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Study of semileptonic vector boson scattering and anomalous quartic gauge coupling from proton-proton collisions at 13 TeV
No full textA measurement of the electroweak production of ZV (V = W, Z) boson pairs associated with two jets in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. The analysis targets final states with two isolated electrons or muons from Z decays and three to four jets, depending on the momentum of the vector boson that decays into quarks. The data, corresponding to an integrated luminosity of 138 fb, were collected at the CERN LHC with the CMS detector during the 2016--2018 data-taking period.
The cross section is measured in a fiducial region characterized by a large invariant mass and pseudorapidity gap between the two forward jets. The electroweak production of ZV in association with two jets is measured with an observed (expected) significance of 1.3 (1.8) standard deviations. Constraints are also placed on effective field theory parameters that describe anomalous electroweak production of WW, WZ, and ZZ boson pair pairs in association with two jets, combining the ZV and WV semileptonic events. Stringent limits are set on anomalous quartic gauge couplings in terms of dimension-8 operators
New physics at Tera-: precision renormalised
No full textWe study the power of a Tera-Z run at FCC-ee for indirectly detecting or constraining heavy new physics. Our main finding is that nearly every new particle which matches at tree level to dimension-six operators of the Standard Model Effective Field Theory (SMEFT) affects electroweak precision observables (EWPOs) at either tree level or via one loop renormalisation group (RG) running. This is true almost regardless of the structure of couplings to the Standard Model; just a handful of exceptions are identified which can produce zeroes in the EWPO RG equations. Under simple flavour assumptions, we perform fits of each state to projected FCC-ee Z pole measurements, showing that all scenarios can be tested at the TeV scale or better, with many projected exclusions reaching tens of TeV. Tera-Z is argued to provide an almost inescapable probe of heavy new physics.We study the power of a Tera- run at FCC-ee for indirectly detecting or constraining heavy new physics. Our main finding is that nearly every new particle which matches at tree level to dimension-six operators of the Standard Model Effective Field Theory (SMEFT) affects electroweak precision observables (EWPOs) at either tree level or via one loop renormalisation group (RG) running. This is true almost regardless of the structure of couplings to the Standard Model; just a handful of exceptions are identified which can produce zeroes in the EWPO RG equations. Under simple flavour assumptions, we perform fits of each state to projected FCC-ee pole measurements, showing that all scenarios can be tested at the TeV scale or better, with many projected exclusions reaching tens of TeV. Tera- is argued to provide an almost inescapable probe of heavy new physics
Measurement of strange baryon production in charged-particle jets in pp and p-Pb collisions with ALICE
No full textThe enhancement of the ratio of strange to non-strange hadrons with increasing charged-particle multiplicity density is often interpreted as a signature of the medium formed in heavy-ion collisions. However, this effect has also been observed in smaller systems, such as pp and p–Pb collisions. Understanding this effect requires a detailed description of the production mechanisms of strange hadrons in and out of jets. In this manuscript published results on the production of KS0, Λ(Λ¯), Ξ± and Ω± hadrons in charged-particle jets and the underlying event in pp and p-Pb collisions measured by ALICE are presented. In addition, a new analysis of in-jet fragmentation into Λ and KS0 hadrons in pp collisions at √s = 13.6 TeV from LHC Run 3 data is shown.The enhancement of the ratio of strange to non-strange hadrons with increasing charged-particle multiplicity density is often interpreted as a signature of the medium formed in heavy-ion collisions. However, this effect has also been observed in smaller systems, such as pp and p-Pb collisions. Understanding this effect requires a detailed description of the production mechanisms of strange hadrons in and out of jets. In this manuscript are presented published results on the production of , , and hadrons in charged-particle jets and the underlying event in pp and p-Pb collisions measured by ALICE. In addition, a new analysis of in-jet fragmentation into and hadrons in pp collisions at TeV using LHC Run 3 data is shown
Calculation of radiation length in materials
No full textThis document briefly introduces an analytical method commonly used to determine the radiation length of elements, elemental molecules, chemical compounds, mixtures, composite materials and structures. The formulas are reliable in the absence of experimental data, but the experimental assessment should be prioritised when possible. The greater the radiation length of a material, the more “transparent” it is to radiation. In the CERN experiments, high material transparency is crucial in several components, such as, for instance, the section of the beam pipe in which the collisions occur. A high material transparency for the beam pipe at the point of collision reduces unwanted interactions that could distort the particle trajectories. This ensures that the primary particles remain intact and travel along predictable paths, allowing precise measurements of their energy, momentum, and other properties; therefore, ensuring that collision data is recorded as cleanly and accurately as possible
Model implementations of axion dark matter from kinetic misalignment
