Tau-related plots from the CSC book
This page contains approved plots and results in the order as they appear in the CSC note. Only the CSC note contains all the relevant information and should thus be consulted if any of the plots is used.
Additional Information
- A full version of the tau CSC chapter is available via CDS (ATL-COM-PHYS-2008-068
)
- If you want to cite the CSC book (full text) in your publication, please do it the following way:
ATLAS Collaboration,
Expected Performance of the ATLAS Experiment,
Detector, Trigger and Physics,
CERN-OPEN-2008-020, Geneva, 2008. - An .eps version of each of the plots displayed below is available by clicking on the corresponding thumbnail.
Introduction
Caption:
The visible transverse energy of τ leptons from different
physics processes: top quark decays, W/Z production, Standard Model
vector boson fusion Higgs boson production for mH=120 GeV with H->ττ,
for τ leptons from low energy Supersymmetry with a light
stau (SU1 sample), heavy Z' bosons, and heavy Higgs bosons from
bbH production in the MSSM with tanβ=20(45) for masses of
400 GeV (800 GeV).
Performance of the ATLAS detector for tau identification
Tracking and Vertexing
Reconstruction efficiency and track quality
Caption:
Reconstruction efficiency for tracks from charged π's for
one- and three-prong hadronic τ decays from W->τν
and Z->ττ signal samples as a function of the
transverse momentum of the track (left) and of the pseudorapidity for three
different ranges of track pT (right).
Charge mis-identification and tracks from conversions
Caption: Percentage of one- and three prong τ lepton hadronic decays within
reconstructed one-, two- and three-prong τhad candidates by the track-based
algorithm, matched
to true τ decays. Tracks in a cone of Δ R=0.2 around the leading good
quality track are considered. A transverse momentum of pT>9 GeV
is required for the leading track. An estimate for electron contamination and
charge misidentification is given in addition. Separately
specified are results for a subsample where no hadronic secondary
interaction of primary charged π was recorded inside the
inner detector volume. Events from Z->ττ and W->τν
samples were used. (eps version).
| Seeds for track-based τhad candidates | Reconstructed as single-prong | Reconstructed as three-prong | Reconstructed as two-prong |
|---|---|---|---|
| Electron contamination (from conversion) | 1.5% | 5.7% | 2.9% |
| τ->π+/- nπ0 ν | 96.1% | 3.8% | 23.8% |
| τ-> 3π+/- nπ0 ν | 3.9% | 96.2% | 76.2% |
| Charge misid. | 1.7% | 3.6% | |
| (no had. interact.) | 0.4% | 2.1% |
Impact parameter
Caption:
Transverse (left) and longitudinal (right) impact
parameter resolution as a function of |η| from a one-prong
Z->ττ sample. The open (full) circles are from
τ->π(π0)ν (τ->μνν) events.
Caption:
Significances of the impact parameters d0 (left)
and z0sin(θ) (right) for 1-prong τhad
candidates reconstructed by the track-based
algorithm. Distributions are shown for τhad candidates
reconstructed from τ decays and for fake candidates which do
not originate from the decays of b- or c-hadrons.
Secondary vertex reconstruction and transverse flight path
Caption:
Residuals of the secondary vertex position parallel and
perpendicular to the direction of flight of the τhad candidate
using the adaptive vertex fitter. Fully (solid) and partially
(open) matched three-prong τhad candidates reconstructed with
the track-based algorithm from Z->ττ and W->τν
processes are used.
