Muon Analysis

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Interface Overview

This interface is used to analyse the data collected on Muon instruments. The interface can be accessed from the main menu of MantidPlot, in Interfaces → Muon → Muon Analysis. For sample datasets, please visit Muon - Downloads.

Home

The Home tab is the MuonAnalysis entry-point. It allows you to load the data, set some basic loading and plotting parameters and plot the data.

In most cases, the initial settings should be fine and the grouping loaded from the data file should be sensible, but these can be easily adjusted using the GroupingOptions and Settings tabs.

Instrument

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1 Instrument Selection of instrument that the experiments were run on. It is an advantage if an Instrument Definition File ( IDF) is available for the instrument selection.
2 Time Zero Time zero value (\mu s). Any bins before that time will be discarded. If From datafile is checked, the value stored in the loaded Muon data file is used.
3 First Good Data Time of the first good data (\mu s). If Time Axis is set appropriately on the Settings tab then it is used as a start value for the X-axis. If From datafile is checked, the value stored in the loaded Muon data file is used.
4 Dead Time Correction

The type of Dead Time Correction to apply to the loaded file. Available choices:

  • None. Don’t apply the correction.
  • From Data File. Use Dead Time table stored in the loaded Muon data file.
  • From Disk. Specify a custom Nexus file that has a Dead Time table. If this is selected, a Dead Time File text box will be shown so you can specify the file or browse to its location.
5 Dead Time File If Dead Time Correction is set to From Disk, you can choose a Nexus file which contains a table with Dead Times, and will be applied to the loaded data file.

Data Files

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1 Load current run Attempt to load current run for the instrument specified (ISIS only)
2 Load current run Specify a data file by typing a run number (for the instrument selected from the Instrument drop-down) or use the Browse button to select a data file. Multiple runs/files can be specified here, in which case they will all be summed to form a single data set. Files should be in the NeXus format (PSI bin files can be converted using the program any2many). Both version 1 and 2 of the muon NeXus data format are supported.
3 Previous/next run Open next or previous run in the series.

Detector Grouping

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1 Group/ Group Pair A group or a pair which will be plotted.
2 Alpha This text box is only visible if a pair is selected. It corresponds to the pair alpha value used for asymmetry calculation. See AsymmetryCalc for a broader explanation. The value is taken from the Pair table on the Grouping Options tab for the selected pair and can be modified there only.
3 Periods Use the two text boxes to select the combination of periods you would like to plot. Each holds a comma-separated list of periods, and the periods in the list on the right will be subtracted from those on the left. For example, to plot the combination (1+2)-(3+4), enter “1,2” in the left-hand box and “3,4” in the right hand box. For single period data only the first box will be active.

Plot Data

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1 Plot Type

Type of the plot. Available choices are:

  • AsymmetryCalc For pairs- the result of AsymmetryCalc for the pair groups. For groups- the result of RemoveExpDecay applied to the group.
  • Counts (groups only). Pure counts of the selected group.
  • Logarithm groups only. Pure counts of the selected group on a logarithmic scale.
2 Plot Plots the loaded data using the parameters set.

Run Information etc.

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1 Run Information Information about the loaded run. See Run for the list of parameters which are looked up in the data files.
2 Connected plot The name of the workspace produced for the last plot, i.e. “connected” to the interface. It will be used for fitting etc.
3 Manage Directories Opens the ManageUserDirectories dialog.

Grouping Options

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The Grouping Options tab allows you to set up detector grouping, which will be applied to the loaded data.

There are two concepts we use when dealing with detector grouping of Muon instruments:

  • Group. A group is essentially a list of detectors. When grouping, the counts of all the detectors in the list are summed together. This makes the group appear as a single detector, represented by a single spectra in the resulting workspace. See GroupDetectors and MuonGroupDetectors for more details.
  • Pair. A pair connects together two groups and has an alpha value assigned to it. It is useful for quickly specifying the parameters of asymmetry calculations.

