Decay Asymmetry Research Articles

Bound on dissipative effects from semileptonic neutral B-meson decays

The semileptonic decay asymmetry mathcal {A}_{{Delta }m} is studied within the open quantum systems approach to the physics of the neutral meson B^0–overline{B^0} system: this extended treatment takes into account possible non-standard, dissipative effects induced by the presence of an external environment. A bound on these effects is provided through the analysis of available experimental data from the Belle Collaboration.

Bs \u2192 K\u2113\u03bd\u2113 and B(s) \u2192 \u03c0(K)\u2113+\u2113\u2212 decays at large recoil and CKM matrix elements

We provide hadronic input for the B-meson semileptonic transitions to a light pseudoscalar meson at large recoil. The Bs → K form factor calculated from QCD light-cone sum rule is updated, to be used for a |Vub| determination from the Bs → Kℓν width. Furthermore, we calculate the hadronic input for the binned observables of B → πℓ+ℓ− and B → Kℓ+ℓ−. In addition to the form factors, the nonlocal hadronic matrix elements are obtained, combining QCD factorization and light-cone sum rules with hadronic dispersion relations. We emphasize that, due to nonlocal effects, the ratio of branching fractions of these decays is not sufficient for an accurate extraction of the |Vtd/Vts| ratio. Instead, we suggest to determine the Wolfenstein parameters A, ρ, η of the CKM matrix, combining the branching fractions of B → Kℓ+ℓ− and B → πℓ+ℓ− with the direct CP -asymmetry in the latter decay. We also obtain the hadronic matrix elements for a yet unexplored channel Bs → Kℓ+ℓ−.

Asymmetry in growth and decay of the geomagnetic dipole revealed in seafloor magnetization

Geomagnetic intensity fluctuations provide important constraints on time-scales associated with dynamical processes in the outer core. PADM2M is a reconstructed time series of the 0–2 Ma axial dipole moment (ADM). After smoothing to reject high frequency variations PADM2M's average growth rate is larger than its decay rate. The observed asymmetry in rates of change is compatible with longer term diffusive decay of the ADM balanced by advective growth on shorter time scales, and provides a potentially useful diagnostic for evaluating numerical geodynamo simulations. We re-analyze the PADM2M record using improved low-pass filtering to identify asymmetry and quantify its uncertainty via bootstrap methods before applying the new methodology to other kinds of records. Asymmetry in distribution of axial dipole moment derivatives is quantified using the geomagnetic skewness coefficient, sg. A positive value indicates the distribution has a longer positive tail and the average growth rate is greater than the average decay rate. The original asymmetry noted by Ziegler and Constable (2011) is significant and does not depend on the specifics of the analysis.A long-term record of geomagnetic intensity should also be preserved in the thermoremanent magnetization of oceanic crust recovered by inversion of stacked profiles of marine magnetic anomalies. These provide an independent means of verifying the asymmetry seen in PADM2M. We examine three near-bottom surveys: a 0 to 780 ka record from the East Pacific Rise at 19°S, a 0 to 5.2 Ma record from the Pacific Antarctic Ridge at 51°S, and a chron C4Ar–C5r (9.3–11.2 Ma) record from the NE Pacific. All three records show an asymmetry similar in sense to PADM2M with geomagnetic skewness coefficients, sg>0. Results from PADM2M and C4Ar–C5r are most robust, reflecting the higher quality of these geomagnetic records. Our results confirm that marine magnetic anomalies can carry a record of the asymmetric geomagnetic field behavior first found for 0–2 Ma in PADM2M, and show that it was also present during the earlier time interval from 9.3–11.2 Ma.

