Measurement of Charged Hadron Production in $Z$-Tagged Jets in Proton-Proton Collisions at $\sqrt{s}=8\mathrm{TeV}$

The production of charged hadrons within jets recoiling against a $Z$ boson is measured in proton-proton collision data at $\sqrt{s}=8\mathrm{TeV}$ recorded by the LHCb experiment. The charged-hadron structure of the jet is studied longitudinally and transverse to the jet axis for jets with transverse momentum $p_T>20\mathrm{GeV}$ and in the pseudorapidity range $2.5<\eta <4$. These are the first measurements of jet hadronization at these forward rapidities and also the first where the jet is produced in association with a $Z$ boson. In contrast to previous hadronization measurements at the Large Hadron Collider, which are dominated by gluon jets, these measurements probe predominantly light-quark jets which are found to be more longitudinally and transversely collimated with respect to the jet axis when compared to the previous gluon dominated measurements. Therefore, these results provide valuable information on differences between quarks and gluons regarding nonperturbative hadronization dynamics.

Figure 1

Distributions of the longitudinal momentum fraction of the hadron with respect to the jet in three bins of jet $p_T$. The bars (boxes) show the statistical (systematic) uncertainties.

Figure 2

Distributions of the transverse momentum of charged hadrons with respect to the jet axis in three bins of jet $p_T$. The bars (boxes) show the statistical (systematic) uncertainties.

Figure 3

Radial profile distributions of hadrons with respect to the jet axis in three bins of jet $p_T$. The bars (boxes) show the statistical (systematic) uncertainties.

Figure 4

The $z$ distribution for jets with $30<p_T<50\mathrm{GeV}$ compared to pythia8 simulation predictions. The bars (boxes) show the statistical (systematic) uncertainties.