Dinko Po cani c, for the Nab...
Transcript of Dinko Po cani c, for the Nab...
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Nab experiment: progress update
Dinko Počanić, for the Nab Collaboration
University of Virginia
FnPB PRAC Review15 December 2010
D. Počanić (UVa) Nab progress update 15 Dec ’10 1 / 27
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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, never before 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◦ independent measurements of a and b.
Typical goal uncertainties: δv/v ≤ 10−3, and δb ≤ 3× 10−3.
D. Počanić (UVa) Nab progress update 15 Dec ’10 2 / 27
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Motivation, goals
Neutron Decay Parameters (SM)
dw
dEedΩedΩν' keEe(E0 − Ee)2
×[
1 + a~ke ·~kνEeEν
+ bm
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. Počanić (UVa) Nab progress update 15 Dec ’10 3 / 27
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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
D. Počanić (UVa) Nab progress update 15 Dec ’10 4 / 27
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CKM matrix: Vud
Status of A and λ in n decay
-0.13 -0.12
Beta Asymmetry A
-0.11 -0.10
Abele-09
Pattie-09
Abele-02
Liaud-97
Yeroz-97
Bopp-86
Average:= -0.1186(9)A
Uncertainty of the averagescaled up by factor 2.3×
Global fit χ2/dof = 28/5 !
Statistical probability for thisχ2 is 5× 10−5.H. Abele, private communication (2009).R.W. Pattie, et al., PRL 102, 012301 (2009).H. Abele et al., PRL 88, 211801 (2002).P. Liaud et al., NP A 612, 53 (1997).B. Yerozolimsky et al., PL B 412, 240 (1997).P. Bopp et al., PRL 56, 919 (1986).
D. Počanić (UVa) Nab progress update 15 Dec ’10 5 / 27
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CKM matrix: Vud
Status of A and λ in n decay (cont’d)
Nab goal value of ∆a:
⇒ ∆λ ' 3.5× 10−4
i.e., an order of magn.improvement.
∆λ
λ' 0.27
∆a
a' 0.24
∆A
A
D. Počanić (UVa) Nab progress update 15 Dec ’10 6 / 27
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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-Čunčić, 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 → ueν̄and limits on ν masses. [Ito + Prézaeu, PRL 94 (2005)]
D. Počanić (UVa) Nab progress update 15 Dec ’10 7 / 27
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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.)
“present limits”(68% 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 /L
RT/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.)
“future limits”(68% C.L.)
muon decay“90% C.L.”
Projected limits; Grey contours:
β compilation [Sev-06]
Improvement from more precise a = −0.1030(1); using b ≡ 0.[G. Konrad, W. Heil, S. Baeßler, D. Počanić, F. Glück, arXiv 1007.3027.]
D. Počanić (UVa) Nab progress update 15 Dec ’10 8 / 27
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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 Δχ2
C.L.
2.30 68.3%
90%
95.4%
4.61
6.17
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
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
VL
T/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
0.04
Projected limits assuming
a = −0.1030(1) ; b = 0 ± 0.003
[G. Konrad, W. Heil, S. Baeßler, D. Počanić, F. Glück, arXiv 1007.3027.]
D. Počanić (UVa) Nab progress update 15 Dec ’10 9 / 27
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Beyond Vud non-V − A interaction terms
Right-handed W bosonsAdding RH gives non-zero δ = m21/m
22, ζ:
W1 = WL cos ζ + WR sin ζ , and W2 = −WL sin ζ + WR cos ζ .
Mixing angle ζ
-0.2 -0.1 0.0 0.10.00
0.02
0.04
0.06
0.08
0.10
Mass
rati
oδ 250Δχ
2C.L.
2.30 68.3%
90%
95.4%
4.61
6.17300
350
400
450500550600
Mas
s m
[G
eV]
2
leptonscattering(90% C.L.)
μ decays(68% C.L.)
μ decays(90% C.L.)
DØ (95% C.L.)
0 →0decays
(68% C.L.)
+ +
“presentlimits”
(68% C.L.)
Present limits
Δχ2
C.L.
2.30 68.3%
90%
95.4%
4.61
6.17
Mixing angle ζM
ass
rati
oδ
400
500
600
900
700800
1000
Mass
m [G
eV
]2
-0.10 -0.05 0.00 0.050.00
0.01
0.02
0.03
0.04
0.05Δχ
2C.L.
2.30 68.3%
90%
95.4%
4.61
6.17
0 →0decays
(68% C.L.)
+ +
μ decays(90% C.L.)
DØ (95% C.L.)
μ decays(68% C.L.)
leptonscattering(90% C.L.)
