Search

The $τ$ 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 $τ$ polarization in inclusive $B\to Xτ\barν$ using the same choice as in the exclusive decays, and construct a sum rule relating the inclusive $τ$ 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., 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., 46 pages, 11 figures, 3 tables

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

Normalizing the recent LHCb measurement of $Λ_b \to Λ_c τ\barν$ to the standard model (SM) prediction for the $Λ_b \to Λ_c μ\barν$ rate, instead of a LEP measurement, provides a more consistent comparison with the SM prediction for the lepton flavor universality ratio $R(Λ_c)$. This modestly increases $R(Λ_c)$ 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 $Λ_b$ decay may be significantly greater than the corresponding fraction in $B$ decays. Possible implications are speculated upon., 3 pages

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 $��_b \to ��_c^*(2595) l ��$ and $��_b \to ��_c^*(2625) l ��$ form factors and decay rates for all possible $b \to c l \bar��$ four-Fermi interactions in and beyond the Standard Model (SM), including nonzero charged lepton masses and terms up to order $\mathcal{O}(��_s, 1/m_{c,b})$ 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 $��_b \to ��_c^*$ form factors at $\mathcal{O}(��_s, 1/m_{c,b})$ to an existing quark model, providing preliminary predictions for the lepton universality ratios $R(��_c^*)$ 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., 17 pages, 3 figures, published version

We revisit the experimental and theoretical status of $B \to ρl \barν$ and $B \to ωl \barν$ 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 $B \to ρl \barν$ and $B \to ωl \barν$ decays and the central values are found to be smaller than values extracted from $B \to πl ν$ or inclusive measurements. We use our fit results to obtain more precise predictions in and beyond the Standard Model for the lepton universality ratios $R(ρ)$ and $R(ω)$, 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 $τ$ polarization, and its forward-backward asymmetry., Fixes and clarifies sign convention of tau polarization in Table V

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

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., 14 pages, 7 figures

We calculate the $��_b \to ��_c \ell ��$ form factors and decay rates for all possible $b\to c \ell\bar��$ four-Fermi interactions beyond the Standard Model, including nonzero charged lepton masses and terms up to order $��_s\, ��_\text{QCD}/m_{c,b}$ and $��_\text{QCD}^2/m_c^2$ in the heavy quark effective theory. At this order, we obtain model independent predictions for semileptonic $��_b \to ��_c$ 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 $��_b\to ��_c\ell\bar��$ decays, including predictions for the ratio $R(��_c) = {\cal B}(��_b\to ��_c ��\bar��) / {\cal B}(��_b\to ��_c ��\bar��)$ 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 $��$ (or $e$) in the final state. We also explore tests of factorization in $��_b \to ��_c��$ decays, and emphasize the importance of measuring at LHCb the double differential rate $d^2��(��_b\to��_c\ell\bar��) / (d q^2\, d\cos��)$, in addition to the $q^2$ spectrum., 30 pages, 7 figures, 1 table

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

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

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 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 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 neutral component of a real pseudoscalar electroweak (EW) triplet can produce a diphoton excess at 750 GeV, if it is somewhat mixed with an EW singlet pseudoscalar. This triplet-singlet mixing allows for greater freedom in the diboson branching ratios than the singlet-only case, but it is still possible to probe the parameter space extensively with 300 fb$^{-1}$. The charged component of the triplet is pair-produced at the LHC, which results in a striking signal in the form of a pair of $W\gamma$ resonances with an irreducible rate of 0.27 fb. Other signatures include multiboson final states from cascade decays of the triplet-singlet neutral states. A large class of composite models feature both EW singlet and triplet pseudo-Nambu Goldstone bosons in their spectrum, with the diboson couplings generated by axial anomalies., Comment: 36 pages, 7 figures

