touschek polarimeter for beam energy measurement of vepp ... · outline 1 introduction 2 resonance...
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Touschek polarimeter for beam energy measurement ofVEPP-4M collider
Ivan Nikolaev
Budker Institute of Nuclear PhysicsNovosibirsk, Russia
Frascati Spring School ”Bruno Touschek”May 12-16 2008
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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
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Introduction
High precission measurement of masses of J/ψ, ψ′,ψ′′, D mesons andτ -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= 10−4 ÷ 4× 10−6
Applied at VEPP-2(M), VEPP-4(M), DORIS-II, CESR, LEP,BESSY-II, SLS, ALS.
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Resonance depolarization method (RDM)
Spin precession frequency depends on beam energy:
Ωspin = Ω0(1 + γµ′
µ0)
Ω0 — revolution frequency, µ0,µ′ — normal and anomal part ofelectron magnetic moment, γ = E/me
Sokolov-Ternov radiation polarization, 1964:
1
τpol' 5√
3
8
λerec
R3γ5
Polarization is destructed by external electromagnetic field withfrequency Ωdep:
Ωspin = nΩ0 + Ωdep, n ∈ Z
Ωs is measured at the moment of depolarization during Ωdep
frequency scan.Polarization destruction can be detected on jump in the rate ofintra-beam scattering.
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Intra-beam scattering (Touschek effect)
Cross section of intra-beam scattering depends on polarization ofscattered particles:
dσ
dΩ=
4r20
v4
(4
sin4 θ− 3
sin2 θ−
~ζ1 ~ζ2
sin2 θ
)
Scattered particles hit scitillator counters
Counting rate:
N =
√πr2
0 cN2
γ5V (σp/p)3
(I1 + ζ2I2
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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: 2× 1030
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Touschek polarimeter
4 pairs of scintillator counters are located in different places ofVEPP-4M. Due to correlation between counters we use only 2 ofthem.
Counting rate is 50÷ 100 kHz/mA2 per counter.
Total counting rate is 0.5− 1.5 MHz.
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Energy calibration procedure
Prepare polarized beam in VEPP-3 storage ring ( 2000 sec). Injectit into VEPP-4M.
Prepare unpolarized beam.
Equalize currents in polarized and unpolarized beam.
Monitor relative difference of counting rate of polarized andunpolarized beams.
∆ =Npol − Nunpol
Nunpol
Turn on the depolarizer and change Ωdep in a region where resonancedepolarization expected.
Find and fit jump in counting rate.
Accuracy of single energy calibration
σE = 1 keV ∼ 5× 10−7
Two energy calibrations using same bunches (partial depolarization).
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Example of energy calibration at τ
Tcount = 13 sec
speed = 0.0003 MeV/sec
step = 0.00075 MeV
initial = 1777.47 MeV
final = 1777.544 MeV
Att = 13 dB
2005-05-12 20:14:10Run 1589
TECU1780.05
H = 1705.919
NEM = 2149.013
SEM = 2138.1
SIM = 2287.158
EM3 = 2474.585
KEDR1 = 6520.76
KEDR2 = -1 RF = 181801194 Hz
U = 323.57 kV J = 7.83 A
Qx = 0.531005 Qz = 0.577331
TZ = -0.126246 mm I1 = 2.224 mA I2 = 2.33 mA
DV4OUT=39.531 C
In = 102.68585 kHz
Out = 61.842769 kHz
33.26 kHz/mA^2
E = (1777.501112+-0.00104)Mev Fd = (-791219.637+-1.94)Hz
0 50 100 150 200 250 3000 50 100 150 200 250 300-0.02
-0.015
-0.01
-0.005
0 / ndf 2χ 11.97 / 17
T 2.1± 157.3 DELTA 0.0009506± 0.01237 CONST 0.0005727± -0.01549 SLOPE1 6.211e-06± 6.555e-06 SLOPE2 9.604e-06± 1.402e-05
/ ndf 2χ 11.97 / 17T 2.1± 157.3 DELTA 0.0009506± 0.01237 CONST 0.0005727± -0.01549 SLOPE1 6.211e-06± 6.555e-06 SLOPE2 9.604e-06± 1.402e-05
delta-1
1777
.469
845
1777
.473
595
1777
.477
345
1777
.481
845
1777
.485
595
1777
.489
345
1777
.493
095
1777
.496
845
1777
.500
595
1777
.505
095
1777
.508
845
1777
.512
595
1777
.516
345
1777
.520
095
1777
.523
845
1777
.528
345
1777
.532
095
1777
.535
845
1777
.539
595
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Energy interpolation between calibrations
E = αHH(1 + αT ∆T ) +∑
i
αi∆Pi
H - guiding magnetic field in calibrating magnet measured by NMRmethod
∆T = TCM − TRING , TRING - average temperature of acceleratorsmagnets.
Pi are:
Temperature of VEPP-4M tunnel.
Temperature of cooling distilled water
Average radial orbit
Air,tech water temperatures,. . .
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Examples of energy interpolation
VEPP-4M energy in tau mass experiment.
200626/12
200627/12
200628/12
200629/12
200630/12
200631/12
200701/01
1776.6
1776.8
1777.0
1777.2
1777.4
VEPP-4M energy reconstructed energy
energy calibrations
CBS
Difference between interpolated energy and the measured energy with allaperiodic dependeces accounted (J/ψ mass experiment)
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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)
2004-2006: 3 scan of ψ′ (230nb−1)
2004: ψ(3770)
Tau mass
2005-2007: 5.2pb−1
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KEDR detector
1 Vacuum chamber2 Vertex detector3 Drift chamber4 Aerogel Cherenkov
counters5 TOF scintillation
counters6 LKr barrel calorimeter7 Superconducting coil (6
kGs)8 Magnet yoke9 Muon tubes10 CsI end cap calorimeter11 Compensating solenoid12 Quadrupole
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J/ψ , ψ′,ψ′′ mesons mass measurement.
MJ/ψ = 3096.917± 0.01± 0.007 MeV (2002)
Mψ(2S) = 3686.117± 0.012± 0.015 MeV (preliminary)
Mψ(3770) = 3773.5± 0.9± 0.6 MeV (preliminary)
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Tau mass measurement
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Summary
Accuracy of single energy calibration is around 1 keV 5× 10−7
More than 2k calibrations done.
Touschek polarimeter is succesfuly applied for high precisioncharmonium and tau masses measurement with KEDR detector.
Accuracy of VEPP-4M energy interpolation is 7 keV for charmoniummass measurement and 30 keV for tau mass measurement.
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