This thesis is focused on the study of the Z -> µ+ µ- process. This process is quite interesting. From the detector performance point of view, it can be used to measure from data muon trigger and reconstruction efficiencies. To extract these efficiencies, in the past three years I developed and optimized a method, called Tag&Probe, using Monte Carlo simulation. In the past few months, with the first ATLAS data, it allowed to measure the muon efficiencies from data for the first time. A data sample of 1.3 pb^-1 of integrated luminosity has been used and the results have been compared with the MC expectations.
The efficiencies estimation is also relevant for the cross-section measurement of all processes involving muons. In fact, when comparing the measured cross-section from data with the theoretical expectations, one has to correct for the detector inefficiencies, which at the start-ip are not perfectly reproduced in the simulation. In this thesis, these muon efficiencies have been used for a first data/MC comparison of the Z -> µ+ µ- cross-section, both inclusive and differential as a function of the jet multiplicity.
[L'angolo del PhD] Sara Borroni - XXIII Ciclo - 2010
1. Study of the pp → Z → µ+ µ− Process at ATLAS:
Detector Performance and First Cross-Section
Measurement at 7 TeV
Candidate: Sara Borroni
Supervisor: Cesare Bini
Co-supervisor: Stefano Rosati
Sapienza, Università di Roma
XXIII Ciclo di Dottorato
November 3, 2010
2. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Theoretical Introduction
The Standard Model of Particle Physics
The past century has seen a really big step forward for the elementary particle physics. The Standard Model (SM)
has been developed which describes the behavior of matter and its interactions. This theoretical framework
managed to give a unified description of strong, electromagnetic and weak interactions but the gravity
The SM has been extensively tested in the last decades at LEP and Tevatron and it successfully explains most of the
known phenomena in elementary particle physics. Nevertheless a number of open problems are still left which need
for further studies to be done.
Experimental facts not explained by SM
evidence that neutrinos have non-zero masses
dark matter must exist
observed matter-antimatter asymmetry
...
Theoretical issues not solved in the SM
the Higgs or some new physics must exist to make the SM consistent
unification of the gauge couplings
unification of gravity is still missing
...
Sara Borroni November 3, 2010 2/36
3. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Theoretical Introduction
The Standard Model of Particle Physics
The past century has seen a really big step forward for the elementary particle physics. The Standard Model (SM)
has been developed which describes the behavior of matter and its interactions. This theoretical framework
managed to give a unified description of strong, electromagnetic and weak interactions but the gravity
The SM has been extensively tested in the last decades at LEP and Tevatron and it successfully explains most of the
known phenomena in elementary particle physics. Nevertheless a number of open problems are still left which need
for further studies to be done.
Experimental facts not explained by SM
evidence that neutrinos have non-zero masses
dark matter must exist
observed matter-antimatter asymmetry
...
Theoretical issues not solved in the SM
the Higgs or some new physics must exist to make the SM consistent
unification of the gauge couplings
unification of gravity is still missing
...
Sara Borroni November 3, 2010 2/36
4. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Theoretical Introduction
The Standard Model of Particle Physics
The past century has seen a really big step forward for the elementary particle physics. The Standard Model (SM)
has been developed which describes the behavior of matter and its interactions. This theoretical framework
managed to give a unified description of strong, electromagnetic and weak interactions but the gravity
The SM has been extensively tested in the last decades at LEP and Tevatron and it successfully explains most of the
known phenomena in elementary particle physics. Nevertheless a number of open problems are still left which need
for further studies to be done.
Experimental facts not explained by SM
evidence that neutrinos have non-zero masses
dark matter must exist
observed matter-antimatter asymmetry
...
Theoretical issues not solved in the SM
the Higgs or some new physics must exist to make the SM consistent
unification of the gauge couplings
unification of gravity is still missing
...
Sara Borroni November 3, 2010 2/36
5. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Theoretical Introduction
The Standard Model of Particle Physics
The past century has seen a really big step forward for the elementary particle physics. The Standard Model (SM)
has been developed which describes the behavior of matter and its interactions. This theoretical framework
managed to give a unified description of strong, electromagnetic and weak interactions but the gravity
The SM has been extensively tested in the last decades at LEP and Tevatron and it successfully explains most of the
known phenomena in elementary particle physics. Nevertheless a number of open problems are still left which need
for further studies to be done.
Experimental facts not explained by SM
evidence that neutrinos have non-zero masses
dark matter must exist
observed matter-antimatter asymmetry
...
Theoretical issues not solved in the SM
the Higgs or some new physics must exist to make the SM consistent
unification of the gauge couplings
unification of gravity is still missing
...
Sara Borroni November 3, 2010 2/36
6. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
The Large Hadron Collider
Motivations and Experiments
Answer these kind of questions is the reason why the Large Hadron Collider (LHC) has been built, with its four
experiments: ATLAS, CMS, LHCb and ALICE.
LHC today
proton - proton collider
7 TeV center of mass energy
(proj. 14 TeV )
instantaneous peak
luminosity 2 · 1032 cm−2 s−1
(proj. 1034 cm−2 s−1 )
integrated luminosity
delivered ∼ 40 pb−1
2011 full year data taking -
2012 technical stop (?)
