We study flavor changing neutral current decays of B and K mesons in the dark U(1) D  model, with the dark photon/dark Z mass between 10 MeV and 2 GeV. Although the model provides an improved fit (compared to the standard model) to the differential decay distributions of B → K (∗) ℓ + ℓ −, with ℓ = μ, e, and B  s  → ϕμ + μ  − , the allowed parameter space is ruled out by measurements of atomic parity violation, K + → μ + + invisible decay, and   <math> <msub> <mi>B</mi> <mi>s</mi> </msub> <mo>−</mo> <msub> <mover> <mi>B</mi> <mo>¯</mo> </mover> <mi>s</mi> </msub> </math>  $$ {B}_s-{\overline{B}}_s $$  mixing, among others. To evade constraints from low energy data, we extend the model to allow for (1) additional invisible Z  D  decay, (2) a direct vector coupling of Z  D  to muons, and (3) a direct coupling of Z  D  to both muons and electrons, with the electron coupling fine-tuned to cancel the Z  D  coupling to electrons via mixing. We find that only the latter case survives all constraints.

United States

Alakabha Datta

South Korea

A. Hammad

Danny Marfatia

Lopamudra Mukherjee

Ahmed Rashed

Dark photon and dark Z mediated B meson decays

We show how, in the <math><mi>B</mi><mo>−</mo><mi>L</mi></math> extension of the SM (BLSM) with an Inverse Seesaw (IS) mechanism for neutrino mass generation, a light <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math> state with moderate couplings to SM objects, hence ‘dark’ in its nature, can be associated, in conjunction with light sterile neutrinos, to some present day data anomalies, such as the anomalous magnetic moment of the muon as well as a possible signal indicating the existence of sterile neutrinos in neutrino beam experiments.

Egypt

United Kingdom

Sweden

S. Moretti

The dark ′ and Sterile Neutrinos Behind Current Anomalies

We investigate the sensitivity of electron-proton (ep) colliders for charged lepton flavor violation (cLFV) in an effective theory approach, considering a general effective Lagrangian for the conversion of an electron into a muon or a tau via the effective coupling to a neutral gauge boson or a neutral scalar field. For the photon, the Z boson and the Higgs particle of the Standard Model, we present the sensitivities of the LHeC for the coefficients of the effective operators, calculated from an analysis at the reconstructed level. As an example model where such flavor changing neutral current (FCNC) operators are generated at loop level, we consider the extension of the Standard Model by sterile neutrinos. We show that the LHeC could already probe the LFV conversion of an electron into a muon beyond the current experimental bounds, and could reach more than an order of magnitude higher sensitivity than the present limits for LFV conversion of an electron into a tau. We discuss that the high sensitivities are possible because the converted charged lepton is dominantly emitted in the backward direction, enabling an efficient separation of the signal from the background.

Switzerland

Stefan Antusch

Searching for charged lepton flavor violation at ep colliders

While charged lepton flavor violation (cLFV) with taus is often expected to be largest in many extensions of the Standard Model (SM), it is currently much less constrained than cLFV with electrons and muons. We study the sensitivity of the LHeC to e-τ (and e-μ) conversion processes <math><mi>p</mi><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>+</mo><mi>j</mi></math> (and <math><mi>p</mi><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>+</mo><mi>j</mi></math>) mediated by a <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math> with flavor-violating couplings to charged leptons in the t-channel. Compared to current tests at the LHC, where cLFV decays of the <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math> (produced in the s-channel) are searched for, the LHeC has sensitivity to much higher <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math> masses, up to O(10) TeV. For cLFV with taus, we find that the LHeC sensitivity from the process <math><mi>p</mi><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>+</mo><mi>j</mi></math> can exceed the current limits from collider and non-collider experiments in the whole considered <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math> mass range (above 500 GeV) by more than two orders of magnitude. In particular for extensions of the SM with a heavy <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math>, where direct production at colliders is kinematically suppressed, <math><mi>e</mi><mo>−</mo><mi>τ</mi></math> conversion at LHeC provides an exciting new discovery channel for this type of new physics.

