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Dr Ulla Blumenschein

Ulla

Lecturer in Particle Physics

Email: u.blumenschein@qmul.ac.uk
Telephone: 020 7882 6967
Room Number: G. O. Jones Building, Room 407
Office Hours: Tuesdays, 10-11am, Wednesdays, 1-2pm

Teaching

2017/18:

  • SPA4601 Professional Skills for Scientists (1st year, Semester A, modul co-organizer)
  • SPA4321 Introduction to C++ (1st year, Semester B, modul organizer)
  • SPA7029U/P Collider Physics (4th year, Semester B, deputy module organizer)

2018/19:

  • SPA4601 Professional Skills for Scientists (1st year, Semester A, modul co-organizer)
  • SPA5201 Physics Laboratory (Semester B, modul co-organizer)
  • SPA7029U/P Collider Physics (4th year, Semester B, deputy module organizer)

I have been organising the NExT School 25-28 June 2018

PhD Students:

  • Jacob Oliver: Production of Z bosons in association with bottom and charm quarks at ATLAS
  • Tong Qiu: Search for a massive Higgs boson with the ATLAS detector at the LHC experiment
  • Arran Freegard: Higher-order QCD & EW corrections for high-energy V+jets production

BSc and MSc Projects:

  • Jets-background in Z+jets processes
    • When we measure the cross section for the associated production of Z and jets in pp collisions, we have to subtract the contributions of other processes which pass our filter. One such process, the jets-background, is extremely hard to simulate as hadronic jets are wrongly identified as isolated electrons and muons. Hence in this project we will use collision data with loosened or even inverted lepton-selection to enrich this background and fit its contribution.
    • The project requires a solid knowledge of C++.
    • Number of project students: 1-2
  • Unfolding in hadron collider measurements
    • When we measure the cross section for the associated production of Z and jets in pp collisions, we have to correct the data for resolution effects and inefficiencies. The method used should be as independent as possible from the specific modelling of the kinematic distributions in our simulation. The student will optimize and compare the performance of several unfolding approaches in unfolding Z+jets events in ATLAS collision data and develop methods to asses the residual model dependence.
    • The project requires a solid knowledge of C++.
    • Number of project students: 1-2
  • Modelling of Top backgrounds in Z+jets selections
    • Whe When we measure the cross section for the associated production of Z and jets in pp collisions, we have to subtract the contributions of other processes which pass our filter. The dominant background is usually the production of top quarks with leptonic decays. In order to check whether these backgrounds are correctly modelled in the simulation, the student will modify the lepton selection to enrich events with top quarks.
    • The project requires a solid knowledge of C++.
    • Number of project students: 1
  • Modelling of collinear Z emission
    • In aselection of pp collisions where a Z boson is produced in association with a high-energetic jet, a large frection consists of events where a Z boson is radiated from a quark, which later becomes a hadronic jet. These collinear-Z events might be responsible for a large part of a missmodelling of Z+jets production observed in pp collisions. The student will investigate this hypothesis by cathegorizing the Z+jets events into collinear and non-collinear events and investigate the modelling of other kinematic distributions.
    • The project requires a solid knowledge of C++.
    • Number of project students: 1
  • Search for additional heavy Higgs bosons
    • In the search for additional heavy higgs bosons, it is crucial to correctly predict backgrounds form Standard-Model processes. We search for a Pseudoscalar heavy Higgs boson, decaying into a lighter Higgs boson and a Z boson, which decay eventually to final states consisting of two leptons and teo q quarks. A dominant background comes from the direct production of Z bosons in association with two b-quarks. The student will develop suitable selection enriched in this process, which resemble the final state of the search for A->HZ, to check, and if necessary improve, the modelling of the Z background.
    • The project requires a solid knowledge of C++.
    • Number of project students: 1

PhD Projects:

  • Production of a Z boson in association with B and C quarks
    • The precision of the theoretical predictions for interaction rates in high-energy collisions has increased dramatically over the past years, promptingus to test the prediction at a high precision level, with the option to find signs for new physics in deviations from the current models. The project is supposed to measure processes where jets of hadrons are produced in association with the neutral massive carriers of the weak force, the Z bosons. Since they result in similar final states as the production of new particles they have to be described at a high precision, lest we confuse them with the latter. The focus of the thesis is on a special class of these processes where the hadronic jets are initiated by heavy B or D mesons. The description of such processes provides additional challenges for theory and several so far barely tested approaches are advertised to predict them with high precision. The process is also sensitive to the bottom and charm content of the proton. The measurement is supposed to be performed in proton-proton colision data collected in the years 2015-2018 at the ATLAS experiment at the Large Hadron Collider at CERN.

