search for heavy neutral resonances in vector boson fusion in pp … · 2017. 10. 28. · search...
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Search for heavy neutral resonances in vectorboson fusion in pp collisions at 𝒔𝒔 = 13 TeV
with the ATLAS detector at the LHC
October 27, 2017
Guangyi Zhang1,2
1University of Science and Technology of China2Institute of Physics, Academia Sinica
PhD thesis defense
Supervisor: Liang Han1, Suen Hou2
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Outline
Search for new resonances (R) in qq → Rqq → ℓ+𝜐𝜐ℓ-�̅�𝜐qq (ℓ = e, µ)
using 3.2 fb-1 data collected in 2015
Search for new resonances (X) in qq → Xqq → WWqq → e𝜐𝜐µ𝜐𝜐qq
using 36.1 fb-1 data collected in full 2015 and 2016
Introduction
Physics analyses
Summary
Standard model
Vector boson fusion
LHC and ATLAS detector
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Introduction
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Electromagnetic force Weak force
Strong force Gravitation (not in the SM)4/48
Standard Model Standard Model (SM)• Most successful and well-tested theory
• Elementary particles: leptons, quraks (spin-½ fermions)
=> constituents of matter gauge bosons (W/Z, γ, g), spin-1
=> force mediators Higgs boson, spin-0
=> origin of mass
describing the elementary particles and their interactions
• Fundamental forces: electromagnetic, weak, strong forces gravitation not described in the SM
• Origin of mass: Higgs Mechanism, EWSB particles acquire mass via interactions
with Higgs field (υ ≠ 0)
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nb
JHEP: 0811.010 (2008)
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Vector boson fusion In the SM, vector boson fusion (VBF) is an important class of processes
• provide a unique means to directly examine the EWSB mechanism
W+W- scattering/fusion without a SM Higgs
W+W- scattering/fusion with a SM Higgs
nb
JHEP: 0811.010 (2008)
unitarity violated
unitarity restored
“u” Mandelstam variable
+
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Vector boson fusion VBF is very sensitive to phenomena beyond the SM
?
• Unknown issues about Higgs boson discovered at the LHC:
fully or only partially unitarizes the VBF amplitude ?
is the coupling H→VV exactly the one that SM predicted ?
(low measurement precision ~20 %)
• New resonance needed:
Higgs partially unitarizes the VBF amplitude => new resonances
Any non-SM HVV coupling => new physics
If new resonance has no/weak coupling to fermions
=> VBF is a leading search channel
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Vector boson fusion Characteristics of VBF
• Relatively small production cross sections
=> Experimental studies of VBF are feasible only at the LHC so far
• Fully-leptonic channels have lower SM background
=> Considered in the analyses
• VBF event topology at the LHC
two charged leptons (ee, μμ, eμ), 𝐸𝐸𝑇𝑇𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚, two forward jets (tagging jets)
VBF signal characteristics:
Large mjj (>500 GeV)
Large Δηjj (>2.4)
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Large Hadron Collider (LHC)
proton-proton (pp) collisions• World’s largest and most powerful particle accelerator
• Purpose: Higgs boson, new physics (eg. dark matter ), etc.
