√s=91.2 GeV calibration
OUTLINE
• Introduction
• Event topology at √s = 91 GeV
• Requirements for detector calibration
• Tables of cross sections and rates at √s = 91 GeV
• Plots of differential rates of two fermion final states
• LEP and CLIC luminosities
• Summary and prospects
November 2016
J-J.Blaising, LAPP/IN2P3
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Introduction
The main calibration issues to address are:
• Detector and particle identification efficiency
• Muon and tracker systems alignment
• Calorimeter calibration, ECAL, HCAL, FCAL
• Charged particle momentum resolution and scale
• Jet energy resolution and scale
• Flavour tagging
To establish a calibration strategy and the corresponding
needs, start from the detector requirements as in CLIC CDR.
List the requirements and questions related to it.
Some assumptions made may be wrong; the discussion
should lead to corrections.
November 2016
J-J.Blaising, LAPP/IN2P3
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Z→μ⁺μ⁻ Event Topology
Events are:
• Pt balanced
• Back to back in ϕ
Same for Z→e⁺e⁻ and Z→q q̄
Nice topology for efficiency and calibration
measurement
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Calibration Requirements
Tracking Systems Alignment
The measurement of the muon transverse momentum is
sensitive to the alignment of the tracker and of the muon
chambers, to the composition and distribution of material
inside the tracking volume, and to the knowledge of the
magnetic field.
Depending on the Pt range the origin of the bias on the Pt
is different. (CMS paper)
In the Pt range < 10 GeV the uncertainty in the modelling
of the detector material and the description of the B field
dominate.
In the Pt range > 10 GeV the alignment dominates
This the case for Z→μ⁺μ⁻ at √s=91 GeV.
November 2016
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Calibration Requirements
Tracking Systems Alignment
• What is the minimum momentum cut for alignment of
the muon and tracker systems?
With a 4T B field a particle with Pt=2 GeV is looping and
does not reach the HCAL.
For the particle rate estimation at √s=91 GeV; use
Pmin=5 GeV.
• Can one set B=0 for alignment?
Unlikely; detector moves when field is switched on
• Can one use cosmics?
Power pulsing active time ~ 10⁻⁵
November 2016
J-J.Blaising, LAPP/IN2P3
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Calibration Requirements
Momentum Resolution and Scale
CMS:
• In the Pt region Pt<10 GeV the measurement of the
momentum scale and resolution is done using low-mass
resonances Ks→π⁺π⁻ and J/Psi→(μ⁺μ⁻).
• In the Pt region Pt>10 GeV the measurement is done
using Z→μ⁺μ⁻.
BR(Z→μ⁺μ⁻ ~5x10⁻²);
BR(Z→bbˉ→J/Psi→(μ⁺μ⁻) ~10⁻³);
CMS uses about 10⁴ di-muons to measure the momentum
resolution: σ(Pt)/Pt=2.3x10⁻² for Pt=50 GeV and the
uncertainty on the global momentum scale is 0.2%
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Calibration Requirements
Momentum Resolution and Scale
• CLIC Momentum resolution is: σ(Pt)/Pt²=2x10̄⁻⁵.
For a 45 GeV track σ(Pt)/Pt=10̄⁻³
This is 5 times smaller than the CMS momentum resolution.
How many events are needed to measure the momentum
scale with an accuracy << 10⁻³?
With 1000 Z→μ⁺μ⁻ events σ(M)=0.063±0.014 GeV (0.7x10⁻³)
Accuracy on the Z mass is ΔM =σ(M)/√n=2x10̄⁻³ GeV
ΔM/M=2x10⁻⁵.
Accuracy on the momentum scale is √2x2x10⁻⁵.
To measure the momentum resolution and scale as a
function of Pt, η, ϕ requires ~ 35000 events (1 GeV Pt bins)
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Calibration Requirements
ECAL, HCAL, Jets
• ECAL energy resolution: CLIC CDR σ(E)/E< 0.15/√E
For a 45 GeV electron or photon σ(E)/E=2.2x10̄⁻²
• HCAL energy resolution: CLIC CDR σ(E)/E< 0.55/√E
• Jet energy resolution: CLIC CDR σ(E)/E<5x10̄⁻².
Jets back to back in ϕ; no jet confusion.
The jet energy resolutions and scale depends largely on the
particle momentum resolution and scale.
The energy calibration needs are driven by the measurement
of the momentum resolution and the scale calibration.
November 2016
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Cross Sections at √s = 91.2 GeV
Calibration Process
σ[fb]
Ef>10 GeV; 10<θ<170°
σ[fb]
Ef>10; 0.5<θ<179.5°
e⁺ e⁻ → μ⁺ μ⁻ (γ)
1.47x10⁶
1.63x⁶
e⁺ e⁻ → e⁺ e⁻ (γ)
5.70x10⁶
1.72x10⁹
e⁺ e⁻ → τ⁺ τ⁻ (γ)
1.47x10⁶
1.63x10⁶
e⁺ e⁻ → q q̄ (γ)
29.6x10⁶
32.5x10⁶
e⁺ e⁻→ b bˉ (γ)
6.4x10⁶
e⁺ e⁻→ c cˉ (γ)
5.1x10⁶
e⁺ e⁻ → udsūd̄ s̄ (γ)
18.1x10⁶
Two fermion final state cross sections at √s=91.2 GeV with
generator level cuts for two different angular regions.