Measurement of CP asymmetry in D0→K−K+ decays

A measurement of the time-integrated $CP$ asymmetry in the Cabibbo-suppressed decay $D^0\rightarrow K^-K^+$ is performed using pp collision data, corresponding to an integrated luminosity of 3fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in $D^{*+}\rightarrow D^0 \pi^+$ and $D^{*-}\rightarrow \bar{D^0} \pi^-$ decays. The time-integrated $CP$ asymmetry $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D^0\rightarrow K^-\pi^+$, $D^+\rightarrow K^-\pi^+\pi^+$ and $D^+\rightarrow \bar{K^0}\pi^+$ decays used as calibration channels. It is found to be $A_{CP}(K^-K^+)=(0.14\pm0.15(stat)\pm0.10(syst))\%$. A combination of this result with previous LHCb measurements yields $A_{CP}(K^-K^+)=(0.04\pm0.12(stat)\pm0.10(syst))\%$, $A_{CP}(\pi^-\pi^+)=(0.07\pm0.14(stat)\pm0.11(syst))\%$. These are the most precise measurements from a single experiment. The result for $A_{CP}(K^-K^+)$ is the most precise determination of a time-integrated $CP$ asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.

Charmed baryon decay asymmetry in e+e− annihilation**Supported by National Natural Science Foundation of China (11375205, 11175146, 11275266, 11235011, 11425524, 11505010, 11565006), Beijing Municipal Government Foundation (KM201610017009, 2015000020124G064), Youth Innovation Promotion Association of CAS.

We propose to measure the decay asymmetry parameters in the hadronic weak decays of singly charmed baryons, such as ,Σ0π+,pK̄0, and . The joint angular formulae for these processes are presented, and are used to extract the asymmetry parameters in e+e− annihilation data. Base on the current data set collected at BESIII, we estimate the experimental sensitivities to measure the parameters αΛπ+ for , αΣ+π0 for and αΣ0π+ for .

Symmetry Analysis of the Multi-band Optical Variability of BL LAC S5 0716+714 in Intranight and Longer Timescales

The well-sampled optical light curves of S5 0716+714 in BVRI bands spanning about 20 years were built. The variability asymmetry could provide independent constraints on physical models for blazars variability. To perform analyses of variability properties, individual flares were decomposed and fitted from the light curves with functions of exponential rise and decay. In order to investigate whether the short term variability (STV) and intraday variability (IDV) had different mechanisms of origin, the light curves of S5 0716+714 with different timescales were analyzed, respectively. Results indicate that both STV and IDV flares of S5 0716+714 are predominantly asymmetric profiles. And there also exist a very weak tendency of positive asymmetry in both timescales variabilities, i.e., rapid rises and gradual decays. The estimated sizes of emission region are and for STV and IDV, respectively. Based on the individual flares decomposed from STV and IDV light curves, the distribution of the peak flux and duration time of flares are consistent with log-normal and Gamma distributions. Minijet-in-a-jet model could interpret the log-normal distribution. Gamma distribution could demonstrate that the emission regions in the jet may be distributed in a Poisson way.

Development of a polarized 31Mg+ beam as a spin-1/2 probe for BNMR

A 28 keV beam of 31Mg+ ions was extracted from a uranium carbide, proton-beam-irradiated target coupled to a laser ion source. The ion beam was nuclear-spin polarized by collinear optical pumping on the \(^{2}\textit {S}_{1/2}\)–\(^{2}\textit {P}_{1/2}\) transition at 280 nm. The polarization was preserved by an extended 1 mT guide field as the beam was transported via electrostatic bends into a 2.5 T longitudinal magnetic field. There the beam was implanted into a single crystal MgO target and the beta decay asymmetry was measured. Both hyperfine ground states were optically pumped with a single frequency light source, using segmentation of the beam energy, which boosted the polarization by approximately 50 % compared to pumping a single ground state. The total decay asymmetry of 0.06 and beam intensity were sufficient to provide a useful spin-1/2 beam for future BNMR experiments. A variant of the method was used previously to optically pump the full Doppler-broadened absorption profile of a beam of 11Be+ with a single-frequency light source.

