arXiv subjects

D. Brett

Publications and source records attributed to D. Brett.

262 records · Page 15Linked to original sources

arXiv2012

Absolute luminosity measurements with the LHCb detector at the LHC

Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of the accelerator. Using data taken in 2010, LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of 7 TeV. In addition to the classic "van der Meer scan" method a novel technique has been developed which makes use of direct imaging of the individual beams using beam-gas and beam-beam interactions. This beam imaging method is made possible by the high resolution of the LHCb vertex detector and the close proximity of the detector to the beams, and allows beam parameters such as positions, angles and widths to be determined. The results of the two methods have comparable precision and are in good agreement. Combining the two methods, an overall precision of 3.5% in the absolute luminosity determination is reached. The techniques used to transport the absolute luminosity calibration to the full 2010 data-taking period are presented.

hep-ex↗

arXiv2012

Measurement of the CP violating phase ϕ_s in Bs->J/ψf0(980)

Measurement of mixing-induced CP violation in Bs decays is of prime importance in probing new physics. So far only the channel Bs->J/ψϕ has been used. Here we report on a measurement using an LHCb data sample of 0.41/fb in the CP odd eigenstate Jψf0(980), where f0(980)->π+ π-. A time dependent fit of the data with the Bs lifetime and the difference in widths of the heavy and light eigenstates constrained to the values obtained from Bs-> J/ψϕ yields a value of the CP violating phase of -0.44 +/- 0.44 +/- 0.02 rad, consistent with the Standard Model expectation.

hep-ex↗

arXiv2012

Observation of $J/ψ$ pair production in pp collisions at $\sqrt{s}=7 TeV$

The production of $J/ψ$ pairs in proton-proton collisions at a centre-of-mass energy of 7 TeV has been observed using an integrated luminosity of $37.5 pb^{-1}$ collected with the LHCb detector. The production cross-section for pairs with both \jpsi in the rapidity range $2<y^{J/ψ}<4.5$ and transverse momentum $p_{T}^{J/ψ}<10 GeV/c$ is $$ σ^{J/ψJ/ψ} = 5.1\pm1.0\pm1.1 nb,$$ where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2011

Measurement of mixing and CP violation parameters in two-body charm decays

A study of mixing and indirect CP violation in D0 mesons through the determination of the parameters y_CP and A_Γ is presented. The parameter y_CP is the deviation from unity of the ratio of effective lifetimes measured in D0 decays to the CP eigenstate K+K- with respect to decays to the Cabibbo favoured mode K-π+. The result measured using data collected by LHCb in 2010, corresponding to an integrated luminosity of 29 pb^-1, is y_CP = (5.5+/-6.3_{stat}+/-4.1_{syst}) x 10^-3. The parameter A_Γ is the asymmetry of effective lifetimes measured in decays of D0 and anti-D0 mesons to K+K-. The result is A_Γ = (-5.9+/-5.9_{stat}+/-2.1_{syst}) x 10^-3. A data-driven technique is used to correct for lifetime-biasing effects.

hep-ex↗

arXiv2011

Measurement of charged particle multiplicities in $pp$ collisions at ${\sqrt{s} =7}$TeV in the forward region

The charged particle production in proton-proton collisions is studied with the LHCb detector at a centre-of-mass energy of ${\sqrt{s} =7}$TeV in different intervals of pseudorapidity $η$. The charged particles are reconstructed close to the interaction region in the vertex detector, which provides high reconstruction efficiency in the $η$ ranges $-2.5<η<-2.0$ and $2.0<η<4.5$. The data were taken with a minimum bias trigger, only requiring one or more reconstructed tracks in the vertex detector. By selecting an event sample with at least one track with a transverse momentum greater than 1 GeV/c a hard QCD subsample is investigated. Several event generators are compared with the data; none are able to describe fully the multiplicity distributions or the charged particle density distribution as a function of $η$. In general, the models underestimate the charged particle production.

hep-ex↗

arXiv2011

First observation of the decay $\bar{B}^0_s \to D^0 K^{0}$ and a measurement of the ratio of branching fractions $\frac{{\cal B}(\bar{B}^0_s \to D^0 K^{0})}{{\cal B}(\bar{B}^0 \to D^0 ρ^0)}$

