arXiv subjects

Th. Bauer

Publications and source records attributed to Th. Bauer.

At least 109 records · Page 6Linked to original sources

arXiv2013

Measurement of the differential branching fraction of the decay $Λ_b^0\rightarrowΛμ^+μ^-$

The differential branching fraction of the decay $Λ_b^0\rightarrowΛμ^+μ^-$ is measured as a function of the square of the dimuon invariant mass, $q^2$. A yield of $78\pm12$ $Λ_b^0\rightarrowΛμ^+μ^-$ decays is observed using data, corresponding to an integrated luminosity of 1.0\,fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7\,TeV. A significant signal is found in the $q^2$ region above the square of the $J/ψ$ mass, while at lower-$q^2$ values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over $q^2$, while excluding the $J/ψ$ and $ψ(2S)$ regions, gives a branching fraction of $\BF($Λ_b^0\rightarrowΛμ^+μ^-$)=(0.96\pm 0.16\stat\pm 0.13\syst\pm 0.21 (\mathrm{norm}))\times 10^{-6}$, where the uncertainties are statistical, systematic and due to the normalisation mode, $$Λ_b^0\rightarrow J/psiΛ$, respectively.

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arXiv2013

First observation of CP violation in the decays of Bs mesons

Using pp collision data, corresponding to an integrated luminosity of $1.0 \mathrm{fb}^{-1}$, collected by LHCb in 2011 at a center-of-mass energy of 7 TeV, we report the measurement of direct CP violation in $B^0_s \to K^-π^+$ decays, $A_{C/!P}(B^0_s \rightarrow K^- π^+)=0.27 \pm 0.04\,\mathrm{(stat)} \pm 0.01\,\mathrm{(syst)}$, with significance exceeding five standard deviations. This is the first observation of CP violation in the decays of $B^0_s$ mesons. Furthermore, we provide an improved determination of direct CP violation in $B^0 \to K^+π^-$ decays, $A_{C/!P}(B^0\rightarrow K^+ π^-)=-0.080 \pm 0.007\,\mathrm{(stat)} \pm 0.003\,\mathrm{(syst)}$, which is the most precise measurement of this quantity to date.

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arXiv2013

Measurement of CP violation in the phase space of $B^{\pm} \to K^{\pm} π^{+} π^{-}$ and $B^{\pm} \to K^{\pm} K^{+} K^{-}$ decays

The charmless decays $B^{\pm}\to K^{\pm}π^+π^-$ and $B^{\pm}\to K^{\pm}K^+K^-$ are reconstructed using data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by LHCb in 2011. The inclusive charge asymmetries of these modes are measured as $A_{C\!P}(B^{\pm}\to K^{\pm}π^+π^-) = 0.032 \pm 0.008 \stat \pm 0.004 \syst \pm 0.007 (JψK^{\pm})$ and $A_{C\!P}(B^{\pm}\to K^{\pm}K^+K^-) = -0.043 \pm 0.009 \stat \pm 0.003 \syst \pm 0.007 (JψK^{\pm})$, where the third uncertainty is due to the $C\!P$ asymmetry of the $B^{\pm}\to JψK^{\pm}$ reference mode. The significance of $A_{C\!P}(B^{\pm}\to K^{\pm}K^+K^-)$ exceeds three standard deviations and is the first evidence of an inclusive $C\!P$ asymmetry in charmless three-body $B$ decays. In addition to the inclusive $C\!P$ asymmetries, larger asymmetries are observed in localised regions of phase space.

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arXiv2013

Measurement of the branching fractions of the decays Bs -> D0bar K- π+ and B0 -> D0bar K+ π-

The first observation of the decay Bs -> D0bar K- π+ is reported. The analysis is based on a data sample, corresponding to an integrated luminosity of 1.0 fb-1 of pp collisions, collected with the LHCb detector. The branching fraction relative to that of the topologically similar decay B0 -> D0bar π+ π- is measured to be BR(Bs -> D0bar K- π+)/BR(B0 -> D0bar π+ π-) = 1.18 +- 0.05 (stat.) +- 0.12 (syst.). In addition, the relative branching fraction of the decay B0 -> D0bar K+ π- is measured to be BR(B0 -> D0bar K+ π-)/BR(B0 -> D0bar π+ π-) = 0.106 +- 0.007 (stat.) +- 0.008 (syst.).

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arXiv2013

Limits on neutral Higgs boson production in the forward region in $pp$ collisions at $\sqrt{s} = 7$ TeV

Limits on the cross-section times branching fraction for neutral Higgs bosons, produced in $pp$ collisions at $\sqrt{s} = 7$ TeV, and decaying to two tau leptons with pseudorapidities between 2.0 and 4.5, are presented. The result is based on a dataset, corresponding to an integrated luminosity of 1.0 $\mathrm{fb}^{-1}$, collected with the LHCb detector. Candidates are identified by reconstructing final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. A model independent upper limit at the 95% confidence level is set on a neutral Higgs boson cross-section times branching fraction. It varies from 8.6 pb for a Higgs boson mass of 90 GeV to 0.7 pb for a Higgs boson mass of 250 GeV, and is compared to the Standard Model expectation. An upper limit on $\tanβ$ in the Minimal Supersymmetric Model is set in the $m_{h^0}^\mathrm{max}$ scenario. It ranges from 34 for a CP-odd Higgs boson mass of 90 GeV to 70 for a pseudo-scalar Higgs boson mass of 140 GeV.