• Two separate rings: 26.7 km, 45-175m underground
• Four major detectors: ATLAS, CMS, ALICE and LHCb
• pp collisions: 2835×2835 bunches, bunch spacing
25 ns (7.5 m), 1011 protons/bunch
• Designed luminosity and center-of-mass energy:
ℒ = 1034𝑐𝑐𝑐𝑐−2𝑠𝑠−1, 𝑠𝑠 =13 TeV (2015-2018), 14 TeV (2021-2037)
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ATLAS detector
44 m
25 m
7000 t
ATLAS detector: a general purpose detector at the LHC
Muon spectrometer (|η|<2.7)-precise tracking and triggering on muons-precision-tracking systems: MDT, CSC-trigger systems: RPC, TGC
Inner detector (|η|<2.5):- precise measurement of trackingand vertices
- Pixel, SCT, TRT
EM calorimeter (|η|<3.2):-e/γ measurement-LAr-Pb accordion
Magnet system:-solenoid magnet (barrel), 2 T-toroid magnets, 0.5 T (barrel), 1 T (end-cap)
HAD calorimeter (|η|<4.9):-hadronic measurements-scintillating tiles-steel (central), LAr-Cu/tungsten (forward)
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Search for new resonances (R) inqq → Rqq → ℓ+𝜐𝜐ℓ-�𝝊𝝊qq (ℓ = e, µ)using 3.2 fb-1 data collected in 2015
ATLAS conference note: ATLAS-CONF-2016-053
Proceeding paper: EPJ Web of Conferences 137, 08016 (2017)
My contributions: All physics analysis work
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Introduction Analysis goal:
• Search for new resonances (R) in VBF qq → Rqq → ℓ+𝜐𝜐ℓ-�̅�𝜐qq (ℓ = e, µ)three decay channels: ee, μμ, eμ
Signal model:
Γ0=g2m3/64πυ2
σ: scalar isoscalarφ: scalar isotensorρ: vector isovectorf: tensor isoscalart: tensor isotensor
• Benchmark model: EW chiral Lagrangian (EWChL) with K-matrix unitarization• New resonances: only couples to vector boson, thus mainly produced via VBF• Free parameters: coupling RVV (g=2.5) & mass [200, 500] GeV
scalar
vector
tensor
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Signal Signal definition:
Signal sample
• New resonance
• SM EW qq→ℓ+𝑣𝑣ℓ-�̅�𝑣qq
• Interference
SM continuumsample
• SM EW qq→ℓ+𝑣𝑣ℓ-�̅�𝑣qq
= Signal (New resonance + interference)
Signal Xsec vs. resonance mass
-
Using Whizard+Pythia8 to generate both samples
SM EW continuum
Signal samples
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Data/MC samples Data samples:
• 25 ns data in 2015, Luminosity = 3.2 fb−1
MC corrections:
• Lepton energy/momemtum scale/resolution• Lepton Reco/ID/Iso/Trig effSF• Jet energy scale/resolution, b−tag effSF• Pile-up reweighting
MC samples:
• 𝑡𝑡 ̅𝑡𝑡: Powheg• Wt: Powheg• Z+jets: MadGraph (QCD) and Sherpa (EW)• diboson: Sherpa (QCD) and Whizard (EW)• Zγ: Sherpa • ttV: MadGraph• SM Higgs: Powheg (ggH and VBF)
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Event selection Event selections for signal region (SR):
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Background estimation
• W+jets• QCD
• Z+jets
• 𝑡𝑡 ̅𝑡𝑡• Wt• ttV• Zγ+jets• diboson (WW/WZ/ZZ)• SM Higgs (ggH, VBF)Backgrouds of
ll'+ETmiss+2jets
SM processes that can produce events with
two OS leptons
SM processes that haveone or two leptons from
jets (faked)
MC prediction
Data driven(Matrix method)
Strategy of background estimation:
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Validation regions (VRs) :
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Dominant background sources :• For ee/μμ channel: Z+jets & 𝑡𝑡 ̅𝑡𝑡• For eμ channel: 𝑡𝑡 ̅𝑡𝑡
Background estimation
• Selection criteria listed on slide 14 is assumed unless otherwise specified
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Z pT reweighting for the Z+jets prediction:
• Some discrepancy is found between data & MC for Z pT distribution • Reweighing function is derived by using a polynomial fit for the spectrum
(Data-Non-Z+jets) /Z+jets• Cut 1-9 in slide 14, |mℓℓ-mZ| < 25 GeV• This reweighting function used in both VRs and SR
Reweighting fit function Before reweighting After reweighting
Data vs. prediction in Z+jets VR
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Data vs. prediction in Z+jets VR Z+jets VR: |mℓℓ-mZ| < 25 GeV, no mjj cut
Reasonable agreement of data and the SM prediction observed in Z+jets VR
MTWW
Njets
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Data vs. prediction in 𝒕𝒕�̅�𝒕 VR 𝑡𝑡 ̅𝑡𝑡 VR: Nb-jets > 1, no mjj cut
Good agreement of data and the SM prediction observed in 𝑡𝑡 ̅𝑡𝑡 VR
MTWW
Nb-jets
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Fake background estimation (matrix method)Matrix Method: a data-driven method to estimate fraction of jets misidentified as leptons.
