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Department of Physics

The Cavendish Laboratory
 
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This list is intended to include all research talks taking place in the Department of Physics.
Updated: 15 min 38 sec ago

Thu 20 Jan 14:00: Title to be confirmed

Fri, 30/07/2021 - 14:58
Title to be confirmed

Abstract not available

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Thu 17 Feb 14:00: Title to be confirmed

Fri, 30/07/2021 - 10:48
Title to be confirmed

Abstract not available

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Fri 15 Oct 16:00: TBA

Wed, 14/07/2021 - 11:57
TBA

TBA

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Fri 08 Oct 16:00: D to K semileptonic decays on the lattice

Tue, 06/07/2021 - 13:15
D to K semileptonic decays on the lattice

The seminar will take place via Zoom here.

Abstract:

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Thu 08 Jul 16:00: D to K semileptonic decays on the lattice

Thu, 24/06/2021 - 14:19
D to K semileptonic decays on the lattice

The seminar will take place via Zoom here.

Abstract:

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Thu 01 Jul 16:00: D to K semileptonic decays on the lattice

Thu, 17/06/2021 - 10:53
D to K semileptonic decays on the lattice

The seminar will take place via Zoom here.

Abstract:

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Tue 22 Jun 16:00: Measurements of angular distance and momentum ratio distributions in three-jet and Z + two-jet final states in pp collisions

Thu, 17/06/2021 - 08:14
Measurements of angular distance and momentum ratio distributions in three-jet and Z + two-jet final states in pp collisions

Collinear (small-angle) and large-angle, as well as soft and hard radiations are investigated in three-jet and Z+two-jet events collected in proton-proton collisions at the LHC . The normalized production cross sections are measured as a function of the ratio of transverse momenta of two jets and their angular separation. The measurements in the three-jet and Z+two-jet events are based on data collected at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.8 fb−1. The Z+two-jet events are reconstructed in the dimuon decay channel of the Z boson. The three-jet measurement is extended to include 13 TeV data corresponding to an integrated luminosity of 2.3 fb−1. The results are compared to predictions from event generators that include parton showers, multiple parton interactions, and hadronization. The collinear and soft regions are in general well described by parton showers, whereas the regions of large angular separation are often best described by calculations using higher-order matrix elements.

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Tue 15 Jun 16:00: Searches for New Physics with Top Quarks at ATLAS: A review from LHCP and beyond

Tue, 08/06/2021 - 15:07
Searches for New Physics with Top Quarks at ATLAS: A review from LHCP and beyond

As the most massive discovered fundamental particle, the top quark has a unique potential to couple to physics new physics at or beyond the TeV scale. In the current ‘golden age’ for top physics, with the LHC often described as a top quark factory, ATLAS has a rich program of research that utilises the top in a variety of ways to hunt for Beyond the Standard Model phenomena. This talk will focus on some of the most recent exploratory ATLAS results presented at LHCP , covering both direct searches for specific models, and model-independent EFT fits on precision measurements. A particular focus is given to rare associated top quark production modes, which represent the furthest reaches of the ATLAS top program to date.

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Tue 15 Jun 16:00: Overview of ATLAS top physicsSearches for New Physics with Top Quarks at ATLAS: A review from LHCP and beyond

Tue, 08/06/2021 - 11:32
Overview of ATLAS top physicsSearches for New Physics with Top Quarks at ATLAS: A review from LHCP and beyond

As the most massive discovered fundamental particle, the top quark has a unique potential to couple to physics new physics at or beyond the TeV scale. In the current ‘golden age’ for top physics, with the LHC often described as a top quark factory, ATLAS has a rich program of research that utilises the top in a variety of ways to hunt for Beyond the Standard Model phenomena. This talk will focus on some of the most recent exploratory ATLAS results presented at LHCP , covering both direct searches for specific models, and model-independent EFT fits on precision measurements. A particular focus is given to rare associated top quark production modes, which represent the furthest reaches of the ATLAS top program to date.

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Fri 11 Jun 16:00: Leading hadronic contribution to the muon magnetic moment from lattice quantum chromodynamics

Mon, 07/06/2021 - 08:38
Leading hadronic contribution to the muon magnetic moment from lattice quantum chromodynamics

The seminar will take place via Zoom here.