Sara Borroni November 3, 2010 3/36
7. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
The ATLAS Experiment
ATLAS in (Very-)Short
Usual collider multi-purpose
experiment: many concentrical layers to
detect different particles
Inner Tracker in a solenoidal magnetic
field (2 T ) for charged particles
detection → resolution order 10 ÷ 100
µm
Electromagnetic and Hadronic
calorimeters for electrons, photons and
hadrons
∆E 11.0%
(EM) = p ⊕ 0.4%
E E[GeV ]
∆E 50%
(HAD) = p ⊕ 3%
E E[GeV ]
External Muon Spectrometer in an
air-core toroidal magnetic field (0.6 T )
for muons → resolution ∼ 50 µm on
the sagitta
Sara Borroni November 3, 2010 4/36
8. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
The ATLAS Experiment
Variables used to describe the
event kinematics in an hadron
collider experiment
only the transverse
components of energies and
momenta (pT , missing
transverse energy..)
azimutal angle φ
pseudo-rapidity
η = ln tan θ/2
Distance between two
reconstructed objects
p
∆R = ∆η 2 + ∆φ2
Sara Borroni November 3, 2010 5/36
9. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
W /Z Bosons Physics
A sketch
The hadronic nature of the proton-proton collisions opens a wide range of exploration possibilities, from the precise
measurements of Standard Model parameters to the search for new physics phenomena up to the TeV scale
H1
p1 x1 p 1 , ν
k1
γ, Z, W ±
k2
p2 x1 p 2 ¯¯
, ν
H2
Uncertainty sources:
During each bunch crossing are
NOT the proton to collide but the
partons inside the protons, each
carrying a momentum fraction x
Uncertainty on the Parton
Distribution Functions (PDF) →
describe the x distribution for
each parton type
Sara Borroni November 3, 2010 6/36
10. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
W /Z Bosons Physics
A sketch
The hadronic nature of the proton-proton collisions opens a wide range of exploration possibilities, from the precise
measurements of Standard Model parameters to the search for new physics phenomena up to the TeV scale
H1
p1 x1 p 1 , ν
k1
γ, Z, W ±
k2
p2 x1 p 2 ¯¯
, ν
H2
Uncertainty sources:
During each bunch crossing are
NOT the proton to collide but the
partons inside the protons, each
carrying a momentum fraction x
Uncertainty on the Parton
Distribution Functions (PDF) →
describe the x distribution for
each parton type
Sara Borroni November 3, 2010 6/36
11. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
W /Z Bosons Physics
A sketch
The measurement of the well known Standard Model processes is the first step towards all new physics searches
theoretical predictions tuning at a
new unexplored energy: which
theoretical model correctly
describes the data?
standard candles both for the
detectors understanding and
performance assessment
Sara Borroni November 3, 2010 7/36
12. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
W /Z Bosons Physics
A sketch
The W ± and Z 0 bosons are suitable
theoretical predictions (NNLO) have a small uncertainty (about 5%) mainly due to the uncertainty on the PDF
measured with high experimental precision at LEP and Tevatron
copiously produced at LHC
leptonic decays are clear and “simple to disentangle from the background
Expected W/Z events @ 7 TeV
σ × BR(Z → ll) ∼ 1 nb : →∼ 33000 evts in 100 pb−1 after selection
σ × BR(W → lν) ∼ 10 nb : → 370000 evts in 100 pb−1 after selection
Sara Borroni November 3, 2010 8/36
13. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
A cross-section measurement
The Standard Model Re-discovery
Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section
measurement!
The cross-section measurement is a counting experiment where one has to deduce how many events NS of a
certain type have been produced when Nsel of them are observed.
Nsel − Nb
NS = L · σ −→ σ =
L·A·
Example: efficiency for Z → µ+ µ− process:
efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be
selected
which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi )
2 3 2 3
Y Y
P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5
i=1,n i=1,n
I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon
P(T |R, ζi )
Sara Borroni November 3, 2010 9/36
14. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
A cross-section measurement
The Standard Model Re-discovery
Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section
measurement!
The cross-section measurement is a counting experiment where one has to deduce how many events NS of a
certain type have been produced when Nsel of them are observed.
Nsel − Nb
NS = L · σ −→ σ =
L·A·
Example: efficiency for Z → µ+ µ− process:
efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be
selected
which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi )
2 3 2 3
Y Y
P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5
i=1,n i=1,n
I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon
P(T |R, ζi )
Sara Borroni November 3, 2010 9/36
15. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
A cross-section measurement
The Standard Model Re-discovery
Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section
measurement!
The cross-section measurement is a counting experiment where one has to deduce how many events NS of a
certain type have been produced when Nsel of them are observed.
Nsel − Nb
NS = L · σ −→ σ =
L·A·
Example: efficiency for Z → µ+ µ− process:
efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be
selected
which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi )
2 3 2 3
Y Y
P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5
i=1,n i=1,n
I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon
P(T |R, ζi )
Sara Borroni November 3, 2010 9/36
16. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
A cross-section measurement
The Standard Model Re-discovery
Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section
measurement!
