2.7/√
Nd 2.9/√
Nd 4.8/√
Nd 7.4/√
Nd
σA (asymm., 1 det.) 4.3/√
Nd 4.8/√
Nd 7.8/√
Nd 11.9/√
Nd
To reach ∆A/A = 1× 10−3 we need Nd = 1.7× 109 or 75 live days.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 26 / 42
Overview of uncertainties Systematic uncertainties
abBA/PANDA systematic uncertainties
Experimental parameter (∆A/A)SYST
Neutron Beam: position not relevantprofile & edge effect smallDoppler effect smallpolarization ≤ 1× 10−3
U inhomogeneity: smallDetector effects: Ee calibration 2× 10−4
Trigger efficiency smallAccidental coincidences smallResidual gas smallBackground small
Sum under study
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 27 / 42
Schedule Milestones
Optimal schedule, excluding major technical, administrative or funding delays:
Milestone Completion0.b Detector prototype detects protons Sep. 20110. Magnet design ready for bidding Sep. 2011
1.a Order for magnet placed (design & option to build) Dec. 20111.b Acceptance of engineering drawings Dec. 20121.c Delivery of magnet Sep. 20131. Spectrometer magnet accepted Dec. 2013
2.a Passive Antimagnetic screen: magnetic design finished Sep. 20122. Passive Antimagnetic screen built Dec. 2013
3.a Detector test chamber available Mar. 2012. . . . . . . . . . . . . . . . . . . . . . . . . . .
3.g Electrode system ready Mar. 20143. Main detectors work in spectrometer Jun. 2014
4.a Shielding calculation for Nab accepted Jun. 2013. . . . . . . . . . . . . . . . . . . . . . . . . . .
4.d Shielding and utilities ready Jun. 20144. Spectrometer ready for data taking Sep. 2014
5.a Magnetometer calibrated Sep. 20125.b Magnetic field mapping system constructed Dec. 20135. Magnetic field of spectrometer mapped Mar. 2014
6. Data acquisition Sep. 2015
7. Data analysis Sep. 2016
Potential shifts in schedule result in a linear translation.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 28 / 42
Schedule Milestones
Schedule overview
2011 2012 2013 2014 2015 2016 2017 2018
dsgn
procurement
Nab setup/daq
†
pol. pgm. setup/daq
† Changeover to polarized program.
Last two items (polarized program) may take place at the new NGCbeamline at NIST (scientific approval granted).
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 29 / 42
Tasks, collaboration
Tasks and responsibilities
SubprojectResponsible
Instit. Person(s)
1 Spectrometer magnet UVa Baeßler/Pocanic2 Passive antimagnetic screen ASU R. Alarcon3 Beamline UT G.L. Greene4 Shielding and utilities ORNL S.I. Penttila
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 Detectors
LANL W.S. WilburnUVa D. Pocanic
U Manitoba M.T. GerickeU Winnipeg J. Martin
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 DAQ UKy C. Crawford7 Electrode System ORNL J.D. Bowman8 Vacuum system UVa S. Baeßler9 B field measurement UVa D. Pocanic
10 Beamline modification ORNL S.I. Penttila11 Polarization & polarimetry UMich T. Chupp
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 30 / 42
Tasks, collaboration Asymptotic manpower commitments
Asymptotic manpower commitments
UVaFaculty:D. Pocanic 50%S. Baeßler 40%Res. Sc./P’doc:E. Frlez 50%A. Salas-B./TBD 67%Grad. St:TBD 100%TBD 100%TBD 100%
UMichFaculty:T. Chupp 30%Grad. St:TBD 100%
NCSUGrad. St:TBD 50%†
ASUFaculty:R. Alarcon 35%Grad. St:TBD 100%
UKyFaculty:C. Crawford 50%Grad. St:TBD 100%
UNHFaculty:J. Calarco 50%Grad. St:TBD 100%
ORNLSr. Scient:S. Penttila 70%D. Bowman 70%
LANLSr. Scient:S. Wilburn 100%†
Postdoc:N. Fomin/TBD 100%†
UTennFaculty:Geoff Greene 30%Postdoc:S. Kucuker/TBD 10%Grad. St:TBD 100%
UNAMFaculty:L. Barron-Palos 20%Grad. St:TBD 100%† Shared with UCNx.
In addition: Karlsruhe, Sussex, Manitoba/Winnipeg, . . .
