Summary and Outlook

Chapter
Part of the Springer Tracts in Modern Physics book series (STMP, volume 268)

Abstract

Jets are versatile tools that are produced abundantly in high-\(p_{\mathrm {T}}\) hadron-hadron collisions. When energy frontiers are probed they enable searches for new phenomena at the highest scales achievable. Owing to the unprecedented experimental precision reached with the new detectors at the LHC, jet measurements have evolved into precision tests of QCD.

Jets are versatile tools that are produced abundantly in high-\(p_{\mathrm {T}}\) hadron-hadron collisions. When energy frontiers are probed they enable searches for new phenomena at the highest scales achievable. Signatures in the form of contact interactions could be detected in jet final states up to around 19\(\,\text {TeV}\) in Run 2 of the LHC.

Owing to the unprecedented experimental precision reached with the new detectors at the LHC, jet measurements have evolved into precision tests of QCD. Such tests must be accompanied by equally accurate theoretical predictions, a fact that has sparked rapid progress in the field of perturbative calculations using both analytic methods and modern Monte Carlo event generators. The potential of some of these new possibilities like cross sections for multi-jet topologies at NLO still needs to be fully exploited, while other developments like the NNLO calculation for jet production are eagerly awaited.

From the interplay between experiment and theory in a multitude of subjects ranging from nonperturbative effects over parton showers and parton distribution functions to the strong coupling constant a more refined and detailed picture of QCD has emerged than ever before. Last but not least the much improved understanding of the QCD dynamics including the ability to precisely predict even complicated high-multiplicity final states helps estimating the background in many searches for new phenomena.

Of particular interest is the unique potential of jet measurements to better characterise the gluon parton distribution function in the proton and to determine the strong coupling constant, both of which represent significant uncertainties in predictions for the Higgs boson production via the gluon fusion channel. The current knowledge on \(\alpha _S(M_Z)\) is dominated by derivations from lattice gauge theory with an estimated precision of around 1 %. Considering the recent experimental and theoretical developments, a similar accuracy should be achievable within Run 2 of the LHC from hadron collider measurements alone, which currently are limited to 3–5 % of precision mostly because of lacking theory ingredients. An accuracy below 1 % will be difficult (but not impossible) to reach, since multiple sources including the modelling of nonperturbative effects contribute at this level to the total uncertainty. Global projections discussed in Refs. [1, 2, 3, 4] conclude on a prospect of further reductions to \(\approx \)0.3 % of uncertainty from lattice gauge theory within the next five years and on a timescale of 10–20 years to \(\approx \)0.1 % from a Giga-Z program at a future \(e^{+}e^{-}\) collider, or from an \(ep\) collider like LHeC.

Precision studies of the running of \(\alpha _S(Q)\) are equally important, since indications on new phenomena might well become visible through a modified evolution of the strong coupling and the PDFs. The latest status is shown in Fig. 8.1, where thanks to the LHC jet data the range in Q has been extended beyond the \(\,\text {TeV}\) scale.
Fig. 8.1

Running of the strong coupling constant as of 2015. Determinations of the strong coupling constant \(\alpha _S\) are shown as a function of the relevant energy scale Q of the respective process. By including LHC data, the range in Q could be extended beyond the \(\,\text {TeV}\) scale. The small uncertainty of a first result from \(t\bar{t}\) production at the LHC with theory at NNLO demonstrates the future potential. (Taken from the 2015 update of Ref. [5])

References

  1. 1.
    D. d’Enterria, P. Skands (eds.), Proceedings of the Workshop on High-Precision \(\alpha _s\) Measurements: From LHC to FCC-ee, October 12–13, 2015 (Geneva, Switzerland, 2015), arXiv:1512.05194
  2. 2.
    J.M. Campbell et al., Working group report: quantum chromodynamics, in Proceedings, Community Summer Study 2013: Snowmass on the Mississippi (CSS2013), July 29–August 6, 2013 (Minneapolis, MN, USA, 2013), arXiv:1310.5189
  3. 3.
    M. Bardeen et al., Planning the Future of U.S. Particle Physics: Report of the 2013 Community Summer Study of the APS Division of Particles and FieldsGoogle Scholar
  4. 4.
    ESPPPG Collaboration, Physics Briefing Book: Input for the Strategy Group to Draft the Update of the European Strategy for Particle PhysicsGoogle Scholar
  5. 5.
    K.A. Olive and others (Particle Data Group), Review of particle physics. Chin. Phys. C 38, 090001 (2014). doi:10.1088/1674-1137/38/9/090001

Copyright information

© Springer International Publishing Switzerland 2017

Authors and Affiliations

  1. 1.Institute for Experimental Nuclear PhysicsKarlsruhe Institute of Technology (KIT)KarlsruheGermany

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