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Jorge Martin Camalich

Publications and source records attributed to Jorge Martin Camalich.

At least 37 records · Page 2Linked to original sources
arXiv2021

Implications of new evidence for lepton-universality violation in $b\to s\ell^+\ell^-$ decays

Motivated by renewed evidence for new physics in $b \to s\ell\ell$ transitions in the form of LHCb's new measurements of theoretically clean lepton-universality ratios and the purely leptonic $B_s\toμ^+μ^-$ decay, we quantify the combined level of discrepancy with the Standard Model and fit values of short-distance Wilson coefficients. A combination of the clean observables $R_K$, $R_{K^*}$, and $B_s\to μμ$ alone results in a discrepancy with the Standard Model at $4.0σ$, up from $3.5σ$ in 2017. One-parameter scenarios with purely left-handed or with purely axial coupling to muons fit the data well and result in a $\sim 5 σ$ pull from the Standard Model. In a two-parameter fit of %$C_9$ and $C_{10}$, new-physics contributions with both vector and axial-vector couplings to muons the allowed region is much more restricted than in 2017, principally due to the much more precise result on $B_s \to μ^+ μ^-$, which probes the axial coupling to muons.Including angular observables data restricts the allowed region further.A by-product of our analysis is an updated average of $\text{BR}(B_s \to μ^+ μ^-) = (2.8\pm 0.3) \times 10^{-9}$.

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arXiv2020

A Complete Framework for Tau Polarimetry in $B\to D^{(*)}τν$ Decays

The meson decays $B\to Dτν$ and $B\to D^* τν$ are sensitive probes of the $b\to cτν$ transition. In this work we present a complete framework to obtain the maximum information on the physics of $B\to D^{(*)}τν$ with polarized $τ$ leptons and unpolarized $D^{(*)}$ mesons. Focusing on the hadronic decays $τ\to πν$ and $τ\toρν$, we show how to extract seven $τ$ asymmetries from a fully differential analysis of the final-state kinematics. At Belle II with $50~\text{ab}^{-1}$ of data, these asymmetries could potentially be measured with percent level statistical uncertainty. This would open a new window into possible new physics contributions in $b\to cτν$ and would allow us to decipher its Lorentz and gauge structure.

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arXiv2020

Charm Physics Confronts High-$p_T$ Lepton Tails

We present a systematic survey of possible short-distance new-physics effects in (semi)leptonic charged- and neutral-current charmed meson decays. Using the Standard Model Effective Field Theory (SMEFT) to analyze the most relevant experimental data at low and high energies, we demonstrate a striking complementarity between charm decays and high invariant mass lepton tails at the LHC. Interestingly enough, high-$p_T$ Drell-Yan data offer competitive constraints on most new physics scenarios. Furthermore, the full set of correlated constraints from $K$, $π$ and $τ$ decays imposed by $SU(2)_L$ gauge invariance is considered. The bounds from $D_{(s)}$ decays, high-$p_T$ lepton tails and $SU(2)_L$ relations chart the space of the SMEFT affecting semi(leptonic) charm flavor transitions.

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arXiv2020

Quark Flavor Phenomenology of the QCD Axion

Axion models with generation-dependent Peccei-Quinn charges can lead to flavor-changing neutral currents, thus motivating QCD axion searches at precision flavor experiments. We rigorously derive limits on the most general effective flavor-violating couplings from current measurements and assess their discovery potential. For two-body decays we use available experimental data to derive limits on $q\to q' a$ decay rates for all flavor transitions. Axion contributions to neutral-meson mixing are calculated in a systematic way using chiral perturbation theory and operator product expansion. We also discuss in detail baryonic decays and three-body meson decays, which can lead to the best search strategies for some of the couplings. For instance, a strong limit on the $Λ\to n a$ transition can be derived from the supernova SN 1987A. In the near future, dedicated searches for $q\to q' a$ decays at ongoing experiments could potentially test Peccei-Quinn breaking scales up to $10^{12}$ GeV at NA62 or KOTO, and up to $10^{9}$ GeV at Belle II or BES III.

