Search for the radiative $$ {\Xi}_b^{-} $$ → Ξ−γ decay

The first search for the rare radiative decay $$ {\Xi}_b^{-} $$ Ξ b − → Ξ−γ is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb−1. The $$ {\Xi}_b^{-} $$ Ξ b − → Ξ−J/ψ channel is used as normalization. No $$ {\Xi}_b^{-} $$ Ξ b − → Ξ−γ signal is found and an upper limit of $$ \mathcal{B} $$ B ($$ {\Xi}_b^{-} $$ Ξ b − → Ξ−γ) < 1.3 × 10−4 at 95% confidence level is obtained.

Induced surface and curvature tension equation of state for hadron resonance gas in finite volumes and its relation to morphological thermodynamics

Here, we develop an original approach to investigate the grand canonical partition function of the multicomponent mixtures of Boltzmann particles with hard-core interaction in finite and even small systems of the volumes above 20 fm3. The derived expressions of the induced surface tension equation of state (EoS) are analyzed in detail. It is shown that the metastable states, which can emerge in the finite systems with realistic interaction, appear at very high pressures at which the hadron resonance gas, most probably, is not applicable at all. It is shown how and under what conditions the obtained results for finite systems can be generalized to include into a formalism the equation for curvature tension. The applicability range of the obtained equations of induced surface and curvature tensions for finite systems is discussed and their close relations to the equations of the morphological thermodynamics are established. The hadron resonance gas model on the basis of the obtained advanced EoS is worked out. Also, this model is applied to analyze the chemical freeze-out of hadrons and light nuclei with the number of (anti-) baryons not exceeding 4. Their multiplicities were measured by the ALICE Collaboration in the central lead–lead collisions at the center-of-mass energy [Formula: see text] TeV.

Feasibility study of measuring $$b\rightarrow s\gamma $$ photon polarisation in $$D^0\rightarrow K_1(1270)^- e^+\nu _e$$ at STCF

We report a sensitive study of measuring $$b\rightarrow s\gamma $$ b → s γ photon polarisation in $$D^{0}\rightarrow K_1(1270)^-e^+\nu _e$$ D 0 → K 1 ( 1270 ) - e + ν e with an integrated luminosity of $$\mathscr {L}$$ L = 1 ab$$^{-1}$$ - 1 at a center-of-mass energy of 3.773 GeV at a future Super Tau Charm Facility. More than 61,000 signals of $$D^{0}\rightarrow K_1(1270)^-e^+\nu _e$$ D 0 → K 1 ( 1270 ) - e + ν e are expected. Based on a fast simulation software package, the statistical sensitivity for the ratio of up-down asymmetry is estimated to be $$1.5\times 10^{-2}$$ 1.5 × 10 - 2 by performing a two-dimensional angular analysis in $$D^{0}\rightarrow K_1(1270)^-e^+\nu _e$$ D 0 → K 1 ( 1270 ) - e + ν e . Combining with measurements of up-down asymmetry in $$B\rightarrow K_1\gamma $$ B → K 1 γ , the photon polarisation in $$b\rightarrow s\gamma $$ b → s γ can be determined model-independently.

Search for a heavy resonance decaying to a top quark and a W boson at $$ \sqrt{s} $$ = 13 TeV in the fully hadronic final state

A search for a heavy resonance decaying to a top quark and a W boson in the fully hadronic final state is presented. The analysis is performed using data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb−1 recorded by the CMS experiment at the LHC. The search is focused on heavy resonances, where the decay products of each top quark or W boson are expected to be reconstructed as a single, large-radius jet with a distinct substructure. The production of an excited bottom quark, b*, is used as a benchmark when setting limits on the cross section for a heavy resonance decaying to a top quark and a W boson. The hypotheses of b* quarks with left-handed, right-handed, and vector-like chiralities are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1 TeV, respectively. These are the most stringent limits on the b* quark mass to date, extending the previous best limits by almost a factor of two.

