Measurement of the photon polarization in Λ0b → Λ γ decays

R. Aaij;A. ???S. ???W. Abdelmotteleb;C. Abell??n Beteta;F. Abudin??n;T. Ackernley;B. Adeva;M. Adinolfi;H. Afsharnia;C. Agapopoulou;C. ???A. Aidala;S. Aiola;Z. Ajaltouni;S. Akar;J. Albrecht;F. Alessio;M. Alexander;A. Alfonso Albero;Z. Aliouche;G. Alkhazov;P. Alvarez Cartelle;S. Amato;J. ???L. Amey;Y. Amhis;L. An;L. Anderlini;A. Andreianov;M. Andreotti;F. Archilli;A. Artamonov;M. Artuso;K. Arzymatov;E. Aslanides;M. Atzeni;B. Audurier;S. Bachmann;M. Bachmayer;J. ???J. Back;P. Baladron Rodriguez;V. Balagura;W. Baldini;J. Baptista Leite;M. Barbetti;R. ???J. Barlow;S. Barsuk;W. Barter;M. Bartolini;F. Baryshnikov;J. ???M. Basels;S. Bashir;G. Bassi;B. Batsukh;A. Battig;A. Bay;A. Beck;M. Becker;F. Bedeschi;I. Bediaga;A. Beiter;V. Belavin;S. Belin;V. Bellee;K. Belous;I. Belov;I. Belyaev;G. Bencivenni;E. Ben-Haim;A. Berezhnoy;R. Bernet;D. Berninghoff;H. ???C. Bernstein;C. Bertella;A. Bertolin;C. Betancourt;F. Betti;Ia. Bezshyiko;S. Bhasin;J. Bhom;L. Bian;M. ???S. Bieker;S. Bifani;P. Billoir;M. Birch;F. ???C. ???R. Bishop;A. Bitadze;A. Bizzeti;M. Bj??rn;M. ???P. Blago;T. Blake;F. Blanc;S. Blusk;D. Bobulska;J. ???A. Boelhauve;O. Boente Garcia;T. Boettcher;A. Boldyrev;A. Bondar;N. Bondar;S. Borghi;M. Borisyak;M. Borsato;J. ???T. Borsuk;S. ???A. Bouchiba;T. ???J. ???V. Bowcock;A. Boyer;C. Bozzi;M. ???J. Bradley;S. Braun;A. Brea Rodriguez;J. Brodzicka;A. Brossa Gonzalo;D. Brundu;A. Buonaura;L. Buonincontri;A. ???T. Burke;C. Burr;A. Bursche;A. Butkevich;J. ???S. Butter;J. Buytaert;W. Byczynski;S. Cadeddu;H. Cai;R. Calabrese;L. Calefice;L. Calero Diaz;S. Cali;R. Calladine;M. Calvi;M. Calvo Gomez;P. Camargo Magalhaes;P. Campana;A. ???F. Campoverde Quezada;S. Capelli;L. Capriotti;A. Carbone;G. Carboni;R. Cardinale;A. Cardini;I. Carli;P. Carniti;L. Carus;K. Carvalho Akiba;A. Casais Vidal;G. Casse;M. Cattaneo;G. Cavallero;S. Celani;J. Cerasoli;D. Cervenkov;A. ???J. Chadwick;M. ???G. Chapman;M. Charles;Ph. Charpentier;G. Chatzikonstantinidis;C. ???A. Chavez Barajas;M. Chefdeville;C. Chen;S. Chen;A. Chernov;V. Chobanova;S. Cholak;M. Chrzaszcz;A. Chubykin;V. Chulikov;P. Ciambrone;M. ???F. Cicala;X. Cid Vidal;G. Ciezarek;P. ???E. ???L. Clarke;M. Clemencic;H. ???V. Cliff;J. Closier;J. ???L. Cobbledick;V. Coco;J. ???A. ???B. Coelho;J. Cogan;E. Cogneras;L. Cojocariu;P. Collins;T. Colombo;L. Congedo;A. Contu;N. Cooke;G. Coombs;I. Corredoira;G. Corti;C. ???M. Costa Sobral;B. Couturier;D. ???C. Craik;J. Crkovsk??;M. Cruz Torres;R. Currie;C. ???L. Da Silva;S. Dadabaev;L. Dai;E. Dall???Occo;J. Dalseno;C. D???Ambrosio;A. Danilina;P. d???Argent;J. ???E. Davies;A. Davis;O. De Aguiar Francisco;K. De Bruyn;S. De Capua;M. De Cian;J. ???M. De Miranda;L. De Paula;M. De Serio;D. De Simone;P. De Simone;F. De Vellis;J. ???A. de Vries;C. ???T. Dean;F. Debernardis;D. Decamp;V. Dedu;L. Del Buono;B. Delaney;H. -P. Dembinski;A. Dendek;V. Denysenko;D. Derkach;O. Deschamps;F. Desse;F. Dettori;B. Dey;A. Di Cicco;P. Di Nezza;S. Didenko;L. Dieste Maronas;H. Dijkstra;V. Dobishuk;C. Dong;A. ???M. 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Martelli;G. Martellotti;L. Martinazzoli;M. Martinelli;D. Martinez Santos;F. Martinez Vidal;A. Massafferri;M. Materok;R. Matev;A. Mathad;V. Matiunin;C. Matteuzzi;K. ???R. Mattioli;A. Mauri;E. Maurice;J. Mauricio;M. Mazurek;M. McCann;L. Mcconnell;T. ???H. Mcgrath;N. ???T. Mchugh;A. McNab;R. McNulty;J. ???V. Mead;B. Meadows;G. Meier;N. Meinert;D. Melnychuk;S. Meloni;M. Merk;A. Merli;L. Meyer Garcia;M. Mikhasenko;D. ???A. Milanes;E. Millard;M. Milovanovic;M. -N. Minard;A. Minotti;L. Minzoni;S. ???E. Mitchell;B. Mitreska;D. ???S. Mitzel;A. M??dden;R. ???A. Mohammed;R. ???D. Moise;S. Mokhnenko;T. Momb??cher;I. ???A. Monroy;S. Monteil;M. Morandin;G. Morello;M. ???J. Morello;J. Moron;A. ???B. Morris;A. ???G. Morris;R. Mountain;H. Mu;F. Muheim;M. Mulder;D. M??ller;K. M??ller;C. ???H. Murphy;D. Murray;P. Muzzetto;P. Naik;T. Nakada;R. Nandakumar;T. Nanut;I. Nasteva;M. Needham;I. Neri;N. Neri;S. Neubert;N. Neufeld;R. Newcombe;E. ???M. Niel;S. Nieswand;N. Nikitin;N. ???S. Nolte;C. Normand;C. 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2022-01-01

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Abstract

The photon polarization in b→sγ transitions is measured for the first time in radiative b -baryon decays exploiting the unique spin structure of Λ0b→Λγ decays. A data sample corresponding to an integrated luminosity of 6  fb−1 collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV is used. The photon polarization is measured to be αγ=0.82+0.17+0.04−0.26−0.13, where the first uncertainty is statistical and the second systematic. This result is in agreement with the Standard Model prediction and previous measurements in b -meson decays. Charge-parity breaking effects are studied for the first time in this observable and found to be consistent with CP symmetry.