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arXiv2020

Towards the discovery of new physics with lepton-universality ratios of $b\to s\ell\ell$ decays

Tests of lepton-universality as rate ratios in $b\to s \ell\ell$ transitions can be predicted very accurately in the Standard Model. The deficits with respect to expectations reported by the LHCb experiment in muon-to-electron ratios of the $B\to K^{(*)}\ell\ell$ decay rates thus point to genuine manifestations of lepton non-universal new physics. In this paper, we analyse these measurements in the context of effective field theory. First, we discuss the interplay of the different operators in $R_K$ and $R_{K^*}$ and provide predictions for $R_{K^*}$ in the Standard Model and in new-physics scenarios that can explain $R_K$. We also provide approximate numerical formulas for these observables in bins of interest as functions of the relevant Wilson coefficients. Secondly, we perform frequentist fits to $R_{K}$ and $R_{K^*}$. The SM disagrees with these measurements at $3.7σ$ significance. We find excellent fits in scenarios with combinations of $\mathcal O_{9(10)}^\ell=\bar sγ^μb_L~\ellγ_μ(γ_5) \ell$ operators, with pulls relative to the Standard Model in the region of $4σ$. An important conclusion of our analysis is that a lepton-specific contribution to $\mathcal O_{10}$ is essential to understand the data. Under the hypothesis that new-physics couples selectively to the muons, we also present fits to other $b\to sμμ$ data with a conservative error assessment, and comment on more general scenarios. Finally, we discuss new lepton universality ratios that, if new physics is the origin of the observed discrepancy, should contribute to the statistically significant discovery of new physics in the near future.

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arXiv2019

Revisiting the new-physics interpretation of the $b\to cτν$ data

We revisit the status of the new-physics interpretations of the anomalies in semileptonic $B$ decays in light of the new data reported by Belle on the lepton-universality ratios $R_{D^{(*)}}$ using the semileptonic tag and on the longitudinal polarization of the $D^*$ in $B\to D^*τν$, $F_L^{D^*}$. The preferred solutions involve new left-handed currents or tensor contributions. Interpretations with pure right-handed currents are disfavored by the LHC data, while pure scalar models are disfavored by the upper limits derived either from the LHC or from the $B_c$ lifetime. The observable $F_L^{D^*}$ also gives an important constraint leading to the exclusion of large regions of parameter space. Finally, we investigate the sensitivity of different observables to the various scenarios and conclude that a measurement of the tau polarization in the decay mode $B\to Dτν$ would effectively discriminate among them.

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arXiv2018

The Mono-Tau Menace: From $B$ Decays to High-$p_T$ Tails

We investigate the crossing-symmetry relation between $b\to cτ^-\barν$ decay and $b\bar c\to τ^-\barν$ scattering to derive direct correlations of New Physics in semi-tauonic $B$-meson decays and the mono-tau signature at the LHC ($pp\toτ_h X$ + MET). Using an exhaustive set of effective operators and heavy mediators we find that the current ATLAS and CMS data constrain scenarios addressing anomalies in $B$-decays. Pure tensor solutions, completed by leptoquark, and right-handed solutions, completed by $W^\prime_R$ or leptoquark, are challenged by our analysis. Furthermore, the sensitivity that will be achieved in the high-luminosity phase of the LHC will probe $all$ the possible scenarios that explain the anomalies. Finally, we note that the LHC is also competitive in the $b\to u$ transitions and bounds in some cases are currently better than those from $B$ decays.

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arXiv2018

Tau Polarimetry in B Meson Decays

This article summarizes recent developments in $B\to D^{(\ast)}τν$ decays. We explain how to extract the tau lepton's production properties from the kinematics of its decay products. The focus is on hadronic tau decays, which are most sensitive to the tau polarizations. We present new results for effects of new physics in tau polarization observables and quantify the observation prospects at BELLE II.

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arXiv2018

A clockwork solution to the flavor puzzle

We introduce a set of clockwork models of flavor that can naturally explain the large hierarchies of the Standard Model quark masses and mixing angles. Since the clockwork only contains chains of new vector-like fermions without any other dynamical fields, the flavor constraints allow for relatively light new physics scale. For two benchmarks with gear masses just above 1 TeV, allowed by flavor constraints, we discuss the collider searches and the possible ways of reconstructing gear spectra at the LHC. We also examine the similarities and differences with the other common solutions to the SM flavor puzzle, i.e., with the Froggatt-Nielsen models, where we identify a new {\it clockworked } version, and with the Randall-Sundrum models.

