LHCb top asymmetry
Lead Research Organisation:
University of Liverpool
Department Name: Physics
Abstract
The Large Hadron Collider is the most powerful particle accelerator ever constructed. LHCb, one of its four major experiments, provides unique detector coverage of proton beam collisions. Specialised for particle identification, utilising advanced tracking and mass determination; the full detector is layered perpendicular to the beams in one 'forward' direction from the interaction point, where the incoming beams define the forward-backward axis. As a result, LHCb can contribute to unprecedented forward region studies.
Matter and antimatter are frequently produced together from the energies accessible in accelerator experiments. Quarks, the building blocks of subatomic matter making up protons, are produced alongside anti-quarks in high energy interactions. The expected angular distributions of the particles being emitted differs between matter and anti-matter; quarks tend to fall closer to the beam-line by comparison. Measuring the direction of these pairs allows us to quantify the differences, or asymmetry, between matter and antimatter.
The top quark has a very short lifetime, so any measurable asymmetry would rely on charge reconstruction through its decay products. Only accessible through quantum mechanical interference, the mechanism for the asymmetry, predicted to be largest in the forward region, is sensitive to new physics. Top quarks are the heaviest known fundamental particle, making them, too, particularly sensitive. As a result, they are anticipated to play a key role in physics beyond the Standard Model.
LHCb observed top production through decays to a bottom quark and a muon using Run I data, becoming the fifth experiment to observe top production and the first in the forward region. In performing angular differential cross section measurements for top and anti-top, this analysis will probe the production asymmetry in this same channel using Run II data. The resultant fourfold increase in statistics and improved to signal to background ratio may determine if first signs of new physics appear.
Matter and antimatter are frequently produced together from the energies accessible in accelerator experiments. Quarks, the building blocks of subatomic matter making up protons, are produced alongside anti-quarks in high energy interactions. The expected angular distributions of the particles being emitted differs between matter and anti-matter; quarks tend to fall closer to the beam-line by comparison. Measuring the direction of these pairs allows us to quantify the differences, or asymmetry, between matter and antimatter.
The top quark has a very short lifetime, so any measurable asymmetry would rely on charge reconstruction through its decay products. Only accessible through quantum mechanical interference, the mechanism for the asymmetry, predicted to be largest in the forward region, is sensitive to new physics. Top quarks are the heaviest known fundamental particle, making them, too, particularly sensitive. As a result, they are anticipated to play a key role in physics beyond the Standard Model.
LHCb observed top production through decays to a bottom quark and a muon using Run I data, becoming the fifth experiment to observe top production and the first in the forward region. In performing angular differential cross section measurements for top and anti-top, this analysis will probe the production asymmetry in this same channel using Run II data. The resultant fourfold increase in statistics and improved to signal to background ratio may determine if first signs of new physics appear.
People |
ORCID iD |
Tara Shears (Primary Supervisor) | |
James Mead (Student) |
Publications
Aaij R
(2017)
Study of prompt D 0 meson production in pPb collisions at s N N = 5 $$ \sqrt{s_{\mathrm{N}\;\mathrm{N}}}=5 $$ TeV
in Journal of High Energy Physics
Aaij R
(2018)
First observation of B+ ? D s + K+K- decays and a search for B+ ? D s + ? decays
in Journal of High Energy Physics
Aaij R
(2017)
Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at s = 7 $$ \sqrt{s}=7 $$ TeV
in Journal of High Energy Physics
Aaij R
(2018)
Search for excited B c + states
in Journal of High Energy Physics
Aaij R
(2017)
Measurement of the Y(nS) polarizations in pp collisions at s = 7 $$ \sqrt{s}=7 $$ and 8 TeV
in Journal of High Energy Physics
Aaij R
(2017)
Measurement of the B± production cross-section in pp collisions at s = 7 $$ \sqrt{s}=7 $$ and 13 TeV
in Journal of High Energy Physics
Aaij R
(2018)
Measurement of branching fractions of charmless four-body ? b 0 and ? b 0 decays
in Journal of High Energy Physics
Aaij R
(2019)
Measurement of the electron reconstruction efficiency at LHCb
in Journal of Instrumentation
Bediaga I
(2019)
LHCb Collaboration
in Nuclear Physics A
Boettcher T
(2019)
Direct photon production at LHCb
in Nuclear Physics A
Studentship Projects
Project Reference | Relationship | Related To | Start | End | Student Name |
---|---|---|---|---|---|
ST/N504142/1 | 30/09/2015 | 30/03/2021 | |||
1796908 | Studentship | ST/N504142/1 | 30/09/2016 | 29/09/2020 | James Mead |
Title | Deep neural network jet heavy flavour classifier for Run II jets at LHCb |
Description | A machine learning repository providing deep learning models to apply to jet flavour identification |
Type Of Material | Data analysis technique |
Year Produced | 2018 |
Provided To Others? | Yes |
Impact | Improved and stabilised MVA response to jets in Run II of particular use for differential measurements and impacting up to 12 ongoing publications with more in the future |
Title | Jet configuration for Run II conditions at LHCb |
Description | Optimised input selection for clustering algorithms, subsequent identification and jet energy corrections |
Type Of Material | Data handling & control |
Year Produced | 2018 |
Provided To Others? | Yes |
Impact | Higher efficiency and better reconstruction resolution for jets in Run II impacting up to 12 ongoing publications with more in the future |
Description | LHCb Starterkit |
Organisation | European Organization for Nuclear Research (CERN) |
Department | CERN LHC LHCb |
Country | Switzerland |
Sector | Public |
PI Contribution | Teaching, demonstrating and developing |
Collaborator Contribution | Teaching, demonstrating and developing Tremendous number of man hours from volunteers has knock on repercussions for a great deal of new researchers moving foward |
Impact | Development of open source teaching tools, cloud based analysis outreach exercises and python resources for sixth form to early postgrad |
Start Year | 2017 |
Title | LHCb outreach cloud analysis |
Description | Cloud based in browser python notebook analysis tools for teaching and outreach |
IP Reference | |
Protection | Protection not required |
Year Protection Granted | 2019 |
Licensed | No |
Impact | Unknown |
Description | CERN-Liverpool Summer School |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | Providing the opportunity to visit CERN and attend seminars from staff and postgraduate researchers, get exposure to areas of particle physics not taught until undergrad and get experience in analysis methods, coding and experimental design from first principles |
Year(s) Of Engagement Activity | 2014,2015,2016,2017,2018,2019 |
URL | https://hep.ph.liv.ac.uk/indico//conferenceDisplay.py?confId=768 |
Description | Open days, applicant discovery days |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | Students, teachers, parents visit and learn about physics, the department and get presentations and hands on demonstrations of concepts and facilities |
Year(s) Of Engagement Activity | 2016,2017,2018,2019 |