High Energy Physics - Phenomenology (hep-ph)

Abstract: Most of the experimental searches of the non-Standard Model Higgs boson(s) at the LHC rely on the QCD induced production modes. However, in some beyond Standard Model frameworks, the additional Higgs bosons can have fermiophobic behaviour. The type I two Higgs doublet considered here is a perfect example where all the additional Higgs bosons exhibit fermiophobic nature over a large parameter space. Thus the Electoweak productions of these new Higgs bosons are more dominant over the QCD induced processes. In scenarios with light pseuodoscalar ($A$) which is bound to decay dominantly to $b\bar{b}$, even being fermiophobic, the $4b + W$ state via $p p \to H^\pm A \to (AW)A \to 4b + W$ and followed by the leptonic decay of $W$ boson can surpass the QCD initiated $4b$ final state. However, the signal gets overshadowed by large $t\bar{t}+$ jets background and hence constructing a suitable discriminator based on the signal hypothesis and signal topology is necessary. We devised a $\chi^2$ variable as the most suitable signal-background discrimintor to reduce the background by a sizable amount and showed the discovery reach ( $>3\sigma$) of the EW initiated $4b+ \ell + {\rlap{\,/}{E}_T}$ final state at the LHC.

Abstract: We study the inclusive decay widths of singly heavy baryons with the improved bag model in which the unwanted center-of-mass motion is removed. Additional insight is gained by comparing the charmed and bottom baryons. We discuss the running of the baryon matrix elements and compare the results with the non-relativistic quark model (NRQM). While the calculated two-quark operator elements are compatible with the literature, those of the four-quark ones deviate largely. In particular, the heavy quark expansion holds well in the bag model for four-quark operator matrix elements but badly broken in the NRQM. We predict $1-\tau(\Omega_b)/ \tau(\Lambda_b^0) = (8.34\pm2.22)\%$ in accordance with the current experimental value of $(11.5^{+12.2}_{-11.6})\%$ but potentially in tension with $(13.2\pm 4.7)\%$ obtained in the NRQM. We find an excellent agreement between theory and experiment for the lifetimes of bottom baryons. For charmed baryons, the calculated decay widths confirm that the established new hierarchy of $\tau(\Xi_c^+)> \tau(\Omega_c^0) > \tau(\Lambda_c^+)>\tau(\Xi_c^0)$ originates from dimension-7 four-quark operators. We recommend to measure some semileptonic inclusive branching fractions in the forthcoming experiments to discern different approaches. For example, we obtain ${\cal BF} (\Xi_c^+ \to X e^+ \nu_e) = (8.59\pm 0.49)\% $ and ${\cal BF} (\Omega_c^0 \to X e^+ \nu_e) = (1.88\pm 1.69)\% $ in sharp contrast to ${\cal BF} (\Xi_c^+ \to X e^+ \nu_e) =(12.74^{+2.54}_{-2.45})\% $ and ${\cal BF} (\Omega_c^0 \to X e^+ \nu_e) = (7.59^{+2.49}_{-2.24})\% $ found in the NRQM.

Abstract: We report a theoretical derivation of the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameters and the accompanying mixing angles. These results are arrived at from the exceptional Jordan algebra applied to quark states, and from expressing flavor eigenstates (i.e. left-chiral states) as superposition of mass eigenstates (i.e. the right-chiral states) weighted by square-root of mass. Flavor mixing for quarks is mediated by the square-root mass eigenstates, and the mass ratios used have been derived in earlier work from a left-right symmetric extension of the standard model. This permits a construction of the CKM matrix from first principles. There exist only four normed division algebras, they can be listed as follows - the real numbers $\mathbb{R}$, the complex numbers $\mathbb{C}$, the quaternions $\mathbb{H}$ and the octonions $\mathbb{O}$. The first three algebras are fairly well known; however, octonions as algebra are less studied. Recent research has pointed towards the importance of octonions in the study of high energy physics. Clifford algebras and the standard model are being studied closely. The main advantage of this approach is that the spinor representations of the fundamental fermions can be constructed easily here as the left ideals of the algebra. Also the action of various Spin Groups on these representations too can be studied easily. In this work, we build on some recent advances in the field and try to determine the CKM angles from an algebraic framework. We obtain the mixing angle values as $\theta_{12}=11.093^o, \theta_{13}=0.172^o, \theta_{23}=4.054^o$. In comparison, the corresponding experimentally measured values for these angles are $13.04^o \pm 0.05^o, 0.201^o \pm 0.011^o, 2.38^o \pm 0.06^o $. The agreement of theory with experiment is likely to improve when running of quark masses is taken into account.

