Search NASA⌕ Search

Engineering topics

Bahinipati, S. (ORCID:0000000237445332)

Publications and source records attributed to Bahinipati, S. (ORCID:0000000237445332).

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Search for baryon and lepton number violating decays D → p ℓ

We search for the baryon and lepton number violating charm decays, D → p ℓ , where D is either a D 0 or a D ¯ 0 and ℓ is a muon or an electron, using a data sample of 921 fb − 1 collected by the Belle detector at the KEKB asymmetric energy e + e − collider. In the absence of significant signals, we set upper limits on the branching fractions in the range ( 5 – 8 ) × 10 − 7 at a 90% confidence level, depending on the decay mode. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Measurement of branching fractions and direct C P asymmetries for B → K π and B → π π decays at Belle II

We report measurements of the branching fractions and direct C P asymmetries of the decays B 0 → K + π − , B + → K + π 0 , B + → K 0 π + , and B 0 → K 0 π 0 , and use these for testing the standard model through an isospin-based sum rule. In addition, we measure the branching fraction and direct C P asymmetry of the decay B + → π + π 0 and the branching fraction of the decay B 0 → π + π − . The data are collected with the elle II detector from e + e − collisions at the ϒ ( 4 S ) resonance produced by the SuperKEKB asymmetric-energy collider and contain 387 × 10 6 bottom-antibottom meson pairs. Signal yields are determined in two-dimensional fits to background-discriminating variables, and range from 500 to 3900 decays, depending on the channel. We obtain − 0.03 ± 0.13 ± 0.04 for the sum rule in agreement with the standard model expectation of zero and with a precision comparable to the best existing determinations. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2023

First Simultaneous Determination of Inclusive and Exclusive | V u b |

The first simultaneous determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element V ub using inclusive and exclusive decays is performed with the full Belle data set at the $Υ$(4S) resonance, corresponding to an integrated luminosity of 711 fb -1 . We analyze collision events in which one B meson is fully reconstructed in hadronic modes. This allows for the reconstruction of the hadronic X u system of the semileptonic b → $πℓe_ℓ$ decay. We separate exclusive B → $πℓ\overline{ν}_ℓ$ decays from other inclusive B → $X_uℓ\overline{ν}_ℓ$ and backgrounds with a two-dimensional fit that utilizes the number of charged pions in the X u system and the four-momentum transfer q 2 between the B and X u systems. Combining our measurement with information from lattice QCD and QCD calculations of the inclusive partial rate as well as external experimental information on the shape of the B → $πℓe_ℓ$ form factor, we determine |$V^{excl}_{ub}$| = (3.78 ± 0.23 ± 0.16 ± 0.14) × 10 -3 and |$V^{incl}_{ub}$| = (3.88 ± 0.20 ± 0.31 ± 0.09) x 10 -3 , respectively, with the uncertainties being the statistical error, systematic errors, and theory errors. The ratio of |$V^{excl}_{ub}$|/|$V^{incl}_{ub}$| 0.97 ± 0.12 is compatible with unity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Precise Measurement of the D s + Lifetime at Belle II

We measure the lifetime of the $D^+_s$ meson using a data sample of 207 fb -1 collected by the Belle II experiment running at the SuperKEKB asymmetric-energy e + e - collider. The lifetime is determined by fitting the decay-time distribution of a sample of 116 × 10 3 $D^+_s$ → φπ + decays. Our result is τ$D^+_s$ = (499.5 ± 1.7 ± 0.9) fs, where the first uncertainty is statistical and the second is systematic. This result is significantly more precise than previous measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of CP asymmetries and branching-fraction ratios for B ± → DK ± and Dπ ± with D → $ {K}_{\textrm{S}}^0 $ K ± π ∓ using Belle and Belle II data

We measure CP asymmetries and branching-fraction ratios for B ± → DK ± and Dπ ± decays with D → $K$$^{0}_{S}$ K ± π ∓ , where D is a superposition of D 0 and $\overline{D}$ 0 . We use the full data set of the Belle experiment, containing 772 × 10 6 $B$$\overline{B}$ pairs, and data from the Belle II experiment, containing 387 × 10 6 $B$$\overline{B}$ pairs, both collected in electron-positron collisions at the Υ(4S) resonance. Our results provide model-independent information on the unitarity triangle angle Φ 3 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for a τ + τ - Resonance in e + e - → μ + μ - τ + τ - Events with the Belle II Experiment

