arXiv subjects

O. Callot

Publications and source records attributed to O. Callot.

At least 37 records · Page 2Linked to original sources

arXiv2014

Study of $J/ψ$ production and cold nuclear matter effects in $p$Pb collisions at $\sqrt{s_{NN}}=5 \mathrm{TeV}$

The production of $J/ψ$ mesons with rapidity $1.5<y<4.0$ or $-5.0<y<-2.5$ and transverse momentum $p_\mathrm{T}<14 \mathrm{GeV}/c$ is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}=5 \mathrm{TeV}$. The analysis is based on a data sample corresponding to an integrated luminosity of about $1.6 \mathrm{nb}^{-1}$. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt $J/ψ$ mesons and $J/ψ$ from $b$-hadron decays. Clear suppression of prompt $J/ψ$ production with respect to proton-proton collisions at large rapidity is observed, while the production of $J/ψ$ from $b$-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.

nucl-ex↗

arXiv2014

Measurements of the $B^+$, $B^0$, $B_s^0$ meson and $Λ_b^0$ baryon lifetimes

Measurements of $b$-hadron lifetimes are reported using $pp$ collision data, corresponding to an integrated luminosity of 1.0fb$^{-1}$, collected by the LHCb detector at a centre-of-mass energy of $7$Tev. Using the exclusive decays $B^+\to J/ψK^+$, $B^0\to J/ψK^*(892)^0$, $B^0\to J/ψK^0_{\rm S}$, $Λ_b^0\to J/ψΛ$ and $B^0_s\to J/ψϕ$ the average decay times in these modes are measured to be $τ_{B^+\to J/ψK^+}$ = $1.637 \pm$ 0.004 $\pm$ 0.003 ps, $τ_{B^0\to J/ψK^*(892)^0}$ = $1.524 \pm$ 0.006 $\pm$ 0.004 ps, $τ_{B^0\to J/ψK^0_{\rm S}}$ = $1.499 \pm$ 0.013 $\pm$ 0.005 ps, $τ_{Λ_b^0\to J/ψΛ}$ = $1.415 \pm$ 0.027 $\pm$ 0.006 ps and $τ_{B^0_s\to J/ψϕ}$ = $1.480 \pm$ 0.011 $\pm$ 0.005 ps, where the first uncertainty is statistical and the second is systematic. These represent the most precise lifetime measurements in these decay modes. In addition, ratios of these lifetimes, and the ratio of the decay-width difference, $ΔΓ_d$, to the average width, $Γ_d$, in the $B^0$ system, $ΔΓ_d/Γ_d = -0.044 \pm 0.025 \pm 0.011$, are reported. All quantities are found to be consistent with Standard Model expectations.

hep-ex↗

arXiv2014

Study of beauty hadron decays into pairs of charm hadrons

First observations of the decays $Λ_b^0 \to Λ_c^+ D_{(s)}^-$ are reported using data corresponding to an integrated luminosity of $3\,{\rm fb}^{-1}$ collected at 7 and 8 TeV center-of-mass energy in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction ${\mathcal{B}(B_s^0 \to D^+D_s^-)}$ is made and a search is performed for the decays $B^0_{(s)} \to Λ_c^+ Λ_c^-$. The results obtained are \begin{eqnarray*} \mathcal{B}(Λ_b^0 \to Λ_c^+ D^-)/\mathcal{B}(Λ_b^0 \to Λ_c^+ D_{s}^-) &=& 0.042 \pm 0.003({\rm stat}) \pm 0.003({\rm syst}), \left[\frac{\mathcal{B}(Λ_b^0 \to Λ_c^+ D_{s}^-)}{\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}_d^0 \to D^+D_s^-)}\right]\big/\left[\frac{\mathcal{B}(Λ_b^0 \to Λ_c^+π^-)}{\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}_d^0 \to D^+π^-)}\right] &=& 0.96 \pm 0.02({\rm stat}) \pm 0.06({\rm syst}), \mathcal{B}(B_s^0 \to D^+D_s^-)/\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}_d^0 \to D^+D_s^-) &=& 0.038\pm0.004({\rm stat})\pm0.003({\rm syst}), \mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}^0 \to Λ_c^+ Λ_c^-)/\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}_d^0 \to D^+D_s^-) & < & 0.0022\; [95\% \; {\rm C.L.}], \mathcal{B}(B^0_{s} \to Λ_c^+ Λ_c^-)/\mathcal{B}(B_s^0 \to D^+D_s^-) & < & 0.30\; [95\% \; {\rm C.L.}]. \end{eqnarray*} Measurement of the mass of the $Λ_b^0$ baryon relative to the $B^0$ meson gives ${M(Λ_b^0) -M(B^0) = 339.72\pm 0.24({\rm stat}) \pm 0.18({\rm syst})}$ MeV$/c^2$. This result provides the most precise measurement of the mass of the $Λ_b^0$ baryon to date.