Caption: Resolution and mean of the distribution of residuals of
the secondary vertex position in the directions parallel and
transverse to that of the reconstructed momentum vector
of the τhad candidate as obtained from the adaptive vertex
fitter. Candidates with up to three associated tracks
reconstructed by the track-based algorithm were used. The
resolution quoted is the σ of the core Gaussian of a
double Gaussian fit in the range [-4 mm, 4mm] in the
parallel direction and [-50 μm, 50μm] in the transverse
direction. The 68.3% and 95% coverages are also quoted. (eps version).
| Resolution | Mean | 68.3% | 95% | |
|---|---|---|---|---|
| Parallel | ||||
| Fully matched 3-prong | 0.593 +/- 0.008 mm | 0.006 +/- 0.006 mm | 1.27mm | 5.33mm |
| Partially matched | 0.703 +/- 0.030 mm | -0.035 +/- 0.020 mm | 3.83 mm | > 15 mm |
| Combined | 0.613 +/- 0.008 mm | 0.004 +/- 0.006 mm | 1.89 mm | 11.37 mm |
| Transverse | ||||
| Fully matched 3-prong | 10.1 +/- 0.2 μm | 0.2 +/- 0.1 μm | 14.4 μm | 36.9 μm |
| Partially matched | 11.3 +/- 0.5 μm | -0.1 +/- 0.2 μm | 20.9 μm | 72.2 μm |
| Combined | 10.5 +/- 0.2 μm | 0.1 +/- 0.1 μm | 16.4 μm | 48.1 μm |
Caption:
Resolution on the transverse flight path reconstructed with
the adaptive vertex fitter for fully matched three-prong τhad
candidates as a function of the transverse momentum (left) and the
pseudorapidity (right). Standard deviations
of Gaussians fitted to central intervals covering 80% of the
residual distributions are shown (black points). In addition the
68.3% and 95% coverages of the distributions of
residuals of the secondary vertex position are shown (dashed and dot-dashed lines).}
Caption:
Significance of the transverse flight path for fully
matched and partially matched three-prong and for fake candidates with and without
hadrons containing b or c quarks (the contribution from semileptonic
decays of b/c jets into τ leptons was not subtracted).
Reconstruction of π0 subclusters
Caption: Single prong candidates: fractions with
zero, one and two or more reconstructed π0 subclusters. (eps version).
| decay mode | no π0 subclusters | 1 π0 subcluster | >= 2 π0 subclusters |
|---|---|---|---|
| all τhadν | 32% | 35% | 33% |
| τ->πν | 65% | 20% | 15% |
| τ->ρν | 15% | 50% | 35% |
| τ->a1 (-> 2π0π)ν | 9% | 34% | 57% |
Caption:
The energy response obtained for the visible
energy from τ->ρν events
using candidates with one π0 subcluster (left). The invariant
mass of the visible decay products for hadronic single-prong
τ->ρν, τ->a1 (-> 2 π0 π) ν,
and τ->πν decays using candidates
from W->τν events with at least one π0 subcluster
reconstructed (right).
Combined veto on electron tracks
Caption:
The efficiency of the electron veto algorithm for
W->τν (rectangles) and W->eν (triangles) events as a
function of |η| and pT of the leading track.
Caption: Veto for ele and muon tracks Efficiency for hadronically decaying
τ leptons and true electrons from W->τν for passing the electron
veto algorithm. The numbers
given are normalized to true electrons with pT >9 GeV and
|η|<2.5 (vs. true e) and to reconstructed one-prong or
three-prong candidates with the leading track being matched to a
π from W->τν events (vs. reconstructed τhad).
The probability that an
electron from W->eν events with pT >9 GeV and
|η|<2.5 is reconstructed as one-prong (three-prong)
candidate is ~70% (~0.7%). In addition the
performance of the standard algorithm for electron reconstruction
is shown. The statistical uncertainty on the numbers presented here is at the
level of (0.1-0.5)%. (eps version).
