Transcript Slajd 1

Tau leptons as an exciting probe
for New Physics in ATLAS
Anna Kaczmarska
NZ14, Institute of Nuclear Physics PAN, Cracow
1.
2.
3.
4.
5.
ATLAS experiment
Tau decays’ properties
Tau signatures of New Physics
Taus in Standard Model channels:
Z→ττ, W→τν, ttbar
Conclusions
Results based on Monte-Carlo simulations at 14 TeV pp centre of mass energy
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
ATLAS (A Toroidal LHC ApparatuS)
Muon Detectors: fast response
for trigger, good p resolution
Energy-scale:
e/γ
~0.1%
muons ~0.1%
Jets
~1%
Inner Detector: high
efficiency tracking, good
impact parameter resolution
Electromagnetic Calorimeters:
excellent e/γ identification,
E and angular resolution,
response uniformity
Anna Kaczmarska
Hadron Calorimeters:
Good jet and ET miss
performance
•40MHz beam crossing
•Readout: 160M channels
(3000 km cables)
•Raw data = 320Mbyte/sec
(1TB/hour)
Przegląd IFJ PAN, 6.02.09 Kraków
IFJ PAN:
Anna Kaczmarska
Elżbieta Richter-Wąs
Tau reconstruction in ATLAS
Decay modes
Branching ratio
leptonic
35.2%
1-prong (τ→nπ0π±ν)
49.5%
3-prong (τ→nπ0π±ππ±ν)
14.6%
Tau hadronic decays in detector:
●Decay products very collimated
• Low track multiplicity
• Displaced secondary vertex
Two ways for reconstruction of taus in ATLAS
Using tracks as seeds and energy from Energy
Flow method (using Tracker + EM Calorimeter)
Using calorimeter clusters as seeds and energy
only from calorimeters
Anna Kaczmarska
π0π+
τ jet
π+
π-
τ decay
Main sources of fake taus:
QCD jets, electrons, muons
Reconstruction efficiency for
candidates reconstructed with
both seeds (1P/3P):
• τ’s in signal events
~60%
• fake τ’s from QCD jets ~4-8%
Przegląd IFJ PAN, 6.02.09 Kraków
Tau identification in ATLAS
Tau ID Algorithms:
Both reconstruction algorithms provide
variables discriminating between taus
and fakes from QCD background
Dedicated algorithms for rejection
of fake candidates from electrons
Efficiency (reco τ)
= 95%
Rejection (e reco as τ) = 60
Anna Kaczmarska
Cut analysis, Projected Likelihood
Probability Density Estimator with
Range Searches, Neural Network,
Boosted Decision Tree
Rejection of fakes from QCD jets
Radius of EM shower
IFJ PAN:
Marcin Wolter
Andrzej Zemła
+
Neural Network
~1000
~600
30%
ATLAS
Efficiency of tau identification
Przegląd IFJ PAN, 6.02.09 Kraków
Higgs and New Physics signatures with tau leptons
Higgs Processes
Standard Model
VBF production, H→ττ
MSSM Higgs
bbH/A , H/A→ττ
H+ in tt→H+b Wb,
gb→bH+, H+→τν
SUSY signatures with τ’s in final states
discovery
tau polarization measurement to constrain the underlying SUSY model
Extra dimensions… exotic physics…
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Standard Model signatures with tau leptons
Looking for New Physics is very exciting but first we have to
… rediscover Standard Model
To understand performance of complex detector
calibration, particle reconstruction algorithms, triggers… etc
To measure basic SM processes (cross-sections…) and compare them
to theory and various Monte-Carlo tools
SM processes are background for New Physics
Direct sensitivity new physics (e.g. rare top decays .. )
LHC will be a factory of W, Z and top
•
•
Large statistics even with low luminosity
- analysis possible already with 100 pb-1 of integrated luminosity
All of those channels have tau signatures: Z→ττ, W→τν, ttbar→W(τ)W(l/jj)bb
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
IFJ PAN:
Anna Kaczmarska
Elżbieta Richter-Wąs
Z→τ(lepton)τ(had) events
Z→τ(e/μ)τ(had) will provide a statistically significant sample of τ leptons for 100 pb-1
measurement of the cross-section and the τ-ID efficiency
selected by lepton trigger -> unbiased sample of τ(had) decays
measurement of the τ trigger efficiencies
detector calibration: ETmiss and τ-jet energy scale determination (precision ~3%)