hep-ex↗

arXiv2014

Measurement of polarization amplitudes and CP asymmetries in $B^0 \to ϕK^*(892)^0$

An angular analysis of the decay $B^0 \to ϕK^*(892)^0$ is reported based on a $pp$ collision data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected at a centre-of-mass energy of $\sqrt{s} = 7$ TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave $K^+ π^-$ and $K^+K^-$ contributions are taken into account and found to be significant. A comparison of the $B^0 \to ϕK^*(892)^0$ and $\bar{B}^0 \to ϕ\bar{K}^*(892)^0$ results shows no evidence for direct CP violation in the rate asymmetry, in the triple-product asymmetries or in the polarization amplitudes and phases.

hep-ex↗

arXiv2014

Measurement of $ψ(2S)$ polarisation in $pp$ collisions at $\sqrt{s}=7$ TeV

The polarisation of prompt $ψ(2S)$ mesons is measured by performing an angular analysis of $ψ(2S)\rightarrow μ^{+} μ^{-}$ decays using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb detector at a centre-of-mass energy of 7 TeV. The polarisation is measured in bins of transverse momentum $p_\mathrm{T}$ and rapidity $y$ in the kinematic region $3.5<p_\mathrm{T}<15$ GeV$/c$ and $2.0<y<4.5$, and is compared to theoretical models. No significant polarisation is observed.

hep-ex↗

arXiv2014

Search for Majorana neutrinos in $B^- \to π^+μ^-μ^-$ decays

A search for heavy Majorana neutrinos produced in the $B^- \to π^+μ^-μ^-$ decay mode is performed using 3 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 TeV and 8 TeV at the LHC. Neutrinos with masses in the range 250-5000 MeV and lifetimes from zero to 1000 ps are probed. In the absence of a signal, upper limits are set on the branching fraction ${\cal{B}}(B^- \to π^+μ^-μ^-)$ as functions of neutrino mass and lifetime. These limits are on the order of $10^{-9}$ for short neutrino lifetimes of 1 ps or less. Limits are also set on the coupling between the muon and a possible fourth-generation neutrino.

hep-ex↗

arXiv2014

Measurement of resonant and $CP$ components in $\overline{B}_s^0\rightarrow J/ψπ^+π^-$ decays

The resonant structure of the decay $\overline{B}_s^0\to J/ψπ^+π^-$ is studied using data corresponding to 3 fb$^{-1}$ of integrated luminosity from $pp$ collisions by the LHC and collected by the LHCb detector. Five interfering $π^+π^-$ states are required to describe the decay: $f_0(980),f_0(1500),f_0(1790),f_2(1270)$, and $f_2^{\prime}(1525)$. An alternative model including these states and a non-resonant $J/ψπ^+π^-$ component also provides a good description of the data. Based on the different transversity components measured for the spin-2 intermediate states, the final state is found to be compatible with being entirely $CP$-odd. The $CP$-even part is found to be $<2.3$% at 95% confidence level. The $f_0(500)$ state is not observed, allowing a limit to be set on the absolute value of the mixing angle with the $f_0(980)$ of $<7.7^{\circ}$ at 90% confidence level, consistent with a tetraquark interpretation of the $f_0(980)$ substructure.

