176 research outputs found
Matching matrix elements and shower evolution for top-quark production in hadronic collisions
We study the matching of multijet matrix elements and shower evolution in the
case of top production in hadronic collisions at the Tevatron and at the LHC.
We present the results of the matching algorithm implemented in the ALPGEN
Monte Carlo generator, and compare them with results obtained at the parton
level, and with the predictions of the MC@NLO approach. We highlight the
consistency of the matching algorithm when applied to these final states, and
the excellent agreement obtained with MC@NLO for most inclusive quantities. We
nevertheless identify also a remarkable difference in the rapidity spectrum of
the leading jet accompanying the top quark pair, and comment on the likely
origin of this discrepancy.Comment: 22 pages, 13 figures, 5 tables. JHEP styl
Monte Carlo studies of the jet activity in Higgs + 2 jet events
Tree-level studies have shown in the past that kinematical correlations
between the two jets in Higgs+2-jet events are direct probes of the Higgs
couplings, e.g. of their CP nature. In this paper we explore the impact of
higher-order corrections on the azimuthal angle correlation of the two leading
jets and on the rapidity distribution of extra jets. Our study includes
matrix-element and shower MC effects, for the two leading sources of Higgs plus
two jet events at the CERN LHC, namely vector-boson and gluon fusion. We show
that the discriminating features present in the previous leading-order matrix
element studies survive.Comment: 12 pages, 10 figures. Version to appear on JHEP. Figs. 5-8 replaced
with colour version
Single-top t-channel hadroproduction in the four-flavour scheme with POWHEG and aMC@NLO
We present results for the QCD next-to-leading order (NLO) calculation of
single-top t-channel production in the 4-flavour scheme, interfaced to Parton
Shower (PS) Monte Carlo programs according to the POWHEG and MC@NLO methods.
Comparisons between the two methods, as well as with the corresponding process
in the 5-flavour scheme are presented. For the first time results for typical
kinematic distributions of the spectator-b jet are presented in an NLO+PS
approach.Comment: 16+1 pages, 8 figures, matches version accepted for publication in
JHE
W+W-, WZ and ZZ production in the POWHEG BOX
We present an implementation of the vector boson pair production processes
ZZ, W+W- and W Z within the POWHEG framework, which is a method that allows the
interfacing of NLO calculations to shower Monte Carlo programs. The
implementation is built within the POWHEG BOX package. The Z/\gamma^*
interference, as well as singly resonant contributions, are properly included.
We also considered interference terms arising from identical leptons in the
final state. As a result, all contributions leading to the desired four-lepton
system have been included in the calculation, with the sole exception of the
interference between ZZ and W+W- in the production of a pair of same-flavour,
oppositely charged fermions and a pair of neutrinos, which we show to be fully
negligible. Anomalous trilinear couplings can be also set in the program, and
we give some examples of their effect at the LHC. We have made the relevant
code available at the POWHEG BOX web site.Comment: 20 pages, 9 figures, 2 tables. Minor corrections and updated
references in revised versio
Scaling Patterns for QCD Jets
Jet emission at hadron colliders follows simple scaling patterns. Based on
perturbative QCD we derive Poisson and staircase scaling for final state as
well as initial state radiation. Parton density effects enhance staircase
scaling at low multiplicities. We propose experimental tests of our theoretical
findings in Z+jets and QCD gap jets production based on minor additions to
current LHC analyses.Comment: 36 pages, 16 figure
Assessment of the impact of multiple mild-steam decontaminations on the protection performance of disposable KN95 filtering facepiece respirators
The COVID-19 pandemic caused tremendous supply bottlenecks of single-use filtering
facepiece respirators (FFRs) leading to a growing need for a potential reuse. This study
assesses the impact of multiple mild-steam decontaminations with 121 °C/2000 mbar/20
min on the protection performance of disposable FFRs. It focuses on FFRs of type KN95
that is recently dominating the markets, but its decontamination is not covered in the
literature. It was found that up to ten cycles, only minor degradation in the filter efficiency,
breathing resistance and none in the material structure is apparent, suggesting a
potential for multiple decontamination cycles at almost unchanged protective properties
of KN95 FFRs
MadGraph/MadEvent v4: The New Web Generation
We present the latest developments of the MadGraph/MadEvent Monte Carlo event
generator and several applications to hadron collider physics. In the current
version events at the parton, hadron and detector level can be generated
directly from a web interface, for arbitrary processes in the Standard Model
and in several physics scenarios beyond it (HEFT, MSSM, 2HDM). The most
important additions are: a new framework for implementing user-defined new
physics models; a standalone running mode for creating and testing matrix
elements; generation of events corresponding to different processes, such as
signal(s) and backgrounds, in the same run; two platforms for data analysis,
where events are accessible at the parton, hadron and detector level; and the
generation of inclusive multi-jet samples by combining parton-level events with
parton showers. To illustrate the new capabilities of the package some
applications to hadron collider physics are presented:
1) Higgs search in pp \to H \to W^+W^-: signal and backgrounds.
2) Higgs CP properties: pp \to H jj$in the HEFT.
3) Spin of a new resonance from lepton angular distributions.
4) Single-top and Higgs associated production in a generic 2HDM.
5) Comparison of strong SUSY pair production at the SPS points.
6) Inclusive W+jets matched samples: comparison with the Tevatron data.Comment: 38 pages, 15 figure
Report of the Snowmass 2013 energy frontier QCD working group
This is the summary report of the energy frontier QCD working group prepared
for Snowmass 2013. We review the status of tools, both theoretical and
experimental, for understanding the strong interactions at colliders. We
attempt to prioritize important directions that future developments should
take. Most of the efforts of the QCD working group concentrate on proton-proton
colliders, at 14 TeV as planned for the next run of the LHC, and for 33 and 100
TeV, possible energies of the colliders that will be necessary to carry on the
physics program started at 14 TeV. We also examine QCD predictions and
measurements at lepton-lepton and lepton-hadron colliders, and in particular
their ability to improve our knowledge of strong coupling constant and parton
distribution functions.Comment: 62 pages, 31 figures, Snowmass community summer study 201
Distortion in a 7xxx aluminum alloy during liquid phase sintering
The distortion in a sintered 7xxx aluminum alloy, Al-7Zn-2.5Mg-1Cu (wt. pct), has been investigated by sintering three rectangular bars in each batch at 893 K (620 °C) for 0 to 40 minutes in nitrogen, followed by air or furnace cooling. They were placed parallel to each other, equally spaced apart at 2 mm, with their long axes being perpendicular to the incoming nitrogen flow. Pore evolution in each sample during isothermal sintering was examined metallographically. The compositional changes across sample mid-cross section and surface layers were analyzed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy depth profiling, respectively. The two outer samples bent toward the middle one, while the middle sample was essentially distortion free after sintering. The distortion in the outer samples was a result of differential shrinkage between their outer and inner surfaces during isothermal sintering. The porous outer surface showed an enrichment of oxygen around the large pores as well as lower magnesium and zinc contents than the interior and inner surface of the same sample, while the inner surface was distinguished by the presence of AlN. The differential shrinkage was caused by different oxygen contents in local sintering atmosphere and unbalanced loss of magnesium and zinc between the outer and inner surfaces
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