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Event rates at √s = 91.2 GeV
Calibration
Process
Nb of events
Ef>10 GeV;
10°<θf<170°
Nb of charged
particles
P>5 GeV
Calibration type
e⁺ e⁻ → μ⁺ μ⁻
1.47x10⁶
2.9x10⁶
Alignment
Momentum resolution and
scale; Missing Et
e⁺ e⁻ → e⁺ e⁻
5.70x10⁶
11.4x10⁶
Alignment
Momentum resolution
ECAL, FCAL calibration
Material budget
e⁺ e⁻ → τ⁺ τ⁻
1.47x10⁶
3x10⁶
Alignment, τ Id
HCAL calibration
e⁺ e⁻ → q q̄
29.6x10⁶
107x10⁶
Alignment, Flavour Tagging
Jet energy resolution an
scale
Event rates and charged particle rates at √s=91.2 GeV assuming an
integrate luminosity ∫Lo = 1 fb⁻¹ . The number of charged particles with P>5
GeV is 124x10⁶. Next plots are scaled to this integrated luminosity.
November 2016
J-J.Blaising, LAPP/IN2P3
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e⁺ e⁻ → μ⁺ μ⁻ (γ)
Left: dN/dM(μ,μ) ; with acollinearity cut (blue) to suppress events
with ISR and FSR γ (without in red). Events for momentum scale
calibration ~10⁶events. Right: dN/dP(μ) with and without acollinearity
selection; all events can be used for tracking alignment; ~ 3x10⁶ tracks.
November 2016
J-J.Blaising, LAPP/IN2P3
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e⁺ e⁻ → μ⁺ μ⁻ (γ)
Left: dN/dθ(μ) with and without acollinearity selection; all events can
be used for tracking alignment; ~ 3x10⁶ tracks; 10⁴ tracks per 1° bin.
Right:dN/dEtmiss; Etmiss=Σ(Ptxμ, Ptyμ, Etxγ, Etyγ) (blue); Etmiss
without energy of ISR γs (red). Etmiss also sensitive to background.
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e⁺ e⁻ → e⁺ e⁻ γ
Left: dN/dθ(e) for 10° < θe < 170° ~ 5x10⁴ particles per 1° bin in the
central region; Tracking alignment; ECAL calibration; > 10⁶ e
Right: dN/dϑ(e) for 0.5° < θe < 179.5° ; > 1x10⁶ particles per 1° bin
in the forward calorimeters. FCAL calibration.
November 2016
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e⁺ e⁻ → τ⁺ τ⁻ γ
Left: dN/dθ(h) for 10° < θh < 170° ~ 2x10⁴ particles per 1°
bin in the central region;
Right: dN/dM(π⁺π⁻); K°s mass peak visible; ~20000 events;
HCAL calibration; low Pt momentum scale.
November 2016
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e⁺ e⁻ → q q̄ γ
Flavour tagging 5x10⁶ cc̄; 6x10⁶ bb̄ and 18x10⁶ light quark di-jets.
Left: dN/dΣE(all particles) after hadronisation of the light quarks,
peak at 91 GeV.
Right: dN/dΣE(all particles) after hadronisation of the b b̄ quarks;
the
law energy tail is due to J-J.Blaising,
semi-leptonic
decays of b’s
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LAPP/IN2P3
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LEP and CLIC luminosity at
√s=91 GeV
At LEP1 the peak luminosity was Lo=3.4x10³⁰ cm⁻²s⁻¹. The
table shows the LEP1 performance in 1994 and 1995.
Year
Beam Energy
[GeV]
Total Luminosity
[pb⁻¹]
Average luminosity
[pb⁻¹/day]
1994
45.6
64
0.31
1995
45.6-70
47
0.23
At LEP1 the total luminosity collected was 110 pb⁻¹.
AT CLIC at √s=350 GeV, Lo=1.5x10³⁴cm⁻²s⁻¹; running at
√s=91.2 GeV the peak luminosity will be reduced by
factor ranging between 4 and 100. Assuming a factor 100
the luminosity per day would be 13 pb⁻¹/day.
In one week collect 91pb⁻¹ ~ LEP1 luminosity
November 2016
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CLIC luminosity
Questions for Daniel Schulte
At √s=350 GeV the expected nominal peak luminosity is
Lo(350)=1.5x10³⁰ cm⁻²s⁻¹.
What is the expected peak luminosity In year 1 Lo(350Y1)?
At √s=91 GeV what is the expected peak luminosity?
Lo(91)=Lo(350)/X; where X ranges between 4 and 100.
Or
Lo(91)=Lo(350Y1)/X; this would bring in an additional
reduction.
November 2016
J-J.Blaising, LAPP/IN2P3
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Summary And Prospects
Running at √s=91 GeV seems attractive.
With an integrated luminosity of 0.1 fb⁻¹:
• The number of tracks available for detector alignment is
about 10⁷ including 3x10⁵ μs.
• There are 1.5x10⁵ Z→μ⁺μ⁻ for the measurement of
momentum resolution and momentum scale calibration.
• There are ~ 3x10⁶ Z→q q̄ events for JES calibration and
flavour tagging.
• To collect this luminosity in about a week implies a peak
luminosity Lo(91)>=2x10³² cm⁻² s ⁻¹.
Next step :make the same estimations at √s = 350 GeV and
define a calibration strategy.
November 2016
J-J.Blaising, LAPP/IN2P3
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Thanks
November 2016
J-J.Blaising, LAPP/IN2P3
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CalibrationRequirements
Flavour tagging
• ??
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