29 research outputs found
Fluctuations, Saturation, and Diffractive Excitation at low x
Diffractive excitation is usually described by the Good--Walker formalism for
low masses, and by the triple-Regge formalism for high masses. In the
Good-Walker formalism the cross section is determined by the fluctuations in
the interaction. By taking the fluctuations in the BFKL ladder into account, it
is possible to describe both low and high mass excitation in the Good-Walker
formalism. In high energy pp collisions the fluctuations are strongly
suppressed by saturation, which implies that pomeron exchange does not
factorise between DIS and pp collisions. The Dipole Cascade Model reproduces
the expected triple-Regge form for the bare pomeron, and the triple-pomeron
coupling is estimated.Comment: 4 pages, proceedings from Diffraction 201
Quasielastic Scattering in the Dipole Model
A series of previous papers develops a dipole model in initial state impact
parameter space that includes subleading effects such as running alpha strong,
unitarity, confinement and saturation. Here some recent work is presented,
where the model is applied to a new set of data: vector meson production in
photon-proton, DVCS and t-dependence in elastic proton-proton collisions. This
allows us to tune a more realistic model of the proton wavefunction from the pp
data, and confirm the predictive power of the model in high Q2 of DVCS and
vector meson production. For low Q2 vector meson resonances dominate the photon
wavefunction, making our predictions depend on a tuned parametrisation in this
range.Comment: Published in Proceedings of the 38th International Symposium on
Multiparticle Dynamics (ISMD08
Exclusive final states in diffractive excitation
In this paper we describe a formalism for generating exclusive final states
in diffractive excitation, based on the optical analogy where diffraction is
fully determined by the absorption into inelastic channels. The formalism is
based on the Good--Walker formalism for diffractive excitation, and it is
assumed that the virtual parton cascades represent the diffractive eigenstates
defined by a definite absorption amplitude. We emphasize that, although
diffractive excitation is basically a quantum-mechanical phenomenon with strong
interference effects, it is possible to calculate the different interfering
components to the amplitude in an event generator, add them and thus calculate
the reaction cross section for exclusive diffractive final states. The
formalism is implemented in the DIPSY event generator, introducing no tunable
parameters beyond what has been determined previously in studies of
non-diffractive events. Some early results from DIS and proton-proton
collisions are presented, and compared to experimental data
SuperFreq: Integrated mutation detection and clonal tracking in cancer.
Analysing multiple cancer samples from an individual patient can provide insight into the way the disease evolves. Monitoring the expansion and contraction of distinct clones helps to reveal the mutations that initiate the disease and those that drive progression. Existing approaches for clonal tracking from sequencing data typically require the user to combine multiple tools that are not purpose-built for this task. Furthermore, most methods require a matched normal (non-tumour) sample, which limits the scope of application. We developed SuperFreq, a cancer exome sequencing analysis pipeline that integrates identification of somatic single nucleotide variants (SNVs) and copy number alterations (CNAs) and clonal tracking for both. SuperFreq does not require a matched normal and instead relies on unrelated controls. When analysing multiple samples from a single patient, SuperFreq cross checks variant calls to improve clonal tracking, which helps to separate somatic from germline variants, and to resolve overlapping CNA calls. To demonstrate our software we analysed 304 cancer-normal exome samples across 33 cancer types in The Cancer Genome Atlas (TCGA) and evaluated the quality of the SNV and CNA calls. We simulated clonal evolution through in silico mixing of cancer and normal samples in known proportion. We found that SuperFreq identified 93% of clones with a cellular fraction of at least 50% and mutations were assigned to the correct clone with high recall and precision. In addition, SuperFreq maintained a similar level of performance for most aspects of the analysis when run without a matched normal. SuperFreq is highly versatile and can be applied in many different experimental settings for the analysis of exomes and other capture libraries. We demonstrate an application of SuperFreq to leukaemia patients with diagnosis and relapse samples
Eccentricity and elliptic flow in proton-proton collisions from parton evolution
It has been argued that high-multiplicity proton-proton collisions at the LHC
may exhibit collective phenomena usually studied in the context of heavy-ion
collisions, such as elliptic flow. We study this issue using DIPSY - a Monte
Carlo event generator based on the QCD dipole model. We calculate the
eccentricity of the transverse area defined by the spatial distribution of
produced gluons. The resulting elliptic flow is estimated to be about 6%,
comparable to the value in nucleus-nucleus collisions at RHIC and the LHC.
Experimentally, elliptic flow is inferred from the azimuthal correlation
between hadrons, which receives contributions from collective flow, and from
various other effects referred to as "nonflow". We discuss how to identify in
experiments the signal of flow in the presence of large nonflow effects.Comment: v2: Four-particle correlation added, improved discussions on the
signatures of flow. v3: Improved treatment of fluctuations in the flow
analysis. v4: Minor changes for journal submissio
Fluctuations, Saturation, and Diffractive Excitation in High Energy Collisions
Diffractive excitation is usually described by the Good--Walker formalism for
low masses, and by the triple-Regge formalism for high masses. In the
Good--Walker formalism the cross section is determined by the fluctuations in
the interaction. In this paper we show that by taking the fluctuations in the
BFKL ladder into account, it is possible to describe both low and high mass
excitation by the Good--Walker mechanism. In high energy collisions the
fluctuations are strongly suppressed by saturation, which implies that pomeron
exchange does not factorise between DIS and collisions. The Dipole Cascade
Model reproduces the expected triple-Regge form for the bare pomeron, and the
triple-pomeron coupling is estimated.Comment: 20 pages, 12 figure
Elastic and quasi-elastic and scattering in the Dipole Model
We have in earlier papers presented an extension of Mueller's dipole cascade
model, which includes sub-leading effects from energy conservation and running
coupling as well as colour suppressed saturation effects from pomeron loops via
a ``dipole swing''. The model was applied to describe the total and diffractive
cross sections in and collisions, and also the elastic cross
section in scattering.
In this paper we extend the model to describe the corresponding quasi-elastic
cross sections in , namely the exclusive production of vector mesons
and deeply virtual compton scattering. Also for these reactions we find a good
agrement with measured cross sections. In addition we obtain a reasonable
description of the -dependence of the elastic and quasi-elastic
cross sections