hep-ex↗

arXiv2014

Observation of double charm production involving open charm in pp collisions at $\sqrt{s}$=7 TeV

The production of $J/ψ$ mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of $355pb^{-1}$ collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured $J/ψ$ and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.

hep-ex↗

arXiv2014

Searches for $B^{0}_{(s)} \rightarrow J/ψ p \overline{p}$ and $B^{+} \to J/ψ p \overline{p} π^{+}$ decays

The results of searches for $B^{0}_{(s)} \rightarrow J/ψ p \overline{p}$ and $B^{+} \to J/ψ p \overline{p} π^{+}$ decays are 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. An excess with 2.8$\,σ$ significance is seen for the decay $B^{0}_{s} \to J/ψ p \overline{p}$ and an upper limit on the branching fraction is set at the 90 % confidence level: ${\cal B}(B^{0}_{s} \to J/ψ p \overline{p}) < 4.8 \times 10^{-6}$, which is the first such limit. No significant signals are seen for $B^{0} \to J/ψ p \overline{p}$ and $B^{+} \to J/ψ p \overline{p} π^{+}$ decays, for which the corresponding limits are set: ${\cal{B}}(B^{0} \to J/ψ p \overline{p}) < 5.2 \times 10^{-7}$, which significantly improves the existing limit; and ${\cal{B}}(B^{+} \to J/ψ p \overline{p} π^{+}) < 5.0 \times 10^{-7}$, which is the first limit on this branching fraction.

hep-ex↗

arXiv2014

Measurements of indirect CP asymmetries in $D^0\to K^-K^+$ and $D^0\toπ^-π^+$ decays

A study of indirect CP violation in $D^0$ mesons through the determination of the parameter $A_Γ$ is presented using a data sample of $pp$ collisions, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected with the LHCb detector and recorded at the centre-of-mass energy of 7 TeV at the LHC. The parameter $A_Γ$ is the asymmetry of the effective lifetimes measured in decays of $D^0$ and $\bar{D}^0$ mesons to the CP eigenstates $K^-K^+$ and $π^-π^+$. Fits to the data sample yield $A_Γ(KK)=(-0.35\pm0.62\pm0.12)\times 10^{-3}$ and $A_Γ(ππ)=(0.33\pm1.06\pm0.14)\times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The results represent the world's best measurements of these quantities. They show no difference in $A_Γ$ between the two final states and no indication of CP violation.

hep-ex↗

arXiv2014

Measurement of the $B_c^+$ meson lifetime using $B_c^+ \to J\!/\!ψμ^+ ν_μ X$ decays

The lifetime of the $B_c^+$ meson is measured using semileptonic decays having a $J\!/\!ψ$ meson and a muon in the final state. The data, corresponding to an integrated luminosity of $2\mathrm{~fb^{-1}}$, are collected by the LHCb detector in $pp$ collisions at a centre-of-mass energy of $8\,\mathrm{TeV}$. The measured lifetime is $$τ= 509 \pm 8 \pm 12 \mathrm{~fs},$$ where the first uncertainty is statistical and the second is systematic.

hep-ex↗

arXiv2014

Updated measurements of exclusive $J/ψ$ and $ψ(2S)$ production cross-sections in $pp$ collisions at $\sqrt{s}=7$ TeV

The differential cross-section as a function of rapidity has been measured for the exclusive production of $J/ψ$ and $ψ(2S)$ mesons in proton-proton collisions at $\sqrt{s}=7$ TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pb$^{-1}$. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be $$\begin{array}{rl} σ_{pp\rightarrow J/ψ\rightarrow{μ^+}{μ^-}}(2.0<η_{μ^\pm }<4.5)=&291\pm 7\pm19 {\rm \ pb},\\ σ_{pp\rightarrowψ(2S)\rightarrow{μ^+}{μ^-}}(2.0<η_{μ^\pm}<4.5)=&6.5\pm 0.9\pm 0.4 {\rm \ pb},\end{array}$$ where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects.