Relation for the event numbers in the different subsamples:
• r1, r2 (f1, f2): the real (fake) rates evaluated for leading(1) and sub-leading(2) leptons
Fake contribution estimation:
• Measure the real rate of electron: tag-probe method is used to extract it from di-el data sample
• Measure the fake rate of electron: obtained from a fake enriched data sample, MC subtraction.
• Measure NTL, NLT, NTT, NLL, then invert the matrix to get the fake contribution--NRF, NFR, NFF
• The matrix method is applied event by event
This matrix method depends on two parameters:
• Real rate: probability for a real lepton identified as a loose lepton to pass tight lepton selection;
• Fake rate: probability for a real jet identified as a loose lepton to pass tight lepton selection.
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Fake background estimation (matrix method) Real rate of electron vs. el_pt, el_η:
Real rate
Fake rate
Fake rate of electron vs. el_pt, el_η:pT η
pT η
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Data vs. prediction in low-mjj VR
Reasonable agreement of data and the SM prediction observed in low-mjj VR
low-mjj VR: mjj < 500 GeV, validate the overall background estimation
MTWW
mjj
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Data vs. prediction in the signal region Signal region (SR):
• Based on all selections on slide 14
No significant data excess above the SM background prediction is observed in SR
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Data vs. prediction in the signal regionee-channel µµ-channel
eµ-channel
-- Due to two neutrinos in the final state,
𝑀𝑀𝑇𝑇𝑊𝑊𝑊𝑊 is a useful discriminating variable:
-- No significant excess beyond the SM
background predication is found
MTWW
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Systematic uncertainties Experimental uncertainties(%) on the backgrounds in the signal region:
Theoretical uncertainties on the production Xsec of the backgrounds
Additional shape systematic uncertainties for two dominant backgrounds
(Z+jets, 𝑡𝑡 ̅𝑡𝑡) are included.
Experimental uncertainties on signal considered (JES/JER, b-tagging, 𝐸𝐸𝑇𝑇𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚etc.)
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95% CL upper limits
σ
No significant excess above the SM background expectation is observed.
95% CL upper limits are derived on σ×Br for new resonances (σ, φ, ρ, f and t)
Number counting as inputs to set limit due to limited signal statistics
The frequentist method (CLs), is used to compute 95% CL upper limits
ρ
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φ
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95% CL upper limits f
t Observed 95% CL exclusion limitsin 200-500 GeV mass region:
380 − 220 fb (σ particle)460 − 240 fb (φ particle)330 − 270 fb (ρ particle)340 − 260 fb (f particle)310 − 260 fb (t particle)
mR < 230 (300) GeV for ρ (f) excluded
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Summary for analysis 1
• SM backgrounds are carefully studied using MC simulation and
data-driven (matrix method) and validated in several VRs.
• all the possible uncertainties are well evaluated
• no significant data excess above the SM prediction is observed
• First 95% CL upper limits derived, mR < 230 (300) GeV for ρ (f) resonance excluded
Search for new resonances (R) in qq → Rqq → ℓ+𝜐𝜐ℓ-�̅�𝜐qq (ℓ = e, µ) using 3.2 fb-1 data
Need to update:
• Published on:
EPJ Web of Conferences 137, 08016 (2017)
ATLAS-CONF-2016-053
• Small data set (3.2 fb-1)
• Signal samples – low statistics
• Three decay channels (ee, μμ, eμ) studied, but the most sensitive one is eμ
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Search for new resonances (X) inqq → Xqq → WWqq → e𝜐𝜐µ𝜐𝜐qqusing 36.1 fb-1 data (2015+2016)
Paper: submitted to Eur. Phys. J. C, arXiv:1710.01123 [hep-ex]
CERN Preprint URL: CERN-EP-2017-214
My contributions: signal Monte Carlo samples generation, signal
acceptance and predictions, event selection optimization, systematic
uncertainties, etc.
