IAS Program on High Energy Physics Polarization Free Methods for Beam Energy Calibration Nickolai Muchnoi Budker INP, Novosibirsk January 20, 2016 Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 1 / 20
TALK OUTLINE Introduction 1 Extending beam energy range? 2 Conclusion 3 Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 2 / 20
Introduction FCC-ee/CEPC aims to improve on electroweak precision measurements, with goals of 100 keV on the Z mass, and a fraction of MeV on the W mass. The resonant depolarization technique is the only known approach that showed the accuracy at the level of ∆ E/E ≃ 10 − 6 . My personal experience is based on beam energy measurement systems for VEPP-4M, BEPC-II and VEPP-2000 colliders. I will try to extend this approach for higher energies. Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 3 / 20
Inverse Compton Scattering photon: ω θ ω photon: ω 0 electron: ε 0 , γ =ε 0 /m θ ε e l e c t r o n : ε Scattering parameters, u and κ : u = ω ε = θ ε ω κ = 4 ω 0 ε 0 = ε 0 − ω ; u ∈ [0 , κ ] ; m 2 . θ ω � κ � θ ω = 1 θ ε = 4 ω 0 u 1 − u � � Scattering angles: u − 1; . γ m κ κ Maximum energy of scattered photon ( θ ω = θ ε = 0): ω max = ε 0 κ 1 + κ. ε 0 = ω max ≃ m � ω max � � � 1 + 1 + m 2 /ω 0 ω max . 2 2 ω 0 Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 4 / 20
Laser backscattering for beam energy calibration HISTORY: Taiwan Light Source 1996 , BESSY-I,II 1998 , 2002 , VEPP-3,4M,2000 2008 , 2005 , 2012 , BEPC-II 2010 , ANKA 2015 e. g. BEPC-II HPGe spectrum e. g. VEPP-2000 HPGe spectrum 2 counts K = 1.31 ± 0.12: χ /NDF = 294.5/296 3500 0 2012.04.20 (16:21:34 - 18:53:59) 2012.04.20 900 ω = 2025.42 ± 0.12 ± 0.20 keV max 3000 800 700 2500 600 2000 500 1500 400 1000 300 200 500 100 1980 2000 2020 2040 2060 2080 1650 1700 1750 1800 1850 1900 1950 E , keV E , keV γ γ m τ =1776 . 91 ± 0 . 12 +0 . 10 − 0 . 13 MeV Backscattering occurs inside the magnet: evident interference Phys.Rev.Lett. 110(2013) 140402 Phys. Rev. D90 (2014) 012001 ✞ ☎ Achieved accuracy is ∆ E/E ≃ 3 × 10 − 5 for E < 2 GeV ✝ ✆ Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 5 / 20
Accurate energy scale transfer: eV → MeV → GeV IR optics, 10P20 CO 2 laser line: ω 0 = 0 . 117065228 eV γ -lines from excited nuclei as a good reference for ω max : 137 Cs τ 1 / 2 ≃ 30 . 07 y E γ = 0661 . 657 ± 0 . 003 keV 60 Co τ 1 / 2 ≃ 5 . 27 y E γ = 1173 . 228 ± 0 . 003 keV E γ = 1332 . 422 ± 0 . 004 keV 208 Tl τ 1 / 2 ≃ 3 m E γ = 2614 . 511 ± 0 . 013 keV 16 O ∗ E γ = 6129 . 266 ± 0 . 054 keV High energy physics scale 1 : J/ψ 3096 . 900 ± 0 . 002 ± 0 . 006 MeV ψ (2 S ) 3686 . 099 ± 0 . 004 ± 0 . 009 MeV 1 Final analysis of KEDR data, Physics Letters B 749 (2015) 50-56 Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 6 / 20
Introduction 1 Extending beam energy range? 2 Conclusion 3 Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 7 / 20
Spectrometer with laser calibration L A S E R B E A M X 0 n s t o h o n p DIPOLE t o m p o C MAGNET BPM θ BPM BPM BPM e l e c t r o n b e a m BPM Compton electrons with min. energy X beam BPM Δ θ Here tiny fraction of the beam electrons X edge are scattered on the laser wave L Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 8 / 20
Spectrometer with laser calibration L ∆ θ = κ = 4 ω 0 E 0 A S E R θ m 2 B E A M X 0 n s t o h o n p DIPOLE t o m p o C MAGNET BPM θ BPM BPM BPM e l e c t r o n b e a m BPM Compton electrons with min. energy X beam BPM Δ θ Here tiny fraction of the beam electrons X edge are scattered on the laser wave L Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 8 / 20
Spectrometer with laser calibration L ∆ θ = κ = 4 ω 0 E 0 A S E R θ m 2 B E A M X 0 n s t o h o n p DIPOLE t o m p o C MAGNET BPM θ BPM BPM BPM e l e c t r o n b e a m BPM Compton electrons with min. energy X beam BPM Δ θ Here tiny fraction of the beam electrons X edge are scattered on the laser wave L θ × m 2 Access to the beam energy: E 0 = ∆ θ 4 ω 0 Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 8 / 20
