k. einsweiler, lbnl on behalf of the atlas collaboration · t2. k. einsweiler -lbnl 20-may-19 13...

ATLAS Physics Highlights for LHCP 2019

First post-Run 2 LHCP Conference => mix of Full Run 2 and 2018 !

• Run 2 from ATLAS Perspective

• Survey of Run 2 Performance

• Recent Highlights from ATLAS Physics

• Large number of full Run 2 (139 fb-1) Exotic/SUSY (+1 Higgs) analyses

• Many interesting Higgs, SM, B-Physics, and HI results on smaller samples.

Only a few of many highlights shown here – will see much more in following plenary and parallel sessions throughout the week !

K. Einsweiler, LBNLon behalf of the ATLAS Collaboration

Overview of Run 2• LHC accelerator performance during Run 2 was simply outstanding !• ATLAS accumulated total of 139 fb-1 “good for physics” data, with lumi up to

2x1034 and initial µ values ~60. The detector performed extremely well !

20-May-19K. Einsweiler - LBNL 2

Overview of Run 2• Overall performance of ATLAS excellent, with operational fractions in all

detectors which were very high (no impact on physics).• Average µ value for the full Run 2 was ~30, but non-negligible lumi with µ~60

(and due to 8b4e fill pattern in 2017, some data up to µ~70 !)


Note: low-µ data-taking peak provided special samples for precision W physics !Many other special runs integrated into the program…

Lepton Performance Results• Excellent Muon performance in 2018, with efficiencies of 98-99% for most

Muon types, and MC versus Data agreement generally within 1%.• Electron energy scale (α) very consistent across 4 years of Run 2 (< 0.2% in

barrel). Also little dependence of energy scale and efficiency on µ values.


Many other performance studies and results under development towards Run 2 publications – not ready yet !

Major benefits to consistent performance and physics due to use of a single coherent software release for full Run 2 !

Endcap Barrel

Full Run 2 Exotic Searches• Search for heavy charged boson W′→lν with 139 fb-1 at 13 TeV.• No significant deviation from SM backgrounds, so limit set on SSM W′ at 95%

CL to be above 6.0 TeV (5.8 TeV) obs (exp) for combined e+µ result.Also provide σ(visible) => provide general constraints on all W′ models.


e

µ

SSM (Combined e+µ) Γ(W′)

arXiv:1905.xxxxxavailable soon…

e σ(visible) limits µ

Full Run 2 Exotic Searches• Search for high-mass di-lepton resonances with 139 fb-1 at 13 TeV.• No significant deviation from data-driven backgrounds, so limit set on a SSM

Z′ at 95% CL to be above 5.1 TeV (5.1 TeV) obs (exp) for combined e+µresult.


e µ

σ(fid) => limits apply to all Z′ models

arXiv:1903.06248

https://arxiv.org/abs/1903.06248

Full Run 2 Exotic Searches• Search for high-mass di-jet resonances with 139 fb-1 at 13 TeV.• No significant deviation from SM backgrounds, so limit set on a q* model at

95% CL to be above 6.7 TeV (6.4 TeV) obs (exp).


q* Model

Gaussian Model

ATLAS-CONF-2019-007

https://cds.cern.ch/record/2668385

Full Run 2 Exotic Searches• Search for high-mass di-jet resonances with 139 fb-1 at 13 TeV.• Highest mass central dijet event observed to date: m(jj) = 8.02 TeV


Full Run 2 Exotic Searches• Search for high-mass di-boson resonances with 139 fb-1 at 13 TeV.• Use R=1.0 jets as input to W/Z Tagger which uses Track-CaloClusters to

reconstruct boosted bosons using m(jet), ntrk, and D2 variables.• No significant deviation from SM backgrounds, so set limits. Consider three

different classes of models (Spin 0, 1, and 2: HVT = heavy vector triplet).


M(J) distribution in control region

ATLAS-CONF-2019-003


Full Run 2 Exotic Searches• Search for high-mass di-boson resonances with 139 fb-1 at 13 TeV.• Use R=1.0 jets as input to W/Z Tagger which uses Track-CaloClusters.

The highest m(JJ) event observed to date has m(JJ) = 4.44 TeV (only tracks with PT > 1.7 GeV are shown).


Full Run 2 SUSY Searches• Search for direct EWK production of charginos and sleptons with 139 fb-1 at

13 TeV in final states with two leptons and missing ET.• Use high values of stranverse mass (mT2) with two lepton PT and missing ET

as inputs. Also categorize as 0J or 1J (non-b-tagged jets). Note very substantial increase in limits compared to previous 8 or 13 TeV publications.


