19 FEB 2025
11:00 - 12:00

Abstract:

We revisit the canonical quantization of free bosonic closed string theory and observe that the physicality of states requires vanishing of the worldsheet Virasoro algebra generators sandwiched between any two physical states. This requirement yields four classes of physical states, depending on discrete worldsheet symmetries: parity and time reversal. The usual string states which are highest weight states of the Virasoro algebra, preserve both, while the other new three classes break one or both. We initiate the quantization of a null p-brane in light-cone gauge using the idea of sandwich quantum constraints and show that solutions to the sandwich conditions are classified into p+1 distinct classes, which we completely specify.

Indico Link:
https://indico.hep.ipm.ir/e/i.rasulian

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

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

17 FEB 2025
11:00 - 12:00

Abstract:

Atomic nuclei are self-organized, many-body quantum systems bound by strong nuclear forces within femtometer-scale space. These complex systems manifest a variety of shapes, traditionally explored using non-invasive spectroscopic techniques at low energies. However, at these energies, their instantaneous shapes are obscured by long-timescale quantum fluctuations, making direct observation challenging. Here we introduce the collective flow assisted nuclear shape imaging method, which images the nuclear global shape by colliding them at ultrarelativistic speeds and analyzing the collective response of outgoing debris. This technique captures a collision-specific snapshot of the spatial matter distribution within the nuclei, which, through the hydrodynamic expansion, imprints patterns on the particle momentum distribution observed in detectors. We benchmark this method in collisions of ground state Uranium-238 nuclei, known for their elongated, axial-symmetric shape. Our findings show a large deformation with a slight deviation from axial symmetry in the nuclear ground state, aligning broadly with previous low-energy experiments. This approach offers a new method for imaging nuclear shapes, enhances our understanding of the initial conditions in high-energy collisions and addresses the important issue of nuclear structure evolution across energy scales.

Based on:
Nature 635, 67-72 (2024)

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

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

5 FEB 2025
11:00 - 12:00

Abstract:

In this paper, we explore the interactions between light axion-like particles (ALPs) and top quarks, gluons, and W-bosons. Utilizing high-energy probes at the LHC, we probe these couplings in the context of single top quark production associated with a W-boson and an ALP. We analyze the latest LHC Run II data on tt spin correlation measurements to establish constraints on these couplings. Additionally, we compare these constraints with those derived from loop-induced couplings and indirect searches involving B-meson decays. Furthermore, we derive two-dimensional limits on the ALP couplings with top quarks and gluons.

Based on:
arXiv:2408.11588

Indico Link:
https://indico.hep.ipm.ir/e/y.hosseini2

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

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

3 FEB 2025
11:00 - 12:00

Abstract:

The proton, one of the components of atomic nuclei, is composed of fundamental particles called quarks and gluons. Gluons are the carriers of the force that binds quarks together, and free quarks are never found in isolation—that is, they are confined within the composite particles in which they reside. The origin of quark confinement is one of the most important questions in modern particle and nuclear physics because confinement is at the core of what makes the proton a stable particle and thus provides stability to the Universe. The internal quark structure of the proton is revealed by deeply virtual Compton scattering, a process in which electrons are scattered off quarks inside the protons, which subsequently emit high-energy photons, which are detected in coincidence with the scattered electrons and recoil protons. Here we report a measurement of the pressure distribution experienced by the quarks in the proton. We find a strong repulsive pressure near the centre of the proton (up to 0.6 femtometers) and a binding pressure at greater distances. The average peak pressure near the centre is about 1035 pascals, which exceeds the pressure estimated for the most densely packed known objects in the Universe, neutron stars. This work opens up a new area of research on the fundamental gravitational properties of protons, neutrons and nuclei, which can provide access to their physical radii, the internal shear forces acting on the quarks and their pressure distributions.

Based on:
https://doi.org/10.1038/s41586-018-0060-z

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

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

27 JAN 2025
13:00 - 14:00

Abstract:

In non-central ultra-relativistic heavy-ion collisions, the angular momentum can reach magnitudes of ${\cal O}(10^4 −10^5)\hbar$, resulting in significant vorticity within the quark-gluon plasma (QGP). One intriguing consequence of this rotation is its impact on the chiral symmetry restoration and deconfinement phase transitions, a topic that has attracted considerable attention in recent years. In this talk, I will review some recent advances in using holographic techniques to explore these rotational effects. Beginning with a basic holographic model, I will discuss its limitations and show how employing more refined models resolves these issues, achieving consistency with lattice QCD results. The findings highlight the necessity of incorporating rotational effects on both gluodynamics and chiral dynamics simultaneously to obtain accurate predictions.

