Exploring the structure of the Higgs sector

The Englert-Brout-Higgs mechanism of spontaneous electroweak symmetry breaking was introduced in the 1960s to complete the formulation of the Standard Model of particle physics by explaining how the W and Z bosons obtain their mass. The Higgs boson is a massive elementary particle which appears in the most economic implementation of the mechanism. The masses of the fermions in the Standard Model are generated through Yukawa couplings to the Higgs boson.

On 4th July 2012, with strong involvement and leadership of the Birmingham group, the ATLAS and CMS Collaborations announced the observation of a particle consistent with the Standard Model Higgs boson with a mass of about 125 GeV. Further details can be found in the official CERN Press Release, University press release and also at BBC News, July 2012. Following the discovery, the experimental focus shifted to the measurement of its properties, notably its couplings to other particles, as well as searches for physics beyond the Standard Model through an extended Higgs sector:

Study of the SM-like Higgs boson (h): The Birmingham group has leading involvement in analyses of ATLAS data, studying its mass and coupling properties using h→ZZ decays, and h→b anti-b decays produced in association with a Z or W boson. We also contribute significantly to the combination of all ATLAS Higgs boson measurements, probing the predictions of the Standard Model.
Study of the Yukawa sector: The group is pioneering the study of the Higgs couplings to fermions of the first two generations: in quarks through searches for h→cc and searches for rare Higgs decays to the exclusive final state h→Qγ, where Q=J/ψ, Υ, and φ, as well as the previously unobserved analogous decays of the Z boson, and in leptons through searches for h→μμ and h→ee.
Search for additional Higgs bosons: We are performing a comprehensive set of searches for additional Higgs bosons, including the pseudo-scalar Higgs boson A in its decay to Zh, the heavy scalar H in its decay through ZZ and the charged Higgs bosons decaying to WZ. We are also looking for beyond the SM contributions to resonant and non-resonant di-Higgs boson production. In parallel, we search for potential production of Dark Matter candidates in association with a Higgs boson.

University of Birmingham main campus at Edgbaston

ExclusiveHiggs was presented to ERC president Prof. J.-P. Bourguignon during his visit to the West Midlands.

You can have a look at our talks in conferences, seminars, and our publications. We have hosted the "ATLAS VH→cc Workshop" (October 28 - 31, 2019), the "ATLAS UK Meeting" (January 4 - 6, 2018), the "ATLAS UK Run 2 Physics and Performance Meeting" (October 20, 2014) and the "ATLAS UK Higgs Meeting" (September 25-26, 2014). A poster for our outreach activity, see here.

We have been awarded University of Birmingham Engineering and Physical Sciences Paper of the Month (September 2016) for searching "for Higgs and Z Boson Decays to φγ with the ATLAS Detector" (Phys. Rev. Lett. 117 (2016) 11, 111802).
Read the full article: here.

The ERC Starting Grant "ExclusiveHiggs" (under grant agreement no 714893) has been awarded for work on the study of the Higgs interactions to the quarks of the first two generations (March 2017 - February 2021).

This project has received funding from the European Union’s 7th Framework Programme for research, technological development and demonstration under grant agreement no 334034 (EWSB), and from European Union's Horizon 2020 research and innovation programme under grant agreement no 660524 (hh) and no 844062 (LightBosons).

Interactions with the phenomenology community have been supported in part by the IPPP Associateship programme.