Probing ′ mediated charged lepton flavor violation with taus at the LHeC

In this work we study the effects of new-physics (NP) operators with different Lorentz structures on the inclusive <math><mrow><mi>B</mi><mo>→</mo><msub><mrow><mi>X</mi></mrow><mrow><mi>c</mi></mrow></msub><mi>τ</mi><mover><mrow><mi>ν</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow></math> decay and make predictions for the ratio of total decay rates <math><mrow><mi>R</mi><mo>(</mo><msub><mrow><mi>X</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>)</mo><mo>=</mo><mfrac><mrow><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><msub><mrow><mi>X</mi></mrow><mrow><mi>c</mi></mrow></msub><mi>τ</mi><msub><mrow><mover><mrow><mi>ν</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mrow><mi>τ</mi></mrow></msub><mo>)</mo></mrow><mrow><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><msub><mrow><mi>X</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>ℓ</mo><msub><mrow><mover><mrow><mi>ν</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mrow><mo>ℓ</mo></mrow></msub><mo>)</mo></mrow></mfrac></mrow></math> with <math><mo>ℓ</mo><mo>=</mo><mi>e</mi></math>, <math><mrow><mi>μ</mi></mrow></math>, the differential decay rates, <math><mrow><mfrac><mrow><mi>d</mi><mi>Γ</mi></mrow><mrow><mi>d</mi><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></mfrac></mrow></math> and <math><mfrac><mrow><mi>d</mi><mi>Γ</mi></mrow><mrow><mi>d</mi><msub><mi>E</mi><mi>τ</mi></msub></mrow></mfrac></math>, forward-backward asymmetry <math><mrow><msub><mrow><mi>A</mi></mrow><mrow><mi>F</mi><mi>B</mi></mrow></msub></mrow></math> and the ratio of the differential decay rates <math><mrow><mi>B</mi><mo>(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>)</mo><mo>=</mo><mfrac><mrow><mi>d</mi><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><msub><mrow><mi>X</mi></mrow><mrow><mi>c</mi></mrow></msub><mi>τ</mi><msub><mrow><mover><mrow><mi>ν</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mrow><mi>τ</mi></mrow></msub><mo>)</mo><mo>/</mo><mi>d</mi><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow><mrow><mi>d</mi><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><msub><mrow><mi>X</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>ℓ</mo><msub><mrow><mover><mrow><mi>ν</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mrow><mo>ℓ</mo></mrow></msub><mo>)</mo><mo>/</mo><mi>d</mi><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></mfrac></mrow></math>. In addition, we introduce some leptoquark models as explicit models of the NP operators and study their effects on the inclusive decay. We consider <math><mi>O</mi><mo>(</mo><msub><mi>α</mi><mi>s</mi></msub><mo>)</mo></math> radiative and <math><mn>1</mn><mo>/</mo><msub><mi>m</mi><mi>b</mi></msub></math> nonperturbative corrections to the Standard Model (SM) decay rate and ignore their small effects in the NP contributions.

Saeed Kamali

New physics in inclusive <math><mi>B</mi><mo>→</mo><msub><mi>X</mi><mi>c</mi></msub><mo>ℓ</mo><mover><mi>ν</mi><mo>¯</mo></mover></math> decay in light of <math><mrow><mi>R</mi><mo>(</mo><msup><mrow><mi>D</mi></mrow><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup><mo>)</mo></mrow></math> measurements

For a number of years, there has been a certain inconsistency among the measurements of the branching ratios and CP asymmetries of the four B → πK decays (B + → π+ K 0, B + → π0 K +, B  d 0 → π − K +, B  d 0 → π 0 K 0). In this paper, we re-examine this B → πK puzzle. We find that the key unknown parameter is |C ′ /T ′|, the ratio of color-suppressed and color-allowed tree amplitudes. If this ratio is large, |C ′ /T ′| = 0.5, the SM can explain the data. But if it is small, |C ′ /T ′| = 0.2, the SM cannot explain the B → πK puzzle —new physics (NP) is needed. The two types of NP that can contribute to B → πK at tree level are Z ′ bosons and diquarks. Z ′ models can explain the puzzle if the Z ′ couples to right-handed uū and/or  <math><mi>d</mi><mover><mi>d</mi><mo>¯</mo></mover></math> $$ d\overline{d} $$, with g  R  dd  ≠ g  R  uu . Interestingly, half of the many Z ′ models proposed to explain the present anomalies in b → sμ + μ − decays have the required Z ′ couplings to uū and/or  <math><mi>d</mi><mover><mi>d</mi><mo>¯</mo></mover></math> $$ d\overline{d} $$. Such models could potentially explain both the b → sμ + μ − anomalies and the B → πK puzzle. The addition of a color sextet diquark that couples to ud can also explain the puzzle.

Canada

Nicolas Beaudry

David London

Jean-Samuel Roux

The B → πK puzzle revisited

In a recent paper we studied the effect of new-physics operators with different Lorentz structures on the semileptonic Λ b → Λ c τ ν ¯ τ $$ {\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau } $$ decay. This decay is of interest in light of the R ( D (*) ) puzzle in the semileptonic B ¯ → D ∗ τ ν ¯ τ $$ \overline{B}\to {D}^{\left(\ast \right)}\tau {\overline{\nu}}_{\tau } $$ decays. In this work we add tensor operators to extend our previous results and consider both model-independent new physics (NP) and specific classes of models proposed to address the R ( D (*) ) puzzle. We show that a measurement of R Λ c = ℬ Λ b → Λ c τ ν ¯ τ / ℬ Λ b → Λ c ℓ ν ¯ ℓ $$ R\left({\Lambda}_c\right)=\mathrm{\mathcal{B}}\left[{\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau}\right]/\mathrm{\mathcal{B}}\left[{\Lambda}_b\to {\Lambda}_c\ell {\overline{\nu}}_{\ell}\right] $$ can strongly constrain the NP parameters of models discussed for the R ( D (*) ) puzzle. We use form factors from lattice QCD to calculate all Λ b → Λ c τ ν ¯ τ $$ {\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau } $$ observables. The Λ b → Λ c tensor form factors had not previously been determined in lattice QCD, and we present new lattice results for these form factors here.