105 research outputs found
Wide-coverage statistical parsing with minimalist grammars
Syntactic parsing is the process of automatically assigning a structure to a string
of words, and is arguably a necessary prerequisite for obtaining a detailed and precise
representation of sentence meaning. For many NLP tasks, it is sufficient to use
parsers based on simple context free grammars. However, for tasks in which precision
on certain relatively rare but semantically crucial constructions (such as unbounded
wh-movements for open domain question answering) is important, more expressive
grammatical frameworks still have an important role to play.
One grammatical framework which has been conspicuously absent from journals
and conferences on Natural Language Processing (NLP), despite continuing to dominate
much of theoretical syntax, is Minimalism, the latest incarnation of the Transformational
Grammar (TG) approach to linguistic theory developed very extensively
by Noam Chomsky and many others since the early 1950s. Until now, all parsers
using genuine transformational movement operations have had only narrow coverage
by modern standards, owing to the lack of any wide-coverage TG grammars or treebanks
on which to train statistical models. The received wisdom within NLP is that
TG is too complex and insufficiently formalised to be applied to realistic parsing tasks.
This situation is unfortunate, as it is arguably the most extensively developed syntactic
theory across the greatest number of languages, many of which are otherwise
under-resourced, and yet the vast majority of its insights never find their way into NLP
systems. Conversely, the process of constructing large grammar fragments can have
a salutary impact on the theory itself, forcing choices between competing analyses of
the same construction, and exposing incompatibilities between analyses of different
constructions, along with areas of over- and undergeneration which may otherwise go
unnoticed.
This dissertation builds on research into computational Minimalism pioneered by
Ed Stabler and others since the late 1990s to present the first ever wide-coverage Minimalist
Grammar (MG) parser, along with some promising initial experimental results.
A wide-coverage parser must of course be equipped with a wide-coverage grammar,
and this dissertation will therefore also present the first ever wide-coverage MG, which
has analyses with a high level of cross-linguistic descriptive adequacy for a great many
English constructions, many of which are taken or adapted from proposals in the mainstream
Minimalist literature. The grammar is very deep, in the sense that it describes
many long-range dependencies which even most other expressive wide-coverage grammars
ignore. At the same time, it has also been engineered to be highly constrained,
with continuous computational testing being applied to minimize both under- and over-generation.
Natural language is highly ambiguous, both locally and globally, and even with a
very strong formal grammar, there may still be a great many possible structures for a
given sentence and its substrings. The standard approach to resolving such ambiguity
is to equip the parser with a probability model allowing it to disregard certain unlikely
search paths, thereby increasing both its efficiency and accuracy. The most successful
parsing models are those extracted in a supervised fashion from labelled data in the
form of a corpus of syntactic trees, known as a treebank. Constructing such a treebank
from scratch for a different formalism is extremely time-consuming and expensive,
however, and so the standard approach is to map the trees in an existing treebank into
trees of the target formalism. Minimalist trees are considerably more complex than
those of other formalisms, however, containing many more null heads and movement
operations, making this conversion process far from trivial. This dissertation will describe
a method which has so far been used to convert 56% of the Penn Treebank trees
into MG trees. Although still under development, the resulting MGbank corpus has
already been used to train a statistical A* MG parser, described here, which has an
expected asymptotic time complexity of O(n3); this is much better than even the most
optimistic worst case analysis for the formalism
Search for the lepton flavour violating decay tau(-) -> mu(-)mu(+)mu(-)
A search for the lepton flavour violating decay is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of 1.0 fb of proton-proton collisions at a centre-of-mass energy of 7 TeV and 2.0 fb at 8 TeV. No evidence is found for a signal, and a limit is set at 90% confidence level on the branching fraction, .A search for the lepton flavour violating decay τ → μ μ μ is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of 1.0 fb of proton-proton collisions at a centre-of-mass energy of 7 TeV and 2.0 fb at 8 TeV. No evidence is found for a signal, and a limit is set at 90% confidence level on the branching fraction, .A search for the lepton flavour violating decay is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of of proton-proton collisions at a centre-of-mass energy of and at . No evidence is found for a signal, and a limit is set at confidence level on the branching fraction,
