NA62 - Activities in Mainz
The Mainz group is strongly involved in both construction of the NA62 detector for the data taking in 2012 and in the analysis of the data collected in 2007/2008.
Muon Veto Detector
To suppress events from the main decay channel K+ → mu+ nu (BR = 68%), a nearly perfect muon-pion separation of 1:10¹¹ is needed. This can only be achieved by an interplay of several detector components: A kinematic separation is done by the tracking system; particle identification is performed by a RICH detector and the calorimetric system. The electromagnetic and hadronic calorimeters need to provide a muon suprression of 105. In the calorimeters, rare K+ → mu+ nu events with a catastropic energy loss of the muon are of particular concern. These events can only be separated from the signal by distinguishing electromagnetic showers (from a muon) from hadronic showers. For this, the performance of the old NA48 hadron calorimeter is not sufficient and a new hadron calorimeter, serving as a muon veto detector, needs to be built. The Mainz group is designing and building this new muon veto detector in collaboration with the IHEP in Protvino/Russia. As the old NA48 hadron calorimeter, it is constructed as a standard iron-scintillator sandwich calorimeter, but with much finer segmentation, also in longitudinal direction. The fine segmentation provides the necessary information on the shower shape to distinguish muon from pion showers.
Online PC Farm
In addition, Mainz will set up the Online PC Farm, which will collect the data from all sub-detectors after a positive level 2 trigger decison. The data are sent via a Gbit Ethernet switch to event builders, where the sub-detector data are merged together. The complete events are then sent to the CERN data storage. The expected data rate from the sub-detectors is about 1 GByte for every burst of about 5 seconds.
Already in NA48, Mainz had a strong group in data analysis of rare and semileptonic kaon decays. In NA62, we perform the analysis of measuring the decay rate ratio Gamma(K+ → e+ nu) / Gamma(K+ → mu+ nu) to a precision of a few per mil from the data taken in 2007/2008. In addition, we are setting up a NA62 analysis group in Mainz for rare and semileptonic K+ decays. These group will analyze the 2007/2008 data as well as performing simulations for the data taking with the new NA62 detector from 2012 on.