Measurement of four-jet differential cross sections in s = 8 $$ \sqrt{s}=8 $$ TeV proton-proton collisions using the ATLAS detector

Abstract

Differential cross sections for the production of at least four jets have been measured in proton-proton collisions at √ s = 8 TeV at the Large Hadron Collider using the ATLAS detector. Events are selected if the four anti-k t R = 0.4 jets with the largest transverse momentum (p T ) within the rapidity range |y| < 2.8 are well separated (∆R min 4j > 0.65), all have p T > 64 GeV, and include at least one jet with p T > 100 GeV. The dataset corresponds to an integrated luminosity of 20.3 fb −1 . The cross sections, corrected for detector effects, are compared to leading-order and next-to-leading-order calculations as a function of the jet momenta, invariant masses, minimum and maximum opening angles and other kinematic variables.Keywords: Jet physics, Hadron-Hadron scattering, QCD A Tables of the measured cross sections 36 The ATLAS collaboration 591 IntroductionThe production of particle jets at hadron colliders such as the Large Hadron Collider (LHC) [1] provides a fertile testing ground for the theory describing strong interactions, Quantum Chromodynamics (QCD). In QCD, jet production is interpreted as the fragmentation of quarks and gluons produced in the scattering process followed by their subsequent hadronisation. At high transverse momenta (p T ) the scattering of partons can be calculated using perturbative QCD (pQCD) and experimental jet measurements are directly related to the scattering of quarks and gluons. The large cross sections for such processes allow for differential measurements in a wide kinematic range and stringent testing of the underlying theory.-1 - JHEP12(2015)105This analysis studies events where at least four jets are produced in a hard-scatter process. These events are of particular interest as the corresponding Feynman diagrams require several vertices even at leading-order (LO) in the strong coupling constant α S . The current state-of-the-art theoretical predictions for such processes are at next-to-leadingorder in α S (next-to-leading-order perturbative QCD, NLO pQCD) [2,3], 1 and they have recently been combined with parton shower (PS) simulations [4]. An alternative approach is taken by generators which provide a matrix element (ME) for the hardest 2 → 2 process while the rest of the jets are provided by a PS model, which implements a resummation of the leading-logarithmic terms (e.g. Pythia 8 [5] and Herwig++ [6]). It is also interesting to test multi-leg (i.e., 2 → n) LO pQCD generators (e.g. Sherpa [7] or MadGraph [8]), since they may provide adequate descriptions of the data in specific kinematic regions and have the advantage of being less computationally expensive than NLO calculations.It is interesting to note that the previous ATLAS measurement of multi-jet production at √ s = 7 TeV [9] indicates that predictions may differ from data by ∼ 30% even at NLO [10]. This work explores a variety of kinematic regimes and topological distributions to test the validity of QCD calculations, including the PS approximation and the necessity of higher-order ME in Monte Car...

The complete NLO corrections to dijet hadroproduction

“…refs. [34][35][36][37][38][39][40][41][42][43][44][45][46] for a list of recent ATLAS and CMS papers approved as publications in the context of jet physics). Having said that, fixed-order perturbation theory is somehow pathological, precisely because a jet can coincide with a photon.…”

Merging high energy with soft and collinear logarithms using HEJ and PYTHIA

“…The analyses of collider data collected at both the Tevatron [1] ( √ s = 1.96 TeV) and the LHC [2][3][4][5][6][7] ( √ s = 7, 8 TeV) indicate that perturbative terms beyond fixed order are required for the description of observables in processes involving at least two jets, in the region of large partonic centre-of-mass energy √ŝ compared to the typical transverse momentum scale p ⊥ , √ŝ /p ⊥ > 5. This corresponds to the jets spanning more than 3 units of rapidity.…”

“…The dominant and large corrections in this particular region of phase space is the focus of one of the applications of the theory of Balitsky-Fadin-Kuraev-Lipatov (BFKL) [8][9][10][11]. The study of such perturbative effects has received renewed interest, not only because the increasing energy of colliders allows for detailed study of observables in these regions, but also because some measurements specifically concentrate on experimental signatures with large rapidity spans [3][4][5][6][7][12][13][14].…”

Azimuthal correlations for inclusive 2-jet, 3-jet, and 4-jet events in pp collisions at $$\sqrt{s}= 13~\hbox {TeV}$$ s = 13 TeV

“…Previous measurements of azimuthal correlation in inclusive 2-jet events were reported by the D0 Collaboration in pp collisions at √ s = 1.96 TeV at the Fermilab Tevatron [1,2], and by the ATLAS Collaboration in pp collisions at √ s = 7 TeV [3] and the CMS Collaboration in pp collisions at √ s = 7 and 8 TeV [4,5] at the LHC. Multijet correlations have been measured by the ATLAS Collaboration at √ s = 8 TeV [6,7].…”

“…the subleading jets, and one can distinguish nearby (nearly collinear) jets (at large ∆φ min 2j ) from other additional high p T jets (small ∆φ min 2j ), yielding information additional to that of the ∆φ 1,2 observable. The 4-jet cross section differential in ∆φ min 2j has also been measured by the ATLAS Collaboration [7]. The measurements are performed using data collected during 2016 with the CMS experiment at the LHC, and the event sample corresponds to an integrated luminosity of 35.9 fb −1 of protonproton collisions at √ s = 13 TeV.…”