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 subdetectors 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 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 kinematically comparable hadronic tau decays.  The ``leading track''
requirement is applied by requiring a realitively 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 rejects QCD
backgrounds by a factor of $\mathcal O(100)$ while a maintaing hadronic tau
identification of approximately 50\%.
Revision:	1.2
Committed:	Thu Apr 22 16:13:12 2010 UTC (15 years ago) by friis
Content type:	application/x-tex
Branch:	MAIN
Changes since 1.1:	+14 -11 lines
Log Message:	Adding NN observables inputs and other miscellaneous stuff
#	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			from subdetectors are combined according to their measured resolutions to
11			improve energy and angular resolution and reduce double counting. The
12			strategies described in this paper use the particle flow objects.
13
14	friis	1.2	Both methods use an ``leading object'' and an isolation requirement to reject
15			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			than a kinematically comparable hadronic tau decays. The ``leading track''
18			requirement is applied by requiring a realitively high momentum object near the
19			center of the jet; typically a charged track with transverse momentum greater
20			than 5 GeV/c within $\Delta R < 0.1$ about the center of the jet axis. The
21			Isolation requirement exploits the collimation of true taus by defining an
22			isolation annulus about the kinematic center of the jet and requiring no
23			detector activity about a threshold in that annulus. This approach rejects QCD
24			backgrounds by a factor of $\mathcal O(100)$ while a maintaing hadronic tau
25			identification of approximately 50\%.