1,530 research outputs found
New experimental evidence that the proton develops asymptotically into a black disk
Recently, the Auger group has extracted the proton-air cross section from
observations of air showers produced by cosmic ray protons (and nuclei)
interacting in the atmosphere and converted it into measurements of the total
and inelastic cross sections and at
the super-LHC energy of 57 TeV. Their results reinforce our earlier conclusions
that the proton becomes a black disk at asymptotic energies, a prediction
reached on the basis of sub-LHC \pbar p and measurements of and , the ratio of the real to the imaginary part of the forward
scattering amplitude [M. M. Block and F. Halzen, Phys. Rev. Lett. {\bf 107},
212002 (2011)]. The same black disk description of the proton anticipated the
values of and measured by the TOTEM
experiment at the LHC cms (center of mass) energy of TeV, as well
as those of measured by ALICE, ATLAS and CMS, as well as
the ALICE measurement at 2.76 TeV. All data are consistent with a proton that
is asymptotically a black disk of gluons: (i) both and
behave as , saturating the Froissart bound, (ii)
the forward scattering amplitude becomes pure imaginary (iii) the ratio
, compatible with the black
disk value of 1/2, and (iv) proton interactions become flavor blind.Comment: 4 pages, 3 figure
Forward hadronic scattering at 8 TeV: predictions for the LHC
The Large Hadron Collider (LHC) recently started operating at 8 TeV. In this
note, we update our earlier LHC forward hadronic scattering predictions
\cite{physicsreports,update7, blackdisk}, giving new predictions, including
errors, for the total and inelastic cross sections, the -value, the
nuclear slope parameter , , and the large gap survival
probability at 8 TeV.Comment: 4 pages, 1 figure, 1 table. arXiv admin note: substantial text
overlap with arXiv:1102.316
Decoupling the coupled DGLAP evolution equations: an analytic solution to pQCD
Using Laplace transform techniques, along with newly-developed accurate
numerical inverse Laplace transform algorithms, we decouple the solutions for
the singlet structure function and of the two
leading-order coupled singlet DGLAP equations, allowing us to write fully
decoupled solutions: F_s(x,Q^2)={\cal F}_s(F_{s0}(x), G_0(x)), G(x,Q^2)={\cal
G}(F_{s0}(x), G_0(x)). Here and are known
functions---found using the DGLAP splitting functions---of the functions
and , the chosen
starting functions at the virtuality . As a proof of method, we compare
our numerical results from the above equations with the published MSTW LO gluon
and singlet distributions, starting from their initial values at . Our method completely decouples the two LO distributions, at the same
time guaranteeing that both distributions satisfy the singlet coupled DGLAP
equations. It furnishes us with a new tool for readily obtaining the effects of
the starting functions (independently) on the gluon and singlet structure
functions, as functions of both and . In addition, it can also be
used for non-singlet distributions, thus allowing one to solve analytically for
individual quark and gluon distributions values at a given and , with
typical numerical accuracies of about 1 part in , rather than having to
evolve numerically coupled integral-differential equations on a two-dimensional
grid in , as is currently done.Comment: 6 pages, 2 figure
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