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arXiv2013

Observation of $B^0_s\rightarrowχ_{c1}ϕ$ decay and study of $B^0\rightarrowχ_{c1,2}K^{*0}$ decays

The first observation of the decay $B^0_s\rightarrowχ_{c1}ϕ$ and a study of $B^0\rightarrowχ_{c1,2}K^{*0}$ decays are presented. The analysis is performed using a dataset, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. The following ratios of branching fractions are measured: \begin{equation*} \begin{array}{lll} \dfrac{\cal{B}(B^0_s\rightarrowχ_{c1}ϕ)}{\cal{B}(B^0_s\rightarrow J/ψϕ)} &=& (18.9 \pm1.8\,(stat)\pm1.3\,(syst)\pm0.8\,(\cal{B})) \times 10^{-2}, \nonumber \\ \noalign{\vskip 3pt} \dfrac{\cal{B}(B^0\rightarrowχ_{c1}K^{*0})}{\cal{B}(B^0\rightarrow J/\psiK^{*0})} &=& (19.8 \pm1.1\,(stat)\pm1.2\,(syst)\pm0.9\,(\cal{B})) \times 10^{-2}, \nonumber \\ \noalign{\vskip 3pt} \dfrac{\cal{B}(B^0\rightarrowχ_{c2}K^{*0})}{\cal{B}(B^0\rightarrowχ_{c 1}K^{*0})} &=& (17.1 \pm5.0\,(stat)\pm1.7\,(syst)\pm1.1\,(\cal{B})) \times 10^{-2}, \nonumber \\ \noalign{\vskip 3pt} \end{array} \end{equation*} \noindent where the third uncertainty is due to the limited knowledge of the branching fractions of ${χ_{c}\rightarrow J/ψγ}$ modes.

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arXiv2013

Search for direct CP violation in D0 -> h- h+ modes using semileptonic B decays

A search for direct CP violation in D0 -> h- h+ (where h=K or pi) is presented using data corresponding to an integrated luminosity of 1.0 fb^-1 collected in 2011 by LHCb in pp collisions at a centre-of-mass energy of 7 TeV. The analysis uses D0 mesons produced in inclusive semileptonic b-hadron decays to the D0 mu X final state, where the charge of the accompanying muon is used to tag the flavour of the D0 meson. The difference in the CP-violating asymmetries between the two decay channels is measured to be Delta A_CP = A_CP(K-K+) - A_CP(pi-pi+) = (0.49 +- 0.30 (stat) +- 0.14 (syst)) % . This result does not confirm the evidence for direct CP violation in the charm sector reported in other analyses.

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arXiv2013

Search for the rare decay $D^0 \to μ^+ μ^-$

A search for the rare decay $D^0 \to μ^+ μ^-$is performed using a data sample, corresponding to an integrated luminosity of 0.9 fb$^{-1}$, of $pp$ collisions collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The observed number of events is consistent with the background expectations and corresponds to an upper limit of \mbox{${\cal B}(D^0 \to μ^+ μ^-) < 6.2(7.6) \times 10^{-9}$} at \mbox{90%} \mbox{(95%)} confidence level. This result represents an improvement of more than a factor twenty with respect to previous measurements.

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arXiv2013

Search for rare $B^0_{(s)}\rightarrow μ^+ μ^- μ^+ μ^-$ decays

\noindent A search for the decays $B^0_{s}\rightarrow μ^+ μ^- μ^+ μ^-$ and $B^0 \rightarrow μ^+ μ^- μ^+ μ^-$ is performed using data, corresponding to an integrated luminosity of 1.0\ensuremath{\{\,fb}^{-1}}\xspace, collected with the LHCb detector in 2011. The number of candidates observed is consistent with the expected background and, assuming phase-space models of the decays, limits on the branching fractions are set: \{${\ensuremath{\cal B}\xspace}(B^0_{s}\rightarrow μ^+ μ^- μ^+ μ^-) < 1.6 \ (1.2) \times 10^{-8}$} and \{${\ensuremath{\cal B}\xspace}(B^0 \rightarrow μ^+ μ^- μ^+ μ^-)< 6.6 \ (5.3) \times 10^{-9}$} at 95\,% (90\,%) confidence level. In addition, limits are set in the context of a supersymmetric model which allows for the $B^0_{(s)}$ meson to decay into a scalar ($S$) and pseudoscalar particle ($P$), where $S$ and $P$ have masses of 2.5 GeV and 214.3 MeV, respectively, both resonances decay into $μ^+μ^-$. The branching fraction limits for these decays are \{${\ensuremath{\cal B}\xspace}(\ensuremath{B^0_{s}\rightarrow SP}\xspace) < 1.6 \ (1.2) \times 10^{-8}$} and \{${\ensuremath{\cal B}\xspace}(\ensuremath{B^0\rightarrow SP}\xspace)< 6.3 \ (5.1) \times 10^{-9}$} at 95% (90%) confidence level.

