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HEP Seminars & Vivas

18 Apr 2024

UCL HEP Seminars 2024

: Jonathan Oppenheim (UCL)

Quantum Gravity

: Karol Lang (UT, Austin)

TBC

: Sarah Mancina (Padova)

IceCube

: Xin Ran Liu (UNDO)

Climate Change Special: UNDO

: Sougato Bose (UCL)

Quantum Gravity

: Paul Newman (Birmingham) -- Physics A1/3

The Electron-Ion Collider

An early perspective is presented on the Electron-Ion Collider, which is currently under intense development towards realisation in the early 2030s at the Brookhaven National Laboratory in the USA . After an introduction to Deep Inelastic Scattering, overviews of the physics motivation, accelerator and detector concepts are given. Finally, the status of the international ‘ePIC’ collaboration and its UK contributions are discussed.

: Alex Keshavarzi (Manchester) -- Physics A1/3

From Muon g-2 to proton EDM

The Muon g-2 Experiment at Fermilab has been an undeniable success, with its most recent results having an overall unprecedented precision of 190 parts-per-billion. The case for new physics rests upon the Standard Model (SM) prediction, also at sub-percent precision, where tensions exist between data-driven dispersive and lattice QCD evaluations of the hadronic vacuum polarisation (HVP) contributions. The former favours a signal of new physics at > 5 sigma when comparing the SM prediction to the Muon g-2 Experiment; the latter is in closer agreement with the experimental measurement. I will review the status of the Muon g-2 Experiment and the theoretical SM predictions, highlighting the efforts to resolve and understand the current discrepancies. I will then propose using the Muon g-2 Experiment's successful techniques to perform the first direct search for a proton EDM. This would improve on the current limit by at least 4 orders of magnitude and is the most promising effort to solve the strong CP problem. It will also probe axionic dark matter, CP-violation for baryon asymmetry, and new physics scenarios covering a wide range of energy scales and interactions.

: Doug Cowen (Penn State) -- Physics A1/3

Detection of Astrophysical Tau Neutrinos with IceCube

Neutrinos are known to be very reticent fundamental particles, but tau neutrinos make electron and muon neutrinos look positively gregarious. The IceCube Neutrino Observatory at the South Pole has sensitivity to all three active neutrino flavors created by atmospheric and astrophysical sources, spanning six orders of magnitude in energy. Using ten years of data and convolutional neural networks to identify astrophysical tau neutrino morphologies, we detected seven tau neutrino candidates on an estimated background of approximately 0.5 events, dominated by other astrophysical neutrino flavors. The estimated average energy of the candidate tau neutrinos is approximately 200 TeV. This is the first high-significance measurement of the most energetic astrophysical tau neutrino candidates ever observed.

: Jessica Turner (Durham, IPPP) -- Physics A1/3

Proton Decay and Gravitational Waves as Complementary Tests of Grand Unification

I will discuss how proton decay, combined with gravitational waves, can be used to test Grand Unified Theories (GUTs). In particular, proton decay searches by large multipurpose neutrino experiments such as DUNE, Hyper-Kamiokande, and JUNO will either discover proton decay or further push the symmetry-breaking scale above 10^16 GeV. Another possible observational consequence of GUTs is the formation of a cosmic string network produced during the breaking of the GUT to the Standard Model gauge group, which can produce a stochastic background of gravitational waves. Several gravitational wave detectors will be sensitive to this over a wide frequency range. I will demonstrate the non-trivial complementarity between the observation of proton decay and gravitational waves produced from cosmic strings in determining SO(10) GUT breaking chains and their compatibility with leptogenesis as a means of producing the observed matter-antimatter asymmetry. Additionally, I will extend this discussion to include supersymmetric GUTs, taking into account recent findings from Pulsar Timing Arrays that have detected gravitational waves in the nanoHertz frequency range.