hep-ex↗

arXiv2014

Observation of B^0_(s) -> J/ψf_1(1285) decays and measurement of the f_1(1285) mixing angle

Decays of Bs and B0 mesons into J/ψπ+π-π+π- final states, produced in pp collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3/fb collected with the LHCb detector. B^0_(s) -> Jψf_1(1285) decays are seen for the first time, and the branching fractions are measured. Using these rates, the f_1(1285) mixing angle between strange and non-strange components of its wave function in the q-qbar structure model is determined to be \pm (24.0^{+3.1+0.6}_{-2.6-0.8}) degrees. Implications on the possible tetraquark nature of the f_1(1285) are discussed.

hep-ex↗

arXiv2014

Observation of associated production of a $Z$ boson with a $D$ meson in the~forward region

A search for associated production of a $Z$ boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of $1.0\,\mathrm{fb}^{-`}$ of proton--proton collisions at a centre-of-mass energy of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for associated production of a $Z$ boson with a $D^0$ meson and four candidate events for a $Z$ boson with a $D^+$ meson are observed with a combined significance of 5.1standard deviations. The production cross-sections in the forward region are measured to be $$σ_{Z\rightarrowμ^+μ^-\!,D^0} = 2.50\pm1.12\pm0.22pb$$ $$σ_{Z\rightarrowμ^+μ^-\!,D^+} = 0.44\pm0.23\pm0.03pb,$$ where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2014

Measurement of the flavour-specific CP-violating asymmetry $a_{\rm sl}^s$ in $B_s^0$ decays

The CP-violating asymmetry a_{sl}^s is studied using semileptonic decays of Bs and anti-Bs mesons produced in pp collisions at a centre-of-mass energy of 7 TeV at the LHC, exploiting a data sample corresponding to an integrated luminosity of 1.0/fb. The reconstructed final states are Ds^(+/-)μ^(-/+), with the Ds^(+/-) particle decaying in the ϕπ^(+/-) mode. The Ds^(+/-)μ^{-/+) yields are summed over Bs and anti-Bs initial states, and integrated with respect to decay time. Data-driven methods are used to measure efficiency ratios. We obtain $a_{sl}^s$ = (-0.06 +/- 0.50 +/- 0.36)%, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2014

Search for CP violation in the decay $D^+ \to π^-π^+π^+$

A search for CP violation in the phase space of the decay $D^+\toπ^-π^+π^+$ is reported using $pp$ collision 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. The Dalitz plot distributions for $3.1\times 10^6$ $D^+$ and $D^-$ candidates are compared with binned and unbinned model-independent techniques. No evidence for CP violation is found.

hep-ex↗

arXiv2014

Search for the doubly charmed baryon Xi_cc^+

A search for the doubly charmed baryon Xi_cc^+ in the decay mode Xi_cc^+ -> Lambda_c^+ K^- pi^+ is performed with a data sample, corresponding to an integrated luminosity of 0.65/fb, of pp collisions recorded at a centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300-3800 MeV/c^2. Upper limits at the 95% confidence level on the ratio of the Xi_cc^+ production cross-section times branching fraction to that of the Lambda_c^+, R, are given as a function of the Xi_cc^+ mass and lifetime. The largest upper limits range from R < 1.5 x 10^-2 for a lifetime of 100 fs to R < 3.9 x 10^-4 for a lifetime of 400 fs.

hep-ex↗

arXiv2013

Observation of the decay $B_s^0\to\bar{D}^0ϕ$

First observation of the decay Bs -> D0bar phi is reported using pp collision 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. The significance of the signal is 6.2 standard deviations. The branching fraction is measured relative to that of the decay Bs -> D0bar K*0bar to be 0.069 +/- 0.013 (stat) +/- 0.007 (syst). The first measurement of the ratio of branching fractions for the decays Bs -> D0bar K*0bar and Bd->D0bar K*0 is found to be 7.8 +/- 0.7 (stat) +/- 0.3 (syst) +/- 0.6 (f_s/f_d), where the last uncertainty is due to the ratio of the Bs and Bd fragmentation fractions.

hep-ex↗