Mar 20 – 22, 2018
University of Washington Seattle
US/Pacific timezone

Fast track segment finding in the Monitored Drift Tubes (MDT) of the ATLAS Muon Spectrometer using a Legendre transform algorithm

Mar 20, 2018, 3:00 PM
Physics-Astronomy Auditorium A118 (University of Washington Seattle)

Physics-Astronomy Auditorium A118

University of Washington Seattle

Oral 2: Real-time pattern recognition and fast tracking Session2


Kostas Ntekas (University of California Irvine (US))


Many of the physics goals of ATLAS in the High Luminosity LHC era,
including precision studies of the Higgs boson, require an unprescaled
single muon trigger with a 20 GeV threshold. The selectivity of the
current ATLAS first-level muon trigger is limited by the moderate
spatial resolution of the muon trigger chambers. By incorporating the
precise tracking of the MDT, the muon transverse momentum can be
measured with an accuracy close to that of the offline reconstruction at
the trigger level, sharpening the trigger turn-on curves and reducing
the single muon trigger rate. A novel algorithm is proposed which
reconstructs segments from MDT hits in an FPGA and find tracks within
the tight latency constraints of the ATLAS first-level muon trigger. The
algorithm represents MDT drift circles as curves in the Legendre space
and returns one or more segment lines tangent to the maximum possible
number of drift circles.  This algorithm is implemented without the need
of resource and time consuming hit position calculation and track
fitting procedures. A low-latency pure-FPGA implementation of a Legendre
transform segment finder will be presented. This logic evaluates in
parallel a total of 128 possible track segment angles for each MDT drift
circle, calculating in a fast FPGA pipeline the offset of each segment
candidate from an arbitrary origin for each angle and circle. The
(angle, offset) pairs, corresponding to the MDT drift circles in one
station, are used to fill a 2D histogram and the segment finder returns
the position and angle of the maximum peak, corresponding to the most
likely tangent line, this defines the reconstructed segment. Segments
are then combined to calculate the muon's transverse momentum with a
parametric approach which accounts for varying magnetic field strength
throughout the muon spectrometer.

Primary author

Kostas Ntekas (University of California Irvine (US))


Julie Hart Kirk (STFC - Rutherford Appleton Lab. (GB))

Presentation materials

Peer reviewing