USE OF IBS IN THE PRECISION EXPERIMENTS WITH POLARIZED BEAMS AT VEPP-4M

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USE OF IBS IN THE PRECISION EXPERIMENTS WITH
POLARIZED BEAMS AT VEPP-4M

• Sergei Nikitin
• for VEPP-4M and KEDR teams
• IBS Mini Workshop,
• Cockcroft Institute, Daresbury
• 28-29 August 2007

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CONTENT

• IBS features in the viewpoint of Beam
  Polarization
• IBS-based polarimeter realization and comparison
  of calculation and experiment
• Resonant Depolarization technique
• Precision experiments with polarized beams using
  IBS polarimeter

Sergei Nikitin
29 August 2007
IBS Workshop
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Spin dependence of IBS

• Non-relativistic cross section for e-e-
  scattering in the center-of mass system (? is a
  relative velocity of particles in the co-moving
  system, ? is a beam polarization)
• Interaction of elementary magnetic moments
  weakens the electric charge interaction (Coulomb
  scattering). In principle, a polarization can be
  observed by measuring a beam lifetime (Baier and
  Khoze, 1968).
• Spin contribution to the multiple Touschek
  process (?ltlt1) has an order of ? -2 and is
  negligible as compared with the main Rutherford
  term ( ? -4).

Sergei Nikitin
29 August 2007
IBS Workshop
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Beam Lifetime increment caused byBeam
Polarization
preliminary
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Beam Lifetime increment due to Polarization
calculated vs. Energy Aperture (preliminary)
E1500 MeV 80 polarization
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Depolarizing influence of IBS
A.M. Kondratenko, PHD Thesis, 1974
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• Polarization contribution to the beam emittance
  and energy spread is negligible.
• Depolarization influence of IBS is usually small
  because of its insignificant contribution to
  energy diffusion as compared with SR.
• Practically, a few percent change in Beam
  Lifetime related to Polarization is too small to
  be measured because of large systematic errors.
• Another way, the detecting of Touschek particles
  in conjunction with the resonant depolarization
  technique, is effectively applied to observe Beam
  Polarization as well as to measure Beam Energy.

Sergei Nikitin
29 August 2007
IBS Workshop
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• Counting rate of Touschek particles registered
  from a polarized electron bunch is a bit below
  than from an unpolarized one.
• One can measure a beam polarization
• and spin precession frequency by a fast change
  in the counting rate during scanning an external
  field depolarizer frequency (Resonant
  Depolarization technique).
• Beam Energy value is determined by the measured
  Spin Frequency.
• 1970, Skrinsky, Shatunov, Tumaikin and
  Serednyakov(BINP, VEPP-2) for the first time
  observed beam polarization using IBS and applied
  a resonant depolarization technique
  (non-published)

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29 August 2007
IBS Workshop
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Observation of Touschek particles

• Because of Lorents transformation, in lab. system
  one of scattering (Touschek) particles gets a
  notable positive momentum additive ( ?p) and
  another gets the same in value but opposite in
  sign (- ?p). As consequence, first starts to
  oscillate about a new mean orbit with larger
  radius while second does it with a smaller one.
• Usually, at ?p1 the Touschek particles can be
  detected (by scintillation counters).
• The counters are moved into a dynamic aperture in
  the median plane up to a position at which they
  do not essentially affect a beam lifetime.

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29 August 2007
IBS Workshop
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Touschek Electron Couple Detection
Out
to C.C.
(Coincidence Circuit)
IBS Event
In
to C.C.
Note If Touschek dominates over Gas-Beam one
can use a sum of the counter rates instead of
their logical production
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29 August 2007
IBS Workshop
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Limitations for Touschek particle detection

• Lower limit on a momemtum deviation ?p1 of
  registered Touschek particles is determined by a
  distance A from the scintillation counter to a
  beam closed orbit.
• Upper limit ?p2 is determined by geometric
  limitations of a vacuum pipe (AG ).
• Touschek particles with ?pgtAE (an energetic
  aperture for VEPP-4M is about 0.6) can be
  detected mainly during only a first turn after
  the scattering (single turn approximation).
• There exist the "dead zones, occupying a part of
  closed orbit, starting from which the scattered
  particles do not reach the counter because of an
  unhappy betatron phase incursion (Single Turn
  approximation).