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Introduction Analysis goal:
• Search for new resonances (X) in VBF qq → Xqq → WWqq → e𝜐𝜐µ𝜐𝜐qq
Main differences with the previous analysis:
• Data: 3.2 fb-1 in 2015 => 36.1 fb-1 in full 2015+2016
• Signal model: EWChL model => several individual signal models covering scalar,
vector and tensor resonances
• Signal mass range: extended from 500 GeV up to 3000 GeV
• Decay channel: ee, μμ, eμ => eμ (most sensitive one and easier to handle the SM bkg)
• Event categories: VBF Njet ≥ 2 => VBF Njet ≥ 2 + VBF Njet =1 (gain more sensitivities)
• Event selection and background estimation: optimized and updated accordingly
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Signal models Signal models: new scalar, vector and tensor resonances introduced
• Heavy Higgs with a Narrow Width Approximation (NWA, scalar)
• Heavy Higgs with a Large Width Assumption (LWA, scalar)
• Georgi-Machacek (GM, scalar) model
width = 4 MeV (same widths for different heavy Higgs masses) mass = [200, 3000] GeV
width = 5%, 10% and 15% of heavy Higgs mass mass = [200, 3000] GeV
new scalar resonance: 𝐻𝐻50 (does not couple to fermions) parameters:
o 𝐻𝐻50𝑉𝑉𝑉𝑉 coupling, proportional to 𝑠𝑠𝑠𝑠𝑠𝑠𝜃𝜃𝐻𝐻 (= 0.4)o mass = [200, 1000] GeV
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Signal models• Heavy Vector Triplet (HVT, vector) model new vector resonance: 𝑍𝑍′ parameters:
o 𝑍𝑍′VV coupling 𝑔𝑔𝑉𝑉 (=1)o mass = [300, 1000] GeVo to suppress the non-VBF contributions, assume that 𝑍𝑍′ bosons
does not couple to fermions
• Effective Lagrangian Model (ELM, tensor)
new tensor resonance (spin-2): T parameters:o TVV coupling 𝑓𝑓𝑚𝑚 (=1)o mass = [200, 1000] GeVo T resonance doesn’t couple to fermions
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Event selection Event selections for signal regions (VBF Njet = 1 SR, VBF Njet ≥ 2 SR)
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Background estimation Backgrounds:
• Top and WW (dominant backgrounds):
Normalization factors obtained from simultaneously fitting top and WW contributions to data in control and signal regions
• W+jets: data driven method - “fake-factor” method
• Z+jets, non-WW diboson, Higgs production: small contribution, MC simulation
Background estimation
• Top, WW, non-WW diboson, Z+jets, W+jets, Higgs production
WW in VBF 2J category which was from MC prediction(small contribution, diffcult to isolate a kinematic region with high purity of WW)
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Control regions Definition of Top and WW control regions (CRs)
• some cuts inverted, removed or loosened to gain more data
statistics and higher purity
WW background:
• VBF Njet = 1: WW CR• VBF Njet ≥ 2: WW MC simulation
Top background:
• Top CR: combined VBF Njet = 1and VBF Njet ≥ 2 to gain morestatistics
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Data vs. prediction in the control regions Top control region:
WW control region:
NF_Top_VBF = 1.12−0.12+0.13
NF_WW_VBF1J =1.0 ± 0.2
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W+jets estimationW+jets estimation
• use a data-driven method - “fake factor method” to estimate its contribution
• two basic components: W+jets control sample and the fake factor
W+jets control sample (𝑁𝑁id+anti−id):
o selected from the data using the same event selections as SR but requiringone pair of id+anti-id leptons
o non-W+jets contributions (eg. Top and WW) 𝑁𝑁id+anti−idEW subtracted using MC
2.5
W+jets control sample fake factor
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barrel end-cap
barrel end-cap
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W+jets estimationW+jets estimation
fake factor ( 𝑁𝑁idNanti−id
):
o measured using a fake-enriched dijet data sample, with EW (W/Z+jets) subtraction o small trigger bias also considered (more in backup)
Electron
Muon
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Data vs. prediction in the signal region Signal region:
No significant data excess above the SM background prediction observed
VBF 1J SR VBF 2J SR
mT
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Systematic uncertainties Uncertainties of Top background (%):
• Only dominant uncer. shown, others included in “Total”• Single top: theoretical uncer. on single-top-quark production
Uncertainties of WW background (%):• Only dominant uncer. shown, others included in “Total”
Shape uncertainties of Top and WW:• mT shape dependence for the PDF uncertainty in the SRs considered
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Systematic uncertainties Uncertainties of W+jets background:
• mainly arise from jet flavor composition, EW subtraction, stat. uncertainty, etc.
• VBF 1J SR: 32%, VBF 2J SR: 35%
Uncertainties of signal (NWA):
• mainly arise from parton shower, PDF, QCD scales, etc.
