United Kingdom

Sebastian Jäger

Italy

Matthew Kirk

Alexander Lenz

Kirsten Leslie

Erratum to: Charming new B-physics

We investigate the sensitivity of future proton-proton colliders to a contact interaction of the form <math><mn>1</mn><mo>/</mo><msup><mi>Λ</mi><mn>2</mn></msup><mo>(</mo><msub><mover><mi>b</mi><mo>¯</mo></mover><mi>L</mi></msub><msub><mi>γ</mi><mi>μ</mi></msub><msub><mi>s</mi><mi>L</mi></msub><mo>)</mo><mo>(</mo><msub><mover><mi>μ</mi><mo>¯</mo></mover><mi>L</mi></msub><msup><mi>γ</mi><mi>μ</mi></msup><msub><mi>μ</mi><mi>L</mi></msub><mo>)</mo></math> as indicated by the longstanding rare <math><mi>B</mi></math>-decay anomalies. We include next to leading order (NLO) QCD and electroweak effects and employ an optimized binning scheme, and carefully validate our background calculation against ATLAS and CMS data. We find that the FCC-hh with <math><mrow><mn>40</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>ab</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> of luminosity is able to exclude scales <math><mi>Λ</mi></math> up to 26 TeV at 95% CL, and discover <math><mi>Λ</mi></math> up to 20 TeV. While this is not quite enough to exclude or discover the current best-fit value of 39 TeV, this can in principle be achieved with more luminosity and/or higher energy, as we study quantitatively. Our analysis is conservative in that it assumes only a <math><mover><mi>b</mi><mo>¯</mo></mover><mi>s</mi><mi>μ</mi><mi>μ</mi></math> contact interaction.

Bradley Garland

Charanjit K. Khosa

United States

Sandra Kvedaraitė

Probing <math><mi>B</mi></math> anomalies via dimuon tails at a future collider

Motivated by renewed evidence for new physics in <math><mi>b</mi><mo>→</mo><mi>s</mi><mo>ℓ</mo><mo>ℓ</mo></math> transitions in the form of LHCb’s new measurements of theoretically clean lepton-universality ratios and the purely leptonic <math><msub><mi>B</mi><mi>s</mi></msub><mo>→</mo><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math> 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 <math><msub><mi>R</mi><mi>K</mi></msub></math>, <math><msub><mi>R</mi><msup><mi>K</mi><mo>*</mo></msup></msub></math>, and <math><msub><mi>B</mi><mi>s</mi></msub><mo>→</mo><mi>μ</mi><mi>μ</mi></math> alone results in a discrepancy with the Standard Model at <math><mn>4.0</mn><mi>σ</mi></math>, up from <math><mn>3.5</mn><mi>σ</mi></math> in 2017. One-parameter scenarios with purely left-handed or with purely axial coupling to muons fit the data well and result in a <math><mo>∼</mo><mn>5</mn><mi>σ</mi></math> pull from the Standard Model. In a two-parameter fit of 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 <math><msub><mi>B</mi><mi>s</mi></msub><mo>→</mo><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math>, 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 <math><mi>BR</mi><mo>(</mo><msub><mi>B</mi><mi>s</mi></msub><mo>→</mo><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup><mo>)</mo><mo>=</mo><mo>(</mo><mn>2.8</mn><mo>±</mo><mn>0.3</mn><mo>)</mo><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>9</mn></mrow></msup></math>.

China

Li-Sheng Geng

Benjamín Grinstein

Shuang-Yi Li

Spain

Jorge Martin Camalich

Rui-Xiang Shi

Implications of new evidence for lepton-universality violation in <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> decays

