Glossary ======== A short reference for the μSR terms and the Asymmetry-specific vocabulary used throughout these pages. The definitions are deliberately brief; where a concept has its own reference page, the entry points there for the full treatment. For a narrative introduction rather than isolated definitions, read the :doc:`musr_primer`. .. glossary:: :sorted: asymmetry The normalised difference between two opposed detector groups, :math:`A(t) = (F - \alpha B)/(F + \alpha B)`, which tracks the projection of the muon-spin polarisation onto the detector axis. It is the primary observable in most μSR analyses and the quantity Asymmetry fits by default. alpha α The calibration constant that balances the forward and backward detector groups, correcting for their unequal efficiency and solid angle. It is usually estimated from a transverse-field run in which the true asymmetry oscillates symmetrically about zero. See :doc:`/reference/data_reduction/alpha_calibration`. beta β The intrinsic-asymmetry balance :math:`\beta = A_{0,b}/A_{0,f}` from musrfit's asymmetry fit (fit type 2): it corrects for the two detector groups observing different asymmetry *amplitudes* (solid-angle and absorption effects), entering the corrected asymmetry as :math:`A = (F - \alpha B)/(\beta F + \alpha B)`. Unlike :math:`\alpha` it is invisible to count totals, so it cannot be estimated from count ratios; it is entered as a fixed value in the Grouping window's **β (asymmetry balance)** card and defaults to 1. ALC avoided level crossing A resonance seen in a longitudinal-field scan when a muon and a neighbouring nuclear (or electronic) spin level are brought close in energy, allowing polarisation to transfer and producing a dip or step in the time-integrated asymmetry. Asymmetry builds ALC scans in the :doc:`Integral scan mode `. Knight shift The small fractional shift of the muon precession frequency, relative to the frequency in a reference material, caused by the local field from polarised conduction electrons or a paramagnetic host. Its temperature or angle dependence probes the local susceptibility and the muon site; see :ref:`knight-shift`. Kubo–Toyabe KT The depolarisation function for muons in a random, quasi-static distribution of local fields — the canonical zero-field lineshape, with a characteristic dip and recovery to a one-third tail. Static and dynamic variants are documented at :ref:`fit-kubo-toyabe`. muonium Mu The bound state of a positive muon and an electron, :math:`\mathrm{Mu} = \mu^{+}e^{-}` — a light isotope of hydrogen whose spin dynamics are governed by the muon–electron hyperfine coupling. See :ref:`fit-muonium`. F–μ–F A muon bound between two fluorine nuclei, whose entangled dipolar three-spin state produces a distinctive, coherent zero-field oscillation that fingerprints the muon stopping site in a fluoride. See :ref:`fit-nuclear-dipolar`. RRF rotating reference frame A display transform that demodulates a fast transverse-field precession down to a slow beat about a chosen reference frequency, making the relaxation envelope legible without changing the fitted physics. See :doc:`/reference/rotating_frame`. TF transverse field A geometry in which the applied field is perpendicular to the initial muon-spin direction, so the spins precess and the asymmetry oscillates; the standard configuration for measuring precession frequencies and α. ZF zero field A geometry with no applied field, so the muon senses only the internal fields of the sample — the configuration for detecting spontaneous magnetic order and nuclear-dipolar structure. LF longitudinal field A geometry in which the applied field is parallel to the initial muon-spin direction, used to decouple the spin from static internal fields and thereby separate static from dynamic behaviour. t0 time-zero The bin at which the muons arrive and the polarisation is maximal, from which the analysis clock is measured. An error in t0 biases early-time amplitudes and phases, so Asymmetry locates it explicitly; see :doc:`/reference/data_reduction/t0_search`. dead time The short interval after a detected event during which a detector cannot register a second one, which suppresses counts at high rate. Asymmetry corrects for dead time during reduction, using the values recorded alongside the detector grouping; see :doc:`/reference/detector_grouping`. good-bin range The span of time bins retained for analysis — after t0 and before the counts fall into noise — excluding the pre-pulse baseline and the exhausted tail. detector group A set of physical detectors summed together into one forward or backward histogram. The grouping defines which detectors oppose which and is where α and dead time are recorded; see :doc:`/reference/detector_grouping`. apodisation Multiplying the time signal by a smooth window before the Fourier transform, which suppresses the ringing (spectral leakage) that an abrupt cut-off would introduce, at the cost of some broadening. See :doc:`/reference/fourier_analysis`. MaxEnt maximum entropy A spectral estimator that reconstructs the frequency spectrum as the least structured distribution consistent with the data, giving sharper lines than a plain Fourier transform on short or noisy records. See :doc:`/reference/fourier_analysis`. penetration depth The length :math:`\lambda` over which a magnetic field is screened at the surface of a superconductor. Its temperature dependence, extracted from the transverse-field lineshape in the vortex state, reports on the superconducting gap structure; see :doc:`/reference/sc_penetration_depth`. superfluid density The density of paired charge carriers in a superconductor, proportional to :math:`1/\lambda^{2}`. Its temperature dependence distinguishes gap symmetries and is a standard target of vortex-state μSR. pulsed source A muon source that delivers muons in intense, widely spaced pulses (as at ISIS). The pulse width sets the highest resolvable precession frequency, but the low background between pulses favours slow relaxation and longer-lived signals. Contrast with a continuous source. continuous source A muon source that delivers muons one at a time (as at PSI). A single muon is timed individually, giving fine time resolution at the cost of a rate-limited data-collection window. Contrast with a pulsed source. decimation Thinning the points drawn on screen when a trace contains more samples than the plot can usefully show, so that panning and zooming stay responsive. Decimation affects only the display — fits always use the full data — and the plot shows a chip whenever it is active. representation In Asymmetry, the way the loaded data is currently expressed for viewing and fitting — F-B asymmetry, individual detector groups, the integral scan, or a frequency spectrum. Switching representation is a single click and does not alter the underlying reduction. integral scan An Asymmetry representation that reduces each run in a series to a single time-integrated asymmetry value and plots it against the swept variable — the basis of ALC and repolarisation scans; see :doc:`/reference/alc_mode`. project .asymp The Asymmetry project file, which persists a whole analysis session — the loaded datasets, reduction choices, fit setups, and trends — so that reopening it reproduces the state exactly. Raw count arrays are not embedded; see :doc:`/reference/project_files`. trend fit Fitting a physical model to a fitted parameter as a function of a scan variable — for example an order parameter against temperature, or the penetration depth against a gap model — rather than to a time spectrum. See :doc:`/reference/parameter_trending`.