TancNote/note/tau_id.tex

The tau identification strategies used in previously published CMS analyses are
fully described in~\cite{PFT08001}.  A summary of the basic methods and
strategies is given here. There are two primary methods for selecting objects
used to reconstruct tau leptons.  The CaloTau algorithm uses tracks
reconstructed by the tracker and clusters of hits in the electromagnetic and
hadronic calorimeter.  The other method (PFTau) uses objects reconstructed by
the CMS particle flow algorithm, which is described in~\cite{PFT09}.  The
particle flow algorithm provides a global and unique description of every
particle (charged hadron, photon, electron, etc.) in the event; measurements
from sub--detectors are combined according to their measured resolutions to
improve energy and angular resolution and reduce double counting.  The
strategies described in this paper use the particle flow objects.

Both methods typically use an ``leading object'' and an isolation requirement to reject
quark and gluon jet background.  Quark and gluon jets are less collimated and
have a higher constituent multiplicity and softer constituent $p_T$ spectrum
than a hadronic tau decay of the same transverse momentum.  The ``leading
track'' requirement is applied by requiring a relatively high momentum object
near the center of the jet; typically a charged track with transverse momentum
greater than 5 GeV/c within $\Delta R < 0.1$ about the center of the jet axis.
The isolation requirement exploits the collimation of true taus by defining an
isolation annulus about the kinematic center of the jet and requiring no
detector activity about a threshold in that annulus.  This approach yields a
misidentification rate of approximately 1\% for QCD backgrounds and a hadronic
tau identification efficiency of approximately 50\%~\cite{PFT08001}.
Revision:	1.4
Committed:	Wed Apr 28 22:15:10 2010 UTC (15 years ago) by friis
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#	User	Rev	Content
1	friis	1.1	The tau identification strategies used in previously published CMS analyses are
2	friis	1.2	fully described in~\cite{PFT08001}. A summary of the basic methods and
3	friis	1.1	strategies is given here. There are two primary methods for selecting objects
4			used to reconstruct tau leptons. The CaloTau algorithm uses tracks
5			reconstructed by the tracker and clusters of hits in the electromagnetic and
6			hadronic calorimeter. The other method (PFTau) uses objects reconstructed by
7	friis	1.2	the CMS particle flow algorithm, which is described in~\cite{PFT09}. The
8	friis	1.1	particle flow algorithm provides a global and unique description of every
9			particle (charged hadron, photon, electron, etc.) in the event; measurements
10	friis	1.3	from sub--detectors are combined according to their measured resolutions to
11	friis	1.1	improve energy and angular resolution and reduce double counting. The
12			strategies described in this paper use the particle flow objects.
13
14	friis	1.4	Both methods typically use an ``leading object'' and an isolation requirement to reject
15	friis	1.2	quark and gluon jet background. Quark and gluon jets are less collimated and
16			have a higher constituent multiplicity and softer constituent $p_T$ spectrum
17	friis	1.3	than a hadronic tau decay of the same transverse momentum. The ``leading
18			track'' requirement is applied by requiring a relatively high momentum object
19			near the center of the jet; typically a charged track with transverse momentum
20			greater than 5 GeV/c within $\Delta R < 0.1$ about the center of the jet axis.
21			The isolation requirement exploits the collimation of true taus by defining an
22	friis	1.2	isolation annulus about the kinematic center of the jet and requiring no
23	friis	1.3	detector activity about a threshold in that annulus. This approach yields a
24			misidentification rate of approximately 1\% for QCD backgrounds and a hadronic
25			tau identification efficiency of approximately 50\%~\cite{PFT08001}.