Search for CP violation using T-odd correlations in D-0 -> K+K-pi(+)pi(-) decays
A search for violation using -odd correlations is performed using the four-body decay, selected from semileptonic decays. The data sample corresponds to integrated luminosities of and recorded at the centre-of-mass energies of 7 TeV and 8 TeV, respectively. The -violating asymmetry is measured to be . Searches for violation in different regions of phase space of the four-body decay, and as a function of the decay time, are also presented. No significant deviation from the conservation hypothesis is found
Study of the rare B-s(0) and B-0 decays into the pi(+) pi(-) mu(+) mu(-) final state
A search for the rare decays and is performed in a data set corresponding to an integrated luminosity of 3.0 fb collected by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5-1.3 GeV/ and with muon pairs that do not originate from a resonance are considered. The first observation of the decay and the first evidence of the decay are obtained and the branching fractions are measured to be and , where the third uncertainty is due to the branching fraction of the decay , used as a normalisation.A search for the rare decays Bs0→π+π−μ+μ− and B0→π+π−μ+μ− is performed in a data set corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb detector in proton–proton collisions at centre-of-mass energies of 7 and 8 TeV . Decay candidates with pion pairs that have invariant mass in the range 0.5–1.3 GeV/c2 and with muon pairs that do not originate from a resonance are considered. The first observation of the decay Bs0→π+π−μ+μ− and the first evidence of the decay B0→π+π−μ+μ− are obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be B(Bs0→π+π−μ+μ−)=(8.6±1.5 (stat)±0.7 (syst)±0.7(norm))×10−8 and B(B0→π+π−μ+μ−)=(2.11±0.51(stat)±0.15(syst)±0.16(norm))×10−8 , where the third uncertainty is due to the branching fraction of the decay B0→J/ψ(→μ+μ−)K⁎(892)0(→K+π−) , used as a normalisation.A search for the rare decays Bs0→π+π−μ+μ− and B0→π+π−μ+μ− is performed in a data set corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb detector in proton–proton collisions at centre-of-mass energies of 7 and 8 TeV . Decay candidates with pion pairs that have invariant mass in the range 0.5–1.3 GeV/c2 and with muon pairs that do not originate from a resonance are considered. The first observation of the decay Bs0→π+π−μ+μ− and the first evidence of the decay B0→π+π−μ+μ− are obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be B(Bs0→π+π−μ+μ−)=(8.6±1.5 (stat)±0.7 (syst)±0.7(norm))×10−8 and B(B0→π+π−μ+μ−)=(2.11±0.51(stat)±0.15(syst)±0.16(norm))×10−8 , where the third uncertainty is due to the branching fraction of the decay B0→J/ψ(→μ+μ−)K⁎(892)0(→K+π−) , used as a normalisation.A search for the rare decays and is performed in a data set corresponding to an integrated luminosity of 3.0 fb collected by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5-1.3 GeV/ and with muon pairs that do not originate from a resonance are considered. The first observation of the decay and the first evidence of the decay are obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be and , where the third uncertainty is due to the branching fraction of the decay , used as a normalisation
Angular analysis of the B-0 -> K*(0) e(+) e(-) decay in the low-q(2) region
An angular analysis of the decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 {\mbox{fb}^{-1}}, collected by the LHCb experiment in collisions at centre-of-mass energies of 7 and 8 TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared () interval between 0.002 and 1.120. The angular observables and which are related to the polarisation and to the lepton forward-backward asymmetry, are measured to be and , where the first uncertainty is statistical and the second systematic. The angular observables and which are sensitive to the photon polarisation in this range, are found to be and . The results are consistent with Standard Model predictions.An angular analysis of the B → K^{*}^{0} e e decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 fb, collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared (q) interval between 0.002 and 1.120 GeV /c. The angular observables F and A which are related to the K^{*}^{0} polarisation and to the lepton forward-backward asymmetry, are measured to be F = 0.16 ± 0.06 ± 0.03 and A = 0.10 ± 0.18 ± 0.05, where the first uncertainty is statistical and the second systematic. The angular observables A and A which are sensitive to the photon polarisation in this q range, are found to be A = − 0.23 ± 0.23 ± 0.05 and A = 0.14 ± 0.22 ± 0.05. The results are consistent with Standard Model predictions.An angular analysis of the decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 {\mbox{fb}^{-1}}, collected by the LHCb experiment in collisions at centre-of-mass energies of 7 and 8 TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared () interval between 0.002 and 1.120. The angular observables and which are related to the polarisation and to the lepton forward-backward asymmetry, are measured to be and , where the first uncertainty is statistical and the second systematic. The angular observables and which are sensitive to the photon polarisation in this range, are found to be and . The results are consistent with Standard Model predictions
