arXiv subjects

M. Charles

Publications and source records attributed to M. Charles.

At least 37 records · Page 2Linked to original sources

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.

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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.

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arXiv2013

Search for the rare decay KS -> mu+ mu-

A search for the decay KS -> mu+ mu- is performed, based on a data sample of 1.0 fb^-1 of pp collisions at \sqrt{s}=7 TeV collected by the LHCb experiment at the Large Hadron Collider. The observed number of candidates is consistent with the background-only hypothesis, yielding an upper limit of BR(KS -> mu+ mu-) < 11 (9) x 10^-9 at 95 (90)% confidence level. This limit is a factor of thirty below the previous measurement.

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arXiv2013

First evidence for the annihilation decay mode $B^{+} \to D_{s}^{+} ϕ$

Evidence for the hadronic annihilation decay mode $B^{+} \to D_s^{+}ϕ$ is found with greater than $3σ$ significance. The branching fraction and \CP asymmetry are measured to be \mathcal{B}(B^{+} \to D_s^{+}ϕ) &=& (1.87^{+1.25}_{-0.73}({\rm stat}) \pm 0.19 ({\rm syst}) \pm 0.32 ({\rm norm})) \times 10^{-6}, \mathcal{A}_{CP}(B^{+} \to D_s^{+}ϕ) &=& -0.01 \pm 0.41 ({\rm stat}) \pm 0.03 ({\rm syst}). The last uncertainty on $\mathcal{B}(B^{+} \to D_s^{+}ϕ)$ is from the branching fractions of the $B^+ \to D_s^+ \kern 0.2em\bar{\kern -0.2em D}{}^0$ normalization mode and intermediate resonance decays. Upper limits are also set for the branching fractions of the related decay modes $B^{+}_{(c)} \to D^{+}_{(s)} K^{*0}$, $B^{+}_{(c)} \to D^{+}_{(s)} \kern 0.2em\bar{\kern -0.2em K}{}^{*0}$ and ${B_c^{+} \to D^{+}_{s}ϕ}$, including the result ${\mathcal{B}(B^+ \to D^+ K^{*0})} < 1.8 \times 10^{-6}$ at the 90% credibility level.

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arXiv2012

First observation of the decays $\bar{B}^0_{(s)}\to D_s^+K^-π^+π^-$ and $\bar{B}^0_s\to D_{s1}(2536)^+π^-$

The first observation of the decays $\bar{B}^0_{s}\to D_s^+K^-π^+π^-$ and $\bar{B}^0\to D_s^+K^-π^+π^-$ are reported using an integrated luminosity of 1.0 fb$^{-1}$ recorded by the LHCb experiment. The branching fractions, normalized with respect to $\bar{B}^0_{s}\to D_s^+π^-π^+π^-$ and $\bar{B}^0_{s}\to D_s^+K^-π^+π^-$, respectively, are measured to be {\br(\bar{B}^0_{s}\to D_s^+K^-π^+π^-)\over\br(\bar{B}^0_{s}\to D_s^+π^-π^+π^-)} &= (5.2\pm0.5\pm0.3)\times10^{-2}, {\br(\bar{B}^0\to D_s^+K^-π^+π^-)\over\br(\bar{B}^0_{s}\to D_s^+K^-^π^+π^-)} &= 0.54\pm0.07\pm0.07, where the first uncertainty is statistical and the second is systematic. The $\bar{B}^0_{s}\to D_s^+K^-π^+π^-$ decay is of particular interest as it can be used to measure the weak phase $γ$. First observation of the $\bar{B}^0_s\to D_{s1}(2536)^+π^-, D_{s1}^+\to D_s^+π^-π^+$ decay is also presented, and its branching fraction relative to $\bar{B}^0_{s}\to D_s^+π^-π^+π^-$ is found to be {\br(\bar{B}^0_s\to D_{s1}(2536)^+π^-, D_{s1}^+\to D_s^+π^-π^+)\over\br(\bar{B}^0_{s}\to D_s^+π^-π^+π^-)} &= (4.0\pm1.0\pm0.4)\times10^{-3}.

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arXiv2012

Measurement of the D+/- production asymmetry in 7 TeV pp collisions

The asymmetry in the production cross-section σof D+/- mesons, A_P = (σ(D+) - σ(D-))/(σ(D+) + σ(D-)), is measured in bins of pseudorapidity ηand transverse momentum p_T within the acceptance of the LHCb detector. The result is obtained with a sample of D+ -> K_S pi+ decays corresponding to an integrated luminosity of 1.0 fb^-1, collected in pp collisions at a centre of mass energy of 7 TeV at the Large Hadron Collider. When integrated over the kinematic range 2.0 < p_T < 18.0 GeV/c and 2.20 < η< 4.75, the production asymmetry is A_P = (-0.96+/-0.26+/-0.18)%. The uncertainties quoted are statistical and systematic, respectively. The result assumes that any direct CP violation in the D+ -> K_S pi+ decay is negligible. No significant dependence on ηor p_T is observed.