Search for resonnances in diJet and multijet events from proton-proton collisions at a center of mass energy of 13 TeV collected with the CMS detector at the CERN LHC

Στην διατριβή αυτή μελετάμε την αναζήτηση φυσικής πέραν του Καθιερωμένου Προτύπου, σε γεγονότα με αδρονικούς πίδακες στη τελική κατάσταση, χρησιμοποιώντας τα δεδομένα του πειράματος CMS από συγκρούσεις πρωτονίου-πρωτονίου με ενέργεια κέντρου μάζας στα 13 TeV. Στο πρώτο μέρος παρουσιάζουμε την ερευνα για αναζήτηση συντονισμών χρησιμοποιώντας γεγονότα με δύο αδρονικούς πίδακες στη τελική κατάσταση, μελετώντας το φάσμα της αναλλοίωτης μάζας τους χρησιμοποιώντας παραμετρικές μεθόδους για την περιγραφή της. Εν συνεχεία παρουσιάζουμε την τρέχουσα ανάλυση που αφορά στην αναζήτηση νέας φυσικής σε γεγονότα με τέσσερις αδρονικούς πίδακες στην τελική κατάσταση, ανά δύο προερχόμενοι από πιθανό νέο συντονισμό, που πραγματοποιείται για πρώτη φορά στον LHC. Αφορμή για την αναζήτηση αυτή έχει σταθεί το γεγονός με την υψηλότερη αναλλοίωτη μάζα στην πρώτη ανάλυση, που έχει χαμηλή πιθανότητα να προέρχεται από το κύριο υπόβαθρο της Κβαντικής Χρωμοδυναμικής. Και για τις δύο αναλύσεις, παρουσιάζουμε λεπτομερείς μελέτες της ποιότητας των συλλεγόμενων δεδομένων και της σταθερότητάς τους σαν συνάρτηση του χρόνου, καθώς και μελέτες για τον προσδιορισμό της απόδοσης του σκανδαλισμού. Μετά παρουσιάζουμε την βελτιστοποίηση των κριτηρίων επιλογής σήματος. Στην συνέχεια παρουσιάζουμε την εκτίμηση του κύριου υποβάθρου και των συστηματικών του αβεβαιοτήτων από τα πραγματικά δεδομένα μέσω προσαρμογών με χρήση εμπειρικών συναρτήσεων. Ιδιαίτερη έμφαση δίδεται στις υψηλές μάζες (> 8 ΤeV) συντονισμών, που παρατηρείται και περίσσεια δεδομένων σε σχέση με την πρόβλεψη από το καθιερωμένο πρότυπο. Τα τελικά αποτελέσματα περιλαμβάνουν την εξαγωγή ανώτερων ορίων στην διαφορική ενεργό διατομή παραγωγής νέων σωματιδίων, αλλά και στην μάζα και την σταθερά σύζευξής τους χρησιμοποιώντας πλειάδα μοντέλων νέας φυσικής. Επιπρόσθετα, προσδιορίζονται και οι σημαντικότητες (τοπική και ολική) όπου παρατηρείται περίσσεια δεδομένων σε σχέση με την πρόβλεψη από το Καθιερωμένο Πρότυπο. Παράλληλα με την ανάλυση φυσικής, παρουσιάζουμε αποτελέσματα σχετικά με τη διόρθωση της ενέργειας των αδρονικών καταιγισμών όλων των διαφορετικών τύπων, οι οποίες χρησιμοποιούνται από όλες τις αναλύσεις του πειράματος. Τέλος, δίνουμε την σύνοψη αλλά και τις δυνατότητες αυτών των αναζητήσεων με τα δεδομένα που αναμένονται για στην Run III (2022-2025) και τo High Luminosity LHC (2025-onwards).

