Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at √s=7 TeV

Bose-Einstein correlations of same-sign charged pions, produced in protonproton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the form of an enhancement of pairs of like-sign charged pions with small four-momentum difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source is investigated, determining both the correlation radius and the chaoticity parameter. The measured correlation radius is found to increase as a function of increasing charged-particle multiplicity, while the chaoticity parameter is seen to decreas

Study of the reactions e+e−→K+K−π0π0π0 , e+e−→KS0K±π∓π0π0 , and e+e−→KS0K±π∓π+π− at center-of-mass energies from threshold to 4.5 GeV using initial-state radiation

We study the processes e+e- -> K+K-a degrees a degrees a degrees y, K degrees SK +/- a -/+ a degrees a degrees y, and K degrees SK +/- a -/+ a+a-y in which an energetic photon is radiated from the initial state. The data were collected with the BABAR detector at the SLAC National Accelerator Laboratory. About 1200, 2600, and 6000 events, respectively, are selected from a data sample corresponding to an integrated luminosity of 469 fb-1. The invariant mass of the hadronic final state defines the effective e+e- center-of-mass energy. The center-of-mass energies range from threshold to 4.5 GeV. From the mass spectra, the first ever measurements of the e+e- -> K+K-a degrees a degrees a degrees, e+e- -> K degrees SK +/- a -/+ a degrees a degrees, and e+e- -> K degrees SK +/- a -/+ a+a- cross sections are performed. The contributions from the intermediate states that include eta, phi, rho, K*(892), and other resonances are presented. We observe the J=psi and psi(2S) in most of these final states and measure the corresponding branching fractions, many of them for the first time

Measurement of additional radiation in the initial-state-radiation processes e+e−→μ+μ−γ and e+e−→π+π−γ at BABAR

A dedicated measurement of additional radiation in e+e−→μ+μ−γ and e+e−→π+π−γ initial-state-radiation events is presented using the full BABAR data sample. For the first time results are presented at next-to- and next-to-next-to-leading order, with one and two additional photons, respectively, for radiation from the initial and final states. Comparison with predictions from phokhara and afkqed Monte Carlo generators is performed, revealing discrepancies in the one-photon rates and angular distributions for the former. This disagreement has a negligible effect on the BABAR measurement of the e+e−→π+π−(γ) cross section, but could affect other measurements significantly. This study sheds a new light on the longstanding discrepancy in this channel that affects the theoretical prediction of hadronic vacuum polarization contributions to the muon magnetic moment anomaly

Collins asymmetries in inclusive charged KK and Kπ pairs produced in e+e- annihilation.

We present measurements of Collins asymmetries in the inclusive process e+e-→h1h2X, h1h2=KK, Kπ, ππ, at the center-of-mass energy of 10.6 GeV, using a data sample of 468 fb-1 collected by the BABAR experiment at the PEP-II B factory at SLAC National Accelerator Center. Considering hadrons in opposite thrust hemispheres of hadronic events, we observe clear azimuthal asymmetries in the ratio of unlike sign to like sign, and unlike sign to all charged h1h2 pairs, which increase with hadron energies. The Kπ asymmetries are similar to those measured for the ππ pairs, whereas those measured for high-energy KK pairs are, in general, larger

Observation of the decay Λb0 → pK−μ+μ− and a search for CP violation

A search for CP violation in the decay Λb 0 → pK−μ+μ− is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb−1. The Λb 0 → pK−μ+μ− decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, (Formula Presented.)where the latter is based on asymmetries in the angle between the μ+μ− and pK− decay planes. These are measured to be(Formula Presented.)and no evidence for CP violation is found.[Figure not available: see fulltext.].</p

Search for heavy neutral leptons using tau lepton decays at BaBaR

This article presents a model-independent search for an additional, mostly sterile, heavy neutral lepton (HNL), that is capable of mixing with the Standard Model tau neutrino with a mixing strength of jU tau 4j2, corresponding to the absolute square of the extended Pontecorvo-Maki-Nakagawa-Sakata matrix element. Data from the BABAR experiment, with a total integrated luminosity of 424 fb-1, are analyzed using a kinematic approach that makes no assumptions on the model behind the origins of the HNL, its lifetime or decay modes. No significant signal is found. Upper limits on jU tau 4j2 at the 95% confidence level, depend on the HNL mass hypothesis and vary from 2.31 x 10-2 to 5.04 x 10-6 (with all uncertainties considered), across the mass range 100 &lt; m4 &lt; 1300 MeV/c2; the more stringent limits being placed at higher masses

Observation of B-s(0) -> K* (+/-) K -/+ and evidence for B-s(0) -> K*(-) pi(+) decays

Measurements of the branching fractions of B0s→ K∗±K∓ and B0s→ K∗±π∓ decays are performed using a data sample corresponding to 1.0 fb-1of proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 7 TeV, where the K∗± mesons are reconstructed in the K0sπ± final state. The first observation of the B0s→ K∗±K∓ decay and the first evidence for the B0s→ K∗-π+decay are reported with branching fractions B(B0s→ K∗±K∓) = (12.7±1.9±1.9) x 10-6, B(B0s→ K∗-π+) = (3.3±1.1±0.5) x 10-6, where the first uncertainties are statistical and the second are systematic. In addition, an upper limit of B(B0→ K∗±K∓) &lt; 0.4 (0.5) × 10-6 is set at 90% (95%) confidence level.</p

Search for B mesogenesis at BaBar

A new mechanism has been proposed to simultaneously explain the presence of dark matter and the matter-antimatter asymmetry in the Universe. This scenario predicts exotic B -meson decays into a baryon and a dark-sector antibaryon (psi D) with branching fractions accessible at B factories. We present a search for B -&gt; ?psi D decays using data collected by the BABAR experiment at SLAC. This reaction is identified by fully reconstructing the accompanying B meson and requiring the presence of a single ? baryon in the remaining particles. No significant signal is observed, and bounds on the B -&gt; ?psi D branching fraction are derived in the range 0.13-5.2 x 10-5 for 1.0 &lt; m psi D &lt; 4.2 GeV/c2. These results set strong constraints on the parameter space allowed by the theory

Precision e− beam polarimetry at an e+e− B factory using tau-pair events

We present a new technique, "tau polarimetry," for measuring the longitudinal beam polarization present in an e(+)e(-) collider through the analysis of e(+)e(-) -&gt; tau(+)tau(-) events. By exploiting the sensitivity of tau decay kinematics to the longitudinal polarization of the beams, we demonstrate that the longitudinal polarization can be measured with a 3 per mil systematic uncertainty at the interaction point using a technique that is independent of spin and beam transport modeling. Using 424.2 +/- 1.8 fb(-1) of BABAR data at root s = 10.58 GeV, the average longitudinal polarization of the PEP-II e(+)e(-) collider has been measured to be &lt; P &gt; = 0.0035 +/- 0.0024(stat) +/- 0.0029(sys). The systematic uncertainty studies are described in detail, which can serve as a guide for future applications of tau polarimetry. A proposed e(-) beam longitudinal polarization upgrade to the SuperKEKB e(+)e(-) collider would benefit from this technique