Search

The CODEX-$\beta$ apparatus is a demonstrator for the proposed future CODEX-b experiment, a long-lived-particle detector foreseen for operation at IP8 during HL-LHC data-taking. The demonstrator project, intended to collect data in 2025, is described, with a particular focus on the design, construction, and installation of the new apparatus.

We develop a new theoretical framework for the treatment of heavy quark (HQ) resonances within heavy quark effective theory (HQET). This framework uses on-shell recursion techniques to express the resonant amplitude as a product of on-shell subamplitudes, which allows one to employ a form-factor representation of the hadronic matrix elements and to obtain an HQ expansion, but at the price of introducing complex momenta. We construct a generalized "holomorphic HQET" onto which such complex-momentum matrix elements can be matched, and we show that $PT$ symmetry ensures the Isgur-Wise functions (and the perturbative corrections) become holomorphic functions of the complex recoil parameter with real coefficients. They are thus an analytic continuation of the standard HQET description. This framework admits a HQ hadron (strong decay) width expansion. At second order, we show it is in good agreement with data for the $B_{1(2)}^{(*)}$ and $D_{1(2)}^{(*)}$ HQ doublets. Taking the $\bar{B} \to (D_1^*(1^-) \to D\pi)l\nu$ system as an example, we compute the holomorphic HQET expansion to first order, as well as the complex-momentum on-shell subamplitudes. A toy numerical study of the resulting differential rates demonstrates that this framework generates HQ resonance lineshapes with large tails, resembling those seen in data., Comment: 65 pages, 6 figures, 1 table

We derive the $\Lambda_b \to \Lambda_c$ form factors for the Standard Model and beyond at second order in Heavy Quark Effective Theory (HQET), applying the recently-proposed Residual Chiral Expansion (RCE) to reduce the set of unknown subsubleading hadronic functions to a single, highly-constrained function, that is fully determined by hadron mass parameters at zero recoil. We fit a form factor parametrization based on these results to all available Lattice QCD (LQCD) predictions and experimental data. We find that the constrained and predictive structure of the form factors under the RCE is in excellent agreement with LQCD predictions and experimental data, as well as prior HQET-based fits., Comment: 37 pages, 5 figures, 10 tables

The $\tau$ polarization in semileptonic $B$ decays provides probes of new physics complementary to decay rate distributions of the three-body final state. Prior calculations for inclusive decays used a definition for the polarization axis that is different from the choice used in calculations (and the only measurement) for exclusive channels. To compare inclusive and exclusive predictions, we calculate the $\tau$ polarization in inclusive $B\to X\tau\bar\nu$ using the same choice as in the exclusive decays, and construct a sum rule relating the inclusive $\tau$ polarization to a weighted sum of exclusive decay polarizations. We use this relation, experimental data, and theoretical predictions for the decays to the lightest charm or up-type hadrons to make predictions for excited channels., Comment: 6 pages, 2 figures

The proposed designs of many auxiliary long-lived particle (LLP) detectors at the LHC call for the instrumentation of a large surface area inside the detector volume, in order to reliably reconstruct tracks and LLP decay vertices. Taking the CODEX-b detector as an example, we provide a proof-of-concept optimization analysis that demonstrates the required instrumented surface area can be substantially reduced for many LLP models, while only marginally affecting the LLP signal efficiency. This optimization permits a significant reduction in cost and installation time, and may also inform the installation order for modular detector elements. We derive a branch-and-bound based optimization algorithm that permits highly computationally efficient determination of optimal detector configurations, subject to any specified LLP vertex and track reconstruction requirements. We outline the features of a newly-developed generalized simulation framework, for the computation of LLP signal efficiencies across a range of LLP models and detector geometries., Comment: 46 pages, 11 figures, 3 tables

