The experimental values of the lepton-flavour-universality tests ${\cal R}(D)$ and ${\cal R}(D^*)$ show a tension of about $3.1σ$ with their Standard Model prediction. Motivated by this tension, we perform a fit of the $b\to cτν$ data. We consider one-particle scenarios imposing consecutive limits on $\text{BR}(B_c\to τν_τ)$, and analyse how these limits affect the fits. We include the polarisation observables available to date and predict those that are still to be measured, and conclude that they have a high model-resolving power. For each scenario we also predict ${\cal R}(Λ_c)$, observing that an enhancement of ${\cal R}(D^{(*)})$ implies an enhancement of ${\cal R}(Λ_c)$ in any scenario. We trace back this enhancement to a sum-rule valid irrespective of the scenario used to fit ${\cal R}(D^{(*)})$.
The polarisation of top quarks produced in high energy processes can be a very sensitive probe of physics beyond the Standard Model. The kinematical distributions of the decay products of the top quark can provide clean information on the polarisation of the produced top and thus can probe new physics effects in the top quark sector. We study some of the recently proposed polarisation observables involving the decay products of the top quark in the context of $H^-t$ and $Wt$ production. We show that the effect of the top polarisation on the decay lepton azimuthal angle distribution, studied re…
We provide a comprehensive analysis of the power of including top quark-polarisation information to kinematically challenging $t\bar t$ resonance searches, for which ATLAS and CMS start losing sensitivity. Following the general modeling and analysis strategies pursued by the experiments, we analyse the semi-leptonic and the di-lepton $t\bar t$ channels and show that including polarisation information can lead to large improvements in the limit setting procedures with large data sets. This will allow us to set limits for parameter choices where sensitivity from $m(t\bar t)$ is not sufficient. T…
We investigate the dependence of polarisation observables in elastic deuteron Compton scattering below the pion production threshold on the spin-independent and spin-dependent iso-scalar dipole polarisabilities of the nucleon. The calculation uses Chiral Effective Field Theory with dynamical Delta(1232) degrees of freedom in the Small Scale Expansion at next-to-leading order. Resummation of the NN intermediate rescattering states and including the Delta induces sizeable effects. The analysis considers cross-sections and the analysing power of linearly polarised photons on an unpolarised target…
The pair production of a $W$ and a $Z$ boson at the LHC is an important process to study the triple-gauge boson couplings as well as to probe new physics that could arise in the gauge sector. In particular the leptonic channel $p p \to W^\pm Z\to 3\ell +ν+ X$ is considered by ATLAS and CMS collaborations. Polarisation observables can help pinning down new physics and give information on the spin of the gauge bosons. Measuring them requires high statistics as well as precise theoretical predictions. We define in this contribution fiducial polarisation observables for the $W$ and $Z$ bosons and …
We discuss top polarisation observables at the Tevatron and the LHC with special attention to some that have not been measured and provide new, independent information about the top polarisation.
New colour octets stand out among the new physics proposals to explain the anomalous forward-backward asymmetry measured in $t \bar t$ production by the CDF experiment at the Tevatron. We perform a fit to $t \bar t$ observables at the Tevatron and the LHC, including total cross sections, various asymmetries and the top polarisation and spin correlations, to find the most likely parameters of a light colour octet to be consistent with data. In particular, an octet coupling only to right-handed quarks gives a good fit to all measurements. The implications from the general fit are drawn in terms …
Realistic modeling of medium-jet interactions in heavy ion collisions is becoming increasingly important to successfully predict jet structure and shape observables. In JEWEL, all partons belonging to the parton showers initiated by hard scattered partons undergo collisions with thermal partons from the medium, leading to both elastic and radiative energy loss. The recoiling medium partons carry away energy and momentum from the jet. Since the thermal component of these recoils' momenta is part of the soft background activity, comparison with data requires the implementation of a subtraction p…
Starting from the effective torsion space-time model, we study its effects on the top pair production cross section at hadron colliders. We also study the effect of this model on top pair asymmetries at the Tevatron and the LHC. We find that torsion space-time can explain forward-backward asymmetry according to measured anomaly at Tevatron. We find an allowed region in the parameters space which can satisfy simultaneously all $t\bar{t}$ observables measured at Tevatron and LHC.
