Search for Invisible Decays of a Dark Photon Produced in e + e − Collisions at BaBar
Not Available
Lees, J. P.↗
Engineering topics
Sun, L.
Publications and source records attributed to Sun, L..
Measurement of the e + e - → K s 0 K ± π ∓ π 0 and K s 0 K ± π ∓ η cross sections using initial-state radiation
The processes e + e - → K$0\atop{S}$ K ± π ∓ π 0 and e + e - → K$0\atop{S}$ K ± π ∓ η are studied over a continuum of energies from threshold to 4 GeV with the initial-state photon radiation method. Using 454 fb -1 of data collected with the BABAR detector at the SLAC PEP-II storage ring, the first measurements of the cross sections for these processes are obtained. The intermediate resonance structures from K* 0 (Kπ) 0 , K *(892) ± (Kπ) ∓ , and K$0\atop{S}$K ± ρ ∓ are studied. Lastly, the J / ψ is observed in all of these channels, and corresponding branching fractions are measured.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Tuning the magnetoresistance symmetry of Pt on magnetic insulators with temperature and magnetic doping
We present a comparison study of the temperature dependence of the intriguing magnetoresistance (MR) in Pt/YIG (yttrium iron garnet), Pt/YIG BB (the YIG substrate has been bombarded with Ar + ), and Pt/SiO 2 (with different Fe doping levels). With decreasing temperature, the MRs in Pt/YIG and Pt/YIG BB change symmetry from R z = R x > R y at room temperature to R x > R z > R y at low temperature. A similar behavior in both Pt/YIG and Pt/YIG BB implies that the underlying physics is due to magnetic scattering, instead of the pure spin current across the interface. By changing the Fe doping level in the SiO 2 substrate, we can further systematically modulate the symmetry of MR in Pt/SiO 2 (Fe doped). The doping level dependent symmetry can also qualitatively explain the controversy over the MRs of Pt/YIG and similar structures at low temperature.
36 MATERIALS SCIENCE↗
Dalitz plot analyses of J / ψ → π + π - π 0 , J / ψ → K + K - π 0 , and J / ψ → K s 0 K ± π ∓ produced via e + e - annihilation with initial-state radiation
Here, we study the processes e + e - → γ ISR J/ψ , where J/ψ → π + π - π 0 , J/ψ → K + K - π 0 , and J / ψ → K$0\atop{S}$ K ± π ∓ using a data sample of 519 fb -1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e + e - collider at center-of-mass energies at and near the Υ (nS) (n = 2 , 3 , 4) resonances. We measure the ratio of branching fractions R 1 = $B(J/ψ →K^+K^- π^0)\atop{B(J/ψ →π^+π^- π^0)}$ and R 2 = $B(J/ψ →K^0_SK^±π^∓)\atop{B(J/ψ →π^+π^- π^0)}$. We perform Dalitz plot analyses of the three J/ψ decay modes and measure fractions for resonances contributing to the decays. We also analyze the J/ψ → $π^+π^- π^0$ decay using the Veneziano model. We observe structures compatible with the presence of ρ (1450) in all three J/ψ decay modes and measure the relative branching fraction: R (p(1450)) = $Bp(1450)→K^+K^-)\atop{B(p(1450)→π^+π^-)}$ +0.307 ± 0.084 (stat) ± 0.082 (sys).
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the inclusive electron spectrum from B meson decays and determination of | V u b |
Based on the full BABAR data sample of 466.5 million $B\bar{B}$ pairs, we present measurements of the electron spectrum from semileptonic B meson decays. We fit the inclusive electron spectrum to distinguish Cabibbo-Kobayashi-Maskawa (CKM) suppressed B → X u eν decays from the CKM-favored B → X c eν decays, and from various other backgrounds, and determine the total semileptonic branching fraction B (B → Xeν) = ( 10.34 ± 0.04 stat ± 0.2 6 syst )%, averaged over B ± and B 0 mesons. We determine the spectrum and branching fraction for charmless B → X u eν decays and extract the CKM element | V ub | , by relying on four different QCD calculations based on the heavy quark expansion. While experimentally, the electron momentum region above 2.1 GeV / c is favored, because the background is relatively low, the uncertainties for the theoretical predictions are largest in the region near the kinematic endpoint. Detailed studies to assess the impact of these four predictions on the measurements of the electron spectrum, the branching fraction, and the extraction of the CKM matrix element |V ub | are presented, with the lower limit on the electron momentum varied from 0.8 GeV / c to the kinematic endpoint. We determine |V ub | using each of these different calculations and find, |V ub | = ( 3.794 ± 0.107 exp $+ 0.292\atop{ - 0.219 SF}$ $+ 0.078 \atop{- 0.068 theory}$ ) × 10 - 3 (De Fazio and Neubert), (4.563 ± 0.126 exp $+ 0.230\atop {- 0.208 SF}$ $+ 0.162\atop{- 0.163 theory}$ ) ×10 -3 (Bosch, Lange, Neubert, and Paz), (3.959 ± 0.104 exp $+ 0.164\atop{- 0.154 SF}$ $+ 0.042\atop{ - 0.079 theory}$ ) × 10 -3 (Gambino, Giordano, Ossola, and Uraltsev), (3.848 ± 0.108 exp $+ 0.084\atop{ - 0.070 theory}$) × 10 -3 (dressed gluon exponentiation), where the stated uncertainties refer to the experimental uncertainties of the partial branching fraction measurement, the shape function parameters, and the theoretical calculations.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Cross sections for the reactions e + e - → K S 0 K L 0 π 0 , K S 0 K L 0 η , and K S 0 K L 0 π 0 π 0 from events with initial-state radiation
