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Combined PDF and strong coupling uncertainties at the LHC with NNPDF2.0

Ubiali, Maria; Ball, Richard D.; Del Debbio, Luigi; Forte, Stefano; Guffanti, Alberto; Latorre, José I.; Rojo, Juan
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
We present predictions for relevant LHC observables obtained with the NNPDF2.0 set. We compute the combined PDFs uncertainties on these observables, and show that combining errors in quadrature yields an excellent approximation to exact error propagation. We then compare the NNPDF2.0 results to the other global PDF fits using a common value of $\alpha_s$. At LHC 7 TeV, reasonable agreement, both in central values and in uncertainties, is found for NNPDF2.0, CTEQ6.6 and MSTW08.; Comment: 4 pages, 2 figures, contribution for the proceedings of the conference "Rencontres de Moriond, QCD and High Energy Interactions", 2010

Probing gluon nuclear PDF with direct photon production in association with a heavy quark

Kovarik, K.; Stavreva, T.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
239.24152%
We investigate a possible use of direct photon production in association with a heavy quark in $pA$ collisions at the large hadron collider to constrain the nuclear gluon parton distribution function. This process is sensitive to both, the nuclear heavy quark and gluon parton distribution functions and is a very promising candidate to help determine the gluon nuclear PDF which is still largely untested.; Comment: 4 pages, proceedings of DIS2011

Using Drell-Yan forward-backward asymmetry to reduce PDF errors in the measurement of electroweak parameters

Bodek, A.; Han, J.; Khukhunaishvili, A.; Sakumoto, W.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
239.24152%
The uncertainties in Parton Distribution Functions (PDFs) are the dominant source of systematic error in precision measurements of electroweak parameters at hadron colliders (e.g. $\sin^2\theta_{eff}(M_Z)$, $\sin^2\theta_{W}=1-M_W^2/M_Z^2$ and the mass of the W boson). We show that measurements of the forward-backward charge asymmetry ($A_{FB}(M,y)$) of Drell-Yan dilepton events produced at hadron colliders provide a new powerful tool to reduce the PDF errors in these measurements,; Comment: 11 pages, 8 Figures, Submitted to EPJC

Constraining the polarized gluon PDF in pp collisions at RHIC

Ellinghaus, Frank; PHENIX, for the; Collaborations, STAR
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
The main focus of the physics program at PHENIX and STAR that makes use of RHIC's polarized proton beams is to figure out how and if at all the gluons inside protons are polarized, or to put it another way, do the spin 1 gluons prefer to have their spins aligned or anti-aligned with the spin of the proton, or do they just not care? This question is an important part of the more general question of how the constituents of protons, gluons and quarks, conspire to make up the overall spin 1/2 of the proton. Measurements of, e.g, jet and hadron, production cross-section differences between the two cases where the two polarized protons colliding have their spins aligned and anti-aligned are sensitive to the gluon polarization, which is encoded in the spin--dependent parton distribution function (PDF) for gluons, Delta-g(x).; Comment: 4 pages, 5 figures, Proceedings of the 34th International Conference on High-Energy Physics (ICHEP 08), Philadelphia, USA, July 29th - August 5th, 2008

Constraining the Intrinsic Heavy Quark PDF via Direct Photon Production in Association with a Heavy Quark Jet

Kovarik, K.; Stavreva, T.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
We investigate a possible use of direct photon production in association with a heavy quark to test different models of intrinsic heavy quark parton distribution function (PDF) at the Tevatron, at the large hadron collider (LHC) and at RHIC.; Comment: 4 pages, to appear in proceedings of DIS2012