Completed Ph.D. theses

R. Turner, PhD June 2020, Detector control systems and Searches for Leptonic Decays of the Higgs boson in the ATLAS experiment at the LHC
E. Reynolds, PhD November 2019, Search for Light Scalars in the decays of the Higgs boson
J. Broughton, PhD, November 2018, Searches for Rare Exclusive Higgs Boson Decays to a Meson and an Associated Photon with the ATLAS Detector
R. E. Owen, PhD, October 2017, Search for Rare Exclusive decays of the Higgs and Z bosons to a meson and a photon with the ATLAS detector
M. Baca, PhD, September 2017, Search for Dark Matter production in association with a Higgs boson
A. Daniells, PhD, March 2016, Pile-up Suppression in the ATLAS Level 1 Calorimeter Trigger and Searches for Higgs Boson Pair Production
R. D. Mudd, PhD, January 2016, Experimental Study of the Properties of the Higgs Boson
B. Allbrooke, PhD, February 2015, Search for the Higgs Boson decaying to a b quark pair produced in association with a W boson, using missing transverse energy-triggered events at ATLAS

Conference/Workshop contributions related to our Higgs sector work

G. Virdee, Searches for Rare Decays of the Higgs Boson, 2020 Annual ATLAS UK Physics Meeting, Cambridge, UK, January 8-10, 2020.
E. Reynolds, Electroweak and Strong Physics, ECFA ECR Strategy Input Meeting, CERN, Novermber 15, 2019.
E. Reynolds, HL-LHC physics with ATLAS detector, QCD@LHC 2019, Buffalo, NY, USA, July 18, 2019.
E. Reynolds, Search for Decays of the Higgs Boson into a Z Boson and a Light Hadronically Decaying Resonance, Joint APP and HEPP Annual Conference, Imperial College, London, UK, April 8-10, 2019.
R. Turner, Search for H->ee using 140/fb of 13 TeV pp collision data with ATLAS experiment, Joint APP and HEPP Annual Conference, Imperial College, London, UK, April 8-10, 2019.
E. Reynolds, Searches for Rare Decays of the Higgs Boson, 2019 Annual ATLAS UK Physics Meeting, RHUL, UK, January 3-5, 2019.
K. Nikolopoulos, Probing the Higgs Yukawa couplings at the LHC, Workshop on Recent Advances in High Energy Physics and Cosmology, Athens, Greece, April 17-20 2019.
A. Chisholm, Recent highlights from Higgs boson studies at ATLAS, Higgs Days at Santander, Santander, Spain, September 10-14, 2018.
R. Owen, Searches for non-Standard Model decays to a light meson and a photon of the Higgs boson, SUSY2018, Barcelona, Spain, July 23-27, 2018.
A. Chisholm, Searches for non-Standard Model decays to a light meson and a photon of the Higgs boson, International Conference on High Energy Physics, Seoul, Korea, July 4-11, 2018.
E. Reynolds, HL-LHC Z(ll)H(cc) Search Prospects, Workshop on the physics of HL-LHC, and perspectives at HE-LHC, CERN, June 19, 2018.
E. Reynolds, Searches for rare and non-Standard Model decays of the Higgs boson, CIPANP 2018, Palm Springs, CA, USA, May 29, 2018.