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 31 / 42
Tasks, collaboration Asymptotic manpower commitments
Asymptotic manpower commitments in FTE
(Teaching load taken into account for university faculty)
UVaFaculty:D. Pocanic .33S. Baeßler .40Res. Sc./P’doc:E. Frlez .50A. Salas-B./TBD .67Grad. St:TBD 1.0TBD 1.0TBD 1.0
UMichFaculty:T. Chupp .20Grad. St:TBD 1.0
NCSUGrad. St:TBD .50†
ASUFaculty:R. Alarcon .22Grad. St:TBD 1.0
UKyFaculty:C. Crawford .33Grad. St:TBD 1.0
UNHFaculty:J. Calarco .33Grad. St:TBD 1.0
ORNLSr. Scient:S. Penttila .70D. Bowman .70
LANLSr. Scient:S. Wilburn .05†
Postdoc:N. Fomin/TBD 1.0†
UTennFaculty:Geoff Greene .25Postdoc:S. Kucuker/TBD .10Grad. St:TBD 1.0
UNAMFaculty:L. Barron-Palos .15Grad. St:TBD 1.0† Shared with UCNx.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 32 / 42
Additional slides Detector response
Additional slides
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 33 / 42
Additional slides Fierz term
∆b = 3×10-3 can be reached (systematically limited)
( ) ( )2 ee
e
1 3 1m
dw E bE
λρ
∝ ⋅ + ⋅ +
The determination of the Fierz Interference term
Electron spectrum:
Systematic uncertainties:
1.Electron energy determination
2.Background
detected [keV] Ee,kin
incoming electron, E = 300 keVe,kin
3% of events in tail (deadlayer, external bremsstrahlung)
0 50 100 150 200 250 300 350
Yield
0 200 400 600 800
Ee,kin (keV)Yield
(arb.uni ts)
b = +0.1
SM
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 34 / 42
Additional slides U inhomogeneity—Kelvin probe
0 4 8 120
4
8
12
16
Hei
ght [m
m]
Work Function [meV]
Width [mm]
0 50 100 150 200 250 300 3500
5
10
15
20
25
30
35
40
Azimuth angle [°]
Hei
ght [m
m]
4900
4950
5000
5050
5100
In collaboration with Prof. I. Baikie, KP Technologies
(arbitrary offset added)
PRELIMINARY
PRELIMINARY
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 35 / 42
Additional slides Detector response
Electron energy response
histoE_NEntries 85243
Mean 1.263
RMS 0.658
Number of bounces
1 2 3 4 5 6 7 8
Yie
ld
10
210
310
410
510
histoE_NEntries 85243
Mean 1.263
RMS 0.658
Number of bounces
above threshold(10 keV upper det.)
(40 keV lower det.)
all bounces
histoEe300idealsum
Entries 85243Mean 298.9RMS 9.131
detected Ee [keV]0 100 200 300 400 500 600 700 800
Yie
ld
1
10
210
310
410
510
histoEe300idealsum
Entries 85243Mean 298.9RMS 9.131
Ee in both detectors
histoEe300escEntries 85243Mean 1.203RMS 12.1
non-detected Ee [keV]0 50 100 150 200 250 300
Yie
ld
1
10
210
310
410
510
histoEe300escEntries 85243Mean 1.203RMS 12.1
Ee loss in escaped particles
in dead layerescaped particle
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 36 / 42
Additional slides Detector response
Detector response:
Electron energy
Note that detectors are made so big that radial walk wouldn’t be visible. We have to study the
edge effect in more detail.
I am quite embarrassed to admit that nothing of what I found is new. E.g, in [Abe93] the power
of the backscattering suppression for electrons on silicon detectors, as well as the remaining tails,
are shown well.
Energy Green off Green ok Red off Red ok
150 keV 1807 78082 5762 74127
300 keV 2103 83140 3999 81244
450 keV 2025 59592 2809 58808
600 keV 1112 24865 1301 24676
750 keV 71 989 83 977
Tab. 1: Errors in electron energy
reconstruction for different
algorithms. “Off” is defined as
being farther away than 5 keV
from the nominal energy.
I summarize the results for other electron energies in the Table 1. The electron response spectra
look similar (see Fig. 4) and can be described analytically with a fit which assumes that some
electrons (a relative amount of about 1 %) are detected with an energy too high by 30 keV, and
some electrons (a relative amount of 7·10-5
·Ee·keV-1
, so 2.1% at 300 keV) are in an exponential
tail with a “growth constant” of 0.13·Ee). The analytical function describes the detector response
sufficiently good for a further study of the sensitivity of Nab to the non-perfect detector response
for electrons.
Fig. 4: Detector response functions for electrons with energies which are multiples of 150 keV. The “data points”
are from the simulation, and the lines show our analytical model.
A consequence for Nab is that the determination of a (and b) is affected by the knowledge of the
low energy tail. To study the effect on the a determination, I used the analytic model for Nab, in
which the magnetic field is simplified so that the proton TOF can be given as an analytical
function. The model includes the neutron beam width, but computes protons only on axis and
omits the electrostatic acceleration. Fig. 5 shows the 1/TOF2 response for protons with different
energies.
