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

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. IBS features in the viewpoint of Beam Polarization

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

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  1. 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

  2. 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 CONTENT Sergei Nikitin IBS Workshop 29 August 2007

  3. 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, ζis 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 (θ<<1) has an order of θ-2 and is negligible as compared with the main Rutherford term (~ θ-4). Sergei Nikitin IBS Workshop 29 August 2007

  4. Beam Lifetime increment caused byBeam Polarization preliminary Sergei Nikitin IBS Workshop 29 August 2007

  5. Beam Lifetime increment due to Polarization calculated vs. Energy Aperture (preliminary) E=1500 MeV 80% polarization Sergei Nikitin IBS Workshop 29 August 2007

  6. Depolarizing influence of IBS A.M. Kondratenko, PHD Thesis, 1974 Sergei Nikitin IBS Workshop 29 August 2007

  7. 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 IBS Workshop 29 August 2007

  8. 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) Sergei Nikitin IBS Workshop 29 August 2007

  9. Observation of Touschek particles • Because of Lorents transformation, in lab. system one of scattering (Touschek) particles gets a notable positive momentum additive (+ |Δp|) and another gets the same in value but opposite in sign (- |Δp|). As consequence, first starts to oscillate about a new mean orbit with larger radius while second does it with a smaller one. • Usually, at Δp≥1% 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. Sergei Nikitin IBS Workshop 29 August 2007

  10. Touschek Electron Couple Detection Out to C.C. (Coincidence Circuit) IBS Event In to C.C. Note: If “Touschek” dominatesover “Gas-Beam” one can use a sum of the counter rates instead of their logical production Sergei Nikitin IBS Workshop 29 August 2007

  11. Lower limit on a momemtum deviation Δp1 of registered Touschek particles is determined by a distance A from the scintillation counter to a beam closed orbit. Upper limit Δp2 is determined by geometric limitations of a vacuum pipe (AG ). Touschek particles with Δp>AE(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). Limitations for Touschek particle detection Sergei Nikitin IBS Workshop 29 August 2007

  12. Lower momentum limit and Dead Zone factorvs. the distance from the counter to the orbit(“Single Turn” approach) VEPP-4M “Dead Zone” Factor Sergei Nikitin IBS Workshop 29 August 2007

  13. 200 kHz per 2 mA in a bunch =(fpol-funpol)/fpol f =IBS counting rate 1 MHz needed for 5·10-9 accuracy Sergei Nikitin IBS Workshop 29 August 2007 Sergei Nikitin 29 June 2006

  14. 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 IBS Workshop 29 August 2007

  15. !!! V.E. Blinov et al., EPAC 2002, p.1954, 2002. Note: it is supposed that Touschek dominates over gas scattering in Beam Lifetime Sergei Nikitin IBS Workshop 29 August 2007

  16. Characteristic behaviors of the relative Touschek Particle Counting Rate in a time Depolarization Jump Sergei Nikitin IBS Workshop 29 August 2007

  17. 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 ! Calculation of Touschek Counting Rate Sergei Nikitin IBS Workshop 29 August 2007

  18. 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. Sergei Nikitin IBS Workshop 29 August 2007

  19. 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 P=80% vs. a counter distance vs. a coupling (A=1 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. Sergei Nikitin IBS Workshop 29 August 2007

  20. Touschek Particle counting rate calculated vs. Beam Energy (preliminary)(P=80%,sl =5 cm,Ey/Ex =1/100, А=10 mm, I=10 mA) Sergei Nikitin IBS Workshop 29 August 2007

  21. Vacuum chamber section with the VEPP-4M polarimeter components Sergei Nikitin IBS Workshop 29 August 2007

  22. Sergei Nikitin IBS Workshop 29 August 2007

  23. Touschek Particle counting rate measured vs. Beam Energy (preliminary)(1.5-3 GeV, VEPP-4M, 2006; a random coincidence contribution subtracted) Against in theory w=w1+w2+w3 Correl. Tousch. Uncorrel. Tousch. background Extrapolation: ~10 kHz at 5 GeV, I=10 mA 3.0 GeV 1.5 GeV Sergei Nikitin IBS Workshop 29 August 2007

  24. Counting Rate vs. Counter Distance V.E. Blinov et al./EPAC 2002, p.1954 Discrepancy grows especially at small distances to a beam (<10 mm) because of a “multi-turn” Touschek and halo (from a non-linearity). Calculated (“Single Turn”) Measured 2 mA/bunch 1548 MeV Sergei Nikitin IBS Workshop 29 August 2007

  25. 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 Sergei Nikitin IBS Workshop 29 August 2007

  26. Energy calibration by IBS polarimeter withan accuracy of 10-6 in the Psi’ mass measurement S(t) A slope is positive at Ipol<Iunpol in a accordance with an estimate Depolarizer frequency scan Sergei Nikitin IBS Workshop 29 August 2007

  27. Depolarization Jump vs. Beam Current at two values of Vertical Beam Size S. Nikitin, I. Nikolaev/Proc. of EPAC 2006, p.1184 Sergei Nikitin IBS Workshop 29 August 2007

  28. “Giant Jump” (70 “sigmas”) A larger jump (in “sigmas”) is a more accurate energy calibration S(t) Sergei Nikitin IBS Workshop 29 August 2007

  29. 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) Sergei Nikitin IBS Workshop 29 August 2007

  30. 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. Sergei Nikitin IBS Workshop 29 August 2007

  31. cross- section vs. Beam Energy V.V. Anashin et al., Pis’ma v ZhETF, vol. 85, iss. 8, p. 429, 2007. KEDR world-averaged Sergei Nikitin IBS Workshop 29 August 2007

  32. “Natural” depolarization process at an energy of tau lepton production threshold(near the spin integer resonance E=1763 MeV) S(t) =1/2Polarization 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. Sergei Nikitin IBS Workshop 29 August 2007

  33. 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. Sergei Nikitin IBS Workshop 29 August 2007

  34. Long-term stability of VEPP-4M energy 22-24 May, 2002 Day-to-night ± 40 keV oscillation • electrons • positrons Cosinus-like Fit Gap < 5 keV Sergei Nikitin IBS Workshop 29 August 2007

  35. Example of “good” long-term stability26-28Dec 2003 Sergei Nikitin IBS Workshop 29 August 2007

  36. A concept of CPT test at a storage ring implies a high-precision comparison of the simultaneouslymeasured 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. Study of possibility to test CPT at a storage ringO. Anchugov et al., EPAC 2006, p. 2787 Sergei Nikitin IBS Workshop 29 August 2007

  37. Comparison of the depolarization frequencies of electrons and positrons in the simultaneous scan(Electron-Positron energy gap measurement)non-published Scan speed=55 eV/sec e- e+ Ep- Ee=(1.32±0.14) keV Sergei Nikitin IBS Workshop 29 August 2007

  38. Depolarization frequency resolution 3 ∙10-9 (5 eV). (Accuracy in CPT Test should not be worse than 10-9)non-published Scan speed=5 eV/sec e- Sergei Nikitin IBS Workshop 29 August 2007

  39. Simultaneous “thin scan” with two polarized electron bunches at their current ratio 2 : 1 (study of the dependence of spin frequency on current) Scan speed=5 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 Sergei Nikitin IBS Workshop 29 August 2007

  40. 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) Discussion Thank you very much! Sergei Nikitin IBS Workshop 29 August 2007

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