Normalizing the recent LHCb measurement of $\Lambda_b \to \Lambda_c \tau \bar\nu$ to the standard model (SM) prediction for the $\Lambda_b \to \Lambda_c \mu \bar\nu$ rate, instead of a LEP measurement, provides a more consistent comparison with the SM prediction for the lepton flavor universality ratio $R(\Lambda_c)$. This modestly increases $R(\Lambda_c)$ compared to the quoted LHCb result, such that it no longer hints at a suppression compared to the SM, which would be hard to accommodate in new physics scenarios that enhance $R(D^{(*)})$. We point out that the fraction of excited states in inclusive semileptonic $\Lambda_b$ decay may be significantly greater than the corresponding fraction in $B$ decays. Possible implications are speculated upon., Comment: 3 pages

We postulate a supplemental power counting within the heavy quark effective theory, that results in a small, highly-constrained set of second-order power corrections, compared to the standard approach. We determine all $\bar{B} \to D^{(*)}$ form factors, both within and beyond the standard model to $\mathcal{O}(\alpha_s/m_{c,b}, 1/m_{c,b}^2)$, under truncation by this power counting. We show that the second-order power corrections to the zero-recoil normalization of the $\bar{B} \to D^{(*)} l \nu$ matrix elements ($l = e$, $\mu$, $\tau$) are fully determined by hadron mass parameters, and are in good agreement with lattice QCD (LQCD) predictions. We develop a parametrization of these form factors under the postulated truncation, that achieves excellent fits to the available LQCD predictions and experimental data, and we provide precise updated predictions for the $\bar{B} \to D^{(*)} \tau \bar\nu$ decay rates, lepton flavor universality violation ratios $R(D^{(*)})$, and the CKM matrix element $|V_{cb}|$. We point out some apparent errors in prior literature concerning the $\mathcal{O}(1/m_cm_b)$ corrections, and note a tension between commonly-used simplified dispersive bounds and current data., Comment: 85 pages, 11 figures, 19 tables; published version; minor typos corrected

In this Snowmass contribution we present a comprehensive status update on the progress and plans for the proposed CODEX-b detector, intended to search for long-lived particles beyond the Standard Model. We review the physics case for the proposal and present recent progress on optimization strategies for the detector and shielding design, as well as the development of new fast and full simulation frameworks. A summary of the technical design for a smaller demonstrator detector (CODEX-$\beta$) for the upcoming Run~3 of the LHC is also discussed, alongside the road towards realization of the full experiment at the High-Luminosity LHC., Comment: 13 pages, 13 figures, Snowmass contribution

In this paper, we propose PATO-a producibility-aware topology optimization (TO) framework to help efficiently explore the design space of components fabricated using metal additive manufacturing (AM), while ensuring manufacturability with respect to cracking. Specifically, parts fabricated through Laser Powder Bed Fusion are prone to defects such as warpage or cracking due to high residual stress values generated from the steep thermal gradients produced during the build process. Maturing the design for such parts and planning their fabrication can span months to years, often involving multiple handoffs between design and manufacturing engineers. PATO is based on the a priori discovery of crack-free designs, so that the optimized part can be built defect-free at the outset. To ensure that the design is crack free during optimization, producibility is explicitly encoded within the standard formulation of TO, using a crack index. Multiple crack indices are explored and using experimental validation, maximum shear strain index (MSSI) is shown to be an accurate crack index. Simulating the build process is a coupled, multi-physics computation and incorporating it in the TO loop can be computationally prohibitive. We leverage the current advances in deep convolutional neural networks and present a high-fidelity surrogate model based on an Attention-based U-Net architecture to predict the MSSI values as a spatially varying field over the part's domain. Further, we employ automatic differentiation to directly compute the gradient of maximum MSSI with respect to the input design variables and augment it with the performance-based sensitivity field to optimize the design while considering the trade-off between weight, manufacturability, and functionality. We demonstrate the effectiveness of the proposed method through benchmark studies in 3D as well as experimental validation.