A. Chisholm, earching for Higgs boson decays to charm quark pairs with charm jet tagging at ATLAS CMS Heavy Flavour Tagging Workshop (Apr. 2018)
R. Owen, Search for exclusive Higgs and Z boson decays to φγ and ργ with the ATLAS detector, Institute of Physics Annual High Energy and Particle Physics Conference, University of Bristol, UK, March 25-28, 2018.
E. Reynolds, Searching for decays of the Higgs boson to charm quarks at ATLAS, Institute of Physics Annual High Energy and Particle Physics Conference, University of Bristol, UK, March 25-28, 2018.
K. Nikolopoulos, Exclusive and rare Higgs boson decays, HiggsHunting, Paris, France, July 24-26, 2017.
P. Thompson, Search for non-standard, rare or invisible decays of the Higgs boson with the ATLAS detector, EPS Conference on High Energy Physics, Venice, Italy, July 5-12, 2017.
R. Owen, Searches for rare exclusive decays of the Higgs boson to a light meson and a photon with the ATLAS detector, EPS Conference on High Energy Physics, Venice, Italy, July 5-12, 2017.
J. Broughton, Searches for rare exclusive Higgs boson decays to quarkonium and a photon with the ATLAS detector, Institute of Physics Annual High Energy and Particle Physics Conference, University of Sheffield, UK, April 10-12, 2017.
R. Owen, Searches for rare exclusive decays of the Higgs boson to a light meson and a photon with the ATLAS detector, Institute of Physics Annual High Energy and Particle Physics Conference, University of Sheffield, UK, April 10-12, 2017.
K. Nikolopoulos, Search for Higgs boson decays to a meson and a photon at the LHC, Precision theory for precise measurements at the LHC and future colliders, International Center of Interdisciplinary Science Education, Vietnam, September 26, 2016.
L. Aperio Bella, Measurement of cross sections and couplings of the SM Higgs boson in the ZZ decay channel using the ATLAS detector, International Conference on High Energy Physics, Chicago, U.S.A., August 4, 2016.
K. Nikolopoulos, Status of the Higgs sector at the LHC, Institute of Physics Annual High Energy and Particle Physics Conference, University of Sussex, UK, March 21, 2016.
K. Nikolopoulos, Probing the Higgs Yukawa couplings with exclusive decays to quarkonia, New Possibilities in Physics of Quarkonia, Institut Henri Poincar\'e, France, September 24, 2015.
K. Nikolopoulos, ATLAS measurements of Higgs boson properties in bosonic decay channels, International Conference on New Frontiers in Physics, Kolymvari, Greece, July 31 - August 6, 2014.
L. Aperio Bella, Combined measurements of the properties of the Higgs boson using the ATLAS detector, Large Hadron Collider Physics Conference, New York, U.S.A., June 2-7, 2014.
P. Thompson, BSM Higgs boson searches, Rencontres de Moriond: EW Interactions and Unified Theories, La Thuile, Italy, March 15-22, 2014.
R. Mudd, Higgs properties with H→ZZ→4l in ATLAS, Les Rencontres de Physique de la Vallée d'Aoste, La Thuile, Italy, February 23-March 1, 2014.
K. Nikolopoulos, Overview of ATLAS Higgs boson measurement, Exploiting the Higgs breakthrough, The Royal Society at Chicheley Hall, Buckinghamshire, UK, January 22-23, 2014.
K. Nikolopoulos, The Higgs boson Spin/CP properties in ATLAS, Higgs Days, Santander, Spain, September 16-20, 2013.
K. Nikolopoulos, H→γγ and H→ZZ at ATLAS, Chicago 2012 Workshop on LHC Physics, Chicago, U.S.A., November 12-14, 2012.
K. Nikolopoulos, H→ZZ→4l at LHC, Higgs Days, Santander, Spain, September 17-21, 2012.
K. Nikolopoulos, Search for the Standard Model Higgs boson in the H→ZZ*→4l decay channel with ATLAS, International Conference on High Energy Physics, Melbourne, Australia, July 4-11, 2012.
P. Thompson, ATLAS H→WW/ZZ, Higgs Hunting, Orsay, France, July 28-30, 2011.