The cross-section measurement is a counting experiment where one has to deduce how many events NS of a
certain type have been produced when Nsel of them are observed.
Nsel − Nb
NS = L · σ −→ σ =
L·A·
Example: efficiency for Z → µ+ µ− process:
efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be
selected
which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi )
2 3 2 3
Y Y
P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5
i=1,n i=1,n
I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon
P(T |R, ζi )
Sara Borroni November 3, 2010 9/36
17. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
A cross-section measurement
The Standard Model Re-discovery
Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section
measurement!
The cross-section measurement is a counting experiment where one has to deduce how many events NS of a
certain type have been produced when Nsel of them are observed.
Nsel − Nb
NS = L · σ −→ σ =
L·A·
Example: efficiency for Z → µ+ µ− process:
efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be
selected
which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi )
2 3 2 3
Y Y
P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5
i=1,n i=1,n
I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon
P(T |R, ζi )
Sara Borroni November 3, 2010 9/36
18. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
A cross-section measurement
The Standard Model Re-discovery
Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section
measurement!
The cross-section measurement is a counting experiment where one has to deduce how many events NS of a
certain type have been produced when Nsel of them are observed.
Nsel − Nb
NS = L · σ −→ σ =
L·A·
Example: efficiency for Z → µ+ µ− process:
efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be
selected
which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi )
2 3 2 3
Y Y
P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5
i=1,n i=1,n
I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon
P(T |R, ζi )
Sara Borroni November 3, 2010 9/36
19. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Reconstruction
Muons in the Muon Spectrometer (MS) are
curved by the toroidal magnetic field
The momentum of the muon is measured
reconstructing the track sagitta (stand-alone
reconstruction)
The stand-alone track can be combined with
an track reconstructed in the inner detector to
have a more precise measurement (combined
reconstruction)
the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS,
due to the energy loss in the calorimeters)
η and φ structure is defined by the geometry and the acceptance of the precision chambers
plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)
Sara Borroni November 3, 2010 10/36
20. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Reconstruction
Muons in the Muon Spectrometer (MS) are
curved by the toroidal magnetic field
The momentum of the muon is measured
reconstructing the track sagitta (stand-alone
reconstruction)
The stand-alone track can be combined with
an track reconstructed in the inner detector to
have a more precise measurement (combined
reconstruction)
the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS,
due to the energy loss in the calorimeters)
η and φ structure is defined by the geometry and the acceptance of the precision chambers
plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)
Sara Borroni November 3, 2010 10/36
21. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Reconstruction
Muons in the Muon Spectrometer (MS) are
curved by the toroidal magnetic field
The momentum of the muon is measured
reconstructing the track sagitta (stand-alone
reconstruction)
The stand-alone track can be combined with
an track reconstructed in the inner detector to
have a more precise measurement (combined
reconstruction)
the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS,
due to the energy loss in the calorimeters)
η and φ structure is defined by the geometry and the acceptance of the precision chambers
plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)
Sara Borroni November 3, 2010 10/36
22. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Reconstruction
Muons in the Muon Spectrometer (MS) are
curved by the toroidal magnetic field
The momentum of the muon is measured
reconstructing the track sagitta (stand-alone
reconstruction)
The stand-alone track can be combined with
an track reconstructed in the inner detector to
have a more precise measurement (combined
reconstruction)
the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS,
due to the energy loss in the calorimeters)
η and φ structure is defined by the geometry and the acceptance of the precision chambers
plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)
Sara Borroni November 3, 2010 10/36
23. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Reconstruction
Muons in the Muon Spectrometer (MS) are
curved by the toroidal magnetic field
The momentum of the muon is measured
reconstructing the track sagitta (stand-alone
reconstruction)
The stand-alone track can be combined with
an track reconstructed in the inner detector to
have a more precise measurement (combined
reconstruction)
the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS,
due to the energy loss in the calorimeters)
η and φ structure is defined by the geometry and the acceptance of the precision chambers
plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)
Sara Borroni November 3, 2010 10/36
24. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Reconstruction
Muons in the Muon Spectrometer (MS) are
curved by the toroidal magnetic field
The momentum of the muon is measured
reconstructing the track sagitta (stand-alone
reconstruction)
The stand-alone track can be combined with
an track reconstructed in the inner detector to
have a more precise measurement (combined
reconstruction)
the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS,
due to the energy loss in the calorimeters)
η and φ structure is defined by the geometry and the acceptance of the precision chambers
plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)
Sara Borroni November 3, 2010 10/36
25. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Trigger
Three trigger levels