I show that the neutral pion decay in $B \to K^{(*)} \pi^0 \gamma$, with $\pi^0 \to ee \gamma$, might generate large sources of lepton flavor universality violation (LFUV) in measurements of the ratios, $R_{K^{(*)}}$: If the photons in the $K^{(*)} e e \gamma \gamma$ final state are reconstructed as Bremsstrahlung, the recovered electron-positron invariant mass can be pushed into the $1$-$6$ GeV$^{2}$ signal region, artificially enhancing the measured $B \to K^{(*)} e e$ branching ratio compared to $B \to K^{(*)} \mu\mu$. I present a conservative estimate and simulation of the $B \to K \pi^0 \gamma$ LFUV background at LHCb, that together suggest this effect could reduce the recovered $R_K$ up to several percent. A reliable assessment of the size of this effect will require dedicated simulations within experimental frameworks themselves., Comment: 6 pages, 6 figures, 1 table; published version; includes estimates for effects of lepton $p_T$ thresholds and magnetic bending power enhancements

We calculate the $\Lambda_b \to \Lambda_c^*(2595) l \nu$ and $\Lambda_b \to \Lambda_c^*(2625) l \nu$ form factors and decay rates for all possible $b \to c l \bar\nu$ four-Fermi interactions in and beyond the Standard Model (SM), including nonzero charged lepton masses and terms up to order $\mathcal{O}(\alpha_s, 1/m_{c,b})$ in the heavy quark effective theory (HQET). We point out a subtlety involving the overcompleteness of the representation of the spin-parity $1/2^+ \to 3/2^-$ antisymmetric tensor form factors, relevant also to other higher excited-state transitions, and present a general method for the counting of the physical form factors for any hadronic transition matrix element and their matching onto HQET. We perform a preliminary fit of a simple HQET-based parametrization of the $\Lambda_b \to \Lambda_c^*$ form factors at $\mathcal{O}(\alpha_s, 1/m_{c,b})$ to an existing quark model, providing preliminary predictions for the lepton universality ratios $R(\Lambda_c^*)$ beyond the SM. Finally, we examine the possible incompatibility of recent lattice QCD results with expectations from the heavy-quark expansion and available experimental data., Comment: 17 pages, 3 figures, published version

We revisit the experimental and theoretical status of $B \to \rho l \bar{\nu}$ and $B \to \omega l \bar{\nu}$ decays. We perform a combined fit of averaged spectra from Belle and Babar measurements with prior light cone sum rule calculations, in order to obtain more precise predictions over the full $q^2$ range. The extracted values of $|V_{ub}|$ from these combined fits exhibit smaller uncertainty compared to previous extractions from $B \to \rho l \bar{\nu}$ and $B \to \omega l \bar{\nu}$ decays and the central values are found to be smaller than values extracted from $B \to \pi l \nu$ or inclusive measurements. We use our fit results to obtain more precise predictions in and beyond the Standard Model for the lepton universality ratios $R(\rho)$ and $R(\omega)$, as well as several angular observables that are sensitive to the full $q^2$ distribution, such as the longitudinal polarization of the vector meson, the $\tau$ polarization, and its forward-backward asymmetry., Comment: Fixes and clarifies sign convention of tau polarization in Table V

The study of lepton flavor universality violation (LFUV) in semitauonic $b$-hadron decays has become increasingly important in light of longstanding anomalies in their measured branching fractions, and the very large datasets anticipated from the LHC and Belle II. In this review, we undertake a comprehensive survey of the experimental environments and methodologies for semitauonic LFUV measurements at the $B$-factories and LHCb, along with a concise overview of the theoretical foundations and predictions for a wide range of semileptonic decay observables. We proceed to examine the future prospects to control systematic uncertainties down to the percent level, matching the precision of Standard Model (SM) predictions. Furthermore, we discuss new perspectives and caveats on combinations of the LFUV data and revisit the world averages for the ${\cal R}(D^{(*)})$ ratios. Here we demonstrate that different treatments for the correlations of uncertainties from $D^{**}$ excited states can vary the current $3\sigma$ tension with the SM within a $1\sigma$ range. Prior experimental overestimates of $D^{**}\tau\nu$ contributions may further exacerbate this. The precision of future measurements is also estimated; their power to exploit full differential information, and solutions to the inherent difficulties in self-consistent new physics interpretations of LFUV observables, are briefly explored., Comment: Published version plus an additional subsection on the new R(Lc) results

