arXiv subjects

A. Affolder

Publications and source records attributed to A. Affolder.

At least 235 records · Page 13Linked to original sources

arXiv2013

Search for the decay Bs -> D*-+ π+-

A search for the decay Bs -> D*-+ π+- is presented using a data sample corresponding to an integrated luminosity of 1.0 fb-1 of pp collisions collected by LHCb. This decay is expected to be mediated by a W-exchange diagram, with little contribution from rescattering processes, and therefore a measurement of the branching fraction will help to understand the mechanism behind related decays such as Bs -> π+ π- and Bs -> D Dbar. Systematic uncertainties are minimised by using B0 -> D*-+ π+- as a normalisation channel. We find no evidence for a signal, and set an upper limit on the branching fraction of BR(Bs -> D*-+ π+-) < 6.1 (7.8) x10^(-6) at 90% (95%) confidence level.

hep-ex↗

arXiv2013

Search for D+(s) to pi+ mu+ mu- and D+(s) to pi- mu+ mu+ decays

A search for non-resonant D+(s) to pi+mu+mu- and D+(s) to pi-mu+mu+ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb-1, at sqrt(s) = 7 TeV recorded by the LHCb experiment in 2011. No signals are observed and the 90% (95%) confidence level (CL) limits on the branching fractions are B(D+ to pi+mu+mu-) < 7.3 (8.3) x 10-8, B(Ds+ to pi+mu+mu-) < 4.1 (4.8) x 10-7, B(D+ to pi-mu+mu+) < 2.2 (2.5) x 10-8, B(Ds+ to pi-mu+mu+) < 1.2 (1.4) x 10-7. These limits are the most stringent to date.

hep-ex↗

arXiv2013

First observation of the decay $B_{s2}^(5840)^0 \to B^{+} K^-$ and studies of excited $B_s$ mesons

Properties of the orbitally excited (L=1) $B_s$ states are studied using 1.0 fb$^{-1}$ of pp collisions at $\sqrt{s} =7$ TeV collected with the LHCb detector. The first observation of the $B_{s2}^*(5840)^0$ meson decaying to $B^{*+} K^-$ is reported, and the corresponding branching fraction measured relative to the $B^+ K^-$ decay mode. The $B_{s1}(5830)^0 \to B^{*+} K^-$ decay is observed as well. The width of the $B_{s2}^*(5840)^0$ state is measured for the first time and the masses of the two states are determined with the highest precision to date. The observation of the $B_{s2}^*(5840)^0 \to B^{*+} K^-$ decay favours the spin-parity assignment $J^P = 2^+$ for the $B_{s2}^*(5840)^0$ meson. In addition, the most precise measurement of the mass difference $m(B^{*+})-m(B^+) = 45.01 \pm 0.30 (stat) \pm 0.23 (syst)$ MeV/$c^2$ is obtained.

hep-ex↗

arXiv2013

Precision measurement of the $B^{0}_{s}$-$\bar{B}^{0}_{s}$ oscillation frequency with the decay $B^{0}_{s}\rightarrowD^{-}_{s}π^{+}$

A key ingredient to searches for physics beyond the Standard Model in $B^{0}_{s}$ mixing phenomena is the measurement of the $B^{0}_{s}$-$\bar{B}^{0}_{s}$ oscillation frequency, which is equivalent to the mass difference $Δm_{s}$ of the $B^{0}_{s}$ mass eigenstates. Using the world's largest $B^{0}_{s}$ meson sample accumulated in a dataset, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb experiment at the CERN LHC in 2011, a measurement of $Δm_{s}$ is presented. A total of about 34,000 $B^{0}_{s}\rightarrowD^{-}_{s}π^{+}$ signal decays are reconstructed, with an average decay time resolution of 44 fs. The oscillation frequency is measured to be \mbox{$Δm_{s}$ = 17.768 $\pm$ 0.023 (stat) $\pm$ 0.006 (syst) ps$^{-1}$}, which is the most precise measurement to date.

