the nedm experiment at the sns christopher crawford university of kentucky for the nedm...
TRANSCRIPT
The nEDM Experiment at the SNS
Christopher CrawfordUniversity of Kentucky
for the nEDM Collaboration
Symposium on Nuclear Physics XXXIII
Cocoyoc, Morelos, México2010-01-07
Outline
• EDM properties – scientific motivation• Properties of neutron – generation• Measurement technique – ILL experiment• Properties of He – new technique• Experimental setup – expected results
Electric Dipole Moment
+
-P or T reversed state
• EDM is a P and T (therefore CP) violating quantity
• Standard model value: dn ~ 10-32 – 10-31 e·cm
(Small! Ideal probe for new Physics)
• Present limit: dn < 2.8x10-26 e·cm (PRL 97, 131801 (2006))
+
-
Evolution of EDM Experiments
CP violation and New Physics
• In SM, quark EDM is zero to first order in GF (one loop), and is also zero at the two-loop level (cancellation among diagrams).
dn ~ 10-32 – 10-31 e·cm• Many extension of SM predict an extra set of particles and CP violating
phases (eg SUSY, LR symmetric model)
• These models predict substantially larger EDMs than SM• Neutron EDM is a very sensitive probe for new sources of CP violation
fL fLf’
W W
e+i e-i
Standard Model€
˜ f
€
˜ f
€
˜ γ €
€
fL
€
fR
€
e+iφL
€
e−iφ R
SUSY
• Cosmic ray contains– consistent with secondary production by protons
• Matter-antimatter symmetry would imply
– both BBN and CMB anisotropy find:• Sakharov conditions:
– B violating interactions– CP and P violation– Departure from thermal equilibrium
€
np /np ~ 10−4
€
NB
Nγ
=N
B
Nγ
~ 10−18 (kTcritical ≈ 20 MeV)
€
NB
Nγ
≈10−9
Baryon Asymmetry of the Universe
EDM and CP Violation in QCD
• QDC Langrangian can in principle has a P- and T-violating term
• The term can generate a neutron EDM
• The current neutron EDM limit gives
• One proposed remedy, Peccei-Quinn symmetry, predicts axions. However, axions have not been observed.
€
Lθ = θgs
2
32π 2˜ G μν Gμν
€
dn ~ O 10−16θ( ) e ⋅cm
€
θ <10−9 Strong CP problem
Properties of the Neutron
mn = mp + me + 782 keV
n = 885.7 ± 0.8 s
qn < 2 x 10-21 e
dn < 3 x 10-26 e cm
n = -1.91 N
rm = 0.889 fm
re2 = -0.116 fm2
– 3 valence quarks + sea– exponential magnetization
distribution– pion cloud:
spin 1/2 isospin 1/2
pp nn
uud uddup down
data from BLAST
Neutron sources - ReactorsILL, Grenoble, France
Spallation Neutron Source (SNS)
• spallation sources: LANL, SNS– pulsed -> TOF -> energy
• LH2 moderator: cold neutrons– thermal equilibrium in ~30 interactions
Oak Ridge National Laboratory, Tennessee
Spallation Neutron Source (SNS) at ORNL
January 25, 20051 GeV, 1.4 mA Proton Linac
•SNS construction completed: 2006•SNS Total Project Cost: 1.411B$
Ultra-Cold Neutrons (UCN)
3mg
• slow enough to be completely reflected by 58Ni optical potential
kinetic: 8 m/sthermal: 4 mKwavelength: 50 nm
nuclear: 335 neV (58Ni)
magnetic: 60 neV (1 T)gravity: 102 neV (1 m)
BE
For B ~ 10mG = 30 Hz
For E = 50 kV/cm and dn= 10-28 e·cm = 5 nHz (precesses every 6.5 yr)(corresponds to a change in magnetic field of 2 x10-12 gauss)
€
hν = −[2μnB ± 2dn E]
dn =−hΔν
4E
δdn ∝1
r E NUCNTstorage
Principle of the Measurement
Ramsey’s method of separated oscillatory fields — “Traditional” method for nEDM
Initial state
/2 pulse
Free precessio
n
Second /2
pulseZ component
of nuclear spin
Spin flip oscillato
r frequen
cy
Slide courtesy of A. Esler and Sussex Neutron EDM group (ILL)
B field
Spin flip is most efficient when the spin arrives at the 2nd coil with the right phase, i.e. the phase advance of spin rotation is the same as the RF phase advance.
Frequency difference between spin flip field and spin’s Larmor precession makes the 2nd pulse be out of phase with the 1st.