• VBF 1J SR: 5.1% - 9.0%, VBF 2J SR: 3.3% - 8%
Uncertainties of other background:
• smaller contributions on the uncertainties
• experimental uncertainties, normalized to high-order Xsec. prediction
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95% CL upper limits No data excess above the SM prediction is observed. 95% CL upper limits are derived on σX×Br(X→WW) The frequentist method (CLs), is used to compute 95% CL upper limits
NWA LWA
GMValues above 1.3 pb at 200 GeV
and above 0.006 pb at 3 TeV for
NWA and 15% LWA are excluded
Scalar resonances
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95% CL upper limits
Current sensitivity not sufficient to exclude the VBF signals from
GM, HVT and ELM models
HVT ELM
Vector resonance Tensor resonance
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Summary for analysis 2
• SM backgrounds are carefully studied using simultaneous fit, fake factor
method and MC simulation, and validated in specific CRs.
• all the possible uncertainties are properly evaluated
• no evidence of such heavy neutral resonances is found
• 95% CL upper limits set on σX×Br(X→WW) of new scalar, vector and tensor
resonances predicted by several individual signal models
Search for new resonances (X) in qq → Xqq → WWqq → e𝜐𝜐µ𝜐𝜐qq using 36.1 fb-1 data
• Published on:
Eur. Phys. J. C, arXiv:1710.01123 [hep-ex] (submitted)
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ATLAS MDT gas work (install, repair and maintain) MDT (Monitored Drift Tubes) gas system repairs and maintenance:
Installation of MDT gas system for BME chambers:
Obtained the ATLAS authorship and took a lot of shift work assigned to USTC
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Publications Publications
• “Search for heavy resonances decaying into WW in the e𝜐𝜐μ𝜐𝜐 final state in pp collisions at 𝑠𝑠 = 13 TeV with the ATLAS detector”Submitted to Eur. Phys. J. C, arXiv:1710.01123 [hep-ex]
• “Search for heavy resonances in vector boson fusion”EPJ Web of Conferences 137, 08016 (2017)
• “Search for heavy neutral resonances in vector boson fusion in pp collisions at𝑠𝑠 = 13 TeV with the ATLAS detector at the Large Hadron Collider”
ATLAS-CONF-2016-053
• “Multi-Boson Simulation for 13 TeV ATLAS Analyses”ATL-PHYS-PUB-2017-005
Paper in ATLAS EB review• “Measurement of 𝑍𝑍𝑍𝑍 → ℓ+ℓ−𝜐𝜐�̅�𝜐 production in proton-proton collisions at 𝑠𝑠 =
13 TeV with ATLAS detector”ATL-COM-PHYS-2016-1801 (aim at Eur. Phys. J. C)
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• “Search for heavy resonances in vector boson fusion at 𝑠𝑠 = 13 TeV with theATLAS detector at the LHC”, The 9th Joint Meeting of Chinese PhysicistsWorldwide, Tsinghua University, Beijing, China, 17-20 July, 2017http://meetings.csp.escience.cn/dct/page/1(2017 APS-OCPA Outstanding Conference Poster Award) 47/48
Conference talks and posters Conference talks
• “Search for heavy resonances in vector boson scattering”, XII Quark Confinement and the Hadron Spectrum, Thessaloniki, Greece, Aug. 29 - Sep. 03, 2016.https://indico.cern.ch/event/353906/contributions/2257680/
• “VBF/VBS Resonances”, ATLAS Beyond the Standard Model Higgs and Exotics Joint Workshop, Grenoble, France, 11-15 April, 2016.https://indico.cern.ch/event/465157/
• “Search for heavy neutral resonances in vector boson fusion qq → ℓ𝜐𝜐ℓ𝜐𝜐qq with the ATLAS detector”, Second China LHC Physics Workshop, Peking University,Beijing, China, 16-19 December, 2016http://indico.ihep.ac.cn/event/6062/contribution/66
