45 research outputs found
Geometrical tests of cosmological models. I. Probing dark energy using the kinematics of high redshift galaxies
We suggest to use the observationally measured and theoretically justified correlation between size and rotational velocity of galactic discs as a viable method to select a set of high redshift standard rods which may be used to explore the dark energy content of the universe via the classical angular-diameter test. Here we explore a new strategy for an optimal implementation of this test.We propose to use the rotation speed of high redshift galaxies as a standard size indicator and show how high resolution multi-object spectroscopy and ACS/HST high quality spatial images, may be combined to measure the amplitude of the dark energy density parameter ΩQ, or to constrain the cosmic equation of state parameter for a smooth dark energy component (w = p/Ï, â1 †w < â1/3). Nearly 1300 standard rods with high velocity rotation in the bin V = 200 ± 20 km sâ1 are expected in a field of 1 sq. degree and over the
redshift baseline 0 < z < 1.4. This sample is sufficient to constrain the cosmic equation of state parameter w at a level of 20% (without priors in the [Ωm,ΩQ] plane) even when the [OII]λ3727 Ă
linewidth-diameter relationship is calibrated with a scatter of âŒ40%. We evaluate how systematics may affect the proposed tests, and find that a linear standard rod evolution, causing galaxy dimensions
to be up to 30% smaller at z = 1.5, can be uniquely diagnosed, and will minimally bias the confidence level contours in the [ΩQ, w] plane. Finally, we show how to derive, without a priori knowing the specific functional form of disc evolution, a cosmologyevolution diagram with which it is possible to establish a mapping between different cosmological models and the amount of galaxy
disc/luminosity evolution expected at a given redshift
Differential branching fraction and angular analysis of the decay B0âKâ0ÎŒ+ÎŒâ
The angular distribution and differential branching fraction of the decay B 0â K â0 ÎŒ + ÎŒ â are studied using a data sample, collected by the LHCb experiment in pp collisions at sâ=7 TeV, corresponding to an integrated luminosity of 1.0 fbâ1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Observation of the decay
The decay is observed for the first
time, using proton-proton collisions collected with the LHCb detector
corresponding to an integrated luminosity of 3fb. A signal yield of
decays is reported with a significance of 6.2 standard deviations.
The ratio of the branching fraction of \B_c \rightarrow J/\psi K^+ K^- \pi^+
decays to that of decays is measured to be
, where the first uncertainty is statistical and the
second is systematic.Comment: 18 pages, 2 figure
Strong constraints on the rare decays Bs -> mu+ mu- and B0 -> mu+ mu-
A search for Bs -> mu+ mu- and B0 -> mu+ mu- decays is performed using 1.0
fb^-1 of pp collision data collected at \sqrt{s}=7 TeV with the LHCb experiment
at the Large Hadron Collider. For both decays the number of observed events is
consistent with expectation from background and Standard Model signal
predictions. Upper limits on the branching fractions are determined to be BR(Bs
-> mu+ mu-) mu+ mu-) < 1.0 (0.81) x 10^-9 at
95% (90%) confidence level.Comment: 2+6 pages; 4 figures; Accepted for publication in Physical Review
Letter
Measurements of the branching fractions of the decays B°s â Dâs K± and B°s â DÂŻsÏ+
The decay mode B°s â Dâs K± allows for one of the theoretically cleanest measurements of the CKM angle Îł through the study of time-dependent CP violation. This paper reports a measurement of its branching fraction relative to the Cabibbo-favoured mode B°s â DÂŻsÏ+ based on a data sample corresponding to 0.37 fbÂŻÂč of proton-proton collisions at âs = 7TeV collected in 2011 with the LHCb detector. In addition, the ratio of B meson production fractions fs/fd, determined from semileptonic decays, together with the known branching fraction of the control channel B°s â DÂŻsÏ+ is used to perform an absolute measurement of the branching fractions: B(B°s â DÂŻsÏ+) = (2.95 ± 0.05 ± 0.17 -0.22 +0.18) Ă 10ÂŻÂł ; B(B°s â Dâs K±) = (1.90 ± 0.12 ± 0.13 -0.14 +0.12) Ă 10ÂŻ4 ; where the first uncertainty is statistical, the second the experimental systematic uncertainty, and the third the uncertainty due to f s/f
Measurement of the CP-violating phase phi_s in the decay Bs->J/psi phi
We present a measurement of the time-dependent CP-violating asymmetry in B_s
-> J/psi phi decays, using data collected with the LHCb detector at the LHC.