We study all possible observables in $B\to D^{(\ast)}τν_τ$ with new physics (NP), including new vector, scalar and tensor interactions, and investigate the prospects of extracting NP Wilson coefficients with optimal observables. Analysis of the full $q^2$ integrated branching fractions of $B\to D^{(\ast)}τν_τ$ show that the overall sensitivity of the observables of $B\to D τν_τ$ is more towards the scalar current, whereas the bin-by-bin analysis of $q^2$ distribution of the differential branching fraction points to regions of $q^2$ sensitive to tensor interactions. Interestingly, the observabl…
We apply the formalism of amplitude symmetries to the angular distribution of the decays $B \to D^* \ell ν$ for $\ell=e,μ,τ$. We show that the angular observables used to describe the distribution of this class of decays are not independent in absence of New Physics contributing to tensor operators. We derive sets of relations among the angular coefficients of the decay distribution for the massless and massive lepton cases which can be used to probe in a very general way the consistency among the angular observables and the underlying New Physics at work. We use these relations to access the …
In the context of the recently measured non-leptonic decays $B_{d}\to K^{*0}\bar{K}^{*0}$ and $B_{s}\to K^{*0}\bar{K}^{*0}$ we analyse the anatomy of the $L_{VV}$ observable that compares the longitudinal components of $B_s \to VV$ and $B_d \to VV$ decays. This observable is cleaner than the longitudinal polarisation fraction as it is afflicted only at subleading order in a $1/m_b$ expansion by the theoretical uncertainties arising in the transverse components entering the polarisation fraction. Focusing on the particular case of $B_{d}\to K^{*0}\bar{K}^{*0}$ and $B_{s}\to K^{*0}\bar{K}^{*0}$,…
While current nuclear parton distribution functions (nPDFs) from global fits to experimental data are spatially homogeneous, many experimental observables in nucleus-nucleus collisions are presented in terms of centrality cuts. These cuts can be related to impact parameter using the Glauber theory and it is thus usual in the description of such observables to convolute an assumed impact parameter distribution with the homogeneous nPDFs. In this study we use the Gribov theory of nuclear shadowing supplemented with information from diffraction to model the impact parameter distributions of nucle…
A comprehensive study of the impact of new-physics on different observables for $B_{s}\to ϕ\ell^{+}\ell^{-}$ has been done. We examine the new physics models such as $Z^{\prime}$ and UED models, where the effects of new physics coming through the modification of Wilson coefficients. We have analyzed these effects through the theoretical prediction of the branching ratio, the forward-backward asymmetry, lepton polarization asymmetries and the helicity fractions of the final state meson. These all observables will definitely be measured in present and future colliders with great precision. We al…
Most of the methods to measure the top quark mass suffer from the jet energy scaling in achieving better precision. As a way to circumvent this issue, the study of $B$-hadron observables is motivated. While they do not involve such an issue, understanding underlying hadronization models is a key to achieve $\sim 0.5\%$ precision or better. In this presentation, we discuss the impact of the hadronization model parameters - for example, implemented in Pythia 8 - on precision measurements of the top quark mass through $B$-hadron observables. We study the sensitivity of the top quark mass to relev…
Automated computation of spin-density matrices and quantum observables for collider physics
Centre for Cosmology, Particle Physics and Phenomenology (CP3), Université Catholique de Louvain（宇宙学、粒子物理与现象学中心（CP3），天主教鲁汶大学）；Dipartimento di Fisica e Astronomia, Università di Bologna（博洛尼亚大学物理与天文学系）；INFN, Sezione di Bologna（意大利国家核物理研究所，博洛尼部分所）；European Organisation for Nuclear Research (CERN)（欧洲核子研究组织（CERN））
The recent LHCb angular analysis of the exclusive decay B->K^*mu+mu- has indicated significant deviations from the Standard Model expectations. Accurate predictions can be achieved at large K*-meson recoil for an optimised set of observables designed to have no sensitivity to hadronic input in the heavy-quark limit at leading order in alpha_s. However, hadronic uncertainties reappear through non-perturbative Lambda_QCD/m_b power corrections, which must be assessed precisely. In the framework of QCD factorisation we present a systematic method to include factorisable power corrections and point…
Deviations with respect to Standard Model predictions have recently shown up in angular distributions of the FCNC induced mode $B^0 \to K^{*0} μ^+ μ^-$. Within New Physics models, such tensions might be explained by new contributions to the Wilson coefficients of the effective Hamiltonian governing this decay. I discuss the issue in the framework of the Randall-Sundrum model with custodial protection (RS$_c$), giving also predictions for other rare $B$ decays.