Conference posters
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Summary
• Search for new resonances (R) in qq → Rqq → ℓ+𝜐𝜐ℓ-�̅�𝜐qq (ℓ = e, µ)
using 3.2 fb-1 data collected in 2015
• Search for new resonances (X) in qq → Xqq → WWqq → e𝜐𝜐µ𝜐𝜐qq
using 36.1 fb-1 data collected in full 2015 and 2016
Two physics analyses performed using pp collision data recoded at
𝑠𝑠 = 13 TeV with the ATLAS detector at the LHC
4 publications, 1 paper under ATLAS review, 3 conference talks,
1 conference poster (outstanding award)
and many important ATLAS group talks (eg. unblinding & approval talks)
ATLAS MDT gas system installation, repair and maintence
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Backup
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Mandelstam variables (analysis 1) Definitions of Mandelstam variables (s, t, u)
• 𝑠𝑠 ≈ 2𝑝𝑝1 � 𝑝𝑝2 ≈ 2𝑝𝑝3 � 𝑝𝑝4• 𝑡𝑡 ≈ −2𝑝𝑝1 � 𝑝𝑝3 ≈ −2𝑝𝑝2 � 𝑝𝑝4• 𝑢𝑢 ≈ −2𝑝𝑝1 � 𝑝𝑝4 ≈ −2𝑝𝑝3 � 𝑝𝑝2
s-channel
t-channel
u-channel
Relativistic limit (large p)
• 𝐸𝐸2 = 𝐩𝐩 � 𝐩𝐩 + 𝑐𝑐02 ⇒ 𝐸𝐸2 ≈ 𝐩𝐩 � 𝐩𝐩
⇒ 𝑠𝑠 = (𝑝𝑝1 + 𝑝𝑝2)2= 𝑝𝑝12 + 𝑝𝑝22 + 2𝑝𝑝1 � 𝑝𝑝2≈ 2𝑝𝑝1 � 𝑝𝑝2
where 𝑝𝑝12 = 𝑐𝑐12, 𝑝𝑝22 = 𝑐𝑐2
2
• 𝑠𝑠 = (𝑝𝑝1 + 𝑝𝑝2)2=(𝑝𝑝3 + 𝑝𝑝4)2
• 𝑡𝑡 = (𝑝𝑝1 − 𝑝𝑝3)2=(𝑝𝑝4 − 𝑝𝑝2)2
• 𝑢𝑢 = (𝑝𝑝1 − 𝑝𝑝4)2=(𝑝𝑝3 − 𝑝𝑝2)2
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Feynman diagrams of VBF (analysis 1) NonVBF-EW process
VBF-QCD process
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Effective theories and Unitarity (analysis 1)
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Adding a resonance (analysis 1)
K-matrix
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K-matrix unitarization (analysis 1)
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K-matrix unitarization (analysis 1)
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Object definition (analysis 1)Selection Electron MuonpT (GeV) >25 >25|η| <2.47, veto 1.37-1.52 <2.5| d0/σ(d0) | <5 <3| z0 sinθ | (mm) <0.5 <0.5ID TightLH (if Et_el<300 GeV)
MediumLH(if Et_el>300 GeV)Medium
Isolation passTightIso passTightIso
Selection JetJet type AntiKt4EMTopoJets
pT (GeV) >30(>50 if 2.5<|η|<4.5)
|η| <4.5
JVT JVT > 0.64 if |η| < 2.4 and pT < 50 GeV
Jet quality Not badjet
Jet flavor tagger MV2c20 (85% efficiency)
Selection METMETContainer MET_Reference_Anti
Kt4EMTopoObjets used to rebuild MET
Electrons, muons, jets
METSoftTerm Track soft terms
MET(GeV) >35
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Triggers and signal acceptance (analysis 1) Single-lepton triggers:
Signal acceptance times efficiency:
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Lepton centrality and frecoil (analysis 1) Lepton centrality ζ :
frecoil:
• Measures the strength of the recoil system relative to the dilepton system
• ϛ in VBF topology tends to be positive
• To reduce the background from strongproduction of double vector boson processes(ϛ > -0.5)
•
• Useful to reject the Z/γ* → ℓℓ background• frecoil < 2
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Real rate of electron (analysis 1)
Selection Tight Electron Loose ElectronpT (GeV) >25 >25|η| <2.47, veto 1.37-1.52 <2.47, veto 1.37-1.52| d0/σ(d0) | <5 <5| z0 sinθ | (mm) <0.5 <0.5ID TightLH
(MediumLH, if Et_el>300GeV)LooseLH
Isolation passTightIso No isolation requirement
Tight/Loose electron definitions:
Cut flow:• Basic event pre-selection, event cleaning/GRL cut/PV cut.
