Experimentalist’s Motivation
description
Transcript of Experimentalist’s Motivation
New limits on spin-dependent Lorentz- and
CPT-violating interactions
Michael Romalis
Princeton University
Experimentalist’s Motivation Is the space truly isotropic?
Remove magnetic field, other known spin interactionsRemove the Earth
E
Spin Up Spin Down
Is there still an “Up” and a “Down” ?
First experimentally addressed by Hughes, Drever (1960)
V.W. Hughes et al, PRL 4, 342 (1960)R. W. P. Drever, Phil. Mag 5, 409 (1960); 6, 683(1961)
Is the space really isotropic? –ask astrophysicists
Cosmic Microwave Background Radiation Map
The universe appears warmer on one side!
v = 369 km/sec ~ 10 c
Well, we are actually moving relative to CMB rest frame
Space and time vector components mix by Lorentz transformation A test of spatial isotropy becomes a true test of Lorentz invariance
(i.e. equivalence of space and time)
A theoretical framework for Lorentz violation Introduce an effective field theory with explicit Lorentz violation
a,b,c,d are vector fields in space with non-zero expectation value Vector and tensor analogues to the scalar Higgs vacuum expectation value
Surprising bonus: incorporates CPT violation effects within field theory Greenberg: Cannot have CPT violation without Lorentz violation (PRL 89,
231602 (2002)
CPT-violating interactions break Lorentz symmetry, give anisotropy signals
Can search for CPT violation without the use of anti-particles
L = – (m + a + b5) +i2 ( + c + d5)
a,b - CPT-oddc,d - CPT-even
Fermions:Alan Kostelecky
Although see arXiv:1103.0168v1
Modified dispersion relations: E2 = m2 + p2 + p3 Jacobson
Amelino-Cameli
n - preferred direction, ~ 1/Mpl
Applied to fermions: H = m2/MPl S·n
Non-commutativity of space-time: [x,x] = Witten, Schwartz
- a tensor field in space, [
Interaction inside nucleus: NNijkjkSi Pospelov,Carroll
Phenomenology of Lorentz/CPT violation
25 )(nL
))(( FFFL
Myers, Pospelov, Sudarsky
Spin coupling to preferred direction
Effective Lagrangian:
Summary of SERF Atomic Magnetometer
Alkali metal vapor in a glass cell
MagnetizationMagnetization
Magnetic Field
Linearly Polarized Probe light
Circularly Polarized Pumping light
Polarization angle rotation
By x
z
y
Cell contents[K] ~ 1014 cm-3
He buffer gas, N2 quenching
K-3He Co-magnetometer1. Optically pump potassium atoms at high density (1013-
1014/cm3)
2. 3He nuclear spins are polarized by spin-exchange collisions with K vapor
3. Polarized 3He creates a magnetic field felt by K atoms
4. Apply external magnetic field Bz to cancel field BK
K magnetometer operates near zero magnetic field
5. At zero field and high alkali density K-K spin-exchange relaxation is suppressed
6. Obtain high sensitivity of K to magnetic fields in spin-exchange relaxation free (SERF) regime
Turn most-sensitive atomic magnetometer into a co-magnetometer!
BK = 83
0MHe
J. C. Allred, R. N. Lyman, T. W. Kornack, and MVR, PRL 89, 130801 (2002)I. K. Kominis, T. W. Kornack, J. C. Allred and MVR, Nature 422, 596 (2003)T.W. Kornack and MVR, PRL 89, 253002 (2002)T. W. Kornack, R. K. Ghosh and MVR, PRL 95, 230801 (2005)
Magnetic field self-compensation
Magnetic field sensitivity
Sensitivity of ~1 fT/Hz1/2 for both electron and nuclear interactionsFrequency uncertainty of 20 pHz/month1/2 for 3He
20 nHz/month1/2 for electrons Reverse co-magnetometer orientation every 20 sec to operate in the region of best sensitivity
Best operating region
Have we found Lorentz violation?
Rotating K-3He co-magnetometer
Rotate – stop – measure – rotate Fast transient response crucial
Record signal as a function of magnetometer orientation
ne
yez
eff
R
PS
b
11
Long-term operation of the experiment
NSNSY
NSX
NS
EWEWY
EWX
EW
CttS
CttS
)2sin()2cos(
)2sin()2cos(
20 days of non-stop running with minimal intervention
sin/;
sin/;NS
YYEWXY
NSXX
EWYX
bb
bb
N-S signal riding on top of Earth rotation signal, Sensitive to calibration
E-W signal is nominally zero Sensitive to alignment
Fit to sine and cosine waves at the sidereal frequency
Two independent determinations of b components in the equatorial plane
Final results Anamolous magnetic field constrained:
xHex
e = 0.001 fT ± 0.019 fTstat ± 0.010 fTsys
yHey
e = 0.032 fT ± 0.019 fTstat ± 0.010 fTsys
Systematic error determined from scatter under various fitting and data selection procedures
Frequency resolution is 0.7 nHz
Anamalous electron couplings be are constrained at the level of 0.002 fT by torsion pendulum experiments (B.R. Heckel et al, PRD 78, 092006 (2008).)