Here, we study the processes e + e - → K$0\atop{S}$ K$0\atop{L}$ π 0 γ , K $0\atop{S}$ K$0\atop{L}$ η γ , and K$0\atop{S}$ K$0\atop{L}$ π 0 π 0 γ , where the photon is radiated from the initial state, providing cross section measurements for the hadronic final states over a continuum of center-of-mass energies. The results are based on 469 fb -1 of data collected at or near the Υ ( 4 S ) resonance with the BABAR detector at SLAC. We present the first measurements of the e + e - → K$0\atop{S}$ K$0\atop{L}$ π 0 , K$0\atop{S}$ K$0\atop{L}$ η , and K$0\atop{S}$ K$0\atop{L}$ π 0 π 0 cross sections up to a center-of-mass energy of 4 GeV and study their intermediate resonance structures. We observe J / ψ decays to all of these final states for the first time, present measurements of their J / ψ branching fractions, and search for ψ (2S) decays.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for B + → K + τ + τ - at the BaBar Experiment
We search for the rare flavor-changing neutral current process B + → K + τ + τ - using data from the BABAR experiment. The data sample, collected at the center-of-mass energy of the Υ ( 4 S ) resonance, corresponds to a total integrated luminosity of 424 fb - 1 and to 471 × 1 0 6 B$\bar{B}$ pairs. We reconstruct one B meson, produced in the Υ ( 4 S ) → B + B - decay, in one of many hadronic decay modes and search for activity compatible with a B + → K + τ + τ - decay in the rest of the event. Each τ lepton is required to decay leptonically into an electron or muon and neutrinos. Comparing the expected number of background events with the data sample after applying the selection criteria, we do not find evidence for a signal. The resulting upper limit, at the 90% confidence level, is B ( B + → K + τ + τ - ) < 2.25 × 10 - 3 .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Magnetic scattering and spin-orbit coupling induced magnetoresistance in nonmagnetic heavy metal and magnetic insulator bilayer systems
Here, we report on the experimental study of the angular dependent magnetoresistance (MR) of heavy metal/ferromagnetic insulator bilayer structures. Through altering the relative composition in heavy metal Pt δ Ta 1–δ alloy, we continuously tune its spin Hall angle from positive, crossing zero, and to negative and study its impact on the MR. Most notably, both spin Hall effect and MR disappear simultaneously in Pt 0.32 Ta 0.68 (3 nm)/YIG when the effective spin Hall angle vanishes, evidencing the essential role of spin-orbit coupling in heavy metal for the MR. By introducing Fe impurities, we further identify that magnetic scattering is also essential to induce the MR in Pt/Fe-doped SiO 2 at large magnetic field, where the MR ratio increases monotonically with doping level.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Measurement of the B 0 → D * - π + π - π + branching fraction
When using a sample of ( 470.9 ± 2.8 ) × 10 6 B$\bar{B}$ pairs, we measure the decay branching fraction B ( B 0 → D * - π + π - π + ) = ( 7.26 ± 0.11 ± 0.31 ) × 10 -3 , where the first uncertainty is statistical and the second is systematic. These measurement will be helpful in studies of lepton universality by measuring B ( B 0 → D * - τ + ν τ ) using τ + → π + π - π + ¯ ν τ decays, normalized to B ( B 0 → D * - π + π - π + ) .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for a muonic dark force at BaBar
Many models of physics beyond the standard model predict the existence of new Abelian forces with new gauge bosons mediating interactions between "dark sectors" and the standard model. We report a search for a dark boson Z' coupling only to the second and third generations of leptons in the reaction e+e-→μ+μ-Z',Z'→μ+μ- using 514 fb -1 of data collected by the BABAR experiment. No significant signal is observed for Z' masses in the range 0.212-10 GeV. Lastly, limits on the coupling parameter g' as low as 7×10 -4 are derived, leading to improvements in the bounds compared to those previously derived from neutrino experiments.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Tests of C P T symmetry in B 0 - B ¯ 0 mixing and in B 0 → c c ¯ K 0 decays
