2,029 research outputs found
Recent investigations of QCD at HERA
The latest results from the H1 and ZEUS collaborations which challenge the
QCD description of high energy collisions are presented. Data from HERA
continue to provide precision measurements and are compared to the latest
theoretical predictions. Measurements of new processes are also presented as
well as investigation of regions where perturbative QCD fails to describe the
data. Four themes are presented here. Measurements of hard QCD processes,
prompt photon and jet production, are used to compare to the latest theoretical
predictions and, in the case of jet production, used to make high-precision
extractions of the strong coupling constant up to next-next-to-leading order in
QCD. All H1 and ZEUS charm and beauty cross sections in deep inelastic
scattering have been combined and used to extract heavy-quark masses, including
the running of the charm-quark mass with the scale of the process.
Factorisation in diffraction has been investigated in charm production in deep
inelastic scattering and prompt photon production in diffractive
photoproduction has been measured for the first time. Finally, the inclusive
data on deep inelastic scattering is presented in various forms in order to
allow investigation of the underlying mechanism at very low photon virtuality
and low Bjorken .Comment: 11 pages, 9 figures. submitted to the proceedings of the "DIS2017"
Workshop, Birmingham, UK. Updated with some additional reference
Heavy quark production at HERA and the LHC
Measurements of heavy quark production, particularly from HERA, their
theoretical understanding and their relevance for the LHC are reviewed. The
status of beauty and charm production is discussed in the context of the
different components of the production process: the parton density function of
the colliding hadrons; the hard scatter; and the fragmentation of the quarks
into hadrons. The theory of QCD at next-to-leading order generally describes
well the hadronic structure and the production of heavy quarks although
sometimes fails in details which are highlighted. The fragmentation of heavy
quarks measured at HERA is consistent with that at LEP and hence supports the
notion of universality.Comment: Write-up of talk at the workshop, "A workshop on the implications of
HERA for LHC physics". To appear in proceedings. 10 pages, 7 figure
The Hadronic Final State at HERA
The hadronic final state in electron-proton collisions at HERA has provided a
rich testing ground for development of the theory of the strong force, QCD. In
this review, over 200 publications from the H1 and ZEUS Collaborations are
summarised. Short distance physics, the measurement of processes at high energy
scales, has provided rigorous tests of perturbative QCD and constrained the
structure of the proton as well as allowing precise measurements of the strong
coupling constant to be made. Non-perturbative or low energy processes have
also been investigated and results on hadronisation interpreted together with
those from other experiments. Searches for exotic QCD objects, such as
pentaquarks, glueballs and instantons have been performed. The subject of
diffraction has been re-invigorated through its precise measurement, such that
it can now be described by perturbative QCD. After discussion of HERA, the H1
and ZEUS detectors and the techniques used to reconstruct differing hadronic
final states, the above subject areas are elaborated. The major achievements
are then condensed further in a final section summarising what has been
learned.Comment: 60 pages, 65 figures, submitted to Reviews of Modern Physics. Updated
version includes comments to the text from journal referee
VHEeP: A very high energy electron-proton collider based on proton-driven plasma wakefield acceleration
Based on current CERN infrastructure, an electron-proton collider is proposed
at a centre-of-mass energy of about 9 TeV. A 7 TeV LHC bunch is used as the
proton driver to create a plasma wakefield which then accelerates electrons to
3 TeV, these then colliding with the other 7 TeV LHC proton beam. The basic
parameters of the collider are presented, which although of very high energy,
has integrated luminosities of the order of 1 pb/year. For such a
collider, with a centre-of-mass energy 30 times greater than HERA, parton
momentum fractions, , down to about are accessible for of 1
GeV and could lead to effects of saturation or some other breakdown of
DGLAP being observed. The total photon-proton cross section can be measured up
to very high energies and also at different energies as the possibility of
varying the electron beam energy is assumed; this could have synergy with
cosmic-ray physics. Other physics which can be pursued at such a collider are
contact interaction searches, such as quark and electron substructure, and
measurements of the proton structure as well as other more conventional
measurements of QCD at high energies and in a new kinematic regime. The events
at very low will lead to electrons and the hadronic final state produced at
very low angles and so a novel spectrometer device will be needed to measure
these. First ideas of the physics programme of such a collider are given.Comment: 7 pages, 4 figures, presented at the DIS 2015 Workshop, Dalla
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