Abstract: Twenty years ago in an experiment at Brookhaven National Laboratory, physicists measured the muon’s anomalous magnetic moment, $a_\mu=(g_\mu-2)/2$, with a remarkable precision of 0.54 parts per million. Since then, the standard model prediction for $a_\mu$ has exhibited a discrepancy with experiment of over 3 standard deviations, raising the tantalizing possibility of physical particles or forces as yet undiscovered. On April 7 a new experiment at Fermilab presented its first results, brilliantly confirming Brookhaven’s measurement and bringing the discrepancy with the standard model to a near discovery level of 4.2 sigma. To fully leverage this and future measurements, and possibly claim the presence of new fundamental physics, it is imperative to check the standard model prediction with independent methods, and to reduce its uncertainties. After an introduction and a discussion of the current experimental and theoretical status of $a_\mu$, I will present a precise lattice QCD calculation, by the BMW collaboration, of the contribution to this quantity that most limits the precision of the standard model prediction. The result of this calculation significantly reduces the gap between the standard model and experiment, and suggests that new physics may not be needed to explain the current, experimental, world-average value of $a_\mu$.

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Thu 24 Jun 16:00: A puzzle in $B\to D^{+*}{\pi,K}$ decays: is it New Physics?

Fri, 04/06/2021 - 17:42
A puzzle in $B\to D^{+*}{\pi,K}$ decays: is it New Physics?

Abstract: The determination of the branching fractions of non-leptonic B decays potentially suffers from large uncertainties. However, among the possible modes, the B → (D+\star) K and B_s → (D_s+\star) pi decays are the cleanest, and recent updates on the inputs needed to predict their branching fraction unveiled a ~ 4sigma discrepancy with respect to the current experimental measurements. A possible explanation of this puzzle is in terms of New Physics particles. In this presentation, I will review the theoretical progress that lead to this puzzle. I will then move to present possible simplified models that can accommodate this puzzle and the constraining power of high-pT data for these scenarios.

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Fri 18 Jun 16:00: TBA

Fri, 04/06/2021 - 17:41
TBA

The seminar will take place via Zoom here.

Abstract:

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Thu 17 Jun 14:00: Detecting fractional chern insulators of few-bosons

Fri, 04/06/2021 - 17:10
Detecting fractional chern insulators of few-bosons

Realizing strongly correlated topological phases of ultracold gases is a central goal for ongoing experiments. While fractional quantum Hall states could soon be implemented in small atomic ensembles, detecting their signatures in few-particle settings remains a fundamental challenge. In this work, we numerically analyze the center-of-mass Hall drift of a small ensemble of hardcore bosons, initially prepared in the ground state of the Harper-Hofstadter-Hubbard model in a box potential. By monitoring the Hall drift upon release, for a wide range of magnetic flux values, we identify an emergent Hall plateau compatible with a fractional Chern insulator state: The extracted Hall conductivity approaches a fractional value determined by the many-body Chern number, while the width of the plateau agrees with the spectral and topological properties of the prepared ground state. Besides, a direct application of Streda’s formula indicates that such Hall plateaus can also be directly obtained from static density-profile measurements. Our calculations suggest that fractional Chern insulators can be detected in cold-atom experiments, using available detection methods.

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Thu 10 Jun 14:00: Symmetric Jordan-Wigner transformation on the square lattice

Tue, 01/06/2021 - 10:06
Symmetric Jordan-Wigner transformation on the square lattice

Interpreted in a restricted sense, the Jordan-Wigner transformation provides a manifestly local representation of a lattice fermionic system using bosonic degrees of freedom. While locality becomes an issue in higher than one spatial dimension in the original formulation, recently it has been shown that the problem can be resolved by invoking a background Z2 gauge theory. Building on these recent developments, we will discuss a way to perform the Jordan-Wigner transformation while keeping not only locality but also the symmetries manifest.