| Candidates | Reconstructed as single-prong | Reconstructed as three-prong | Overall |
|---|---|---|---|
| Electron-veto algorithm | |||
| τ from W->τν (vs reconstructed τhad) | 94.1% | 96.2% | 94.9% |
| Electron from W->eν (vs true e) | 1.5% | <0.1% | 1.6% |
| Standard algorithm (tight selection) | |||
| τ from W->τν (vs reconstructed τhad) | 99.9% | 99.9% | 99.9% |
| Electron from W->eν (vs true e) | 15.6% | 0.4% | 16.4% |
| Standard algorithm (medium selection) | |||
| τ from W->τν (vs reconstructed τhad) | 90.6% | 95.1% | 92.1% |
| Electron from W->eν (vs true e) | 4.2% | 0.2% | 4.6% |
Offline algorithms for tau reconstruction
The calorimeter-based algorithm
Caption:
The ratio of the reconstructed ET and the true (ETτ-vis)
transverse energy of the hadronic τ decay products is shown as a function of
the visible true transverse energy ETτ-vis
(left), calculated in |η|<2.5 and |η| (right) for taus from Z->ττ (triangles)
and A->ττ with mA=800 GeV (squares) decays. The ordinate value is the mean and
the error bars correspond to the sigma of the Gaussian fit performed
in the range 0.8<ET/ETτ-vis.
The results are obtained after applying the loose likelihood
selection, see below.
Caption:
The distributions of a few discriminating variables
(electromagnetic radius, energy isolation,
transverse energy width in the η strip layer and ET over pT, 1 of the leading track)
used in the calorimeter-based tau identification for true tau decays and jets with visible transverse
cluster energies ET in the range from 40 to 60 GeV and track multiplicities between 1 and 3.
Caption:
Left: The log likelihood (LLH) distribution for τ leptons (solid) and jets from QCD production
(dashed). The likelihood is applied after a preselection on the number of associated
tracks, i.e. requiring 1<= Ntr<=3.
(Candidates with LLH<-10 had variables outside the boundaries
of histograms used when obtaining the PDFs for the likelihood calculation).
Right: Efficiency for τ leptons and rejection against jets for different ET ranges,
achieved with the likelihood selection.
The track-based algorithm
The energy-flow approach
Caption:
The fractional energy response for single-prong (left) and
three-prong (right) true τhad candidates reconstructed with the
track-based algorithm. Events from a W->τν sample
are shown.
Identification with calorimetric and tracking variables
Caption:
The distributions for signal and backgrounds
for the visible mass mviseflow and ratio of the transverse energy in the isolation and core region
ETisol/ETcore
for single-prong candidates, and variance Wtracksτ and invariant mass
of the track system mtrk3p for three-prong candidates. Distributions are shown for the
candidates in the transverse energy range ET=20-40 GeV.
Overall efficiency and rejection
Caption: Efficiencies and rejection rates for different discrimination
techniques for the track-based algorithm for fixed efficiencies.
The efficiencies are normalized to all hadronic τ decays.
The rejection rates are calculated with respect to
jets reconstructed from true particles in the Monte Carlo. Events from
Z->ττ signal samples and QCD dijets were used. The
errors given are statistical only. (eps version).
| Selection | Efficiency | Rejection | Rejection | Rejection | Rejection |
|---|---|---|---|---|---|
| cuts | TMVA cuts | NN | PDRS | ||
| ET = 10-30 GeV : | |||||
| one-prong | 0.33 | 225 +/- 10 | 435 +/- 30 | 510 +/- 40 | 460 +/- 40 |
| three-prong | 0.28 | 360 +/- 25 | 470 +/- 40 | 740 +/- 70 | 670 +/- 60 |
| ET = 30-60 GeV : | |||||
| one-prong | 0.42 | 140 +/- 10 | 170 +/- 10 | 440 +/- 40 | 320 +/- 30 |
| three-prong | 0.45 | 60 +/- 2 | 9 0 +/- 10 | 160 +/- 10 | 130 +/- 10 |
Comparison of the two algorithms
Caption:
Expected performance for the track-based algorithm with a neural-network
selection (left) and the calorimeter-based algorithm with the likelihood
selection (right). The rejection rates against jets from Monte-Calo particles as a
function of the efficiency for hadronic τ decays for various ranges
of the visible transverse energy are shown. For signal events
Z->ττ and bbH, H->ττ with mH=800 GeV were used,
for the background QCD dijet samples were used.