No full textThe axion kinetic misalignment mechanism (KMM) opens the possibility of explaining dark matter for almost any axion mass and decay constant that is not accessible by the standard misalignment mechanism, in particular at low values of the axion decay constant (i.e. large coupling). This is a new opportunity for most axion experiments which could be sensitive to dark matter and probe new regimes of axion cosmology.We scrutinise UV completions that lead to the KMM mechanism.These mainly rely on the early dynamics of the axion partner, the radial mode of the complex scalar field, from which the axion inherits kinetic energy. The damping of the radial-mode energy density is then a necessary ingredient. We study in detail thermal damping from interactions in the plasma.A minimal and rather natural implementation consists of a KSVZ-type model with a nearly-quadratic potential for the radial mode extended by U(1)-breaking higher-dimensional operators.Furthermore, we study Higgs portal interactions as an alternative damping mechanism and improve upon previously proposed implementations based on quartic potentials.These implementationscan lead to the QCD axion being dark matter and in the reach of IAXO, while MADMAX, IAXO and ALPS II can be sensitive to a generic Axion-Like-Particle (ALP) as dark matter. Such models typically feature a kination era. We also show that ALP dark matter from KMM points to a particular realization of inflation.The axion kinetic misalignment mechanism (KMM) opens the possibility of explaining dark matter for almost any axion mass and decay constant that are not accessible by the standard misalignment mechanism, in particular at low values of the axion decay constant (i.e. large coupling). This is a new opportunity for most axion experiments which could be sensitive to dark matter and probe new regimes of axion cosmology. We scrutinise UV completions that lead to the KMM mechanism. These mainly rely on the early dynamics of the axion partner, the radial mode of the complex scalar field, from which the axion inherits kinetic energy. The damping of the radial-mode energy density is then a necessary ingredient. We study in detail thermal damping from interactions in the plasma. A minimal and rather natural implementation consists of a KSVZ-type model with a nearly-quadratic potential for the radial mode extended by U(1)-breaking higher-dimensional operators. Furthermore, we study Higgs portal interactions as an alternative damping mechanism and improve upon previously proposed implementations based on quartic potentials. These implementations can lead to the QCD axion being dark matter and in the reach of IAXO, while MADMAX, IAXO and ALPS II can be sensitive to a generic Axion-Like-Particle (ALP) as dark matter. Such models typically feature a kination era. We also show that ALP dark matter from KMM points to a particular realization of inflation
New insights into strange-quark hadronization measuring multiple (multi-)strange hadron production in small collision systems with ALICE
No full textAmong the most important results from the Run-1 and Run-2 of the LHC is the observation of an enhanced production of (multi-)strange to non-strange hadron yields, gradually rising from low-multiplicity to highmultiplicity pp and p–Pb collisions, reaching values close to those measured in peripheral Pb–Pb collisions [1]. The observed behaviour cannot be quantitatively reproduced by any of the available QCD-inspired MC generators. In this contribution an extension of this study is presented: the measurement of the Ks0, Λ, Ξ− and Ω− (together with antiparticles) multiplicity distributions in pp collisions at √s = 5.02 TeV as a function of the charged-particle multiplicity, together with the average probability for the multiplets production, extending the study of strangeness production beyond its average. This novel method, based on counting the number of strange particles event-by-event, represents a new test bench for production mechanisms, probing events with a large imbalance between strange and non-strange content.Among the most important results from the Run-1 and Run-2 of the LHC is the observation of an enhanced production of (multi-)strange to non-strange hadron yields, gradually rising from low-multiplicity to high-multiplicity pp and p--Pb collisions, reaching values close to those measured in peripheral Pb--Pb collisions. The observed behaviour cannot be quantitatively reproduced by any of the available QCD-inspired MC generators. In this contribution an extension of this study is presented: the measurement of the , , and (together with their antiparticles) multiplicity distributions in pp collisions at = 5.02 TeV as a function of the charged-particle multiplicity, together with the average probability for the multiplets production, extending the study of strangeness production beyond its average. This novel method, based on counting the number of strange particles event-by-event, represents a new test bench for production mechanisms, probing events with a large imbalance between strange and non-strange content
Student Sessions 2025
No full textHello! I’m Zhoie, a first year masters’ student in physics studying at the University of the Philippines Diliman. I joined the High Energy Physics and Phenomenology group at the National Institute of Physics during my third undergraduate year and have been conducting research in particle physics ever since.
Di-Higgs production provides direct sensitivity to the Higgs self-coupling parameter. My project focuses on the HH → bbgg channel, which has a relatively high branching ratio but is challenging due to the overwhelming QCD background in the H → gg decay. This analysis uses Monte Carlo simulations to study the separation between H → bb and H → gg jets using jet substructure variables, and to improve their discrimination against the background using track multiplicity cuts and BDT-based tagging