Expected events in 100 pb-1
• Cross check between τ(e)τ(had) and
τ(μ)τ(had) final states
• Use of opposite-sign and same-sign
e/μ-τ(had) events to control background
•Dominant backgrounds
• QCD jets
• We
Signal-to-background ratio 6:1
Visible mass (GeV)
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
IFJ PAN:
Paweł Malecki
Elżbieta Richter-Wąs
W→τν events
The most abundant source of τ‘s in SM processes
measurement of the cross-section
branching ratios for leptonic W decays: BR(W→τν)/BR(W→eν)
Expected events in 100 pb-1
ratio of the τ and electron electroweak coupling to charged current: gτ/ge
ATLAS
Track multiplicity of tau candidates
Anna Kaczmarska
• Triggered on single tau + ETmiss
• Dominant backgrounds
• QCD jets
• We
•Signal purity and cross-section
estimated on the basis of
characteristic double peak structure in
the track multiplicity distribution.
Signal-to-background ratio 3:1
Przegląd IFJ PAN, 6.02.09 Kraków
IFJ PAN:
Tadeusz Szymocha
Involvement starting now
ttbar events
Gives larger pT range of τ’s complementary to that from the W and Z processes
studies of τ trigger and tau ID efficiency
to complete the scan of the ttbar channels for cross-section measurements
to search for the effects beyond the SM in the top quark decay:
R
τ
Anna Kaczmarska
t
t
t   b
(  e,  ) R  1  t  bH 
t   b
• ttbar→W(τν )W( qq‘ )bb channel
• about 300 signal events with S:B of
20:1 are expected for 100 pb-1
• ttbar →W(τν )W(lν)bb channel
• dominated by W→lν+3jets events.
• about 67 events can be observed
with S:B of 1:1 for 100 pb-1
Przegląd IFJ PAN, 6.02.09 Kraków
Summary
Events with τ’s from Standard Model will be observed with the first data of LHC
excellent possibility of understanding detector performance
Tau leptons will be the key to the Higgs and New Physics discovery:
SM Higgs, MSSM Higgs, SUSY, extra dimensions, new theories…
ATLAS group in IFJ PAN strongly involved in:
τ leptons reconstruction and identification algorithms
Standard Model physics with τ’s in final states
Important for our success are strong links with expertise of IFJ PAN Theory group (NO4), MC
package Tauola for tau decays
Leading role of IFJ PAN group in preparation of 9 Internal Notes documenting expected tau
performance (2007-2008); E. Richter-Was convener of the ATLAS Tau WG in years 2007-2008
External funding:
EU Marie Curie reintegration grant 2006-2007; Polish Government grant 2007-2008 (supplement to
EU MC grant); Polish Government grant N202 006434 2008-2010; IN2P3 Collaboration 08-129 IFJ
PAN- LAPP Annecy
We hope to have early measurements with
tau data this year!
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Backup Slides
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Why are tau leptons so interesting?
massive particles
measurable lifetime
undergo electroweak interaction only
production and decay well separated in time
potential for measurement of the polarisation, spin correlations, parity
excellent knowledge about tau decay modes from low-energy experiments
Ideal signature to probe “New Physics” !
however .....
several decay modes possible
jet-like signature
huge background from QCD multi-jet production
Make it quite difficult for being observed in the
experimental environment of pp collisions at ATLAS
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
The very first beam-splash event in ATLAS
10:19, 10th September 2008
Online display
The LHC has been fully installed and it
started operation with single beams on
10.09.08. Now it is delayed until summer
2009 after an incident that happened on
19.10.08
Anna Kaczmarska
Offline display
13
Przegląd IFJ PAN, 6.02.09 Kraków
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków
Anna Kaczmarska
Przegląd IFJ PAN, 6.02.09 Kraków