A dark QCD sector is a relatively minimal extension of the Standard Model (SM) that admits Dark Matter (DM) candidates but requires no portal to the visible sector beyond gravitational interactions: A "nightmare scenario" for DM detection. We consider a secluded dark sector containing a single flavor of light, vector-like dark quark gauged under $SU(N)$. In the large-$N$ limit, this single-flavor theory becomes highly predictive, generating two DM candidates whose masses and dynamics are described by few parameters: A light quark-antiquark bound state, the dark analog of the $\eta'$ meson, and a heavy bound state of $N$ quarks, the dark analog of the $\Delta^{++}$ baryon. We show that the latter may freeze-in with an abundance independent of the confinement scale, forming DM-like relics for $N \lesssim 10$, while the former may generate DM via cannibalization and freeze-out. We study the interplay of this two-component DM system and determine the characteristic ranges of the confinement scale, dark-visible sector temperature ratio, and $N$ that admit non-excluded DM, once the effects of self-interaction constraints and bounds on effective degrees of freedom at the BBN and CMB epochs are included., Comment: 28 pages, 6 figures

Precise measurements of $b\to c\tau\bar\nu$ decays require large resource-intensive Monte Carlo (MC) samples, which incorporate detailed simulations of detector responses and physics backgrounds. Extracted parameters may be highly sensitive to the underlying theoretical models used in the MC generation. Because new physics (NP) can alter decay distributions and acceptances, the standard practice of fitting NP Wilson coefficients to SM-based measurements of the $R(D^{(*)})$ ratios can be biased. The newly developed HAMMER software tool enables efficient reweighting of MC samples to arbitrary NP scenarios or to any hadronic matrix elements. We demonstrate how HAMMER allows avoidance of biases through self-consistent fits directly to the NP Wilson coefficients. We also present example analyses that demonstrate the sizeable biases that can otherwise occur from naive NP interpretations of SM-based measurements. The HAMMER library is presently interfaced with several existing experimental analysis frameworks and we provide an overview of its structure., Comment: 19 pages, 4 figures, published version

We present new precision predictions for semitauonic decays involving $\rho$ and $\omega$ final state mesons. These decay channels offer an interesting orthogonal probe to study the existing B anomalies in semitauonic transitions and are accessible with the Belle II experiment. The predictions are based on combining existing light-cone sum-rule calculations for the form factors with measured experimental spectra from the BaBar and Belle collaborations. This allows us to reliably extrapolate the light-lepton form factor predictions to large values of the four-momentum transfer squared, $q^2$, and in turn to derive precise predictions for $R_{\rho}$ and $R_{\omega}$, the ratio of the total decay rates of $B \rightarrow \rho \tau \nu_\tau$ and $B \rightarrow \omega \tau \nu_\tau$ for $\tau$ final states with respect to light leptons in the SM. In addition, we investigate the impact of all four-fermi operators on the semitauonic $q^2$ spectra and these ratios., Comment: Contribution to the European Physical Society Conference on High Energy Physics - EPS-HEP2019

This document presents the physics case and ancillary studies for the proposed CODEX-b long-lived particle (LLP) detector, as well as for a smaller proof-of-concept demonstrator detector, CODEX-$\beta$, to be operated during Run 3 of the LHC. Our development of the CODEX-b physics case synthesizes `top-down' and `bottom-up' theoretical approaches, providing a detailed survey of both minimal and complete models featuring LLPs. Several of these models have not been studied previously, and for some others we amend studies from previous literature: In particular, for gluon and fermion-coupled axion-like particles. We moreover present updated simulations of expected backgrounds in CODEX-b's actively shielded environment, including the effects of shielding propagation uncertainties, high-energy tails and variation in the shielding design. Initial results are also included from a background measurement and calibration campaign. A design overview is presented for the CODEX-$\beta$ demonstrator detector, which will enable background calibration and detector design studies. Finally, we lay out brief studies of various design drivers of the CODEX-b experiment and potential extensions of the baseline design, including the physics case for a calorimeter element, precision timing, event tagging within LHCb, and precision low-momentum tracking., Comment: 99 pages, 36 figures. Journal version

