High Energy Physics - Phenomenology (hep-ph)

Abstract: Axion-like particles (ALPs) arise naturally in many extensions of the Standard Model (SM). We explore the discovery potential for ALPs of the Large Hadron electron Collider (LHeC) via the $W^{+}W^{-}$ fusion process. For concreteness, both cases of the ALP decaying to muon pairs and $b\overline{b}$ pairs are investigated. Our numerical results show that the LHeC with the center of mass energy of $1.3$ TeV and the integrated luminosity of $1$ ab$^{-1}$ might be more sensitive than the LHC in probing ALPs over a range of masses from a few tens of GeV to $900$ GeV, where the promising sensitivities to the coupling of ALP with $W^{\pm}$ bosons reach nearly $0.15$ TeV$^{-1}$ and $0.32$ TeV$^{-1}$ for the signal processes $e^{-}p\rightarrow\nu_{e}ja(a\rightarrow\mu^{+}\mu^{-})$ and $e^{-}p\rightarrow\nu_{e}ja(a\rightarrow b\overline{b})$, respectively.

Abstract: It is shown that the axion-photon coupling leads to an appearance of time-dependent electric dipole moments of leptons and contributes to electric dipole moments of hadrons. The relation between these moments and the axion-photon coupling constant is rigorously determined. The results obtained open a possibility to compare a sensitivity of search for dark matter axions (and axion-like particles) in optical experiments and experiments with massive particles.

Abstract: In both Run 1 and Run 2 of the LHC, the CMS collaboration has observed an excess of events in the searches for low-mass Higgs bosons in the diphoton final state at a mass of about 95 GeV. After a recent update of the experimental analysis, in which the full Run 2 data collected at 13 TeV has been included and an improved experimental calibration has been applied, the local significance of the excess amounts to $2.9\sigma$. The presence of this diphoton excess is especially interesting in view of a further excess observed by CMS in ditau final states at a comparable mass and similar local significance. Moreover, an excess of events with about $2\sigma$ local significance and consistent with a mass of 95 GeV was observed in LEP searches for a Higgs boson decaying to pairs of bottom quarks. We interpret the CMS diphoton excess in combination with the ditau excess in terms of a pseudoscalar resonance in the CP-conserving two-Higgs-doublet model (2HDM). Furthermore, we discuss the possibility that, if CP-violation is taken into account, a CP-mixed scalar state can in addition describe the LEP result, thus accommodating all three excesses simultaneously. We find that the region of parameter space where both the CMS diphoton and ditau excesses can be fitted is in tension with current constraints from the flavour sector, potentially calling for other new-physics contributions to flavour-physics observables, most notably $b \to s\gamma$ transitions.

Abstract: Neutrino oscillation phenomenon is a definite evidence of physics beyond the Standard Model (SM) and high precision measurement of neutrino properties will certainly give us clue about what lies beyond the SM. In particular, precise measurements of the mixing matrix elements $U_{\alpha i}$ which relate the neutrino flavor $\alpha$ and mass $i$ eigenstates are crucial since new physics at scale beyond experimental reach can lead to a nonunitary $U$. This in turns results in nonorthogonal neutrino flavor states. How to calculate the oscillation probability in this scenario is an important theoretical issue that will be treated here. We show that probability constructed using theory of projection probability will ensure that the theory remains unitary in time evolution and the probabilities of neutrino of certain flavor being detected as all possible flavor states always sum up to unity. This result is crucial for discovery of new physics through neutrino oscillation phenomena.

Abstract: We present a major update of the program pySecDec, a toolbox for the evaluation of dimensionally regulated parameter integrals. The new version enables the evaluation of multi-loop integrals as well as amplitudes in a highly distributed and flexible way, optionally on GPUs. The program has been optimised and runs up to an order of magnitude faster than the previous release. A new integration procedure that utilises construction-free median Quasi-Monte Carlo rules is implemented. The median lattice rules can outperform our previous component-by-component rules by a factor of 5 and remove the limitation on the maximum number of sampling points. The expansion by regions procedures have been extended to support Feynman integrals with numerators, and functions for automatically determining when and how analytic regulators should be introduced are now available. The new features and performance are illustrated with several examples.

Abstract: The calculations based on the next-to-leading logarithm (NLL) approximation for the Balitsky-Fadin-Kuraev-Lipatov (BKFL) evolution are presented for the Mueller-Navelet (MN) dijet production cross section, as well as for their ratios at different collision energies. The MN dijet denotes the jet pair consists of jets, which were selected with $p_{\perp} > p_{\perp\min}$ and with maximal rapidity separation in the event. The NLL BFKL predictions for the MN cross sections are given for the $pp$ collisions at $\sqrt{s}=2.76$, 8 and 13 TeV, for $p_{\perp\min} = 20$ and $35$ GeV. The results are in an agreement with the measurement by the CMS experiment in $pp$ collisions at $\sqrt{s}=2.76$ TeV and $p_{\perp\min} = 35$ GeV within the theoretical and experimental uncertainties. The predictions of the NLL BFKL calculation of ratios of the MN cross sections at different collision energies and $p_{\perp\min}$ are also presented.

Abstract: We calculate the medium modification factor $I_{pA}$ for the photon-tagged jet fragmentation functions for scenario with the quark-gluon plasma formation in $pA$ and $pp$ collisions. We perform calculations of radiative and collisional parton energy loss in the quark-gluon plasma with running $\alpha_s$ which has a plateau around $Q\sim \kappa T$ with $\kappa$ fitted to the LHC data on the heavy ion $R_{AA}$. We find that the theoretical prediction for $I_{pA}$ in $5.02$ TeV $p$+Pb collisions are within errors consistent with the data from ALICE [1]. However, a definite conclusion about the presence or absence of jet quenching in $pA$ collisions cannot be drawn due to large experimental errors of the ALICE data [1]. Our calculations show that this requires a significantly more accurate measurement of $I_{pA}$.

Abstract: We compute for the first time the $\tau$ data-driven Euclidean windows for the hadronic vacuum polarization contribution to the muon $g-2$. We show that $\tau$-based results agree with the available lattice window evaluations and with the full result. On the intermediate window, where all lattice evaluations are rather precise and agree, $\tau$-based results are compatible with them. This is particularly interesting, given that the disagreement of the $e^+e^-$ data-driven result with the lattice values in this window is the main cause for their discrepancy, affecting the interpretation of the $a_\mu$ measurement in terms of possible new physics.