We report the first search for a nonstandard-model resonance decaying into $τ$ pairs in $e^+e^-$ → $μ^+μ^-τ^+τ^-$ events in the 3.6–10 GeV/c 2 mass range. We use a 62.8 fb -1 sample of $e^+e^-$ collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II experiment at the SuperKEKB collider. The analysis probes three different models predicting a spin-1 particle coupling only to the heavier lepton families, a Higgs-like spin-0 particle that couples preferentially to charged leptons (leptophilic scalar), and an axionlike particle, respectively. We observe no evidence for a signal and set exclusion limits at 90% confidence level on the product of cross section and branching fraction into $τ$ pairs, ranging from 0.7 to 24 fb, and on the couplings of these processes. We obtain world-leading constraints on the couplings for the leptophilic scalar model for masses above 6.5 GeV/c 2 and for the axionlike particle model over the entire mass range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of C P Violation in B 0 → K S 0 π 0 Decays at Belle II

We report a measurement of the C P -violating parameters C and S in B 0 → K S 0 π 0 decays at Belle II using a sample of 387 × 10 6 B B ¯ events recorded in e + e − collisions at a center-of-mass energy corresponding to the ϒ ( 4 S ) resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain C = − 0.0 4 − 0.15 + 0.14 ± 0.05 and S = 0.7 5 − 0.23 + 0.20 ± 0.04 , where the first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2023

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the τ -lepton mass with the Belle II experiment

We present a measurement of the τ-lepton mass using a sample of about 175 million $e^+$$e^-$ → ${{\tau}}^+{{\tau}}^-$ events collected with the Belle II detector at the SuperKEKB $e^+$$e^-$ collider at a center-of-mass energy of 10.579GeV. This sample corresponds to an integrated luminosity of $190$ $\mathrm{fb}$$^{-1}$. We use the kinematic edge of the ${{\tau}}$ pseudomass distribution in the decay ${{\tau}}^-$ → $π^-π^+π^-ν_τ$ and measure the ${{\tau}}$ mass to be $1777.09±0.08±0.11$ $\mathrm{MeV}$ $/{c^2}$, where the first uncertainty is statistical and the second systematic. This result is the most precise to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Test of Light-Lepton Universality in the Rates of Inclusive Semileptonic B-Meson Decays at Belle II

We present the first measurement of the ratio of branching fractions of inclusive semileptonic B -meson decays, R ( X e / μ ) = B ( B → X e ν ) / B ( B → X μ ν ) , a precision test of electron-muon universality, using data corresponding to 189 fb - 1 from electron-positron collisions collected with the Belle II detector. In events where the partner B meson is fully reconstructed, we use fits to the lepton momentum spectra above 1.3 GeV / c to obtain R ( X e / μ ) = 1.007 ± 0.009 ( stat ) ± 0.019 ( syst ) , which is the most precise lepton-universality test of its kind and agrees with the standard-model expectation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of differential distributions of B → D*$\ell\bar{v}_{\ell}$ and implications on | V cb |

We present a measurement of the differential shapes of exclusive B → D*$\ell\bar{v}_{\ell}$ (B = B - , $\bar{B}$ 0 and $\ell$ = e, μ) decays with hadronic tag-side reconstruction for the full 711 fb -1 Belle dataset. We extract the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) form factor parameters and use an external input for the absolute branching fractions to determine the Cabibbo-Kobayashi-Maskawa matrix element and find |V cb | CLN = (40.2 ± 0.9) x 10 -3 and |V cb | BGL = (40.7 ± 1.0) x 10 -3 with the zero-recoil lattice QCD point $\mathcal{F}$(1) = 0.906 ± 0.013. We also perform a study of the impact of beyond zero-recoil lattice QCD calculations on the |V cb | determinations. Additionally, we present the lepton-flavor universality ratio R eμ = $\mathcal{B}$(B → D*e$\bar{v}$ e )/$\mathcal{B}$(B → D*μ$\bar{v}$ μ ) = 0.993 ± 0.023 ± 0.023, the electron and muon forwardbackward asymmetry and their difference ΔA FB = 0.028 ± 0.028 ± 0.008, and the electron and muon D* longitudinal polarization fraction and their difference ΔF$^{D*}_L$ = 0.030 ± 0.025 ± 0.007. The uncertainties quoted correspond to the statistical and systematic uncertainties, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Novel method for the identification of the production flavor of neutral charmed mesons

