We present a model for the <math><mi>J</mi><mo>/</mo><mi>ψ</mi><mspace width="0.2em"></mspace><mi>Λ</mi></math> spectrum in <math><msup><mrow><mi>B</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><mspace width="0.2em"></mspace><mi>Λ</mi><mspace width="0.2em"></mspace><mover><mrow><mi>p</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> decays, including the <math><msubsup><mrow><mi>P</mi></mrow><mrow><mi>ψ</mi><mi>s</mi></mrow><mrow><mi>Λ</mi></mrow></msubsup><mo>(</mo><mn>4338</mn><mo>)</mo></math> baryon recently observed by the LHCb collaboration. We assume production via triangle diagrams which couple to the final state via non-perturbative interactions which are constrained by heavy-quark and <math><mi>S</mi><msub><mrow><mi>U</mi></mrow><mrow><mn>3</mn></mrow></msub></math>-flavor symmetry. The bulk of the distribution is described by a triangle diagram with a color-favored electroweak vertex, while the sharp <math><msubsup><mrow><mi>P</mi></mrow><mrow><mi>ψ</mi><mi>s</mi></mrow><mrow><mi>Λ</mi></mrow></msubsup><mo>(</mo><mn>4338</mn><mo>)</mo></math> enhancement is due to the triangle singularity in another diagram featuring a <math><mn>1</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>−</mo></mrow></msup></math> baryon consistent with <math><msub><mrow><mi>Σ</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>(</mo><mn>2800</mn><mo>)</mo></math>. We predict a comparable <math><msubsup><mrow><mi>P</mi></mrow><mrow><mi>ψ</mi><mi>s</mi></mrow><mrow><mi>Λ</mi></mrow></msubsup><mo>(</mo><mn>4338</mn><mo>)</mo></math> signal in <math><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub><mspace width="0.2em"></mspace><mi>Λ</mi></math>, and anticipate possible large isospin mixing effects through decays to <math><mi>J</mi><mo>/</mo><mi>ψ</mi><mspace width="0.2em"></mspace><msup><mrow><mi>Σ</mi></mrow><mrow><mn>0</mn></mrow></msup></math> and <math><msub><mrow><mi>η</mi></mrow><mrow><mi>c</mi></mrow></msub><mspace width="0.2em"></mspace><msup><mrow><mi>Σ</mi></mrow><mrow><mn>0</mn></mrow></msup></math>.

United Kingdom

T.J. Burns

United States

E.S. Swanson

The LHCb state As a Triangle Singularity

We examine whether the LHCb vector <math><mi>u</mi><mi>d</mi><mover><mrow><mi>c</mi></mrow><mrow><mo>¯</mo></mrow></mover><mover><mrow><mi>s</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> state <math><mi>X</mi><mo>(</mo><mn>2900</mn><mo>)</mo></math> can be interpreted as a kinematical cusp effect arising from <math><msup><mrow><mover><mrow><mi>D</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mrow><mo>⁎</mo></mrow></msup><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math> and <math><msub><mrow><mover><mrow><mi>D</mi></mrow><mrow><mo>¯</mo></mrow></mover></mrow><mrow><mn>1</mn></mrow></msub><msup><mrow><mi>K</mi></mrow><mrow><mo>(</mo><mo>⁎</mo><mo>)</mo></mrow></msup></math> interactions. The production amplitude is modelled as a triangle diagram with hadronic final state interactions. A satisfactory fit to the Dalitz plot projection is obtained that leverages the singularities of the production diagram without the need for <math><mover><mrow><mi>D</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>K</mi></math> resonances. A somewhat better fit is obtained if the final state interactions are strong enough to generate resonances, although the evidence in favour of this scenario is not conclusive.

Kinematical cusp and resonance interpretations of the (2900)

A variety of options for interpreting the DØ state, X(5568) , are examined. We find that threshold, cusp, molecular, and tetraquark models are all unfavoured. Several experimental tests for unravelling the nature of the signal are suggested.

Interpreting the X (5568)

A.J. Bevan

Slovenia

B. Golob

Germany

Th. Mannel

S. Prell

Australia

B.D. Yabsley

Japan

H. Aihara

Italy

F. Anulli

France

N. Arnaud

Russia

T. Aushev

M. Beneke

J. Beringer

F. Bianchi

I.I. Bigi

M. Bona

N. Brambilla

Poland

J. Brodzicka

Taiwan

P. Chang

M.J. Charles

C.H. Cheng

China

H.Y. Cheng

R. Chistov

P. Colangelo

J.P. Coleman

A. Drutskoy

V.P. Druzhinin

S. Eidelman

Norway

G. Eigen

A.M. Eisner

R. Faccini

K.T. Flood

P. Gambino

A. Gaz

W. Gradl

H. Hayashii

T. Higuchi

W.D. Hulsbergen

T. Hurth

T. Iijima

R. Itoh

P.D. Jackson

R. Kass

Yu. G. Kolomensky

E. Kou

P. Križan

A. Kronfeld

S. Kumano

South Korea

Y.J. Kwon

T.E. Latham

D.W.G.S. Leith

V. Lüth

Spain

F. Martinez-Vidal

B.T. Meadows

R. Mussa

M. Nakao

S. Nishida

J. Ocariz

S.L. Olsen

P. Pakhlov

G. Pakhlova

A. Palano

A. Pich

S. Playfer

A. Poluektov

F.C. Porter

Canada

S.H. Robertson

J.M. Roney

A. Roodman

Y. Sakai

Austria

C. Schwanda

A.J. Schwartz

R. Seidl

S.J. Sekula

M. Steinhauser

K. Sumisawa

F. Tackmann

K. Trabelsi

S. Uehara

S. Uno

R. van de Water

G. Vasseur

W. Verkerke

R. Waldi

M.Z. Wang

F.F. Wilson

J. Zupan

A. Zupanc

I. Adachi

J. Albert

Sw. Banerjee

M. Bellis

E. Ben-Haim

P. Biassoni

R.N. Cahn

C. Cartaro

J. Chauveau

C. Chen

C.C. Chiang

R. Cowan

J. Dalseno

The Physics of the B Factories