A Quartz Cherenkov Detector for Polarimetry at the ILC. Mainz, 13.02.2014 Jenny List, Annika Vauth Spin-Optimierung polarisierter Leptonstrahlen an Beschleunigern (BMBF-Verbundforschungsprojekt mit UHH, Mainz, Bonn) Teil-Projekt "Spin-Umsetzung": Erreichbare Genauigkeit von Compton-Polarimetern
ILC Polarimetry Design Application Conclusion Polarimetry at the ILC Quarz detector design Detector application Summary and Outlook Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 0/19
ILC Polarimetry Design Application Conclusion Polarimetry at the ILC Quarz detector design Detector application Summary and Outlook Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 1/19
ILC Polarimetry Design Application Conclusion Polarimetry at the ILC. Polarisation at the ILC: P ( e + ) � 30 % , P ( e − ) ≈ 80 % Goal for ILC polarimetry: per mille level precision by combining ② spin tracking ① downstream polarimeter 1 5 0 m ① upstream polarimeter ③ e ⁺ e ⁻ 1650m collisions e ⁻ e ⁺ 1 Compton polarimeter measurements upstream and downstream of the e + e − interaction point 2 Spin tracking studies to relate these measurements to the polarization at the e + e − interaction point 3 Long-term average determined from e + e − collision data as absolute scale calibration Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 1/19
ILC Polarimetry Design Application Conclusion Compton polarimeters. ➤ O ( 10 3 ) Compton scatterings/bunch ➤ Energy spectrum of scattered e + /e − depends on polarisation ➤ Magnetic chicane: energy distibution → spacial distribution ( ∼ 20 cm wide) ⇒ Measure number of e + /e − per detector channel Dipole Dipole Dipole Dipole 45.6 GeV Laser IP e ⁺ /e ⁻ 250 GeV IP Č erenkov detector 24 cm total length: ~75 m Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 2/19
ILC Polarimetry Design Application Conclusion Measurement principle. Compton rate asymmetry is proportional to the beam polarisation: 5.0 [mbarn/GeV] 4.0 Compton 3.0 σ 2.0 λ P e = + 1 (same) λ P e = − 1 1.0 (opposite) 0.0 0 50 100 150 200 250 Energy of the Compton−scattered electrons [GeV] Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 3/19
ILC Polarimetry Design Application Conclusion Measurement principle. Compton rate asymmetry is proportional to the beam polarisation: 5.0 [mbarn/GeV] P ∝ Asymmetry 4.0 A = N + − N − N + + N − Compton 3.0 σ 2.0 λ P e = + 1 (same) λ P e = − 1 1.0 (opposite) 0.0 0 50 100 150 200 250 Energy of the Compton−scattered electrons [GeV] Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 3/19
ILC Polarimetry Design Application Conclusion Detector requirements. Requirements for the Compton electron detector behind the magnetic chicane: ➤ read out signals of 1000-2000 Compton electrons (25-250 GeV) every bunch crossing ➤ either very linear response or “counting“ electrons ➤ alignment to ∼ 100 µm and ∼ 1 mrad ➤ suppression of background from low energetic particles Simple, robust, fast: Cherenkov detectors ➤ Cherenkov light emission proportional to number of electrons ➤ independent of electron energy (once relativistic) ➤ successfully used in best polarimeter so far at SLC Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 4/19
ILC Polarimetry Design Application Conclusion Detector options. Goal: total uncertainty ∆ P / P ≈ 0 . 25 %, of which ➤ laser: 0 . 1 % ➤ analysing power (i.e. asymmetry at P = 1 ): 0 . 2 % ⇒ Cherenkov detector design ⇒ ➤ detector linearity: 0 . 1 % photodetector calibration LED calibration Gas Cherenkov detector system Photomultiplier 2-channel prototype: Č erenkov tilt alignment of 0 . 1°reached photons [JINST 7, P01019 (2012)] gas-filled e ⁻ beam Al-channel Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 5/19
ILC Polarimetry Design Application Conclusion Detector options. Goal: total uncertainty ∆ P / P ≈ 0 . 25 %, of which ➤ laser: 0 . 1 % ➤ analysing power (i.e. asymmetry at P = 1 ): 0 . 2 % Cherenkov detector design ⇒ ➤ detector linearity: 0 . 1 % ⇒ photodetector calibration LED driver developed for differential calibration method → fulfils requirements [thesis B. Vormwald] Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 5/19