: Frank Close (Oxford) -- G08 Chadwick Building

Half Life - the two lives of Bruno Pontecorvo: "Mr Neutrino"

Bruno Pontecorvo is credited with the idea of solar neutrinos, of neutrinos with flavour, of neutrino oscillations and of neutrinos from supernovae. Halfway through his life, in 1950, he vanished from Harwell where he was based, and reappeared years later in the Soviet Union. Folklore is that while there, Soviet paranoia prevented him from discovering the neutrino at a nuclear reactor and of demonstrating the correctness of neutrino flavours at CERN. It is also claimed he invented strangeness but this was suppressed by Soviet secrecy. How much of this is true? Could Pontecorvo have shared in two Nobel Prizes had he not fled to the USSR? And why did he do so anyway? Was he involved in espionage? Frank Close examined his classified logbooks at Dubna, including evidence he was consulted on aspects of thermonuclear weapons. As for Pontecorvo’s defection, Frank’s investigations led to The Observer headline: “Revealed: X led to flight of nuclear scientist” ; the talk will reveal the identity of X.

: Maria Olalla Romacho (LPENS Paris) -- Physics A1/3

Exploring Cosmological Phase Transitions in the upcoming decades: from the LHC to LISA

In this seminar, we investigate the potential for probing cosmological phase transitions using the Large Hadron Collider (LHC) and the Laser Interferometer Space Antenna (LISA) in the upcoming decades. The LHC is expected to remain in operation until 2025, before undergoing a high-luminosity upgrade and operating until 2039. Additionally, LISA, set for launch in the mid-2030s, offers sensitivity to primordial stochastic Gravitational Wave (GW) backgrounds, generated during a First-Order Phase Transition (FOPT) in the early universe. Economical additions of the Standard Model (SM), such as Higgs doublet extensions, are capable of accommodating a first-order electroweak (EW) phase transition, while predicting new particles at the EW scale that may be detectable at the LHC. We demonstrate that the LHC plays a crucial role in shaping the prospects for detecting GW signals from such scenarios. Furthermore, even if new physics resides at higher energy scales inaccessible to the LHC, we can use LISA to probe models incorporating extra B-L gauge forces, explaining dark matter as primordial black holes and accommodating leptogenesis and neutrino masses.

: Josh McFayden (Sussex) -- Physics A1/3

First results from FASER(v): Observation of collider neutrinos and a new search for Dark Matter

There are a billion ghost-like particles passing through an area the size of your thumbnail every second. These neutrinos play a crucial role in our understanding of the Universe, from how the Sun shines, to exploding supernovae. There are also lots of open questions about neutrinos - we know they have mass, but the Standard Model predicts them to be massless. FASER is adding to the long history of neutrino physics by being the first experiment to observe directly neutrinos produced in a collider (the Large Hadron Collider). New measurements from FASER open up a new window to look for beyond the Standard Model physics. FASER stands for “ForwArd Search ExpeRiment” so one of its other aims is to search exotic long-lived new particles that are candidates to explain the existence of Dark Matter. If they exist, these exotic particles would be produced in collisions inside the ATLAS detector and be detected nearly 500m away in FASER. FASER is able to look for a type of these Dark Matter particles that no experiment until now has had sensitivity to. I will present the first results from FASER, including the first observation of collider neutrinos and our first search for Dark Photons. I will finish with a description of a proposal for a new dedicated facility at CERN to expand the physics potential of detectors such as FASER in the far-forward region.

: Chayan Majumdar (UCL) -- Physics A1/3

Constraining the SMEFT with Right-Handed Neutrinos at FCC-ee

The existence of right-handed neutrinos (RHNs), or heavy neutral leptons (HNLs), is strongly motivated by the observation of small but finite neutrino masses and mixings. In this work, we have extended the Standard Model (SM) particle content with a pair of gauge-singlet fermions, which can be Dirac or Majorana in nature. Adopting a model-independent effective field theory (EFT) framework, more specifically NRSMEFT, we consider all possible operators of different Lorentz structures i.e., scalar-pseudoscalar (SP), vector-axial vector (VA), and tensor-axial tensor (TAT) types upto mass dimension 6. With these operators, we analyze the future electron positron circular collider (FCC-ee) prospects and constrain the corresponding new physics (NP) cut-off scale ΛNP in the monophoton channel with √s = 91.2 GeV at 100 ab−1 as well as √s = 240 GeV at 5 ab−1 integrated luminosities.