Nikhef National Institute for Subatomic Physics

Amsterdam, Netherlands

Nikhef National Institute for Subatomic Physics

Amsterdam, Netherlands
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Deigaard I.,Nikhef National Institute for Subatomic Physics
EPJ Web of Conferences | Year: 2016

Despite the absence of experimental evidence, weak scale supersymmetry remains one of the best motivated and studied Standard Model extensions. This talk summarises recent ATLAS results on inclusive searches for supersymmetric squarks and gluinos, including third generation squarks produced in the decay of gluinos. The searches involved final states containing jets, including those tagged as originating from b-quark decays, missing transverse momentum with and without light leptons, taus or photons. Sensitivity projections for the data that will be collected in 2015 are also presented. © 2016 The Authors.


Ciezarek G.,Nikhef National Institute for Subatomic Physics | Franco Sevilla M.,University of California at Santa Barbara | Hamilton B.,University of Maryland University College | Kowalewski R.,University of Victoria | And 3 more authors.
Nature | Year: 2017

One of the key assumptions of the standard model of particle physics is that the interactions of the charged leptons, namely electrons, muons and taus, differ only because of their different masses. Whereas precision tests comparing processes involving electrons and muons have not revealed any definite violation of this assumption, recent studies of B-meson decays involving the higher-mass tau lepton have resulted in observations that challenge lepton universality at the level of four standard deviations. A confirmation of these results would point to new particles or interactions, and could have profound implications for our understanding of particle physics. © 2017 Macmillan Publishers Limited, part of Springer Nature.


Aaij R.,Nikhef National Institute for Subatomic Physics
Acta Physica Polonica B | Year: 2011

One of the key physics goals of the LHCb experiment at the LHC is the measurement of mixing induced CP violation in decays of Bs→ J/ψℙ. The interference between mixing and decay gives rise to a CP-violating phase, ℙsJ/ψℙ. Assuming a proper-time resolution and tagging performance as observed in simulated data, together with an expected luminosity of 1 fb-1 by the end of 2011, LHCb is expected to be able to measure ℙs J/ψℙ with an error of 0.07 rad.


Del Pozzo W.,Nikhef National Institute for Subatomic Physics | Li T.G.F.,Nikhef National Institute for Subatomic Physics | Agathos M.,Nikhef National Institute for Subatomic Physics | Van Den Broeck C.,Nikhef National Institute for Subatomic Physics | Vitale S.,Massachusetts Institute of Technology
Physical Review Letters | Year: 2013

Fisher matrix and related studies have suggested that, with second-generation gravitational-wave detectors, it may be possible to infer the equation of state of neutron stars using tidal effects in a binary inspiral. Here, we present the first fully Bayesian investigation of this problem. We simulate a realistic data analysis setting by performing a series of numerical experiments of binary neutron-star signals hidden in detector noise, assuming the projected final design sensitivity of the Advanced LIGO-Virgo network. With an astrophysical distribution of events (in particular, uniform in comoving volume), we find that only a few tens of detections will be required to arrive at strong constraints, even for some of the softest equations of state in the literature. Thus, direct gravitational-wave detection will provide a unique probe of neutron-star structure. © 2013 American Physical Society.


van Tilburg J.,Nikhef National Institute for Subatomic Physics | van Veghel M.,Nikhef National Institute for Subatomic Physics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

An overview of current experimental bounds on CPT violation in neutral meson mixing is given. New values for the CPT asymmetry in the B0 and Bs0 systems are deduced from published BaBar, Belle and LHCb results. With dedicated analyses, LHCb will be able to further improve the bounds on CPT violation in the D0, B0 and Bs0 systems. Since CPT violation implies violation of Lorentz invariance in an interacting local quantum field theory, the observed CPT asymmetry will exhibit sidereal- and boost-dependent variations. Such CPT-violating and Lorentz-violating effects are accommodated in the framework of the Standard Model Extension (SME). The large boost of the neutral mesons produced at LHCb results in a high sensitivity to the corresponding SME coefficients. For the B0 and Bs0 systems, using existing LHCb results, we determine with high precision the SME coefficients that are not varying with sidereal time. With a full sidereal analysis, LHCb will be able to improve the existing SME bounds in the D0, B0 and Bs0 systems by up to two orders of magnitude. © 2015 The Authors.


Van Den Broeck C.,Nikhef National Institute for Subatomic Physics
Journal of Physics: Conference Series | Year: 2014

The second-generation interferometric gravitational wave detectors, currently under construction are expected to make their first detections within this decade. This will firmly establish gravitational wave physics as an empirical science, and will open up a new era in astrophysics, cosmology, and fundamental physics. Already with the first detections, we will be able to, among other things, establish the nature of short-hard gamma ray bursts, definitively confirm the existence of black holes, measure the Hubble constant in a completely independent way, and for the first time gain access to the genuinely strong-field dynamics of gravity. Hence, it is time to consider the longer-term future of this new field. The Einstein Telescope (ET) is a concrete conceptual proposal for a third-generation gravitational wave observatory, which will be ∼ 10 times more sensitive in strain than the second-generation detectors. This will give access to sources at cosmological distances, with a correspondingly higher detection rate. We have given an overview of the science case for ET, with a focus on what can be learned from signals emitted by coalescing compact binaries. Third-generation observatories will allow us to map the coalescence rate out to redshifts z ∼ 3, determine the mass functions of neutron stars and black holes, and perform precision measurements of the neutron star equation of state. ET will enable us to study the large-scale structure and evolution of the Universe without recourse to a cosmic distance ladder. Finally, we have discussed how it will allow for high-precision measurements of strong-field, dynamical gravity. © Published under licence by IOP Publishing Ltd.