“future limit”(68% C.L.)
Projected limits
[G. Konrad, W. Heil, S. Baeßler, D. Počanić, F. Glück, arXiv 1007.3027.]
D. Počanić (UVa) Nab progress update 15 Dec ’10 10 / 27
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Beyond Vud Fierz interference term
The Fierz interference term bb can be estimated from nuclear beta decays:
bF =CSCV
|CS |2 + |CV |2bGT =
CTCA|CT |2 + |CA|2
These terms vanish for pure ν(R) coupling.b 6= 0 only for S , T coupling to ν(L). (leptoquarks?)From 0+ → 0+ decays [Towner + Hardy ’98]:
|bF | '|CS ||CV |
≤ 0.0077 (90 % c.l.)
From analysis of GT decays [Deutsch + Quin, ’95]:
bGT = −0.0056(51) 'CT|CA|
(small FT from πe2γ!?)
⇒ a ∼ 10−3 measurement of bn is very interesting!D. Počanić (UVa) Nab progress update 15 Dec ’10 11 / 27
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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)〉 =
ūp(pp)
(f1(q
2)γµ − if2(q2)
Mnqµ +
f3(q2)
Mnqµ + g1(q
2)γµγ5
− ig2(q2)
Mnσµνγ5qν +
g3(q2)
Mnγ5q
µ
)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. Počanić (UVa) Nab progress update 15 Dec ’10 12 / 27
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Beyond Vud Second class currents
0.4 0.5 0.6 0.7 0.8 0.9
x
-0.008
-0.006
-0.004
-0.002
0
0.002
0.004a(
1) a
nd A
(1)
D. Počanić (UVa) Nab progress update 15 Dec ’10 13 / 27
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Comparison w/other experiments
Current experiments aiming to measure a
1. Nab: goal is to measure ∆a/a ∼ 10−3I Best statistical sensitivity,I Challenging but manageable systematics, esp. in asymm. design.
2. abBA: goal is to measure ∆a/a ∼ 10−3I Similar to Nab, but with spectrometer configured for A,B/C,I Detection function is very broad, syst. uncert. for a very demanding.
3. aCORN: goal is to measure ∆a/a ∼ 0.5− 2 %I Funded, under construction,I Uses only part of neutron decays.
4. aSPECT: aims to measure ∆a/a ∼ 10−3I 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 Easier determination of detection function than in Nab at the presentlevel of accuracy. Singles measurement!
D. Počanić (UVa) Nab progress update 15 Dec ’10 14 / 27
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Nab measurement principles
Nab Measurement principles: Proton phase space
Ee (MeV)
p p2
(M
eV2 /
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. Počanić (UVa) Nab progress update 15 Dec ’10 15 / 27
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Nab measurement principles
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. Počanić (UVa) Nab progress update 15 Dec ’10 16 / 27
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Nab apparatus and installation
Nab spectrometer: 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. Počanić (UVa) Nab progress update 15 Dec ’10 17 / 27
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Nab apparatus and installation
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. Počanić (UVa) Nab progress update 15 Dec ’10 18 / 27
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Nab apparatus and installation
Spectrometerinstallation:
D. Počanić (UVa) Nab progress update 15 Dec ’10 19 / 27
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Nab apparatus and installation
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. Počanić (UVa) Nab progress update 15 Dec ’10 20 / 27
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Nab apparatus and installation
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. Počanić (UVa) Nab progress update 15 Dec ’10 21 / 27
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Schedule, milestones
Milestone Completion0.a Start of project Jul 20110.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 Anti-Magnetic screen: magnetic design finished Sep. 20122. Passive Anti-Magnetic 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
D. Počanić (UVa) Nab progress update 15 Dec ’10 22 / 27
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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. Frlež2, M.T. Gericke7, F. Glück8, 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. Penttilä3‡, D. Počanić2†,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. Počanić (UVa) Nab progress update 15 Dec ’10 23 / 27
http://nab.phys.virginia.edu
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Additional slides Detector response
Additional slides
D. Počanić (UVa) Nab progress update 15 Dec ’10 24 / 27
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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. Počanić (UVa) Nab progress update 15 Dec ’10 25 / 27
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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. Počanić (UVa) Nab progress update 15 Dec ’10 26 / 27
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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. Počanić (UVa) Nab progress update 15 Dec ’10 27 / 27
n-decay program at FnPBOverall motivation and goalsCKM matrix: VudBeyond Vudnon-V-A interaction termsFierz interference termSecond class currents
Comparison w/other experimentsNab measurement principlesNab apparatus and installationSchedule, milestonesNab collaboratorsAdditional slidesDetector response