ILC Polarimetry Design Application Conclusion Detector options. Goal: total uncertainty ∆ P / P ≈ 0 . 25 %, of which ➤ laser: 0 . 1 % ➤ analysing power (i.e. asymmetry at P = 1 ): 0 . 2 % ⇒ Cherenkov detector design ⇒ ➤ detector linearity: 0 . 1 % photodetector calibration In the scope of the BMBF spin optimisation project: Alternate detector concept studied: Quartz as Cherenkov material. Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 5/19
ILC Polarimetry Design Application Conclusion Polarimetry at the ILC Quarz detector design Detector application Summary and Outlook Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 6/19
ILC Polarimetry Design Application Conclusion Why quartz? Self-calibrationg detector. For a large enough number of photons per Compton electron, e.g. for 15 e − per detector channel: � 200 photons per e − resolution of single peaks possible ⇒ self-calibration! number of events PMT gain N ⁻ N ⁺ detector signal Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 6/19
ILC Polarimetry Design Application Conclusion Why quartz? Self-calibrationg detector. For a large enough number of photons per Compton electron, e.g. for 15 e − per detector channel: � 200 photons per e − resolution of single peaks possible ⇒ self-calibration! a) less Compton electrons: smaller channels b) higher light yield: quartz as Cherenkov material Properties of fused silica ◮ refractive index n ≈ 1.45 (for comparision: n ( C 4 F 10 ) = 1 . 0014) ◮ Cherenkov angle θ c ≈ 46 ◦ ◮ Cherenkov threshold E thr ≈ 0 . 9 MeV Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 6/19
ILC Polarimetry Design Application Conclusion GEANT4 Simulation. Multiple quartz bars / channels (rotated → more space for photomultipliers and read-out) Side view PMT PMT quartz block e ⁺ /e ⁻ beam angle e ⁺ /e ⁻ Cherenkov photons top view PMT e ⁺ /e ⁻ Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 7/19
Side view PMT e ⁺ /e ⁻ top view PMT e ⁺ /e ⁻ ILC Polarimetry Design Application Conclusion GEANT4 Simulation. Multiple quartz bars / channels (rotated → more space for photomultipliers and read-out) Implementation in GEANT4: PMT ◮ Fused silica blocks quartz block ◮ photomultiplier (PMT) window and cathode beam angle ◮ coupled with optical e ⁺ /e ⁻ Cherenkov grease photons ◮ different surface properties Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 7/19
ILC Polarimetry Design Application Conclusion Detector geometry. Simulation of different incident angles, channel dimensions, ... Number of photon hits on PMT with different detector geometries (length, height and angle chosen so that distance between electrons and PMT is 3 cm) : photon hits for different simulated geometries y α 60 2500 55 2000 50 1500 45 1000 40 35 500 30 0 0 20 40 60 80 100 120 140 quarz halflength [mm] Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 8/19
ILC Polarimetry Design Application Conclusion Quartz prototype. Photo- 18 mm Quartz prototype with four channels: cathode Quartz ◮ channels: quartz bars channels (5 mm × 18 mm × 100 mm) ◮ using photomultipliers with four anodes (two per quartz bar) ◮ angle w.r.t. beam axis: adjustable in 0 . 5°steps quartz bars adjustable adjustable angle angle PMT ⇒ Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 9/19
ILC Polarimetry Design Application Conclusion Quartz prototype. Quartz prototype with four channels: ⇒ DESY II Testbeam 22.04. - 05.05.2013 Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 9/19
ILC Polarimetry Design Application Conclusion Polarimetry at the ILC Quarz detector design Detector application Summary and Outlook Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 10/19
ILC Polarimetry Design Application Conclusion DESY Testbeam 2013. Goals for the testbeam: ◮ Test detector signal for single electrons ◮ Compare light output to expectations ◮ Study detector response for different angles and positions Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 10/19
ILC Polarimetry Design Application Conclusion DESY Testbeam: Setup. ◮ Angle of the quartz bars: controlled with stepping motor ◮ Movement of the whole detector: used testbeam x-y table t i n y U c i g o L r e Trigger g Scintillators g i r T z x Pulse Generator Signal Beam x-y table Delay C D e Q t a G ◮ Trigger: coincidence of four scintillators ◮ Generate QDC (charge digitizer) gate on trigger signal ◮ Delay photomultiplier signal long enough to fall inside gate Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 11/19
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