Rapid Acquisition Pair Distribution Function (RA-PDF) Analysis

Chupas, Peter J.; Qiu, Xiangyun; Hanson, Jonathan C.; Lee, Peter L.; Grey, Clare P.; Billinge, Simon J. L.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
An image plate (IP) detector coupled with high energy synchrotron radiation was used for atomic pair distribution function (PDF) analysis, with high probed momentum transfer \Qmax $\leq 28.5$ \RAA from crystalline materials. Materials with different structural complexities were measured to test the validity of the quantitative data analysis. Experimental results are presented here for crystalline Ni, crystalline \alf, and the layered Aurivillius type oxides \bivo and \bivtio . Overall, the diffraction patterns show good counting statistics with measuring time from one to tens of seconds. The PDFs obtained are of high quality. Structures may be refined from these PDFs, and the structural models are consistent with the published literature. Data sets from similar samples are highly reproducible.; Comment: 5 pages, 4 figures, submitted to J. Appl. Cryst

Multifractal Analysis of Various PDF in Turbulence based on Generalized Statistics: A Way to Tangles in Superfluid He

Arimitsu, Toshihico; Arimitsu, Naoko
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
By means of the multifractal analysis (MFA), the expressions of the probability density functions (PDFs) are unified in a compact analytical formula which is valid for various quantities in turbulence. It is shown that the formula can explain precisely the experimentally observed PDFs both on log and linear scales. The PDF consists of two parts, i.e., the {\it tail} part and the {\it center} part. The structure of the tail part of the PDFs, determined mostly by the intermittency exponent, represents the intermittent large deviations that is a manifestation of the multifractal distribution of singularities in physical space due to the scale invariance of the Navier-Stokes equation for large Reynolds number. On the other hand, the structure of the center part represents small deviations violating the scale invariance due to thermal fluctuations and/or observation error.; Comment: 10 pages and 5 figures

Nuclear PDF for neutrino and charged lepton data

Kovarik, K.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
Neutrino Deep Inelastic Scattering on nuclei is an essential process to constrain the strange quark parton distribution functions in the proton. The critical component on the way to using the neutrino DIS data in a proton PDF analysis is understanding the nuclear effects in parton distribution functions. We parametrize these effects by nuclear parton distribution functions. Here we compare results from two analysis of NPDF both done at next-to-leading order in QCD. The first uses neutral current charged-lepton lA Deeply Inelastic Scattering and Drell-Yan data for several nuclear targets and the second uses neutrino-nucleon DIS data. We compare the nuclear corrections factors F_2^Fe/F_2^D for the charged-lepton data with other results from the literature. In particular, we compare and contrast fits based upon the charged-lepton DIS data with those using neutrino-nucleon DIS data.; Comment: 3 pages, 2 figures, to be published in Proceedings of 12th International Workshop on Neutrino Factories, Super beams and Beta Beams, 2010

A search for b(c) quark pdf uncertainties at TeV scale ep collider

Aksakal, Husnu; Kara, S. Okan
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
We discuss c\bar{c} and b\bar{b} pair productions at ep collider for studying extremely small x(g) region. It has been shown that Large Hadron electron Collider (LHeC) has a reach of about x(g)>10^{-6}. The aim of this work is to show that the PDF uncertainties in the heavy flavour production. Maximum difference of cross section between PDFs 60% has been found in the process of ep\rightarrow eq\bar{q}X.

Inclusion of W^+- single-spin asymmetry data in a polarised PDF determination via Bayesian reweighting

Nocera, Emanuele R.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
We discuss how the experimental information from longitudinal single-spin asymmetries for $W^{\pm}$ boson production in polarised proton-proton collisions can be included in a polarised parton determination by Bayesian reweighting of a Monte Carlo set of polarised PDF replicas. We explicitly construct a prior ensemble of polarised parton distributions using available fits to inclusive and semi-inclusive DIS data and we discuss the potential impact of existing and future RHIC measurements on it.; Comment: 5 pages, 4 figures, to appear in the proceedings of the 3rd Workshop on the QCD Structure of the Nucleon (QCD-N'12), Bilbao October 2012

