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Measurements of the Higgs boson mass and its spin and CP properties with the ATLAS Detector Tulin Varol Tulin Varol SMU Dallas SMU Dallas Presented on behalf of the ATLAS Collaboration Presented on behalf of the ATLAS Collaboration

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Measurements of the Higgs boson mass and its spin and CP properties with the ATLAS Detector

Tulin Varol Tulin Varol

SMU – Dallas SMU – Dallas Presented on behalf of the ATLAS Collaboration Presented on behalf of the ATLAS Collaboration at the International Conference on at the International Conference on Weak Interactions and Neutrinos 2017 – UC Irvine Weak Interactions and Neutrinos 2017 – UC Irvine

Slides prepared by Stephen Sekula Slides prepared by Stephen Sekula

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Stephen J. Sekula - SMU 2/25

Programme

  • Theoretical Motivation
  • Higgs Mass
  • Higgs Spin and Parity
  • Conclusions and Outlook
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Theoretical Motivation

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Stephen J. Sekula - SMU 4/25

The Standard Model and the Higgs Boson

Once the mass of the Higgs boson is established, the Standard Model (SM) is highly predictive of other properties of the Higgs boson. Given the history of parameter measurement within the SM context,

  • nce you actually find the Higgs boson its couplings to other particles

snap into view.

Ratio of Measured Coupling to SM Prediction

μ τ b W Z t

JHEP 08 (2016) 045

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Stephen J. Sekula - SMU 5/25

Higgs Production and Decay at LHC

“Gluon Fusion”

Other Production Mechanisms Decay Mechanisms

Goal: probe production and decay across many channels

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Stephen J. Sekula - SMU 6/25

Probing New Physics Contributions

A + Spin-0 model: a CP-odd scalar mixes with a CP-even scalar. The mixing angle is and the anomalous couplings to vector α bosons are written κHVV and κAVV. If the SM is correct, we observe that: κHVV = κAVV = 0 and = 0. α

JHEP 1311 (2013) 043

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Stephen J. Sekula - SMU 7/25

Probing New Physics Contributions

?

X Spin-2 model: select a spin-2 model with graviton-like couplings. One then has to try different parameter spaces for quark and gluon couplings and assess their compatibility with data. This model allows us to probe tensor couplings, which are expected to be zero in the SM. X

?

q q +

JHEP 1311 (2013) 043

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Higgs Mass

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Stephen J. Sekula - SMU 9/25

Well-Resolved Higgs Decays: ZZ* and γγ

Event Display with Overview

  • f Reconstruction
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Stephen J. Sekula - SMU 10/25

Invariant Mass Distributions

Detector resolution dominates the measurements – the natural width is expected to be almost 500x smaller than the widths seen here.

  • Phys. Rev. D 90, 052004
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Stephen J. Sekula - SMU 11/25

Mass Measurement – channel-by-channel

Dominant Systematic Errors:

  • ZZ

4l: Z ee calibration → →

  • : EM Calorimeter shower

γγ modeling (material modeling, energy response, shower shape, calibration)

  • Phys. Rev. D 90, 052004

Masses compatible at 1.98 σ

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Higgs Spin and Parity

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Angular Momentum Analysis Example: H ZZ* decays →

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Angular Momentum Analysis Example: H ZZ* decays →

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Stephen J. Sekula - SMU 15/25

Angular Momentum Analysis Example: H ZZ* decays →

OR

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Stephen J. Sekula - SMU 16/25

Angular Momentum Analysis Example: H ZZ* decays →

OR

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Stephen J. Sekula - SMU 17/25

Angular Momentum Analysis Example: H ZZ* decays →

OR

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Stephen J. Sekula - SMU 18/25

Hypothesis Discrimination: backgrounds vs. signal hypotheses

For each final state (ZZ*, WW*, and ) the background shapes are γγ included and data compared to the combination of background and a pair of signal hypotheses: JP=0+ and an alternative (e.g. 0-, 0+

h, 2+, etc).

