Measurement of the $k_T$ Distribution of Particles in Jets Produced in $p\overline{p}$ Collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We present a measurement of the transverse momentum with respect to the jet axis ($k_t$) of particles in jets produced in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. Results are obtained for charged particles in a cone of 0.5 radians around the jet axis in events with dijet invariant masses between 66 and $737\mathrm{GeV}/c^2$. The experimental data are compared to theoretical predictions obtained for fragmentation partons within the framework of resummed perturbative QCD using the modified leading log and next-to-modified leading log approximations. The comparison shows that trends in data are successfully described by the theoretical predictions, indicating that the perturbative QCD stage of jet fragmentation is dominant in shaping basic jet characteristics.

Figure 1

NMLLA predictions [2] of the $k_T$ distribution in jets. The figures show how the distribution depends on (a) the jet hardness (shown for a gluon jet), (b) the origin of the jet (quark or gluon), and (c) the parton shower cutoff $Q_{\mathrm{eff}}$. $N^{\prime }$ is the number of partons in the region $-0.2<\ln [k_T/(\mathrm{GeV}/c)]<0.0$.

Figure 2

The $k_T$ distribution of particles in the restricted cone of size ${\theta }_c=0.5$ around the jet axis in dijet mass bins with (a) $Q=27$, (b) $Q=68$, and (c) $Q=119\mathrm{GeV}$. The data are compared to the analytical MLLA and NMLLA predictions and to the predictions of the pythia tune A Monte Carlo generator for partons and charged hadrons (shown as histograms). The distribution for partons is obtained using a parton shower cutoff value of 500 MeV. Ranges of validity for MLLA and NMLLA predictions are shown by arrows. $N^{\prime }$ is the number of particles in the region $-0.2<\ln [k_T/(\mathrm{GeV}/c)]<0.0$.