L1 hardware based on geometrical coincidences,
with 6 programmable pT thresholds (selects
muons with pT threshold). It defines the
Regions of Interest (ROIs)
L2 refinement of the raw pT measurement done
at L1, accessing ony data of the tracking
detectors in the RoI
EF (Event Filter) refinement of trigger decision
using the whole event and sub-detectors info
pT structure of the trigger turn-on curves is defined by the threshold logic
η and φ structure is defined by the geometry and the acceptance of the trigger chambers
plateau value is around 85% due to the detector acceptance (mainly in the barrel)
Sara Borroni November 3, 2010 11/36
26. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Trigger
Three trigger levels
L1 hardware based on geometrical coincidences,
with 6 programmable pT thresholds (selects
muons with pT threshold). It defines the
Regions of Interest (ROIs)
L2 refinement of the raw pT measurement done
at L1, accessing ony data of the tracking
detectors in the RoI
EF (Event Filter) refinement of trigger decision
using the whole event and sub-detectors info
pT structure of the trigger turn-on curves is defined by the threshold logic
η and φ structure is defined by the geometry and the acceptance of the trigger chambers
plateau value is around 85% due to the detector acceptance (mainly in the barrel)
Sara Borroni November 3, 2010 11/36
27. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Trigger
Three trigger levels
L1 hardware based on geometrical coincidences,
with 6 programmable pT thresholds (selects
muons with pT threshold). It defines the
Regions of Interest (ROIs)
L2 refinement of the raw pT measurement done
at L1, accessing ony data of the tracking
detectors in the RoI
EF (Event Filter) refinement of trigger decision
using the whole event and sub-detectors info
pT structure of the trigger turn-on curves is defined by the threshold logic
η and φ structure is defined by the geometry and the acceptance of the trigger chambers
plateau value is around 85% due to the detector acceptance (mainly in the barrel)
Sara Borroni November 3, 2010 11/36
28. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Trigger
Three trigger levels
L1 hardware based on geometrical coincidences,
with 6 programmable pT thresholds (selects
muons with pT threshold). It defines the
Regions of Interest (ROIs)
L2 refinement of the raw pT measurement done
at L1, accessing ony data of the tracking
detectors in the RoI
EF (Event Filter) refinement of trigger decision
using the whole event and sub-detectors info
pT structure of the trigger turn-on curves is defined by the threshold logic
η and φ structure is defined by the geometry and the acceptance of the trigger chambers
plateau value is around 85% due to the detector acceptance (mainly in the barrel)
Sara Borroni November 3, 2010 11/36
29. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Trigger
Three trigger levels
L1 hardware based on geometrical coincidences,
with 6 programmable pT thresholds (selects
muons with pT threshold). It defines the
Regions of Interest (ROIs)
L2 refinement of the raw pT measurement done
at L1, accessing ony data of the tracking
detectors in the RoI
EF (Event Filter) refinement of trigger decision
using the whole event and sub-detectors info
pT structure of the trigger turn-on curves is defined by the threshold logic
η and φ structure is defined by the geometry and the acceptance of the trigger chambers
plateau value is around 85% due to the detector acceptance (mainly in the barrel)
Sara Borroni November 3, 2010 11/36
30. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Trigger
Three trigger levels
L1 hardware based on geometrical coincidences,
with 6 programmable pT thresholds (selects
muons with pT threshold). It defines the
Regions of Interest (ROIs)
L2 refinement of the raw pT measurement done
at L1, accessing ony data of the tracking
detectors in the RoI
EF (Event Filter) refinement of trigger decision
using the whole event and sub-detectors info
pT structure of the trigger turn-on curves is defined by the threshold logic
η and φ structure is defined by the geometry and the acceptance of the trigger chambers
plateau value is around 85% due to the detector acceptance (mainly in the barrel)
Sara Borroni November 3, 2010 11/36
31. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement
The Concept
to measure the efficiency of the Muon Spectrometer
(MS) we need to select a muon without using the
MS and test if the MS reconstructed/triggered it
how to recognize a muon without using the MS?!?
take advantage of a known process:
Z → µ + µ−
the TagProbe method has been developed to
provide an in-situ determination of muon trigger
and reconstruction efficiency taking advantage of
the kinematic correlation between muons coming
from Z boson decay
Sara Borroni November 3, 2010 12/36
32. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement
The Concept
to measure the efficiency of the Muon Spectrometer
(MS) we need to select a muon without using the
MS and test if the MS reconstructed/triggered it
how to recognize a muon without using the MS?!?
take advantage of a known process:
Z → µ + µ−
the TagProbe method has been developed to
provide an in-situ determination of muon trigger
and reconstruction efficiency taking advantage of
the kinematic correlation between muons coming
from Z boson decay
Sara Borroni November 3, 2010 12/36
33. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement
The Concept
to measure the efficiency of the Muon Spectrometer
(MS) we need to select a muon without using the
MS and test if the MS reconstructed/triggered it
how to recognize a muon without using the MS?!?
take advantage of a known process:
Z → µ + µ−
the TagProbe method has been developed to
provide an in-situ determination of muon trigger
and reconstruction efficiency taking advantage of
the kinematic correlation between muons coming
from Z boson decay
Sara Borroni November 3, 2010 12/36
34. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement
The Concept
to measure the efficiency of the Muon Spectrometer
(MS) we need to select a muon without using the
MS and test if the MS reconstructed/triggered it
how to recognize a muon without using the MS?!?
