Jet axes and universal transverse-momentum dependent fragmentation

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We study the transverse momentum spectrum of hadrons in jets. By measuring the transverse momentum with respect to a judiciously chosen axis, we find that this observable is insensitive to ( the recoil of) soft radiation. Furthermore, for small transverse momenta we show that the effects of the jet boundary factorize, leading to a new transverse-momentum-dependent (TMD) fragmentation function. In contrast to the usual TMD fragmentation functions, it does not involve rapidity divergences and is universal in the sense that it is independent of the type of process and number of jets. These results directly apply to sub-jets instead of hadrons. We discuss potential applications, which include studying nuclear modification effects in heavy-ion collisions and identifying boosted heavy resonances.
© The Authors. We thank A. Papaefstathiou, M. Procura, J. Thaler and L. Zoppi for comments on this manuscript. I.S. is supported by the Spanish MECD grants FPA2014-53375-C2-2-P, FPA2016-75654-C2-2-P and the group UPARCOS. W.W. is supported by the ERC grant ERC-STG-2015-677323 and the D-ITP consortium, a program of the Netherlands Organization for Scientific Research (NWO) that is funded by the Dutch Ministry of Education, Culture and Science (OCW). D.N. acknowledges support from US Department of Energy contract DE-AC52-06NA25396 and through the LANL/LDRD Program. We also thank the Erwin Schr¨odinger Institute program “Challenges and Concepts for Field Theory and Applications in the Era of the LHC Run-2”, where this work was initiated.
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