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29 August 2007
IBS Workshop
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Lower momentum limit and Dead Zone factorvs. the
distance from the counter to the orbit(Single
Turn approach)
VEPP-4M
Dead Zone Factor
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200 kHz per 2 mA in a bunch
?(fpol-funpol)/fpol f IBS counting rate
1 MHz needed for 510-9 accuracy
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IBS Workshop
29 August 2007
Sergei Nikitin
29 June 2006
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• Quantity under observation is
  ,
• where are counting rates for
  Touschek electrons from a polarized and
  unpolarized bunches respectively.
• Depolarizer must forces on both bunches
  concurrently if one of them is unpolarized.
• Selective depolarization is resonable in a case
  of both bunches being polarized.
• Systematic errors in , depending upon the
  beam sizes and fluctuations in beam lifetime of
  not Touschek origin, are minimized (currents of
  bunches are equalized with an accuracy of 1).

Sergei Nikitin
29 August 2007
IBS Workshop
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!!!
V.E. Blinov et al., EPAC 2002, p. 1954, 2002.
Note it is supposed that Touschek dominates over
gas scattering in Beam Lifetime
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29 August 2007
IBS Workshop
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Characteristic behaviors of the relative Touschek
Particle Counting Rate in a time
Depolarization Jump
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IBS Workshop
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Calculation of Touschek Counting Rate

• Counting rate of Touschek particles
• A is a distance between the orbit and the
  counter
• AG is a geometric aperture
• J1 and J2 are the integrals (different in 1D and
  2D theories)
• Magnitude of the effect
• (Depolarization Jump)
• Account of the distribution function
  two-dimensionality changes a jump magnitude !

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29 August 2007
IBS Workshop
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Integrals for Counting Rate calculation S.
Nikitin, I. Nikolaev/Proc. of EPAC 2006, p.1184
2D Theory
1D Theory
Note No relativity the counter of finite
sizes.
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29 August 2007
IBS Workshop
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Depolarization Jump in 1D and 2D theories S.
Nikitin, I. Nikolaev/Proc. of EPAC 2006, p.1184
1D the observed jump about 2
contradicts the prediction
2D in agreement with the experiment
Typical work area
P80
vs. a counter distance
vs. a coupling (A1 cm)
Prehistory The first 2D relativistic
consideration to describe the Touschek lifetime
including the polarization effect was made in
V.N.Bayer et al., Doklady Akademii Nauk SSSR, v.
241, n.4, p.797 (1978). Yu. Shatunov adverted to
this problem in his doctoral thesis.
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29 August 2007
IBS Workshop
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Touschek Particle counting rate calculated
vs. Beam Energy (preliminary)(P80, sl 5
cm, Ey/Ex 1/100, ?10 mm, I10 mA)
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29 August 2007
IBS Workshop
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Vacuum chamber section with the VEPP-4M
polarimeter components
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IBS Workshop
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29 August 2007
IBS Workshop
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Touschek Particle counting rate
measured vs. Beam Energy (preliminary)(1.5-3
GeV, VEPP-4M, 2006 a random coincidence
contribution subtracted)
Against in theory
ww1w2w3
Correl. Tousch.
Uncorrel. Tousch.
background
Extrapolation 10 kHz at 5 GeV, I10 mA
3.0 GeV
1.5 GeV
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29 August 2007
IBS Workshop
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Counting Rate vs. Counter Distance
V.E. Blinov et al./EPAC 2002, p.1954
Discrepancy grows especially at small distances
to a beam (lt10 mm) because of a multi-turn
Touschek and halo (from a non-linearity).
Calculated (Single Turn)
Measured
2 mA/bunch 1548 MeV
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29 August 2007
IBS Workshop
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200 kHz counting rate at 2 mA/bunch achieved By
now, an additional scintillation counters have
been installed with the aim to enhance the rate
up to 1 MHz
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29 August 2007
IBS Workshop
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Energy calibration by IBS polarimeter withan
accuracy of 10-6 in the Psi mass measurement
S(t)
A slope is positive at IpolltIunpol in a
accordance with an estimate
Depolarizer frequency scan
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IBS Workshop
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Depolarization Jump vs. Beam Current at two
values of Vertical Beam Size
S. Nikitin, I. Nikolaev/Proc. of EPAC 2006,
p.1184
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29 August 2007
IBS Workshop
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Giant Jump (70 sigmas)
A larger jump (in sigmas) is a more
accurate energy calibration
S(t)
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IBS Workshop
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Experiments at VEPP-4M using RD and IBS
polarimeter