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arXiv2017

$B$ decay anomalies from nonabelian local horizontal symmetry

Recent anomalies in $B\to K^{(*)}\ell\ell$ meson decays are consistent with exchange of a heavy $Z'$ vector boson. Here we try to connect such new physics to understanding the origin of flavor, by gauging generation number. Phenomenological and theoretical considerations suggest that the smallest viable flavor symmetry (not including any extra U(1) factors) is chiral ${\rm SU(3)}_L\times{\rm SU(3)}_R$, which acts only on generation indices and does not distinguish between quarks and leptons. Spontaneous breaking of the symmetry gives rise to the standard model Yukawa matrices, and masses for the 16 $Z'$-like gauge bosons, one of which is presumed to be light enough to explain the $B\to K^{(*)}\ell\ell$ anomalies. We perform a bottom-up study of this framework, showing that it is highly constrained by LHC dilepton searches, meson mixing, $Z$ decays and CKM unitarity. Similar anomalies are predicted for semileptonic decays of $B$ to lighter mesons, with excesses in the $ee,ττ$ channels and deficits in $μμ$, but no deviation in $νν$. The lightest $Z'$ mass is $\lesssim 6\,$TeV if the gauge coupling is $\lesssim 1$.

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arXiv2017

Renormalization-group evolution of new physics contributions to (semi)leptonic meson decays

We study the renormalization group evolution (RGE) of new physics contributions to (semi)leptonic charged-current meson decays, focusing on operators involving a chirality flip at the quark level. We calculate their evolution under electroweak and electromagnetic interactions, including also the three-loop QCD running and provide numerical formulas that allow us to connect the values of the corresponding Wilson coefficients from scales at the TeV to the low-energy scales. The large mixing of the tensor operator into the (pseudo)scalar ones has important phenomenological implications, such as the RGE of new physics bounds obtained from light quark decays or in $b\to c\ellν$ transitions. For instance, we study scenarios involving tensor effective operators, which have been proposed in the literature to address the $B$-decay anomalies, most notably those concerning the $R_{D^{(*)}}$ ratios. We conclude that the loop effects are important and should be taken into account in the analysis of these processes, especially if the operators are generated at an energy scale of $\sim 1$ TeV or higher.

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arXiv2017

Tau properties in $B\to Dτν$ from visible final-state kinematics

In semi-leptonic $B$ decays with a tau lepton, features of the production process are imprinted on the tau helicity states. Since the tau momentum cannot be fully reconstructed experimentally, the available information on the tau properties is encoded in its visible decay products. Focusing on the process $B\to Dτν$, we find explicit relations between the tau properties and the kinematics of the charged particles in the decays $τ\toπν$, $τ\toρν$, and $τ\to\ellν\barν$. In particular, we show that the perpendicular polarization, $P_\perp$, and the forward-backward asymmetry, $A_τ$, of the tau lepton can simultaneously be extracted from an angular asymmetry of the charged particle against the $D$ meson. For the most sensitive decay channel, $τ\toπν$, we expect a relative statistical precision of about $10\%$ for $P_\perp$ and $A_τ$ in a measurement based on $50\,$ab$^{-1}$ of data at BELLE II.

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arXiv2016

Global Effective-Field-Theory analysis of New-Physics effects in (semi)leptonic kaon decays

We analyze the decays $K\toπ\ellν$ and $P\to\ellν$ ($P=K,π$, $\ell=e,\,μ$) using a low-energy Effective-Field-Theory approach to parametrize New Physics and study the complementarity with baryon $β$ decays. We then provide a road map for a global analysis of the experimental data, with all the Wilson coefficients simultaneously, and perform a fit leading to numerical bounds for them and for $V_{us}$. A prominent result of our analysis is a reinterpretation of the well-known $V_{ud}-V_{us}$ diagram as a strong constraint on new physics. Finally, we reinterpret our bounds in terms of the $SU(2)_L\times~U(1)_Y$-invariant operators, provide bounds to the corresponding Wilson coefficients at the TeV scale and compare our results with collider searches at the LHC.