3He nuclear spin mostly comes from the neutron (87%) and some from proton (5%) Friar et al, Phys. Rev. C 42, 2310 (1990) and V. Flambaum et al, Phys. Rev. D 80, 105021 (2009).
bxn = (0.1 ± 1.6)10GeV
byn = (2.5 ± 1.6)10GeV
|bnxy| < 3.7 10GeV at 68% CL
Previous limit |bn
xy| = (6.4 ± 5.4) 1032 GeVD. Bear et al, PRL 85, 5038 (2000)
J. M. Brown, S. J. Smullin, T. W. Kornack, and M. V. R., Phys. Rev. Lett. 105, 151604 (2010)
Improvement in spin anisotropy limits
Recent compilation of CPT limits
V.A. Kostelecky and N. Russell
arXiv:0801.0287v3
Many new limits in last 10 years
plM
mb
2~
m - fermion mass or SUSY breaking scale
Existing limits: ~ 10 10
1/Mpl effects are quite excluded
Natural size for CPT violation ?
Need 10GeV for 1/Mpl
2 effects
10 GeV
CPT-even Lorentz violation
Maximum attainable particle velocity
Implications for ultra-high energy cosmic rays, Cherenkov radiation, etc Best limit c00 ~ 10-23 from Auger ultra-high energy cosmic rays
Many laboratory limits (optical cavities, cold atoms, etc)
Motivation for Lorentz violation (without breaking CPT) Doubly-special relativity Horava-Lifshitz gravity
L = – (m + a + b5) +i2 ( + c + d5)
a,b - CPT-oddc,d - CPT-even
)ˆˆˆ1( 000 kjjkjjMAX vvcvcccv Coleman and Glashow
Jacobson
Something special needs to happen when particle momentum reaches Plank scale!
Search for CPT-even Lorentz violation with nuclear spin
Need nuclei with orbital angular momentum and total spin >1/2 Quadrupole energy shift proportional to the kinetic energy of the
valence nucleon
Previosly has been searched for in two experiments using 201Hg and 21Ne with sensitivity of about 0.5 Hz
Bounds on neutron cn~10 – already most stringent bound on c coefficient!
222332211 2)2(~ zyxQ pppcccE
Suppressed by vEarth
First results with Ne-Rb-K co-magnetometer Replace 3He with 21Ne
A factor of 10 smaller gyromagnetic ratio of 21Ne makes the co-magnetometer have 10 times better energy resolution for anomalous interactions
Use hybrid optical pumping KRb21Ne Allows control of optical density for pump beam, operation with 1015/cm3 Rb density,
lower 21Ne pressure.
Eventually expect a factor of 100 gain in sensitivity Differences in physics:
Larger electron spin magnetization (higher density and larger 0)
Faster electric quadrupole spin relaxation of 21Ne Quadrupole energy shifts due to coherent wall interactions
Sensitivity already better than K-3HeFast damping of transients
21Ne Semi-sidereal Fits Data not perfect, but already an order of magnitude more sensitive
than previous experiments
N-S
E-W
A< 1 fT
Systematic errors Most systematic errors are due to two preferred directions in
the lab: gravity vector and Earth rotation vector If the two vectors are aligned, rotation about that axis will
eliminate most systematic errors Amundsen-Scott South Pole Station
Within 100 meters of geographic South Pole
No need for sidereal fitting, direct measurement of Lorentz violation on 20 second time scale!
Classic axion-mediated forces
Monopole-Monopole:
Monopole-Dipole:
Dipole-Dipole:
221
~4
fr
eggV
mrss
mm
3222
21
~1
)ˆˆ(8 f
err
mrS
M
ggV mrps
md
4322132
2
2121
211
~1
)ˆˆ(33
)ˆˆ)(ˆˆ(16 f
err
mSS
rr
m
r
mrSrS
MM
ggV mrpp
dd
J. E. Moody and F. Wilczek, Phys. Rev. D 30, 130 (1984)
Uncertainty (1) = 18 pHz or 4.3·1035 GeV 3He energy after 1 month (smallest energy shift ever measured)
2= 0.87aTaTbb ne 56.005.0
K-3He co-magnetometer
Sensitivity: 0.7 fT/Hz1/2
Search for nuclear spin-dependent forces
Spin Source: 1022 3He spins at 20 atm.
Spin direction reversed every 3 sec with Adiabatic Fast Passage
New limits on neutron spin-dependent forces
Constraints on pseudo-scalar coupling:
Anomalous spin forces between neutrons are:< 210 of their magnetic interactions< 210 of their gravitational interactions
Present workLimit from gravitational experiments for Yukawa coupling only (Adelberger et al)
)()()(2 5 xxx
m
gLDer
)()()( 5 xxxigLYuk
Limit on proton nuclear-spin dependent forces (Ramsey)
First constraints of sub-gravitational strength!
Recent limit from Walsworth et alPRL 101, 261801 (2008)
G. Vasilakis, J. M. Brown, T. W. Kornack, MVR, Phys. Rev. Lett. 103, 261801 (2009)
Conclusions Set new limit on Lorentz and CPT violation for neutrons at
3×10-33 GeV, improved by a factor of 30
Highest energy resolution among Lorentz-violating experiments
Search for anomalous spin-dependent forces between neutrons with energy resolution of 4×10-35 GeV, first constrain on spin forces of sub-gravitational strength
Search for CPT-even Lorentz violation with 21Ne is underway, limits maximum achievable velocity for neutrons (cn-c)~10-28
Can achieve frequency resolution as low as 20 pHz, path to sub-pHz sensitivity, search for 1/MPl
2 effects