Observation of the Λ b → J/ψ pπ - Decay (original) (raw)
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Observation of the Λb0rightarrowJ/ψpπ−Λ_b^0\rightarrow J/ψp π^-Λb0rightarrowJ/ψpπ− decay
2014
The first observation of the Cabibbo-suppressed decay Λ 0 b → J/ψpπ − is reported using a data sample of proton-proton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb −1. A prominent signal is observed and the branching fraction relative to the decay mode Λ 0 b → J/ψpK − is determined to be B(Λ 0 b → J/ψpπ −) B(Λ 0 b → J/ψpK −) = 0.0824 ± 0.0025 (stat) ± 0.0042 (syst). A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be A CP (Λ 0 b → J/ψpπ −) − A CP (Λ 0 b → J/ψpK −) = (+5.7 ± 2.4 (stat) ± 1.2 (syst))%, which is compatible with CP symmetry at the 2.2σ level.
Search for CP Violation and Observation of P Violation in Λ0b → p π− π+ π− Decays
A search for CP violation in the Λ 0 b → pπ − π þ π − decay is performed using LHCb data corresponding to an integrated luminosity of 6.6 fb −1 collected in pp collisions at center-of-mass energies of 7, 8 and 13 TeV. The analysis uses both triple product asymmetries and the unbinned energy test method. The highest significances of CP asymmetry are 2.9 standard deviations from triple product asymmetries and 3.0 standard deviations for the energy test method. Once the global p-value is considered, all results are consistent with no CP violation. Parity violation is observed at a significance of 5.5 standard deviations for the triple product asymmetry method and 5.3 standard deviations for the energy test method. The reported deviations are given in regions of phase space. The violation of CP symmetry, where C and P are the charge-conjugation and parity operators, is a well-established phenomenon in the decays of K and B mesons [1-3]. Recently, it has also been observed in the decays of D mesons by the LHCb collaboration [4]. However, CP violation has yet to be established in baryonic decays, although first evidence was recently found [5]. Such decays offer a novel environment to probe the mechanism for quark-flavor mixing and for CP violation, which is regulated by the Cabibbo-Kobayashi-Maskawa (CKM) matrix in the Standard Model (SM) [6,7]. In this paper searches for CP and P violation with Λ 0 b → pπ − π þ π − decays are reported. Throughout, the inclusion of charge-conjugate processes is implied, unless otherwise indicated. This decay is mediated mainly by tree and loop processes of similar magnitudes, proportional to the product of the CKM matrix elements V ub V Ã ud and V tb V Ã td , respectively. This allows for significant interference effects with a relative weak phase α of the unitary triangle between the amplitudes. If matter and antimatter exhibit different effects, CP violation manifests as either global asymmetries in decay rates, or as local asymmetries within the phase space. The Λ 0 b → pπ − π þ π − decay is particularly well suited for CP-violation searches [8] due to a rich resonant structure in the decay. The dominant contributions proceed through the N Ãþ → Δ þþ ð1234Þπ − (referred as Δ þþ hereinafter), Δ þþ → pπ þ , a − 1 ð1260Þ → ρ 0 ð770Þπ − and ρ 0 ð770Þ → π þ π − decays, where the proton excited states are indicated as N Ãþ. The searches for CP violation are performed by separating the P-odd and P-even contributions [9], as discussed below. In these studies, a large control sample of Cabibbo-favored Λ 0 b → Λ þ c ð→pK − π þ Þπ − decays is used, where no CP violation is expected, to assess potential experimental biases and systematic effects. The LHCb collaboration has previously studied the Λ 0 b → pπ − π þ π − decay and found evidence for CP violation with a significance of 3.3 standard deviations including systematic uncertainties [5]. This paper supersedes the previous results using pp collision data corresponding to an integrated luminosity of 6.6 fb −1 collected from 2011 to 2017 at center-of-mass energies of 7, 8 and 13 TeV that represents a four times larger sample in signal yield. The LHCb detector [10,11] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks. The detector elements that are particularly relevant to this analysis are: a silicon-strip vertex detector surrounding the pp interaction region that allows b hadrons to be identified from their characteristically long flight distance; a tracking system that provides a measurement of the momentum, p, of charged particles; and two ring-imaging Cherenkov detectors that are able to discriminate between different species of charged hadrons. Simulation is required to model the effects of the detector acceptance and the selection requirements. The pp collisions are generated using PYTHIA [12] with a specific LHCb configuration [13], and neither CP-nor P-violating effects are present in the signal channel. Decays of unstable particles are described by EVTGEN [14], in which final-state radiation is generated * Full author list given at the end of the article.