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arXiv2012

Measurement of the cross-section ratio $σ(χ_{c2})/σ(χ_{c1})$ for prompt $χ_c$ production at $\sqrt{s}=7$ TeV

The prompt production of the charmonium $χ_{c1}$ and $χ_{c2}$ mesons has been studied in proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The $χ_c$ mesons are identified through their decays $χ_c\to J/ψ\,γ$ with $J/ψ\to μ^+ μ^-$ using 36 $\mathrm{pb^{-1}}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two $χ_c$ spin states, $σ(χ_{c2})/σ(χ_{c1})$, has been determined as a function of the $J/ψ$ transverse momentum, $p_{\mathrm{T}}^{J/ψ}$, in the range from 2 to 15 GeV/$c$. The results are in agreement with the next-to-leading order non-relativistic QCD model at high $p_{\mathrm{T}}^{J/ψ}$ and lie consistently above the pure leading-order colour singlet prediction.

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arXiv2012

Measurement of the ratio of prompt $χ_{c}$ to $J/ψ$ production in $pp$ collisions at $\sqrt{s}=7$ TeV

The prompt production of charmonium $χ_{c}$ and $J/ψ$ states is studied in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV at the Large Hadron Collider. The $χ_{c}$ and $J/ψ$ mesons are identified through their decays $χ_{c}\rightarrow J/ψγ$ and $J/ψ\rightarrow μ^+μ^-$ using 36 pb$^{-1}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for $χ_{c}$ and $J/ψ$, $σ(χ_{c}\rightarrow J/ψγ)/ σ(J/ψ)$, is determined as a function of the $J/ψ$ transverse momentum in the range $2 < p_{\mathrm T}^{J/ψ} < 15$ GeV/$c$. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low $p_{\mathrm T}^{J/ψ}$ region.

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arXiv2012

Observation of excited Lambda_b0 baryons

Using pp collision data corresponding to 1.0 fb-1 integrated luminosity collected by the LHCb detector, two narrow states are observed in the Lambda_b0pi+pi- spectrum with masses 5911.97 +- 0.12(stat) +- 0.02(syst) +- 0.66(Lambda_b0 mass) MeV/c^2 and 5919.77 +- 0.08(stat) +- 0.02(syst) +- 0.66(Lambda_b0 mass) MeV/c^2. The significances of the observations are 5.2 and 10.2 standard deviations, respectively. These states are interpreted as the orbitally-excited Lambda_b0 baryons, Lambda_b*0(5912) and Lambda_b*0(5920).

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arXiv2012

Measurement of the $B^0_s\rightarrow J/ψK^{*0}$ branching fraction and angular amplitudes

A search for the decay $B^0_s\rightarrow J/ψK^{*0}$ with $K^{*0} \rightarrow K^-π^+$ is performed with 0.37 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 7 TeV collected by the LHCb experiment, finding a $\Bs \to JψK^-π^+$ peak of $114 \pm 11$ signal events. The $K^-π^+$ mass spectrum of the candidates in the $B^0_s$ peak is dominated by the $K^{*0}$ contribution. Subtracting the non-resonant $K^-π^+$ component, the branching fraction of \BsJpsiKst is $(4.4_{-0.4}^{+0.5} \pm 0.8) \times 10^{-5}$, where the first uncertainty is statistical and the second systematic. A fit to the angular distribution of the decay products yields the \Kst polarization fractions $f_L = 0.50 \pm 0.08 \pm 0.02$ and $f_{||} = 0.19^{+0.10}_{-0.08} \pm 0.02$.

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arXiv2012

A study of the $Z$ production cross-section in $pp$ collisions at $\sqrt{s} = 7$ TeV using tau final states

A measurement of the inclusive $Z \to ττ$ cross-section in $pp$ collisions at $\sqrt{s} = 7$ TeV is presented based on a dataset of 1.0 fb$^{-1}$ collected by the LHCb detector. Candidates for $Z \to ττ$ decays are identified through reconstructed final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. The production cross-section for $Z$ bosons, with invariant mass between 60 and 120 GeV/$c^2$, which decay to $τ$ leptons with transverse momenta greater than 20 GeV/$c$ and pseudorapidities between 2.0 and 4.5, is measured to be $σ_{pp \to Z \to ττ} = 71.4 \pm 3.5 \pm 2.8 \pm 2.5$ pb; the first uncertainty is statistical, the second uncertainty is systematic, and the third is due to the uncertainty on the integrated luminosity. The ratio of the cross-sections for $Z \to ττ$ to $Z \to μμ$ is determined to be $0.93 \pm 0.09$, where the uncertainty is the combination of statistical, systematic, and luminosity uncertainties of the two measurements.