The decay time distribution of B_s -> J/psi phi is characterized by the decay
widths Gamma_H and Gamma_L of the heavy and light mass eigenstates of the
B_s-B_s-bar system and by a CP-violating phase phi_s. In a sample of about 8500
B_s -> J/psi phi events isolated from 0.37 fb^-1 of pp collisions at sqrt(s)=7
TeV we measure phi_s = 0.15 +/- 0.18 (stat) +/- 0.06 (syst) rad. We also find
an average B_s decay width Gamma_s == (Gamma_L + Gamma_H)/2 = 0.657 +/- 0.009
(stat) +/- 0.008 (syst) ps^-1 and a decay width difference Delta Gamma_s ==
Gamma_L - Gamma_H} = 0.123 +/- 0.029 (stat) +/- 0.011 (syst) ps^-1. Our
measurement is insensitive to the transformation (phi_s,DeltaGamma_s --> pi -
phi_s, - Delta Gamma_s.Comment: 9 pages, 3 figure
Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution
Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with nââ=ââ2 RMP maintaining good confinement . Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes
Observation of the decay Bc+âÏ(2S)Ï+
The decay Bc+âÏ(2S)Ï+ with Ï(2S)âÎŒ+ÎŒ- is observed with a significance of 5.2Ï using pp collision data corresponding to an integrated luminosity of 1.0ââfb-1 collected by the LHCb experiment. The branching fraction of Bc+âÏ(2S)Ï+ decays relative to that of the Bc+âJ/ÏÏ+ mode is measured to be B(Bc+âÏ(2S)Ï+)/B(Bc+âJ/ÏÏ+)=0.250±0.068(stat)±0.014(syst)±0.006(B). The last term is the uncertainty on the ratio B(Ï(2S)âÎŒ+ÎŒ-)/B(J/ÏâÎŒ+ÎŒ-)
Measurement of the cross-section ratio for prompt production at TeV
The prompt production of the charmonium and mesons
has been studied in proton-proton collisions at the Large Hadron Collider at a
centre-of-mass energy of TeV. The mesons are identified
through their decays with
using 36 of data collected by the LHCb detector in 2010. The
ratio of the prompt production cross-sections for the two spin states,
, has been determined as a function of the
transverse momentum, , in the range from 2 to
15 GeV/. The results are in agreement with the next-to-leading order
non-relativistic QCD model at high and lie
consistently above the pure leading-order colour singlet prediction.Comment: 13 pages, 3 figure
Measurement of b hadron production fractions in 7 TeV pp collisions
Measurements of hadron production ratios in proton-proton collisions at a
centre-of-mass energy of 7 TeV with an integrated luminosity of 3 pb are
presented. We study the ratios of strange meson to light meson
production and baryon to light meson
production as a function of the charmed hadron-muon
pair transverse momentum and the hadron pseudorapidity , for
between 0 and 14 GeV and between 2 and 5. We find that
is consistent with being independent of and ,
and we determine = 0.134 0.004 , where
the first error is statistical and the second systematic. The corresponding
ratio is found to be dependent upon the transverse
momentum of the charmed hadron-muon pair, , where Br reflects an absolute scale
uncertainty due to the poorly known branching fraction Br(\Lambda_c^+ \to
pK^-\pi^+)BBf_s/f_d\bar{B}_s \to
D_S^+ \pi ^-\bar{B}^0 \to D^+K^-\bar{B}^0 \to D^+\pi^-f_s/f_d=0.267^{+0.021}_{-0.020}$.Comment: 28 pages, 12 figures, version accepted for publication in Physical
Review D, few more detailed explanations on analysis methods adde