128301. |
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128302. |
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128303. |
- Lönnblad, L., et al.
(författare)
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Mass reconstruction with a neural network
- 1992
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Ingår i: Physics Letters B. - 0370-2693. ; 278:1-2, s. 181-186
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Tidskriftsartikel (refereegranskat)abstract
- A feed-forward neural network method is developed for reconstructing the invariant mass of hadronic jets appearing in a calorimeter. The approach is illustrated in W→qq, where W-bosons are produced in pp reactions at SPS collider energies. The neural network method yields results that are superior to conventional methods. This neural network application differs from the classification ones in the sense that an analog number (the mass) is computed by the network, rather than a binary decision being made. As a by-product our application clearly demonstrates the need for using "intelligent" variables in instances when the amount of training instances is limited.
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128304. |
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128305. |
- Lönnblad, Leif, et al.
(författare)
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Matching tree-level matrix elements with interleaved showers
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :3
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Tidskriftsartikel (refereegranskat)abstract
- We present an implementation of the so-called CKKW-L merging scheme for combining multi-jet tree-level matrix elements with parton showers. The implementation uses the transverse-momentum-ordered shower with interleaved multiple interactions as implemented in PYTHIA8. We validate our procedure using e(+)e(-)-annihilation into jets and vector boson production in hadronic collisions, with special attention to details in the algorithm which are formally sub-leading in character, but may have visible effects in some observables. We find substantial merging scale dependencies induced by the enforced rapidity ordering in the default PYTHIA8 shower. If this rapidity ordering is removed the merging scale dependence is almost negligible. We then also find that the shower does a surprisingly good job of describing the hardness of multi-jet events, as long as the hardest couple of jets are given by the matrix elements. The effects of using interleaved multiple interactions as compared to more simplistic ways of adding underlying-event effects in vector boson production are shown to be negligible except in a few sensitive observables. To illustrate the generality of our implementation, we also give some example results from di-boson production and pure QCD jet production in hadronic collisions.
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128306. |
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128307. |
- Lönnblad, Leif, et al.
(författare)
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Modeling Bose-Einstein correlations at LEP-2
- 1998
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 2:1, s. 165-180
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Tidskriftsartikel (refereegranskat)abstract
- We present new algorithms for simulating Bose–Einstein correlations among final-state bosons in an event generator. The algorithms are all based on introducing Bose–Einstein correlations as a shift of final-state momenta among identical bosons, and differ only in the way energy and momentum conservation is ensured. The benefits and shortcomings of this approach, that may be viewed as a local reweighting strategy, is compared to the ones of recently proposed algorithms involving global event reweighting. We use the new algorithms to improve on our previous study of the effects of Bose–Einstein correlations on the W mass measurement at LEP 2. The intrinsic uncertainty could be as high as 100 MeV but is probably reduced to the order of 30 MeV with realistic experimental reconstruction procedures.
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128308. |
- Lönnblad, Leif
(författare)
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Modeling diffractive final states
- 2002
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Ingår i: Acta Physica Polonica B. - 0587-4254. ; 33:10, s. 3231-3236
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Konferensbidrag (refereegranskat)abstract
- I will discuss some aspects of modeling diffractive final states with event generators. In the first part of the talk I will discuss multiple scatterings in hard diffraction in hadron collisions and its effects on gap survival and hadronization corrections. In the second part I will argue that the study of the 'pomeron remnant' in hard diffraction at HERA may be the best way of distinguishing resolved pomeron models from dipole models and soft colour interaction models.
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128309. |
- Lönnblad, Leif
(författare)
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Modelling pp, pA and AA in Pythia8
- 2019
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 208, s. 11003-11003
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present a new model for generating complete exclusive hadronic final states in high energy collisions involving heavy ions. The model is called Angantyr and is inspired by the old Fritiof model, building on the concept of wounded nucleons.
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128310. |
- Lönnblad, Leif
(författare)
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Monte Carlo generators
- 2005
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Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 36:2, s. 401-408
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Tidskriftsartikel (refereegranskat)abstract
- I discuss some recent development of Monte Carlo event generators and point out some problems. Starting with the issue of combining matrix element generators and parton shower algorithms, I will continue with discussing the problems associated with describing small-x final states and discuss some recent model developments for describing multiple partonic scatterings and underlying events in hadron collisions. Finally I will briefly present the THEPEG project of creating a general platform in C++ for implementing Monte Carlo event generators.
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