Caption: Rejection against jets from Monte Carlo true particles for a 30%
efficiency and separately for the one-prong (1p) and three-prong
(3p) candidates. The efficiencies are normalized to true
hadronic τ decays. For the signal Z->ττ events
and events from bbH, H->ττ with mH=800 GeV
were used; for the background QCD dijet-samples were used. The
errors given are statistical only. (eps version).
| Algorithm | ET = 10-30 GeV | ET = 30-60 GeV | ET = 60-100 GeV | ET > 100 GeV |
|---|---|---|---|---|
| Track-based | 1p: 740 +/- 70 | 1p: 1030 +/- 160 | ||
| (neural network) | 3p: 590 +/- 50 | 3p: 590 +/- 70 | ||
| Calo-based | 1p: 1130 +/- 50 | 1p: 2240 +/- 140 | 1p: 4370 +/- 280 | |
| (likelihood) | 3p: 187 +/- 3 | 3p: 310 +/- 7 | 3p: 423 +/- 8 |
Caption:
Track multiplicity distributions obtained for hadronic
τ decays with a visible transverse energy above 20 GeV and below
60 GeV using the track-based τ identification algorithm. The
distributions are shown after reconstruction, after cut-based
identification and finally after applying the neural network (NN)
discrimination technique for an efficiency of 30% for the signal
(left) and the background (right).
Caption:
Track multiplicity distributions obtained for hadronic
τhad-decays with visible transverse energy above 20 GeV and below
60 GeV using the calorimeter-based τ identification. The
distributions are shown after reconstruction and after applying the
likelihood discrimination technique (medium selection) for the
signal (left) and the background (right).
Fake-rates from QCD di-jet samples
Caption:
Example of selections on a MC dijet sample, generated
with 70<=pT<= 140 GeV. The two jets have to fulfill
Δφ >= (π -0.3) in order to be back to back in φ
(left) and have similar pT values
(right).
Caption: The τhad fake rate from QCD jets and its statistical
uncertainty for the available Monte Carlo statistics and for
expected 100 pb-1 of data in bins of pT for both
τhad reconstruction algorithms. (eps version).
| Calorimeter-based algorithm | Track-based algorithm | |||
|---|---|---|---|---|
| pT range | MC stat. | Expected stat. error | MC stat. | Expected stat. error |
| (GeV) | (%) | for 100 pb-1 (%) | (%) | for 100 pb-1 (%) |
| 15-40 | 2.3 +/- 0.3 | +/- 0.02 | 2.5+/-0.5 | +/- 0.02 |
| 40-80 | 5.2 +/- 2.2 | +/- 0.01 | 6.7+/-2.2 | +/- 0.01 |
| 80-120 | 0.5 +/- 0.2 | +/- 0.001 | 1.8+/-0.6 | +/- 0.002 |
| 120-160 | 0.2 +/- 0.2 | +/- 0.002 | 1.4+/-0.6 | +/- 0.004 |
Tau leptons in Standard Model processes
W->τν inclusive production
Caption: Expected number of events in 100 pb-1 of data for signal and
background after subsequent steps of the selection.
The track-based algorithm has been used for τhad reconstruction. The QCD background has
been estimated combining fast and full simulation. Given are the expected number of events
of track multiplicity one to three, i.e. contributing
to signal region only. (eps version).
