1,721,103 research outputs found
Monte Carlo methods for TMD analyses
Get PDFMonte Carlo simulations are an indispensable tool in experimental high-energy physics. Indeed, many discoveries rely on realistic modeling of background processes. In the field of transverse-momentum-dependent parton distribution and fragmentation functions there is a clear lack of a reliable Monte Carlo physics generator that can be used in experimental and phenomenological analyses. The need for such Monte Carlo generators, the status of some solutions and prospects are discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
a Monte Carlo Generator for Transverse-Momentum-Dependent Distribution and Fragmentation Functions
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Overview of Recent Results from the HERMES Experiment
No full textHERMES has taken a wealth of deep-inelastic scattering (DIS) data using the 27.6 GeV polarized lepton beam at HERA and various pure gas targets, both unpolarized and polarized, which opened the door to several unique results. Among them are the first evidences for the naive-T-odd Sivers and Collins effects but also the recent first measurements of azimuthal modulations in the unpolarized semi-inclusive DIS cross section for charged kaons and pions and of beam-helicity asymmetries in exclusive leptoproduction of real photons using recoil-proton detection. An overview of HERMES results is given with emphasis on the exploration of the three-dimensional structure of the nucleon
30 years of HERMES - exploiting self-polarization in storage rings at HERA
No full textThree decades ago it became that the simple quark model approach for the proton failed in describing the spin structure — the spin contribution from quarks, as measured by the European Muon Collaboration (EMC), came out small, by far insufficient to explain the proton spin of 1/2. The experiment utilized the polarized muon beam from CERN’s SPS, which is naturally polarized originating from the weak decay of mainly pions. The EMC results triggered a wealth of activity trying to explain the “spin puzzle”, but also to confirm (or falsify) those findings.Already some twenty years early, it had been demonstrated that electrons in a storage ring will also be polarized — under certain conditions and in particular if waiting sufficiently long enough. The verification of this Sokolov-Ternov effect will be celebrated today in a different talk from this one. However, this talk will concentrate on how the Sokolov-Ternov effect got exploited in the East Hall of the HERA storage rings at DESY to study the spin structure of the proton. It took five hard years to convince DESY to host a spin experiment and in particular that it was feasible to achieve sizable polarization of the 27.6 GeV electrons/positrons of HERA. Part of this effort also included convincing people to install a gas storage cell internal to the HERA lepton ring as part of a polarized gas target system. When this experiment, HERMES, finally turned on in 1995, it marked the beginning of an extremely successful physics program that ran until 2007, the shutdown of the HERA facility. During those years, HERMES took a wealth of data with longitudinally polarized H, D, and 3He targets, with transversely polarized H, as well as a wide range of unpolarized nuclei. In fact, analysis and publication of these data are still ongoing, as for the other HERA experiments. This talk will focus on some of the highlights of the HERMES program, with emphasis of exploiting the polarized beam, but also remembering some of the pioneering measurements, e.g., the first observation of the Sivers and Collins effects in semi-inclusive deep-inelastic scattering. Besides the discussion of the physics results, the talk will also reflect on the early years, e.g., on how the experiment and the collaboration was formed, to celebrate this milestone in nucleon-spin physics
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