Speaker
Description
Identified-hadron measurements in $e^{+}e^{-}$ collisions provide a clean environment for studying parton fragmentation and hadronization, without the partonic initial-state structure, beam remnants, and underlying-event activity characteristic of hadronic collisions. This analysis uses the particle-identification capabilities of DELPHI, combining TPC $dE/dx$ and RICH information making it well-suited for this investigation at LEP energies. Using the archived DELPHI data [1] taken at the $Z$ pole ($\sqrt{s}=91.2$ GeV) during 1994-1995, we study the production of charged pions, kaons, and protons through identified-particle spectra, particle-species ratios, and transverse-momentum observables. The momentum is measured transverse to the event thrust axis, $P_{hT}$ differentially in the hadron energy fraction, $z_h = 2E_h/Q$ and in event thrust, which is sensitive to the transverse-momentum-dependent (TMD) fragmentation dynamics.
Measurements by Belle at $\sqrt{s}=10.58$ GeV have previously demonstrated a pronounced dependence of identified-hadron transverse-momentum spectra on hadron species, energy fraction, and event topology [2]. The DELPHI measurement extends such studies to the much larger scale $Q=M_Z$. The low $P_{hT}$ Gaussian widths of each species are compared between the two energies as inputs to TMD fragmentation-function analyses [3,4]. The substantially larger hard scale may also provide complementary sensitivity to the transverse-distance dependence of TMD evolution, for which the Belle analysis found limited sensitivity in the small-$b_T$ region [5].
In addition to the differential $P_{ hT}$ measurements, the energy dependence of $\langle P_{hT}\rangle$ and its particle-species ratios is also studied across LEP-1 and LEP-2 center-of-mass energies. Baryon-to-meson ratios, such as $p/\pi$, are also studied as functions of $P_{ hT}$ in various multiplicity classes, providing a differential comparison of their production within the fragmentation process. Thus, these results provide a high-$Q$ vacuum benchmark for hadronization and new experimental input for constraining the species dependence and scale evolution of transverse fragmentation.
[1] DELPHI Collaboration, open data, http://doi.org/10.7483/OPENDATA.DELPHI.0XNE.G96F, http://doi.org/10.7483/OPENDATA.DELPHI.K4LR.4PQ4
[2] Belle Collaboration, R. Seidl, et al., Phys. Rev. D 99 (2019) 112006.
[3] Y. Makris, F. Ringer, W. J. Waalewijn, JHEP 02 (2021) 070;
M. Boglione, A. Simonelli, JHEP 02 (2021) 076.
[4] A. Bacchetta, M. G. Echevarria, P. J. Mulders, M. Radici, A. Signori, JHEP 11, 76 (2015).
[5] M. Boglione, J. O. Gonzalez-Hernandez, A. Simonelli, Phys. Rev. D 106, 074024 (2022)