Probing for New Physics in Polarized ${\Lambda }_b$ decays at the Z

Abstract

Polarized ${\Lambda }_b\to \Lambda \gamma$ decays at the Z pole are shown to be well suited for probing a large variety of New Physics effects. A new observable is proposed, the angular asymmetry between the ${\Lambda }_b$ spin and photon momentum, which is sensitive to the relative strengths of the opposite chirality and Standard Model chirality $b\to s\gamma$ dipole operators. Combination with the $\Lambda$ decay polarization asymmetry and comparison with the ${\Lambda }_b$ polarization extracted from semileptonic decays allows important tests of the $V-A$ structure of the Standard Model. Modifications of the rates and angular asymmetries which arise at next-to-leading order are discussed. Measurements for ${\Lambda }_b\to \Lambda \gamma$ and the CP conjugate mode, with branching ratios of a few times $10^{-5}$, are shown to be sensitive to non-standard sources of CP violation in the ${\Lambda }_b\to \Lambda \gamma$ matrix element. Form factor relations for heavy-to-light baryon decays are derived in the large energy limit, which are of general interest.

18 pages, 2 figures, comments and references on 1/m effects added, conclusions unchanged, version to appear in PRD

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• Constraints on new physics from radiative $B$ decays
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• Rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma : Differential and total rates, lepton- and hadron-side forward-backward asymmetries
• Rare Decays of Λ_b->Λ+ γand Λ_b ->Λ+ l^{+} l^{-} in the Light-cone Sum Rules
• The photon polarization in B -> X gamma in the standard model
• Angular Analysis of the Decay ${\Lambda }_b\to \Lambda (\to N\pi ){\ell }^{+}{\ell }^{-}$
• New Physics at a Super Flavor Factory
• R-parity-violating SUSY and CP violation in B --> phi K_s
• Heavy-to-light baryonic form factors at large recoil
• Time-dependent CP Asymmetry in B->K* gamma as a (Quasi) Null Test of the Standard Model
• Photon polarization in radiative B decays
• Mixing-Induced CP Violation in B -> P_1 P_2 gamma in Search of Clean New Physics Signals
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• Photon polarization from helicity suppression in radiative decays of polarized Lambda_b to spin-3/2 baryons
• Factorization of Heavy-to-Light Baryonic Transitions in SCET
• New-Physics Effects on Triple-Product Correlations in Lambda_b Decays
• Light-Cone Distribution Amplitudes of the Ground State Bottom Baryons in HQET
• Exclusive (Lambda_b -> Lambda l^+ l^-) decay beyond standard model
• T-Violating Triple-Product Correlations in Charmless Lambda_b Decays
• Rare radiative charm decays within the standard model and beyond
• Exclusive semileptonic decays of ${\Lambda }_b\to \Lambda l^{+}{l}^{-}$ in supersymmetric theories
• Model independent analysis of 'Lambda' baryon polarizations in (Lambda_b -> Lambda l^+ l^-) decay
• Angular distribution of polarised ${\Lambda }_b$ baryons decaying to $\Lambda {\ell }^{+}{\ell }^{-}$
• The CP asymmetry in B^0(t) -> K_S π^0 γin the Standard Model
• (Lambda_b -> Lambda l^+ l^-) decay in universal extra dimensions
• T violation in ${\Lambda }_b\to \Lambda {\ell }^{+}{\ell }^{-}$ decays with polarized $\Lambda$
• FCNC $B_s$ and ${\Lambda }_b$ transitions: Standard Model versus a single Universal Extra Dimension scenario
• Rare decays of ${\Lambda }_b\to \Lambda \gamma$ and ${\Lambda }_b\to \Lambda l^{+}{l}^{-}$ in universal extra dimension model
• First observation of the radiative decay ${\Lambda }_b^0\to \Lambda \gamma$
• Heavy Flavour Physics and CP Violation at LHCb: a Ten-Year Review
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• Polarization effects in exclusive semileptonic (Lambda_b -> Lambda l^+ l^-) decay
• Photon helicity in Lambda_b --> p K gamma decays
• Squark Flavor Implications from B --> K(*) l+ l-
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• Effect of both Z and Z'-mediated flavor-changing neutral currents on the baryonic rare decay $lambd{a}_b$ decays into $lambda{l}^{+}{l}^{-}$
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• The photon polarization in radiative $D$ decays, phenomenologically
• CP violation in multibody decays of beauty baryons
• Unparticle physics effects in (Lambda_b -> Lambda + missing energy) processes
• Pinning down $|\Delta c|=|\Delta u|=1$ couplings with rare charm baryon decays
• Note on new interesting baryon channels to measure the photon polarization in b -> s gamma
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• Lambda hyperon as helicity analyzer of s quark in B decay
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• Contribution of low-lying vector resonances to polarization observables in \bar B_d^0 -> \bar K*0 e+ e- decay
• On the photon polarization in radiative B -> phi K gamma decay
• Probing photon helicity in radiative B decays via charmonium resonance interference
• ${\Xi }_b\to \Xi$ form factors from lattice QCD and Standard-Model predictions for ${\Xi }_b\to \Xi {\mu }^{+}{\mu }^{-}$ and ${\Xi }_b\to \Xi \gamma$ decays
• Recent progress in decays of $b$ and $c$ hadrons
• Probing new physics effects in ${\Lambda }_b\to \Lambda (\to p{\pi }^{-}){\ell }^{+}{\ell }^{-}$ decay via model independent approach