SLIDE 38 Spin precession
- The spin precession of a charged particle is induced
by the interaction
its electromagnetic dipole moments, e.g. MDM and EDM, with external electromagnetic fields.
- The intense electric field between the crystal planes,
!, which deflects charged particles, transforms into a strong electromagnetic field !∗ ≈ $!, %∗ ≈ −$'×!/* in the instantaneous rest frame of the particle and induces spin precession. In the limit of large boost, the spin precession induced by the MDM is: + = - − 2 2 $/0
- Thanks to the extremely large magnitude of the
electric field, the spin rotation angle in the crystal of several centimetres in length can reach several radians. Monday, 28 May 2018 Frontier Detectors for Frontier Physics - 14th Pisa meeting
§
- V. G. Baryshevsky, Pis’ma. Zh. Tekh. Fiz. 5 (1979), 182
§ V.L. Lyuboshits, Sov. J. Nucl. Phys. 31(1980), 509 §
- V. G. Baryshevsky, arXiv:1504.06702v1 (2015)
§
- F. J. Botella et al., Eur. Phys. J. C 77 (2017), 181
VOLUME 69, NUMBER 23
PH YSICAL REVI EW LETTERS
7 DECEMBER 1992
Py
X' beam
po1 a[ i zati on
0.1—
Oownbend Upbend
Pz
polarizations and uncertainties
(Io statist-
ical errors) after spins have been precessed
by the two crystals.
The dashed
arrows show the expected precessions.
tance which
is a function of the apparatus,
beam, trigger,
and analysis. A similar distribution was obtained
for the
spin-down
case.
We extract the polarization P;
by averaging
the difference
- ver the sum of the above equation
for spin-up
and spin-down
data. The measured
polarizations are list- ed in Table I. For the two crystals the average of the ab- solute values
polarization vectors
is P=(11. 8
+'3.6)%, consistent
with
the
value
sured [14] without the Z+ precession by the crystals.
These polarizations are plotted
in Fig. 3. The predict-
ed precessions of the Z+ magnetic moments based on pre- vious measurements
[6] are also shown.
The measured
precession angles for the down-bending and up-bending crystals are +51'~23' and —
72'+'26',
respectively. The average of the magnitude
value
is consistent with
the predicted
value
62'+'2'.
As anticipated, the spins
in the two crystals
precess
in
directions. The Z+
spin
precesses around the x axis; hence, P„should be zero. This is in agreement
with
(Table I). Since the
magnitude
polarization
after
precession
is con-
sistent
with the undeflected
measurement, there
is no evi-
dence of depolarization during channeling. The X+ mag- netic moments
and
their statistical errors derived from the down-bending and up-bending crystals are
(2.15
+ 0.61)ptv
and
(2.74+ 0.71)ptv,
respectively.
Their
average of p
(2.40~0.46)ptv
is consistent with the ex-
perimental
world average [6] of (2.42 ~ 0.05)@tv.
Systematic uncertainties
in the crystals'
bend angles and
in
the incident
hyperon momentum
contribute
0.03p~ and 0.0lpN
to the uncertainty
in our measure-
ment.
The major contribution
comes from studies of the stability of our result to reasonable changes
in data selection
variables
(R, e, hE, missing
mass, and z,,). This experiment has confirmed
spin precession
for par- ticles channeled
in bent crystals.
This phenomenon
may
the
way
for magnetic
moment measurements
short-lived
particles
such as charm baryons. A candidate might be the Ac which current experiments
[6] have al-
ready
shown
has a large asymmetry parameter and may be produced
with significant
polarization
[17].
We wish to thank the staffs of Fermilab
and the Peters- burg
Nuclear Physics Institute for their assistance. Da-
vid Daniels made important
contributions
in the summers
he worked with us. This work is supported
in part by the
U.S. Department
under
Contracts
AC0280ER10587, No. DE-AC02-76CH0300,
AC02-76ER03075,
and
the Russian Academy
I.F.A. was supported
by
FAP ESP, Brazil. P.G.
was partially supported by
FAPESP and CNPq, Brazil. A.M. is a graduate
student from CINVESTAV-IPN,
Mexico and was partially
sup- ported by CONACyT,
Mexico.
' Present
address: Department
University
Maryland, College Park, MD 20742.
~ ~Present
address: Department
Stanford Uni-
versity, Stanford, CA 94309.
[1]A. F. Elishnev
et al., Phys. Lett. SSB, 387 (1979).
[2] V. Samsonov,
Relativistic
Channeling, edited by R. A.
Carrigan,
Jr., and J. A. Ellison
(Plenum, New
York,
1987), p. 129. [3] S. I. Baker
et al. , Nucl. Instrum. Methods
- Phys. Res. ,
- Sect. A 24$, 301 (1986).
[4] A. A. Asseev et al. , Nucl. Instrum.
Methods
- Phys. Res.,
- Sect. A 309, I (1991).
[5] S. P. Moiler
et al. , Phys. Lett. B 256, 91 (1991).
[6] Review of Particle Properties,
- Phys. Rev. D 45, I (1992).
[7] V. G. Baryshevskii,
Pis'ma Zh. Tekh. Fiz. 5, 182 (1979) [Sov. Tech. Phys. Lett. 5, 73 (1979)].
[8] L. Pondrom,
in Proceedings of the l982 Division of Par-
ticles and Fields Summer School on Elementary Particle
Physi'cs and Future Facilities, Sno~mass,
Colorado, edit-
ed by R. Donaldson,
and F. Paige (Fermi- lab, Batavia, 1983).
[9] V. L. Lyuboshits,
- Yad. Fiz. 31, 986 (1980) [Sov. J. Nucl.
- Phys. 31, 509 (1980)].
[10] I. J. Kim, Nucl. Phys. B 229, 251 (1983).
[11]We have observed
channeling
at crystal
bends a factor of
10 larger
than used
in this
experiment. At twice the momentum
used here these factors would imply effective magnetic fields of = 1000 T.
[12]J. Lach and L. Pondrom,
Annu.
- Rev. Nucl. Part. Sci. 29,
203 (1979); L. Pondrom,
- Phys. Rep. 122, 57 (1985).
[13]V. M. Samsonov
and
Report No.
LNPI-1476, Leningrad, 1989 (unpublished). [14] Dong Chen, Ph. D. thesis, State University
at Albany,
1992 (unpublished).
[15] M. Foucher
et al. , Phys. Rev. Lett. 6S, 3004 (1992).
[16]J. Lindhard,
Mat.
Dan
(1965). [17] A. N. Aleev
et al., Yad. Fiz. 43, 619 (1986) [Sov. J.
- Nucl. Phys. 43, 395 (1986)].
3289
- D. Chen et al., Phys. Rev. Letters 69 (1992), 3286
- E. Bagli et al., Eur. Phys J. C, 77 (2017), 828
INFN - Nicola Neri – nicola.neri@mi.infn.it