Semileptonic decays of $$\Lambda _c$$ Λ c baryons in the relativistic quark model

Motivated by recent experimental progress in studying weak decays of the $\Lambda_c$ baryon we investigate its semileptonic decays in the framework of the relativistic quark model based on the quasipotential approach with the QCD-motivated potential. The form factors of the $\Lambda_c\to \Lambda l\nu_l$ and $\Lambda_c\to nl\nu_l$ decays are calculated in the whole accessible kinematical region without extrapolations and additional model assumptions. Relativistic effects are systematically taken into account including transformations of baryon wave functions from the rest to moving reference frame and contributions of the intermediate negative-energy states. Baryon wave functions found in the previous mass spectrum calculations are used for the numerical evaluation. Comprehensive predictions for decay rates, asymmetries and polarization parameters are given. They agree well with available experimental data.

Production asymmetries of b and c hadrons at LHCb

Using a data sample corresponding to an integrated luminosity of 1.0 fb-1, collected by LHCb in pp collisions at a centre-of-mass energy of 7 TeV, the D+, D+, B0 and Bs0 production asymmetries are determined. These quantities are measured by means of Ds+ →ϕ(K+K-)π+, D+ →Ks0(π+π-)π+, B0→J/ψ(μ+μ-)K*0(K+ π-), B0→D-(K+π-π-)π+ and Bs0→Ds-(K+K-π-)π+ decays. Moreover, using the full LHCb Run 1 integrated luminosity, corresponding to 1.0 fb-1 at 7 TeV and 2.0 fb-1 at 8 TeV, the production and decay asymmetry of the Λ0b baryon, AP+D(Λ0b), is determined by means of Λ0b →J/ φ(μ+μ-)pK– decays. All asymmetries are measured as a function of pT and y (or η in the D+, B0 and Bs0 cases) of the involved hadrons, in order to check if there is a dependence on kinematics.

New Physics searches at Belle

Precise measurements of B meson decays are important to test the flavour sector of the Standard Model and to search for New Physics. New Physics models predict contributions beyond the Standard Model that may change observables like branching fractions by a measurable amount. For instance, a new charged current, as for example predicted in two-Higgs-Doublet-Models, can occur in tree-level as well as in loop or box diagrams and interfere with the weak charged current of the Standard Model.The Belle experiment collected a dataset of 977 fb-1, mainly recorded at the ϒ(4S) resonance, and provides an excellent environment to study decays of B and Bs mesons.We discuss measurements of the branching fractions of the tree level decays B→τν and B→D(⁎)τν. In addition, we measure the forward-backward asymmetry in the inclusive decay B→Xsℓ+ℓ− and search for a significant, New Physics induced, time-dependent CP violation in B→ηKSγ. The branching fraction of Bs→ϕγ is measured and searches for Bs→γγ and further, a Dark Photon from a secluded sector are carried out on.

Branching Fraction and CP Asymmetry Measurements in Inclusive B → Xsℓ+ℓ− and B → Xsγ Decays from BaBar

We present an update on total and partial branching fractions and on CP asymmetries in the semi-inclusive decay B→Xsℓ+ℓ−. Further, we summarize our results on branching fractions and CP asymmetries for semi-inclusive and fully-inclusive B→Xsγ decays. We present the first result on the CP asymmetry difference of charged and neutral B→Xsγ decays yielding the first constraint on the ratio of Wilson coefficients Im(C8eff/C7eff).

Decay properties of b-hadrons with the ATLAS experiment

Recent results of the ATLAS experiment at LHC on decay properties of b-hadrons are reviewed. The time-dependent CP asymmetry parameters have been measured in Bs0→J/ψϕ decays using flavour tagging. The parity-violating decay asymmetry parameter αb and the helicity amplitudes have been measured for the decay Λb0→J/ψΛ0. The branching fraction B(B+→χc1K+) has been measured with χc1 reconstruction in the decay χc1→J/ψγ. An excited Bc± state has been observed through its decays to the ground Bc± state and two oppositely charged pions. The mass and decay of this state are consistent with expectations for the second S -wave state of the Bc± meson, Bc±(2S).