Measurement of CP asymmetry in B-s(0) -> D-s(-/+) K--/+ decays
We report on measurements of the time-dependent CP violating observables in decays using a dataset corresponding to 1.0 fb of pp collisions recorded with the LHCb detector. We find the CP violating observables , , , , , where the uncertainties are statistical and systematic, respectively. We use these observables to make the first measurement of the CKM angle in decays, finding = (115) modulo 180 at 68% CL, where the error contains both statistical and systematic uncertainties.We report on measurements of the time-dependent CP violating observables in B → D K decays using a dataset corresponding to 1.0 fb of pp collisions recorded with the LHCb detector. We find the CP violating observables C = 0.53±0.25±0.04, A = 0.37 ± 0.42 ± 0.20, , S = −1.09±0.33±0.08, , where the uncertainties are statistical and systematic, respectively. Using these observables together with a recent measurement of the B mixing phase −2β leads to the first extraction of the CKM angle γ from B → D K decays, finding γ = (115 )° modulo 180° at 68% CL, where the error contains both statistical and systematic uncertainties.We report on measurements of the time-dependent CP violating observables in decays using a dataset corresponding to 1.0 fb of pp collisions recorded with the LHCb detector. We find the CP violating observables , , , , , where the uncertainties are statistical and systematic, respectively. Using these observables together with a recent measurement of the mixing phase leads to the first extraction of the CKM angle from decays, finding = (115) modulo 180 at 68% CL, where the error contains both statistical and systematic uncertainties
Measurement of the Z plus b-jet cross-section in pp collisions at root s=7 TeV in the forward region
The associated production of a Z boson or an off-shell photon with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of . The Z bosons are reconstructed in the final state from muons with a transverse momentum larger than , while two transverse momentum thresholds are considered for jets ( and ). Both muons and jets are reconstructed in the pseudorapidity range , and \sigma(\text{\text{Z}/\gamma^*(\mu^{+}\mu^{-})+b-jet}) = 167 \pm 47 (\text{stat}) \pm 29 (\text{syst}) \pm 6 (\text{lumi}) {\,{fb}} for {p_{\rm T}}(jet)
Precise measurements of the properties of the B-1(5721)(0,+) and B-2*(5747)(0,+) states and observation of B-+,B-0 pi(-,+) mass structures
Invariant mass distributions of and combinations are investigated in order to study excited B mesons. The analysis is based on a data sample corresponding to of collision data, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses and widths of the and states are reported. Clear enhancements, particularly prominent at high pion transverse momentum, are seen over background in the mass range - MeV in both and combinations. The structures are consistent with the presence of four excited B mesons, labelled and , whose masses and widths are obtained under different hypotheses for their quantum numbers.Invariant mass distributions of B π and B π combinations are investigated in order to study excited B mesons. The analysis is based on a data sample corresponding to 3.0 fb of pp collision data, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses and widths of the B(5721) and B(5747) states are reported. Clear enhancements, particularly prominent at high pion transverse momentum, are seen over background in the mass range 5850-6000 MeV in both B π and B π combinations. The structures are consistent with the presence of four excited B mesons, labelled B (5840) and B (5960), whose masses and widths are obtained under different hypotheses for their quantum numbers.Invariant mass distributions of B+pi- and B0pi+ combinations are investigated in order to study excited B mesons. The analysis is based on a data sample corresponding to 3.0 fb-1 of pp collision data, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses and widths of the B_1(5721)^(0,+) and B_2*(5747)^(0,+) states are reported. Clear enhancements, particularly prominent at high pion transverse momentum, are seen over background in the mass range 5850--6000 MeV in both B+pi- and B0pi+ combinations. The structures are consistent with the presence of four excited B mesons, labelled B_J(5840)^(0,+) and B_J(5960)^(0,+), whose masses and widths are obtained under different hypotheses for their quantum numbers
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