A test of lepton universality, performed by measuring the ratio of the branching fractions of the $B^0 → K^{*0}μ^+μ^-$ and $B^0$ → $K^{*0}e^+e^-$ decays, $R_{K^{*0}}$, is presented. The $K^{*0}$ ...meson is reconstructed in the final state $K^+π^-$, which is required to have an invariant mass within 100 MeV/c2 of the known $K^*$ (892)0 mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb-1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q2, to be R K ∗ 0 = { 0.66 − + 0.07 0.11 ( s t a t ) ± 0.03 ( s y s t ) f o r 0.045 < q 2 < 1.1 G e V 2 / c 4 , 0.69 − + 0.07 0.11 ( s t a t ) ± 0.05 ( s y s t ) f o r 1.1 < q 2 < 6.0 G e V 2 / c 4 . The corresponding 95.4% confidence level intervals are 0.52, 0.89 and 0.53, 0.94. The results, which represent the most precise measurements of $R_{K^{*0}}$ to date, are compatible with the Standard Model expectations at the level of 2.1–2.3 and 2.4–2.5 standard deviations in the two q2 regions, respectively.
A search for the rare decays $B^0_s$→$μ$+$μ$- and B0→$μ$+$μ$- is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb-1. An ...excess of $B^0_s$→$μ$+$μ$- decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be $B$($μ$+$μ$-)=(3.0 ± $0.6^{+0.3}_{-0.2}$) × 10-9, where the first uncertainty is statistical and the second systematic. The first measurement of the $B^0_s$→$μ$+$μ$- effective lifetime, τ($B^0_s$→($μ$+$μ$-) = 2.04 ± 0.44 ± 0.05 ps, is reported. No significant excess of B0→($μ$+$μ$- decays is found, and a 95% confidence level upper limit, $B$(B0→($μ$+$μ$-) < 3.4 × 10-10, is determined. All results are in agreement with the standard model expectations.
The $\Xi{^+_c}$$K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb-1, collected by the LHCb experiment. The $\Xi{^+_c}$ is ...reconstructed in the decay mode $pK^-$$π^+$. Five new, narrow excited $Ω_c^0$ states are observed: the $Ω_c$(3000)$^0$, $Ω_c$(3050)$^0$, $Ω_c$(3066)$^0$, $Ω_c$(3090)$^0$, and $Ω_c$(3119)$^0$. Measurements of their masses and widths are reported.
The first full amplitude analysis of B+→J/ψϕK+ with J/ψ→μ+μ−, ϕ→K+K− decays is performed with a data sample of 3 fb−1 of pp collision data collected at s=7 and 8 TeV with the LHCb detector. The data ...cannot be described by a model that contains only excited kaon states decaying into ϕK+, and four J/ψϕ structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed X(4140) state. The model includes significant contributions from a number of expected kaon excitations, including the first observation of the K*(1680)+→ϕK+ transition.
A
bstract
Production cross-sections of prompt charm mesons are measured with the first data from
pp
collisions at the LHC at a centre-of-mass energy of 13 TeV. The data sample corresponds to an ...integrated luminosity of 4.98 ± 0.19 pb
−1
collected by the LHCb experiment. The production cross-sections of
D
0
,
D
+
,
D
s
+
, and
D
*+
mesons are measured in bins of charm meson transverse momentum,
p
T
, and rapidity,
y
, and cover the range 0 <
p
T
< 15GeV/c and 2.0 <
y
< 4.5. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of 1 <
p
T
< 8 GeV/c are found to be
σ
pp
→
D
0
X
=
2460
±
3
±
130
μ
b
σ
pp
→
D
+
X
=
1000
±
3
±
110
μ
b
σ
pp
→
D
s
+
X
=
460
±
13
±
100
μ
b
σ
pp
→
D
∗
+
X
=
880
±
5
±
140
μ
b
where the uncertainties are due to statistical and systematic uncertainties, respectively.
Search for the Decays Bs0→τ+τ- and B0→τ+τ Badalov, Alexey; Calvo Gómez, Míriam; Camboni, Alessandro ...
Physical review letters,
06/2017, Letnik:
118, Številka:
25
Journal Article
Recenzirano
Odprti dostop
A search for the rare decays Bs0→τ+τ- and B0→τ+τ- is performed using proton-proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb-1 ...collected in 2011 and 2012. The τ leptons are reconstructed through the decay τ-→π-π+π-ντ. Assuming no contribution from B0→τ+τ- decays, an upper limit is set on the branching fraction B (Bs0→τ+τ- )<6.8 ×10-3 at the 95% confidence level. If instead no contribution from Bs0→τ+τ- decays is assumed, the limit is B (B0→τ+τ- )<2.1 ×10-3 at the 95% confidence level. These results correspond to the first direct limit on B (Bs0→τ+τ- ) and the world's best limit on B (B0→τ+τ- ).
The B 0 s π ± invariant mass distribution is investigated in order to search for possible exotic meson states. The analysis is based on a data sample recorded with the LHCb detector corresponding to ...3 fb − 1 of p p collision data at √ s = 7 and 8 TeV. No significant excess is found, and upper limits are set on the production rate of the claimed X ( 5568 ) state within the LHCb acceptance. Upper limits are also set as a function of the mass and width of a possible exotic meson decaying to the B 0 s π ± final state. The same limits also apply to a possible exotic meson decaying through the chain B * 0 s π ± , B * 0 s → B 0 s γ where the photon is excluded from the reconstructed decays.
A
bstract
The production cross-section of
J/ψ
pairs is measured using a data sample of
pp
collisions collected by the LHCb experiment at a centre-of-mass energy of
s
=
13
TeV, corresponding to an ...integrated luminosity of 279 ±11 pb
−1
. The measurement is performed for
J/ψ
mesons with a transverse momentum of less than 10 GeV/
c
in the rapidity range 2
.
0
< y <
4
.
5. The production cross-section is measured to be 15
.
2 ± 1
.
0 ± 0
.
9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the
J/ψ
pair are measured and compared to theoretical predictions.
The first observation of the decays Λ$^0_b$ → $χ$c1$pK$- and Λ$^0_b$ → $χ$c2$pK$- is reported using a data sample corresponding to an integrated luminosity of 3.0 fb-1, collected by the LHCb ...experiment in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured: $$\frac{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}=0.242 ± 0.014 ± 0.013 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}= 0.248 ± 0.020 ± 0.014 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}= 1.02 ± 0.10 ± 0.02 ± 0.05$$ where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the $Χ_{c1}$ → $Jψγ$ and $Χ_{c2}$ → $Jψγ$ decays. Using both decay modes, the mass of the Λ$^0_b$ baryon is also measured to be $m$Λ$^0_b$ = 5619.44 ± 0.28 ± 0.26 MeV/$c$2, where the first and second uncertainties are statistical and systematic, respectively.
The B−→D+K−π− decay is observed in a data sample corresponding to 3.0 fb−1 of pp collision data recorded by the LHCb experiment during 2011 and 2012. Its branching fraction is measured to be ...B(B−→D+K−π−)=(7.92±0.23±0.24±0.42)×10−5 where the uncertainties are statistical, systematic and from the branching fraction of the normalisation channel B−→D+π−π−, respectively. An amplitude analysis of the resonant structure of the B−→D+K−π− decay is used to measure the contributions from quasi-two-body B−→D∗0(2400)0K−, B−→D∗2(2460)0K−, and B−→D∗J(2760)0K− decays, as well as from nonresonant sources. The D∗J(2760)0 resonance is determined to have spin~1.
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