J.H.Smith, E.M.Purcell, and N.F.Ramsey, Phys. Rev. 108, 120 (1957)
ILL Measurement
P.G. Harris et al., RPL 82, 904 (1999) C. A. Baker et al., PRL 97, 131801 (2006)
• Precession measurement:– Ramsey’s separated
oscillatory field magnetic resonance method
• Magnetometry:– Mercury co-magnetometer
• Neutron source:– Ultra-Cold Neutrons from
ILL reactor• Selected parameters:
– E=4.5kV/cm– Tstorage = 130s– N=15000
• Results– dn< 2.8x10-26 ecm (90%CL)
199Hg Co-Magnetometer
• Co-magnetometer: – Magnetometer that occupies the same volume over the
same precession time interval as the species on which an EDM is sought
Systematic effects due to the interaction of the vE field with B field gradients
€
Br =r
2
∂BZ
∂z= arRadial gradient
Bv = v x E field changes sign with direction
€
ω =−2av 2E
c ω02 −ωr
2( )
Particle following roughly circular orbit with orbital frequency ωr
•Pendlebury et al PRA 70 032102 (2004)•Lamoreaux and Golub PRA 71, 032104 (2005)•Barabanov, Golub, Lamoreaux, PRA 74, 052115 (2006)
After averaging over rotational direction
Need
€
1
Bz
∂Bz
∂z≈10−6 /cm at 10 mG
EDM CollaborationR. Alarcon, S. Balascuta, L. Baron-Palos
Arizona State University, Tempe, AZ, USAD. Budker, B. Park
University of California at Berkeley, Berkeley, CA 94720, USAG. Seidel
Brown University, Providence, RI 02912, USAE. Hazen, A. Kolarkar, V. Logashenko, J. Miller,
L. RobertsBoston University, Boston, MA 02215, USA
A. Perez-Galvan, J. Boissevain, R. Carr, B. Filippone,M. Mendenhall, R. Schmid
California Institute of Technology, Pasadena, CA 91125, USAM. Ahmed, M. Busch, W. Chen, H. Gao, X. Qian, Q. Ye,
W.Z. Zheng, X. F. Zhu, X. ZongDuke University, Durham NC 27708, USA
F. MezeiHahn-Meitner Institut, D-14109 Berlin, Germany
C.-Y. Liu, J. Long, H.-O. Meyer, M. SnowIndiana University, Bloomington, IN 47405, USA
L. Bartoszek, D. Beck, P. Chu, C. Daurer, A. Esler,J.-C. Peng, S. Williamson, J. Yoder
University of Illinois, Urbana-Champaign, IL 61801, USAC. Crawford, T. Gorringe, W. Korsch, B. Plaster, H. Yan
University of Kentucky, Lexington KY 40506, USAE. Beise, H. Breuer, T. Langford
University of Maryland, College Park, MD 20742, USA
P. Barnes, S. Clayton, M. Cooper, M. Espy, R. Hennings- Yeomans, T. Ito, M. Makela, A. Matlachov, E. Olivas, J.
Ramsey, I. Savukov, W. Sondheim, S. Tajima, J. Torgerson, P. Volegov, S. Wilburn
Los Alamos National Laboratory, Los Alamos, NM 87545, USAK. Dow, D. Hassel, E. Ihloff, J. Kelsey, R. Milner,
R. Redwine, J. Steele, E. Tsentalovich, C. VidalMassachusetts Institute of Technology, Cambridge, MA 02139,
USAJ. Dunne, D. Dutta, E. Leggett
Mississippi State University, Starkville, MS 39762, USAF. Dubose, R. Golub, C. Gould, D. Haase, P. Huffman,
E. Korobkina, C. Swank, A. YoungNorth Carolina State University, Raleigh, NC 27695, USA
R. Allen, V. Cianciolo, S. PenttilaOak Ridge National Laboratory, Oak Ridge, TN 37831, USA
M. HaydenSimon-Fraser University, Burnaby, BC, Canada V5A 1S6
N. Fomin, G. GreeneUniversity of Tennessee, Knoxville, TN 37996, USA
S. StanislausValparaiso University, Valparaiso, IN 46383, USA
S. BaesslerUniversity of Virgina, Charlottesville, VA 22902, USA
S. Lamoreaux, D. McKinsey, A. SushkovYale University, New Haven, CT 06520, USA
EDM Experiment at SNS
• General strategy: perform experiment in superfluid liquid 4He– Produce UCN in measurement cell via superthermal process– Use polarized 3He as comagnetometer– Use 3He-n interaction as spin precession analyzer
• Figure of merit:
• Expected gain over the ILL measurement
A 2 orders of magnitude overall gain in sensitivity is expected€
E NT
€
E ⇒ 5E T ⇒ 5T N ⇒ 100N
R.Golub and S.K.Lamoreaux Phys. Rep. 237, 1 (1994)
•8.9 Å cold neutrons get down-scattered in superfluid 4He by exciting elementary excitation
•Up-scattering process is suppressed by a large Boltzman factor
•No nuclear absorption
R.Golub and J.M.Pendlebury, Phys.Lett.A 62,337,(77)
Superthermal Production of UCN
• Expect a production of ~ 0.3 UCN/cc/s• With a 500 second lifetime, UCN~150/cc and NUCN~1.2x106 for
an 8 liter volume
3He as comagnetometer
Neutron n~29 Hz3He 3~32 Hz
Change in magnetic field due to the rotating magnetization of 3He by SQUID magnetometers
Pickup coils
Measurement cell filled with SF 4He