Time-dependent analysis ofB0→KS0π−π+γdecays and studies of theK+π−π+system inB+→K+π−π+γdecays

We measure the time-dependent $CP$ asymmetry in the radiative-penguin decay $B^0 \to {{K^0_{S}}} \pi^- \pi^+ \gamma$, using a sample of $471$ million $\Upsilon(4S) \to B{\kern 0.18em\overline{\kern -0.18em B}}$ events recorded with the BaBar detector at the PEP-II $e^+e^-$ storage ring at SLAC. Using events with $m_{K\pi\pi}<1.8{\mathrm{\,Ge\kern -0.1em V/}c^2}$, we measure the branching fractions of $B^+ \to K^+ \pi^- \pi^+ \gamma$ and $B^0 \to K^0 \pi^+ \pi^- \gamma$, the branching fractions of the kaonic resonances decaying to $K^+ \pi^- \pi^+$, as well as the overall branching fractions of the $B^+ \to \rho^0 K^+ \gamma$, $B^+ \to K^{*0} \pi^+ \gamma$ and S-wave $B^+ \to (K \pi)^{*0}_0 \pi^+ \gamma$ components. For events from the $\rho$ mass band, we measure the $CP$-violating parameters ${\mathcal{S}_{{{K^0_{S}}}\pi^+\pi^-\gamma}} = 0.14 \pm 0.25 \pm 0.03$ and ${\mathcal{C}_{{{K^0_{S}}}\pi^+\pi^-\gamma}} = -0.39 \pm 0.20^{+0.03}_{-0.02}$, where the first uncertainties are statistical and the second are systematic. We extract from this measurement the time-dependent $CP$ asymmetry related to the $CP$ eigenstate $\rho^0 {{K^0_{S}}}$ and obtain ${\mathcal{S}_{{{K^0_{S}}}\rho\gamma}} = -0.18 \pm 0.32^{+ 0.06}_{-0.05}$, which provides information on the photon polarization in the underlying $b \to s \gamma$ transition.

CP asymmetry in heavy Majorana neutrino decays at finite temperature: the nearly degenerate case

In a model where Majorana neutrinos heavier than the electroweak scale couple to Standard Model Higgs bosons and leptons, we compute systematically thermal corrections to the direct and indirect CP asymmetries in the Majorana neutrino decays. These are key ingredients entering the equations that describe the thermodynamic evolution of the induced lepton-number asymmetry eventually leading to the baryon asymmetry in the universe. We compute the thermal corrections in an effective field theory framework that assumes the temperature smaller than the masses of the Majorana neutrinos and larger than the electroweak scale, and we provide the leading corrections in an expansion of the temperature over the mass. In this work, we consider the case of two Majorana neutrinos with nearly degenerate masses.

New Precision Measurement for Proton Zemach Radius with Laser Spectroscopy

In this proceeding, a new proposal aiming to improve the precision of the proton Zemach radius will be presented. A circularly polarized laser will be shed on a sample of muonic hydrogen in its ground state. By observing the maximum muon decay asymmetry during scanning laser wave length, the ground-state hyperfine splitting energy can be identified, which is directly related to Zemach radius.citedupays The precision of Zemach radius by this measurement is estimated to be three times better compared to PSI experiment. This result will contribute to the solution of proton size puzzle.

Search for matter-antimatter asymmetries in multi-body decays with GPUs

The LHCb experiment has recorded the world's largest sample of charmed meson decays. The search for matter-antimatter asymmetries in charm sector uses large event samples and requires high precision analysis and thus intensive computing. This paper describes a powerful method to measure matter-antimatter asymmetries in multi-body decays where GPU systems have been successfully exploited. In this method, local asymmetries in the phase-space distributions were explored with an unbinned approach, and the parallelisation of GPU makes this approach usable in practice for the first time. The performance including GPUs on the Grid will be discussed in detail. With this new method, the world's best sensitivities to particular decay channels have been achieved.

Hadronic decay asymmetries of the Top quark

We study some New Physics effects on the hadronic decays of the Top quark, like and on a forward-backward-like CP even asymmetry At constructed in such a way that it is zero in the SM. We find that an anomalous right-handed contribution of the effective tbW vertex may induce an asymmetry At of the order of 20%.

