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Forti, F. (ORCID:0000000165357965)

Publications and source records attributed to Forti, F. (ORCID:0000000165357965).

36 records Β· Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

New graph-neural-network flavor tagger for Belle II and measurement of sin 2β’πœ™ 1 in 𝐡 0 β†’ 𝐽/πœ“β’πΎ$^0_ S$ decays

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral 𝐡 mesons produced in ϒ⁑(4⁒𝑆) decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using 𝐡 decays to flavor-specific hadronic final states reconstructed in a 362 fb βˆ’1 sample of electron-positron collisions collected at the ϒ⁑(4⁒𝑆) resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of (37.40 Β± 0.43 Β± 0.36%), where the first uncertainty is statistical and the second systematic, which is 18% better than the previous Belle II algorithm. Demonstrating the algorithm, we use 𝐡 0 →𝐽/πœ“β’πΎ$^0_ S$ decays to measure the mixing-induced and direct 𝐢⁒𝑃 violation parameters, 𝑆 = (0.724 Β± 0.035 Β± 0.009) and 𝐢 = (βˆ’0.035 Β± 0.026 Β± 0.029).

CP violation↗
DOE OSTI2024

Study of Ξ₯(10753) decays to Ο€+Ο€βˆ’Ξ₯(nS) final states at Belle II

Abstract We present an analysis of the processe + e βˆ’ β†’Ο€ + Ο€ βˆ’ Ξ₯(nS) (wheren= 1, 2, or 3) reconstructed in 19.6 fb βˆ’1 of Belle II data during a special run of the SuperKEKB collider at four energy points near the peak of the Ξ₯(10753) resonance. By analyzing the mass distribution of theΟ€ + Ο€ βˆ’ Ξ₯(nS) system and the Born cross sections of thee + e βˆ’ β†’Ο€ + Ο€ βˆ’ Ξ₯(nS) process, we report the first observation of Ξ₯(10753) decays to theΟ€ + Ο€ βˆ’ Ξ₯(1S) andΟ€ + Ο€ βˆ’ Ξ₯(2S) final states, and find no evidence for decays toΟ€ + Ο€ βˆ’ Ξ₯(3S). Possible intermediate states in theΟ€ + Ο€ βˆ’ Ξ₯(1S,2S) transitions are also investigated, and no evidence for decays proceeding via the$$ {\pi}^{\mp }{Z}_b^{\pm } $$ Ο€ βˆ“ Z b Β± orf 0 (980)Ξ₯(nS) intermediate states is found. We measure Born cross sections for thee + e βˆ’ β†’Ο€ + Ο€ βˆ’ Ξ₯(nS) process that, combined with results from Belle, obtain the mass and width of Ξ₯(10753) to be (10756.6 Β± 2.7 Β± 0.9) MeV/c 2 and (29.0 Β± 8.8 Β± 1.2) MeV, respectively. The relative ratios of the Born cross sections at the Ξ₯(10753) resonance peak are also reported for the first time.

Physics↗
DOE OSTI2024

Measurement of the branching fraction of the decay B βˆ’ β†’ D 0 ρ ( 770 ) βˆ’ at Belle II

We measure the branching fraction of the decay B βˆ’ β†’ D 0 ρ ( 770 ) βˆ’ using data collected with the Belle II detector. The data contain 387 million B B Β― pairs produced in e + e βˆ’ collisions at the Ο’ ( 4 S ) resonance. We reconstruct 8360 Β± 180 decays from an analysis of the distributions of the B βˆ’ energy and the ρ ( 770 ) βˆ’ helicity angle. We determine the branching fraction to be ( 0.939 Β± 0.021 ( stat ) Β± 0.050 ( syst ) ) % , in agreement with previous results. Our measurement improves the relative precision of the world average by more than a factor of two. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Search for a ΞΌ + ΞΌ βˆ’ resonance in four-muon final states at Belle II

We report on a search for a resonance X decaying to a pair of muons in e + e βˆ’ β†’ ΞΌ + ΞΌ βˆ’ X events in the 0.212 – 9.000 GeV / c 2 mass range, using 178 fb βˆ’ 1 of data collected by the Belle II experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of X beyond the standard model: a Z β€² vector boson in the L ΞΌ βˆ’ L Ο„ model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the L ΞΌ βˆ’ L Ο„ model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below 6 GeV / c 2 , the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the L ΞΌ βˆ’ L Ο„ model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

First Measurement of R ( X Ο„ / β„“ ) as an Inclusive Test of the b β†’ c Ο„ Ξ½ Anomaly

