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Galli, P., Goldstein, K., & Perz, J. (2013). On anharmonic stabilisation equations for black holes. J. High Energy Phys., 03(3), 036–7pp.
Abstract: We investigate the stabilisation equations for sufficiently general, yet regular, extremal (supersymmetric and non-supersymmetric) and non-extremal black holes in four-dimensional N = 2 supergravity using both the H-FGK approach and a generalisation of Denef's formalism. By an explicit calculation we demonstrate that the equations necessarily contain an anharmonic part, even in the static, spherically symmetric and asymptotically flat case.
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Villaescusa-Navarro, F., Vogelsberger, M., Viel, M., & Loeb, A. (2013). Neutrino signatures on the high-transmission regions of the Lyman alpha forest. Mon. Not. Roy. Astron. Soc., 431(4), 3670–3677.
Abstract: We quantify the impact of massive neutrinos on the statistics of low-density regions in the intergalactic medium as probed by the Lyman alpha forest at redshifts z = 2.2-4. Based on mock but realistic quasar (QSO) spectra extracted from hydrodynamic simulations with cold dark matter, baryons and neutrinos, we find that the probability distribution of weak Lyman alpha absorption features, as sampled by Lyman alpha flux regions at high transmissivity, is strongly affected by the presence of massive neutrinos. We show that systematic errors affecting the Lyman alpha forest reduce but do not erase the neutrino signal. Using the Fisher matrix formalism, we conclude that the sum of the neutrino masses can be measured, using the method proposed in this paper, with a precision smaller than 0.4 eV using a catalogue of 200 high-resolution (signal-to-noise ratio similar to 100) QSO spectra. This number reduces to 0.27 eV by making use of reasonable priors in the other parameters that also affect the statistics of the high-transitivity regions of the Lyman alpha forest. The constraints obtained with this method can be combined with independent bounds from the cosmic microwave background, large-scale structures and measurements of the matter power spectrum from the Lyman alpha forest to produce tighter upper limits on the sum of the masses of the neutrinos.
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Resta-Lopez, J. (2013). Nonlinear protection of beam delivery systems for multi-TeV linear colliders. J. Instrum., 8, P11010–19pp.
Abstract: The post-linac energy collimation system of future e(+)e(-) multi-TeV linear colliders is designed to fulfil an essential function of protection of the Beam Delivery System (BDS) against miss-steered or errant beams likely generated by failure modes in the main linac. For the case of the Compact Linear Collider (CLIC), the energy collimators are required to withstand the impact of a full bunch train in case of failure. This condition makes the design of the energy collimation system especially challenging, if we take into account the need to dispose of an unprecedented transverse beam energy density per beam of the order of GJ/mm(2), when assuming the nominal CLIC beam parameters at 3 TeV centre-of-mass energy, which translates into an extremely high damage potential of uncontrolled beams. This leads to research activities involving new collimator materials and novel collimation techniques. The increase of the transverse spot size at the collimators using nonlinear magnets is a potential solution to guarantee the survival of the collimators. In this paper we present an alternative nonlinear optics based on a multipole magnet pair for energy collimation. In order to preserve an acceptable luminosity performance, we carefully study the general conditions for self-cancellation of optical aberrations between two multipoles. This nonlinear optics scheme is adapted to the requirements of the post-linac energy collimation system for the CLIC BDS, and its performance is investigated by means of beam tracking simulations. Although applied to the CLIC case, this nonlinear protection system could be adapted to other future colliders.
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Tortola, M. (2013). Status of three-neutrino oscillation parameters. Fortschritte Phys.-Prog. Phys., 61(4-5), 427–440.
Abstract: Here we review the current status of global fits to neutrino oscillation data within the three-flavour framework. In our analysis we include the most recent data from solar and atmospheric neutrino experiments as well as the latest results from the long-baseline accelerator neutrino experiments and the recent measurements of reactor neutrino disappearance reported by Double Chooz, Daya Bay and RENO. We present updated determinations for the two neutrino mass splittings and the three mixing angles responsible for neutrino oscillations that, for the first time, have all been measured with 1 sigma accuracies ranging from 3 to 15%. A weak sensitivity for the CP violating phase is also reported from the global analysis.
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Bonnet, F., Hirsch, M., Ota, T., & Winter, W. (2013). Systematic decomposition of the neutrinoless double beta decay operator. J. High Energy Phys., 03(3), 055–34pp.