Essentially, this tab allows you to create/modify groups and form pairs out of them. There are basic load/save functions for using predefined instrument groupings and for saving custom ones. Predefined instrument groupings are usually stored in the Instrument/Grouping directory of the Mantid install directory.

This tab also provides some basic plotting functionality, which allows you to experiment with groupings and plot the results without any additional effort.

Controls and description

1 Load Grouping File Opens a file browser window. Use it to select a grouping file for loading.
2 Save Grouping Opens a file browser window. Use it to select a file to save a grouping to.
3 Clear Grouping Clear group and pair tables.
4 Description Description of the current grouping. Is loaded/saved together with the grouping information.

Group table

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1 Group (Name) column The name of the group. Should be unique.
2 Detector IDs column A list of detectors associated with the group. One detector might be in multiple groups. Ranges are allowed, e.g. “1,2-5,7-9,11” represents detectors with IDs 1,2,3,4,5,7,8,9 and 11
3 Ndet column Number of detectors associated with the group. This column is not editable and is updated automatically when the list of group detectors changes.
4 Plot type What kind of plot to produce when Plot button is pressed. See the Home page for an explanation of available plot types.
5 Plot Plots the group highlighted most recently.

Pair table

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1 Group Pair (Name) column Name of the pair. Should be unique.
2 Forward (Group name) column The first (“forward”) group of the pair.
3 Backward (Group name) column The second (“backward”) group of the pair.
4 Alpha column Alpha value of the pair.
5 Guess alpha Guess a new alpha value for the pair highlighted most recently. Uses AlphaCalc (AlphaCalc) to do that.
6 Plot Type What kind of plot to produce when the Plot button is pressed. See the Home page for an explanation of available plot types.
7 Plot Plots the pair highlighted most recently

Data Analysis

This tab is designed for the user to make a fit against the data just plotted. Since Mantid 3.8, this tab has been enhanced to include fits of multiple datasets at once.

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Fit Function

The tab is divided into three sections vertically. The uppermost of these is the Fit Function section, which is a FunctionBrowser just like in the General/Multi dataset fitting interface (and numerous other places in Mantid). Functions can be added by right-clicking. If more space is needed, this section can be expanded by dragging its lower edge downwards.

The function browser has three columns - property, value and global. The values shown are those of the currently selected/plotted dataset. The global column contains a checkbox for each function parameter which, when checked, sets this parameter to be shared between all fits.

Parameters can be fixed, tied and constrained by right-clicking. In addition, just as in the general multi dataset fitting interface, when highlighting a non-global function parameter, a small button will appear next to its value. This button will open the “Edit local parameter values” dialog, which offers greater control of function parameters for each dataset.

Data

The central section of the tab is the data selector, which controls the dataset(s) that will be fitted. By default, this will be a single dataset, the same as the data loaded on the Home tab. The dataset(s) can be changed here and, if more than one is selected, they will all be fitted simultaneously.

For a multi-dataset fit, the “Label” box is enabled. This allows the user to input a label for the simultaneous fit.

The drop-down list shows all datasets currently selected, and the left and right buttons cycle through them. The currently selected dataset has its parameters shown in the Fit Function (upper) widget, and will be plotted.

Fits can be done across runs, groups, periods or all three. From left to right, the options to select are:

Runs

A single run, or range (e.g. 15189-91, 15193) can be typed into the box here. The radio buttons below control whether the runs should be co-added together or fitted separately in a simultaneous fit. It is also possible to adjust the start and end time here.

Groups

There is a checkbox in this section for each group defined in the GroupingOptions tab. One or multiple groups can be selected.

Periods

There is a checkbox in this section for each period of the data. (This section is only visible for multi-period data). One or multiple periods can be selected. In addition, the “Combination” option can be used to fit a sum or difference of periods.