Search for a heavy Higgs boson decaying into two lighter Higgs bosons in the ττbb final state at 13 TeV

A search for a heavy Higgs boson H decaying into the observed Higgs boson h with a mass of 125 GeV and another Higgs boson hS is presented. The h and hS bosons are required to decay into a pair of tau leptons and a pair of b quarks, respectively. The search uses a sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb−1. Mass ranges of 240–3000 GeV for mH and 60–2800 GeV for $$ {m}_{{\mathrm{h}}_{\mathrm{S}}} $$ m h S are explored in the search. No signal has been observed. Model independent 95% confidence level upper limits on the product of the production cross section and the branching fractions of the signal process are set with a sensitivity ranging from 125 fb (for mH = 240 GeV) to 2.7 fb (for mH = 1000 GeV). These limits are compared to maximally allowed products of the production cross section and the branching fractions of the signal process in the next-to-minimal supersymmetric extension of the standard model.

Interpretation of LHC excesses in ditop and ditau channels as a 400-GeV pseudoscalar resonance

Since the discovery in 2012 of the Higgs boson at the LHC, as the last missing piece of the Standard Model of particle physics, any hint of new physics has been intensively searched for, with no confirmation to date. There are however slight deviations from the SM that are worth investigating. The CMS collaboration has reported, in a search for heavy resonances decaying in t$$ \overline{t} $$ t ¯ with a 13-TeV center-of-mass energy and a luminosity of 35.9 fb−1, deviations from the SM predictions at the 3.5σ level locally (1.9σ after the look-elsewhere effect). In addition, in the ditau final state search performed by the ATLAS collaboration at $$ \sqrt{s} $$ s = 13 TeV and $$ \mathcal{L} $$ L = 139 fb−1, deviations from the SM at the 2σ level have been also observed. Interestingly, both slight excesses are compatible with a new pseudoscalar boson with a mass around 400 GeV that couples at least to fermions of the third generation and gluons. Starting from a purely phenomenological perspective, we inspect the possibility that a 400-GeV pseudoscalar can account for these deviations and at the same time satisfy the constraints on the rest of the channels that it gives contributions to and that are analyzed by the ATLAS and CMS experiments. After obtaining the range of effective couplings compatible with all experimental measurements, we study the gauge invariant UV completions that can give rise to this type of pseudoscalar resonance, which can be accommodated in an SO(6)/SO(5) model with consistency at the 1σ level and in a SO(5) × U(1)P × U(1)X/SO(4) × U(1)X at the 2σ level, while exceedingly large quartic couplings would be necessary to account for it in a general two Higgs doublet model.

Measurement of prompt open-charm production cross sections in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13 TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb−1. The differential production cross sections of the D∗±, D±, and D0$$ \left({\overline{\mathrm{D}}}^0\right) $$ D ¯ 0 mesons are presented in ranges of transverse momentum and pseudorapidity 4 < pT< 100 GeV and |η| < 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.

Properties of ρ(770)0, K*(892), ϕ(1020), ∑(1385)±, Λ(1520) and Ξ(1530)0 resonances in heavy-ion collisions at a center of mass energy of SNN=4-11GeV and their reconstruction using the MPD detector at NICA

The short-lived hadronic resonances are used to study properties of the hot and dense medium produced in relativistic heavy-ion collisions. Due to their short lifetimes, the resonance yields and masses measured in the hadronic channels are sensitive to rescattering and regeneration effects in the hadronic phase. The measurement of resonances is foreseen in the physical program of the MPD experiment at NICA in heavy-ion collisions at S N N = 4 - 11 GeV , in the range of energies where extensive measurements of resonances are not experimentally available. In this contribution, we explore the sensitivity of the ρ(770)0, K*(892), ϕ(1020), ∑(1385)±, Λ(1520) and Ξ(1530)0 resonances measured in the hadronic decay channels to different stages of the heavy-ion collisions at NICA energies and report the feasibility studies for the reconstruction of resonances in the MPD setup

Center of mass energy of charged particles about Reissner–Nordström black hole

We study the acceleration of charged particles by Reissner Nordström black hole by taking into account the term appearing in the formula of the center of mass energy due to charge of the particle. We consider that the particle is radially falling towards the black hole, i.e., [Formula: see text]. It is found that the center of mass energy is infinitely large at the outer horizon without any constraint.