Ultraviolet completions for axion-like particles (ALPs) lighter than the neutral pion generically induce ALP-neutral pion mixing, and are therefore sensitive to direct constraints on the mixing angle. For ALPs below the pion mass, we demonstrate that strong and novel bounds on the ALP-pion mixing angle can be extracted from existing rare pion decay data, measured by the PIENU and PIBETA experiments., Comment: 7 pages, 4 figures, published version

The determination of $|V_{cb}|$ from exclusive semileptonic $B\to D^*\ell\nu$ decays is sensitive to the choice of form factor parametrization. Larger $|V_{cb}|$ values are obtained fitting the BGL versus the CLN parametrization to recent Belle measurements. For the BGL parametrization, published fits use different numbers of parameters. We propose a method based on nested hypothesis tests to determine the optimal number of BGL parameters to fit the data, and find that six parameters are optimal to fit the Belle tagged and unfolded measurement. We further explore the differences between fits that use different numbers of parameters. The fits which yield $|V_{cb}|$ values in better agreement with determinations from inclusive semileptonic decays, tend to exhibit tensions with heavy quark symmetry expectations. These have to be resolved before the determinations of $|V_{cb}|$ from exclusive and inclusive decays can be considered understood., Comment: 7 pages, section on toy MC added, published version

We calculate the $\Lambda_b \to \Lambda_c \ell \nu$ form factors and decay rates for all possible $b\to c \ell\bar\nu$ four-Fermi interactions beyond the Standard Model, including nonzero charged lepton masses and terms up to order $\alpha_s\, \Lambda_\text{QCD}/m_{c,b}$ and $\Lambda_\text{QCD}^2/m_c^2$ in the heavy quark effective theory. At this order, we obtain model independent predictions for semileptonic $\Lambda_b \to \Lambda_c$ decays in terms of only two unknown sub-subleading Isgur-Wise functions, which can be determined from fitting LHCb and lattice QCD data. We thus obtain model independent results for $\Lambda_b\to \Lambda_c\ell\bar\nu$ decays, including predictions for the ratio $R(\Lambda_c) = {\cal B}(\Lambda_b\to \Lambda_c \tau\bar\nu) / {\cal B}(\Lambda_b\to \Lambda_c \mu\bar\nu)$ in the presence of new physics, that are more precise than prior results in the literature, and systematically improvable with better data on the decays with $\mu$ (or $e$) in the final state. We also explore tests of factorization in $\Lambda_b \to \Lambda_c\pi$ decays, and emphasize the importance of measuring at LHCb the double differential rate $d^2\Gamma(\Lambda_b\to\Lambda_c\ell\bar\nu) / (d q^2\, d\cos\theta)$, in addition to the $q^2$ spectrum., Comment: 30 pages, 7 figures, 1 table

Run 5 of the HL-LHC era (and beyond) may provide new opportunities to search for physics beyond the standard model (BSM) at interaction point 2 (IP2). In particular, taking advantage of the existing ALICE detector and infrastructure provides an opportunity to search for displaced decays of beyond standard model long-lived particles (LLPs). While this proposal may well be preempted by ongoing ALICE physics goals, examination of its potential new physics reach provides a compelling comparison with respect to other LLP proposals. In particular, full event reconstruction and particle identification could be possible by making use of the existing L3 magnet and ALICE time projection chamber. For several well-motivated portals, the reach competes with or exceeds the sensitivity of MATHUSLA and SHiP, provided that a total integrated luminosity of approximately $100\, \text{fb}^{-1}$ could be delivered to IP2., Comment: 14 pages, 7 figures

