Imperial College London


Faculty of Natural SciencesDepartment of Physics

Senior Lecturer



+44 (0)20 7594 1551a.tapper Website




508Blackett LaboratorySouth Kensington Campus





Particle physics is about understanding what our Universe is made of and how it came to be as it is today. After centuries of study we know that there are two kinds of matter, leptons and quarks, and that there are four forces that mediate their interactions: the electromagnetic, the strong, the weak and the gravitational force. This knowledge of fundamental particles and the interactions between them forms what is known as the Standard Model of particle physics.

Despite its overwhelming success, the Standard Model leaves many fascinating questions unanswered. What is the reason for the hierarchy of particle masses we observe? What is the origin of the huge matter-antimatter imbalance in the universe? Why is gravity so much weaker than the other forces? Why do we observe three generations of quarks and leptons? What is the origin of Dark Matter? It’s clear that the Standard Model cannot be the complete picture, but what would the bigger picture look like? and how can we find out?

I have been involved in several different aspects of research in large particle physics experiments. The majority of my work has been on data analysis, but I have also been closely involved in the design, commissioning and operation of the complex detectors typical of particle physics experiments. In addition I have worked in the management of the CMS and ZEUS experiments, coordinating scientific priorities and planning future research programmes. The twin focuses of my current research are searches for supersymmetry and the trigger system of the CMS experiment at the Large Hadron Collider at CERN.

The CMS experiment

In September 2016 I was appointed Project Manager for the CMS Level-1 Trigger system. I am responsible for all aspects of the project, including the day-to-day operation, planning and setting priorities and long term upgrades for High-Luminosity LHC, planned for 2026 onwards.

In 2015 and 2016 coordinated the commissioning of the upgrade to the CMS Level-1 Calorimeter Trigger, which ran from late 2015 onwards. In 2015 I was also responsible for the continued running of the Global Calorimeter Trigger, built by the Imperial and Bristol groups.

In 2012 and 2013 I coordinated the project to upgrade the CMS Level-1 Trigger system to cope with the higher luminosity delivered by the LHC from 2015 onwards. We wrote a Technical Design Report which I defended through several stages of international review successfully.

In 2010 and 2011 I was co-convenor of the CMS supersymmetry physics analysis group. Under my leadership the group analysed the 2010 and 2011 LHC data for signs of physics beyond the Standard Model, producing some of the most stringent limits on supersymmetry in the world and publishing several ground-breaking papers. I was responsible for all aspects of the group’s work, from the overall scientific strategy to the scope and detailed content of the papers.

The ZEUS experiment

From 2003 to 2006 I was coordinator of the ZEUS High-Q2 and Exotics working group. The group pursued a wide range of activities ranging from precision cross-section measurements, QCD and electroweak fitting, measurements of rare phenomena to searches for new physics. Highlights included publishing the first ZEUS paper on supersymmetry and the first measurement of the dependence of the deep inelastic scattering cross sections on the longitudinal polarisation of the lepton beam. We also used jet cross-section measurements to constrain proton structure in QCD fits for perhaps the first time.

I was involved in the design, installation and commissioning of the upgrade to the HERA transverse polarimeter and contributed strongly to the operation of the ZEUS Central Tracking Detector.


ZEUS Collaboration, Deutsches Elektronen-Synchroton, DESY, 1998

CMS Collaboration, Centre Europeen de Recherche Nucleaire, CERN, 2006

Research Staff


Research Student Supervision

Summers,S, Firmware development studies for high energy physics

Milosevic,V, Search for Dark Matter in Vector Boson Fusion production at the LHC

Shtipliyski,A, CMS Level-1 Trigger Upgrades

Elwood,A, A search for supersymmetry in sqrt(s)=13 TeV proton-proton collisions with the CMS detector at the LHC

Baber,M, Search for supersymmetry in the first √s = 13 TeV pp-collisions using the αT variable with the CMS detector


Lucas,R, Searches for Supersymmetry with compressed mass spectra using monojet events with the CMS detector at the LHC

Marrouche,J, Triggering and W-Polarisation Studies with CMS at the LHC

Mathias,B, Search for supersymmetry in pp collisions with all-hadronic final states using the αT variable with the CMS detector at the LHC

Sparrow,A, Measurement of the Polarisation of the W Boson and Application to Supersymmetry Searches at the Large Hadron Collider