take advantage of a known process:
Z → µ + µ−
the TagProbe method has been developed to
provide an in-situ determination of muon trigger
and reconstruction efficiency taking advantage of
the kinematic correlation between muons coming
from Z boson decay
Sara Borroni November 3, 2010 12/36
35. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement
The Concept
to measure the efficiency of the Muon Spectrometer
(MS) we need to select a muon without using the
MS and test if the MS reconstructed/triggered it
how to recognize a muon without using the MS?!?
take advantage of a known process:
Z → µ + µ−
the TagProbe method has been developed to
provide an in-situ determination of muon trigger
and reconstruction efficiency taking advantage of
the kinematic correlation between muons coming
from Z boson decay
Sara Borroni November 3, 2010 12/36
36. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement: the TagProbe Method
The Concept
Tag A TAG muon is selected requiring tight criteria to ensure
a pure selection
A fundamental requirement to not to bias the analysis is
to ask the tag to have fired the trigger
Probe Then for each tag, taking advantage from the kinematical
correlation:
select the second muon to be used as a PROBE from the
tracks in the inner tracker and never using the MS info
−→ has this track been reconstructed by
MS?
select the second muon to be used as a PROBE from
reconstructed muons and never using the Muon
Trigger info −→ has this track been
triggered?
Muons The efficiencies are measured wrt a certain muon
reconstruction definition i.e. the same used in the
physics analysis the efficiencies are meant to be used
for
Sara Borroni November 3, 2010 13/36
37. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement: the TagProbe Method
The Concept
Tag A TAG muon is selected requiring tight criteria to ensure
a pure selection
A fundamental requirement to not to bias the analysis is
to ask the tag to have fired the trigger
Probe Then for each tag, taking advantage from the kinematical
correlation:
select the second muon to be used as a PROBE from the
tracks in the inner tracker and never using the MS info
−→ has this track been reconstructed by
MS?
select the second muon to be used as a PROBE from
reconstructed muons and never using the Muon
Trigger info −→ has this track been
triggered?
Muons The efficiencies are measured wrt a certain muon
reconstruction definition i.e. the same used in the
physics analysis the efficiencies are meant to be used
for
Sara Borroni November 3, 2010 13/36
38. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement: the TagProbe Method
The Concept
Tag A TAG muon is selected requiring tight criteria to ensure
a pure selection
A fundamental requirement to not to bias the analysis is
to ask the tag to have fired the trigger
Probe Then for each tag, taking advantage from the kinematical
correlation:
select the second muon to be used as a PROBE from the
tracks in the inner tracker and never using the MS info
−→ has this track been reconstructed by
MS?
select the second muon to be used as a PROBE from
reconstructed muons and never using the Muon
Trigger info −→ has this track been
triggered?
Muons The efficiencies are measured wrt a certain muon
reconstruction definition i.e. the same used in the
physics analysis the efficiencies are meant to be used
for
Sara Borroni November 3, 2010 13/36
39. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement: the TagProbe Method
The Concept
Tag A TAG muon is selected requiring tight criteria to ensure
a pure selection
A fundamental requirement to not to bias the analysis is
to ask the tag to have fired the trigger
Probe Then for each tag, taking advantage from the kinematical
correlation:
select the second muon to be used as a PROBE from the
tracks in the inner tracker and never using the MS info
−→ has this track been reconstructed by
MS?
select the second muon to be used as a PROBE from
reconstructed muons and never using the Muon
Trigger info −→ has this track been
triggered?
Muons The efficiencies are measured wrt a certain muon
reconstruction definition i.e. the same used in the
physics analysis the efficiencies are meant to be used
for
Sara Borroni November 3, 2010 13/36
40. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement: the TagProbe Method
The Concept
Tag A TAG muon is selected requiring tight criteria to ensure
a pure selection
A fundamental requirement to not to bias the analysis is
to ask the tag to have fired the trigger
Probe Then for each tag, taking advantage from the kinematical
correlation:
select the second muon to be used as a PROBE from the
tracks in the inner tracker and never using the MS info
−→ has this track been reconstructed by
MS?
select the second muon to be used as a PROBE from
reconstructed muons and never using the Muon
Trigger info −→ has this track been
triggered?
Muons The efficiencies are measured wrt a certain muon
reconstruction definition i.e. the same used in the
physics analysis the efficiencies are meant to be used
for
Sara Borroni November 3, 2010 13/36
41. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement: the TagProbe Method
The Concept
Tag A TAG muon is selected requiring tight criteria to ensure
a pure selection
A fundamental requirement to not to bias the analysis is
to ask the tag to have fired the trigger
Probe Then for each tag, taking advantage from the kinematical
correlation:
select the second muon to be used as a PROBE from the
tracks in the inner tracker and never using the MS info
−→ has this track been reconstructed by
MS?
select the second muon to be used as a PROBE from
reconstructed muons and never using the Muon
Trigger info −→ has this track been
triggered?