We derive compact expressions for the helicity amplitudes of the many-body $B \to D^{(*)}(\to DY)��(\to X��)��$ decays, specifically for $X = \ell ��$ or $��$ and $Y = ��$ or $��$. We include contributions from all ten possible new physics four-Fermi operators with arbitrary couplings. Our results capture interference effects in the full phase space of the visible $��$ and $D^*$ decay products which are missed in analyses that treat the $��$ or $D^*$ or both as stable. The $��$ interference effects are sizable, formally of order $m_��/m_B$ for the standard model, and may be of order unity in the presence of new physics. Treating interference correctly is essential when considering kinematic distributions of the $��$ or $D^*$ decay products, and when including experimentally unavoidable phase space cuts. Our amplitude-level results also allow for efficient exploration of new physics effects in the fully differential phase space, by enabling experiments to perform such studies on fully simulated Monte Carlo datasets via efficient event reweighing. As an example, we explore a class of new physics interactions that can fit the observed $R(D^{(*)})$ ratios, and show that analyses including more differential kinematic information can provide greater discriminating power for new physics, than single kinematic variables alone., 32 pages, 5 figures

We derive a new flavor symmetry relation for the determination of the weak phase $��=��_1$ from time-dependent CP asymmetries and $B \to J/��P$ decay rates. In this relation, the contributions to $\sin2��$ proportional to $V_{ub}$ are parametrically suppressed compared to the contributions in the $B \to J/��K^0$ time-dependent CP asymmetry alone. This relation uses only $SU(3)$ flavor symmetry, and does not require further diagrammatic assumptions. The current data either fluctuate at the $2��$ level from expectations, or may hint at effects of unexpected magnitude from contributions proportional to $V_{ub}$ or from isospin breaking., 5 pages, 1 figure, published version

We show that the parity of the $h Z��$ vertex can be probed by interference between the gluon fusion Higgs production, $gg \to h \to ��Z \to ��\ell^+\ell^-$, and the background, $gg \to ��Z \to ��\ell^+\ell^-$, amplitudes. In the presence of a parity violating $hZ��$ vertex, this interference alters the kinematic distribution of the leptons and photon compared to Standard Model (SM) expectations. For a Higgs with SM-sized width and couplings, we find that the size of the effect enters at most at the $10^{-2}$ level. Such a small effect cannot be seen at the LHC, even with futuristic high luminosities. Should there exist other broader scalar particles with larger production cross-section times branching ratio to $Z��$, then the parity structure of their $Z��$ couplings can be probed with this technique., 20 pages, 4 figures

We re-examine the possibility to measure the photon polarization in $B \to K^*��$ decays, via decays in which the photon subsequently undergoes nuclear conversion to a lepton pair. We obtain compact expressions for the full decay-plus-conversion amplitude. With these results we show that interference between the $B \to (K^*\to K��)��$ decay and the $��N \to \ell^+\ell^-N$ conversion permits both the ratio and relative weak phase between the left- and right-handed photon amplitudes to be probed by an angular observable, constructed from the final state dilepton, kaon and pion kinematic configuration. Exploiting this technique will be experimentally challenging. However, we present special kinematic cuts that enhance the statistical power of this technique by an $\mathcal{O}(1)$ factor. We verify this effect and extract pertinent angular kinematic distributions with dedicated numerical simulations., 24 pages, 6 figures. Corrected minor typo in one formula

We study Higgs diphoton decays, in which both photons undergo nuclear conversion to electron- positron pairs. The kinematic distribution of the two electron-positron pairs may be used to probe the CP violating (CPV) coupling of the Higgs to photons, that may be produced by new physics. Detecting CPV in this manner requires interference between the spin-polarized helicity amplitudes for both conversions. We derive leading order, analytic forms for these amplitudes. In turn, we obtain compact, leading-order expressions for the full process rate. While performing experiments involving photon conversions may be challenging, we use the results of our analysis to construct experimental cuts on certain observables that may enhance sensitivity to CPV. We show that there exist regions of phase space on which sensitivity to CPV is of order unity. The statistical sensitivity of these cuts are verified numerically, using dedicated Monte-Carlo simulations., 49 pages, 15 figures; updated to match JHEP and fixed minor typos