hep-ex↗

arXiv2013

Measurement of the time-dependent CP asymmetry in B0 -> J/ψ KS0 decays

This Letter reports a measurement of the CP violation observables S_J/ψKS0 and C_J/ψKS0 in the decay channel B0 -> J/ψ KS0 performed with 1.0/fb of pp collisions at sqrt(s) = 7 TeV collected by the LHCb experiment. The fit to the data yields S_J/ψKS0 = 0.73 +- 0.07 (stat) +- 0.04 (syst) and C_J/ψKS0 = 0.03 +- 0.09 (stat) +- 0.01 (syst). Both values are consistent with the current world averages and within expectations from the Standard Model.

hep-ex↗

arXiv2013

Study of B0 -> D- pi+ pi- pi+ and B0 -> D- K+ pi- pi+ decays

Using proton-proton collision data collected by the LHCb experiment at sqrt(s) = 7 TeV, corresponding to an integrated luminosity of 1.0 fb^{-1}, the ratio of branching fractions of the B0 -> D*- pi+ pi- pi+ decay relative to the B0 -> D*- pi+ decay is measured to be B(B0 -> D*- pi+ pi- pi+) / B(B0 -> D*- pi+) = 2.64 \pm 0.04 (stat.) \pm 0.13 (syst.). The Cabibbo-suppressed decay B0 -> D*- K+ pi- pi+ is observed for the first time and the measured ratio of branching fractions is B(B0 -> D*- K+ pi- pi+) / B(B0 -> D*- pi+ pi- pi+) = (6.47 \pm 0.37 (stat.) \pm 0.35 (syst.)) x 10^{-2}. A search for orbital excitations of charm mesons contributing to the B0 -> D*- pi+ pi- pi+ final state is also performed, and the first observation of the B0 -> Dbar_{1}(2420)^0 pi+ pi- decay is reported with the ratio of branching fractions B(B0 -> (Dbar_{1}(2420)^0 -> D*- pi+) pi- pi+) / B(B0 -> D*- pi+ pi- pi+) = (2.04 \pm 0.42 (stat.) \pm 0.22 (syst.)) x 10^{-2}, where the numerator represents a product of the branching fractions B(B0 -> Dbar_{1}(2420)^0 pi- pi+) and B(Dbar_{1}(2420)^0 -> D*- pi+).

hep-ex↗

arXiv2013

Measurement of the $B^0$--$\bar B^0$ oscillation frequency $Δm_d$ with the decays $B^0 \to D^- π^+$ and $B^0 \to J/ ψK^{*0}$

The $B^0$--$\bar B^0$ oscillation frequency $Δm_d$ is measured by the LHCb experiment using a dataset corresponding to an integrated luminosity of $1.0\,$fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 7\,$TeV, and is found to be $Δm_d = 0.5156 \pm 0.0051\,($stat.$) \pm 0.0033\,($syst.$)\,$ps$^{-1}$. The measurement is based on results from analyses of the decays $B^0 \to D^- π^+$ ($D^- \to K^+ π^- π^-$) and $B^0 \to J/ ψK^{*0}$ ($ J/ ψ\to μ^+ μ^-$, $K^{*0} \to K^+ π^-$) and their charge conjugated modes.

hep-ex↗

arXiv2013

Measurement of CP observables in B0 -> D K*0 with D -> K+ K-

The decay B0 -> D K*0 and the charge conjugate mode are studied using 1.0fb-1 of pp collision data collected by the LHCb experiment at sqrt(s) = 7TeV in 2011. The CP asymmetry between the B0 -> D K*0 and the B0bar -> D K*0bar decay rates, with the neutral D meson in the CP-even final state K+K-, is found to be A_d_KK = -0.45 +- 0.23 +- 0.02, where the first uncertainty is statistical and the second is systematic. In addition, favoured B0 -> D K*0 decays are reconstructed with the D meson in the non-CP eigenstate K+ pi-. The ratio of the B-flavour averaged decay rates in D decays to CP and non-CP eigenstates is measured to be R_d_KK = 1.36 (+0.37) (-0.32) +- 0.07, where the ratio of the branching fractions of D0 -> K- pi+ to D0 -> K+ K- decays is included as multiplicative factor. The CP asymmetries measured with two control channels, the favoured B0 -> DK*0 decay with D -> K+ pi- and the Bs0bar -> D K*0 decay with D K+ K-, are also reported.