Muons The efficiencies are measured wrt a certain muon
reconstruction definition i.e. the same used in the
physics analysis the efficiencies are meant to be used
for
Sara Borroni November 3, 2010 13/36
42. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Efficiencies Measurement: the TagProbe Method
The Concept
Tag A TAG muon is selected requiring tight criteria to ensure
a pure selection
A fundamental requirement to not to bias the analysis is
to ask the tag to have fired the trigger
Probe Then for each tag, taking advantage from the kinematical
correlation:
select the second muon to be used as a PROBE from the
tracks in the inner tracker and never using the MS info
−→ has this track been reconstructed by
MS?
select the second muon to be used as a PROBE from
reconstructed muons and never using the Muon
Trigger info −→ has this track been
triggered?
Muons The efficiencies are measured wrt a certain muon
reconstruction definition i.e. the same used in the
physics analysis the efficiencies are meant to be used
for
Sara Borroni November 3, 2010 13/36
43. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
TagProbe on the first 1.3 pb−1
The method has been applied to a data integrated luminosity of 1.3 pb−1 (April-August 2010 data-taking periods)
Indet probes −→ for
reconstruction efficiency
Muon probes −→ for trigger
efficiency (L1_MU10 is taken as
example)
The disagreement between data
and MC is manly due to the
difference in the efficiencies (see
next slide). No correction factors
are applied in the plot
Probes Selected with 1.3 pb−1
Indet probes Muon probes
# selected probes 655 567
Expected from MC 714.0 ± 1.4 686.98 ± 0.59
Background estimation (MC) 1.8 ± 0.4% 1.0 ± 0.1%
Sara Borroni November 3, 2010 14/36
44. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Reconstruction Efficiency from Data
Muon reconstruction efficiency vs pT (left) and η (right)
Reconstruction Efficiencies
Region η value Efficiency Scale Factor
Barrel 0.1 |η| 1.05 0.90 ± 0.02 0.94 ± 0.02
End-Caps 1.05 |η| 2.4 0.85 ± 0.03 0.91 ± 0.01
Crack |η| 0.1 0.69 ± 0.09 1.36 ± 0.17
Average −2.4 η 2.4 0.89 ± 0.01 0.95 ± 0.01
Sara Borroni November 3, 2010 15/36
45. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Trigger Efficiency from Data
Muon trigger efficiency vs pT (left) and η (right)
Relative Trigger Efficiencies L1_MU10
Region η value Efficiency Scale Factor
Barrel |η| 1.05 0.81 ± 0.02 1.02 ± 0.02
End-Caps 1.05 |η| 2.4 0.85 ± 0.02 0.89 ± 0.02
Average |η| 2.4 0.83 ± 0.01 0.94 ± 0.02
Sara Borroni November 3, 2010 16/36
46. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Z → µ+ µ− + jets cross-section measurement
With the same 1.3 pb−1 data
sample a first cross-section
measurement of the
Z → µ+ µ− process has
been performed
430
Z → µ+ µ− candidates
have been found in a mass
window of 71 mµµ 111
GeV
correcting for the measured
efficiencies and all the other
factors the resulting inclusive
cross-section is:
σ = 427.3 ± 10.0(stat)+53.5 (syst) ± 47.0(lumi) pb
−11.4
Sara Borroni November 3, 2010 17/36
47. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Z → µ+ µ− + jets cross-section measurement
It’s interesting to perform a
differential cross-section
measurement
The shape of the differential
distributions strongly
depend on the MC models
These measurements are
important to be compared
to the theoretical predictions
and to tune the MC
It necessary to know the
efficiencies in # of jets bins!
Sara Borroni November 3, 2010 18/36
48. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Dependence on the # of Jets
Muon reconstruction (left) and trigger (right) efficiencies vs # of jets in the event
The dependence studied in MC is not jet significative in data (due to the statistics)
Sara Borroni November 3, 2010 19/36
49. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Inclusive Z → µ+ µ− cross-section: a comparison
Published inclusive cross-section measurement with ∼ 300 nb−1
Sara Borroni November 3, 2010 20/36
50. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Summary and Conclusions
Development and optimization of a TagProbe method to measure the muon trigger and reconstruction
efficiencies from data
Optimization using MC samples
Application to the first 1.3 pb−1 of data @ 7 TeV → efficiencies measurement and comparison with MC
expectations
Application of the efficiencies to measure the inclusive pp → Z → µ+ µ− cross-section
ATLAS Collaboration, “Measurement of the W → lν and Z /γ ∗ → ll production cross sections in proton-proton collisions
√
at s = 7 TeV with the ATLAS detector , arXiv:1010.2130v1 , submitted to JHEP
Study of the efficiencies dependence from the jets variables to estimate the production of a Z boson in
association with jets
√
A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a Z -boson in pp collisions at s =
7 TeV, in preparation
√
A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a W -boson in pp collisions at s =
7 TeV, ATL-COM-PHYS-2010
THANKS!
