Search for the electric dipole of the neutron
Transcript of Search for the electric dipole of the neutron
Why is there more matter
than antimatter in the Universe?
π =ππ΅βπ π΅ππΎ
β 1per billion
Sakharovβs baryogenesis recipe (1967)
β’ Universe out of equilibrium
β’ Baryon number not conserved
β’ Violation of C and CP symmetry
69 %
Dark
Energy
5 % Baryons
26% Dark
matter
3/35
Antibaryons in the Universe
1015 GeVInflation ends?
100 GeVElectroweak
transition
1 MeV
1 eVDecoupling
of CMB
1 meVtoday
AMS onboard the
International Space Station
4 billion of helium events
collected, no antihelium
4/35
Cosmic microwave background
1015 GeVInflation ends?
100 GeVElectroweak
transition
1 MeV
1 eVDecoupling
of CMB
1 meVtoday
[Planck (2016)]
πCMB = 6.09 Β± 0.05 Γ 10β10
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Big Bang nucleosynthesis
1015 GeVInflation ends?
100 GeVElectroweak
transition
1 MeV
1 eVDecoupling
of CMB
1 meVtoday
[Deuterium abundance from LyΞ±, Cooke et al (2014) πBBN = 6.0 Β± 0.1 Γ 10β10
6/35
Electroweak baryogenesis?
1015 GeVInflation ends?
100 GeVElectroweak
transition
1 MeV
1 eVDecoupling
of CMB
1 meVToday
Sakharovβs conditions
β’ Baryon number not
conserved
β’ Universe out of
equilibrium
β’ Violation of CP
symmetry
T = 300 GeV
T β 100 GeV
T = 20 GeV
symmetric phaseπ = π
boiling
broken phaseπ β π
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CP violation in weak interactions
β’ Tiny (βΌ 10β3) CP asymmetry discovered by Cronin and Fitch (1964)
looking at πΎ0 β π+πβ
πβ²π β²πβ²
=
ππ’π ππ’π ππ’ππππ πππ πππππ‘π ππ‘π ππ‘π
ππ π
β’ Explained by the Kobayashi-Maskawa mechanism (1973)
Complex CKM matrix
Mass eigenstates
Flavoureigenstates
β’ Confirmed with βB factoriesβ in 2000βs with many observables, e.g.
Ξ π΅0 β π+πβ β Ξ π΅0 β πβπ+
Asymmetry β 30% !
π π π’ ππ’ π ββ
π π π’ ππ’ π ββ
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Departure from thermal
equilibrium: the EW
phase transition is 2d
order in SM. New physics
is required in the scalar
sector.
Non-conservation
of B: ok in the SM
with sphalerons
transitions!
CP violation: SM not
good enough.
Requires CP violation
beyond the Standard
Model at the ~TeV
scale
Failure of SM
electroweak
baryogenesis:
needs new
physics
9/35
β π» = π ππ¬
Electric dipoles & CP symmetry
ππ < 3 Γ 10β26 π cm (Grenoble, 2006)
ππ < 1 Γ 10β29 π cm (Harvard, 2018)
EDM = CP-violating fermion-photon coupling
-imaginary part of the diagram-
generated by radiative corrections
β = βππ
2 πππππΎ5π πΉ
ππ
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β π» = π ππ¬
Electric dipoles & CP symmetry
ππ < 3 Γ 10β26 π cm (Grenoble, 2006)
ππ < 1 Γ 10β29 π cm (Harvard, 2018)
EDM = CP-violating fermion-photon coupling
-imaginary part of the diagram-
generated by radiative corrections
β = βππ
2 πππππΎ5π πΉ
ππ
ππ β ππ2
16π2sinπ
ππ
πCPV2
β1 TeV
πCPV
2
sinπ Γ 10β25 π cm
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Two sources of EDMs in the SM
CKM contribution to
the quark EDM
vanishes at two loopsβ¦
The QCD contribution πΌ
8ππ πΊππ πΊππ
Generates an enormous EDM
ππ β π Γ 10β16 π cm
β π < 10β10
