A Quartz Cherenkov Detector for Polarimetry at the ILC. Mainz, - - PowerPoint PPT Presentation

A Quartz Cherenkov Detector for Polarimetry at the ILC.

Jenny List, Annika Vauth

Mainz, 13.02.2014

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

1650m 1 5 m

e⁻ e⁺

e⁺e⁻ collisions ③ upstream polarimeter ① downstream polarimeter ① spin tracking ②

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(103) 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

24 cm 45.6 GeV Laser IP Dipole Dipole Dipole Dipole total length: ~75 m IP e⁺/e⁻ Čerenkov detector 250 GeV

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:

50 100 150 200 250 0.0 1.0 2.0 3.0 4.0 5.0

σ

Energy of the Compton−scattered electrons [GeV] [mbarn/GeV] Compton λ Pe = +1

(same)

λ Pe = −1

(opposite) 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:

50 100 150 200 250 0.0 1.0 2.0 3.0 4.0 5.0

σ

Energy of the Compton−scattered electrons [GeV] [mbarn/GeV] Compton λ Pe = +1

(same)

λ Pe = −1

(opposite)

P ∝ Asymmetry A = N+−N−

N++N−

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 Gas Cherenkov detector 2-channel prototype: tilt alignment of 0.1°reached [JINST 7, P01019 (2012)]

e⁻ beam Čerenkov photons Photomultiplier LED calibration system gas-filled 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!

PMT gain

detector signal number of events N⁻ N⁺

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(C4F10) = 1.0014) ◮ Cherenkov angle θc ≈ 46◦ ◮ Cherenkov threshold Ethr ≈ 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)

e⁺/e⁻ e⁺/e⁻ PMT Side view top view PMT

Cherenkov photons quartz block PMT e⁺/e⁻ beam angle

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 7/19

ILC Polarimetry Design Application Conclusion

GEANT4 Simulation.

Multiple quartz bars / channels (rotated → more space for photomultipliers and read-out)

e⁺/e⁻ e⁺/e⁻ PMT Side view top view PMT

Implementation in GEANT4:

◮ Fused silica blocks ◮ photomultiplier (PMT)

window and cathode

◮ coupled with optical

grease

◮ different surface

properties

Cherenkov photons quartz block PMT e⁺/e⁻ beam angle

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):

quarz halflength [mm] 20 40 60 80 100 120 140

y

α 30 35 40 45 50 55 60 500 1000 1500 2000 2500

photon hits for different simulated geometries

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 8/19

ILC Polarimetry Design Application Conclusion

Quartz prototype.

Quartz prototype with four channels:

quartz bars PMT adjustable angle adjustable angle

Quartz channels Photo- cathode 18 mm

◮ channels: quartz bars

(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 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

Beam Trigger Scintillators T r i g g e r L

• g

i c U n i t Pulse Generator z x y Q D C Delay Signal G a t e x-y table

◮ 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

ILC Polarimetry Design Application Conclusion

Number of photons (data).

Cherenkov photons e⁻

Anode 2 Anode 1

run 0875

With the gain / HV settings used: 1 photon ≈ 1.5 QDC bins Predicted by simulation: ∼ 40 photons per anode

QDC bins above pedestal

50 100 150 200

events

500 1000 1500 2000

Example: QDC signal for both anodes on one quartz channel top anode bottom anode

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 12/19

ILC Polarimetry Design Application Conclusion

X-position scan (data).

Cherenkov photons e⁻

Anode 2 Anode 1

detector x-position [mm]

60 70 80 90 100

signal events

100 200 300 3 10 ×

◮ x=5 mm wide channels ◮ scan across x-direction → determine beam spot size

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 13/19

ILC Polarimetry Design Application Conclusion

X-position scan (data).

Cherenkov photons e⁻

Anode 2 Anode 1

detector x-position [mm]

60 70 80 90 100

signal events

100 200 300 3 10 ×

35 mm ~13 mm

varied in simulation:

→ beam profile with

σ ≈ 4.7 mm

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 13/19

ILC Polarimetry Design Application Conclusion

Angle scan (simulation).

Cherenkov photons e⁻

Anode 2 Anode 1

Use two anodes per channel for alignment?

350 700

combined anode 2 anode 1 angle to incident electron photon hits

30 40 50 60

Ratio between anodes of a channel angle dependent

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 14/19

ILC Polarimetry Design Application Conclusion

Angle scan (data).

Cherenkov photons e⁻

Anode 2 Anode 1

Qualitatively similar behaviour as in the simulation

angle to incident electron

30 40 50 60

6

electrons / 10

50 100 150

Anode 2 Anode 1 Combined

→ Comparison with simulation to determine tilts/shifts of detector:

work in progress

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 15/19

ILC Polarimetry Design Application Conclusion

Multi-electron spectra (simulation).

How many Compton electrons per channel would be possible? Simulation with 200 detected photons per Compton electron

(from Compton electrons to spectrum at the charge-to-digital converter (QDC))

QDC bin 500 1000 1500 2000 2500 entries 50 100 150 200

input: 14 Compton electrons 100 photons per C. e⁻ fitted: 14.01 ± 0.01 C. e⁻

→ for ≤20 electrons majority of single peaks can be separated

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 16/19

ILC Polarimetry Design Application Conclusion

Comparison to requirements (simulation).

Simulated polarisation measurement:

(80 % polarsation, 3 mm wide detector channels)

detector channel 20 40 60 mean electrons / event 10 20

Simulation: 60 channels 3 mm width 80% polarisation

laser left laser right

→ nearly all channels ≤20 electrons.

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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 | 18/19

ILC Polarimetry Design Application Conclusion

Summary and Outlook (1).

Quartz detector:

◮ Option for polarimeter detector: quartz as Cherenkov medium ◮ Prototype designed, constructed & and tested at DESY II testbeam:

◮ Test detector signal for single electrons

• ◮ Compare light output to expectations

()

◮ Study detector response for different angles

and positions

()

Qualitative agreement with simulation, more detailed alignment work in progress

Outlook:

◮ Study application on full polarisation measurement

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 18/19

ILC Polarimetry Design Application Conclusion

Summary and Outlook (2).

Compton polarimetry at ILC: Precision goal for ILC polarimetry: ∆P/P ≈ 0.25% Needs combination of:

◮ scale calibration from e+e− collision data ◮ spin tracking and understanding of collision effects ◮ upstream (UP) and downstream (DP) polarimeters

◮ UP: time resolution ◮ DP: collision effects ◮ combined: cross-check, lumi-weighted polarisation @ IP

Outlook:

◮ site specific studies ◮ detectors: prototypes → full-scale, DAQ, ...

Quartz Detector for ILC Polarimetry | A. Vauth | Mainz, 13.02.14 | 19/19