Sara Borroni November 3, 2010 21/36
51. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Summary and Conclusions
Development and optimization of a TagProbe method to measure the muon trigger and reconstruction
efficiencies from data
Optimization using MC samples
Application to the first 1.3 pb−1 of data @ 7 TeV → efficiencies measurement and comparison with MC
expectations
Application of the efficiencies to measure the inclusive pp → Z → µ+ µ− cross-section
ATLAS Collaboration, “Measurement of the W → lν and Z /γ ∗ → ll production cross sections in proton-proton collisions
√
at s = 7 TeV with the ATLAS detector , arXiv:1010.2130v1 , submitted to JHEP
Study of the efficiencies dependence from the jets variables to estimate the production of a Z boson in
association with jets
√
A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a Z -boson in pp collisions at s =
7 TeV, in preparation
√
A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a W -boson in pp collisions at s =
7 TeV, ATL-COM-PHYS-2010
THANKS!
Sara Borroni November 3, 2010 21/36
52. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Publications
Contributions to Conferences:
XVIII International Workshop on Deep-Inelastic Scattering and Related Subjects, Convitto della Calza, Firenze,
19 - 23 April 2010; talk given W/Z Production at ATLAS, ATL-COM-PHYS-2010-179
Incontri di Fisica delle Alte Energie, Sapienza Univeristá di Roma, Italy April 7 - 9 2010; poster presented
Inclusive Muon Production in 900 GeV p-p Collisions with ATLAS Detector
”The 2009 Europhysics Conference on High Energy Physics, Krakow, Poland July 16 - 22 2009; poster
presented ”ATLAS Electroweak Measurements With Early Data, ATL-PHYS-SLIDE-2009-196
”Signaling the Arrival of the LHC Era, ICTP Trieste, Italy December 8 - 13 2008; talk given ”Studies on ATLAS
muon efficiency measurement with Z → µµ, ATL-MUON-SLIDE-2009-151, ATL-COM-MUON-2008-017
Publications with major contribution:
A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a Z -boson in pp
√
collisions at s = 7 TeV, in preparation
A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a W -boson in pp
√
collisions at s = 7 TeV, ATL-COM-PHYS-2010
J. Barreiro Guimaraes da Costa et al., “W → µν and Z → µµ cross-sections measurements in
√
proton-proton collisions at s = 7 TeV with the ATLAS Detector, ATL-COM-PHYS-2010-685
ATLAS Collaboration, “Measurement of the W → lν and Z /γ ∗ → ll production cross sections in
√
proton-proton collisions at s = 7 TeV with the ATLAS detector , arXiv:1010.2130v1 , submitted to JHEP
P.Bagnaia et al.,“Calibration model for the MDT chambers of the ATLAS Muon Spectrometer, ATLAS group
note, ATL-MUON-PUB-2008-004, ATL-COM-MUON-2008-006
Sara Borroni November 3, 2010 22/36
53. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Publications
Other publications:
ATLAS Collaboration, Measurement of inclusive jet and di-jet cross sections in proton-proton collisions at 7
TeV centre-of-mass energy with the ATLAS detector, arXiv:1009.5908v2, submitted to EPJC
ATLAS Collaboration, Search for Quark Contact Interactions in Di-jet Angular Distributions in pp Collisions at
sqrt(s) = 7 TeV Measured with the ATLAS Detector, arXiv:1009.5069v1, submitted to PLB
ATLAS Collaboration, Search for New Particles in Two-Jet Final States in 7 TeV Proton-Proton Collisions with the
ATLAS Detector at the LHC, Phys. Rev. Lett. 105, 161801 (2010), arXiv:1008.2461v2
√
ATLAS Collaboration, Charged-particle multiplicities in pp interactions at s = 900 GeV measured with the
ATLAS detector at the LHC, CERN-PH-EP-2010-004, arXiv:1003.3124, Phys Lett B 688, 2010, Issue 1, 21-42
ATLAS Collaboration, Readiness of the ATLAS Liquid Argon Calorimeter for LHC Collisions, arXiv:0912.2642,
submitted to EPJC
ATLAS Collaboration, Drift Time Measurement in the ATLAS Liquid Argon Electromagnetic Calorimeter using
Cosmic Muons, arXiv:1002.4189, submitted to EPJC
ATLAS Collaboration, ATLAS Inner Detector commissioning and calibration, arXiv:1004.5293, submitted to EPJC
Sara Borroni November 3, 2010 23/36
54. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Backup
Sara Borroni November 3, 2010 24/36
55. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
W /Z Bosons Physics
A sketch
The hadronic nature of the proton-proton collisions opens a wide range of exploration possibilities, from the precise
measurements of Standard Model parameters to the search for new physics phenomena up to the TeV scale
H1
p1 x1 p 1 , ν
k1
γ, Z, W ±
k2
p2 x1 p 2 ¯¯
, ν
H2
Uncertainty sources:
extrapolation to a new kinematical
x region → x = momentum
fraction carried by the colliding
parton
uncertainty on the Parton
Distribution Functions (PDF) →
describe the x distribution for
each parton type
Sara Borroni November 3, 2010 25/36
56. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
TagProbe Selection Details
Muon Pre-selection Cuts
Muon Pre-Selection Cuts
Type Combined Muon
pT 15.0 GeV
|η| 2.5
Track Isolation (0.2) 1.8 GeV
# PIX hits 1
# SCT hits 5
# TRT hits 0 (only for |η| 2.0)
|pID − pMS |/pID
T T T 0.5
pMS
T 10 GeV
d0 0.1 mm
z0 10 mm
Table: Muon pre-selection cuts. This is chosen to be the same used for the inclusive Z and Z+jets 7 TeV analysis. The variables used
in the selection are defined in the text.