De Bruyn K.,Nikhef National Institute for Subatomic Physics
Journal of Physics: Conference Series | Year: 2014

Studies of CP violation play a key role in the search for physics beyond the Standard Model. In the B0 s system these mainly consist of measurements of mixing-induced CP violation, which arises from the interference between the B0 s-B¯0 s mixing process and the subsequent decay. This report focusses on two such asymmetry measurements recently published by the LHCb collaboration. The first analysis presents the measurement of a CP violating phase in B0 s → φφ, which is found to be φφφ -0.17±0.15(stat)±0.03(syst)rad. The second provides an updated measurement of the B0 s-B¯0 s mixing phase φs using the B0 s → J/ψπ+π- channel. It yields φs 0.070 ± 0.068 (stat) ± 0.008 (syst) rad. Both results are consistent with the Standard Model expectations and no indication for direct CP violation was found in either decay mode. © Published under licence by IOP Publishing Ltd.


Del Pozzo W.,University of Birmingham | Del Pozzo W.,Nikhef National Institute for Subatomic Physics | Veitch J.,University of Birmingham | Veitch J.,University of Cardiff | Vecchio A.,University of Birmingham
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

Second-generation interferometric gravitational-wave detectors, such as Advanced LIGO and Advanced Virgo, are expected to begin operation by 2015. Such instruments plan to reach sensitivities that will offer the unique possibility to test general relativity in the dynamical, strong-field regime and investigate departures from its predictions, in particular, using the signal from coalescing binary systems. We introduce a statistical framework based on Bayesian model selection in which the Bayes factor between two competing hypotheses measures which theory is favored by the data. Probability density functions of the model parameters are then used to quantify the inference on individual parameters. We also develop a method to combine the information coming from multiple independent observations of gravitational waves, and show how much stronger inference could be. As an introduction and illustration of this framework-and a practical numerical implementation through the Monte Carlo integration technique of nested sampling-we apply it to gravitational waves from the inspiral phase of coalescing binary systems as predicted by general relativity and a very simple alternative theory in which the graviton has a nonzero mass. This method can (and should) be extended to more realistic and physically motivated theories. © 2011 American Physical Society.


Zhao W.,University of Cardiff | Van Den Broeck C.,Nikhef National Institute for Subatomic Physics | Baskaran D.,University of Cardiff | Li T.G.F.,Nikhef National Institute for Subatomic Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

A design study is currently in progress for a third-generation gravitational-wave (GW) detector called the Einstein Telescope (ET). An important kind of source for ET will be the inspiral and merger of binary neutron stars up to z∼2. If binary neutron star mergers are the progenitors of short-hard γ-ray bursts, then some fraction of them will be seen both electromagnetically and through GW, so that the luminosity distance and the redshift of the source can be determined separately. An important property of these "standard sirens" is that they are self-calibrating: the luminosity distance can be inferred directly from the GW signal, with no need for a cosmic distance ladder. Thus, standard sirens will provide a powerful independent check of the ΛCDM model. In previous work, estimates were made of how well ET would be able to measure a subset of the cosmological parameters (such as the dark energy parameter w0) it will have access to, assuming that the others had been determined to great accuracy by alternative means. Here we perform a more careful analysis by explicitly using the potential Planck cosmic microwave background data as prior information for these other parameters. We find that ET will be able to constrain w0 and wa with accuracies Δw0=0.099 and Δw a=0.302, respectively. These results are compared with projected accuracies for the JDEM baryon acoustic oscillations project and the SNAP type Ia supernovae observations. © 2011 The American Physical Society.


Vitale S.,Massachusetts Institute of Technology | Del Pozzo W.,Nikhef National Institute for Subatomic Physics | Del Pozzo W.,University of Birmingham
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The upcoming direct detection of gravitational waves will open a window to probing the strong-field regime of general relativity. As a consequence, waveforms that include the presence of deviations from general relativity have been developed (e.g., in the parametrized post-Einsteinian approach). TIGER, a data analysis pipeline which builds Bayesian evidence to support or question the validity of general relativity, has been written and tested. In particular, it was shown that the LIGO and Virgo detectors can probe deviations from general relativity in a regime than cannot be tested by Solar System tests or pulsar timing measurements. However, evidence from several detections is required before a deviation from general relativity can be confidently claimed. An interesting consequence is that, should general relativity not be the correct theory of gravity in its strong field regime, using standard general relativity templates for the matched filter analysis of interferometer data will introduce biases in the gravitational wave measured parameters with potentially serious consequences on the astrophysical inferences, such as the coalescence rate or the mass distribution. In this work we consider three heuristic possible deviations from general relativity and show that the biases introduced in the estimated parameters of gravitational waves emitted during the inspiral phase of spinless compact binary coalescence systems assuming the validity of general relativity manifest in various ways. The mass parameters are usually the most affected, with biases that can be as large as 30 standard deviations for the symmetric mass ratio, and nearly one percent for the chirp mass, which is usually estimated with subpercent accuracy. Other parameters do not show a significant bias. We conclude that statements about the nature of the observed sources, e.g., if both objects are neutron stars, depend critically on the explicit assumption that general relativity is the right theory of gravity in the strong field regime. © 2014 American Physical Society.

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