174 research outputs found
Determination of from Gross-Llewellyn Smith sum rule by accounting for infrared renormalon
We recapitulate the method which resums the truncated perturbation series of
a physical observable in a way which takes into account the structure of the
leading infrared renormalon. We apply the method to the Gross-Llewellyn Smith
(GLS) sum rule. By confronting the obtained result with the experimentally
extracted GLS value, we determine the value of the QCD coupling parameter which
turns out to agree with the present world average.Comment: invited talk by G.C. in WG3 of NuFact02, July 1-6, 2002, London; 4
pages, revte
Heavy quarks in deeply virtual Compton scattering
A detailed study of the heavy quark h=c,b,... contributions to deeply virtual
Compton scattering is performed at both the amplitude and the cross section
level, and their phenomenological relevance is discussed. For this purpose I
calculate the lowest order off-forward photon-gluon scattering amplitude with a
massive quark loop and the corresponding hard scattering coefficients. In a
first numerical analysis these fixed order perturbation theory results are
compared with the conventional intrinsic "massless" parton approach considering
generalized parton distributions for the heavy quarks. The differences between
these two prescriptions can be quite significant, especially at small
skewedness where the massless approach largely overestimates the deeply virtual
Compton scattering cross section.Comment: 15 pages, 12 eps-figures, LaTeX2e; (V2) include correct figure 3b,
remove 'bottom' from figure caption
Twist-2 Heavy Flavor Contributions to the Structure Function
The twist--2 heavy flavor contributions to the polarized structure function
are calculated. We show that this part of is related
to the heavy flavor contribution to by the Wandzura--Wilczek
relation to all orders in the strong coupling constant. Numerical results are
presented.Comment: 17 pages LATEX, 1 style files, 4 figure
Single-top production at future ep colliders
The production of top quarks in single mode at future ep colliders is
studied, the attention being mainly focused to the case of the proposed LEPXLHC
collider. We are motivated to reanalyse such a process following the discovery
of the top quark at Fermilab. Thanks to the measurement of its mass one is now
able to establish more accurately the relevance of single top production for
itself and for many other processes to which it may act as a background. In
addition, the recent improvement of our knowledge of the quark and gluon
dynamics inside the proton now allows one to pin down the dependence of single
top production on the partonic structure functions. Both the leptonic and
hadronic decay channels of the top quark are studied and compared to the yield
of the corresponding irreducible background in presence of b-taggingComment: 28 pages, latex, epsfig, 10 postscript figures, complete paper
available at ftp://axpa.hep.phy.cam.ac.uk/moretti/cavendish_9704 and at
http://www.hep.phy.cam.ac.uk/theory/papers
BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
The Keck Array is a system of cosmic microwave background (CMB) polarimeters,
each similar to the BICEP2 experiment. In this paper we report results from the
2012 and 2013 observing seasons, during which the Keck Array consisted of five
receivers all operating in the same (150 GHz) frequency band and observing
field as BICEP2. We again find an excess of B-mode power over the
lensed-CDM expectation of in the range
and confirm that this is not due to systematics using jackknife tests and
simulations based on detailed calibration measurements. In map difference and
spectral difference tests these new data are shown to be consistent with
BICEP2. Finally, we combine the maps from the two experiments to produce final
Q and U maps which have a depth of 57 nK deg (3.4 K arcmin) over an
effective area of 400 deg for an equivalent survey weight of 250,000
K. The final BB band powers have noise uncertainty a factor of 2.3
times better than the previous results, and a significance of detection of
excess power of .Comment: 13 pages, 9 figure
BICEP2 / Keck Array VIII: Measurement of gravitational lensing from large-scale B-mode polarization
We present measurements of polarization lensing using the 150 GHz maps which
include all data taken by the BICEP2 & Keck Array CMB polarization experiments
up to and including the 2014 observing season (BK14). Despite their modest
angular resolution (), the excellent sensitivity (K-arcmin) of these maps makes it possible to directly reconstruct the
lensing potential using only information at larger angular scales (). From the auto-spectrum of the reconstructed potential we measure an
amplitude of the spectrum to be (Planck
CDM prediction corresponds to ), and reject
the no-lensing hypothesis at 5.8, which is the highest significance
achieved to date using an EB lensing estimator. Taking the cross-spectrum of
the reconstructed potential with the Planck 2015 lensing map yields
. These direct measurements of
are consistent with the CDM cosmology, and with
that derived from the previously reported BK14 B-mode auto-spectrum (). We perform a series of null tests and consistency
checks to show that these results are robust against systematics and are
insensitive to analysis choices. These results unambiguously demonstrate that
the B-modes previously reported by BICEP / Keck at intermediate angular scales
() are dominated by gravitational lensing. The
good agreement between the lensing amplitudes obtained from the lensing
reconstruction and B-mode spectrum starts to place constraints on any
alternative cosmological sources of B-modes at these angular scales.Comment: 12 pages, 8 figure
Heavy Flavours at Colliders
I review some topics in the production and decays of heavy flavours that are
relevant for collider physics. In particular, I discuss the present status and
some recent progress related to masses, parton densities and fragmentation
functions of heavy quarks, as well as threshold resummation, polarized onium
production at high transverse momentum, and a factorization theorem for decays.Comment: 12 pages. Plenary talk given at UK Phenomenology Workshop on Collider
Physics, Durham, England, 19-24 Sep 1999 Comments and references adde
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