Abstract: We discuss the systematic decomposition of the dimension nine neutrinoless double beta decay operator, focusing on mechanisms with potentially small contributions to neutrino mass, while being accessible at the LHC. We first provide a (d = 9 tree-level) complete list of diagrams for neutrinoless double beta decay. From this list one can easily recover all previously discussed contributions to the neutrinoless double beta decay process, such as the celebrated mass mechanism or “exotics”, such as contributions from left-right symmetric models, R-parity violating supersymmetry and leptoquarks. More interestingly, however, we identify a number of new possibilities which have not been discussed in the literature previously. Contact to earlier works based on a general Lorentz-invariant parametrisation of the neutrinoless double beta decay rate is made, which allows, in principle, to derive limits on all possible contributions. We furthermore discuss possible signals at the LHC for mediators leading to the short-range part of the amplitude with one specific example. The study of such contributions would gain particular importance if there were a tension between different measurements of neutrino mass such as coming from neutrinoless double beta decay and cosmology or single beta decay.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2020). Fluctuations of anisotropic flow in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector. J. High Energy Phys., 01(1), 051–59pp.
Abstract: Multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 μb(-1) of Pb+Pb collisions at root s(NN) = 5.02TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of harmonic flow coefficients v(n) and correlated fluctuations between two harmonics v(n) and v(m). For the first time, a non-zero four-particle cumulant is observed for dipolar flow, v(1). The four-particle cumulants for elliptic flow, v(2), and triangular flow, v(3), exhibit a strong centrality dependence and change sign in ultra-central collisions. This sign change is consistent with significant non-Gaussian fluctuations in v(2) and v(3). The four-particle cumulant for quadrangular flow, v(4), is found to change sign in mid-central collisions. Correlations between two harmonics are studied with three- and four-particle mixed-harmonic cumulants, which indicate an anti-correlation between v(2) and v(3), and a positive correlation between v(2) and v(4). These correlations decrease in strength towards central collisions and either approach zero or change sign in ultra-central collisions. To investigate the possible flow fluctuations arising from intrinsic centrality or volume fluctuations, the results are compared between two different event classes used for centrality definitions. In peripheral and mid-central collisions where the cumulant signals are large, only small differences are observed. In ultra-central collisions, the differences are much larger and transverse momentum dependent. These results provide new information to disentangle flow fluctuations from the initial and final states, as well as new insights on the influence of centrality fluctuations.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2010). Charged-particle multiplicities in pp interactions at root s=900 GeV measured with the ATLAS detector at the LHC. Phys. Lett. B, 688(1), 21–42.
Abstract: The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range vertical bar eta vertical bar < 2.5 and p(T) > 500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity eta = 0 is measured to be 1.333 +/- 0.003(stat.) +/- 0.040(syst.), which is 5-15% higher than the Monte Carlo models predict.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Search for quark contact interactions in dijet angular distributions in pp collisions at sqrt(s)=7 TeV measured with the ATLAS detector. Phys. Lett. B, 694(4-5), 327–345.
Abstract: Dijet angular distributions from the first LHC pp collisions at center-of-mass energy root s = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb(-1). Dijet chi distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the chi distributions excludes quark contact interactions with a compositeness scale Lambda below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Measurement of angular correlations in Drell-Yan lepton pairs to probe Z/gamma* boson transverse momentum at root s=7 TeV with the ATLAS detector. Phys. Lett. B, 720(1-3), 32–51.
Abstract: A measurement of angular correlations in Drell-Yan lepton pairs via the phi(eta)* observable is presented. This variable probes the same physics as the Z/gamma* boson transverse momentum with a better experimental resolution. The Z/gamma* -> e(+)e(-) and Z/gamma* -> mu(+)mu(-) decays produced in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV are used. The data were collected with the ATLAS detector at the LHC and correspond to an integrated luminosity of 4.6 fb(-1). Normalised differential cross sections as a function of phi(eta)* are measured separately for electron and muon decay channels. These channels are then combined for improved accuracy. The cross section is also measured double differentially as a function of phi(eta)* for three independent bins of the Z boson rapidity. The results are compared to QCD calculations and to predictions from different Monte Carlo event generators. The data are reasonably well described, in all measured Z boson rapidity regions, by resummed QCD predictions combined with fixed-order perturbative QCD calculations or by some Monte Carlo event generators. The measurement precision is typically better by one order of magnitude than present theoretical uncertainties.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). Measurement of the b-hadron production cross section using decays to D*(+)mu X- final states in pp collisions at root s=7 TeV with the ATLAS detector. Nucl. Phys. B, 864(3), 341–381.
Abstract: The b-hadron production cross section is measured with the ATLAS detector in pp collisions at root s = 7 TeV, using 3.3 pb(-1) of integrated luminosity, collected during the 2010 LHC run. The b-hadrons are selected by partially reconstructing D*(+)mu X- final states. Differential cross sections are measured as functions of the transverse momentum and pseudorapidity. The measured production cross section for a b-hadron with p(T) > 9 GeV and vertical bar eta vertical bar < 2.5 is 32.7 +/- 0.8(stat.)(-6.8)(+4.5)(syst.) μb, higher than the next-to-leading-order QCD predictions but consistent within the experimental and theoretical uncertainties.
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