31 research outputs found
Unintegrated gluon distributions and Higgs boson production in proton-proton collisions
Inclusive cross sections for Higgs boson production in proton-proton
collisions are calculated in the formalism of unintegrated gluon distributions
(UGDF). Different UGDF from the literature are used. Although they were
constructed in order to describe the HERA deep-inelastic scattering data,
they lead to surprisingly different results for Higgs production. We present
both two-dimensional invariant cross section as a function of Higgs rapidity
and transverse momentum, as well as corresponding projections on rapidity or
transverse momentum. We quantify the differences between different UGD's by
applying different cuts on interrelations between transverse momentum of Higgs
and transverse momenta of both fusing gluons. We focus on large rapidity
region. The interplay of the gluon-gluon fusion and weak-boson fusion in
rapidity and transverse momentum is discussed. We find that above
50-100 GeV the weak-gauge-boson fusion dominates over gluon-gluon fusion.Comment: 32 pages, 18 figures, corrected version, restructured, misprints
removed, discussion added, new figure added, in print in EPJ
How local crustal thermal properties influence the amount of denudation derived from low temperature thermochronometry
ranslating amounts and rates of rock cooling derived from low-temperature thermochronometry into denudation requires assumptions about the local geothermal gradient. The temperature gradient in the crust depends on many factors, including basal heat flow, crustal heat production, and thermal conductivity. Consequently, geothermal gradients may be variable on time scales over which rock cooling is tracked by thermochronometry. Using one-dimensional numerical modeling of heat transfer in rocks of varying thermal characteristics, we show that the geothermal gradient of the eroded layer is the most important factor for accurate estimation of denudation amounts. Using a three-dimensional numerical model (Pecube), we demonstrate the impact of crustal heat production and thermal conductivity on estimates of total denudation derived from apatite fission track data from central west Britain. We show that the regional variation in cooling ages measured in Caledonian granites can be explained by geothermal gradient variation due to the presence of a heat-producing granite batholith and removal of insulating sedimentary rocks, and does not require variable denudation. Neglecting the blanketing effect leads to twofold overestimation of the amount of denudation. The occurrence of heat-producing basement that was once covered by a sedimentary blanket is common, in particular in the core of mountain belts. Accurate determination of the amount and rate of denudation from thermochronometric studies in these situations must take into account the composition of the eroded rocks
Subdominant terms in the production of pairs in proton-proton collisions
At high-energies the gluon-gluon fusion is the dominant mechanism of production. This process was calculated in the NLO collinear as well as in
the k-factorization approaches in the past. We show that the present
knowledge of gluon distributions does not allow to make a precise predictions
for production at LHC, in particular at forward rapidities. In this
paper we study production of pairs including several subleading
mechanisms. This includes: , , , . In this context we use
MRST-QED parton distributions which include photon as a parton in the proton as
well as elastic photon distributions calculated in the equivalent photon
approximation. We present distributions in the quark ( antiquark)
rapidity and transverse momenta and compare them to the dominant gluon-gluon
fusion contribution. We discuss also inclusive single and central diffractive
processes using diffractive parton distribution found from the analysis of HERA
diffractive data. As in the previous case we present distribution in () rapidity and transverse momentum. Finally we present results for exclusive
central diffractive mechanism discussed recently in the literature. We show
corresponding differential distributions and compare them with corresponding
distributions for single and central diffractive components.Comment: 20 pages, 19 figure
Nonphotonic electrons at RHIC within -factorization approach and with experimental semileptonic decay functions
We discuss production of nonphotonic electrons in proton-proton scattering at
RHIC. The distributions in rapidity and transverse momentum of charm and bottom
quarks/antiquarks are calculated in the -factorization approach. We use
different unintegrated gluon distributions from the literature. The
hadronization of heavy quarks is done by means of Peterson and Braaten et al.
fragmentation functions. The semileptonic decay functions are found by fitting
recent semileptonic data obtained by the CLEO and BABAR collaborations. We get
good description of the data at large transverse momenta of electrons and find
a missing strength concentrated at small transverse momenta of electrons.
Plausible missing mechanisms are discussed.Comment: 16 pages, 11 figure
Exclusive meson pair production in peripheral ultrarelativistic heavy ion collisions
The cross sections for exclusive and meson pair
production in peripheral nucleus - nucleus collisions are calculated and
several differential distributions are presented. The calculation of the
elementary cross section is done within the
heavy-quark approximation and in the Brodsky- Lapage formalism with
distribution amplitudes describing recent CLEO data on leptonic decay.
Realistic (Fourier transform of charge density) charge form factors of nuclei
are used to generate photon flux factors. Absorption effects are discussed and
quantified. The cross sections of a few nb are predicted for RHIC and of a few
hundreds of nb for LHC with details depending on the approximation made in
calculating elementary cross sections.Comment: 11 pages, 8 figure
Exclusive production of large invariant mass pion pairs in ultraperipheral ultrarelativistic heavy ion collisions
The cross section for exclusive production of and
meson pairs in ultrarelativistic heavy ion collisions is calculated for LHC
energy 3.5 TeV taking into account photon-photon mechanism.