Here, using the eight time dependences e- Γt (1 + C i cos Δmt + S i sin Δmt) for the decays Y(4S)→B 0 $\bar{B}$ 0 →f j f k , with the decay into a flavor-specific state f j = ± X before or after the decay into a CP eigenstate f k =c$\bar{c}$ K S,L , as measured by the BABAR experiment, we determine the three CPT-sensitive parameters Re(z) and Im(z) in B 0 $\bar{B}$ 0 mixing and |$\bar{A}$/A| in B 0 →c$\bar{c}$ K 0 decays. We find Im(z) = 0.010 ± 0.030 ± 0.013, Re(z) = -0.065 ± 0.028 ± 0.014, and |$\bar{A}$/A|=0.999±0.023±0.01, in agreement with CPT symmetry.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the neutral D meson mixing parameters in a time-dependent amplitude analysis of the D 0 → π + π - π 0 decay
Here we perform the first measurement on the D 0 -D 0 mixing parameters using a time-dependent amplitude analysis of the decay D 0 →π + π - π 0 . The data were recorded with the BABAR detector at center-of-mass energies at and near the $Y$(4S) resonance, and correspond to an integrated luminosity of approximately 468.1 fb -1 . The neutral D meson candidates are selected from D*(2010) + →D 0 π$+\atop{s}$ decays where the flavor at the production is identified by the charge of the low-momentum pion, π$+\atop{s}$. The measured mixing parameters are x=(1.5±1.2±0.6)% and y=(0.2±0.9±0.5)%, where the quoted uncertainties are statistical and systematic, respectively.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for mixing-induced C P violation using partial reconstruction of B ¯ 0 → D * + X ℓ - ν ¯ ℓ and kaon tagging
We describe in detail a previously published measurement of CP violation in B 0 -B¯ 0 oscillations, based on an integrated luminosity of 425.7 fb -1 collected by the BABAR experiment at the PEPII collider. We apply a novel technique to a sample of about 6 million B¯ 0 →D* + ℓ - ν ℓ ¯ decays selected with partial reconstruction of the D*+ meson. The charged lepton identifies the flavor of one B meson at its decay time, the flavor of the other B is determined by kaon tagging. We determine a CP violating asymmetry ACP=(N(B0B0)-N(B¯ 0 B¯ 0 ))/(N(B 0 B 0 )+N(B¯ 0 B¯ 0 ))=(0.06±0.17 +0.38 -0.32 )% corresponding to Δ CP =1-|q/p|=(0.29±0.84 +1.88 -1.61 )×10 -3 . This measurement is consistent and competitive with those obtained at the B factories with dilepton events.
Experiment-HEP,HEPEX↗
Measurement of Angular Asymmetries in the Decays B->K*l+l-
Abstract Not Provided
Experiment-HEP,HEPEX↗
Magnetic stripe domains of [Pt/Co/Cu]{sub 10} multilayer near spin reorientation transition
The dependence of magnetic anisotropy, magnetic domain patterns and magnetization reversal processes in [Pt/Co(t{sub Co})/Cu]{sub 10} film stack epitaxied on Cu (111) substrate have been studied as a function of the Co layer thickness t{sub Co}, by magneto-optic polar Kerr magnetometry and microscopy. We find the film undergoes spin reorientation transition from out-of-plane to in-plane as t{sub Co} increases. The SRT thickness is verified by Rotating-field Magneto-Optic Kerr effect method. The film exhibits the stripe domain structures at remanence with the width decreasing while t{sub Co} approaches SRT. As demonstrated by the first order reversal curve measurement, the magnetization reversal process encompasses irreversible domain nucleation, domain annihilation at large field and reversible domain switching near remanence.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Time-dependent analysis of B 0 → K S 0 π - π + γ decays and studies of the K + π - π + system in B + → K + π - π + γ decays
We measure the time-dependent CP asymmetry in the radiative-penguin decay B 0 → K S 0 π - π + γ , using a sample of 471×10 6 Υ(4S)→BB-events recorded with the BABAR detector at the PEP-II e+e- storage ring at SLAC. Using events with m Kππ < 1.8 GeV/c 2 , we measure the branching fractions of B+→K+π-π+γ and B0→K0π-π+γ, the branching fractions of the kaonic resonances decaying to K+π-π+, as well as the overall branching fractions of the B+→ρ0K+γ, B+→K*0π+γ and S-wave B+→(Kπ)0*0π+γ components. For events from the ρ mass band, we measure the CP-violating parameters SKS0π+π-γ=0.14±0.25±0.03 and CKS0π+π-γ=-0.39±0.20-0.02+0.03, 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 ρ0KS0 and obtain SKS0ργ=-0.18±0.32-0.05+0.06, which provides information on the photon polarization in the underlying b→sγ transition.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