Triangle Singularity in the Production of $T_{cc}^+$(3875) and a Soft Pion

Abstract

The double-charm tetraquark meson T + cc (3875) can be produced in high-energy proton-proton collisions by the creation of the charm mesons D * + D 0 at short distances followed by their binding into T + cc . The T + cc can also be produced by the creation of D * + D * + at short distances followed by their rescattering into T + cc π + . A charm-meson triangle singularity produces a narrow peak in the T + cc π + invariant mass distribution 6.1 MeV above the threshold with a width of about 1 MeV. Well beyond the peak, the differential cross section decreases with the invariant kinetic energy E of T + cc π + as E −1/2 . The fraction of T + cc that are accompanied by π + with E < m π is estimated to be roughly 3%. The fraction of T + cc events with T + cc π + in the narrow peak from the triangle singularity could be comparable.

An updated review of the new hadron states

“…The productions of the T + cc in the γp reaction, proton-proton collisions, and heavy ion collisions were studied in Refs. [529,530,396,531] as the DD * molecular state of I(J P ) = 0(1 + ), and its quasifission phenomenon induced by the nucleons was studied in Ref. [532].…”

Chiral perturbation theory for heavy hadrons and chiral effective field theory for heavy hadronic molecules

“…The D * D molecular states had been predicted [261,262,263,264] before the experimental observations. The discovery of the T cc also inspired huge amounts of investigations [265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285].…”

“…55(b). Recently, the similar triangle singularity was investigated for the production of the T + cc [281]. We refer to the review [1022] for details of triangle singularity.…”

Triangle singularities in the $T^+_{cc}\to D^{*+}D^0\toπ^+D^0D^0$ decay width

“…Over the next days, weeks and months, a very interesting discussion is going on in the literature about the possible internal structure of the T + cc state, about the mechanisms of its production and decay through intermediate states D * + D 0 and D * 0 D + , on the possible values of its total decay width and partial decay widths into coupled channels π + D 0 D 0 , π 0 D 0 D + and γD 0 D + , about its line shape and the shapes of the two-particle mass spectra DD and πD, as well as about the possible existence of other similar states. A detailed discussion of all these issues can be found in [5][6][7][8][9][10][11][12][13][14][15], see also the references cited therein.…”