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Tue 01 Jun 16:00: Lepton Flavour Universality - measuring BR(W->τν)/BR(W->μν) at the LHC

Mon, 31/05/2021 - 15:14
Lepton Flavour Universality - measuring BR(W->τν)/BR(W->μν) at the LHC

In the Standard Model on of the fundamental principles is that the couplings of the W-boson to the different lepton flavours (e, mu, tau) should be identical. Therefore, outside of small phase space effects, the branching ratio of W->lν should be identical for all flavours of lepton. The most precise previous measurements of the branching ratios of the W boson to the different lepton flavours were from the Large Electron-Positron Collider (LEP) at CERN and showed some tension with the Standard Model. This seminar will describe an ATLAS analysis at the LHC measuring the ratio BR(W->τν)/BR(W->μν) with higher precision than the previous LEP measurements to test this tension with the Standard Model expectation. Top—anti-Top events are used to provide a large sample of W-bosons with which to perform the measurement. One top is then used to trigger and tag the events and the other is used to test the ratio in question.

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Wed 16 Jun 11:30: Systematic study of magnetotransport responses with Berry-Boltzmann equations and Wannier functions

Fri, 28/05/2021 - 15:49
Systematic study of magnetotransport responses with Berry-Boltzmann equations and Wannier functions

There has recently been a huge renewed interest in the literature to the study of currents generated in solids by external electrical and magnetic fields, especially in relation with topology, Berry curvature and Weyl points. The responses of interest include nonlinear anomalous Hall effect, crystal Hall effect, planar Hall effect, unidirectional magnetoresistance and electrical magnetochiral anisotropy among others. In this talk I would like to show how all these responses are classified according to their properties with respect to the inversion and time-reversal symmetry, and how they can be systematically described by the Boltzmann equations modified by Berry curvature and intrinsic magnetic moment of Bloch states – the so-called “Berry-Boltzmann” equations. In addition the different terms contributing to the conductivity tensors are classified due to there microscopic origin as being classical or due to Berry curvature and/or intrinsic magnetic moment. I will also discuss what we should call “Hall” and “Ohmic” conductivities in the nonlinear responses, and how they may be extracted from a particular conductivity tensor. If time permits, I will also address some aspects of ab initio evaluation of such responses within Wannier functions formalism, and how we implement it in the WannierBerri code.

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Fri 28 May 16:00: Towards NNLO QCD+NLO EW PDF fits with NNPDF

Fri, 28/05/2021 - 15:48
Towards NNLO QCD+NLO EW PDF fits with NNPDF

The seminar will take place via Zoom here.

Abstract: I will present an effort within the NNPDF collaboration to perform a PDF fit including, for the first time, a fully consistent treatment of higher-order EW corrections. As PDFs are determined more or more precisely, the effects of previously neglected corrections are beginning to be important. This implies the inclusion of EW corrections for every theoretical prediction going into the PDF fit, and, on the other hand, a different treatment of the measured observables. Finally, a few technical tools had to be developed, which I am going to present as well.

The slides are available here

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Fri 04 Jun 16:00: A model of muon anomalies

Thu, 27/05/2021 - 16:05
A model of muon anomalies

The seminar will take place via Zoom here.

Recent R(K) update from the LHCb experiment at CERN reinforced the tension of B-meson decays into muons. The Muon g-2 experiment at Fermilab strengthened the tension in the muon anomalous magnetic moment. Can muon anomalies be coherently addressed in models beyond the SM, and if so, where else should we look for confirmation? I will discuss extensions of the SM based on 2103.13991 and some work in progress.

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Wed 09 Jun 16:00: First principles simulations of electrolyte materials with a view toward all solid state battery technology

Wed, 26/05/2021 - 16:25
First principles simulations of electrolyte materials with a view toward all solid state battery technology

The development of an international consensus on the need to pay attention to conserving our fragile planet has inspired many computational research efforts in the condensed matter community. While several of these effort focus on predicting new materials, another approach focuses on detailed analyses of the properties of known materials. This latter approach, while often more of academic interest not necessarily leading to promising technological breakthroughs, is important for determining and refining the relationships of simulation techniques to modeling properties of real material. This talk presents the example study of the alkali-metal hexathiohypodiphosphate materials Li4P2S6 and Na4P2S6 and their alloys which are of interest to the effort of developing all solid state batteries. While Li4P2S6 has been identified as an unwanted decomposition product in the preparation of lithium thiophosphate electrolytes with very poor ionic conductivity, Na4P2S6 appears to be a competitive electrolyte for sodium ion batteries. With the help of Yan Li (WFU) and Zach Hood (ANL) as well as several others, the study of these compounds over several years has finally lead to a plausible understanding of their structures and properties. Ref. Phys. Rev. Materials 4, 045406 (2020).

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