Sara Borroni November 3, 2010 26/36
57. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
TagProbe Selection Details
Probes Selection Cuts
TagProbe Selection @ 7 TeV
Cut Tag Indet Probes Muon Probes
Type Combined Muon InDet Track Pre-selected Muon
Charge - OS OS
Trigger L1_MU10 - -
pT 10.0 GeV 5.0 GeV -
|η| 2.5 2.5 -
d0 - 0.1 mm -
∆z0 - 0.5 mm 0.5 mm
Track Isolation - 0.1 -
∆Φ - 2.14 rad 2.14 rad
CaloMuon matching - True False
∆M - MZ ± 20 GeV MZ ± 20 GeV
Table: TagProbe selection for 7 TeV analysis. Jet selection: pT 20 GeV in |y| 2.8
Sara Borroni November 3, 2010 27/36
58. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
TagProbe Selection Details
Selection Variables Distributions
Sara Borroni November 3, 2010 28/36
59. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
TagProbe Cut-Flow
Event Selection
Cut Data MC
Initial Events 24105444 –
GRL 21793697 –
Indet Probes Selection
Cut Data MC
pT 1727031 15972.56
|η| 1718121 15856.2
Charge 862812 8655.86
d0 152147 3055.87
∆z0 118744 2911.73
Track Isolation 21933 1499.05
∆Φ 12567 1178.82
CaloMuon 1675 953.79
∆M 655 713.99 ± 1.40
Muon Probes Selection
Cut Data MC
Type 5883 7059.27
Charge 880 890.23
∆z0 825 878.68
∆Φ 715 796.73
∆M 567 686.98 ± 0.59
Table: Probes selection cut-flow, data and MC expectations. MC is normalized to the data integrated luminosity (1.3 pb−1 )
Sara Borroni November 3, 2010 29/36
60. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
TagProbe Systematic Uncertainties
Systematic Uncertainties
Cut Reconstruction Absolute Trigger Relative Trigger
Efficiency Efficiency Efficiency
d0 0.3% 0.2% –
Isolation 1.2% 0.4% –
∆z0 0.6% 0.6% 0.3%
∆Φ 0.5% 0.8% 0.6%
∆M 0.6% 0.1% 0.6%
1.6% 1.1% 0.9%
Table: Systematics uncertainties on efficiencies measurement. The unceratinties are evaluated varying the selection cuts in the range
explained in the text and estimating the corresponding maximal average efficiency variation.
Sara Borroni November 3, 2010 30/36
61. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Dependence on # of Jets
Efficiencies vs Number of Jets
Cut Reconstruction Relative Trigger Absolute Trigger
Efficiency Efficiency Efficiency
Data
No cut 0.889 ± 0.013% 0.782 ± 0.016% 0.825 ± 0.016
0 0.902 ± 0.023% 0.762 ± 0.030% 0.823 ± 0.030
1 0.942 ± 0.035% 0.811 ± 0.046% 0.808 ± 0.054
2 0.909 ± 0.097% 0.800 ± 0.090% 0.818 ± 0.113
Monte Carlo
No cut 0.924 ± 0.001% 0.903 ± 0.001% 0.859 ± 0.001
0 0.920 ± 0.003% 0.898 ± 0.003% 0.857 ± 0.001
1 0.915 ± 0.007% 0.895 ± 0.007% 0.857 ± 0.004
2 0.913 ± 0.017% 0.875 ± 0.008% 0.883 ± 0.020
Systematicsl Uncertainty
0 0.4% 0.5% 0.2%
1 0.9% 0.8% 0.2%
2 1.1% 2.7% 2.4%
Table: Dependence on the muon efficiencies from the number of jets in the event from data and Monte Carlo. Within the statistical
errors data don’t show a clear dependence from the jets so the average value can be considered instead of the binned one. The
systematic error introduced integrating over this variable can be estimated from the Monte Carlo samples.
Sara Borroni November 3, 2010 31/36
62. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Details of Z +Jets Analysis
Sara Borroni November 3, 2010 32/36
63. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Details of Z +Jets Analysis
Sara Borroni November 3, 2010 33/36
64. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Resolution
Sara Borroni November 3, 2010 34/36
65. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Muon Resolution
Sara Borroni November 3, 2010 35/36
66. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup
Example: Efficiency for 2 Muons Process
Single object and event efficiencies
Suppose to measure the cross-section of a 2 muon process (e.g Z → µ+ µ− ):
Efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be
selected Z
df
= dζ1 dζ2 P(event, ζ1 , ζ2 )
dζ1 dζ2
which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi )
2 3 2 3
Y Y
P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5
i=1,n i=1,n
I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon
P(T |R, ζi )
Sara Borroni November 3, 2010 36/36