130 research outputs found

    Initial-state splitting kernels in cold nuclear matter

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    We derive medium-induced splitting kernels for energetic partons that undergo interactions in dense QCD matter before a hard-scattering event at large momentum transfer Q2Q^2. Working in the framework of the effective theory SCETG{\rm SCET}_{\rm G}\,, we compute the splitting kernels beyond the soft gluon approximation. We present numerical studies that compare our new results with previous findings. We expect the full medium-induced splitting kernels to be most relevant for the extension of initial-state cold nuclear matter energy loss phenomenology in both p+A and A+A collisions.Comment: 8 pages, 4 figure

    QCD resummation for semi-inclusive hadron production processes

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    We investigate the resummation of large logarithmic perturbative corrections to hadron production in electron-positron annihilation and semi-inclusive deep-inelastic scattering. We find modest, but significant, enhancements of hadron multiplicities in the kinematic regimes accessible in present high-precision experiments. Our results are therefore relevant for the determination of hadron fragmentation functions from data for these processes.Comment: 14 pages, 11 figure

    Effective field theory approach to open heavy flavor production in heavy-ion collisions

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    We develop a version of Soft Collinear Effective Theory (SCET) which includes finite quark masses, as well as Glauber gluons that describe the interaction of collinear partons with QCD matter. In the framework of this new effective field theory, labeled SCETM,G_{\mathrm{M,G}}, we derive the massive splitting functions in the vacuum and the QCD medium for the processes QQgQ\to Qg, QgQQ\to gQ and gQQˉg\to Q\bar Q. The numerical effects due to finite quark masses are sizable and our results are consistent with the traditional approach to parton energy loss in the soft gluon emission limit. In addition, we present a new framework for including the medium-induced full splitting functions consistent with next-to-leading order calculations in QCD for inclusive hadron production. Finally, we show numerical results for the suppression of DD- and BB-mesons in heavy ion collisions at sNN=5.02\sqrt{s_{\mathrm{NN}}}=5.02 TeV and 2.76 TeV and compare to available data from the LHC.Comment: 43 pages, 14 figure

    Threshold and jet radius joint resummation for single-inclusive jet production

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    We present the first threshold and jet radius jointly resummed cross section for single-inclusive hadronic jet production. We work at next-to-leading logarithmic accuracy and our framework allows for a systematic extension beyond the currently achieved precision. Longstanding numerical issues are overcome by performing the resummation directly in momentum space within Soft Collinear Effective Theory. We present the first numerical results for the LHC and observe an improved description of the available data. Our results are of immediate relevance for LHC precision phenomenology including the extraction of parton distribution functions and the QCD strong coupling constant.Comment: 5 pages, 3 figures, minor text changes, PDF uncertainties included and more references added. Replaced to match the published versio

    The semi-inclusive jet function in SCET and small radius resummation for inclusive jet production

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    We introduce a new kind of jet function: the semi-inclusive jet function Ji(z,ωJ,μ)J_i(z, \omega_J, \mu), which describes how a parton ii is transformed into a jet with a jet radius RR and energy fraction z=ωJ/ωz = \omega_J/\omega, with ωJ\omega_J and ω\omega being the large light-cone momentum component of the jet and the corresponding parton ii that initiates the jet, respectively. Within the framework of Soft Collinear Effective Theory (SCET) we calculate both Jq(z,ωJ,μ)J_q(z, \omega_J, \mu) and Jg(z,ωJ,μ)J_g(z, \omega_J, \mu) to the next-to-leading order (NLO) for cone and anti-kT_{\rm T} algorithms. We demonstrate that the renormalization group (RG) equations for Ji(z,ωJ,μ)J_i(z, \omega_J, \mu) follow exactly the usual DGLAP evolution, which can be used to perform the lnR\ln R resummation for {\it inclusive} jet cross sections with a small jet radius RR. We clarify the difference between our RG equations for Ji(z,ωJ,μ)J_i(z, \omega_J, \mu) and those for the so-called unmeasured jet functions Ji(ωJ,μ)J_i(\omega_J, \mu), widely used in SCET for {\it exclusive} jet production. Finally, we present applications of the new semi-inclusive jet functions to inclusive jet production in e+ee^+e^- and pppp collisions. We demonstrate that single inclusive jet production in these collisions shares the same short-distance hard functions as single inclusive hadron production, with only the fragmentation functions Dih(z,μ)D_i^h(z, \mu) replaced by Ji(z,ωJ,μ)J_i(z, \omega_J, \mu). This can facilitate more efficient higher-order analytical computations of jet cross sections. We further match our lnR\ln R resummation at both LLR_{R} and NLLR_{R} to fixed NLO results and present the phenomenological implications for single inclusive jet production at the LHC.Comment: 35 pages, 11 figures, published version at JHE

    The Jet Shape at NLL'

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    The jet shape is the fraction of the jet energy within a cone rr centered on the jet axis. We calculate the jet shape distribution at next-to-leading logarithmic accuracy plus next-to-leading order (NLL'), accounting for logarithms of both the jet radius RR and the ratio r/Rr/R. This is the first phenomenological study that takes the recoil of the jet axis due to soft radiation into account, which is needed to reach this accuracy, but complicates the calculation of collinear radiation and requires the treatment of rapidity logarithms and non-global logarithms. We present numerical results, finding good agreement with ATLAS and CMS measurements of the jet shape in an inclusive jet sample, ppjet+Xpp \to {\rm jet}+X, for different kinematic bins. The effect of the underlying event and hadronization are included using a simple one-parameter model, since they are not part of our perturbative calculation.Comment: 36 pages, 14 figures, v2: extended discussion of non-global logarithms, journal versio
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