Β« Strong CP problem Β»
Prediction: ππ β 10β33π cm
Kobayashi-Maskawa
background negligible
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EDMs beyond the SM: SUSY
Ellis, Ferrara, Nanopoulos, PLB 114 (1982).EDM induced by soft mass terms for squarksand gluinos
ππ β ππΌ
4π
ππ
ππΆππ2 β
1 TeV
ππΆππ
2
Γ10β25 π cm
Β« SUSY CP problem Β»
MSSM contains ~40 CP violating imaginary parametersβ¦
Split SUSY scenario
with anarchic flavor
mass matrix
Altmannshofer, Harnik, Zupan, JHEP 1311 (2013)
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EDMs beyond the SM: modified Higgs couplings
Barr, Zee, PRL 65 (1990)
Modified Higgs-fermion Yukawa coupling: β = βπ¦π
2π π ππβ + π π π ππΎ5πβ
CP violating
Brod, Haich, Zupan, 1310.1385Brod, Stamou, 1810.12303Brod, Skodras, 1811.05480
0.001
0.01
0.1
1
10
d u s c b t
90% C.L. limits from eEDM
90% C.L. limits from nEDM
Generates EDM at 2 loops π π
Violation of time reversal
>> PLAY >> << REWIND <<
If ππ β 0 the process and its time
reversed version are different.
Violation of T
Violation of CP
Detecting the neutron electric dipole
π» = βππ πΈ β π
If the neutron EDM is ππ = 10β27 π cmAnd the electric field is πΈ = 15 kV/cmThe neutron spin will make one full turn in a timeπβ
πππΈ= 1.4 Γ 106 s = π π²πππ«π¬
In order to detect such a minuscule coupling we need:
β’ The slowest possible neutrons
to maximize the interaction time in the electric field
β’ An intense source of such neutrons
to maximize the statistical sensitivity
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Importance of the magnetic field
ππΏ ββ β ππΏ ββ = β2
πβππ πΈ
ππ =πππβ
π΅ βπππβ
|πΈ|
30Hz @ 1 Β΅T 7 Γ 10β7 Hz @ 15 kV/cm
for ππ = 1 Γ 10β27πcm
Basic measurement strategy
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Neutrons with energy < 200
neV, are totally reflected by
material walls.
They can be stored in material
bottles for long times , up to
15 minutes.
They are significantly affected
by gravity.
Neutron optics, cold and ultracold neutrons
Thermal neutrons, E=25 meV
Cold neutrons, E<25 meV
Ultracold neutrons E< 200 neV
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The Sussex/RAL/ILL apparatus
Apparatus installed at the
ILL reactor Grenoble
(~1980-2009)
Best limit: ππ < 3 Γ 10β26 π cm
Baker et al, PRL (2006); Pendlebury et al, PRD (2015)
History of the venerable UCN nEDM apparatus
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
Move of the apparatus at
Paul Scherrer Institute (PSI)
ILL data production PSI data
Dismantling nEDM
Installing n2EDM
UCN source startup
& nEDM upgrade
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UCN source at the
Paul Scherrer Institute
600 MeV, 2.2 mA
pulsed UCN source
One kick per 5 min
online since 2011
Intensity
frontier!!
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Scheme of the
apparatus at
PSI during EDM
data-taking
2015-2016
SWITCH
Magnetized iron analyser
5T polarizer(SC magnet)
UCN source
High voltage, E = Β± 132 kV 12 cm
Adiabatic Spin Flipper
4 layers mu-metal shield
Ramseyβs method
Free
precession...
Apply Ο /2 spin-
flip pulse...
βSpin upβ
neutron...