    •  Basic programming skills required

  • Associated Higgs and Z boson production in final states with b quarks and leptons
    • After the observation of the coupling of the Higgs boson to b-quarks, we would like to measure the properties of the H->bb  decay exactly in order to check whether if follows the predictions from the Standard model. The optimal channel for this endevour is the associated HZ production. In order to minimize the systematic uncertainty, we want to improve the description of the most important background, the associated Z+bb production and optimize the discrimination between signal and background using multivariate discriminants which make use of advanced ML techniques. The student is supposed to optimize and carry out the measurement of the H->bb coupling strength in teh data collected in Run3 with the ATLAS detector.

    • Basic programming skills required
  • Search for a massive Higgs boson with the ATLAS detector at the LHC experiment
    • Several hypothetical extensions of the Standard-Model of particle physics  predict the existence of additional heavier Higgs bosons. The project aims to perform a search for the production of a heavy pseudo-scalar Higgs, A, decaying into a Z boson and a light Higgs boson, in proton-proton collisions recorded at the ATLAS experiment at the Large Hadron Collider at CERN. The project will focus on the most promising channel, where the Z boson decays into electrons or muons and the Higgs boson decays into b-quarks. A particular emphasis will be put on  reducing the dominating systematic uncertainties by  improving the identification of b-quarks and  the modelling of the largest background source,  the associate production of Z bosons and b-quarks. The student will also develop a multivariate discriminant, to optimize the sensitivity  of the search. Eventually, the student will carry out the direct search for  a heavy pseudiscalar Higgs boson in the recorded collision data.

    • Basic programming skills required

Research

Research Interests:

I am interested in the fundamental forces in nature, which in our current model are introduced by imposing local symmetries on the Lagrangian density. By recreating conditions of the early universe in powerful synchrotrons like the Large Hadron Collider (LHC), we aim to improve our understanding of the  various forces with the hope to eventually be able to describe them in a unified theory.

Due to novel theoretical approaches, the precision of the theoretical predictions for interaction rates in high-energy collisions has increased dramatically over the past years, promptingus to test the prediction at a high precision level, with the option to find signs for new physics in deviations from the current models. In the ATLAS experiment, I have been investigating in particular the Strong Force by measuring processes where jets of hadrons are produced in association with the massive carriers of the weak force (JHEP 07 (2013) 032 Eur. Phys. J. C77 (2017) 361). Since they result in  similar final states as the production of new particles they have to be described at a high precision, lest we confuse them with the latter. Currently I am focusing on a special class of these processes where the hadronic jets are initiated by heavy bottom or charm quarks. The description of such processes provides additional challenges for theory and several  so far barely tested approaches are advertised to predict them with high precision.

In our Standard Model, the breaking of Electroweak symmetry by the Higgs field leads to massive force carriers and Higgs bosons. The later has been  discovered by ATLAS and CMS experiments in 2012 in interactions with electroweak gauge bosons. In contrast, we have only recently  obtained first evidence for the  Yukawa coupling of the Higgs field to fermions, which is expected to generate the fermion masses. I have participated in this measurement in ATLAS which selected  Higgs decays into two  tau leptons  (JHEP 04 (2015) 117) and I am involved in a follow-up  measurement  at nearly twice the center-of-mass energy. I am now starting to work on a measurement of Higgs decays into massive bottom quarks. First evidence for this process has just been reported and with a larger data set we expect to be a able to not only observe the process with higher significance but as well to measure key kinematic distributions of the decay products. I want to focus in particular on the associated production of a Higgs boson and an electroweak gauge boson for which the  above mentioned associated direct production of electroweak bosons with bottom quarks constitutes  a major background.