The heavy quark effective theory makes model independent predictions for semileptonic $\Lambda_b \to \Lambda_c$ decays in terms of a small set of parameters. No subleading Isgur-Wise function occurs at order $\Lambda_{\rm QCD}/m_{c,b}$, and only two sub-subleading functions enter at order $\Lambda_{\rm QCD}^2/m_c^2$. These features allow us to fit the form factors and decay rates calculated up to order $\Lambda_{\rm QCD}^2/m_c^2$ to LHCb data and lattice QCD calculations. We derive a significantly more precise standard model prediction for the ratio ${\cal B}(\Lambda_b\to \Lambda_c \tau\bar\nu) / {\cal B}(\Lambda_b\to \Lambda_c \mu\bar\nu)$ than prior results, and find the expansion in $\Lambda_{\rm QCD}/m_c$ well-behaved, addressing a long-standing question. Our results allow more precise and reliable calculations of $\Lambda_b\to \Lambda_c\ell\bar\nu$ rates, and are systematically improvable with better data on the $\mu$ (or $e$) modes., Comment: 5 pages, 7 figures

We explore scenarios where the $R(D^{(*)})$ anomalies arise from semitauonic decays to a right-handed sterile neutrino. We perform an EFT study of all five simplified models capable of generating at tree-level the lowest dimension electroweak operators that give rise to this decay. We analyze their compatibility with current $R(D^{(*)})$ data and other relevant hadronic branching ratios, and show that one simplified model is excluded by this analysis. The remainder are compatible with collider constraints on the mediator semileptonic branching ratios, provided the mediator mass is of order TeV. We also discuss the phenomenology of the sterile neutrino itself, which includes possibilities for displaced decays at colliders and direct searches, measurable dark radiation, and gamma ray signals., Comment: 30 pages, 13 figures. Updated collider constraints and discussions. Matches published version in JHEP

We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of Standard Model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). In most cases the LLP lifetime can be treated as a free parameter from the $\mu$m scale up to the Big Bang Nucleosynthesis limit of $\sim 10^7$m. Neutral LLPs with lifetimes above $\sim$ 100m are particularly difficult to probe, as the sensitivity of the LHC main detectors is limited by challenging backgrounds, triggers, and small acceptances. MATHUSLA is a proposal for a minimally instrumented, large-volume surface detector near ATLAS or CMS. It would search for neutral LLPs produced in HL-LHC collisions by reconstructing displaced vertices (DVs) in a low-background environment, extending the sensitivity of the main detectors by orders of magnitude in the long-lifetime regime. In this white paper we study the LLP physics opportunities afforded by a MATHUSLA-like detector at the HL-LHC. We develop a model-independent approach to describe the sensitivity of MATHUSLA to BSM LLP signals, and compare it to DV and missing energy searches at ATLAS or CMS. We then explore the BSM motivations for LLPs in considerable detail, presenting a large number of new sensitivity studies. While our discussion is especially oriented towards the long-lifetime regime at MATHUSLA, this survey underlines the importance of a varied LLP search program at the LHC in general. By synthesizing these results into a general discussion of the top-down and bottom-up motivations for LLP searches, it is our aim to demonstrate the exceptional strength and breadth of the physics case for the construction of the MATHUSLA detector., Comment: 213 pages, 73 figures. Extended Section 2 to add more detailed discussion of LLP reconstruction and analysis, and background rejection. Updated comparison of MATHUSLA RH neutrino sensitivity to other experiments. Updated analysis of long-lived ALPs produced in weak-scale processes and decaying to jets. Various clarifications, fixed typos, and added references. Results and conclusions unchanged