Geant4 simulation of the PSI LEM beam line: energy loss and muonium formation in thin foils and the impact of unmoderated muons on the μSR spectrometer

The PSI low-energy μSR spectrometer is an instrument dedicated to muon spin rotation and relaxation measurements. Knowledge of the muon beam parameters such as spatial, kinetic energy and arrival-time distributions at the sample position are important ingredients to analyze the μSR spectra. We present here the measured energy losses in the thin carbon foil of the muon start detector deduced from time-of-flight measurements. Muonium formation in the thin carbon foil (10 nm thickness) of the muon start detector also affect the measurable decay asymmetry and therefore need to be accounted for. Muonium formation and energy losses in the start detector, whose relevance increase with decreasing muon implantation energy (<10 keV), have been implemented in Geant4 Monte Carlo simulation to reproduce the measured time-of-flight spectra. Simulated and measured time-of-flight and beam spot agrees only if a small fraction of so called ``unmoderated'' muons which contaminate the mono-energetic muon beam of the μSR spectrometer is introduced. Moreover the sensitivity of the beam size and related upstream-downstream asymmetry for a specially shaped ``nose'' sample plate has been studied for various beam line settings, which is of relevance for the study of thermal muonium emission into vacuum from mesoporous silica at cryogenic temperatures.

Long-distance weak annihilation contribution to theB±→(π±,K±)ℓ+ℓ−decays

We propose an alternative evaluation of the long-distance weak annihilation (WA, also called one-photon exchange in this paper) contribution to the rare semileptonic $B^{\pm}\to (\pi^{\pm},K^{\pm})\ell^+\ell^-$ ($\ell=e,\,\mu$) decays. This hadronic description at low energies is matched at intermediate energies to its short-distance counterpart in terms of quark and gluon degrees of freedom. Although the WA contribution does not contribute to solve the possible breaking of lepton-universality observed by LHCb in the $B^{\pm}\to K^{\pm}(\mu^+\mu^-/e^+e^-)$ ratio, nor provides an important hadronic contamination to their decay rates, its contribution to the branching ratios (and direct CP asymmetry) of the $B^{\pm}\to \pi^{\pm}\ell^+\ell^-$ transitions turns out to be significant. This hadronic pollution should be taken into account when looking for new physics effects in decays into pions, which suggests to restrict these searches to squared lepton-pair invariant mass in the $(1,8)$ GeV$^2$ range. The interference of the one-photon exchange contribution with the dominant short-distance one-loop amplitude induces a sizable CP asymmetry in these rare decays, which calls for dedicated measurements.

Λb→pℓ−ν¯ℓandΛb→Λcℓ−ν¯ℓform factors from lattice QCD with relativistic heavy quarks

Measurements of the $\Lambda_b \to p \ell^- \bar{\nu}_\ell$ and $\Lambda_b \to \Lambda_c \ell^- \bar{\nu}_\ell$ decay rates can be used to determine the magnitudes of the CKM matrix elements $V_{ub}$ and $V_{cb}$, provided that the relevant hadronic form factors are known. Here we present a precise calculation of these form factors using lattice QCD with 2+1 flavors of dynamical domain-wall fermions. The $b$ and $c$ quarks are implemented with relativistic heavy-quark actions, allowing us to work directly at the physical heavy-quark masses. The lattice computation is performed for six different pion masses and two different lattice spacings, using gauge-field configurations generated by the RBC and UKQCD collaborations. The $b \to u$ and $b \to c$ currents are renormalized with a mostly nonperturbative method. We extrapolate the form factor results to the physical pion mass and the continuum limit, parametrizing the $q^2$-dependence using $z$-expansions. The form factors are presented in such a way as to enable the correlated propagation of both statistical and systematic uncertainties into derived quantities such as differential decay rates and asymmetries. Using these form factors, we present predictions for the $\Lambda_b \to p \ell^- \bar{\nu}_\ell$ and $\Lambda_b \to \Lambda_c \ell^- \bar{\nu}_\ell$ differential and integrated decay rates. Combined with experimental data, our results enable determinations of $|V_{ub}|$, $|V_{cb}|$, and $|V_{ub}/V_{cb}|$ with theory uncertainties of 4.4%, 2.2%, and 4.9%, respectively.