The angular distribution and differential branching fraction of the decay $B^{0} \to K^{*0} \mu^{+}\mu^{-}$ are studied using a data sample, collected by the LHCb experiment in $pp$ collisions at ...$\sqrt{s}=7\,{\rm TeV}$, corresponding to an integrated luminosity of $1.0\,{\rm fb}^{-1}$. Several angular observables are measured in bins of the dimuon invariant mass squared, $q^{2}$. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be $q_{0}^{2} = 4.9 \pm 0.9 \,{\rm GeV}^{2}/c^{4}$, where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions.
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 5911.95 +- ...0.12(stat) +- 0.03(syst) +- 0.66(Lambda_b0 mass) MeV/c^2 and 5919.76 +- 0.07(stat) +- 0.02(syst) +- 0.66(Lambda_b0 mass) MeV/c^2. The significances of the observations are 4.9 and 10.1 standard deviations, respectively. These states are interpreted as the orbitally-excited Lambda_b0 baryons, Lambda_b*0(5912) and Lambda_b*0(5920).
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 355 pb−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.
Measurements of CP observables in B±→DK± and B±→Dπ± decays are presented where the D meson is reconstructed in the final states K±π∓, π±K∓, K+K−, π+π−, K±π∓π+π−, π±K∓π+π− and π+π−π+π−. This analysis ...uses a sample of charged B mesons from pp collisions collected by the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb−1. Various CP-violating effects are reported and together these measurements provide important input for the determination of the unitarity triangle angle γ. The analysis of the four-pion D decay mode is the first of its kind.
A
bstract
A measurement of the cross-section for
W
→
eν
production in
pp
collisions is presented using data corresponding to an integrated luminosity of 2 fb
−1
collected by the LHCb experiment at a ...centre-of-mass energy of
s
=
8
TeV. The electrons are required to have more than 20 GeV of transverse momentum and to lie between 2
.
00 and 4
.
25 in pseudorapidity. The inclusive
W
production cross-sections, where the
W
decays to
eν
, are measured to be
σ
W
+
→
e
+
ν
e
=
1124.4
±
2.1
±
21.5
±
11.2
±
13.0
p
b
,
σ
W
−
→
e
−
ν
¯
e
=
809.0
±
1.9
±
18.1
±
7.0
±
9.4
p
b
,
where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination.
Differential cross-sections as a function of the electron pseudorapidity are measured. The
W
+
/W
−
cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of
W
boson branching fractions is determined to be
ℬ
W
→
e
ν
/
ℬ
W
→
μ
ν
=
1.020
±
0.002
±
0.019
,
where the first uncertainty is statistical and the second is systematic.
Bottom baryons decaying to a J/ψ meson and a hyperon are reconstructed using 1.0 fb(-1) of data collected in 2011 with the LHCb detector. Significant Λ(b)(0) → J/ψΛ, Ξ(b((-) → J/ψΞ(-) and Ω(b)(-) → ...J/ψΩ(-) signals are observed and the corresponding masses are measured to be M(Λ(b)(0))=5619.53 ± 0.13(stat.) ± 0.45(syst.) MeV/c(2), M(Ξ(b)(-)) = 5795.8 ± 0.9(stat.) ± 0.4(syst.) MeV/c(2), M(Ω(b)(-)) = 6046.0 ± 2.2(stat.) ± 0.5(syst.) MeV/c(2) , while the differences with respect to the Λ(b)(0) mass are M(Ξ(b)(-))-M(Λ(b)(0))=176.2 ± 0.9(stat.) ± 0.1(syst.) MeV/c(2), M(Ω(b)(-))-M(Λ(b)(0))=426.4 ± 2.2(stat.) ± 0.4(syst.) MeV/c(2). These are the most precise mass measurements of the Λ(b)(0), Ξ(b)(-) and Ω(b)(-) baryons to date. Averaging the above Λ(b)(0) mass measurement with that published by LHCb using 35 pb(-1) of data collected in 2010 yields M(Λ(b)(0)) = 5619.44 ± 0.13(stat.)± 0.38(syst.) MeV/c(2).
Observation of D0-D0 oscillations Abellan Beteta, C; Adametz, A; Alves, Jr, A A ...
Physical review letters,
2013-Mar-08, Letnik:
110, Številka:
10
Journal Article
Recenzirano
Odprti dostop
We report a measurement of the time-dependent ratio of D(0) → K(+) π- to D(0) → K(-) π(+) decay rates in D(*+)-tagged events using 1.0 fb(-1) of integrated luminosity recorded by the LHCb experiment. ...We measure the mixing parameters x('2) = (-0.9 ± 1.3) × 10(-4), y' = (7.2 ± 2.4) × 10(-3), and the ratio of doubly-Cabibbo-suppressed to Cabibbo-favored decay rates R(D) = (3.52 ± 0.15) × 10^{-3}, where the uncertainties include statistical and systematic sources. The result excludes the no-mixing hypothesis with a probability corresponding to 9.1 standard deviations and represents the first observation of D0-D0 oscillations from a single measurement.
The first observation of the decay ηc(2S)→pp¯ is reported using proton–proton collision data corresponding to an integrated luminosity of 3.0 fb−1 recorded by the LHCb experiment at centre-of-mass ...energies of 7 and 8 TeV. The ηc(2S) resonance is produced in the decay B+→cc¯K+. The product of branching fractions normalised to that for the J/ψ intermediate state, Rηc(2S), is measured to beRηc(2S)≡B(B+→ηc(2S)K+)×B(ηc(2S)→pp¯)B(B+→J/ψK+)×B(J/ψ→pp¯)=(1.58±0.33±0.09)×10−2, where the first uncertainty is statistical and the second systematic. No signals for the decays B+→X(3872)(→pp¯)K+ and B+→ψ(3770)(→pp¯)K+ are seen, and the 95% confidence level upper limits on their relative branching ratios are found to be RX(3872)<0.25×10−2 and Rψ(3770)<0.10. In addition, the mass differences between the ηc(1S) and the J/ψ states, between the ηc(2S) and the ψ(2S) states, and the natural width of the ηc(1S) are measured asMJ/ψ−Mηc(1S)=110.2±0.5±0.9 MeV,Mψ(2S)−Mηc(2S)=52.5±1.7±0.6 MeV,Γηc(1S)=34.0±1.9±1.3 MeV.
A
bstract
The forward-backward charge asymmetry for the process
q
q
¯
→
Z
/
γ
∗
→
μ
+
μ
−
is measured as a function of the invariant mass of the dimuon system. Measurements are performed using proton ...proton collision data collected with the LHCb detector at
s
=
7
and 8 TeV, corresponding to integrated luminosities of 1 fb
−1
and 2 fb
−1
respectively. Within the Standard Model the results constrain the effective electroweak mixing angle to be
sin
2
θ
W
eff
=
0.23142
±
0.00073
±
0.00052
±
0.00056
,
where the first uncertainty is statistical, the second systematic and the third theoretical. This result is in agreement with the current world average, and is one of the most precise determinations at hadron colliders to date.
PDF
