Searching for enhancement in coalescence of in-jet (anti-)deuterons in proton-proton collisions

Recent measurements from ALICE report that “in-jet” nucleons carry a higher probability of forming a deuteron via coalescence than the nucleons from the underlying event (UE). This study makes use of an event shape classifier to separate the “in-jet” deuterons and the deuterons in the UE produced in high multiplicity proton-proton collisions at $\sqrt{s}=13$ TeV. Event shape variables such as transverse spherocity allow the categorization of hard and soft components of an event, which can be divided into two respective classes; “jetty” and “isotropic”. The “jetty” deuterons minus the contribution of the deuterons from the “isotropic” event are taken as “in-jet” deuterons, and the coalescence mechanism is tested. The coalescence is performed with a Wigner function formalism, augmented as an afterburner to pythia8. The possible enhancement of the coalescence probability of “in-jet” deuterons is investigated by calculating the coalescence parameter ($B_2$) in different spherocity classes in high-multiplicity $pp$ collisions.

Figure 1

Charged-particle multiplicity distributions from pythia8 $+$ Monash (dotted lines) for $pp$ collisions at $\sqrt{s}=$ 13 TeV. Data from ALICE (solid lines) for the midrapidity multiplicity estimator ($N_{\mathrm{tracklet}}^{\left|\eta \right|<0.8}$) and the V0M detector are presented for comparison [41, 42].

Figure 2

Wigner probability distributions of different deuteron wave functions.

Figure 3

Pictorial depiction of the resonance source model to describe the emission of (anti-)nucleon pairs in $pp$ collisions.

Figure 4

Source radius ($r_0$ and $r_{\mathrm{core}}$) as a function of pair transverse mass ($\langle m_{\mathrm{T}}\rangle$) extracted from ALICE measurements [31].

Figure 5

Source functions for $p-p$ for primordial $r_{\mathrm{core}}$ = 1.2 fm and from decay emission $r_0$ = 1.28 fm. The markers are extracted from the ALICE measurement that shows $p-p$ sources with one proton coming from a resonance decay. The points are fitted using a modified exponential Gaussian function (solid red line) [31].

Figure 6

Transverse spherocity distributions from pythia8 $+$ Monash (lines) for $pp$ collisions at $\sqrt{s}=$ 13 TeV. Data points from ALICE (markers) in the 0–1 % multiplicity for the midrapidity estimator ($N_{\mathrm{tracklet}}^{\left|\eta \right|<0.8}$ I) and the V0M detector (V0M I) with events having $N_{\mathrm{ch}}>10$ are presented for comparison [44].

Figure 7

Transverse momentum spectra of (anti-)protons from pythia8 (left), and deuterons and anti-deuterons from $pp$ collisions at $\sqrt{s}=$ 13 TeV with pythia8$+$Coalescence in MB I and HM I class at midrapidity ($\left|y\right|<0.5$) in two detector acceptances. (Center) Predictions from a single Gaussian deuteron wave-function scaled twice to their actual values. (Right) Predictions from a two-Gaussian deuteron wave function. Results are compared to measurements from ALICE in respective multiplicity intervals [9, 10].

Figure 8

Transverse momentum spectra of (anti)-protons with pythia8 and (anti-)deuterons with pythia8$+$Coalescence in “jetty”, “isotropic”, and $S_{\mathrm{O}}$-integrated intervals at midrapidity ($\left|y\right|<0.5$) in $pp$ collisions at $\sqrt{s}=$ 13 TeV. Predictions from the model are presented in MB I (left) and HM I multiplicity interval (right).

Figure 9

Coalescence parameter of (anti-)deuterons $B_2$ as a function of proton transverse momentum at midrapidity ($\left|y\right|<0.5$) in $pp$ collisions at $\sqrt{s}=$ 13 TeV. Solid and dashed lines represent the predictions from single and double Gaussian wave functions, respectively. The results are compared to experimental measurements from ALICE [9, 10].