Spectrometer with laser calibration E 0 = 100 GeV, ω 0 = 1 eV: L A S E ∆ θ R B ≃ 1 . 53 E A θ M X 0 n s t o h o n p DIPOLE t o m p o C MAGNET BPM θ BPM BPM BPM e l e c t r o n b e a m BPM Compton electrons with min. energy X beam BPM Δ θ Here tiny fraction of the beam electrons X edge are scattered on the laser wave L θ × m 2 Access to the beam energy: E 0 = ∆ θ 4 ω 0 Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 8 / 20
What do one has from ∆ θ measurement? ✎ ☞ ∆ θ m 2 = 1 � Bdl 4 ω 0 c ✍ ✌ ∆ θ is a measure of a B-field integral along the trajectory which is very close to the beam orbit (see next slides). ∆ θ is independent of beam energy: fast energy changes may be detected by BPMs. I. e. increase of ∆ θ measurement time does not influence the beam energy measurement accuracy. Measurement of θ is outside of this talk. One can have a look at the experience of LEP spectrometer as well as ILC beam energy spectrometer studies. Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 9 / 20
Two arcs in a dipole of length L L ✞ ☎ Δθ Note that R e = R 0 / (1 + κ ) . ✝ ✆ S 0 , R 0 – black arc length & radius, ΔX S e , R e – red arc length & radius. So θ � L � S 0 = 2 R 0 arcsin and R e R 0 2 R 0 � √ � L 2 + ∆ X 2 S e = 2 R e arcsin , 2 R e � � � 2 � 2 � LR e � L − LR e where ∆ X = R 2 e − − R 2 e − . 2 R 0 2 R 0 Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 10 / 20
Apparatus: general consideration 20 m L 20 m ΔX θ Δθ D Let κ = 1 . 53 ( E = 100 GeV, ω 0 = 1 eV): θ ∆ θ L ∆ X ∆ S/S D mrad mrad m mm mm ∆ S/S ∝ κθ a) 2 . 59 · 10 − 7 1 1 . 53 10 3 . 83 46 1 . 04 · 10 − 6 2 3 . 06 10 7 . 65 92 ∆ X ∝ κθ · L dipole b) 2 . 59 · 10 − 7 1 1 . 53 5 1 . 91 46 D ∝ κθ · L arm c) 1 . 04 · 10 − 6 2 3 . 06 5 3 . 83 92 An ideal case: a) small angle; b) short dipole; c) long arm. Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 11 / 20
2D detector for scattered electrons? A Transverse Polarimeter for a Linear Collider of 250 GeV e Beam Energy Itai Ben Mordechai and Gideon Alexander (LC-M-2012-001) “... For the detection of the scattered electrons we consider only a position measurement using a Silicon pixel detector placed at a distance of 37.95 m from the Compton IP. The active dimension of the detector is 2 × 200 mm 2 . The size of the pixels cell taken is 50 × 400 µ m 2 similar to the one used in the ATLAS detector [9]. This scheme yields an approximate two dimensional resolution of 14.4 × 115.5 µ m 2 [10] with a data read-out rate of ...” Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 12 / 20
Scattering cross sections & e-beam polarisation. Unpolarised Longitudinal Transverse 1.5 18 3 2.5 16 1 2 14 1.5 0.5 12 1 10 0.5 0 0 8 -0.5 -0.5 6 -1 4 -1.5 -1 2 -2 -1.5 0 -2.5 1 1 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 -1 -0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1-1 -1 -0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1-1 -1 -0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 1-1 0 0 0 -0.2 -0.2 -0.2 y y -0.4 -0.4 -0.4 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 x x x In the plane of electron angles θ x , θ y (after scattering and bending in a dipole) cross section lies within the elliptical kinematic-bounded area. Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 13 / 20
200 × 100 pixels “detector”. ξ � ζ � = − 0 . 5 κ ϑ = 3.26, = 500, P = [ 0.0, 0.0, -0.5, 0.0 ] 0 HD HD Entries Entries 1e+07 1e+07 χ χ 2 2 / ndf / ndf 2662 / 2709 2662 / 2709 − − ± ± X X 0.1313 0.1313 0.1649 0.1649 1 1 ± ± X X 1630 1630 0.06344 0.06344 2 2 σ σ ± ± 21.62 21.62 0.05565 0.05565 X X − − ± ± Y Y 1.63 1.63 0.0001923 0.0001923 1 1 ± ± Y Y 1.63 1.63 0.0001942 0.0001942 2 2 σ σ ± ± 0.1045 0.1045 0.0001082 0.0001082 Y Y − − ± ± P P 0.5 0.5 0.00103 0.00103 ± ± 0.0005721 0.0005721 0.002095 0.002095 P P 40000 ± ± norm norm 1.735e+06 1.735e+06 772.3 772.3 35000 30000 25000 20000 15000 10000 5000 2 1 1.5 0 − 0 0.5 0 200 400 600 8001000 0.5 ϑ − 1 Y − 1.5 1200 − 2 1400 ϑ 1600 X Nickolai Muchnoi IAS Program on High Energy Physics January 20, 2016 14 / 20
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