We give a comprehensive account of the flavour physics of Beyond-Standard-Model (BSM) effects in b → c   <math> <mover> <mi>c</mi> <mo>¯</mo> </mover> </math>  $$ \overline{c} $$  cs transitions, considering the full set of 20 four-quark operators. We discuss the leading-order structure of their RG mixing with each other as well as the QCD-penguin, dipole, and FCNC semileptonic operators they necessarily mix with, providing compact expressions. We also provide the first complete results for BSM effects in the lifetime observables ∆Γ s  and τ (B  s )/τ(B  d ), as well as for the semileptonic CP-asymmetry   <math> <msubsup> <mi>a</mi> <mi>sl</mi> <mi>s</mi> </msubsup> </math>  $$ {a}_{sl}^s $$ . From a global analysis, we obtain stringent constraints on 16 of the 20 BSM operators, including the 10 operators   <math> <msubsup> <mi>Q</mi> <mrow> <mn>1</mn> <mo>…</mo> <mn>10</mn> </mrow> <mrow> <mi>c</mi> <mo>′</mo> </mrow> </msubsup> </math>  $$ {Q}_{1\dots 10}^{c\prime } $$  involving a right-handed strange quark. Focussing on CP-conserving new physics, the constraints correspond to NP scales of order 10 TeV in most cases, always dominated by exclusive and/or radiative B-decays via RGE mixing. For the remaining four operators, including the two Standard-Model (SM) ones, larger effects are experimentally allowed, as previously noted in [1]. We extend that paper’s scope to the CP-violating case, paying attention to the impact on the decay rate and time-dependent CP-violation in B  d  → J/ψK  S . Contrary to common lore, we show that quantifiable constraints arise for new physics in either of the two SM operators, with the uncertain non-perturbative matrix element of the colour-suppressed (or equivalently, colour-octet) operator determined from the data. For new physics in the coefficient   <math> <msubsup> <mi>C</mi> <mn>1</mn> <mi>c</mi> </msubsup> </math>  $$ {C}_1^c $$ , suppressed in the SM, we find (in addition to CP-conserving new physics) two perfectly viable, narrow bands of complex Wilson coefficients. Somewhat curiously, one of them contains a region where the fitted matrix element for the colour-suppressed operator is in agreement with naive factorization, contrarily to a widely held belief that large non- factorizable contributions to B  d  → J/ψK  S  are implied by experimental data.

Charming new B-physics

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 → D  *  τν,   <math> <msubsup> <mi>F</mi> <mi>L</mi> <mrow> <mi>D</mi> <mo>∗</mo> </mrow> </msubsup> </math>  $$ {F}_L^{D\ast } $$ . 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   <math> <msubsup> <mi>F</mi> <mi>L</mi> <mrow> <mi>D</mi> <mo>∗</mo> </mrow> </msubsup> </math>  $$ {F}_L^{D\ast } $$  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 → Dτν would effectively discriminate among them.

Jorge Camalich

Revisiting the new-physics interpretation of the b → cτν data

We consider the impact on W W production of the unique dimension-six operator coupling gluons to the Higgs field. In order to study this process, we have to appropriately model the effect of a veto on additional jets. This requires the resummation of large logarithms of the ratio of the maximum jet transverse momentum and the invariant mass of the W boson pair. We have performed such resummation at the appropriate accuracy for the Standard Model (SM) background and for a signal beyond the SM (BSM), and devised a simple method to interface jet-veto resummations with fixed-order event generators. This resulted in the fast numerical code MCFM-RE, the Resummation Edition of the fixed-order code MCFM. We compared our resummed predictions with parton-shower event generators and assessed the size of effects, such as limited detector acceptances, hadronisation and the underlying event, that were not included in our resummation. We have then used the code to compare the sensitivity of W W and Z Z production at the HL-LHC to the considered higher-dimension operator. We have found that W W can provide complementary sensitivity with respect to Z Z, provided one is able to control theory uncertainties at the percent-level. Our method is general and can be applied to the production of any colour singlet, both within and beyond the SM.

Luke Arpino

Andrea Banfi

Nikolas Kauer

BSM W W production with a jet veto

Colored and colorless particles that are stable on collider scales and carry exotic electric charges, so-called Multiply-Charged Heavy Stable Particles (MCHSPs), exist in extensions of the Standard Model, and can include the top partner(s) in solutions of the hierarchy problem. To obtain bounds on color-triplets and color-singlets of charges up to |Q| = 8, we recast searches for signatures of two production channels: the “open” channel — where the particles are pair-produced above threshold, and are detectable in dedicated LHC searches for stable multiply charged leptons, and the “closed” channel — where a particle-antiparticle pair is produced as a bound state, detectable in searches for a diphoton resonance. We recast the open lepton searches by incorporating the relevant strong-interaction effects for color-triplets. In both open and closed production, we provide a careful assessment of photon-induced processes using the accurate LUXqed PDF, resulting in substantially weaker bounds than previously claimed in the literature for the colorless case. Our bounds for colored MCHSPs are shown for the first time, as the LHC experiments have not searched for them directly. Generally, we obtain nearly charge-independent lower mass limits of around 970 GeV (color-triplet scalar), 1200 GeV (color-triplet fermion), and 880-900 GeV (color-singlet fermion) from open production, and strongly charge-dependent limits from closed production. In all cases there is a cross-over between dominance by open and closed searches at some charge. We provide prospective bounds for   <math> <msqrt> <mi>s</mi> </msqrt> <mo>=</mo> <mn>13</mn> </math>  $$ \sqrt{s}=13 $$  TeV LHC searches at integrated luminosities of 39.5 fb−1, 100 fb−1, and 300 fb−1. Moreover, we show that a joint observation in the open and the closed channels allows to determine the mass, spin, color, and electric charge of the particle.