We concentrate on the production of large two-pion invariant masses where the
mechanism of the elementary process is not fully
understood. In order to include a size of nuclei we perform calculation in the
impact-parameter equivalent photon approximation (EPA). Realistic charge
densities are used to calculate charged form factor of Pb nucleus and
to generate photon fluxes associated with ultrarelativistic heavy ions.
Sizeable cross sections are obtained that can be measured at LHC. The cross
section for elementary is calculated in the
framework of pQCD Brodsky-Lepage (BL) mechanism with the distribution amplitude
used to descibe recent data of the BABAR collaboration on pion transition form
factor, using hand-bag mechanism advocated to describe recent Belle data as
well as and -channel meson/reggeon exchanges. We present distributions
in two-pion invariant mass as well as the pion pair rapidity for the nuclear
process.Comment: 13 pages, 10 figure
Early Cenozoic denudation of central west Britain in response to transient and permanent uplift above a mantle plume
Upwelling mantle plumes beneath continental crust are predicted to produce difficult to quantify, modest uplift and denudation. The contribution of permanent and transient components to the uplift is also difficult to distinguish. A pulse of denudation in Britain in the Early Paleogene has been linked, although with some controversy, with the arrival of the proto-Iceland mantle plume. In this contribution we show that combining apatite and zircon (U-Th-Sm)/He and apatite fission track analyses from central west Britain with numerical modeling clearly identifies a pulse of early Cenozoic denudation. The data indicate that rock uplift and denudation were centered on the northern East Irish Sea Basin and 1.0–2.4 km of rocks were removed during the latest Cretaceous-early Paleogene. Uplift and erosion appears to have started a few million years before the earliest magmatism in the region. The regional denudation pattern mirrors the distribution of low-density magmatic rocks that has been imaged in the deep crust. However, the injection of the underplating melt is not enough to account for the total denudation. An additional regional uplift of at least 300 m is required, which is consistent with a transient thermal effect from the hot mantle plume. The rapid exhumation event ceased by ~40 Ma and the data do not require significant Neogene exhumation
The reaction and the pair production in exclusive ultraperipheral ultrarelativistic heavy ion collisions
We calculate the cross section for the
process. Two mechanisms are considered: box (two-loop) diagrams of the order of
and two-gluon exchange of the order of
. The first mechanism is calculated in the
heavy-quark non-relativistic approximation while the second case we also
include the effects of quantum motion of quarks in the bound state. The box
contribution dominates at energies close to the threshold ( 15 GeV) while
the two-gluon mechanism takes over at 15 GeV. Including the bound-state
wave function effects for the two-gluon exchange mechanism gives a cross
section 0.1 - 0.4 pb, substantially smaller than that in the non-relativistic
limit (0.4 - 1.6 pb). We also find a strong infrared sensitivity which
manifests itself in a rather strong dependence on the mass for the -channel
gluons. The elementary cross section is then used in the Equivalent Photon
Approximation (EPA) in the impact parameter space to calculate the cross
section for
reaction. Distributions in rapidity of the pair and invariant
mass of the pair are shown.Comment: 15 pages, 11 figure
The State of Art of Production of Automotive Structural Die Casted Elements
Wobec wprowadzenia coraz bardziej rygorystycznych norm emisji spalin, współczesne samochody muszą cechować się coraz mniejszym spalaniem paliwa. Jedną z możliwości osiągnięcia tego celu jest zmniejszenie całkowitej masy auta, co może być uzyskane poprzez wykorzystanie aluminiowych odlewów strukturalnych, stanowiących odpowiedzialne części zawieszenia, stref zgniotu czy też karoserii samochodów. W artykule przedstawiono zarówno przyczyny, dla których odlewy strukturalne stają się coraz bardziej pożądane przez największych producentów motoryzacji na świecie, jak również aktualny stan zagadnienia na temat ich produkcji w procesie ciśnieniowego odlewania aluminium.The paper presents the reasons for structural castings are becoming necessary by major automotive manufacturers in the world, as well as current issues regarding their production by the aluminum die-casting process
Commentary: The King is Naked – a very subjective look at child and adolescent psychiatry
There is a great crisis in child-adolescent psychiatry, but we will not solve it just only by increasing the number of psychiatrists nor the number of psychiatric wards. The young patients described in Agnieszka Wlazło's editorial indeed should not end up in a psychiatry department, but that does not mean they do not need any institutional support at all. In this commentary I would like to add two simple but important remarks: we need a serious discussion of the consequences of childhood trauma and mental problems in adolescence and also a well-functioning prevention system to avoid them