The LHC p+Pb run from the nuclear PDF perspective

Paukkunen, Hannu
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
The p+Pb and Pb+Pb runs at the LHC have opened a possibility to investigate the validity of collinear factorization in a clearly higher center-of-mass energy scale than earlier in nuclear collisions. Indeed, some processes that have been measured routinely in p+p($\overline {\rm p}$) collisions and utilized for years in free proton PDF fits, can now finally be reached also in the nuclear case. Such new data are expected to provide conclusive answers concerning the universality of the nuclear PDFs. In this talk, I will contrast some of the first p+Pb and Pb+Pb measurements to the predictions based on the nuclear PDFs.; Comment: Transcription of the talk given in DIS2014 conference

Local 3D real space atomic structure of the simple icosahedral Ho11Mg15Zn74 quasicrystal from PDF data

Bruehne, S.; Uhrig, E.; Gross, C.; Assmus, W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
We present a new complementary strategy to quasicrystalline structure determination: The local atomic structure of simple icosahedral (si) Ho11Mg15Zn74 [a(6D)=5.144(3)A] in a sphere of up to r=17A was refined using the atomic pair distribution function (PDF) from in-house X-ray powder diffraction data (MoKa1, Qmax=13.5A-1; R=20.4%). The basic building block is a 105-atom Bergman-Cluster {Ho8Mg12Zn85}. Its center is occupied by a Zn atom - in contrast to a void in face centred icosahedral (fci) Ho9Mg26Zn65. The center is then surrounded by another 12 Zn atoms, forming an icosahedron (1st shell). The 2nd shell is made up of 8 Ho atoms arranged on the vertices of a cube which in turn is completed to a pentagon dodecahedron by 12 Mg atoms, the dodecahedron then being capped by 12 Zn atoms. The 3rd shell is a distorted soccer ball of 60 Zn atoms, reflecting the higher Zn content of the si phase compared to the fci phase. In our model, 7% of all atoms are situated in between the clusters. The model corresponds to a hypothetical 1/1-approximant of the icosahedral (i) phase. The local coordinations of the single atoms are of a much distorted Frank-Kasper type and call to mind those present in 0/1-Mg2Zn11.; Comment: 18 pages, 8 figures, to appear in Cryst. Res. Tech

PDF reweighting in the Hessian matrix approach

Paukkunen, Hannu; Zurita, Pia
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
239.24152%
We introduce the Hessian reweighting of parton distribution functions (PDFs). Similarly to the better-known Bayesian methods, its purpose is to address the compatibility of new data and the quantitative modifications they induce within an existing set of PDFs. By construction, the method discussed here applies to the PDF fits that carried out a Hessian error analysis using a non-zero tolerance $\Delta\chi^2$. The principle is validated by considering a simple, transparent example. We are also able to establish an agreement with the Bayesian technique provided that the tolerance criterion is appropriately accounted for and that a purely exponential Bayesian likelihood is assumed. As a practical example, we discuss the inclusive jet production at the LHC.; Comment: The final version, to appear in JHEP

Including heavy flavour production in PDF fits

Cooper-Sarkar, A M
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
AT HERA heavy quarks may contribute up to 30% of the structure function $F_2$. The introduction of heavy quarks requires an extension of the DGLAP formalism. The effect of using different heavy flavour number schemes, and different approaches to the running of $\alpha_s$, are compared using the ZEUS PDF fit formalism. The potential of including charm data in the fit is explored, using $D^*$ double differential cross-sections rather than the inclusive quantity $F_2^{c\bar{c}}$.; Comment: 7 pages, 10 figures, contribution to discussion at HERA-LHC workshop 2007

