Results are reported from a search for the rare decays Bs0→τ±μ∓ and B0→τ±μ∓, where the τ lepton is reconstructed in the channel τ−→π−π+π−ντ. These processes are effectively forbidden in the standard ...model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to 3 fb−1 of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected τ neutrino, the Bs0 and B0 signal regions are highly overlapping. Assuming no contribution from B0→τ±μ∓, the upper limit B(Bs0→τ±μ∓)<4.2×10−5 is obtained at 95% confidence level. If no contribution from Bs0→τ±μ∓ is assumed, a limit of B(B0→τ±μ∓)<1.4×10−5 is obtained at 95% confidence level. These results represent the first limit on B(Bs0→τ±μ∓) and the most stringent limit on B(B0→τ±μ∓).
We report the observation of a new structure in the Λb0π+π− spectrum using the full LHCb data set of pp collisions, corresponding to an integrated luminosity of 9 fb−1, collected at s=7, 8, and 13 ...TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be mΛb(6146)0=6146.17±0.33±0.22±0.16 MeV,mΛb(6152)0=6152.51±0.26±0.22±0.16 MeV,ΓΛb(6146)0=2.9±1.3±0.3 MeV,ΓΛb(6152)0=2.1±0.8±0.3 MeV,with a mass splitting of Δm=6.34±0.32±0.02 MeV, where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the Λb0 baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of Λb(1D)0 states.
Using pp collision data corresponding to an integrated luminosity of 8.5 fb−1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ ...state in the Bc+π+π− invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc*(2S31)+ state reconstructed without the low-energy photon from the Bc*(1S31)+→Bc+γ decay following Bc*(2S31)+→Bc*(1S31)+π+π−. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date.
The production of χc1(3872) and ψ(2S) hadrons is studied as a function of charged particle multiplicity in p p collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated ...luminosity of 2 fb−1. For both states, the fraction that is produced promptly at the collision vertex is found to decrease as charged particle multiplicity increases. The ratio of χc1(3872) to ψ(2S) cross sections for promptly produced particles is also found to decrease with multiplicity, while no significant dependence on multiplicity is observed for the equivalent ratio of particles produced away from the collision vertex in b-hadron decays. This behavior is consistent with a calculation that models the χc1(3872) structure as a compact tetraquark. Comparisons with model calculations and implications for the binding energy of the χc1(3872) state are discussed.
Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and ...mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the (DD0)-D-0 pi(+) mass spectrum just below the D*+D-0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T-cc(+), tetraquark with a quark content of cc (u) over bar(d) over bar and spin-parity quantum numbers J(P) =1(+). Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D*(+) mesons is consistent with the observed D-0 pi(+) mass distribution. To analyse the mass of the resonance and its coupling to the DID system, a dedicated model is developed under the assumption of an isoscalar axial-vector T-cc(+), state decaying to the D*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T-cc(+), state. In addition, an unexpected dependence of the production rate on track multiplicity is observed.
We report here measurement of the cross section of e+e- → π+π-ψ ( 2S ) between 4.0 and 5.5 GeV, based on an analysis of initial state radiation events in a 980fb-1 data sample recorded with the Belle ...detector. The properties of the Y ( 4360 ) and Y ( 4660 ) states are determined. Fitting the mass spectrum of π+π-ψ ( 2S ) with two coherent Breit-Wigner functions, we discover two solutions with identical mass and width but different couplings to electron-positron pairs: MY ( 4360 ) = ( 4347±6±3 ) MeV / c2 , Γ Y ( 4360 ) = ( 103±9±5 ) MeV , MY ( 4660 ) = ( 4652±10±8 ) MeV / c2 , Γ Y ( 4660 ) = ( 68±11±1 ) MeV ; and B Y ( 4360 ) → π+π-ψ ( 2S ) · Γ Y ( 4360 ) e+e-= ( 10.9±0.6±0.7 ) eV and B Y ( 4660 ) → π+π-ψ ( 2S ) · Γ Y ( 4660 ) e+e-= ( 8.1±1.1±0.5 ) eV for one solution; or B Y ( 4360 ) → π+π-ψ ( 2S ) · Γ Y ( 4360 ) e+e-= ( 9.2±0.6±0.6 ) eV and B Y ( 4660 ) → π+π=ψ ( 2S ) · Γ Y ( 4660 ) e+e-= ( 2.0±0.3±0.2 ) eV for the other. Here, the first errors are statistical and the second systematic. Evidence for a charged charmoniumlike structure at 4.05GeV / c2 is observed in the π±ψ ( 2S ) intermediate state in the Y ( 4360 ) decays. decays.
The first amplitude analysis of the B^{±}→π^{±}K^{+}K^{-} decay is reported based on a data sample corresponding to an integrated luminosity of 3.0 fb^{-1} of pp collisions recorded in 2011 and 2012 ...with the LHCb detector. The data are found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from ππ↔KK S-wave rescattering. The dominant contributions in the π^{±} K^{∓} and K^{+} K^{-} systems are the nonresonant and the B^{±}→ρ(1450)^{0}π^{±} amplitudes, respectively, with fit fractions around 30%. For the rescattering contribution, a sizable fit fraction is observed. This component has the largest CP asymmetry reported to date for a single amplitude of (-66±4±2)%, where the first uncertainty is statistical and the second systematic. No significant CP violation is observed in the other contributions.
The doubly charmed baryon decay Ξ_{cc}^{++}→Ξ_{c}^{+}π^{+} is observed for the first time, with a statistical significance of 5.9σ, confirming a recent observation of the baryon in the ...Λ_{c}^{+}K^{-}π^{+}π^{+} final state. The data sample used corresponds to an integrated luminosity of 1.7 fb^{-1}, collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV. The Ξ_{cc}^{++} mass is measured to be 3620.6±1.5(stat)±0.4(syst)±0.3(Ξ_{c}^{+}) MeV/c^{2} and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be B(Ξ_{cc}^{++}→Ξ_{c}^{+}π^{+})×B(Ξ_{c}^{+}→pK^{-}π^{+})/B(Ξ_{cc}^{++}→Λ_{c}^{+}K^{-}π^{+}π^{+})×B(Λ_{c}^{+}→pK^{-}π^{+})=0.035±0.009(stat)±0.003(syst).
A
bstract
The
ϒ
(1
S
)
μ
+
μ
−
invariant-mass distribution is investigated for a possible exotic meson state composed of two
b
quarks and two
b
¯
quarks,
X
b
b
¯
b
b
¯
. The analysis is based on a ...data sample of
pp
collisions recorded with the LHCb detector at centre-of-mass energies
s
=
7
, 8 and 13 TeV, corresponding to an integrated luminosity of 6.3 fb
−1
. No significant excess is found, and upper limits are set on the product of the production cross-section and the branching fraction as functions of the mass of the
X
b
b
¯
b
b
¯
state. The limits are set in the fiducial volume where all muons have pseudorapidity in the range 2
.
0
,
5
.
0, and the
X
b
b
¯
b
b
¯
state has rapidity in the range 2
.
0
,
4
.
5 and transverse momentum less than 15 GeV/
c
.
The cross section for prompt antiproton production in collisions of protons with an energy of 6.5 TeV incident on helium nuclei at rest is measured with the LHCb experiment from a data set ...corresponding to an integrated luminosity of 0.5 nb−1. The target is provided by injecting helium gas into the LHC beam line at the LHCb interaction point. The reported results, covering antiproton momenta between 12 and 110 GeV/c, represent the first direct determination of the antiproton production cross section in p−He collisions, and impact the interpretation of recent results on antiproton cosmic rays from space-borne experiments.
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