10 JUN 2025
11:00 - 12:00

Abstract:


Long-lived particles (LLPs) are predicted in a wide range of extensions to the Standard Model, including R-parity violating supersymmetry, gauge-mediated SUSY breaking, exotic Higgs decays, heavy neutral leptons, and other scenarios. These models are often connected to fundamental questions in particle physics, such as naturalness, dark matter, baryogenesis, and the origin of neutrino masses.
In this talk, I present recent results from the CMS experiment on searches for LLPs using proton-proton collision data from the LHC. The focus is on advanced techniques for identifying displaced signatures, reducing Standard Model backgrounds, and setting upper limits on the production cross-section and branching fractions of LLPs.


Meeting Place:
Seminar Room, School of Particles and Accelerators, IPM

Link to Join Virtually:
https://www.skyroom.online/ch/ipm-particles/journal-club

10 JUN 2025
14:00 - 15:00

Date and time

Tuesday, June 10th, 2025 (20 Khordadt), 2:00 pm (Tehran zone)




Link

https://www.skyroom.online/ch/schoolofphysics/highenergyseminar


Abstract
After a brief summary of our knowledge of the role of neutrinos in the early universe, we review the most important cosmological observables and discuss how they can help in our understanding of neutrinos and their properties. In particular, we focus on how neutrino properties change the effective number of relativistic species (Neff). Among new physics scenarios, we discuss the case of light sterile neutrinos and non-standard interactions between neutrinos and electrons or neutrinos and nucleons, presenting how they affect Neff and Big Bang Nucleosynthesis (BBN). We also show a low-temperature reheating model, which provides modifications to the expansion rate that also can affect Neff and BBN predictions.

10 JUN 2025
11:00 - 12:30

Massive stars, upon exhausting their thermonuclear fuel, undergo gravitational collapse followed by supernova explosions, leaving behind black holes (BHs) as remnants. These explosions aren't perfectly symmetrical, and the uneven ejection of mass imparts a "natal kick" to the newborn BH. The magnitude of these kicks remains a subject of debate, creating uncertainty about the initial population of BHs retained in star clusters. High natal kicks lead to the immediate ejection of BHs from their host clusters, while gentler kicks allow them to stay put, forming a sub-system of BHs right in the cluster's heart. This BH sub-system (BHSub) acts like a bustling, dynamic factory at the cluster's core, pumping energy into its surroundings and dramatically influencing its evolutionary path.
In this talk, I'll first address the dynamical processes governing clusters that harbor a BHSub. Then, I'll demonstrate how assuming low natal kicks for BHs—and the subsequent formation of a BHSub at the cluster's core—can provide explanations for several outstanding open questions regarding globular clusters:
1. The nature of faint, ambiguous satellites: dark clusters vs. dark matter
2. The origin of high dark remnant fractions in Milky Way globular clusters
3. The dichotomy between metal-rich and metal-poor globular clusters in the Milky Way
4. The mysterious lack of metal-poor globular clusters in the inner regions of early-type galaxies
By the end, you'll see just how far-reaching the effects of BH retention can be in the grand story of star cluster evolution.

2 JUN 2025
16:00 - 18:00

Our Contribution to Others' Wrongdoing

2 JUN 2025
11:00 - 12:00

Abstract:

A search for resonances in top quark pair (ttˉ) production in final states with two charged leptons and multiple jets is presented. The analysis is based on proton-proton collision data collected by the CMS experiment at the CERN Large Hadron Collider (LHC) at a center-of-mass energy of TeVs=13 TeV, corresponding to an integrated luminosity of 138 fb−1. The study investigates the invariant mass distribution of the ttˉ system, along with two angular observables that provide direct sensitivity to the spin correlations between the top quark and antiquark. A significant excess of events is observed near the kinematic ttˉ threshold when compared to the expectations from nonresonant production as predicted by fixed-order perturbative quantum chromodynamics (pQCD). This observed enhancement is compatible with the production of a color-singlet pseudoscalar quasi-bound toponium state in the 1S0[1] configuration, as predicted by nonrelativistic quantum chromodynamics (NRQCD). Within the framework of a simplified model for 1S0[1] toponium, the cross section of the excess above the pQCD prediction is measured to be: pbσexcess=8.8−1.4+1.2 pb.

Based on:
https://arxiv.org/abs/2503.22382, https://arxiv.org/abs/2503.22382, https://arxiv.org/abs/2503.22382, https://arxiv.org/abs/2503.22382

Meeting Place:
Seminar Room, School of Particles and Accelerators, IPM

Link to Join Virtually:
https://www.skyroom.online/ch/ipm-particles/journal-club

28 MAY 2025
11:00 - 12:00

Abstract:

Singularities in Newton's gravitation, in general relativity (GR), in Coulomb's law, and elsewhere in classical physics, stem from two ill-conceived assumptions: a) there are point-like entities with finite masses, charges, etc., packed in zero volumes, and b) the non-quantum assumption that these point-likes can be assigned precise coordinates and momenta. In the case of GR, we argue that the classical energy-momentum tensor in Einstein's field equation is that of a collection of point particles and is prone to singularity. In compliance with Heisenberg's uncertainty principle, we suggest replacing each constituent of the gravitating matter with a suitable quantum mechanical equivalent, here a Klien-Gordon (KG) or a Yukawa-ameliorated version of it, YKG field. KG and YKG fields are spatially distributed entities. They do not end up in singular spacetime points nor predict singular blackholes. On the other hand, YKG waves reach infinity as 〖1/r e〗^(-(κ±ik)r). They create the Newtonian r^(-2) term as well as a non-Newtonian r^(-1) force. The latter can explain the observed flat rotation curves of spiral galaxies, and is interpretable as an alternative gravity, a dark matter scenario, etc. There are ample observational data on flat rotation curves of spiral galaxies, coded in the Tully-Fisher relation, to support our propositions.


Indico Link:
https://indico.hep.ipm.ir/e/h.sheikhahmadi1

Meeting Place:
Seminar Room, School of Particles and Accelerators, IPM

Link to Join Virtually:
https://www.skyroom.online/ch/ipm-particles/weekly-seminar

28 MAY 2025
14:00 - 15:00

Solid-state spin defects in 3D materials have shown remarkable capabilities in quantum sensing and information processing. While these materials are effective, the search for scalable alternatives is ongoing. Two-dimensional materials like hexagonal boron nitride (hBN) are emerging as promising candidates. The negatively charged boron vacancy (VB) in hBN exhibits exceptional room-temperature properties, positioning it as a compelling platform for scalable quantum technologies. This lecture explores recent advances in harnessing VB centers for quantum technologies, focusing on three interconnected pillars: spin control, strain-mediated coupling, and decoherence mitigation. First, we demonstrate efficient nuclear spin hyperpolarization using active spin driving and the Holstein-Primakoff transformation. This enables the initialization of large-scale quantum simulators from thermal spin baths. Second, we propose a strain-induced coupling scheme in hBN nanoribbons. This scheme demonstrates robust room-temperature entanglement and Dicke-Ising simulations. Finally, we investigate the decoherence dynamics of VB centers, focusing on the interplay between dipolar hyperfine interactions and spin-phonon coupling. Our findings provide a foundation for developing practical quantum devices that leverage the advantages of van der Waals materials.


Venue: Room D, 3rd Floor, Farmanieh Building, IPM
Link: https://vmeeting2.ipm.ir/b/nan-gkn-wmh-exh