QwCompton

Files
file	QwSIS3320_Accumulator.cc
	Implementation of the SIS3320 sampling ADC accumulator.
file	QwSIS3320_Channel.cc
	Implementation of the decoding of SIS3320 sampling ADC data.
file	QwSIS3320_LogicalAccumulator.cc
	Implementation of the SIS3320 sampling ADC accumulator.
file	QwSIS3320_Samples.cc
	Implementation of the SIS3320 sampling ADC samples.
file	QwCompton.cc
	Compton data analysis.
file	QwComptonPhotonDetector.cc
	Implementation of the analysis of Compton photon detector data.

Data Structures
class	QwSIS3320_Accumulator
	SIS3320 sampling ADC accumulator. More...
class	QwSIS3320_Channel
	Class for the decoding of the SIS3320 sampling ADC data. More...
class	QwSIS3320_LogicalAccumulator
	SIS3320 sampling ADC accumulator. More...
class	QwSIS3320_Samples
	SIS3320 sampling ADC samples. More...
class	QwComptonElectronDetector
	Class for the analysis of Compton electron detector data. More...
class	QwComptonPhotonDetector
	Class for the analysis of Compton photon detector data. More...

Detailed Description

Inclusion of the Compton polarimeter in the Qweak framework

Although an existing analysis framework, developed at CMU, was available (and has been successfully used for beam tests at HIgS), we decided that it would be easier to incorporate the Compton polarimeter analysis in the Qweak framework. The main advantages are that parity-type operations are readily available, that delayed helicity reporting is handled transparently to the user (i.e. the detector subsystem analysis writer), and that the particulars of the CODA data structure are abstracted away completely.

Analysis philosophy

In the Qweak analysis code all variables (i.e. electronic module channels) can be 'added' and 'subtracted' between helicity states. This makes it easy to get an asymmetry on a helicity multiplet level, but also to get asymmetries or sums between different variables.

It might seem funny at first sight that there are functions that define the sum, difference or ratio of two Compton detectors. But, after a moment's thought, that is exactly what you need when you calculate an asymmetry over a helicity multiplet:

In this case you perform all three of these operations between the data collected during the different beam helicity states (or alternatively, between the two laser helicity states, which could give us access to systematic differences between the two beam helicity states).

The details of how this addition and subtraction is performed have to be specified by the subsystem developer. For example, in the case of the QwComptonPhotonDetector, each helicity window consists of a varying number of sampled photon detector pulses. The goal could be to use the above formula to get an 'asymmety spectrum' of the pulses. In this case, one would have to take care not to add 10 positive helicity events and only 8 negative helicity events. The normalization has to be included in the addition and subtraction. The same thing is true in accumulator mode, where the zeroth accumulator (sample counter) should be used to normalize.

Photon detector subsystem

The only subsystem of the Compton polarimeter that has been implemented (partially) at the moment is the photon detector. The sampling ADC, and integrating ADC/TDC have CODA readout support in the Qweak analysis code, making it easy to take asymmetries of different helicity events.

The main difficulty in the code will be to access the laser helicity state through EPICS.

Electron detector subsystem

The electron detector has not been implemented yet. The GEM detectors in region 1 of Qweak use the same V1495 boards and are partially implemented.