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arXiv2012

Measurement of $b$-hadron branching fractions for two-body decays into charmless charged hadrons

Based on data corresponding to an integrated luminosity of 0.37 fb^-1 collected by the LHCb experiment in 2011, the following ratios of branching fractions are measured: B(B0 -> pi+ pi-) / B(B0 -> K+pi-) = 0.262 +/- 0.009 +/- 0.017, (fs/fd) * B(Bs -> K+K-) / B(B^0 -> K+pi-) = 0.316 +/- 0.009 +/- 0.019, (fs/fd) * B(Bs ->pi+ K-) / B(B0 -> K+pi-) = 0.074 +/- 0.006 +/- 0.006, (fd/fs) * B(B0 -> K+K-) / B(Bs -> K+K-) = 0.018 {+ 0.008 - 0.007} +/- 0.009, (fs/fd) * B(Bs -> pi+pi-) / B(B0 -> pi+pi-) = 0.050 {+ 0.011 - 0.009} +/- 0.004, B(Lambda_b -> p pi-) / B(Lambda_b -> p K-) = 0.86 +/- 0.08 +/- 0.05, where the first uncertainties are statistical and the second systematic. Using the current world average of B(B0 -> K+pi-) and the ratio of the strange to light neutral B meson production fs/fd measured by LHCb, we obtain: B(B0 -> pi+pi-) = (5.08 +/- 0.17 +/- 0.37) x 10^-6, B(Bs -> K+K-) = (23.0 +/- 0.7 +/- 2.3) x 10^-6, B(Bs -> pi+K-) = (5.4 +/- 0.4 +/- 0.6) x 10^-6, B(B0 -> K+K-) = (0.11 {+ 0.05 - 0.04} +/- 0.06) x 10^-6, B(Bs -> pi+pi-) = (0.95 {+ 0.21 - 0.17} +/- 0.13) x 10^-6. The measurements of B(Bs -> K+K-), B(Bs -> pi+ K-) and B(B0 -> K+K-) are the most precise to date. The decay mode Bs -> pi+pi- is observed for the first time with a significance of more than 5 sigma.

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arXiv2012

Measurement of the Bs effective lifetime in the J/psi f0(980) final state

The effective lifetime of the Bs meson in the decay mode Bs->J/ψf0(980) is measured using 1.0/fb of data collected in pp collisions at sqrt(s) = 7 TeV with the LHCb detector. The result is 1.700 +/- 0.040 +/- 0.026 ps where the first uncertainty is statistical and the second systematic. As the final state is CP-odd, and CP violation in this mode is measured to be small, the lifetime measurement can be translated into a measurement of the decay width of the heavy Bs mass eigenstate, Γ_H = (0.588 +/- 0.014 +/- 0.009)/ps.

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arXiv2012

Evidence for the decay $B^0\to J/ψω$ and measurement of the relative branching fractions of $B^0_s$ meson decays to $J/ψη$ and $J/ψη^{'}$

First evidence of the $B^0\to J/ψω$ decay is found and the $B_{s}^0\to J/ψη$ and $B_{s}^0\to J/ψη^{\prime}$ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 $\mathrm{fb}^{-1}$ collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 7$ TeV. The branching fractions of these decays are measured relative to that of the $\mathrm{B}^0\to J/ψρ^0$ decay: $$\frac{Br(B^0\to J/ψω)}{Br(B^0\to J/ψρ^0)} = 0.89 \pm0.19(stat)^{+0.07}_{-0.13}(syst)$$ $$\frac{Br(B^0_s\to J/ψη)}{Br(B^0\to J/ψρ^0)} = 14.0 \pm 1.2(stat)^{+1.1}_{-1.5}(syst)^{+1.1}_{-1.0}(\frac{f_d}{f_s}),$$ $$\frac{Br(B^0_s\to J/ψη^{\prime})}{Br(B^0\to J/ψρ^0)} = 12.7\pm1.1(stat)^{+0.5}_{-1.3}(syst)^{+1.0}_{-0.9}(\frac{f_d}{f_s}),$$ where the last uncertainty is due to the knowledge of $f_d/f_s$, the ratio of b-quark hadronization factors that accounts for the different production rate of $B^0$ and $B^0_s$ mesons. The ratio of the branching fractions of $B^0_s\to J/ψη^{\prime}$ and $B^0_s\to J/ψη$ decays is measured to be $$ \frac{Br(B^0_s\to J/ψη^{\prime})}{Br(B^0_s\to J/ψη)} = 0.90\pm0.09(stat)^{+0.06}_{-0.02}(syst).$$