We measure the tau-to-light-lepton ratio of inclusive B -meson branching fractions R ( X Ο„ / β„“ ) ≑ B ( B β†’ X Ο„ Ξ½ ) / B ( B β†’ X β„“ Ξ½ ) , where β„“ indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed B meson and a charged lepton candidate from 189 fb βˆ’ 1 of electron-positron collision data collected with the Belle II detector. We find R ( X Ο„ / β„“ ) = 0.228 Β± 0.016 ( stat ) Β± 0.036 ( syst ) , in agreement with standard-model expectations. This is the first direct measurement of R ( X Ο„ / β„“ ) . Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

Search for the e + e βˆ’ β†’ Ξ· b ( 1 S ) Ο‰ and e + e βˆ’ β†’ Ο‡ b 0 ( 1 P ) Ο‰ processes at s = 10.745 GeV

We search for the e + e βˆ’ β†’ Ξ· b ( 1 S ) Ο‰ and e + e βˆ’ β†’ Ο‡ b 0 ( 1 P ) Ο‰ processes at a center-of-mass energy of 10.745 GeV, which is close to the peak of the Ο’ ( 10753 ) state. We use data collected by the Belle II experiment during a special run, corresponding to an integrated luminosity of 9.8 fb βˆ’ 1 . We reconstruct Ο‰ β†’ Ο€ + Ο€ βˆ’ Ο€ 0 decays and use the Ο‰ meson’s recoil mass to search for the signals. We do not find evidence for either process, and set upper limits on the corresponding Born-level cross sections of 2.5 pb and 7.8 pb, respectively, at the 90% confidence level. The Ο‡ b 0 ( 1 P ) Ο‰ limit is the result of a combination of this analysis and a previous search using full reconstruction. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
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 Γ— 10 3 $D^+_s$ β†’ φπ + decays. Our result is Ο„$D^+_s$ = (499.5 Β± 1.7 Β± 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 Β± β†’ DK Β± and DΟ€ Β± with D β†’ $ {K}_{\textrm{S}}^0 $ K Β± Ο€ βˆ“ using Belle and Belle II data

We measure CP asymmetries and branching-fraction ratios for B Β± β†’ DK Β± and DΟ€ Β± decays with D β†’ $K$$^{0}_{S}$ K Β± Ο€ βˆ“ , where D is a superposition of D 0 and $\overline{D}$ 0 . We use the full data set of the Belle experiment, containing 772 Γ— 10 6 $B$$\overline{B}$ pairs, and data from the Belle II experiment, containing 387 Γ— 10 6 $B$$\overline{B}$ pairs, both collected in electron-positron collisions at the Ξ₯(4S) resonance. Our results provide model-independent information on the unitarity triangle angle Ξ¦ 3 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of C P Violation in B 0 β†’ K S 0 Ο€ 0 Decays at Belle II

We report a measurement of the C P -violating parameters C and S in B 0 β†’ K S 0 Ο€ 0 decays at Belle II using a sample of 387 Γ— 10 6 B B Β― events recorded in e + e βˆ’ collisions at a center-of-mass energy corresponding to the Ο’ ( 4 S ) resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain C = βˆ’ 0.0 4 βˆ’ 0.15 + 0.14 Β± 0.05 and S = 0.7 5 βˆ’ 0.23 + 0.20 Β± 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

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 / ΞΌ ) = B ( B β†’ X e Ξ½ ) / B ( B β†’ X ΞΌ Ξ½ ) , 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 / ΞΌ ) = 1.007 Β± 0.009 ( stat ) Β± 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

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 – β†’$c\bar{c}$ 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 Ξ₯(4S) mass. The effective tagging efficiency in data is (47.91Β±0.07 (stat) Β±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* Β± 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

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

The $L_ΞΌ – L_Ο„$ 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 $e^+e^– β†’ ΞΌ^+ΞΌ^–$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 Γ— 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 β†’ D(*) – Ο€ + decays collected by the Belle II experiment in asymmetric-energy e + ⁒e – collisions produced by the SuperKEKB collider operating at the Ξ₯⁑(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 Ο„ B 0 = (1.499 Β± 0.013 Β± 0.008) ps, Δ⁒m d = (0.516 Β± 0.008 Β± 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↗
DOE OSTI2023

Search for Lepton-Flavor-Violating Ο„ Decays to a Lepton and an Invisible Boson at Belle II