Publications

Publications with significant contributions

  •  Sfermions at LEP2, Higgs and Supersymmetry Conference, 2001 in Orsay on behalf of the LEP experiments.
  • A. Heister et al., [ALEPH Collaboration],Absolute Lower Limits on the Masses of Selectrons and Sneutrinos in the MSSM , Phys. Lett. B 544 (2002) 73-88.
  • V. M. Abazov et al. [D0 Collaboration], Search for supersymmetry via associated production of charginos and neutralinos in final states with three leptons , Phys. Rev. Lett. 95 (2005) 151805.
  • K. J. Anderson et al., A Mobile Data Acquisition System , JINST 2, P07002 (2007).
  • G. Aad et al. [ATLAS Collaboration], Measurement of the Z to tau tau cross section with the ATLAS detector , Phys. Rev. D 84, 112006 (2011).
  • G. Aad et al. [ATLAS Collaboration], Measurement of the production cross section for W-bosons in association with jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector , Phys. Lett. B 698 (2011) 325.
  • G. Aad et al. [ATLAS Collaboration], Measurement of the production cross section for Z/gamma* in association with jets in pp collisions at sqrt{s}=7 TeV with the ATLAS detector , Phys. Rev. D 85 (2012) 032009.
  • G. Aad et al. [ATLAS Collaboration], Search for the Standard Model Higgs boson in the H to tau+ tau- decay mode in sqrt{s}=7 TeV pp collisions with ATLAS , JHEP {09} (2012) 070.
  • G. Aad et al. [ATLAS Collaboration], Measurement of the production cross section of jets in association with a Z boson in pp collisions at sqrt{s} = 7 TeV with the ATLAS detector , JHEP 07(2013) 032.
  • G. Aad et al.[ATLAS Collaboration], Evidence for the Higgs-boson Yukawa coupling to tau leptons with the ATLAS detector , JHEP 04 (2015) 117.
  • G.Aad et al. [ATLAS Collaboration], Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in pp colllisions at sqrt{s} = 8 TeV , Eur. Phys. J. C (2015).
  • U. Blumenschein, Jet production in association with vector bosons or top quarks ,Int. J. Mod. Phys. A, 30, 1546007 (2015).
  • G. Aad et al. [ATLAS Collaboration], Measurement of W and Z-boson production cross sections in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector , arXiv:1603.09222, Phys. Lett. B 759 (2016) 601.
  • G. Aad et al. [ATLAS Collaboration], Measurements of the production cross section of a Z boson in association with jets in pp collisions at sqrt(s) =13 TeV with the ATLAS detector , Eur. Phys. J. C77 (2017) 361.
  • U. Blumenschein et al., Pushing the precision frontier at the LHC with V+jets', hep-ex/1802.02100 .
  • M. Aaboud et al. [ATLAS Collaboration], Cross-section measurements of the Higgs boson decaying to a pair of tau leptons in proton-proton collisions at sqrt{s}=13 TeV with the ATLAS detector, ATLAS-CONF-2018-021 

All publications

PhD Supervision

This is not an exhaustive list and I would be happy to discuss other project possibilities.

Project Title
Production of a Z boson in association with b and c quarks at ATLAS
Associated Higgs and Z boson production in final states with b quarks and leptons

 

Public Engagement

Master Classes:
In 2018, I have organised the EPPOG Master Classes in QMUL

Performance

Conference organisation

Talks at international conferences:

  • Sfermions at LEP2, Higgs and Supersymmetry Conference, 2001 in Orsay on behalf of the LEP experiments.
  • Limits on the mass of the lightest supersymmetric particle at LEP, 16th Int. Conf. on Particles and Nuclei (PANIC) 2002 in Osaka on behalf of the LEP experiments. Search for Associate Chargino Neutralino Production in Trilepton Final States , Meeting of the Division of Particles and Fields of the American Physical Society, (DPF) 2004 in Riverside, on behalf of the D0 Collaboration
  • Jets and Jets+MET Studies at the LHC , Rencontres de Moriond, QCD and High Energy Interactions 2008, on behalf of the ATLAS Collaboration
  • ATLAS WZ Physics, LHC days 2010 in Split, Croacia, on behalf of the ATLAS Collaboration
  • ATLAS W/Z+jets, LHC EW WG meeting, Nov 2011 in Geneva, on behalf of the ATLAS Collaboration
  • ATLAS SM and top Physics, 13th Marcel Grossmann Meeting, July 2012 in Stockholm, on behalf of the ATLAS Collaboration.
  • Measurements of the production of vector bosons in association with heavy flavour quarks at the LHC, LHCP in New York, June 2014,on behalf of the ATLAS Collaboration.
  • Top and electroweak measurements , plenary presentation at the 38th International Conference on High Energy Physics (ICHEP 2016) in Chicago, August 2016.
  • Differential measurements of the Drell-Yan cross-sections, presentation at the XXVI International Workshop on Deep Inelastic Scattering and Related Subjects, DIS, in Kobe, Japan, April 2018.
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