Advanced muon-spin spectroscopy with high lateral resolution using Si-pixel detectors

Muon-spin spectroscopy at continuous sources has stagnated at a stopped muon rate of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mo>∼</a:mo> <a:mn>40</a:mn> <a:mspace width="0.16em"/> <a:mi>kHz</a:mi> </a:mrow> </a:math> for the last few decades. The major limiting factor is the requirement of a single muon in the sample during the typical <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mn>10</c:mn> <c:mspace width="0.16em"/> <c:mi>µ</c:mi> <c:mi mathvariant="normal">s</c:mi> </c:mrow> </c:math> data gate window. To overcome this limit and to be able to perform muon-spin relaxation/rotation (µSR) measurements on millimeter-sized samples, one can use vertex reconstruction methods to construct µSR spectra. This is now possible thanks to the availability of very thin monolithic Si-pixel chips, which offer minimal particle scattering and high count rate. Here, we present results from a Si-pixel-based spectrometer that utilizes vertex reconstruction schemes for the incoming muons and emitted positrons. With this spectrometer, we were able to obtain a first vertex reconstructed ( <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mtext>vx-</f:mtext> <f:mi>μ</f:mi> <f:mi mathvariant="normal">SR</f:mi> </f:math> ) spectrum. The unique capabilities and benefits of such a vx-µSR spectrometer are discussed.