Langevin PDF simulation of particle deposition in a turbulent pipe flow

Chibbaro, Sergio; Minier, Jean-Pierre
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
The paper deals with the description of particle deposition on walls from a turbulent flow over a large range of particle diameter, using a Langevin PDF model. The first aim of the work is to test how the present Langevin model is able to describe this phenomenon and to outline the physical as- pects which play a major role in particle deposition. The general features and characteristics of the present stochastic model are first recalled. Then, results obtained with the standard form of the model are presented along with an analysis which has been carried out to check the sensitivity of the predictions on different mean fluid quantities. These results show that the physical repre- sentation of the near-wall physics has to be improved and that, in particular, one possible route is to introduce specific features related to the near-wall coherent structures. In the following, we propose a simple phenomenological model that introduces some of the effects due to the presence of turbulent coherent structures on particles in a thin layer close to the wall. The results obtained with this phenomenological model are in good agreement with experimental evidence and this suggests to pursue in that direction, towards the development of more general and rigorous stochastic models that provide a link between a geometrical description of turbulent flow and a statistical one.; Comment: 40 pages...

Mean-field/PDF numerical approach for polydispersed turbulent two-phase flows

Peirano, Eric; Chibbaro, Sergio; Pozorski, Jacek; Minier, Jean-Pierre
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
239.24152%
The purpose of this paper is to give an overview in the realm of numerical computations of polydispersed turbulent two-phase flows, using a mean-field/PDF approach. In this approach, the numerical solution is obtained by resorting to a hybrid method where the mean fluid properties are computed by solving mean-field (RANS) equations with a classical finite volume procedure whereas the local instantaneous properties of the particles are determined by solving stochastic differential equations (SDEs). The fundamentals of the general formalism are recalled and particular attention is focused on a specific theoretical issue: the treatment of the multiscale character of the dynamics of the discrete particles, that is the consistency of the system of SDEs in asymptotic cases. Then, the main lines of the particle/mesh algorithm are given and some specific problems, related to the integration of the SDEs, are discussed, for example, issues related to the specificity of the treatment of the averaging and projection operators, the time integration of the SDEs (weak numerical schemes consistent with all asymptotic cases), and the computation of the source terms. Practical simulations, for three different flows, are performed in order to demonstrate the ability of both the models and the numerics to cope with the stringent specificities of polydispersed turbulent two-phase flows.; Comment: 88 pages...

Dynamic Properties of Materials: Phonons from Neutron Scattering

Cope, Elizabeth Ruth
Fonte: University of Cambridge; Christ's College; Department of Earth Sciences Publicador: University of Cambridge; Christ's College; Department of Earth Sciences
Tipo: Thesis; doctoral; PhD
Português
Relevância na Pesquisa
239.24152%
Related article - "FORTRAN routines for the new SQW and PDF modules of GULP and TOBYFIT" at http://www.dspace.cam.ac.uk/handle/1810/225173 in the Data sets - Mineral Science Collection; A detailed understanding of fundamental material properties can be obtained through the study of atomic vibrations, performed experimentally with neutron scattering techniques and coupled with the two powerful new computational methodologies I have developed. The first approach involves phonon-based simulations of the pair distribution function -- a histogram of localised atomic positions generated experimentally from total scattering data. This is used to reveal ordering behaviour, to validate interatomic models and localised structure, and to give insights into how far dynamic behaviour can be studied using total scattering techniques. Most importantly, the long-standing controversy over dynamic disorder in $\beta$-cristobalite is resolved using this technique. Inelastic neutron spectroscopy (INS) allows \emph{direct} study of vibrational modes through their interaction with the neutron beam, and is the experimental basis for the second strand of the new methodology. I have developed new simulation and refinement tools based on the next generation of spectrometers currently being commissioned at the ISIS pulsed neutron source. This allows a detailed powder spectroscopy study of cristobalite and vitreous silica demonstrating that the Bose peak and so-called `fast sound' features can be derived from standard lattice dynamics in both the crystal and the amorphous counterpart...