We search for lepton-flavor-violating $Ο„^– \rightarrow e^–α$ $Ο„^– \rightarrow ΞΌ^–α$ decays, where Ξ± is an invisible spin-0 boson. The search uses electron-positron collisions at 10.58 GeV center-of-mass energy with an integrated luminosity of 62.8 fb –1 , produced by the SuperKEKB collider and collected with the Belle II detector. We search for an excess in the lepton-energy spectrum of the known $Ο„^–\rightarrow e^–\bar{v}_{e}v_Ο„$ decays. We report 95% confidence-level upper limits on the branching-fraction ratio $\mathscr{B}(Ο„^–\rightarrow e^–α) \ / \mathscr{B}(Ο„^–\rightarrow e^– \bar{v}_{e}v_Ο„)$ in the range (1.1-9.7) Γ— 10 –3 and on $\mathscr{B}(Ο„^–\rightarrow ΞΌ^–α) \ / \mathscr{B}(Ο„^–\rightarrow ΞΌ^– \bar{v}_{ΞΌ}v_Ο„)$ in the range (0.7-12.2)Γ—10 –3 for Ξ± masses between 0 and 1.6 GeV/c 2 . These results provide the most stringent bounds on invisible boson production from Ο„ decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Observation of e + e – β†’ Ο‰ Ο‡ b J ( 1 P ) and Search for X b β†’ Ο‰ Ξ₯ ( 1 S ) at s near 10.75 GeV

We study the processes $e^{+}e^{–} β†’ ωχ_{bJ}$(1P) (J=0, 1, or 2) using samples at center-of-mass energies $\sqrt{s}$ = 10.701, 10.745, and 10.805 GeV, corresponding to 1.6, 9.8, and 4.7 fb –1 of integrated luminosity, respectively. These data were collected with the Belle II detector during special operations of the SuperKEKB collider above the Ξ₯(4S) resonance. We report the first observation of $ωχ_{bJ}$(1P) signals at $\sqrt{s}$ = 10.745 GeV. By combining Belle II data with Belle results at $\sqrt{s}$ = 10.867 GeV, we find energy dependencies of the Born cross sections for $e^{+}e^{–} β†’ ωχ_{b1,b2}$(1P) to be consistent with the shape of the Ξ₯(10753) state. These data indicate that the internal structures of the Ξ₯(10753) and Ξ₯(10860) states may differ. Including data at $\sqrt{s}$ = 10.653 GeV, we also search for the bottomonium equivalent of the X(3872) state decaying into Ο‰Ξ₯(1S). No significant signal is observed for masses between 10.45 and 10.65 GeV/c 2 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the $Ξ©_c^0$ lifetime at Belle II

We report on a measurement of the $Ξ©_c^0$ lifetime using $Ξ©_c^0$ β†’ Ξ©-Ο€ + decays reconstructed in c data collected by the Belle II experiment and corresponding to 207 fb -1 of integrated e + e - β†’ c luminosity. The result, Ο„ ($Ξ©_c^0$) = 243 Β± 48 (stat) Β± 11 (syst) fs, agrees with recent measurements indicating that the $Ξ©_c^0$ is not the shortest-lived weakly decaying charmed baryon.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for a Dark Photon and an Invisible Dark Higgs Boson in $ΞΌ^+ ΞΌ^–$ and Missing Energy Final States with the Belle II Experiment

The dark photon $\textit{A'}$ and the dark Higgs boson $\textit{h'}$ are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of A' and h' in the dark Higgsstrahlung process $e^+e^– β†’ A' h'$ with $A' β†’ ΞΌ^+ΞΌ^–$ and $\textit{h'}$ invisible in electron-positron collisions at a center-of- mass energy of 10.58 GeV in data collected by the Belle II experiment in 2019. With an integrated luminosity of 8.34 fb –1 , we observe no evidence for signal. We obtain exclusion limits at 90% Bayesian credibility in the range of 1.7-5.0 fb on the cross section and in the range of 1.7 Γ— 10 –8 -200 Γ— 10 –8 on the effective coupling $Ξ΅^2 Γ— Ξ±_D$ for the $\textit{A'}$ mass in the range of 4.0 GeV/$c^2 < M_{A'}$ < 9.7 GeV/$c^2$ and for the $\textit{h'}$ mass $M_{h'} < M_{A'}$, where $\textit{Ξ΅}$ is the mixing strength between the standard model and the dark photon and $Ξ±_D$ is the coupling of the dark photon to the dark Higgs boson. Our limits are the first in this mass range. Phtysuc

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the Ξ›$^+_c$ Lifetime

An absolute measurement of the Ξ›$^+_c$ lifetime is reported using Ξ›$^+_c β†’ pK^– Ο€^+$ decays in events reconstructed from data collected by the Belle II experiment at the SuperKEKB asymmetric-energy electron-positron collider. The total integrated luminosity of the data sample, which was collected at center-of-mass energies at or near the $\textit{Ξ₯}(4S)$ resonance, is 207.2 fb –1 . The result, $Ο„(Ξ›^+_c)$ = 203.20 Β± 0.89 Β± 0.77 fs , where the first uncertainty is statistical and the second

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