Christos AnastopoulosDr Christos Anastopoulos

Research Fellow

Contact Details

Group web page

www.hep.shef.ac.uk/

 

General

About me

I am a Royal Society University Research Fellow at the University of Sheffield and a member of the ATLAS collaboration

Research Summary

My research focuses on the understanding of fundamental particles and forces of nature, in particular the origin of mass. I played a crucial role to the analysis that led to the discovery of the Higgs boson at the LHC, for which The Nobel Prize in Physics 2013 was awarded.

Research

Research Summary

My primary research interests are on experimental particle physics as a member of the ATLAS collaboration. ATLAS is a multi-purpose detector operating at the Large Hadron Collider at CERN in Europe. It has been designed to search for signals that will enable physicists to understand the fundamental laws of nature and in particular the acquisition of mass through the so-called Higgs mechanism. Thus, data from the ATLAS experiment are probing the basic forces that have shaped our Universe since the beginning of time and that will eventually determine its fate.

I made substantial contributions to the direct discovery of the Higgs boson announced in July 2012 by the ATLAS and CMS collaborations. This discovery led to the award of the 2013 Nobel Prize to Peter Higgs and François Englert “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles”. Over time I have also worked on the reconstruction of electrons in ATLAS by combining the information from the ATLAS tracker and electromagnetic calorimeter. This constituted the ground-work for the discovery of the Higgs boson via its decays to four leptons which I was involved in.

The discovery of the Higgs boson opens the way to a new phase of particle physics in which the study of its properties will allow an examination of the nature of the Higgs in detail and perhaps will also provide the means for new discoveries. We know that the particle we have discovered is a brand new boson. Even though it fulfils the basic requirements of a Higgs boson, it is not clear that its properties correspond exactly to those predicted for the Higgs boson by the standard model of particle physics, which is currently the best theory we have for describing the fundamental particles and their interactions.

The ongoing LHC RUN II is expected to produce four times more Higgs boson candidates that will allow us to further study the new particle properties. The most promising way to study the properties of the Higgs boson is via its decays to into two Z bosons which in turn each decay into an oppositely charged pair of electrons or muons, as they have the lower level of background noise.

In the standard model the Higgs and its associated field are predicted to have a spin of 0. This means that, unlike electomagnetism, they lack directionality. Further Higgs production will allow us to confirm this hypothesis. A more powerful LHC could also reveal whether the Higgs has siblings. For example one popular way to extend the standard model is a theory called supersymmetry, which specifies a minimum of five types of Higgs boson. Another open question is the determination of the rate with which the Higgs boson is produced via different mechanisms, and its comparison with the standard model predictions.

We currently stand at the cross roads of either achieving a more thorough understanding of the SM Higgs mechanism, or the perhaps more exciting prospect of discovering new physics phenomena, and is to this questions that my research will be addressed. As such it will have a profound and lasting impact on our understanding of the fundamental nature of matter and expand humanity’s understanding of the fundamental laws of nature.

Higgs 4 lepton

The Sheffield High Energy Physics group is an active participant in the ATLAS experiment, one of the general purpose detectors being built to exploit the exciting physics potential of the Large Hadron Collider (LHC) at CERN. ATLAS has been designed to search for signals that will enable physicists to understand the fundamental laws of nature and in particular the acquisition of mass through the so-called Higgs mechanism. Thus, data from the ATLAS experiment are probing the basic forces that have shaped our Universe since the beginning of time and that will eventually determine its fate.

I played a leading role in direct discovery of the Higgs boson announced in July 2012 by the ATLAS and CMS collaborations. This discovery led to the award of the 2013 Nobel Prize to Peter Higgs and François Englert “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles”.

The main interest of the group is the study of the properties of the Higgs boson via its decays into two Z bosons which in turn each decay into an oppositely charged pair of electrons or muons. These decays are so-called the "golden" channel as they have the lower level of background noise.

Electron Reconstruction

The remarkable discovery of the Higgs boson in the experimentally harsh LHC environment would not have been possible without the deep understanding of the detector performance and optimisation of the reconstruction and identification algorithms.

An electron is reconstructed using energy deposits in the calorimeter (clusters), matched with tracks that provide information on the particle’s origin and direction and therefore of its momentum

I have been playing a leading role in the area electron performance and co-ordinated the development of the new electron reconstruction algorithm used by the ATLAS experiment in the Higgs discovery. This improved electron reconstruction resulted of 30% in the expected sensitivity for the Higgs discovery in the H → ZZ(*) → 4l channel.

Publications

Research Summary

My research focuses on the understanding of fundamental particles and forces of nature, in particular the origin of mass. I played a crucial role to the analysis that led to the discovery of the Higgs boson at the LHC, for which The Nobel Prize in Physics 2013 was awarded.

The next steps are detailed studies of the Higgs boson properties coupled with searches for new particles that will allow us to elucidate the generation of mass and probe the existence of new physics phenomena. These studies are top priority in the particle physics field and my experience and leadership responsibilities in a major experimental collaboration allows me to maximise my impact.

Key publications

  • 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. B 716, 1 (2012). The ATLAS Higgs Discovery Paper with more than 5000 citations, where I was corresponding editor of the H → ZZ(∗) → 4` section. To be submitted for next REF.
  • Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC ATLAS Collaboration ,Phys. Lett. B 726, 88 (2013). The first ATLAS paper establishing the Higgs boson couplings to dibosons with more than 250 citations, where I was convener of the relevant ATLAS H → ZZ(∗) → 4` analysis group.
  • Evidence for the spin-0 Nature of the Higgs boson using ATLAS data ATLAS Collaboration, Phys. Lett. B 726, 120 (2013) . The first ATLAS paper establishing the spin-0 nature of the
    Higgs boson with more than 250 citations, where I was leader of the relevant ATLAS H → ZZ(∗) → 4` analysis group.
  • Measurement of the Higgs boson mass from the H → γγ and H → ZZ(∗) → 4` channels with the ATLAS detector using 25 fb-1 of pp collision data. ATLAS Collaboration, Phys. Rev. D 90,052004
    9(2014). The most precise measurement of the Higgs bosons mass with more than 100 citations, where I was convener of the relevant ATLAS H → ZZ(∗) → 4` analysis group in the first stages of the measurement. To be submitted for next REF.
  • Electron reconstruction and identification efficiency measurements with the ATLAS detector using the 2011 LHC proton-proton collision data ATLAS Collaboration, Eur.Phys.J. C74 (2014) 7, 2941.
    The most recent description of the Electron reconstruction and identification in ATLAS with more than 100 citations, where I contributed to the reconstruction development and efficiency measurements.

Esteem indicators

  • Holder of the prestigious Royal Society University Research Fellowship at the University of Sheffield.  2015-Today
  • Holder of the prestigious Leverhulme Trust Early Career Fellowship at the University of Sheffield.  2013-2015