Abstract: We study the dissociation of $\psi (3770)$, $\psi (4040)$, $\psi (4160)$, and $\psi (4415)$ mesons in collisions with nucleons, which takes place in high-energy proton-nucleus collisions. Quark interchange between a nucleon and a $c\bar c$ meson leads to the dissociation of the $c\bar c$ meson. We consider the reactions: $pR \to \Lambda_c^+ \bar{D}^0$, $pR \to \Lambda_c^+ \bar{D}^{*0}$, $pR \to \Sigma_c^{++} D^-$, $pR \to \Sigma_c^{++} D^{*-}$, $pR \to \Sigma_c^{+} \bar{D}^0$, $pR \to \Sigma_c^{+} \bar{D}^{*0}$, $pR \to \Sigma_c^{*++} D^-$, $pR \to \Sigma_c^{*++} D^{*-}$, $pR \to \Sigma_c^{*+} \bar{D}^0$, and $pR \to \Sigma_c^{*+} \bar{D}^{*0}$, where $R$ stands for $\psi (3770)$, $\psi (4040)$, $\psi (4160)$, or $\psi (4415)$. A reaction of a neutron and a $c\bar c$ meson corresponds to a reaction of a proton and the $c\bar c$ meson by replacing the up quark with the down quark and vice versa. Transition-amplitude formulas are derived from the $S$-matrix element. Unpolarized cross sections are calculated with the transition amplitudes for scattering in the prior form and in the post form. The cross sections relate to nodes in the radial wave functions of $\psi (3770)$, $\psi (4040)$, $\psi (4160)$, and $\psi (4415)$ mesons.

Abstract: In the wake of measurements on $B_c^+ \to J/\psi K^+$, $B_c^+ \to J/\psi \pi^+\pi^-\pi^+$, and $B_c^+ \to J/\psi K^+ K^-\pi^+$ at Large Hadron Collider experiments, we propose to study the decays $B_c^+ \to J/\psi M^+$ comprehensively, with $M$ being the light charged pseudoscalar ($P$), vector ($V$), scalar ($S$), axial-vector ($A$), and tensor ($T$) mesons, within the improved Perturbative QCD (iPQCD) formalism at leading order in the Standard Model. The theoretical predictions for experimental observables such as branching fractions, relative ratios, and longitudinal polarization fractions in the iPQCD formalism await near future examinations relying on the upgraded Large Hadron Collider, even the forthcoming Circular Electron Positron Collider. We emphasize that the investigations on the factorizable-emission-suppressed or -forbidden decays like $B_c^+ \to J/\psi S^+$, $B_c^+ \to J/\psi A^+_{1^1\!P_1}$, and $B_c^+ \to J/\psi T^+$, should go definitely beyond naive factorization to explore the rich dynamics, which could, in turn, further help understand the QCD nature of $B_c$ meson, as well as that of related hadrons. The future confirmations on those predictions about the relative ratios between the branching fractions of $B_c^+ \to J/\psi b_1(1235)^+ (a_0(980)^+, a_0(1450)^+, a_2(1320)^+)$ and $B_c^+ \to J/\psi \pi^+$ could further examine the reliability of this iPQCD formalism. Because of containing only tree-level $\bar b \to \bar c$ transitions, the CP asymmetries in the $B_c^+ \to J/\psi M^+$ decays exhibit naturally zero.