Search for CP violation in Λb0→pK− and Λb0→pπ− decays
Physics Letters B
A search for CP violation in Λ 0 b → pK − and Λ 0 b → pπ − decays is presented using a sample of pp collisions collected with the LHCb detector and corresponding to an integrated luminosity of 3.0 fb −1. The CP-violating asymmetries are measured to be A pK − CP = −0.020 ± 0.013 ± 0.019 and A pπ − CP = −0.035 ± 0.017 ± 0.020, and their difference A pK − CP − A pπ − CP = 0.014 ± 0.022 ± 0.010, where the first uncertainties are statistical and the second systematic. These are the most precise measurements of such asymmetries to date.
Journal of High Energy Physics, 2018
A search for CP and P violation using triple-product asymmetries is performed with Λ b 0 → pK − π + π −, Λ b 0 → pK − K + K − and Ξ b 0 → pK − K − π + decays. The data sample corresponds to integrated luminosities of 1.0 fb−1 and 2.0 fb−1, recorded with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV, respectively. The CP - and P - violating asymmetries are measured both integrating over all phase space and in specific phase-space regions. No significant deviation from CP or P symmetry is found. The first observation of Λ b 0 → pK − χ c0(1P)(→π + π −, K + K −) decay is also reported.
Study of Direct CP Violation in B±→J/ψK±(π±) Decays
Physical Review Letters, 2008
We present a search for direct CP violation in B ± → J/ψK ± (π ± ) decays. The event sample is selected from 2.8 fb −1 of pp collisions recorded by D0 experiment in Run II of the Fermilab Tevatron Collider. The charge asymmetry ACP (B + → J/ψK + ) = +0.0075 ± 0.0061(stat.)±0.0027(syst.) is obtained using a sample of approximately 40 thousand B ± → J/ψK ± decays. The achieved precision is of the same level as the expected deviation predicted by some extensions of the standard model. We also measured the charge asymmetry ACP (B + → J/ψπ + ) = −0.09 ± 0.08(stat.)±0.03(syst.).
Physical Review D, 2002
We have studied the B ± → J/ψ π ± and B ± → J/ψ K ± decays using a 20.7 fb −1 data set collected with the BABAR detector. We observe a signal of 51 ± 10 B ± → J/ψ π ± events and determine the ratio B(B ± → J/ψ π ± )/B(B ± → J/ψ K ± ) to be [3.91 ± 0.78(stat.) ± 0.19(syst.)]%. The CPviolating charge asymmetries for the B ± → J/ψ π ± and B ± → J/ψ K ± decays are determined to be Aπ = 0.01 ± 0.22(stat.) ± 0.01(syst.) and AK = 0.003 ± 0.030(stat.) ± 0.004(syst.). PACS numbers: 13.25.Hw, 14.40.Nd The decay B ± → J/ψ π ± is both Cabibbo-suppressed and color-suppressed. If the leading-order tree diagram
Evidence for CP Violation in B0→J/ψπ0 Decays
Physical Review Letters, 2008
We present measurements of the branching fraction and time-dependent CP asymmetries in B 0 → J/ψ π 0 decays based on 466 million Υ (4S) → BB events collected with the BABAR detector at the SLAC PEP-II asymmetric-energy B factory. We measure the CP asymmetry parameters S = −1.23 ± 0.21(stat) ± 0.04(syst) and C = −0.20 ± 0.19(stat) ± 0.03(syst), where the measured value of S is 4.0 standard deviations from zero including systematic uncertainties. The branching fraction is determined to be B(B 0 → J/ψ π 0 ) = (1.69 ± 0.14(stat) ± 0.07(syst)) × 10 −5 .