We provide an ultraviolet (UV) complete model for the $R(D^{(*)})$ anomalies, in which the additional contribution to semi-tauonic $b \to c$ transitions arises from decay to a right-handed sterile neutrino via exchange of a TeV-scale $SU(2)_L$ singlet $W'$. The model is based on an extension of the Standard Model (SM) hypercharge group, $U(1)_Y$, to the $SU(2)_V\times U(1)'$ gauge group, containing several pairs of heavy vector-like fermions. We present a comprehensive phenomenological survey of the model, ranging from the low-energy flavor physics, direct searches at the LHC, to neutrino physics and cosmology. We show that, while the $W'$ and $Z'$-induced constraints are important, it is possible to find parameter space naturally consistent with all the available data. The sterile neutrino sector also offers rich phenomenology, including possibilities for measurable dark radiation, gamma ray signals, and displaced decays at colliders., Comment: 26 pages, 5 figures

We propose a new framework to generate the Standard Model (SM) quark flavor hierarchies in the context of two Higgs doublet models (2HDM). The `flavorful' 2HDM couples the SM-like Higgs doublet exclusively to the third quark generation, while the first two generations couple exclusively to an additional source of electroweak symmetry breaking, potentially generating striking collider signatures. We synthesize the flavorful 2HDM with the `flavor-locking' mechanism, that dynamically generates large quark mass hierarchies through a flavor-blind portal to distinct flavon and hierarchon sectors: Dynamical alignment of the flavons allows a unique hierarchon to control the respective quark masses. We further develop the theoretical construction of this mechanism, and show that in the context of a flavorful 2HDM-type setup, it can automatically achieve realistic flavor structures: The CKM matrix is automatically hierarchical with $|V_{cb}|$ and $|V_{ub}|$ generically of the observed size. Exotic contributions to meson oscillation observables may also be generated, that may accommodate current data mildly better than the SM itself., Comment: 34 pages, 2 tables, 2 figures

We explore semileptonic $B$ decays to the four lightest excited charm mesons, $D^{**} = \{D_0^*,\, D_1^*,$ $D_1,\, D_2^*\}$, for nonzero charged lepton mass and for all $b\to c \ell\bar\nu$ four-Fermi interactions, including calculation of the ${\cal O}(\Lambda_\text{QCD}/m_{c,b})$ and ${\cal O}(\alpha_s)$ corrections to the heavy quark limit for all form factors. In the heavy quark limit some form factors are suppressed at zero recoil, therefore, the ${\cal O}(\Lambda_\text{QCD}/m_{c,b})$ corrections can be very important. The $D^{**}$ rates exhibit sensitivities to new physics in $b\to c\tau\bar\nu$ mediated decays complementary to the $D$ and $D^*$ modes. Since they are also important backgrounds to $B\to D^{(*)}\tau\bar\nu$, the correct interpretation of future semitauonic $B\to D^{(*)}$ rate measurements requires consistent treatment of both the $D^{**}$ backgrounds and the signals. Our results allow more precise and more reliable calculations of these $B\to D^{**}\ell\bar\nu$ decays, and are systematically improvable by better data on the $e$ and $\mu$ modes. As an example, we show that the $D^{**}$ rates are more sensitive to a new $\bar c\, \sigma_{\mu\nu} b$ tensor interaction than the $D^{(*)}$ rates., Comment: 17 pages, 4 figures, 5 tables; published version

We advocate for the construction of a new detector element at the LHCb experiment, designed to search for displaced decays of beyond standard model long-lived particles, taking advantage of a large shielded space in the LHCb cavern that is expected to soon become available. We discuss the general features and putative capabilities of such an experiment, as well as its various advantages and complementarities with respect to the existing LHC experiments and proposals such as SHiP and MATHUSLA. For two well-motivated beyond Standard Model benchmark scenarios -- Higgs decay to dark photons and $B$ meson decays via a Higgs mixing portal -- the reach either complements or exceeds that predicted for other LHC experiments., Comment: 12 pages, 8 figures, 2 tables; published version

