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Jet fragmentation transverse momentum measurements from di-hadron correlations in $\sqrt{s}$ = 7 TeV pp and $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV p-Pb collisions

The transverse structure of jets was studied via jet fragmentation transverse momentum ($j_{\rm{T}}$) distributions, obtained using two-particle correlations in proton-proton and proton-lead collisions, measured with the ALICE experiment at the LHC. The highest transverse momentum particle in each event is used as the trigger particle and the region $3 <~ p_{\rm{Tt}} <~ 15$ GeV/$c$ is explored in this study. The measured distributions show a clear narrow Gaussian component and a wide non-Gaussian one. Based on Pythia simulations, the narrow component can be related to non-perturbative hadronization and the wide component to quantum chromodynamical splitting. The width of the narrow component shows a weak dependence on the transverse momentum of the trigger particle, in agreement with the expectation of universality of the hadronization process. On the other hand, the width of the wide component shows a rising trend suggesting increased branching for higher transverse momentum. The results obtained in pp collisions at $\sqrt{s}$ = 7 TeV and in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV are compatible within uncertainties and hence no significant cold nuclear matter effects are observed. The results are compared to previous measurements from CCOR and PHENIX as well as to Pythia 8 and Herwig 7 simulations.

 

J. High Energ. Phys. (2019) 2019: 169
HEP Data
e-Print: arXiv:1811.09742 | PDF | inSPIRE
CERN-EP-2018-303

Figures

Figure 1

. Illustration of $\vjt{}$ and $\xlong$. The jet fragmentation transverse momentum, $\vjt{}$, is defined as the transverse momentum component of the associated particle momentum, $\vec{p}_{\mathrm{a}}$, with respect to the trigger particle momentum, $\vec{p}_{\mathrm{t}}$. The fragmentation variable $\xlong$ is the projection of $\vec{p}_{\mathrm{a}}$ to $\vec{p}_{\mathrm{t}}$ divided by $p_{\mathrm{t}}$.
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Figure 2

. Results from a \textsc{Pythia}~8 study with a di-gluon initial state. The circular symbols are obtained when the final-state shower is enabled. The square symbols show the distribution without final-state showering. The diamond symbols representing soft radiation are obtained as a difference between the other two distributions. The distribution without final-state showering is fitted with a Gaussian and the soft radiation part with an inverse gamma function.
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Figure 3

. \emph{Left:} Measured $\jt{}$ distribution including a three-component fit. The three components describe the background (circular symbols), hadronization (long dashed line), and showering (short dashed line). \emph{Right:} The same $\jt{}$ distribution but with background subtracted.
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Figure 4

. RMS values of the narrow and wide $\jt{}$ components. Results from $\pp$ collisions at $\sqrtSE{7}$ (circular symbols) and from $\pPb$ collisions at $\sqrtSnnE{5.02}$ (square symbols) are compared to \textsc{Pythia}~8 tune 4C simulations at $\sqrtSE{7}$ (short dashed line) and at $\sqrtSE{5.02}$ (long dashed line). Different panels correspond to different $\xlong$ bins with $0.2 < \xlong < 0.4$ on the left, $0.4 < \xlong < 0.6$ in the middle, and $0.6 < \xlong < 1.0$ on the right. The statistical errors are represented by bars and the systematic errors by boxes.
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Figure 5

. Yields of the narrow and wide $\jt{}$ components. Results from $\pp$ collisions at $\sqrtSE{7}$ (circular symbols) and from $\pPb$ collisions at $\sqrtSnnE{5.02}$ (square symbols) are compared to \textsc{Pythia}~8 tune 4C simulations at $\sqrtSE{7}$ (short dashed line) and at $\sqrtSE{5.02}$ (long dashed line). Different panels correspond to different $\xlong$ bins with $0.2 < \xlong < 0.4$ on the left, $0.4 < \xlong < 0.6$ in the middle, and $0.6 < \xlong < 1.0$ on the right. The statistical errors are represented by bars and the systematic errors by boxes
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Figure 6

. RMS values of the narrow and wide $\jt{}$ components for $\pp$ collisions at $\sqrtSE{7}$ (circular symbols) compared to \textsc{Pythia}~8 tunes 4C (dashed line) and Monash (short dashed line), and Herwig~7 LHC-MB tune (long dashed line) at the same energies. Different panels correspond to different $\xlong$ bins with $0.2 < \xlong < 0.4$ on the left, $0.4 < \xlong < 0.6$ in the middle, and $0.6 < \xlong < 1.0$ on the right. The statistical errors are represented by bars and the systematic errors by boxes
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Figure 7

. Yields of the narrow and wide $\jt{}$ components for $\pp$ collisions at $\sqrtSE{7}$ (circular symbols) compared to \textsc{Pythia}~8 tunes 4C (dashed line) and Monash (short dashed line), and Herwig~7 LHC-MB tune (long dashed line) at the same energies. Different panels correspond to different $\xlong$ bins with $0.2 < \xlong < 0.4$ on the left, $0.4 < \xlong < 0.6$ in the middle, and $0.6 < \xlong < 1.0$ on the right. The statistical errors are represented by bars and the systematic errors by boxes
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Figure 8

. Narrow component RMS in different $\xlong$ bins compared with lower beam energy single component results from PHENIX~ and CCOR~.
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