• J/Psi, Psi mass measurements
• Tau lepton mass measurement at its
  production threshold
• Study of Beam-Energy long-term
  stability
• High resolution comparison of the
  depolarization frequencies of bunches (study of
  systematic errors in a possible CPT test
  experiment)

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IBS Workshop
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Results of J/Psi and Psi mass measurements
The achieved accuracy of measurement of J/Psi-
and Psi- meson masses surpasses the
world-average one in 3 and 4 times, accordingly.
The relative accuracy of J/Psi meson mass is
4x10-6, that is the absolute record of accuracy
in measurement of narrow short-lived resonances.
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29 August 2007
IBS Workshop
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cross- section vs. Beam Energy V.V.
Anashin et al., Pisma v ZhETF, vol. 85, iss. 8,
p. 429, 2007.
KEDR
world-averaged
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29 August 2007
IBS Workshop
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Natural depolarization process at an energy of
tau lepton production threshold(near the spin
integer resonance E1763 MeV)
S(t)
1/2 Polarization Life-Time
After injection of a polarized beam from VEPP-3
at 1.85 GeV the VEPP-4M energy is lowered to tau
threshold energy 1777 MeV where the
depolarization becomes significant.
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29 August 2007
IBS Workshop
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Spin resonance structure measurement

• experiment
• ---- calculation
• (synchrotron modulation
  accounted)
• . spin resonance
• of 2d order
• (in betatron tunes) due to
• sextupoles

Tau threshold
Bogomyagkov et al., EPAC 2004, p. 737.
29 August 2007
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IBS Workshop
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Long-term stability of VEPP-4M energy
22-24 May, 2002
Day-to-night 40 keV oscillation

• electrons
• positrons

Cosinus-like Fit
Gap lt 5 keV
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IBS Workshop
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Example of good long-term stability26-28 Dec
2003
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IBS Workshop
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Study of possibility to test CPT at a storage
ringO. Anchugov et al., EPAC 2006, p. 2787

• A concept of CPT test at a storage ring implies a
  high-precision comparison of the simultaneously
  measured spin precession frequencies of e and e-
  depending on a combination of constants (g-2)/2
  and e/mc.
• Prehistory
• 1. VEPP-2M, 1987. Comparison of the polarization
  extents of e and e? after adiabatic crossing
  the spin resonance. Treated as AMM comparison
  (10-8) assuming q e q e?.
• 2. Van Dyck, et al. 1987. Electrons/Positrons in
  the Penning trap (3 10-9).
• It is of interest to measure difference
  ?-??with an accuracy of the order of 10-9 .
  This will be a next step as compared even with
  Van Dyck (non-relativistic, not all constants
  included).
• At the first stage of our experiments, we
  compare the spin precession frequencies of two
  electron bunches, simultaneously circulating in
  the VEPP-4M storage ring, with the aim to reach a
  minimal statistic error and to investigate some
  systematic errors.

Sergei Nikitin
IBS Workshop
29 August 2007
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Comparison of the depolarization frequencies of
electrons and positrons in the simultaneous
scan(Electron-Positron energy gap
measurement)non-published
Scan speed55 eV/sec
e-
e
Ep - Ee (1.320.14) keV
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29 August 2007
IBS Workshop
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Depolarization frequency resolution 3 10-9 (5
eV). (Accuracy in CPT Test should not be worse
than 10-9)non-published
Scan speed5 eV/sec
e-
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29 August 2007
IBS Workshop
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Simultaneous thin scan with two polarized
electron bunches at their current ratio 2 1
(study of the dependence of spin frequency on
current)
Scan speed5 eV/sec
non-published
e-1
e-2
E1(1850.899835 3.6e-05) MeV
E2(1850.899853 5.6e-05) MeV
E2-E1(18 66) eV
With an accuracy of 3 10-8 a difference in
current does not effect on the spin frequency
difference
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29 August 2007
IBS Workshop
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Discussion

• High efficient IBS-based polarimeter is developed
  for various precision experiments with polarized
  beams
• J/Psi, Psi and tau-lepton masses are defined
  more accurately
• Record resolution in the depolarization frequency
  of 3 10-9 (and 2 10-8 in e-e- spin frequency
  comparison) achieved gives an incentive to next
  studies of possibility to realize the CPT Test
  experiment at a storage ring
• Developed methods and skills may be useful in a
  study of other IBS aspects (for example, the
  Touschek background in the section with the
  detector)

Thank you very much!
Sergei Nikitin
29 August 2007
IBS Workshop