hep-ex↗

arXiv2013

Measurement of the fraction of \Y1S originating from \chib1P decays in $pp$ collisions at $\sqrt{s} = 7\tev$

The production of \chib1P mesons in $pp$ collisions at a centre-of-mass energy of $7\tev$ is studied using $32\invpb$ of data collected with the \lhcb detector. The $\chib1P$ mesons are reconstructed in the decay mode $\chib1P \to \Y1S\g \to \mumu\g$. The fraction of \Y1S originating from \chib1P decays in the \Y1S transverse momentum range $6 < \pt^{\Y1S} < 15\gevc$ and rapidity range $2.0 < y^{\Y1S} < 4.5$ is measured to be $(20.7\pm 5.7\pm 2.1^{+2.7}_{-5.4})%$, where the first uncertainty is statistical, the second is systematic and the last gives the range of the result due to the unknown \Y1S and \chib1P polarizations.

hep-ex↗

arXiv2013

Observation of the decay $B_c^+ \to ψ(2S)π^+$

The decay $B_c^+ \to ψ(2S)π^+$ with $ψ(2S) \to μ^+μ^-$ is observed with a significance of $5.2\,σ$ using $pp$ collision data corresponding to an integrated luminosity of $1.0\,\invfb$ collected by the LHCb experiment. The branching fraction of $B_c^+ \to ψ(2S)π^+$ decays relative to that of the $B_c^+ \to J/ψπ^+$ mode is measured to be \begin{equation*} \frac{\mathcal{B}(B_c^+ \to ψ(2S)π^+)}{\mathcal{B}(B_c^+ \to J/ψπ^+)} = 0.250 \pm 0.068 \,\text{stat} \pm 0.014 \,\text{\syst} \pm 0.006 \,(\mathcal{B}). \end{equation*} The last term is the uncertainty on the ratio $\mathcal{B}(ψ(2S) \to μ^+μ^-)/\mathcal{B}(J/ψ\to μ^+μ^-)$.

hep-ex↗

arXiv2013

Observation of D0-D0bar oscillations

We report a measurement of the time-dependent ratio of D0->K+pi- to D0->K-pi+ decay rates in D*+-tagged events using 1.0 fb^{-1} of integrated luminosity recorded by the LHCb experiment. We measure the mixing parameters x'2=(-0.9+-1.3)x10^{-4}, y'=(7.2+-2.4)x10^{-3} and the ratio of doubly-Cabibbo-suppressed to Cabibbo-favored decay rates R_D=(3.52+-0.15)x10^{-3}, where the uncertainties include statistical and systematic sources. The result excludes the no-mixing hypothesis with a probability corresponding to 9.1 standard deviations and represents the first observation of D0-D0bar oscillations from a single measurement.

hep-ex↗

arXiv2013

Observations of $B^0_s \rightarrowψ(2S)η$ and $B^0_{(s)}\rightarrowψ(2S)π^+π^-$ decays

First observations of the $B^0_s \rightarrow ψ(2S) η$, $B^0 \rightarrow ψ(2S) π^+ π^-$ and $B^0_s \rightarrow ψ(2S) π^+ π^-$ decays are made using a dataset corresponding to an integrated luminosity of 1.0~$fb^{-1}$ collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The ratios of the branching fractions of each of the $ψ(2S)$ modes with respect to the corresponding $J/ψ$ decays are \[ \frac{\mathcal{B}(B^0_s \rightarrow ψ(2S) η) }{\mathcal{B}(B^0_s \rightarrow J/ψη)} =0.83\pm0.14\,(stat)\pm0.12\,(syst)\pm0.02\,(\mathcalB}), \] \[ \frac{\mathcal{B}(B^0 \rightarrow ψ(2S) π^+ π^-)}{\mathcal{B}(B^0 \rightarrow J/ψπ^+ π^-)} =0.56\pm0.07\,(stat)\pm0.05\,(syst)\pm0.01\,(\mathcal{B}), \] \[ \frac{\mathcal{B}(B^0_s \rightarrow ψ(2S) π^+ π^-)}{\mathcal{B}(B^0_s \rightarrow J/ψπ^+ π^-)} =0.34\pm0.04\,(stat)\pm0.03\,(syst)\pm0.01\,(\mathcal{B}), \] where the third uncertainty corresponds to the uncertainties of the dilepton branching fractions of the $J/ψ$ and $ψ(2S)$ meson decays.

