2 OCT 2023
11:00 - 12:00

Abstract:
A search for high-mass dimuon resonance production in association with one or more b quark jets is presented. The study uses proton-proton collision data collected with the CMS detector at the LHC corresponding to an integrated luminosity of 138 fb−1 at a center-of-mass energy of 13 TeV. Model-independent limits are derived on the number of signal events with exactly one or more than one b quark jet. Results are also interpreted in a lepton-flavor-universal model with Z′ boson couplings to a bb
quark pair (gb ), an sb quark pair (gb δbs ), and any same-flavor charged lepton (gℓ ) or neutrino pair (gν ), with | gν | = | gℓ |. For a Z′ boson with a mass mZ' = 350 GeV (2 TeV) and |δbs | < 0.25, the majority of the parameter space with 0.0057 < | gℓ | < 0.35 (0.25 < | gℓ | < 0.43) and 0.0079 < | gb | < 0.46 (0.34 < | gb | < 0.57) is excluded at 95% confidence level. Finally, constraints are set on a Z′ model with parameters consistent with low-energy b → s ℓℓ measurements. In this scenario, most of the allowed parameter space is excluded for a Z′ boson with 350 < mZ′ < 500 GeV, while the constraints are less stringent for higher mZ hypotheses. This is the first dedicated search at the LHC for a high-mass dimuon resonance produced in association with multiple b quark jets, and the constraints obtained on models with this signature are the most stringent to date.

Link to Join Virtually:
https://meet.google.com/fnv-dfkk-ghb

28 SEP 2023
11:00 - 12:00

Abstract:
We construct microstates of 3d black holes in the Hilbert space of tensionless null strings with non-zero winding along the bifurcation horizon. Counting these string states we recover the Bekenstein-Hawking entropy and its semiclassical logarithmic corrections.

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

27 SEP 2023
11:00 - 12:00

Abstract:

We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement.

Based on :
https://arxiv.org/abs/2107.11369

Link to join virtually:
https://meet.google.com/fnv-dfkk-ghb

25 SEP 2023
11:00 - 12:00

Abstract:

Examining the validity of hydrodynamics series near the phase transition points is of great importance either in the theoretical or phenomenological point of view for heavy-ion physics research. We investigate this in the framework of gauge/gravity duality by using the Einstein-Klein-Gordon model which is a bottom-up string theory construction and a parameter B_4 in this model is responsible for mimicking the various kinds of phase transition of the strongly coupled field theory that lives on the boundary. We study both the thermodynamics and dynamics of time-dependent linearized perturbations on top of this background for the spin-2, spin-1 and spin-0 sectors of perturbations extensively.

Indico Link:
https://indico.hep.ipm.ir/e/f.taghinavaz

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

Link to join virtually:
https://meet.google.com/fnv-dfkk-ghb

21 SEP 2023
11:00 - 12:00

Abstract:

Inertia is the intrinsic tendency of matter to remain in a given condition. The state of a particle in spacetime is determined by its mass and spin, which characterize the irreducible unitary representations of the inhomogeneous Lorentz group. Therefore, the inertial attributes of a particle are determined by its mass and spin. The inertial properties of mass are well known; hence, I concentrate on the inertial properties of intrinsic spin.

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