  • ZZ* analysis
  • WW* analysis
  • γγ
  • Eur. Phys. J. C75 (2015) 231
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Stephen J. Sekula - SMU 19/25

Hypothesis Discrimination: backgrounds vs. signal hypotheses

For each final state (ZZ*, WW*, and ) the background shapes are γγ included and data compared to the combination of background and a pair of signal hypotheses: JP=0+ and an alternative (e.g. 0-, 0+

h, 2+, etc).

  • ZZ* analysis
  • WW* analysis
  • γγ
  • Eur. Phys. J. C75 (2015) 231
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Stephen J. Sekula - SMU 20/25

Hypothesis Discrimination: backgrounds vs. signal hypotheses

For each final state (ZZ*, WW*, and ) the background shapes are γγ included and data compared to the combination of background and a pair of signal hypotheses: JP=0+ and an alternative (e.g. 0-, 0+

h, 2+, etc).

  • ZZ* analysis
  • WW* analysis
  • analysis

γγ

ATLAS-CONF-2015-008

In this channel, events are categorized in ways consistent with hypothetical Higgs production mechanism. Gluon/Quark coupling alterations would then change the “fingerprints” of these categories.

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Stephen J. Sekula - SMU 21/25

Results – pairwise hypothesis comparisons

Conclusions: in pairwise hypothesis comparisons, 0+ is favored. This measurement is still statistics-limited.

  • Eur. Phys. J. C75 (2015) 476

Note: spin-2 EFT only valid up to a certain energy scale, necessitating pT cuts to make the interpretation (see right)

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Stephen J. Sekula - SMU 22/25

Results – Tensor Structure Analysis

Conclusions: SM still favored compared to this extension.

  • Eur. Phys. J. C75 (2015) 476

Anomalous Anomalous even-parity even-parity coupling coupling Anomalous Anomalous

  • dd-parity
  • dd-parity

coupling coupling

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Conclusions and Outlook

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Stephen J. Sekula - SMU 24/25

Data-taking exceeded expectations in 2016. Public results from H ZZ*,WW*,

  • verall use only a

→ γγ fraction of available data so far, some using Run 1

  • nly. Watch for updates on full 2015-2016 data sets!

LHC planning to deliver 90fb-1 for 2017+2018. Expect the textbooks to continue to need rewriting as ATLAS and CMS improve our knowledge of the Higgs Boson.

ATLAS-CONF-2017-032 and ATLAS-CONF-2016-112 and ATLAS-CONF-2016-067

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Stephen J. Sekula - SMU 25/25

Conclusions

  • The 125-GeV boson is highly compatible with the Standard Model

Higgs Boson

  • Mass:

– ATLAS: (125.36 ± 0.37stat. ± 0.18syst.) GeV – ATLAS+CMS: (125.09 ± 0.21stat. ± 0.11syst.) GeV

  • Spin and Parity

– Favors strongly the JP=0+ hypothesis in pairwise comparisons with alternative

hypotheses.

  • Couplings are another way to look at all of this. See JHEP 08 (2016) 045
  • Future
  • The Higgs is “re-discovered” in Run 2. ATLAS continuing with detailed

analyses of the Higgs Boson. Watch for updates.

  • LHC planning to deliver 90fb-1 more in Run 2!
  • Phys. Rev. Lett. 114 (2015) 191803
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Appendix

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Mass Measurement - Extras

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Mass Systematics – ZZ* and γγ

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Stephen J. Sekula - SMU 29/25

Mass Systematics – breakdown γγ

Systematics in are subdivided into the case where the photon does or γγ does not convert ( ee) in material as it traverses the ATLAS detector. γ →

  • Converted photons are electron pairs and can be calibrated more reliably

using the Z ee measurement. Otherwise, dominant systematics are Liquid → Argon (LAr) calorimeter cell linearity (of response to energy) and the layer calibration.

  • Unconverted photons have a larger systematic from the Z

ee calibration → and otherwise are dominated by the same effects as the converted photons.

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Spin-Parity Measurement - Extras

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Confidence Levels – Channel-by-Channel

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Confidence Levels – Combined