Large eddy simulation of supersonic combustion with application to scramjet engines

Cocks, Peter
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
Português
Relevância na Pesquisa
239.24152%
This work evaluates the capabilities of the RANS and LES techniques for the simulation of high speed reacting flows. These methods are used to gain further insight into the physics encountered and regimes present in supersonic combustion. The target application of this research is the scramjet engine, a propulsion system of great promise for efficient hypersonic flight. In order to conduct this work a new highly parallelised code, PULSAR, is developed. PULSAR is capable of simulating complex chemistry combustion in highly compressible flows, based on a second order upwind method to provide a monotonic solution in the presence of high gradient physics. Through the simulation of a non-reacting supersonic coaxial helium jet the RANS method is shown to be sensitive to constants involved in the modelling process. The LES technique is more computationally demanding but is shown to be much less sensitive to these model parameters. Nevertheless, LES results are shown to be sensitive to the nature of turbulence at the inflow; however this information can be experimentally obtained. The SCHOLAR test case is used to validate the reacting aspects of PULSAR. Comparing RANS results from laminar chemistry and assumed PDF combustion model simulations...

Modelling of Turbulent Lifted Jet Flames using flamelets: a priori assessment and a posteriori validation

Ruan, S.; Swaminathan, N.; Darbyshire, O.
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Article; accepted version
Português
Relevância na Pesquisa
239.24152%
This is an Accepted Manuscript of an article published by Taylor & Francis in Combustion Theory and Modelling on 4 April 2014, available online: http://wwww.tandfonline.com/10.1080/13647830.2014.898409.; This study focuses on the modelling of turbulent lifted jet flames using flamelets and presumed PDF approach with interests on both flame lift-off height and flame brush structure. First, flamelet models used to capture contributions from premixed and non-premixed modes to the partially premixed combustion in the lifted jet flame are assessed using a Direct Numerical Simulation (DNS) data for turbulent lifted hydrogen jet flame. The joint PDFs of mixture fraction, Z, and progress variable, c, including their statistical correlation are obtained using a copula method, which is also validated using the DNS data. The statistically independent PDFs are found to be generally inadequate to represent the joint PDFs from the DNS data. The effects of Z-c correlation and contribution from non-premixed combustion mode on the flame lift-off height are studied systematically by including one effect at a time in the simulations used for a posteriori validation. A simple model including the effects of chemical kinetics and scalar dissipation rate is suggested and used for non-premixed combustion contributions. The results clearly show that both Z-c correlation and non-premixed combustion effects are required in the premixed flamelets approach to get a good agreement with the measured flame lift-off heights as function of jet velocity. The flame brush structure reported in earlier experimental studies is also captured reasonably well for various axial positions. It seems that the flame stabilisation is influenced by both premixed and non-premixed combustion modes...

FORTRAN routines for the new SQW and PDF modules of GULP and TOBYFIT

Cope, Elizabeth Ruth
Fonte: Mineral Physics Group, Earth Science Dept., University of Cambridge Publicador: Mineral Physics Group, Earth Science Dept., University of Cambridge
Tipo: Dataset; not applicable
Português
Relevância na Pesquisa
239.24152%
This contains the source code for new modules for GULP and TOBYFIT, and is to be used in conjunction with these pre-exisiting codes.; A detailed understanding of fundamental material properties can be obtained through the study of atomic vibrations, performed experimentally with neutron scattering techniques and coupled with the two powerful new computational methodologies I have developed. The first approach involves phonon-based simulations of the pair distribution function -- a histogram of localised atomic positions generated experimentally from total scattering data. Inelastic neutron spectroscopy (INS) allows \emph{direct} study of vibrational modes through their interaction with the neutron beam, and is the experimental basis for the second strand of the new methodology. I have developed new simulation and refinement tools based on the next generation of spectrometers currently being commissioned at the ISIS pulsed neutron source. The new methodology also encompasses refinement of interatomic models against powder INS data, and simulated one-phonon coherent INS spectra for the single crystal and powder (the later including approximations to multi-phonon and multiple scatter) fully convolved with experimental resolution functions. The new modules are written in FORTRAN...