Heating triangle singularities in heavy ion collisions

Abstract

We predict that triangle singularities of hadron spectroscopy can be strongly affected in heavy ion collisions. To do it we examine various effects on the singularity-inducing triangle loop of finite temperature in the terminal hadron phase. It appears that peaks seen in central heavy ion collisions are more likely to be hadrons than rescattering effects under two conditions. First, the flight-time of the intermediate hadron state must be comparable to the lifetime of the equilibrated fireball (else, the reaction mostly happens in vacuo after freeze out). Second, the medium effect over the triangle-loop particle mass or width must be sizeable. When these (easily checked) conditions are met, the medium quickly reduces the singularity: at T about 150 MeV, even by two orders of magnitude, acting then as a spectroscopic filter.

New 𝒁𝒄 spectroscopy or Landau singularities? Searches in Heavy Ion Collisions could help decide

“…𝑍 𝑐 (3900) ±/0 𝑍 𝑐 (3885) ±/0 𝑍 𝑐 (4020) ±/0 𝑍 𝑐 (4025) Aside from the examples analyzed earlier [1], we have recently examined whether heavy ion collisions can make a statement about the nature of two of those new exotic states: the 𝑍 𝑐 (3900) state seen in 𝑌 (4260) → 𝐽/𝜓𝜋𝜋 decays [6], and the 𝑍 𝑐𝑠 (3985) structure newly observed by the BESIII Collaboration [7]. We here present another emblematic illustration in this series of studies on the interpretation of the exotic hadronic states, turning to the charged 𝑍 𝑐 (4020) state, the third entry in table 1.…”

“…We have recently suggested [1] that triangle singularities, engendered by kinematics complying with the Coleman-Norton theorem, might be strongly affected by the medium in a heavy-ion collision environment. The effect takes place only under the following conditions: the triangle reaction must be completed in the lifetime of the fireball; and the mass or width of the particles in the triangle diagram must be sufficiently altered from their vacuum values.…”

“…Analogously to the 𝑍 𝑐 (3900) structure investigated in [6], this is a typical reaction that should see the triangle singularity notably influenced by the medium in a heavy-ion collision, due to the fulfillment of the two alluded conditions. First, the time of flight of the particles in the triangle (as computed in [1]) is 𝜏 𝐴 ∼ 9 fm/c (with the values of 𝑚 𝐶 = 4020 MeV and Γ 𝐷 1 = 31 MeV), sufficiently short for the triangle reaction to often be completed in a relativistic heavy ion collision (remarking that the duration of the hadronic phase is of the order of 10 fm/c). And second, the masses and widths of the 𝐷-family mesons in the triangle diagram are sufficiently altered from their vacuum values, as shown in Table 2.…”

“…We assumed 𝑚 𝜋 to be constant (see Ref. [1] for a detailed discussion). The mass of the initial state is fixed at 𝑚 𝐴 = 4.430 GeV.…”

Exotic hadrons in heavy ion collisions

“…Here we introduce the formalism employed to describe the time evolution of the abundance of a given state during the hadronic stage of heavy ion collisions. It is influenced by the interactions among and other light particles (denoted henceforth as ) constituting the medium, and can be investigated using the momentum-integrated evolution equation [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]39]…”