Recently several papers extracted $|V_{cb}|$ using the Belle measurement of the exclusive $\bar B \to D^* \ell\bar\nu$ unfolded differential decay rates, available for the first time. Depending on the theoretical inputs, some of the fits yield higher $|V_{cb}|$ values, compatible with those from inclusive semileptonic $B$ decays. Since these four fits use mostly the same data, if their correlations were close to 100\%, the tension between them would be over $5\sigma$. We determine the correlations, find that the tension between the results is less than $3\sigma$, and explore what might lead to improving the consistency of the fits. We find that fits that yield the higher values of $|V_{cb}|$, also suggest large violations of heavy quark symmetry. These fits are also in tension with preliminary lattice QCD data on the form factors. Without additional experimental data or lattice QCD input, there are no set of assumptions under which the tension between exclusive and inclusive determinations of $|V_{cb}|$ can be considered resolved., Comment: 5 pages, 3 figures

We summarize the new results on $B$ meson mixing and mixing-related $CP$ violation presented at CKM2016. We place these results in the context of both previous experimental measurements and the most recent theoretical developments in the field, and discuss prospects for ongoing and future mixing and mixing-related $CP$ violation measurements., Comment: To appear in the proceedings of the 9th International Workshop on the CKM Unitarity Triangle, Nov 28- Dec 2 2016, Mumbai

The measured $\bar{B}\to D^{(*)} l \bar\nu$ decay rates for light leptons ($l=e,\mu$) constrain all $\bar{B}\to D^{(*)}$ semileptonic form factors, by including both the leading and ${\cal O}(\Lambda_{\text{QCD}}/m_{c,b})$ subleading Isgur-Wise functions in the heavy quark effective theory. We perform a novel combined fit to the $\bar{B}\to D^{(*)} l \bar\nu$ decay distributions to predict the $\bar{B} \to D^{(*)} \tau\bar\nu$ rates and determine the CKM matrix element $|V_{cb}|$. Most theoretical and experimental papers have neglected uncertainties in the predictions for form factor ratios at order $\Lambda_{\text{QCD}}/m_{c,b}$, which we include. We also calculate ${\cal O}(\Lambda_{\text{QCD}}/m_{c,b})$ and ${\cal O}(\alpha_s)$ contributions to semileptonic $\bar{B}\to D^{(*)} \ell \bar\nu$ decays for all possible $b \to c$ currents. This result has not been available for the tensor current form factors, and for two of those, which are ${\cal O}(\Lambda_{\text{QCD}}/m_{c,b})$, the corrections are of the same order as approximations used in the literature. These results allow us to determine with improved precision how new physics may affect the $\bar{B}\to D^{(*)} \tau\bar\nu$ rates. Our predictions can be systematically improved with more data; they need not rely on lattice QCD results, although these can be incorporated., Comment: 32 pages, 5 figures, 11 tables; v2: additional fit scenario added; plots 3 & 4 corrected; numerical results unchanged; v3: transcription of Eqs (A1a,b) corrected; all results unchanged; v4: corrected typo in eq 19b

Very high multiplicity, spherically-symmetric distributions of soft particles, with $p_T$ ~ few hundred MeV, may be a signature of strongly-coupled hidden valleys that exhibit long, efficient showering windows. With traditional triggers, such "soft bomb" events closely resemble pile-up and are therefore only recorded with minimum bias triggers at a very low efficiency. We demonstrate a proof-of-concept for a high-level triggering strategy that efficiently separates soft bombs from pile-up by searching for a "belt of fire": A high density band of hits on the innermost layer of the tracker. Seeding our proposed high-level trigger with existing jet, missing transverse energy or lepton hardware-level triggers, we show that net trigger efficiencies of order 10% are possible for bombs of mass several hundred GeV. We also consider the special case that soft bombs are the result of an exotic decay of the 125 GeV Higgs. The fiducial rate for "Higgs bombs" triggered in this manner is marginally higher than the rate achievable by triggering directly on a hard muon from associated Higgs production., Comment: 38 pages, 5 tables, 14 figures