Examples/Use cases

  1. Individual fit:
    • One run selected in the box, or a range with the “Co-add” option set.
    • One group selected
    • (One period selected, if multi-period)
    • In this case the “global” option is meaningless as only one dataset will be fitted.
    • Example: MUSR15189, group long, period 1
  2. Simultaneous fit across runs:
    • Range or selection of runs in box, with “Simultaneous” option set.
    • One group selected
    • (One period selected)
    • Example: MUSR{15189, 15190, 15191}, group long, period 1
  3. Simultaneous fit across groups or periods:
    • One run selected in the box, or a range with the “Co-add” option set.
    • Multiple groups or periods selected
    • Example: MUSR15189, groups {fwd, bwd}, period 1
  4. Sequential fit of simultaneous fits:
    • One run only selected in the box.
    • Multiple groups or periods selected
    • Under “Fit”, click “Sequential fit” and type a range of runs in the dialog. (See SequentialFitting below) For each run in turn, a simultaneous fit of the selected groups/periods will be performed.
  5. Multiple options
    • It is, of course, possible to select several runs, groups, periods all at once and a simultaneous fit will be performed across all the selected datasets.
    • Example: MUSR{15189, 15190, 15191}, groups {fwd, bwd}, periods {1, 2}: 12 datasets in all.

Options

The bottom of the tab contains selected fit options that can be adjusted, just as elsewhere in Mantid. The only option specific to the Muon Analysis interface is Fit To Raw Data. When this option is set to True, the fitting process is done using the raw (unbinned) data, even if the DataBinning is set.

Compatibility mode

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To revert to the interface as it was pre-Mantid 3.8, use the checkbox for “Compatibility mode” on the Settings tab.

In this case, the only thing that this tab will contain is a specialised version of the Fit Property Browser. When the tab is open, this fit property browser is used by default within MantidPlot.

Note that, in “Compatibility mode”, simultaneous fits are not possible. The intention is that this mode could be useful for users who are accustomed to the existing UI, or if a bug is found in the new UI.

Sequential fitting

In MantidPlot 3.1 a specialized sequential fitting dialog for MuonAnalysis was introduced. It allows users to fit various data sets to the chosen fit model, applying all of the interface settings.

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The dialog can be opened from the Fit menu in FitSequential Fit.

1 Runs

A list of run data files to fit. Two types of input are accepted:

  • List of files on the disk separated by comma. These can be specified using the Browse button.
  • Run numbers separated by comma. Specific files will then be searched in the archive for the instrument selected on the interface. Ranges are allowed, e.g. “15189-15199”.
2 Label Text label to use for the sequential fit. It is used to find the results on the ResultsTable tab. The resulting workspace group and the fit-result workspaces will have the label in their names.
3 Parameters This option specifies the initial fit parameters for every fit. Choices should be self-explanatory.
4 Progress Shows the progress of the fit.
5 Start/stop button Starts a new fit or stops the current one.
6 Diagnosis table Displays the intermediate results of the fit. This includes run number, fit quality (see OutputChi2overDoF in Fit) and fitted values of all the parameters.

After the options have been set and the Start button has been pressed, the dialog goes through every data file and does the following:

  1. Loads the file
  2. Applies all of the settings as set on the interface, e.g. dead time correction, grouping, binning.
  3. Runs the Fit algorithm using the fit model specified in the Fit Property Browser on this tab.
  4. Puts the fit-result workspaces inside the MuonSeqFit_%LABEL% group.

After that’s done, you can retrieve the results in two ways:

  • Go to the ResultsTable tab and export fitted parameters as a table.
  • Use the workspaces in the MuonSeqFit_%LABEL% group to plot the fitted curves.

Results Table

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This tab allows users to export the fitting results alongside log values as a table.

Values

The table contains a list of log values present in all of the workspaces in the Fitting results table. The ones selected will be included in the results table.