Seminars/Colloquia related to our Higgs sector work

E. Reynolds, "Higgs Boson Decays to Light Scalars at ATLAS", Seminar, University of Warwick, Warwick, UK, June 18, 2020
E. Reynolds, "Higgs Boson Decays to Light Scalars at ATLAS", Seminar, University of Manchester, Manchester, UK, May 29, 2020
E. Reynolds, "Higgs Boson Decays to Light Scalars at ATLAS", Seminar, University of Birmingham, Birmingham, UK, April 22, 2020
T. Neep, "Heavy quarks and the Higgs: ttbar+bbbar with ATLAS", Seminar, University of Warwick, UK, October 2019
T. Neep, "Heavy quarks and the Higgs: ttbar+bbbar with ATLAS", Seminar, University of Birmingham, UK, October 2019
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, Centre d'Etudes Nucleaires de Bordeaux Gradignan, Bordeaux, France, July 2, 2019
A. Chisholm, "Searching for H→cc decays with the ATLAS experiment", Seminar, STFC RAL, February 2019
A. Chisholm, "Searching for H→cc decays with the ATLAS experiment", Seminar, University of Oxford, January 2019
A. Chisholm, "Searching for H→cc decays with the ATLAS experiment", Seminar, UCL, November 2018
A. Chisholm, "Searching for H→cc decays with the ATLAS experiment", Seminar, Imperial College London, November 2018
A. Chisholm, "Searching for H→cc decays with the ATLAS experiment", Seminar, QMUL, November 2018
A. Chisholm, "Searching for H→cc decays with the ATLAS experiment", Seminar, University of Manchester, November 2018
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, Argonne National Laboratory, USA, September 26, 2018
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, Northwestern University, USA, September 24, 2018
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, State University of California (East-Bay), USA, September 20, 2018
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, University of California Santa Cruz, USA, September 18, 2018
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, Brookhaven National Laboratory, USA, September 13, 2018
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, University of Liverpool, UK, May 16, 2018
R. Owen, "Searches at ATLAS for Rare Higgs Boson Decay Modes", Seminar, Imperial College London, UK, February 7, 2018
A. Chisholm, "Recent ATLAS Higgs highlights and the charm frontier", Seminar, IPPP Durham, December 2018
P. Thompson, "Latest Higgs boson results from the LHC", Seminar, University of Liverpool, UK, July 26, 2017
R. Owen, "Searches at ATLAS for Rare Higgs boson Decays", Seminar, Rutherford Appleton Laboratory, UK, May 24, 2017
R. Owen, "Searches at ATLAS for Rare Higgs boson Decays", Seminar, University of Birmingham, UK, January 11, 2017
K. Nikolopoulos, "Searches for Higgs boson decays to a meson and a photon", Seminar, University of Mainz, Germany, December 13, 2016
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, University of Bristol, UK, December 2, 2015
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, Laboratoire de Physique Nucléaire et de Hautes énergies Paris, France, November 30, 2015
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, Laboratoire de l'Accélérateur Linéaire Orsay, France, September 25, 2015.
A. Chisholm, "Probing Higgs Yukawa couplings with rare decays", Seminar, University of Birmingham, UK, May 13, 2015.
K. Nikolopoulos, "Probing the Higgs Yukawa couplings at the LHC", Seminar, University of Sussex, UK, April 23, 2015.
R. Mudd, "ATLAS Higgs Coupling measurements", Seminar, University of Sheffield, UK, April 16, 2015.
R. Mudd, "ATLAS Higgs Coupling measurements", Seminar, University of Warwick, UK, February 16, 2015.
K. Nikolopoulos, "Recent ATLAS results on the Higgs sector", Seminar, Imperial College London, UK, February 11, 2015.
R. Mudd, "Higgs Coupling Measurements at ATLAS", Seminar, University of Birmingham, UK, November 12, 2015.
L. Aperio Bella, "ATLAS Higgs results", Seminar, University of Edinburgh, UK, November 4, 2014.
P. Thompson, "The Search with ATLAS for Higgs Decays to Beauty", Seminar, University of Birmingham, UK, October 15, 2014.
L. Aperio Bella, "Probing the Higgs Boson Properties at ATLAS", Seminar, University of Birmingham, UK, January 15, 2014.
K. Nikolopoulos, "The discovery of a SM-like Higgs boson at the LHC", Colloqium, University of Birmingham, UK, May 15, 2013.
K. Nikolopoulos, "Higgs boson physics with ATLAS", Seminar, LIP, Portugal, November 18, 2013.
K. Nikolopoulos, "Higgs boson physics with ATLAS", Seminar, University of Oxford, UK, October 29, 2013.
K. Nikolopoulos, "Observation of an excess of events in the Search for the Higgs Boson with ATLAS at the LHC", Seminar, University of Birmingham, UK, July 26, 2012.