hep-ex↗

arXiv2013

Determination of the X(3872) meson quantum numbers

The quantum numbers of the X(3872) meson are determined to be JPC = 1++ based on angular correlations in B+ to X(3872) K+ decays, where X(3872) to pi+pi- J/psi and J/psi to μ+μ-. The data correspond to 1.0 fb-1 of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements, JPC=2-+, is rejected with a confidence level equivalent to more than eight Gaussian standard deviations using the likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the X(3872) state.

hep-ex↗

arXiv2013

Amplitude analysis and branching fraction measurement of Bs->J/ψK+K-

An amplitude analysis of the final state structure in the Bs->J/ψK+K- decay mode is performed using 1.0/fb of data collected by the LHCb experiment in 7 TeV center-of-mass energy pp collisions produced by the LHC. A modified Dalitz plot analysis of the final state is performed using both the invariant mass spectra and the decay angular distributions. Resonant structures are observed in the K+K- mass spectrum as well as a significant non-resonant S-wave contribution. The largest resonant component is the ϕ(1020), accompanied by f0(980), f'2(1525), and four additional resonances. The overall branching fraction is measured to be B(Bs->J/ψK+K-)=(7.70 +/-0.08 +/- 0.39 +/- 0.60)x 10^(-4), where the first uncertainty is statistical, the second systematic, and the third due to the ratio of the number of Bs to B- mesons produced. The mass and width of the f'2(1525) are measured to be 1522.2 +/- 2.8^{+5.3}_{-2.0} MeV and 84 +/- 6^{+10}_{-5} MeV, respectively. The final state fractions of the other resonant states are also reported.

hep-ex↗

arXiv2013

First observations of $\bar{B}_s^0\to D^+D^-$, $D_s^+D^-$ and $D^0\bar{D}^0$ decays

First observations and measurements of the branching fractions of the $\bar{B}_s^0\to D^+D^-$, $\bar{B}_s^0\to D_s^+D^-$ and $\bar{B}_s^0\to D^0\bar{D}^0$ decays are presented using 1.0 fb$^{-1}$ of data collected by the LHCb experiment. These branching fractions are normalized to those of $\bar{B}^0\to D^+D^-$, $B^0\to D_s^+D^-$ and $B^-\to D^0D_s^-$, respectively. An excess of events consistent with the decay $\bar{B}^0\to D^0\bar{D}^0$ is also seen, and its branching fraction is measured relative to that of $B^-\to D^0D_s^-$. Improved measurements of the branching fractions ${\cal{B}}(\bar{B}_s^0\to D_s^+D_s^-)$ and ${\cal{B}}(B^-\to D^0D_s^-)$ are reported, each relative to ${\cal{B}}(B^0\to D_s^+D^-)$. The ratios of branching fractions are {-0.2in} {center} {align*} {\cal{B}(\bar{B}_s^0\to D^+D^-)\over {\cal{B}}(\bar{B}^0\to D^+D^-)} &= 1.08\pm 0.20\pm0.10, {\cal{B}(\bar{B}_s^0\to D_s^+D^-)\over {\cal{B}}(B^0\to D_s^+D^-)} &= 0.050\pm 0.008\pm0.004, {\cal{B}(\bar{B}_s^0\to D^0\bar{D}^0)\over {\cal{B}}(B^-\to D^0D_s^-)} &= 0.019\pm 0.003\pm0.003, {\cal{B}(\bar{B}^0\to D^0\bar{D}^0)\over {\cal{B}}(B^-\to D^0D_s^-)} &= 0.0014\pm 0.0006\pm0.0002,{\cal{B}(\bar{B}_s^0\to D_s^+D_s^-)\over {\cal{B}}(B^0\to D_s^+D^-)} &= 0.56\pm 0.03\pm0.04, {\cal{B}(B^-\to D^0D_s^-)\over {\cal{B}}(B^0\to D_s^+D^-)} &= 1.22\pm 0.02\pm0.07, {align*} {center} \noindent where the uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2013

