Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions

Alwall, Johan; Höche, Stefan; Krauss, Frank; Lavesson, Nils; Lönnblad, Leif; Maltoni, Fabio; Mangano, M.; Moretti, M.; Papadopoulos, Costas G.; Piccinini, F.; Schumann, Steffen; Treccani, M.; Winter, Jan; Worek, Małgorzata

doi:10.1140/epjc/s10052-007-0490-5

Cited by 797 publications

(520 citation statements)

References 47 publications

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“…In agreement with Ref. [28], both alpgen + pythia and sherpa are found to show a sensitivity to the choice of scales which is similar to that of a LO pQCD prediction, reflecting a limited predictive power. For the leading jet at p T = 100 GeV, the prediction of sherpa with both scales shifted down by a factor of two is about three times higher than the alpgen + pythia prediction with both scales shifted up.…”

Section: Pacssupporting

confidence: 88%

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Measurements of differential cross sections of Z/γ∗+jets+X events in pp
Abazov¹,
Abbott²,
Abolins³
et al. 2009
Physics Letters B
42
0
11
0
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We present cross section measurements for Z /γ * + jets + X production, differential in the transverse momenta of the three leading jets. The data sample was collected with the DØ detector at the Fermilab Tevatron pp collider at a center-of-mass energy of 1.96 TeV and corresponds to an integrated luminosity of 1 fb −1 . Leading and next-to-leading order perturbative QCD predictions are compared with the measurements, and agreement is found within the theoretical and experimental uncertainties. We also make comparisons with the predictions of four event generators. Two parton-shower-based generators show significant shape and normalization differences with respect to the data. In contrast, two generators combining tree-level matrix elements with a parton shower give a reasonable description of the shapes observed in data, but the predicted normalizations show significant differences with respect to the data, reflecting large scale uncertainties. For specific choices of scales, the normalizations for either generator can be made to agree with the measurements. Letters B 678 (2009) [45][46][47][48][49][50][51][52][53][54] The production of jets in association with vector bosons (V + jets) in hadron collisions is an important process in quantum chromodynamics (QCD) and is a significant source of background for many standard model measurements (e.g., tt production) and in searches for new phenomena (e.g., supersymmetry). Such measurements at the Fermilab Tevatron collider and the CERN Large Hadron Collider (LHC) rely on accurate descriptions of V + jets production by particle-level event generators. These models require validation with measurements of the properties of the V + jets system, especially as a function of jet multiplicity. DØ Collaboration / PhysicsIn In particular, we have investigated to what extent the differential p T distributions for the higher jet multiplicities can be described by parton-shower-based event generators like pythia [6] and herwig [7], and how they compare to event generator predictions where matrix element and parton shower merging procedures are adopted, as in alpgen + pythia [8] and sherpa [9]. For each prediction, the renormalization and factorization scale uncertainties are evaluated, and the choices of scales are modified to achieve an improved description of the measurements. The presented studies are of vital importance to understand the predictive power of the various event generator models for V + jets processes at both the Tevatron and the LHC.The data set was recorded using the DØ Run II detector, which is described in detail elsewhere [10]. Here we give a brief overview of the most relevant components for this analysis. The trajectories of charged particles are reconstructed using a silicon vertex tracker and a scintillating fiber tracker located inside a superconducting solenoidal coil that provides a magnetic field of approximately 2 T. The tracking volume is surrounded by a liquidargon and uranium calorimeter, divided into electromagnetic and hadronic sections with...

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Section: Pacssupporting

confidence: 88%

“…Both generators combine tree-level matrix elements with parton showers [27][28][29], thereby utilizing matrix elements also for sub-leading jets. For the central alpgen + pythia prediction, the factorization scale is…”

Section: Pacsmentioning

confidence: 99%

Measurements of differential cross sections of Z/γ∗+jets+X events in pp
Abazov¹,
Abbott²,
Abolins³
et al. 2009
Physics Letters B
42
0
11
0
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show abstract

“…To avoid double counting, we have matched the matrix element to the parton shower through the MLM scheme [22] implemented in MadGraph5. This generation procedure allows to include nontrivial p T distributions.…”

Section: Angular Distribution In Tt Productionmentioning

confidence: 99%

Top-antitop resonance searches beyond 1 TeV

2013

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We perform a general parton level analysis for the search of heavy resonant states in the production of tt pairs at the LHC with an integrated luminosity of 30 fb −1 . We assume the existence of resonances that only couple to quarks and propose kinematic cuts in order to increase the amount of events produced through quark-annihilation. We study the interplay between different variables and their impact on the purity of the selected sample. We make focus on the longitudinal (β) and transverse (p T ) momentum of the tt pair, and the scattering angle (θ) in the center of mass reference frame. We observe that β is replaced by θ as a suitable discriminating variable of quark-annihilation processes for invariant masses above 1 TeV. Finally, we illustrate the analysis with a gluon resonance of 1.5 TeV and show the improvement in the sensitivity of the signal when cuts on θ are imposed.

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“…We have showered the parton level outcome with Pythia [15] to include the initial state radiation. To avoid double counting, we have matched the matrix element with up to one extra jet to the parton shower through the MLM scheme [17] implemented in MadGraph5. We have used a K-factor of 1.55 which comes out from comparing the same simulation at 7 TeV to tt production at NNLL order [18] at this energy.…”

mentioning

confidence: 99%

Enhancing the sensitivity to new physics in thett¯invariant mass distribution

Álvarez

2012

Phys. Rev. D

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We propose selection cuts on the LHC tt production sample which should enhance the sensitivity to New Physics signals in the study of the tt invariant mass distribution. We show that selecting events in which the tt object has little transverse and large longitudinal momentum enlarges the quark-fusion fraction of the sample and therefore increases its sensitivity to New Physics which couples to quarks and not to gluons. We find that systematic error bars play a fundamental role and assume a simple model for them. We check how a non-visible new particle would become visible after the selection cuts enhance its resonance bump. A final realistic analysis should be done by the experimental groups with a correct evaluation of the systematic error bars.

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Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions

Cited by 797 publications

References 47 publications

Measurements of differential cross sections of Z/γ∗+jets+X events in pp
Abazov¹,
Abbott²,
Abolins³
et al. 2009
Physics Letters B
42
0
11
0
View full text Add to dashboard Cite

Measurements of differential cross sections of Z/γ∗+jets+X events in pp
Abazov¹,
Abbott²,
Abolins³
et al. 2009
Physics Letters B
42
0
11
0
View full text Add to dashboard Cite

Top-antitop resonance searches beyond 1 TeV

Enhancing the sensitivity to new physics in thett¯invariant mass distribution

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Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions

Cited by 797 publications

References 47 publications

Measurements of differential cross sections of Z/γ∗+jets+X events in ppAbazov1, Abbott2, Abolins3 et al. 2009Physics Letters B420110View full textAdd to dashboardCite

Measurements of differential cross sections of Z/γ∗+jets+X events in ppAbazov1, Abbott2, Abolins3 et al. 2009Physics Letters B420110View full textAdd to dashboardCite

Top-antitop resonance searches beyond 1 TeV

Enhancing the sensitivity to new physics in thett¯invariant mass distribution

Contact Info

Product

Resources

About

Measurements of differential cross sections of Z/γ∗+jets+X events in pp
Abazov¹,
Abbott²,
Abolins³
et al. 2009
Physics Letters B
42
0
11
0
View full text Add to dashboard Cite

Measurements of differential cross sections of Z/γ∗+jets+X events in pp
Abazov¹,
Abbott²,
Abolins³
et al. 2009
Physics Letters B
42
0
11
0
View full text Add to dashboard Cite