LHC-PHYS · Probing electrically charged Higgs bosons at the CERN's Large Hadron Collider: a collaboration between theory and experiment

Probing electrically charged Higgs bosons at the CERN's Large Hadron Collider: a collaboration between theory and experiment

The research project focused on the phenomenology of Higgs bosons at the CERN Large Hadron Collider (LHC), and has realised 8 publications in primary journals with high impact factors. The results have been presented at conferences (both national and international) and in seminars given to particle physics groups at universities and research institutions. The announcement of the discovery of a new boson at the LHC in July 2012 has ensured that much of the work which was carried out in the project will continue to have an impact for the foreseeable future. It is widely believed that the new particle is a species of Higgs boson, a particle which was predicted in 1964. Its search at the LHC has generated much public / media interest, culminating in worldwide attention in July 2012 when the discovery was announced. The term 'Higgs boson', which was previously an esoteric name for a fictitious particle, has become a household name and (probably) a scientific fact. This is the first big discovery of the experimental programme of the LHC, which is a triumph for both theoretical physics (which predicted its existence) and for experimental physics (i.e. the construction of the vast accelerator and detectors, and the interpretation of the data). One of the main goals of the LHC's physics programme is now to measure the properties of this new particle precisely in order to see if it is indeed the Higgs boson of the original and minimal model, in which one (and only one) electrically neutral Higgs boson is predicted. Alternatively, this new particle could belong to a family of Higgs bosons, and the further studies of its properties with the increasing data samples at the LHC will shed light on this possibility. Searches for additional Higgs bosons (whose properties could be quite different to those of the minimal model) have always formed an important part of the research programme of high-energy colliders. However, with the above discovery (which is widely believed to be a species of Higgs boson) the importance of searching for other types of these particles has become paramount now. The focus of the project LHC-Phys has been on the study of Higgs bosons with electric charge (i.e. with integer multiples of the charge of the electron). Some of the publications have already had an impact on the ongoing searches for such Higgs bosons at the LHC. Emphasis was given to the study of 'doubly charged Higgs bosons', because searches for these particles were carried out at the LHC as early as March 2011. Below, I summarise the results and the impact of the eight publications: (1) Paper Phys.Rev D.86.035015 has immediate consequences for the interpretation of the discovery of the new boson at the LHC. Current data from the LHC are consistent with the new boson having a larger-than-expected preference for decaying into two particles of light ('photons'). If this result is confirmed with the future data then there would be strong evidence that the new particle is one of a family of Higgs bosons. The proposal in the above paper is that charged Higgs bosons exist and (being electrically charged) they contribute to the decay into photons. This topic is generating much interest in the scientific literature, and paper Phys.Rev D.86.035015 was released just before the announcement of the discovery in July 2012. This paper has generated 18 citations in the space of 4 months, and its impact is expected to continue as more data is accumulated at the LHC. (2) The three papers Phys.Rev.D.84.035010, Phys.Rev.D.85.055026 and Phys.Rev.D.84.035028 proposed new ways to produce doubly charged Higgs bosons at the LHC, which would improve the discovery potential of such particles at the LHC. Current searches and their interpretation do not yet include our proposals, but we expect our results to influence the future searches for such particles. The content of the papers has already been emphasised and developed in an article (Phys.Rev.D85.055018) by an eminent European particle physicist, which exemplifies the immediate impact our work. In writing these three papers, and together with the paper in 1) above, a computer code has been developed which will be made publically available at a date in the future. Its release will facilitate the interpretation of searches for such particles, and will be of great benefit to experimentalists who are involved in their search. (3) The results of paper Phys.Rev.D.85.115002 are of direct relevance to an ongoing search for charged Higgs bosons from the decay of top quarks at the LHC. We suggested a way to improve the detection prospects for a specific type of charged Higgs boson which can decay preferentially into a charm and a bottom quark. We have already established contact with a member of an experiment at the LHC with the eventual aim of convincing the collaboration to perform a dedicated search in this channel. (4) Paper JHEP12(2011)088 studied a very rare decay of the B meson (which is expected to be observed soon at the LHC), and involved collaboration with an experimentalist at the LHC-b experiment. Its results have been made known to the LHC-b collaboration members by internet communication and internal collaboration meetings. The paper has generated 26 citations in just over a year. (5) Paper Phys.Rev.D.83.095003 discussed electrically neutral Higgs bosons which do not couple to quarks and leptons. Such a species of Higgs boson is actively searched for at high-energy colliders, and the paper has been mentioned explicitly in searches (arXiv:1109.0576 (hep-ex)) by the CDF and D0 collaborations at the Fermilab Tevatron in the United States of America (USA), and by a recent search (arXiv:1205.0701 (hep-ex)) at the LHC. (6) Paper JHEP11(2010)005 helped lead to the inclusion of an overlooked production mechanism of doubly charged Higgs bosons at the LHC (which was emphasised in our original research proposal). By establishing contact with experimentalists and providing one of the LHC collaborations with simulated data, our proposal was carried out in the LHC search in arXiv:1207.2666 (hep-ex). Consequently, this has increased the detection prospects of doubly charged Higgs bosons at the LHC. Aside from collaboration with the host researcher, the above papers involved collaboration with researchers of various nationalities: Taiwan, Japan, Mexico, India, Chile, and with researchers based at CERN. The day-to-day interaction with the members of the host institution (whose expertise covers a wide range of research topics) has been greatly beneficial to Dr Akeroyd. During the course of the two years he also had the status of 'visiting researcher' at the Experimental Particle Physics Group of Rutherford Appleton Laboratory. He made visits there for discussion and seminar attendance (as well as presenting his work twice). The two-year duration of the project has given Dr Akeroyd the opportunity to re-establish himself in the United Kingdom after a long period abroad, and currently he is at the host institute (University of Southampton) on a fixed-term contract.

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