Second Ο /2
spin-flip pulseStatistical sensitivity: πππ =
β
2 πΌ πΈ π π
duration π
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Typical measurement sequence at PSI, 1 cycle every 5 minutes
+1
32
kV
Black:
uncorrected
neutron
frequency
Green: corrected
with the mercury
co-magnetometer,
compensates for
the residual
magnetic field
fluctuations
-1
32
kV
+ - + -
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πΓ = 14.6 Β± 1.1 Γ 10β26π cm
Analysis of the 2015/2016 PSI data, still ongoing
Preliminary blind result, west analysis
π corr =πππHg
βπΎππΎHg
βπΏEarth +π΅π2
2π΅02
45,283 cycles with HV = Β±132 kV
8,070 cycles with HV = 0 kV
980 cyclesCut during analysis
n2EDM concept & baseline design
1. Large double UCN chamber
β’ Vertically stacked
β’ Height H = 12 cm each
β’ Diameter D = 80 cm
2. Magnetometry
β’ Hg co-magnetometers
β’ Array of Cs magnetometers
β’ B0 = 1 Β΅T
ππ,ββ β ππ,ββ =2πΈ
πβππ
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n2EDM science reach
Error due to UCN
counting statistics
π ππ =β
2πΌπΈ π π
β’ We have a precise plan (baseline design) for an improved
measurement by a factor of 10 (i.e. 10 for the BSM mass reach)
with 500 live days of data described in the 2019 TDR.
β’ Start of data production in 2022
β’ We have ideas to go beyond that with future upgrades
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Credits to the nEDM collaboration
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49 members
10 PhD students
8 countries
16 laboratories(LPSC, LPCC, CSNSM in France)
Announcements
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1 The LPSC group is recruiting 1 postdoc
2 the nEDM collaboration is open to new collaborators
β’ Software: data quality monitoring, automatic detection of
system failures with machine learning, online and offline
analysis, data blinding, data storage and legacy
β’ Hardware for upgrades: new UCN chambers with storage
properties and higher electric fields
Electroweak phase transition
36
1015 GeVInflation ends?
100 GeVElectroweak
transition
1 MeV
1 eVDecoupling
of CMB
1 meVToday
symmetric phaseπ = π
Boiling?
broken phaseπ β π
Standard Model:
2d order
Phase transition
Beyond
Standard Model:
1st order
Phase transition?
37/22
Free precession in
E and B fields ...
C: Apply RF pulse
Ο/2 spin-flip...A: spin polarizer
Cβ :Second RF pulse
Aβ: spin
analyzer
D: counter
First EDM experiment with a neutron beam
Smith, Purcell and Ramsey, Phys. Rev. 108, 120 (1957)
ππ = β0.1 Β± 2.4 Γ 10β20 π cm
Vary the RF frequency
and measure the resonance
curve to extract ππΏ. Do it for
parallel and antiparallel E
and B fields.
Statistical sensitivity:
πππ =β
2 πΌ πΈ π π
π β 1 ms
International competition
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@SNS US novel cryogenic concept, UCN produced in-situ (operation
planned 2023)
@Los Alamos US room temperature experiment (design & funding
phase) at a D2 UCN source (existing)
@TRIUMF Canada room temperature experiment (design phase) at a
He UCN source (in construction)
@ILL(Munich+PNPI) room temperature experiment (in construction)
at a He UCN source (in construction)
@ESS neutron beam experiment (concept phase)
@Seattle indirect access of the nEDM by measuring the EDM of the
199Hg atom (improving since decades)
The co-magnetometer problem: vxE/c2
ππβHgfalse =
β|πΎππΎHg|
2π2 0
β
ππ‘ cosππ‘ π©π π π π + π©π π π π
Simulation, Hg atoms in nEDM Γ47cm
Frequency shift from a transverse
magnetic noise B (Redfield theory)πΏπ =
πΎ2
4π 0
β
ππ Im πβπππ π΅ 0 π΅β(π)
Linear in E field frequency shift:
co-magnetometer
equationβ =
πππHg
=πΎππΎHg
1 +2πΈ
πβπHgππtrue + ππ
false +πΊ π§
π΅0+
π΅π2
2π΅02 +β―
Gravitational shift
Transverse shift