Based on:
https://arXiv:2405.06386v1, arXiv:2010.14478v2

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

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

22 JAN 2025
11:00 - 12:00

Abstract:

In this talk, I will explore the use of Krylov complexity as a diagnostic tool for understanding the chaotic nature of quantum systems. The concept of Krylov complexity is introduced within the framework of the Lanczos algorithm, allowing us to study the system's dynamics in a finite Krylov subspace. By analyzing the time evolution and saturation of complexity, it is possible to demonstrate how it distinguishes between chaotic and integrable many-body systems. These distinctions will be illustrated with numerical results from spin models, providing insights into the interplay between Krylov complexity and quantum chaos.

Indico Link:
https://indico.hep.ipm.ir/e/m.vasli

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

13 JAN 2025
12:00 - 13:00

Abstract:

The atomic nucleus is made of protons and neutrons (nucleons), which are themselves composed of quarks and gluons. Understanding how the quark–gluon structure of a nucleon bound in an atomic nucleus is modified by the surrounding nucleons is an outstanding challenge. Although evidence for such modification—known as the EMC effect—was first observed over 35 years ago, there is still no generally accepted explanation for its cause. Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei. Here we report simultaneous, high-precision measurements of the EMC effect and SRC abundances. We show that EMC data can be explained by a universal modification of the structure of nucleons in neutron–proton SRC pairs and present a data-driven extraction of the corresponding universal modification function. This implies that in heavier nuclei with many more neutrons than protons, each proton is more likely than each neutron to belong to an SRC pair and hence to have distorted quark structure. This universal modification function will be useful for determining the structure of the free neutron and thereby testing quantum chromodynamics symmetry-breaking mechanisms and may help to discriminate between nuclear physics effects and beyond-the-standard-model effects in neutrino experiments.

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

8 JAN 2025
11:00 - 12:00

Abstract:

In the Standard Model at high temperatures, anomalous effects contribute to the violation of baryon number (B) and lepton number (L), separately, while B−L remains conserved. There are also corresponding changes in the helicity of the hypermagnetic field (h) and the Chern-Simons numbers of the non-Abelian gauge fields (NCS,W and NCS,S). In this study, we investigate a baryogenesis process in the symmetric phase of the early Universe by taking into account the Abelian and non-Abelian anomalous effects as well as the perturbative chirality-flip processes of all fermions. We calculate explicitly the time evolution of all relevant physical quantities, including those of h and NCS,W, and show that there is another conserved global charge involving total matter-antimatter asymmetry B+L, hypermagnetic helicity hB and NCS,W.

Indico Link:
https://indico.hep.ipm.ir/e/s.abbaslou

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

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

1 JAN 2025
11:00 - 12:00

Abstract:

In this talk, I will give an overview of the gravitational memory effect, its observable aspects and its consequences for fundamental physics. I will report some of my works in this area.

Indico Link:
https://indico.hep.ipm.ir/e/a.seraj

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

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

30 DEC 2024
11:00 - 12:00

Abstract:

In the CMS Muon system, the RPC Link System will upgrade to cope with high luminosity LHC (HL-LHC) conditions and improve the time resolution of the Muon hits detected by the present RPC chambers from 25 ns to 1.5 ns. The upgrade program for the RPC Link System was started in 2017 and endorsed in 2018 by the CMS muon Technical Design Report (TDR). By the end of 2027, the CMS RPC system will install brand-new electronics designed and fabricated by the Tehran IPM. The upgraded RPC Link System consists of several key components: link board (LB), control board (CB), high-speed front panel called Samtec, and control front panel called Harting. For the phase-2 upgrade, 1376 LBs and 216 CBs will be produced. Production of these electronics is split into two phases: pilot production and full production. During the pilot production, only 10% of the boards will be manufactured to ensure the quality of electronics and address any potential failure or complexities in the production process. In this talk, we will review the latest status of the IPM electronics project and explain the following plan for qualification these electronics.

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

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