Photon polarization from helicity suppression in radiative decays of polarized Lambda_b to spin-3/2 baryons

Abstract

We give a general parameterization of the Lambda_b --> Lambda(1520) gamma decay amplitude, applicable to any strange isosinglet spin-3/2 baryon, and calculate the branching fraction and helicity amplitudes. Large-energy form factor relations are worked out, and it is shown that the helicity-3/2 amplitudes vanish at lowest order in soft-collinear effective theory (SCET). The suppression can be tested experimentally at the LHC and elsewhere, thus providing a benchmark for SCET. We apply the results to assess the experimental reach for a possible wrong-helicity b --> s gamma dipole coupling in Lambda_b --> Lambda(1520) gamma --> p K gamma decays. Furthermore we revisit Lambda_b-polarization at hadron colliders and update the prediction from heavy-quark effective theory. Opportunities associated with b --> d gamma afforded by high-statistics Lambda_b samples are briefly discussed in the general context of CP and flavour violation.

elsart, 15 pages, 1 figure; final version as published in Phys. Lett. B

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• Measurements of the Lambda_b0 -> J/psi Lambda decay amplitudes and the Lambda_b0 polarisation in pp collisions at sqrt(s) = 7 TeV
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• FCNC $B_s$ and ${\Lambda }_b$ transitions: Standard Model versus a single Universal Extra Dimension scenario
• ${\Lambda }_b\to {\Lambda }^{\ast }(1520){\ell }^{+}{\ell }^{-}$ form factors from lattice QCD
• Endpoint Relations for Baryons
• Rare b hadron decays at the LHC
• Measurement of the ${\Lambda }_b^0\to J/\psi \Lambda$ angular distribution and the ${\Lambda }_b^0$ polarisation in $pp$ collisions
• Angular analysis of the rare decay ${\Lambda }_b\to \Lambda (1520)(\to NK){\ell }^{+}{\ell }^{-}$
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• Note on new interesting baryon channels to measure the photon polarization in b -> s gamma
• Sizable Time-reversal violating effects in bottom baryon decays
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• Asymmetry in ${\Lambda }_b$ and ${\bar{\Lambda }}_b$ production
• Using an amplitude analysis to measure the photon polarisation in $B\to K\pi \pi \gamma$ decays
• Theoretical Status of Rare B Decays with Muons
• Di-vector boson production in association with a Higgs boson at hadron colliders
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• Heavy quark expansion of ${\Lambda }_b\to {\Lambda }^{\ast }(1520)$ form factors beyond leading order
• Probing new physics effects in ${\Lambda }_b\to \Lambda (\to p{\pi }^{-}){\ell }^{+}{\ell }^{-}$ decay via model independent approach
• Search for the semileptonic decays ${\Xi }_c^0\to {\Xi }^0{\ell }^{+}{\ell }^{-}$ at Belle