Israel

Gilad Perez

Inbar Savoray

Bounds and prospects for stable multiply charged particles at the LHC

We conduct a systematic study of the impact of new physics in quark-level <math><mrow><mi>b</mi><mo>→</mo><mi>c</mi><mover><mrow><mi>c</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>s</mi></mrow></math> transitions on <math><mi>B</mi></math> physics, in particular rare <math><mi>B</mi></math> decays and <math><mi>B</mi></math>-meson lifetime observables. We find viable scenarios where a sizable effect in rare semileptonic <math><mi>B</mi></math> decays can be generated, compatible with experimental indications and with a possible dependence on the dilepton invariant mass, while being consistent with constraints from radiative <math><mi>B</mi></math> decay and the measured <math><msub><mi>B</mi><mi>s</mi></msub></math> width difference. We show how, if the effect is generated at the weak scale or beyond, strong renormalization-group effects can enhance the impact on semileptonic decays while leaving radiative <math><mi>B</mi></math> decay largely unaffected. A good complementarity of the different <math><mi>B</mi></math>-physics observables implies that precise measurements of lifetime observables at LHCb may be able to confirm, refine, or rule out this scenario.

Charming new physics in rare <math><mrow><mi>B</mi></mrow></math> decays and mixing?

We discuss the implications of the significant excesses in the diphoton final state observed by the LHC experiments ATLAS and CMS around a diphoton invariant mass of 750 GeV. The interpretation of the excess as a spin-zero s -channel resonance implies model-independent lower bounds on both its branching ratio and its coupling to photons, which stringently constrain dynamical models. We consider both the case where the excess is described by a narrow and a broad resonance. We also obtain model-independent constraints on the allowed couplings and branching fractions to final states other than diphotons, by including the interplay with 8 TeV searches. These results can guide attempts to construct viable dynamical models of the resonance. Turning to specific models, our findings suggest that the anomaly cannot be accounted for by the presence of only an additional singlet or doublet spin-zero field and the Standard Model degrees of freedom; this includes all two-Higgs-doublet models. Likewise, heavy scalars in the MSSM cannot explain the excess if stability of the electroweak vacuum is required, at least in a leading-order analysis. If we assume that the resonance is broad we find that it is challenging to find a weakly coupled explanation. However, we provide an existence proof in the form of a model with vectorlike quarks with large electric charge that is perturbative up to the 100 TeV scale. For the narrow-resonance case a similar model can be perturbative up to high scales also with smaller charges. We also find that, in their simplest form, dilaton models cannot explain the size of the excess. Some implications for flavor physics are briefly discussed.

Rick Gupta

Yevgeny Kats

Emmanuel Stamou

Interpreting a 750 GeV diphoton resonance

We present a new analysis of the ratio ε ′/ ε within the Standard Model (SM) using a formalism that is manifestly independent of the values of leading ( V − A ) ⊗ ( V − A ) QCD penguin, and EW penguin hadronic matrix elements of the operators Q 4 , Q 9 , and Q 10 , and applies to the SM as well as extensions with the same operator structure. It is valid under the assumption that the SM exactly describes the data on CP-conserving K → ππ amplitudes. As a result of this and the high precision now available for CKM and quark mass parameters, to high accuracy ε ′ /ε depends only on two non-perturbative parameters, B 6 (1/2) and B 8 (3/2) , and perturbatively calculable Wilson coefficients. Within the SM, we are separately able to determine the hadronic matrix element 〈 Q 4 〉 0 from CP-conserving data, significantly more precisely than presently possible with lattice QCD. Employing B 6 (1/2) = 0 . 57 ± 0 . 19 and B 8 (3/2) = 0 . 76 ± 0 . 05, extracted from recent results by the RBC-UKQCD collaboration, we obtain ε ′ /ε = (1 . 9 ± 4 . 5) × 10 −4 , substantially more precise than the recent RBC-UKQCD prediction and 2 . 9 σ below the experimental value (16 . 6 ± 2 . 3) × 10 −4 , with the error being fully dominated by that on B 6 (1/2) . Even discarding lattice input completely, but employing the recently obtained bound B 6 (1/2)  ≤  B 8 (3/2)  ≤ 1 from the large- N approach, the SM value is found more than 2 σ below the experimental value. At B 6 (1/2)  =  B 8 (3/2)  = 1, varying all other parameters within one sigma, we find ε ′ /ε = (8 . 6 ± 3 . 2) × 10 −4 . We present a detailed anatomy of the various SM uncertainties, including all sub-leading hadronic matrix elements, briefly commenting on the possibility of underestimated SM contributions as well as on the impact of our results on new physics models.