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arXiv2013

Measurement of the effective B_s^0 -> J/ψ K_S^0 lifetime

This paper reports the first measurement of the effective B_s^0 -> J/ψ K_S^0 lifetime and an updated measurement of its time-integrated branching fraction. Both measurements are performed with a data sample, corresponding to an integrated luminosity of 1.0 fb^{-1} of pp collisions, recorded by the LHCb experiment in 2011 at a centre-of-mass energy of 7 TeV. The results are: tau_J/ψK_S^0 = 1.75 +/- 0.12 (stat) +/- 0.07 (syst) and BR(B_s^0 -> J/ψ K_S^0) = (1.97 +/- 0.23) X 10^{-5}. For the latter measurement, the uncertainty includes both statistical and systematic sources.

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arXiv2013

Measurement of the $B^0 \rightarrow K^{*0}e^+e^-$ branching fraction at low dilepton mass

The branching fraction of the rate decay $B^0 \rightarrow K^{*0}e^+e^-$ in the dilepton mass region from 30 to 1000 MeV$/c^2$ has been measured by the LHCb experiment, using $pp$ collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, at a centre-of-mass energy of 7 TeV. The decay mode $B^0 \rightarrow J/ψ(e^+e^-) K^{*0}$ is utilized as a normalization channel. The branching fraction $B^0 \rightarrow K^{*0}e^+e^-$ is measured to be $$ B(B^0 \rightarrow K^{*0}e^+e^-)^{30-1000 MeV/c^2}= (3.1\, ^{+0.9\mbox{} +0.2}_{-0.8\mbox{}-0.3} \pm 0.2)\times 10^{-7}, $$ where the first error is statistical, the second is systematic, and the third comes from the uncertainties on the B^0 \rightarrow J/ψK^{*0}$ and $J/ψ\rightarrow e^+e^- $ branching fractions.

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arXiv2013

Measurement of the forward energy flow in pp collisions at sqrt(s)=7 TeV

The energy flow created in pp collisions at sqrt(s)=7 TeV is studied within the pseudorapidity range 1.9<eta<4.9 with data collected by the LHCb experiment. The measurements are performed for inclusive minimum-bias interactions, hard scattering processes and events with an enhanced or suppressed diffractive contribution. The results are compared to predictions given by PYTHIA-based and cosmic-ray event generators, which provide different models of soft hadronic interactions.

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arXiv2013

Observation of the suppressed ADS modes $B^\pm \to [π^\pm K^\mp π^+π^-]_D K^\pm$ and $B^\pm \to [π^\pm K^\mp π^+π^-]_D π^\pm$

An analysis of $B^{\pm}\to DK^{\pm}$ and $B^{\pm}\to Dπ^{\pm}$ decays is presented where the $D$ meson is reconstructed in the four-body final state $K^{\pm}π^{\mp} π^+ π^-$. Using LHCb data corresponding to an integrated luminosity of $1.0{\rm \,fb}^{-1}$, first observations are made of the suppressed ADS modes $B^{\pm}\to [π^{\pm} K^{\mp}π^+π^-]_D K^{\pm}$ and $B^{\pm}\to [π^{\pm} K^{\mp} π^+π^- ]_Dπ^{\pm}$ with a significance of $5.1σ$ and greater than $10σ$, respectively. Measurements of CP asymmetries and CP-conserving ratios of partial widths from this family of decays are also performed. The magnitude of the ratio between the suppressed and favoured $B^{\pm}\to DK^{\pm}$ amplitudes is determined to be $r^K_B = 0.097 \pm{0.011}$.

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arXiv2013

Implications of LHCb measurements and future prospects

During 2011 the LHCb experiment at CERN collected 1.0 fb-1 of sqrt{s} = 7 TeV pp collisions. Due to the large heavy quark production cross-sections, these data provide unprecedented samples of heavy flavoured hadrons. The first results from LHCb have made a significant impact on the flavour physics landscape and have definitively proved the concept of a dedicated experiment in the forward region at a hadron collider. This document discusses the implications of these first measurements on classes of extensions to the Standard Model, bearing in mind the interplay with the results of searches for on-shell production of new particles at ATLAS and CMS. The physics potential of an upgrade to the LHCb detector, which would allow an order of magnitude more data to be collected, is emphasised.

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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.

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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.

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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.

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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.

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