| Selection | W->τν | W->eν | W->μν | QCD dijet | ttbar, Z->ee, Z->ττ |
|---|---|---|---|---|---|
| Trigger tau20i+EFxE30 | 8.8 104 | 6.1 105 | 3.2 104 | 4.8 108 | 3.0 105 |
| Identified τ + ETmiss > 30 GeV | 2.0 104 | 2600 | 200 | 3.0 106 | 1600 |
| ETmiss > 50 GeV | 4200 | 530 | 90 | 5.0 104 | 550 |
| Veto fake ETmiss topology | 3600 | 500 | 80 | 1.8 104 | 150 |
| Require jet pT > 15 GeV | 3240 | 450 | 60 | 3200 | 80 |
| Increase to ETmiss > 60 GeV | 1550 | 150 | 25 | 500 | 30 |
The Z->ττ inclusive production
Caption:
Left: The reconstructed visible mass of the (l τhad) pair
for Z->ττ decays (solid line) and
QCD, W->lν, Z->ll backgrounds (dashed line). Right:
The reconstructed visible mass of the (l τhad) pair from Z->ττ
decays as a function of the τhad energy scale
(right). The dashed lines correspond to +/- 1 σ and +/- 3 σ
with respect to the reconstructed peak position. The
results were obtained with the calorimeter-based algorithm.
Caption: Expected number of events in 100 pb-1 of data for signal and
background after reconstruction of the τ candidate with the
calorimeter-based algorithm and after application of the selection cuts
for the Z->ττ channel. The QCD background has
been estimated combining fast and full simulation. (eps version).
| Selection | Z->ττ | W->lν | QCD dijet | ttbar | Z->ll |
|---|---|---|---|---|---|
| Isolated lepton | 1.5 104 | 16.7 105 | 1.1 107 | 2.6 104 | 2.2 105 |
| ETmiss > 20 GeV | 4750 | 14.3 105 | 3.2 105 | 2.4 104 | 1.0 104 |
| mT(l, ETmiss) > 30 GeV | 3200 | 2.6 104 | 1.8 105 | 3650 | 3200 |
| ΣET < 400 GeV | 3000 | 2.4 104 | 1.7 105 | 1280 | 2800 |
| b-jet veto | 2780 | 2.4 104 | 2.7 104 | 135 | 2600 |
| τhad -id + Δφ(l, τhad) cuts | 630+/-30 | 210 +/-10 | 74+/-11 | 10+/-2 | 30+/-5 |
| OS events, ml, τhad = 37-75 GeV | 520+/-30 | 45 +/-5 | 29+/-5 | < 5 | 10 +/-5 |
The τ leptons from ttbar production
Caption:
Combined b-tagging weights using impact parameter and
secondary vertex information for the first two leading ET
jets, both in ttbar->W(eνe, μνμ)W(τhadντ)bbbar and
W+3-jets background. The eτ (μτ) channel is
shown on the left (right). The cut value of 7 on the b-tagging weight is indicated
with the arrows. An integrated luminosity of 100 pb-1 of data is
assumed.
Caption: Expected number of events in 100 pb-1 of data for ttbar->
W(lν)W(τhad, ντ) bbbar signal and
background after subsequent steps in the selection. The track-based algorithm
has been used for τhad reconstruction. (eps version).
| Selection | ttbar (l, τhad) | W->lν + 3 jets | single t | Z->ll + 2 jets |
|---|---|---|---|---|
| Isolated lepton pT > 20 GeV | 1300 | 3.9 105 | 4300 | 630 |
| Identified τhad pT > 15 GeV | 190 | 22000 | 210 | 120 |
| 1st jet ET > 50 GeV, 2nd jet ET > 30 GeV | 170 | 4000 | 170 | 35 |
| ETmiss > 25 GeV | 150 | 3400 | 150 | 15 |
| ΣET > 250 GeV | 150 | 1750 | 130 | 10 |
| Opposite-sign events | 130 | 850 | 54 | <10 |
| 1 b-jet tag | 67 | 28 | 20 |
Major updates:
-- WolfgangMader - 24 Oct 2008 -- ChristophAnders - 22 Jul 2008 -- ChristophAnders - 19 Jul 2008 Responsible: MichelJanus and ChristophAnders
Last reviewed by: Never reviewed
Topic revision: r26 - 2011-01-26 - PatrickJussel
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