• Single-electron trigger chain(e24_lhmedium_L1EM20VH || e60_lhmedium || e120_lhloose)
• Exactly two LOOSE electrons with opposite sign
• mZ -10GeV < mee < mZ +10GeV
• At least one Tight lepton as Tag
• For the probe lepton, real rate = NTight/NLoose
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Fake rate of electron (analysis 1)
Selection Tight Electron Loose ElectronpT (GeV) >25 >25|η| <2.47, veto 1.37-1.52 <2.47, veto 1.37-1.52| d0/σ(d0) | <5 <5| z0 sinθ | (mm) <0.5 <0.5ID TightLH
(MediumLH, if Et_el>300GeV)LooseLH
Isolation passTightIso No isolation requirement
Tight/Loose electron definitions:
Cut flow:• Basic event pre-selection, event cleaning/GRL cut/PV cut.
• use single-electron trigger chain (e24_lhloose_L1EM20VH || e60 _lhloose || e120_lhloose)
• At least one LOOSE electrons
• reject events with two loose electrons in Z mass window(|Mee-MZ|<20GeV)
• reject events with two or more tight electrons
• MET<25GeV
• Fill histrograms, fake rate = NTight/NLoose
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Signal models (analysis 2) Signal models: new scalar, vector and tensor resonances introduced
• Heavy Higgs with a Narrow Width Approximation (NWA)
• Heavy Higgs with a Large Width Assumption (LWA)
• Georgi-Machacek (GM) model
width = 4 MeV (same widths for different heavy Higgs masses) mass = [200, 3000] GeV
width = 5%, 10% and 15% of heavy Higgs mass Mass = [200, 3000] GeV
extend Higgs sector with additional one real and one complex triplets scalar potential determined to keep the ratio of charged to neutral currents as
in SM (ρ parameter = 1)
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• Georgi-Machacek (GM) model reorganize the physical states to have
• 2 singlet neutrals (ℎ,𝐻𝐻)• triplet (𝐻𝐻3+,𝐻𝐻30,𝐻𝐻3−)• fiveplet (𝐻𝐻5++,𝐻𝐻5+,𝐻𝐻50,𝐻𝐻5−,𝐻𝐻5−−)
parameters• All the H5VV couplings are proportional to 𝑠𝑠𝑠𝑠𝑠𝑠𝜃𝜃𝐻𝐻 (fraction of the gauge
boson masses 𝑐𝑐𝑊𝑊 and 𝑐𝑐𝑍𝑍 generated by the vev of the triplets)• resonance mass: [200, 1000] GeV• H5 scalars does not couple to fermions
• Heavy Vector Triplet (HVT) model parameterizes the couplings of the HVT bosons to the SM gauge bosons and
Higgs with 𝑐𝑐ℎ𝑔𝑔𝑉𝑉, to the fermions with 𝑔𝑔2𝑐𝑐𝐹𝐹/𝑔𝑔𝑉𝑉 new resonances (𝑍𝑍′, 𝑊𝑊′) parameters
• XVV coupling 𝑔𝑔𝑉𝑉 (=1), resonance mass [300, 1000] GeV• to suppress the non-VBF contributions, assume that HVT bosons
does not couple to fermions (𝑐𝑐𝐹𝐹=0)
Signal models (analysis 2)
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• An an effective Lagrangian model (ELM)
introduce general spin-2 fields 𝑇𝑇𝜇𝜇𝜇𝜇 (singlet) and 𝑇𝑇𝑗𝑗𝜇𝜇𝜇𝜇(triplet)
spin-2 singlet case considered, its effective Lagrangian
a form factor introduced to multiply with the amplitudes topreserve unitarization
parameters• characteristic energy scale: Λ = 1.5 TeV• cut-off energy scale and suppression power: Λ𝑓𝑓𝑓𝑓 = 3 TeV, 𝑠𝑠𝑓𝑓𝑓𝑓 = 4• variable coupling parameters: 𝑓𝑓1 = 𝑓𝑓2 = 𝑓𝑓5 = 1• resonance mass: [200, 1000] GeV• Spin-2 resonances doesn’t couple to fermions
Signal models (analysis 2)
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GM model (analysis 2)https://cds.cern.ch/record/2002500/files/LHCHXSWG-2015-001_2.pdf
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GM model (analysis 2)https://cds.cern.ch/record/2002500/files/LHCHXSWG-2015-001_2.pdf
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Triggers and mT definition (analysis 2) Nominal triggers
Triggers for selecting dijet sample in W+jets estimation
mT definition
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Data/MC sample for analysis 2 Data samples:
• Full data in 2015+2016, Luminosity = 36.5 fb−1
MC samples:
• Signal samples
NWA: Powheg + Pythia8 LWA: MG5_aMC@Nlo + Pythia8 GM/HVT: MG5_aMC@Nlo + Pythia8 ELM: VBFNLO + Pythia8
• Background samples
Top: Powheg + Pythia8 WW: Sherpa 2.2.1 Non-WW diboson: Sherpa 2.2.1 Z+jets: Sherpa 2.1.1 Higgs: Powheg + Pythia8
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Signal acceptance times efficiency (analysis 2)
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W+jets estimation (analysis 2)
• selected using the single-lepton prescaled triggers with the low-pT
thresholds of 12 (14) GeV for electrons (muons)
Dijet sample for fake factor measurement:
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W+jets estimation - trigger bias (analysis 2) A small trigger bias:
• Introduced when the anti-lepton fires the triggers while the id leptondoes not fire the triggers.