Radiation damage in the LHCb Vertex Locator

The LHCb Vertex Locator (VELO) is a silicon strip detector designed to reconstruct charged particle trajectories and vertices produced at the LHCb interaction region. During the first two years of data collection, the 84 VELO sensors have been exposed to a range of fluences up to a maximum value of approximately $\rm{45 \times 10^{12}\,1\,MeV}$ neutron equivalent ($\rm{1\,MeV\,n_{eq}}$). At the operational sensor temperature of approximately $-7\,^{\circ}\rm{C}$, the average rate of sensor current increase is $18\,\upmu\rm{A}$ per $\rm{fb^{-1}}$, in excellent agreement with predictions. The silicon effective bandgap has been determined using current versus temperature scan data after irradiation, with an average value of $E_{g}=1.16\pm0.03\pm0.04\,\rm{eV}$ obtained. The first observation of n-on-n sensor type inversion at the LHC has been made, occurring at a fluence of around $15 \times 10 ^{12}$ of $1\,\rm{MeV\,n_{eq}}$. The only n-on-p sensors in use at the LHC have also been studied. With an initial fluence of approximately $\rm{3 \times 10^{12}\,1\,MeV\,n_{eq}}$, a decrease in the Effective Depletion Voltage (EDV) of around 25\,V is observed, attributed to oxygen induced removal of boron interstitial sites. Following this initial decrease, the EDV increases at a comparable rate to the type inverted n-on-n type sensors, with rates of $(1.43\pm 0.16) \times 10 ^{-12}\,\rm{V} / \, 1 \, \rm{MeV\,n_{eq}}$ and $(1.35\pm 0.25) \times 10 ^{-12}\,\rm{V} / \, 1 \, \rm{MeV\,n_{eq}}$ measured for n-on-p and n-on-n type sensors, respectively. A reduction in the charge collection efficiency due to an unexpected effect involving the second metal layer readout lines is observed.

physics.ins-det↗

arXiv2013

Measurement of the CP asymmetry in B0 -> K*0 mu+ mu- decays

A measurement of the CP asymmetry in B0 -> K*0 mu+ mu- decays is presented, based on 1.0fb-1 of pp collision data recorded by the LHCb experiment during 2011. The measurement is performed in six bins of invariant mass squared of the mu+ mu- pair, excluding the J/psi and psi(2S) resonance regions. Production and detection asymmetries are removed using the B0 -> J/Psi K*0 decay as a control mode. The integrated CP asymmetry is found to be -0.072 +- 0.040 (stat.) +- 0.005 (syst.), consistent with the Standard Model.

hep-ex↗

arXiv2013

Measurement of J/psi production in pp collisions at sqrt(s)=2.76 TeV

The production of J/psi mesons is studied with the LHCb detector using data from pp collisions at sqrt(s)=2.76 TeV corresponding to an integrated luminosity of 71 nb^-1. The differential cross-section for inclusive J/psi production is measured as a function of its transverse momentum pT. The cross-section in the fiducial region 0<pT<12 GeV/c and rapidity 2.0<y<4.5 is measured to be 5.6 +/- 0.1(stat) +/- 0.4 (syst) mub, with the assumption of unpolarised J/psi production. The fraction of J/psi production from b-hadron decays is measured to be (7.1 +/- 0.6 (stat) +/- 0.7 (syst)) %.

hep-ex↗