Proton TOF
10
100
1000
10000
100000
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02
1/TOF^2 [us^-2]
Yie
ld
Ee = 75 keVEe = 75 keV, Ee responseEe = 225 keVEe = 225 keV, Ee responseEe = 375 keVEe = 375 keV, Ee responseEe = 525 keVEe = 525 keV, Ee responseEe = 675 keVEe = 675 keV, Ee response
Fig. 5: 1/TOF
2 spectra for protons. The solid lines show the 1/TOF
2 spectra for perfect electron detection. The
dashed lines show the modification due to the low energy tail in the electron energy response. The ideal shape (sharp edges, slope of top line proportional to a) is modified by the TOF
response function, and the neutron beam width. In particular, the TOF response leads to a tail at
the low energy (low 1/TOF2) side. The electron energy response leads to tails at the other side,
too. The high energy tail could serve to verify the detection function, this is not studied.
There is some structure in the tails which are probably due to the rather coarse binning for the
electron energies. The main result is that the fitted value for a is sensitive to the size of the tail,
and an uncertainty the in the relative amount of electrons in the tail of 2% (out of the couple of
percent of electrons which are in the tail) would lead to ∆a/a ~ 10-3
.
Fig. 6: Camel hump curve, showing
the time difference (defined as the
impact time on the upper minus the
impact time on the lower detector)
between hits in different detectors.
Furthermore, the event reconstruction goes wrong if our timing resolution is not good enough to
determine the earlier detector. This is only important for observables for which the detector
being hit first is significant. In Fig. 6, we show the time difference between different hits in the
detectors. The black line shows cases in which the lower detector is hit first and the upper
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 37 / 42
Additional slides Detector response
histoETOF300du
Entries 5134Mean 33
RMS 6.017
TOF [ns]-200 -150 -100 -50 0 50 100 150 200
Yie
ld
1
10
210
310
histoETOF300du
Entries 5134Mean 33
RMS 6.017
Camel hump curve
lower det hit first upper det hit first
TOF = time of upper det. hit − time of lower det. hit
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 38 / 42
Additional slides
Nab anti-magnetic shield (AMS)
X
Y 3020
10010
5
30
50
20100
Antimagnetic solenoids
Inner solenoids
Top view: Side view:
Spectrometer magnet
Nab: Passive AntiMagnetic Screen (WBS 4)
Staging area for Nab would save FnPB beam time during AMS testing.
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 39 / 42
Additional slides
Nab:DAQ
Det
ecto
r &
pre
amps
PIX
IE-
16
R5400n
contr
oll
er
PNChp
30 kV
rear
I/O
module
FS725
Rb freqP
IXIE
-
16
PXI
crate
PX
I-P
CI
8336
…
x8
…
x16
…
x16
DAQ
workstation
Analysis
workstation
RAID
storageD
etec
tor
&
pre
amps
PIX
IE-
16
R5400n
contr
oll
er
PNChp
30 kV
rear
I/O
module
PIX
IE-
16
PXI
crate
PX
I-P
CI
8336
…
x8
…
x16
…
x16
optical
signal
Isolation
transformer
power
120 V
Isolation
transformer
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 40 / 42
Additional slides Nab collaborators
R. Alarcon1, L.P. Alonzi2§, S. Baeßler2∗, S. Balascuta1§, J.D. Bowman3†,M.A. Bychkov2, J. Byrne4, J.R. Calarco5, V. Cianciolo3, C. Crawford6,
E. Frlez2, M.T. Gericke7, F. Gluck8, G.L. Greene9, R.K. Grzywacz9,V. Gudkov10, F.W. Hersman5, A. Klein11, M. Lehman2§, J. Martin12,
S. McGovern2§, S.A. Page6, A. Palladino2§, S.I. Penttila3‡, D. Pocanic2†,R. Rodgers2§, K.P. Rykaczewski3, W.S. Wilburn11, A.R. Young13.
1Arizona State University 2University of Virginia3Oak Ridge National Lab 4University of Sussex5Univ. of New Hampshire 6University of Kentucky7University of Manitoba 8Uni. Karlsruhe/RMKI Budapest9University of Tennessee 10University of South Carolina11Los Alamos National Lab 12University of Winnipeg13North Carlolina State Univ.†Co-spokesmen ∗Experiment Manager‡On-site Manager §Graduate Students
Home page: http://nab.phys.virginia.edu/
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 41 / 42
Search for Standard Model Parameters
-1.290 -1.280 -1.270 -1.260
λ = gA/gV
0.960
0.965
0.970
0.975
0.980
Vud
τ n[S
ereb
rov0
5]τ n
[MA
MBO
II]
τ n[P
DG
201
0]
ft(0+→0+) [Hardy09]
ft(0+→0+) [Liang09 – PKO1]
ft(0+→0+) [Liang09 – DD-ME2]
PIBETA [Pocanic04]
λ[P
DG
201
0]
A[U
CN
A 2
010
]
A [PERKEO II,
prel.]
Kaons
+Unitarity [PDG 2010]
D. Pocanic (UVa) n beta correlations at SNS 15 Apr ’11 42 / 42
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