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arXiv2012

A model-independent Dalitz plot analysis of $B^\pm \to D K^\pm$ with $D \to K^0_{\rm S} h^+h^-$ ($h=π, K$) decays and constraints on the CKM angle $γ$

A binned Dalitz plot analysis of $B^\pm \to D K^\pm$ decays, with $D \to K^0_{\rm S} π^+π^-$ and $D \to K^0_{\rm S} K^+ K^-$, is performed to measure the CP-violating observables $x_{\pm}$ and $y_{\pm}$ which are sensitive to the CKM angle $γ$. The analysis exploits 1.0 $\rm fb^{-1}$ of data collected by the LHCb experiment. The study makes no model-based assumption on the variation of the strong phase of the D decay amplitude over the Dalitz plot, but uses measurements of this quantity from CLEO-c as input. The values of the parameters are found to be $x_- = (0.0 \pm 4.3 \pm 1.5 \pm 0.6) \times 10^{-2}$, $y_- = (2.7 \pm 5.2 \pm 0.8 \pm 2.3) \times 10^{-2}$, $x_+ = (-10.3 \pm 4.5 \pm 1.8 \pm 1.4)\times 10^{-2}$ and $y_+ = (-0.9 \pm 3.7 \pm 0.8 \pm 3.0)\times 10^{-2}$. The first, second, and third uncertainties are the statistical, the experimental systematic, and the error associated with the precision of the strong-phase parameters measured at CLEO-c, respectively. These results correspond to $γ= (44^{\,+43}_{\,-38})^\circ$, with a second solution at $γ\to γ+ 180^\circ$, and $r_B = 0.07 \pm 0.04$, where $r_B$ is the ratio between the suppressed and favoured B decay amplitudes.

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arXiv2012

Analysis of the resonant components in Bs->J/ψπ+π-

The decay Bs->J/ψπ+π- can be exploited to study CP violation. A detailed understanding of its structure is imperative in order to optimize its usefulness. An analysis of this three-body final state is performed using a 1.0/fb sample of data produced in 7 TeV pp collisions at the LHC and collected by the LHCb experiment. A modified Dalitz plot analysis of the final state is performed using both the invariant mass spectra and the decay angular distributions. The π+π- system is shown to be dominantly in an S-wave state, and the CP-odd fraction in this Bs decay is shown to be greater than 0.977 at 95% confidence level. In addition, we report the first measurement of the J/ψπ+π- branching fraction relative to J/ψϕ of (19.79 +/- 0.47 +/- 0.52)%.

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arXiv2012

Differential branching fraction and angular analysis of the $B^{+} \rightarrow K^{+}μ^{+}μ^{-}$ decay

The angular distribution and differential branching fraction of the decay $B^{+} \rightarrow K^{+}μ^{+}μ^{-}$ are studied with a dataset corresponding to $1.0\,\mathrm{fb}^{-1}$ of integrated luminosity, collected by the LHCb experiment. The angular distribution is measured in bins of dimuon invariant mass squared and found to be consistent with Standard Model expectations. Integrating the differential branching fraction over the full dimuon invariant mass range yields a total branching fraction of $\mathcal{B}(B^{+} \rightarrow K^{+}μ^{+}μ^{-}) = (4.36 \pm 0.15 \pm 0.18)\times 10^{-7}$. These measurements are the most precise to date of the $B^{+} \rightarrow K^{+}μ^{+}μ^{-}$ decay.

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arXiv2012

Measurement of the effective $B_s^0 \rightarrow K^+ K^-$ lifetime

A precise determination of the effective $B_s^0 \rightarrow K^+ K^-$ lifetime can be used to constrain contributions from physics beyond the Standard Model in the $B_s^0$ meson system. Conventional approaches select $B$ meson decay products that are significantly displaced from the $B$ meson production vertex. As a consequence, $B$ mesons with low decay times are suppressed, introducing a bias to the decay time spectrum which must be corrected. This analysis uses a technique that explicitly avoids a lifetime bias by using a neural network based trigger and event selection. Using 1.0 fb$^{-1}$ of data recorded by the LHCb experiment, the effective $B_s^0 \rightarrow K^+ K^-$ lifetime is measured as $1.455 \pm 0.046 \; \mathrm{(stat.)} \pm 0.006 \; \mathrm{(syst.)} \, \mathrm{ps}.$

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