• Triggered fake factor:using the nominal unprescaled single-lepton triggers to select dijet sample
Nominal fake factor: applied to the most of events (92%) in the W+jets control sample
Triggered fake factor: only applied to the events (8%) where the anti-lepton fires the triggers and the id lepton does not fire the triggers.
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W+jets estimation - CR (analysis 2) VBF 1J category
VBF 2J category
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W+jets estimation (analysis 2)
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W+jets estimation (analysis 2)
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mT shape uncertainties of Top and WW (analysis 2)
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mT shape uncertainties of NWA signal (analysis 2)
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Correlations among nuisance parameters (analysis 2) NWA m = 800 GeV:
correlation coefficients > 0.4 are shown
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ATLAS MDT gas system work Off-detector MDT gas system
• Supplies a steady gas flow
• Baseline of MDT gas mixture:
Ar ~93%, CO2 ~ 7%, H2O~0.075%
• Chamber volume: ~725000 nl
• Operating pressure: 3 bar
• Running in a loop, driven by a pump
• Fresh gas input is 10% per day,
10% of gas is flushed per day.
• 15 distribution racks , each one
contains 16 ~ 24 gas channels
• Controlled by GCS.https://atlasop.cern.ch/twiki/bin/view/Main/MDTGasSystemOverview
Off-detector MDT gas system
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ATLAS MDT gas system work On-detector MDT gas system
https://atlasop.cern.ch/twiki/bin/view/Main/MDTGasSystemOverview
On-detector MDT gas system
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ATLAS MDT gas system workMDT leak measurement
Leak rate = 104 mbar/d
Procedure:
-- Rack channel closed-- Measuring temperature
and pressure-- Calculating temperature
corrected pressure (normalized to Tn=20℃)
Calculating gas loss usingp1V0/T1=pnVn/Tn
-- p1 : measured (uncorr.) pressure-- V0: channel gas volume-- T1: measured temperature-- Vn: norm volume(3*V0)-- Tn: norm temperature(293K)-- Pn: derived normalized
pressure
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ATLAS MDT gas system workMDT EO gas leak repairs (2014-2015)
2015
2014
EO gas leaks improved a lot.
1: gas-jumpers made of NORYL (old), 2 : gas-jumper made of POCAN (new)
EO A side:Philipp Fleischmann, Guangyi ZhangEO C side:Anatoli Kozhin ,Vladimir Gushchin
In the most case, gas leaks ofEO are caused by cracks of gasjumpers made of NORYL
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ATLAS MDT gas system workMDT Barrel gas leak repairs (2014-2015)
BOL5A01_ML2BOL2A03_ML1BIS6C14_ML1
MDT Barrel gas leak measurement (2014-2017)
BME4A13_ML1 BMF2A14_ML1 EIL2A11_ML2 BIL4A01 ML1
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ATLAS MDT gas system workMDT EO gas leak measurement and repairs (2016-2017)
Gas connections and leak measurement for all new MDT BMG chambers (2017):
Before repairs(2016)
After repairs(2017)
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Data taking
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LHC / HL-LHC Plan