ATLAS-CONF-2019-008


Full Run 2 SUSY Searches• Search for SUSY particles in models with compressed mass spectra using

139 fb-1 at 13 TeV in final states with same-flavor oppositely-charged low-PTleptons, missing ET and ISR radiation.

• Limits are set assuming the lightest neutralino has a mass similar to a chargino, heavier neutralino, or slepton. Sensitivity to mass splittings of ~1 GeV are achieved for masses of ~100 GeV.


Important improvements on LEP, 8/13 TeV results.Substantial exclusions extend to 150-250 GeV on neutral χ2, charged χ1, and sleptons. Some exclusions down to mass splittings of 1-5 GeV.

ATLAS-CONF-2019-014available soon…

Full Run 2 SUSY Searches• Search for direct stau production with 139 fb-1 at 13 TeV in final states with two

hadronically decaying tau leptons.• Limits are set assuming two mass-degenerate staus in simplified models which

each decay into lightest neutralino and tau lepton. Two signal regions with asymmetric di-tau (low mass) and di-tau + missing ET (high mass). Use mT2.


Note: LEP limits are below 100 GeV => don’t appear.

Previous 8 TeV analysis very limited exclusions…

ATLAS-CONF-2019-018 available soon…

Full Run 2 SUSY Searches• Search for pair production of bottom squarks with 139 fb-1 at 13 TeV in final

states with no leptons, three or more b-jets and missing ET. Previously Run 1 !• Naturalness suggests third generation squarks may be “light”…• Develop three orthogonal sets of signal regions (SRA, SRB, SRC) with a total

of 8 sub-regions, based on topology and PT of b-jets.


Background-only fit extrapolation into signal regions.

ATLAS-CONF-2019-011


Full Run 2 SUSY Searches• Search for LLP with displaced vertex and muon with 136 fb-1 at 13 TeV in final

states with either a high-PT Muon Spectrometer track or very large missing ET.• Dedicated reconstruction needed for vertices/muons (d0 < 30cm z0 < 30/50cm).

Interpretation based on long-lived stop decays. Parallel Missing ET/Muon SRs.


• With all selection cuts applied, very low background, but still signal sensitivity (see above). Missing ET (Muon) selections result in 0 (1) event, consistent with bkgd.

• For lifetimes of 0.1 – 30 ns, exclude m(stop) < 1.3 TeV.• More powerful than non-LLP search !

ATLAS-CONF-2019-006


Full Run 2 SUSY Searches• Search for stop pair production accompanied by Z decaying to leptons using

139 fb-1 at 13 TeV in final states with at least three leptons, two of which are compatible with a Z boson, many jets (some of which are b-jets), and large missing ET.

• Two sets of signal regions are established, one set optimized for stop1 pair production, and one set optimized for stop2 pair production.


Significantly larger exclusion regions than in previous analyses, particularly for stop1and for larger χ1 or χ2 masses.


Full Run 2 SUSY Searches• Search for third generation squarks and gluinos using 2 SS or 3 leptons and jets.• Five signal regions: 2 for gluinos (RPC + RPV), 2 for sbottom, 1 for stop.


Gluino limits extend to above 1600 GeV

Sbottom/stop limits extend to above 750 GeV


Higgs Combination Results for 36 fb-1/80 fb-1

• Combination of a comprehensive set of Higgs production and decay measurements at 13 TeV, providing state of the art overview of Higgs sector.


Global µ valueuncertainty now

only 8-9%

All five production modes are now reasonably well measured, and correlations are modest !

ATLAS-CONF-2019-005





Combine and compare κ parameters for different fermionic and bosonic processes.Agreement and consistency are excellent. Note: assumes no invisible or undetected modes…

Currently κV = 1.05 ± 0.04 and κF = 1.05 ± 0.09

To probe BSM contributions to loops, look at the effective coupling to γ and g. Assume κi=1 for other κ, no invisible or undetected modes:

Currently κγ = 1.00 ± 0.06 and κg = 1.03 +0.07-0.06

Additional models provide constraints on invisible or undetected modes…




Stage 1 STXS (Simplified Template Cross-section) analysis framework => partitions available phase-space into non-overlapping regions based on kinematics and topology. Maximize sensitivity to BSM deviations, minimize sensitivity to theory uncertainties and extrapolations. Focus on production/initial state.

More powerful than global coupling κ’s.

Full Run 2 Higgs Measurement• New measurement of ttH production with H→γγ updated to 139 fb-1 at 13 TeV.• Use leptonic (at least one e or µ and one b-jet) and hadronic (no e or µ, at

least one b-jet, and two additional jets) categories. Then individual BDTs are optimized, and categories are sorted by signal purity into sub-categories.


Weighted sum

Unweighted sum

Total signal ~40 events, with significance 4.9σ (4.2σ) obs (exp).