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arXiv2016

The lifetime of the $B_c^-$ meson and the anomalies in $B\to D^{(*)}τν$

We investigate a new constraint on new-physics interpretations of the anomalies observed in $B\to D^{(*)}τν$ decays making use of the lifetime of the $B_c^-$ meson. A constraint is obtained by demanding that the rate for $B_c^-\toτ^-\barν$ does not exceed the fraction of the total width that is allowed by the calculation of the lifetime in the standard model. This leads to a very strong bound on new-physics scenarios involving scalar operators since they lift the slight, but not negligible, chiral suppression of the $B_c^-\toτ^-\barν$ amplitude in the standard model. The new constraint renders a scalar interpretation of the enhancement measured in $R_{D^*}$ implausible, including explanations implementing extra Higgs doublets or certain classes of leptoquarks. We also discuss the complementarity of $R_{D^{(*)}}$ and a measurement of the longitudinal polarization of the $τ$ in the $B\to D^*τν$ decay in light of our findings.

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arXiv2016

New physics in the kinematic distributions of $\bar B\to D^{(*)}τ^-(\to\ell^-\barν_\ellν_τ)\barν_τ$

We investigate the experimentally-accessible kinematic distributions of the $\bar B\to D^{(*)}τ^-(\to\ell^-\barν_\ellν_τ)\barν_τ$ decays. Specifically, we study the decay rates as functions of the $B\to D^{(*)}$ transferred squared momentum, the energy of the final charged lepton and the angle of its 3-momentum relative to the 3-momentum of the recoiling $D^{(*)}$. The angular distribution allows to introduce new observables, like a forward-backward asymmetry, which are complementary to the total rates. We present analytic formulas for the observable 3-fold 5-body differential decay rates, study the predictions in the Standard Model and investigate the effects in different new-physics scenarios that we characterize using an effective field theory framework.

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arXiv2016

Reassessing the discovery potential of the $B \to K^{*} \ell^+\ell^-$ decays in the large-recoil region: SM challenges and BSM opportunities

We critically examine the potential to disentangle Standard Model (SM) and New Physics (NP) in $B \to K^* μ^+μ^-$ and $B\to K^* e^+ e^-$ decays, focusing on $(i)$ the LHCb anomaly, $(ii)$ the search for right-handed currents, and $(iii)$ lepton-universality violation. Restricting ourselves to the large-recoil region, we advocate a parameterisation of the hadronic matrix elements that separates model-independent information about nonperturbative QCD from the results of model calculations. We clarify how to estimate corrections to the heavy-quark limit that would generate a right-handed (virtual) photon in the $b\to sγ$ contribution to the decay. We then apply this approach to the discussion of various sets of observables of increasing theoretical cleanness. First, we show that angular observables in the optimized $P_i^{(\prime)}$ basis are, in general, not robust against the long-distance QCD effects. While a fit to data favours a NP contribution to the semileptonic operators of the type $δC_9\simeq-1.5$, this comes at a relatively small statistical significance of $\lesssim2 σ$, once power corrections are properly accounted for. Second, two of these observables, $P_1$ and $P_3^{CP}$ are particularly clean at very low $q^2$ and sensitive probes of right-handed quark currents. We discuss their potential to set stringent bounds on the Wilson coefficient $C_7^\prime$, especially using data of the electronic mode. Finally, in light of the recent hint of lepton-universality violation in $B^+\to K^+\ell\ell$, we introduce and investigate new lepton-universality observables involving angular observables of the muonic and electronic modes and their zero crossings, and show that, if the effect is of the size suggested by experiment, these can clearly distinguish between different NP explanations in terms of underlying semileptonic operators.

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arXiv2015

Weak decays of unstable $b$-mesons

We investigate the decays of the excited $(b\bar q)$ mesons as probes of the short-distance structure of the weak $ΔB=1$ transitions. These states are unstable under the electromagnetic or strong interactions although their widths are typically suppressed by phase space. As compared to the pseudoscalar $B$ meson, the purely leptonic decays of the vector $B^*$ are not chirally suppressed and are sensitive to different combinations of the underlying weak effective operators. An interesting example is $B^*_s\to \ell^+\ell^-$, which has a rate that can be accurately predicted in the standard model. The branching fraction is $\mathcal{B}\sim10^{-11}$, irrespective of the lepton flavor and where the main uncertainty stems from the unmeasured and theoretically not-well known $B_s^*$ width. We discuss the prospects for producing this decay mode at the LHC and explore the possibility of measuring the $B_s^*\to\ell\ell$ amplitude, instead, through scattering experiments at the $B_s^*$ resonance peak. Finally we also discuss the charged-current $B_{u,c}^*\to\ellν$ decay which can provide complementary information on the $b\to u\ellν$ and $b\to c\ellν$ transitions.

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