We propose a new algorithm for the identification of the production flavor of neutral D mesons in the Belle II experiment. The algorithm exploits the correlation between the flavor of a reconstructed neutral D meson (signal D meson) and the electric charges of particles reconstructed in the rest of the e + e – →$c\bar{c}$ event. These include those originating from the decay of the other charm hadron produced in the event, as well as those possibly produced in association with the signal D meson. We develop the algorithm using simulation and calibrate it in data using decay modes that identify the flavor of the decaying neutral D meson. We use a data sample of e + e – collisions, corresponding to 362 fb –1 of integrated luminosity, collected by Belle II at center-of-mass energies near the Υ(4S) mass. The effective tagging efficiency in data is (47.91±0.07 (stat) ±0.51 (syst)) %, independent of the neutral-D-meson decay mode. This charm flavor tagger will approximately double the effective sample size of many CP-violation and charm-mixing measurements that so far have exclusively relied on neutral D mesons originating from D* ± decays. While developed for Belle II, the basic principles underlying the charm flavor tagger can be used in other experiments, including those at hadron colliders.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the branching fraction and CP asymmetry of B 0 →π 0 ⁢π 0 decays using 198×1⁢0 6 $B\overline{B}$ pairs in Belle II data

We report measurements of the branching fraction and C P asymmetry in B 0 → π 0 π 0 decays reconstructed at Belle II in an electron-positron collision sample containing 198 × 10 6 B B ¯ pairs. We measure a branching fraction B ( B 0 → π 0 π 0 ) = ( 1.38 ± 0.27 ± 0.22 ) × 10 - 6 and a C P asymmetry A C P ( B 0 → π 0 π 0 ) = - 0.14 ± 0.46 ± 0.07 , where the first uncertainty is statistical and the second is systematic.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Search for an Invisible Z ' in a Final State with Two Muons and Missing Energy at Belle II

The $L_μ – L_τ$ extension of the standard model predicts the existence of a lepton-flavor-universality-violating Z' boson that couples only to the heavier lepton families. We search for such a Z' through its invisible decay in the process $e^+e^– → μ^+μ^–$Z'. We use a sample of electron-positron collisions at a center- of-mass energy of 10.58 GeV collected by the Belle II experiment in 2019-2020, corresponding to an integrated luminosity of 79.7 fb –1 . We find no excess over the expected standard-model background. We set 90%-confidence-level upper limits on the cross section for this process as well as on the coupling of the model, which ranges from 3 × 10 –3 at low Z' masses to 1 at Z' masses of 8 GeV=$c^2$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the B 0 lifetime and flavor-oscillation frequency using hadronic decays reconstructed in 2019–2021 Belle II data

We measure the B0 lifetime and flavor-oscillation frequency using B 0 → D(*) – π + decays collected by the Belle II experiment in asymmetric-energy e + ⁢e – collisions produced by the SuperKEKB collider operating at the Υ⁡(4⁢S) resonance. We fit the decay-time distribution of signal decays, where the initial flavor is determined by identifying the flavor of the other B meson in the event. The results, based on 33000 signal decays reconstructed in a data sample corresponding to 190 fb –1 , are τ B 0 = (1.499 ± 0.013 ± 0.008) ps, Δ⁢m d = (0.516 ± 0.008 ± 0.005) ps –1 , where the first uncertainties are statistical and the second are systematic. These results are consistent with the world-average values.

79 ASTRONOMY AND ASTROPHYSICS↗