Publications

Measuring rare and exclusive Higgs boson decays into light resonances, A. Chisholm, S. Kuttimalai, K. Nikolopoulos, and M. Spannowsky, Eur. Phys. J. C76 (2016) 501.
Handbook of LHC Higgs Cross Sections: 4. Deciphering the Nature of the Higgs Sector, D. de Florian et al., arXiv:1610.07922 [hep-ph].
Higgs Physics at the CLIC Electron-Positron Linear Collider, H. Abramowicz et al., arXiv:1608.07538 [hep-ex].
Physics at a 100 TeV pp collider: Higgs and EW symmetry breaking studies, R. Contino et al., arXiv:1606.09408 [hep-ph].

The following ATLAS publications related to the Higgs sector had a strong contribution from our group.

Search for Higgs boson decays into a Z boson a light hadronically decaying resonance using 13 TeV pp collision data from the ATLAS detector, arXiv:2004.01678.
Search for the Higgs boson decays H→ee and H→eμ in pp collisions at √s=13 TeV with the ATLAS detector, Phys. Lett. B 801 (2020) 135148.
Search for scalar resonances decaying into μ+μ- in events with and without b-tagged jets produced in proton-proton collisions at √s=13 TeV with the ATLAS detector, JHEP 07 (2019) 117.
Searches for exclusive Higgs and Z boson decays into J/ψγ, ψ(2S)γ, and Υ(nS)γ at √s=13 TeV with the ATLAS detector, Phys. Lett. B786 (2018) 134.
Search for the Decay of the Higgs Boson to Charm Quarks with the ATLAS Experiment, Phys. Rev. Lett. 120 (2018) 211802.
Search for exclusive Higgs and Z boson decays to φγ and ργ with the ATLAS detector, JHEP 07 (2018) 127.
Evidence for the H→bb decay with the ATLAS detector, JHEP 12 (2017) 024.
Search for Dark Matter Produced in Association with a Higgs Boson Decaying to bb using 36 fb^{−1} of pp collisions at √s=13 TeV with the ATLAS detector, ATLAS Collaboration, Phys. Rev. Lett 119 (2017) 181804.
Search for the dimuon decay of the Higgs boson in pp collisions at √s=13 TeV with the ATLAS detector, ATLAS Collaboration, submitted to Phys. Rev. Lett. 119 (2017) 051802.
Search for dark matter in association with a Higgs boson decaying to b-quarks in pp √s=13 TeV with the ATLAS detector, ATLAS Collaboration, Phys. Lett. B765 (2017) 11-31.
Search for Higgs and Z Boson Decays to φγ with the ATLAS Detector, ATLAS Collaboration, Phys. Rev. Lett. 117 (2016) 11, 111802.
Searches for Higgs boson pair production in the hh→bbττ,γγWW,γγbb,bbbb channels with the ATLAS detector, ATLAS Collaboration, Phys. Rev. D92 (2015) 092004.
Constraints on new phenomena via Higgs boson couplings and invisible decays with the ATLAS detector, ATLAS Collaboration, JHEP 11 (2015) 206.
Measurements of the Higgs boson production and decay rates and coupling strengths using pp collision data at √s=7 and 8 TeV in the ATLAS experiment, ATLAS Collaboration, Eur. Phys. J C76 (2016) 6.
Constraints on new phenomena via Higgs boson couplings and invisible decays with the ATLAS detector, ATLAS Collaboration, Journal of HEP 11 (2015) 206.
Searches for Higgs boson pair production in the hh→bbττ,γγWW*, γγbb, bbbb channels with the ATLAS detector, ATLAS Collaboration, Phys. Rev. D 92 (2015) 092004.
Search for a CP-odd Higgs boson decaying to Zh in pp collisions at √s = 8 TeV with the ATLAS detector, ATLAS Collaboration, Phys. Lett. B744 (2015) 163.
Search for Higgs and Z Boson Decays to J/ψγ and Υ(nS)γ with the ATLAS Detector, ATLAS Collaboration, Phys. Rev. Lett. 114 (2015) 12, 121801.