Decays based on the $b\to sγ$ transition are expected to yield left-handed photons in the Standard Model, but could be particularly sensitive to New Physics contributions modifying the short-distance Wilson coefficients $\mathcal{C}_7$ and $\mathcal{C}_{7'}$ defined in the low-energy Effective Field Theory. These coefficients can be determined by combining observables of several modes, among which $B_s\toϕee$ at low $q^2$, in a kinematic range where the photon-pole is dominant. We investigate the impact of $B_s-\bar{B}_s$ mixing on the angular observables available for this mode, which induces…
The heavy-ion collisions can produce extremely strong transient magnetic and electric fields. We study the azimuthal fluctuation of these fields and their correlations with the also fluctuating matter geometry (characterized by the participant plane harmonics) using event-by-event simulations. A sizable suppression of the angular correlations between the magnetic field and the 2nd and 4th harmonic participant planes is found in very central and very peripheral collisions, while the magnitudes of these correlations peak around impact parameter b~8-10 fm for RHIC collisions. This can lead to not…
Impact on $L$-observables of a new combined analysis of $B_{d,s}\to K^{(*)}$ form factors
Universität Siegen（锡根大学）；University of Cambridge（剑桥大学）；Universitat Autònoma de Barcelona（巴塞罗那自治大学）；Institut de Física d’Altes Energies (IFAE)（高能物理研究所）；The Barcelona Institute of Science and Technology（巴塞罗那科学技术研究所）
本研究开展$B_{d,s}\ o K^{(*)}$形状因子联合分析，探究其对$L$-可观测量的影响，给出形状因子精确结果，发现相关因素对可观测量影响显著，并更新新物理相关预测。
The quenching of jets (particles with $p_T>>T, Λ_{QCD}$) in ultra-relativistic heavy-ion collisions has been one of the main prediction and discovery at RHIC. We have studied, by a simple jet quenching modeling, the correlation between different observables like the nuclear modification factor $\Rapt$, the elliptic flow $v_2$ and the ratio of quark to gluon suppression $R_{AA}(quark)/R_{AA}(gluon)$. We show that the relation among these observables is strongly affected by the temperature dependence of the energy loss. In particular the large $v_2$ and and the nearly equal $\Rapt$ of quarks and…
In this paper we revisit the model of $κ$-deformed complex scalar field. We find that this model possesses ten conserved Noether charges that form, under commutators, a representation of (undeformed) Poincaré algebra. It follows that the theory is relativistic and does not break Lorentz invariance. However the spacetime representation of boosts is not standard, and contains a non-local translation, different for positive and negative energy modes. It then follows that although the masses of particles and anti-particles are equal, the theory violates CPT symmetry in a subtle way. We explain why…
Impact of QCD Energy Evolution on Observables in Heavy-Ion Collisions
University of Jyväskylä（于韦斯屈莱大学）；Helsinki Institute of Physics（赫尔辛基物理研究所）；Brookhaven National Laboratory（布鲁克海文国家实验室）；Wayne State University（韦恩州立大学）；Central China Normal University（华中师范大学）
We study the impact of perturbative reheating on primordial observables in models of multiple-field inflation. By performing a sudden decay calculation, we derive analytic expressions for the local-type non-linearity parameter $f_{\rm NL}^{\rm local}$, the scalar spectral index $n_ζ$, and the tensor-to-scalar ratio $r_T$ as functions of the decay rates of the inflationary fields. We compare our analytic results to a fully numerical classical field theory simulation, finding excellent agreement. We find that the sensitivity of $f_{\rm NL}$, $n_ζ$, and $r_T$ to the reheating phase depends heavil…