The first observation of the decay $\bar{B}^0_s \to D^0 K^{*0}$ using $pp$ data collected by the LHCb detector at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 36 pb$^{-1}$, is reported. A signal of $34.4 \pm 6.8$ events is obtained and the absence of signal is rejected with a statistical significance of more than nine standard deviations. The $\bar{B}^0_s \to D^0 K^{*0}$ branching fraction is measured relative to that of $\bar{B}^0 \to D^0 ρ^0$: $\frac{{\cal B}(\bar{B}^0_s \to D^0 K^{*0})}{{\cal B}(\bar{B}^0 \to D^0 ρ^0)} = 1.48 \pm 0.34 \pm 0.15 \pm 0.12$, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the $B^0$ and $B^0_s$ hadronisation fractions.

hep-ex↗

arXiv2011

Search for CP violation in $D^{+} \to K^{-}K^{+}π^{+}$ decays

A model-independent search for direct CP violation in the Cabibbo suppressed decay $D^+ \to K^- K^+π^+$ in a sample of approximately 370,000 decays is carried out. The data were collected by the LHCb experiment in 2010 and correspond to an integrated luminosity of 35 pb$^{-1}$. The normalized Dalitz plot distributions for $D^+$ and $D^-$ are compared using four different binning schemes that are sensitive to different manifestations of CP violation. No evidence for CP asymmetry is found.

hep-ex↗

arXiv2011

Measurements of the Branching fractions for $B_(s) -> D_(s)πππ$ and $Λ_b^0 -> Λ_c^+πππ$

Branching fractions of the decays $H_b\to H_cπ^-π^+π^-$ relative to $H_b\to H_cπ^-$ are presented, where $H_b$ ($H_c$) represents B^0-bar($D^+$), $B^-$ ($D^0$), B_s^0-bar ($D_s^+$) and $Λ_b^0$ ($Λ_c^+$). The measurements are performed with the LHCb detector using 35${\rm pb^{-1}}$ of data collected at $\sqrt{s}=7$ TeV. The ratios of branching fractions are measured to be B(B^0-bar -> D^+π^-π^+π^-)/ B(B^0-bar -> D^+π^-) = 2.38\pm0.11\pm0.21 B(B^- -> D^0π^-π^+π^-) / B(B^- -> D^0π^-) = 1.27\pm0.06\pm0.11 B(B_s^0-bar -> D_s^+π^-π^+π^-) / B(B_s^0-bar -> D_s^+π^-) = 2.01\pm0.37\pm0.20 B(Λ_b^0->Λ_c^+π^-π^+π^-) / B(Λ_b^0 -> Λ_c^+π^-) = 1.43\pm0.16\pm0.13. We also report measurements of partial decay rates of these decays to excited charm hadrons. These results are of comparable or higher precision than existing measurements.

hep-ex↗

arXiv2011

Measurement of the inclusive phi cross-section in pp collisions at sqrt(s) = 7 TeV

The cross-section for inclusive phi meson production in pp collisions at a centre-of-mass energy of sqrt(s) = 7 TeV has been measured with the LHCb detector at the Large Hadron Collider. The differential cross-section is measured as a function of the phi transverse momentum p_T and rapidity y in the region 0.6 < p_T < 5.0 GeV/c and 2.44 < y < 4.06. The cross-section for inclusive phi production in this kinematic range is sigma(pp -> phi X) = 1758 pm 19(stat) ^{+43}_{-14}(syst) pm 182(scale) microbarn, where the first systematic uncertainty depends on the p_T and y region and the second is related to the overall scale. Predictions based on the Pythia 6.4 generator underestimate the cross-section.

hep-ex↗

arXiv2002

SuperWASP: Wide Angle Search for Planets

SuperWASP is a fully robotic, ultra-wide angle survey for planetary transits. Currently under construction, it will consist of 5 cameras, each monitoring a 9.5 x 9.5 deg field of view. The Torus mount and enclosure will be fully automated and linked to a built-in weather station. We aim to begin observations at the beginning of 2003.

astro-ph↗