In the case of start and end times (run_start and run_end), the option is given to write these either as text or number. The text option gives an ISO- formatted string (eg. 2016-07-06T10:10:34) and the numeric option gives the time as a number of seconds. Zero seconds is taken as the start time of the first run in the selected set.

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Fitting Results

This table contains a list of fitted workspaces. You can choose whether you want to see individual fits only, or a specific sequential (see SequentialFitting ) or simultaneous (see DataAnalysis) fit label.

Fitted parameters of the selected workspaces will be added to the results table.

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Workspaces might be coloured differently. Workspaces of different colours have different fitting models and therefore couldn’t be included in the same Results table. (If looking at simultaneous fits, different colours could also indicate that the fits had different numbers of datasets).

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As well as selecting workspaces, the fourth radio button - “Multiple” - can be used to create a table of multiple simultaneous fits, one row per label. In such a table, each global parameter gets one column and local parameters get one column per dataset.

Table

This allows you to specify the name of the resulting table and create it using the log values and workspaces you’ve selected.

Settings

This tab allows users to specify various plotting style options, loaded data binning and other general options.

Data Plot Style

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These options control the style of the plot. They will be applied to all new plots. The currently connected plot (if any) is updated as well.

1 Connect Points

Option for how the points will be represented on the plot:

  • Scatter. Data points only.
  • Line + symbol. Data points connected by a line.
  • Line. A line without data points.
2 Time axis

Type of the start value of the X-axis:

  • Start at First Good Data. Uses the First Good Data value from the Home tab.
  • Start at Time Zero. Uses 0. Worth noting that workspaces will be cropped according to the Time Zero value on the Home (HomeInstrument) tab, which means that X-value of 0 will essentially be equal to the Time Zero value.
  • Custom Value. Uses the specified value.
3 Start First value of the X-axis (\mu s).
4 Finish Last value of the X-axis (\mu s). If empty, the last available value is used.
5 Minimum Minimum value on the Y-axis. If empty, is determined automatically.
6 Maximum Maximum value on the Y-axis. If empty, is determined automatically.
7 Autoscale If checked, the values of Minimum and Maximum are determined automatically based on the max/min values of the data.
8 Show error bars If checked, the curves will have error bars attached to them.

Data Binning

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1 Bin size Display the size of the bin in the currently loaded data. This is usually 0.016 \mu s for Muon instruments.
2 Binning type

What type of binning is applied to the loaded data:

  • None. No binning is applied - raw data.
  • Fixed. Binning with fixed steps.
  • Variable. Binning with varying steps.
3 Binning parameters
  • For fixed binning: number of bins in a single step. For example, if data is collected in bins of size 0.016 and we specify 5 here, then the data will be re-binned using a bin size of 0.08.
  • For variable binning: see the Params property of Rebin. Note Rebin is executed with FullBinsOnly=True.

General

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1 Plot Creation
  • Auto-Update. When settings are changed on the interface, the new plot is created automatically.
  • Overwrite. When plotting, if the plot of the same type exists already, it is overwritten instead of creating a new one.
  • Auto-Update + Overwrite. Both above settings at the same time
  • None. None of the settings
2 New plot policy
  • Use previous window. Each new plot will be drawn in the same window. By default, the previous fit curve will remain on the graph when the run is changed - the number of curves to keep can be adjusted here (set to 0 to always clear previous fits). The “clear fit curves” option on the Data Analysis tab will clear any fit curves present.
  • Create new window. When plotting a new run, it is plotted in a new window each time.
3 Hide Toolbars If enabled, opening the interface up hides the MantidPlot toolbars. This is useful on smaller screens.
4 Compatibility mode If enabled, the DataAnalysis tab will be reverted to the UI it had in previous versions of Mantid (pre-3.8). Note that simultaneous fits are not possible in this mode.

Feedback & Comments

If you have any questions or comments about this interface or this help page, please contact the Mantid team or the Muon group.

Categories: Interfaces | Muon