Search for the $b\bar{b}$ decay of the Standard Model Higgs boson in associated (W/Z)H production with the ATLAS detector, ATLAS Collaboration, JHEP 1501 (2015) 069.
Measurements of Higgs boson production and couplings in the four-lepton channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector, ATLAS Collaboration, Phys. Rev. D91 012006 (2015).
Fiducial and differential cross sections of Higgs boson production measured in the four-lepton decay channel in pp collisions at √s=8 TeV with the ATLAS detector, ATLAS Collaboration, Phys. Lett. B738 (2014) 234-253.
Measurement of the Higgs boson mass from the H→γγ and H→ ZZ*→4l channels with the ATLAS detector using 25 fb^{-1} of pp collision data, ATLAS Collaboration, Phys. Rev. D90 (2014) 052004 with Synopsis.
Search for Higgs boson decays to a photon and a Z boson in pp collisions at √s=7 and 8 TeV with the ATLAS detector, ATLAS Collaboration, Phys. Lett. B732 (2014) 8-27
Evidence for the spin-0 nature of the Higgs boson using ATLAS data, ATLAS Collaboration, Phys. Lett. B726 (2013) 120-144
Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC, ATLAS Collaboration, Phys. Lett. B726 (2013) 88-119.
Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC, ATLAS Collaboration, Phys. Lett. B716 (2012) 1-29.
Combined search for the Standard Model Higgs boson in pp collisions at √s = 7 TeV with the ATLAS detector, ATLAS Collaboration, Phys. Rev. D86 (2012) 032003
Search for the Standard Model Higgs boson produced in association with a vector boson and decaying to a b-quark pair with the ATLAS detector, ATLAS Collaboration, Phys. Lett. B718 (2012) 369-390.
Search for a Standard Model Higgs boson in the mass range 200-600 GeV in the H→ZZ→llqq decay channel, ATLAS Collaboration, Phys. Lett. B717 (2012) 70-88.
Search for a Standard Model Higgs boson in the H→ZZ→llνν decay channel using 4.7 fb^{-1} of √s = 7 TeV data with the ATLAS detector, ATLAS Collaboration, Phys. Lett. B717 (2012) 29-48.
Combined search for the Standard Model Higgs boson using up to 4.9 fb^{-1} of pp collision data at √s = 7 TeV with the ATLAS detector at the LHC, ATLAS Collaboration, Phys. Lett. B710 (2012) 49-66.
Search for the Standard Model Higgs boson in the decay channel H→ZZ(*)→4l with 4.8 fb^{-1} of pp collisions at √s =7 TeV with ATLAS, ATLAS Collaboration, Phys. Lett. B710 (2012) 383-402.
Search for a heavy Standard Model Higgs boson in the channel H→ZZ→ ll qq using the ATLAS detector, ATLAS Collaboration, Phys. Lett. B707 (2012) 27-45.
Search for the Standard Model Higgs boson in the decay channel H→ZZ(*)→4l with the ATLAS detector, ATLAS Collaboration, Phys. Lett. B705 (2011) 435-451.
Search for a Standard Model Higgs boson in the mass range 200-600 GeV in the H→ZZ→llνν decay channel with the ATLAS Detector, ATLAS Collaboration, Phys. Rev. Lett. 107 (2011) 221802.
Limits on the production of the Standard Model Higgs Boson in pp collisions at √s =7 TeV with the ATLAS detector, ATLAS Collaboration, Eur. Phys. J. C71, 1728 (2011).

ATLAS Public Notes

Search for the Standard Model Higgs and Z Boson decays to J/ψγ: HL-LHC projections, ATLAS Collaboration, ATL-PHYS-PUB-2015-043, 2015
Projections for measurements of Higgs boson cross sections, branching ratios and coupling parameters with the ATLAS detector at a HL-LHC, ATLAS Collaboration, ATL-PHYS-PUB-2013-014, 2013