Abstract: In SU(N) gluodynamics, at high temperature the spontaneous magnetization, b(T) not equal to 0, of a vacuum happens in the approximation to the effective potential - the tree plus the one-loop, plus daisy diagrams, W(b)= b^2/2 g^2 + W^(1)(b) + W^(daisy)(b). At the same time, in two-loop approximation, W(A_0)= W^(1)(A_0) + W^(2)(A_0), other classical field - A_0 condensate directly related to the Polyakov loop - is also spontaneously generated. To investigate the creation of the condensates together, the two loop effective potential of both fields should be calculated. This program was realized recently for SU(2) in [1]. However, the generation of magnetic field in two-loop order was not studied in detail. In the present paper, we compute the value of chromomagnetic field b(T) for latter case. Then, considering the spectrum of color charged gluons at the background of both condensates, we conclude that the A_0 stabilizes the magnetized vacuum at high temperature. This is in agreement with the lattice simulations carried out already and clarifies the mechanism of the magnetic field stabilization.

Abstract: We investigate two extensions of the standard model that include particle dark matter candidates: the N2HDM and the NMSSM. These models feature a non-SM-like CP-even scalar with a sub-TeV mass, denoted by $H_2$, among other particles. At a 13 TeV proton-proton collider, the primary production channel for such scalars is via the fusion of a pair of gluons. Subsequently, these scalars can decay invisibly into a pair of dark matter candidates, with some regions of the parameter space exhibiting a dominance of such decay over other modes. In the supersymmetric model, it is possible for the LSP and NLSP to be mass degenerate, leading to quasi-invisible $H_2$ decays to LSP+NLSP and NLSP+NLSP. We present the predictions of both models for this challenging scenario while ensuring compatibility with recent experimental constraints.

Abstract: The baryon-meson scattering amplitude is computed at tree level within the $1/N_c$ expansion of QCD, where $N_c$ is the number of color charges. The most general expression is obtained by accounting for explicitly the effects of the decuplet-octet baryon mass difference. Although the resultant expression is general enough that it can be applied to any incoming and outgoing baryons and mesons, provided that the Gell-Mann--Nishijima scheme is respected, results for nucleon-pion scattering processes are explicitly dealt with. With these, some isospin relations are verified to be valid at the physical value $N_c=3$. Corrections due to $SU(3)$ flavor symmetry breaking are only sketched so they are left for future work. The three-level expressions obtained here represent a first effort toward understanding scattering processes in the context of the $1/N_c$ expansion.

Abstract: Recent analyses on high-energy inclusive Higgs-boson rates in proton collisions via the gluon-fusion channel, matched with the state of-the-art fixed-order N$^3$LO accuracy, have shown that the impact of high-energy resummation corrections reaches 10% at the FCC nominal energies. This supports the statement that electroweak physics at 100 TeV is expected to receive relevant contributions from small-$x$ physics. In this preliminary study we present novel predictions for transverse-momentum and rapidity distributions sensitive to the inclusive emission of a Higgs boson in association with a light-flavored jet in proton collisions, calculated within the NLL accuracy of the energy-logarithmic resummation. We highlight how high-energy signals for this process are already present and visible at current LHC energies, and they are also sizable at the FCC ones. We come out with the message that the improvement of fixed-order calculations on Higgs-sensitive QCD distributions is a core ingredient to reach the precision level in the description of observables relevant for the Higgs physics at the FCC.

Abstract: We present a python-based program for phenomenological investigations in particle physics using machine learning algorithms, called \verb"MLAnalysis". The program is able to convert LHE and LHCO files generated by \verb"MadGraph5_aMC@NLO" into data sets for machine learning algorithms, which can analyze the information of the events. At present, it contains three machine learning (ML) algorithms: isolation forest (IF) algorithm, nested isolation forest (NIF) algorithm, kmeans anomaly detection (KMAD), and some basic functionality to analyze the kinematic features of a data set. Users can use this program to improve the efficiency of searching for new physics signals.