B
A dilute admixture of polarized 3He atoms is introduced to the bath of SF 4He (x = N3/N4 ~ 10-10 or 3He ~ 1012/cc)
3He as spin analyzer / 4He as a Detector • 3He-n reaction cross section
• 3He-UCN reaction rate
• Detect Scintillation light from the reaction products traveling in LHe– Convert EUV light to blue light using wavelength shifter– Detect the blue light with PMTs
• Signature of EDM would appear as a shift in ω3-ωn corresponding to the reversal of E with respect to B with no change in ω3
€
1− p3 ⋅ pn =1− p3 pn cos (γ n − γ 3)Bt[ ] 10/3 nn =−
4He superfluid filledmeasurement cellmade of acrylic andcoated with wavelength shifter
3He + n t + p + 760 keV
J=0 = 5333 b /0 J=1 ¼ 0 nn + nn pp ppnn ppnn +pp
Critical properties of liquid helium
• 4He dispersion curve
– 8.9 Å down-scatter to UCNs by emitting phonon
• 3He spin 90% from unpaired neutron3He EDM ~0 by Schiff theorem
– effective comagnetometer
• n + 3He -> p + t + 760 keV
– spin-precession analyzer
• 4He is an effective scintillator• 4He dielectric constant – HV• 4He is a superfluid (T < 1.7 K)
– heat flush purification
nn + nnpp
ppnnpp
nn +pp
Alternative approach Dressed spin technique• By applying a strong non-resonant RF field, the
gyromagnetic ratios can be modified or “dressed”
• For a particular value of the dressing field, the neutron and 3He magnetic moments can be made equal (n’=3’)
• Can tune the dressing parameter until the relative precession is zero.
• Measure this parameter vs. direction of E
€
′ =J0 γBrf /ωrf( )
B
Brf = Brf cos(ωrf t) e
Brf = 1 gauss, ωrf = 2 x 3 kHz
3He System
Volume Displacement
Purifiers
Purifier isolation Valves
3He Atomic Beam Source (ABS)
Polarized 3He
Collection System
Pressurizer
Purifier Control Valve
Collection Isolation
Valve
Pressurizer Standoff
Valve
Pressurizer Isolation
Valve
6a 6b 4
5 3
2
1a
1b
7
ABS Shutter
Measurement Cell
Measurement Cell
Cell isolation valve
T = 0 - 100 s Fill 4He with 3He
L He
3He E , B
Fill LinesT = 1100 - 1110 s /2 pulse
E , B
L Hen
3He
T = 1110 - 1610 s Precession about E & Bt
p
3He
L He
n E , B
XUV
XUV
Deuterated TPBon Walls
Light to PMT
Light to PMT
SQUID
T = 1610 - 1710 s Remove 3He
Emptying Lines
E , B
Experiment Cycle
T = 100 - 1100 s UCN from Cold n
L He
8.9 Å neutrons
Refrigerator
UCN ~ 500 Å
Phonon
(UCN)=P
E , B
SNS Fundamental Neutron Physics Beamline (FNPB)
Experiments expected to run
Cold neutron beamline
• Hadronic PV interaction• decay correlation• Neutron lifetime
UCN beamline
•Neutron EDM
Dilution Refrigerator (DR: 1 of 2)
Upper Cryostat Services Port
DR LHe Volume 450 Liters
3He Polarized Source
3He Injection Volume
Central LHe Volume (300mK, ~1000 Liters)
Re-entrant Insert for Neutron Guide
Lower Cryostat
Upper Cryostat
5.6m
4 Layer μ-metal Shield
EDM Experiment SchematicVertical Section View
Electrodes
Measurementcells
Light guides
Gain capacitor
PMTs
Lower Cryostat Cutaway View
Cold neutron beam
Magnets and Magnetic Shielding
Not shown: /2 spin-flip coil and gradient coils
B0 field direction
r = 61 cm
r = 48 cm
r = 37 cm
r = 65 cm
r = 62 cm
R&D – nearing completionActivity Name Institution
Neutron storage time LANL
Beamline Monte-Carlo simulation Kentucky
ABS at 45° LANL3He relaxation time Illinois
Light collection LANL
Valve development Illinois
Geometric phase effect in 3He NCState
Magnet Development Caltech
High voltage studies Indiana4He evaporative purification NCState
SQUID NMR signal Yale3He injection Duke
Laser induced fluorescence Yale
Slow Controls NCState
EDM Status & Schedule
• Approved by SNS FNPB PRAC - Fall 2005
• US DOE CD0 granted - December 2005
• R&D and design continue - 2006, 2007
• US DOE CD1 granted - February 2007
• US DOE CD2 review - late 2009
• Construction starts - 2010
• Commissioning of the experiment expected ~ 2015
Summary
• The nEDM is sensitive to new sources of CP-violation
• The SNS experiment based on new concept of measuring the nEDM directly in liquid 4He doped with polarized 3He.– uses many important properties of He which contribute
towards a ~100 x improvement in sensitivity– design sensitivity: 2 x 10-28 e cm
• The collaboration is nearing completion of various R&D phase.– CD2 review later this year– Construction to be completed ~2015