Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 1 / 16

Size: px

Start display at page:

Download "Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 1 / 16"

Sharyl Weaver
6 years ago
Views:

1 Touschek polarimeter for beam energy measurement of VEPP-4M collider Ivan Nikolaev Budker Institute of Nuclear Physics Novosibirsk, Russia Frascati Spring School Bruno Touschek May Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 1 / 16

2 Outline 1 Introduction 2 Resonance depolarization method (RDM) 3 Intra-beam scattering 4 VEPP-4M accelerating-storage complex 5 Touschek polarimeter 6 Energy calibration 7 Energy interpolation 8 Application of RDM in experiments with KEDR detector 9 Summary Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 2 / 16

3 Introduction High precission measurement of masses of J/ψ, ψ,ψ, D mesons and τ-lepton is very important: Metrology and spectroscopy Theory test (QCD and Lepton universality) Calibration of energy scale of accelerators. It requires absolute calibration of collider s energy. Resonance depolarization method: BINP Novosibirsk Russia, 1975: K ±, K 0, ω, φ, J/ψ, ψ, Υ, Υ, Υ m m = Applied at VEPP-2(M), VEPP-4(M), DORIS-II, CESR, LEP, BESSY-II, SLS, ALS. Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 3 / 16

4 Resonance depolarization method (RDM) Spin precession frequency depends on beam energy: Ω spin = Ω 0 (1 + γ µ µ 0 ) Ω 0 revolution frequency, µ 0,µ normal and anomal part of electron magnetic moment, γ = E/m e Sokolov-Ternov radiation polarization, 1964: τ pol 8 λ e r e c R 3 γ5 Polarization is destructed by external electromagnetic field with frequency Ω dep : Ω spin = nω 0 + Ω dep, n Z Ω s is measured at the moment of depolarization during Ω dep frequency scan. Polarization destruction can be detected on jump in the rate of intra-beam scattering. Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 4 / 16

5 Intra-beam scattering (Touschek effect) Cross section of intra-beam scattering depends on polarization of scattered particles: ( dσ dω = 4r v 4 sin 4 θ 3 sin 2 θ ζ ) 1ζ2 sin 2 θ Scattered particles hit scitillator counters Counting rate: Ṅ = πr 2 0 cn 2 γ 5 V (σ p /p) 3 ( I1 + ζ 2 I 2 ) Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 5 / 16

6 VEPP-4 accelerating-storage complex Linear accelerator LINAC (50 MeV). booster synchrotron (350 MeV). VEPP-3 storage ring (2 GeV). VEPP-4M collider Beam energy 1 6 GeV Bunch number 2 2 Luminocity, E = 1.5 GeV: Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 6 / 16

Touschek polarimeter 4 pairs of scintillator counters are located in different places of VEPP-4M. Due to correlation between counters we use only 2 of them.

7 Touschek polarimeter 4 pairs of scintillator counters are located in different places of VEPP-4M. Due to correlation between counters we use only 2 of them. Counting rate is khz/ma 2 per counter. Total counting rate is MHz. Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 7 / 16

8 Energy calibration procedure Prepare polarized beam in VEPP-3 storage ring ( 2000 sec). Inject it into VEPP-4M. Prepare unpolarized beam. Equalize currents in polarized and unpolarized beam. Monitor relative difference of counting rate of polarized and unpolarized beams. = Ṅpol Ṅ unpol Ṅ unpol Turn on the depolarizer and change Ω dep in a region where resonance depolarization expected. Find and fit jump in counting rate. Accuracy of single energy calibration σ E = 1 kev Two energy calibrations using same bunches (partial depolarization). Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 8 / 16

9 Example of energy calibration at τ delta :14:10 Run χ / ndf / 17 T ± 2.1 DELTA ± CONST ± SLOPE e-06 ± 6.211e-06 SLOPE e-05 ± 9.604e-06 TECU Tcount = 13 sec speed = MeV/sec step = MeV initial = MeV final = MeV Att = 13 db H = NEM = SEM = SIM = EM3 = KEDR1 = KEDR2 = -1 RF = Hz U = kv J = 7.83 A Qx = Qz = TZ = mm I1 = ma I2 = 2.33 ma DV4OUT= C In = khz E = ( )Mev Fd = ( )Hz Out = khz khz/ma^2 Touschek polarimeter for beam energy measurement of VEPP-4M collider LNFSS-08 9 / 16

10 Energy interpolation between calibrations E = α H H(1 + α T T ) + i α i P i P i are: H - guiding magnetic field in calibrating magnet measured by NMR method T = T CM T RING, T RING - average temperature of accelerators magnets. Temperature of VEPP-4M tunnel. Temperature of cooling distilled water Average radial orbit Air,tech water temperatures,... Touschek polarimeter for beam energy measurement of VEPP-4MLNFSS-08 collider 10 / 16

11 Examples of energy interpolation VEPP-4M energy in tau mass experiment. VEPP-4M energy reconstructed energy energy calibrations CBS / / / / / / / Difference between interpolated energy and the measured energy with all aperiodic dependeces accounted (J/ψ mass experiment) Touschek polarimeter for beam energy measurement of VEPP-4MLNFSS-08 collider 11 / 16

12 Application of RDM in experiments with KEDR detector Charmonium masses 2002: Scan of J/ψ (40 nb 1 ) 2002: Scan of ψ (76nb 1 ) 2005: J/ψ (230nb 1 ) : 3 scan of ψ (230nb 1 ) 2004: ψ(3770) Tau mass : 5.2pb 1 Touschek polarimeter for beam energy measurement of VEPP-4MLNFSS-08 collider 12 / 16

KEDR detector 1 Vacuum chamber 2 Vertex detector 3 Drift chamber 4 Aerogel Cherenkov counters 5 TOF scintillation counters 6 LKr barrel calorimeter 7 Superconducting coil (6

13 KEDR detector 1 Vacuum chamber 2 Vertex detector 3 Drift chamber 4 Aerogel Cherenkov counters 5 TOF scintillation counters 6 LKr barrel calorimeter 7 Superconducting coil (6 kgs) 8 Magnet yoke 9 Muon tubes 10 CsI end cap calorimeter 11 Compensating solenoid 12 Quadrupole Touschek polarimeter for beam energy measurement of VEPP-4MLNFSS-08 collider 13 / 16

14 J/ψ, ψ,ψ mesons mass measurement. M J/ψ = ± 0.01 ± MeV (2002) M ψ(2s) = ± ± MeV (preliminary) M ψ(3770) = ± 0.9 ± 0.6 MeV (preliminary) Touschek polarimeter for beam energy measurement of VEPP-4MLNFSS-08 collider 14 / 16

15 Tau mass measurement Touschek polarimeter for beam energy measurement of VEPP-4MLNFSS-08 collider 15 / 16

16 Summary Accuracy of single energy calibration is around 1 kev More than 2k calibrations done. Touschek polarimeter is succesfuly applied for high precision charmonium and tau masses measurement with KEDR detector. Accuracy of VEPP-4M energy interpolation is 7 kev for charmonium mass measurement and 30 kev for tau mass measurement. Touschek polarimeter for beam energy measurement of VEPP-4MLNFSS-08 collider 16 / 16

BINP, Novosibirsk. Sergei Nikitin EPAC 06, Edinburgh

BINP, Novosibirsk. Sergei Nikitin EPAC 06, Edinburgh Record-high Resolution Experiments on Comparison of Spin Precession Frequencies of Electron Bunches Using the Resonant Depolarization Technique in the Storage Ring O. Anchugov, V. Blinov, A. Bogomyagkov,V.