arXiv subjects

G. Busetto

Publications and source records attributed to G. Busetto.

At least 235 records · Page 13Linked 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

Searches for the Higgs boson decaying to W^{+} W^{-} -> l^{+}nu l^{-}nubar with the CDF II detector

We present a search for a standard model Higgs boson decaying to two $W$ bosons that decay to leptons using the full data set collected with the CDF II detector in $\sqrt{s}=1.96$ TeV $p\bar{p}$ collisions at the Fermilab Tevatron, corresponding to an integrated luminosity of 9.7 fb${}^{-1}$. We obtain no evidence for production of a standard model Higgs boson with mass between 110 and 200 GeV/$c^2$, and place upper limits on the production cross section within this range. We exclude standard model Higgs boson production at the 95% confidence level in the mass range between 149 and 172 GeV/$c^2$, while expecting to exclude, in the absence of signal, the range between 155 and 175 GeV/$c^2$. We also interpret the search in terms of standard model Higgs boson production in the presence of a fourth generation of fermions and within the context of a fermiophobic Higgs boson model. For the specific case of a standard model-like Higgs boson in the presence of fourth-generation fermions, we exclude at the 95% confidence level Higgs boson production in the mass range between 124 and 200 GeV/$c^2$, while expecting to exclude, in the absence of signal, the range between 124 and 221 GeV/$c^2$.

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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

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

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

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

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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arXiv2013

Measurement of the top quark forward-backward production asymmetry and its dependence on event kinematic properties

We present new measurements of the inclusive forward-backward ttbar production asymmetry, AFB, and its dependence on several properties of the ttbar system. The measurements are performed with the full Tevatron data set recorded with the CDF II detector during ppbar collisions at sqrt(s) = 1.96 TeV, corresponding to an integrated luminosity of 9.4 fb^(-1). We measure the asymmetry using the rapidity difference Delta-y=y_(t)-y_(tbar). Parton-level results are derived, yielding an inclusive asymmetry of 0.164+/-0.047 (stat + syst). We observe a linear dependence of AFB on the top-quark pair mass M(ttbar) and the rapidity difference |Delta-y| at detector and parton levels. Assuming the standard model, the probabilities to observe the measured values or larger for the detector-level dependencies are 7.4*10^(-3) and 2.2*10^(-3) for M(ttbar) and |Delta-y| respectively. Lastly, we study the dependence of the asymmetry on the transverse momentum of the ttbar system at the detector level. These results are consistent with previous lower-precision measurements and provide additional quantification of the functional dependencies of the asymmetry.

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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 $\mathcal{B}(ψ(2S) \to μ^+μ^-)/\mathcal{B}(J/ψ\to μ^+μ^-)$.

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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.

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