Observation of Several Sources of CP Violation in B + → π + π + π − Decays
Observations are reported of different sources of CP violation from an amplitude analysis of B þ → π þ π þ π − decays, based on a data sample corresponding to an integrated luminosity of 3 fb −1 of pp collisions recorded with the LHCb detector. A large CP asymmetry is observed in the decay amplitude involving the tensor f 2 ð1270Þ resonance, and in addition significant CP violation is found in the π þ π − S wave at low invariant mass. The presence of CP violation related to interference between the π þ π − S wave and the P wave B þ → ρð770Þ 0 π þ amplitude is also established; this causes large local asymmetries but cancels when integrated over the phase space of the decay. The results provide both qualitative and quantitative new insights into CP-violation effects in hadronic B decays. Violation of symmetry under the combined charge-conjugation and parity-transformation operations, CP violation , gives rise to differences between matter and anti-matter. Violation of CP symmetry can occur in the amplitudes that describe hadron decay, in neutral hadron mixing, or in the interference between mixing and decay (for a review, see, e.g., Ref. [1]). For charged mesons, only CP violation in decay is possible, where an asymmetry in particle and antiparticle decay rates can arise when two or more different amplitudes contribute to a transition. In particular, the phase of each complex amplitude can be decomposed into a weak phase, which changes sign under CP, and a strong phase, which is CP invariant. Differences in both the weak and strong phases of the contributing amplitudes are required for an asymmetry to occur. In the standard model, weak phases arise from the elements of the Cabibbo-Kobayashi-Maskawa matrix [2,3] that are associated with quark-level transition amplitudes. Decays of B hadrons that do not contain any charm quarks in the final state, such as B þ → π þ π þ π − , are of particular interest as both tree-level and loop-level amplitudes are expected to contribute with comparable magnitudes , so that large CP-violation effects are possible. Indeed, significant asymmetries have been observed in the two-body B 0 → K þ π − [4-6] and B 0 → π þ π − [4,6,7] decays. In two-body decays, nontrivial strong phases can arise from rescattering or other hadronic effects. In three-body or multibody decays, variation of the strong phase is also expected due to the intermediate resonance structure, and hence amplitude analyses can provide additional sensitivity to CP-violation effects. Analysis of the distribution of B þ → π þ π þ π − decays (the inclusion of charge-conjugated processes is implied throughout this Letter, except where asymmetries are discussed) across the Dalitz plot [8,9], which provides a representation of the two-dimensional phase space for the decays, has been previously performed by the BABAR collaboration [10,11]. A model-independent analysis by the LHCb collaboration, with over an order of magnitude more signal decays and much better signal purity compared to the BABAR data sample, subsequently observed an intriguing pattern of CP violation in its phase space, notably in regions not associated to any known resonant structure [12,13]. The observed variation of the CP asymmetry across the Dalitz plot is expected to be related to the changes in strong phase associated with hadronic resonances, but, to date, it has not yet been explicitly described with an amplitude model. Many phenomenological studies [14-20] have provided possible interpretations of the asymmetries. Particular attention has been devoted to whether large CP-violation effects could arise from the interference between the broad low-mass spin-0 contributions and the spin-1 ρð770Þ 0 resonance [21-24], from mixing between the ρð770Þ 0 and ωð782Þ resonances [25-27], or from ππ ↔ KK rescattering [21,23,24,28]. Further experimental studies are needed to clarify which of these sources are connected to the observed CP asymmetries. In this Letter, results are reported on the amplitude structure of B þ → π þ π þ π − decays, obtained by employing decay models that account for CP violation. The results are based on a data sample corresponding to 3 fb −1 of pp collisions at center-of-mass energies of 7 and 8 TeV, collected with the LHCb detector. A more detailed *
Physical Review Letters, 2004
We study B^+/- --> J/psi pi^+/- and B^+/- --> J/psi K^+/- decays in a sample of about 89 million BB~ pairs collected with the BABAR detector at the PEP-II asymmetric B-factory at SLAC. We observe a signal of 244 +/- 20 B^+/- --> J/psi pi^+/- events and determine the ratio BF(B^+/- --> J/psi pi^+/-)/BF(B^+/- --> J/psi K^+/-) to be [5.37 +/- 0.45 (stat.) +/- 0.11 (syst)]%. The charge asymmetries for the B^+/- --> J/psi pi^+/- and B^+/- --> J/psi K^+/- decays are determined to be A_pi = 0.123 +/- 0.085 (stat.) +/- 0.004 (syst.) and A_K = 0.030 +/- 0.015 (stat.) +/- 0.006 (syst.), respectively.