Measure σ(ttH x Bγγ) = 1.59 +0.43 -0.39 fb (SM = 1.15+0.09

-0.12 fb). Consistent with SM expectation.

Analysis clearly indicates this channel is an ideal “tool” to use when evaluating Higgs coupling to top quarks in the HL-LHC era !

ATLAS-CONF-2019-004


SM Electroweak Results for 80 fb-1

• Recent analysis searching for SM production of three massive gauge bosons.• Look for:

• dileptons (WWW→lνlνqq), • trileptons (WWW→lνlνlν and WWZ→lνqqll), • four-leptons (WWZ→lνlνll and qqllll).

• Combined significance is 4.0σ (3.1σ) obs/exp.• Good agreement with SM expectations !


Significant signal in regions with high S/B !

arXiv:1903.10415


CP-violation in Bs → J/ψφ Results for 80.5 fb-1

• New analysis based on 2015-2017 data (combined with Run 1) achieves comparable precision to new LHCb result on nine relevant parameters.

• Reconstruct Bs → J/ψ(µ+µ-)φ(K+K-), fitting tracks to common vertex. Use 3D impact parameter to associate to primary vertex (µ~30 !), estimate proper time.

• Perform opposite side flavor tagging using e/µ/jets, calibrate with self-tagging B± → J/ψK± decays. Combine with previous Run 1 results for 7/8 TeV 19.2 fb-1.


Above: fitted parameter values for the Run 1 + Run 2 combination (19.2 + 80.5 fb-1).

Right: 68% CL contours, stat+syst in quadrature. Plot CP-violating phase φs vs decay width difference for mass eigenstates.

ATLAS-CONF-2019-009

SM value for φs derived from CKM is small => BSM sources of CP violation could appear…


Heavy Ion Results for 1.7 nb-1

• Recent analysis searching for more significant “light-by-light” scattering signal using the full 2018 PbPb data sample (~4 times the 2015 sample).

• Use low total ET to reject essentially all non-peripheral events. • Distribution of Aφ (deviation from back-to-back in φ) is before final cut Aφ < 0.01. • Next two plots are final event sample (42 total events, expect 25 ± 3 signal and

6 ± 2 bkgd):

• Significance is 8.2σ (6.2σ) obs/exp.• Fiducial cross-section is: 78 ± 13 (stat) ± 7 (syst) ± 3 (lumi) nb.

This is about 1.5 ± 0.3 times the expected value.


arXiv:1904.03536


Heavy Ion Results for 1.7 nb-1

• Recent analysis searching for more significant “light-by-light” scattering signal using the full 2018 PbPb data sample (~4 times the 2015 sample). Photons have PT ~10 GeV. Calo cells above 400/800/1000 MeV, tracks above 100 MeV are shown. Extremely peripheral => only see the two photons !


Summary…

• Large number of full Run 2 results already available for this conference – much more to come prior to the start of Run 3…

• ATLAS is busy repairing and improving the existing detector, and installing and commissioning the phase-1 upgrades during LS2.

• Expect Run 3 to provide at least a comparable event sample with the commissioning of the new injector chain and modest improvements to the LHC. Ideally, this would be at 14 TeV !

• Phase-2 upgrades have six approved TDRs and most MoUs now open for signature. Precision timing detector rapidly progressing towards TDR.


Backup





Examine ratios of κ to avoid dependence on Higgs width (e.g. λtg = κt/κg). Most model-independent approach to constrain BSM from Higgs relies on λtgand λZg parameters (no assumptions on other κi).

Compare consistency of all κ values, and relax assumptions about invisible and undetected and BSM couplings => no significant changes.

CP-violation in Bs → J/ψφ Results for 80.5 fb-1

• New analysis based on 2015-2017 data (combined with Run 1) achieves comparable precision to new LHCb result (see below) on nine relevant params.

• Reconstruct Bs → J/ψ(µ+µ-)φ(K+K-), fitting tracks to common vertex. Use 3D impact parameter to associate to primary vertex (µ~30 !), estimate proper time.

• Perform opposite side flavor tagging using e/µ/jets, calibrate with self-tagging B± → J/ψK± decays. Combine with previous Run 1 results for 7/8 TeV 19.2 fb-1.


Above: fitted parameter values for the Run 1 + Run 2 combination (19.2 + 80.5 fb-1).

Right: 68% CL contours, stat+syst in quadrature. Plot CP-violating phase φs vs decay width difference for mass eigenstates.

ATLAS-CONF-2019-009

SM value for φs derived from CKM is small => BSM sources of CP violation could appear…


k. einsweiler, lbnl on behalf of the atlas collaboration · t2. k. einsweiler -lbnl 20-may-19 13...

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