Symmetric Moeller Luminosity Monitor

Status Report

Frank Maas

Institut für Kernphysik

Johannes Gutenberg-Universität Mainz

Symmetric Moeller Luminosity Monitor

New Team Members

Roberto Benito Perez (PostDoc, from November 1)

Dmitry Khaneft (PhD, Hardware/Chrystals)

Eric Göbel (Diploma Student, from November 15)

Symmetric Moeller Luminosity Monitor

Principle: Based on (symmetric)

Moeller (e-e-) and Bhabha (e+e-) scattering,

up to 400 kHz rate

Symmetric Moeller Luminosity Monitor

Mechanics

Symmetric Moeller Luminosity Monitor

PbF2 crystals used in the A4-Experiment at MAMI

Symmetric Moeller Luminosity Monitor

PbF2-Modules: precalibrated, transit time diff. < 1ns

PbF2 crystals

Symmetric Moeller Luminosity Monitor

•  Two Arrays of PbF2 crystals with PMT at small scattering angles

•  Location: Between BLAST coils and beam line quadrupole

=> Tight space limitations

=> Careful consideration of magnetic fringe fields

New Magnetic Simulations

10e6

10e4

10e2

1

10e-2

10e-

Gauss

Field Inside the Box < 0,01 Gauss: More than OK

Lead Brick Shield (~70Kg) ‏

Accurate Rails

System

Collimator (~25Kg) ‏

Beam

Installation into beam line

Distance to beam is adjustable Setup in the beam line

•  Mechanical design finished •  Parts are in the Institute's workshop

Installation into beam line

Setup in the beam line

•  Mechanical design finished •  Parts are in the Institute's workshop

Optimization of collimator design

by MC studies

Symmetric Moeller Luminosity Monitor

• Mechanics:

Crystal Modules: holder mechanically modified,

gluing starts coming week, need to be tested after

Need light fiber system for stability monitoring

• Mechanical Support:

Parts in Institute Workshop

Technical Drawings in preparation: Movable tables on rails

Potentiometer for position readout

Symmetric Moeller Luminosity Monitor

Electronics

Symmetric Moeller Luminosity Monitor

Electronics: Analogue Sum, 1 GHz analogue Bandwidh,

50 MHz histogramming, dead time: 20ns

Data aqcuisition principle

Three types of triggers:

•  Trigger on Lumi A

•  Trigger on Lumi B

•  Trigger on Lumi A&B

PVA4 trigger cards ready for use

Data aqcuisition principle More in detail:

Symmetric Moeller Luminosity Monitor

Electronics:

All parts are in electronics workshop

Probably ready by end of December 2010

Symmetric Moeller Luminosity Monitor

Simulations

Optimization of collimator design (simulation) ‏

Kilian Lessmeier and Yue Ma: Definition of Geometry

Lead Brick Shield (~70Kg) ‏

Accurate Rails

System

Collimator (~25Kg) ‏

Beam

Optimization of collimator design (simulation) ‏

•  Example: Energy deposit inside PbF2 crystals from Moeller/Bhaba events for a certain collimator thickness/diameter

•  Peak width dominated by energy spread of Moeller/Bhaba events over the detector acceptance

Region I Region II

•  Variation of the collimator thickness at fixed diameter

•  Variation of collimator diameter at fix thickness

Optimization of collimator design (simulation) ‏

Quality parameter

Optimal value Optimal value

Symmetric Moeller Luminosity Monitor

Simulations:

Refine collimator optimisation

Studies of cuts in energy spectrum on luminosity signal

Detailed study of systematics

Include two-photon effects in Moeller and Bhabha-scattering too.

Symmetric Moeller Luminosity Monitor

“Production” of crystals starts soon

Electronics ready by end of December

Collimator and Systematics needs more studies

First system ready for test beam in February

Very reluctant to put PbF2-crystals into ring without

good knowledge of potentially “dangerous” beam properties.