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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenFri, 08 Dec 2023 21:41:38 +0000Nucleon Structure Functions from ν_µ-Fe Interactions and a Study of the Valence Quark Distribution
https://resolver.caltech.edu/CaltechTHESIS:04082013-111418042
Authors: Purohit, Milind Vasant
Year: 1984
DOI: 10.7907/4RBK-RV59
<p>Data were taken in 1979-80 by the CCFRR high energy neutrino experiment at Fermilab. A total of 150,000 neutrino and 23,000 antineutrino charged current events in the approximate energy range 25 < E<sub>v</sub> < 250 GeV are measured and analyzed. The structure functions F<sub>2</sub> and xF<sub>3</sub> are extracted for three assumptions about σ<sub>L</sub>/σ<sub>T</sub>: R = 0., R = 0.1 and R = a QCD based expression. Systematic errors are estimated and their significance is discussed. Comparisons or the X and Q<sup>2</sup> behaviour or the structure functions with results from other experiments are made.</p>
<p>We find that statistical errors currently dominate our knowledge of the valence quark distribution, which is studied in this thesis. xF<sub>3</sub> from different experiments has, within errors and apart from level differences, the same dependence on x and Q<sup>2</sup>, except for the HPWF results. The CDHS F<sub>2</sub> shows a clear fall-off at low-x from the CCFRR and EMC results, again apart from level differences which are calculable from cross-sections.</p>
<p>The result for the the GLS rule is found to be 2.83 ± .15 ± .09 ± .10 where the first error is statistical, the second is an overall level error and the third covers the rest of the systematic errors. QCD studies of xF<sub>3</sub> to leading and second order have been done. The QCD evolution of xF<sub>3</sub>, which is independent of R and the strange sea, does not depend on the gluon distribution and fits yield</p>
<p>ʌ<sub>LO</sub> = 88<sup>+163</sup><sub>-78</sub> <sup>+113</sup><sub>-70</sub>MeV</p>
<p>The systematic errors are smaller than the statistical errors. Second order fits give somewhat different values of ʌ, although α<sub>s</sub> (at Q<sup>2</sup><sub>0</sub> = 12.6 GeV<sup>2</sup>) is not so different.</p>
<p>A fit using the better determined F<sub>2</sub> in place of xF<sub>3</sub> for x > 0.4 i.e., <span style="text-decoration:overline">q</span> = 0 in that region, gives</p>
<p>ʌ<sub>LO</sub> = 266<sup>+114</sup><sub>-104</sub> <sup>+85</sup><sub>-79</sub>MeV</p>
<p>Again, the statistical errors are larger than the systematic errors. An attempt to measure R was made and the measurements are described. Utilizing the inequality <span style="text-decoration:overline">q</span>(x) ≥ 0 we find that in the region x > .4 R is less than 0.55 at the 90% confidence level.</p>
https://thesis.library.caltech.edu/id/eprint/7585A Study of the Iota in Radiative J/PSI Decays
https://resolver.caltech.edu/CaltechETD:etd-10162008-153536
Authors: Richman, Jeffrey David
Year: 1985
DOI: 10.7907/09yd-ka21
<p>An analysis of the production, decay, and quantum numbers of the ι(1440) in radiative J/Ψ decays is presented. The ι(1440), because of its large production in this OZI-suppressed channel, is considered a possible gluonic bound-state, or glueball. Such states appear to be a natural consequence of the non-Abelian structure of the SU(3) color gauge group of QCD. The data, 2.7 x 10<sup>6</sup> produced J/Ψ's, were obtained using the Mark III detector at the SPEAR e<sup>+</sup>e<sup>-</sup> storage ring.</p>
<p>The spin-parity of the ι(1440) is independently determined to be 0<sup>-</sup> using two decay modes, ι → K<sup>0</sup><sub>S</sub>K<sup>±</sup>π<sup>∓</sup> and ι → K<sup>+</sup>K<sup>-</sup>π<sup>0</sup>. The technique used is based on the three-body helicity formalism, which provides a means of studying the decay angular distributions in a manner independent of the structure of the Dalitz plot. This is particularly useful in the case of ι → KK̅π, where the limited phase space makes it difficult to unambiguously identify the two-body modes. In addition, the measured angular distributions provide direct visual evidence supporting the spin-parity assignment. Measurements of the ι mass, width, and branching fractions are obtained using ι → K<sup>0</sup><sub>S</sub>K<sup>±</sup>π<sup>∓</sup>, ι → K<sup>+</sup>K<sup>-</sup>π<sup>0</sup>, and ι → K<sup>0</sup><sub>S</sub>K<sup>0</sup><sub>S</sub>π<sup>0</sup>. The relative branching fractions are consistent with the isospin 0 predictions. From a study of the KK̅π Dalitz plot, an upper limit for ι → K<sup>*</sup>K̅+ c.c. is obtained. These results are discussed in the context of the current experimental status of the E(1420).</p>
<p>Upper limits are presented for B(ι → ηππ), B(ι → δπ → ηππ), B(ι → KK̅ππ), and B(ι → ρππ). The limit on B(ι → δπ → ηππ) appears to be inconsistent with a large value of B(ι → δπ → KK̅π). However, the very uncertain status and properties of the δ(980) make it difficult to pinpoint the source of this inconsistency. Together, these upper limits provide evidence that, apart from a possible ι → ρρ signal, KK̅π is the dominant ι decay and that inclusive ι production is dominated by J/Ψ → γι, ι → KK̅π.</p>
<p>The double radiative channels J/Ψ → γX, X → γ+ Vector, where Vector = ρ<sup>0</sup>, φ, ω are studied to probe the quark content of the object X. Many pseudoscalar mixing models predict that the ι acquires a large radiative width into γρ<sup>0</sup> through mixing with the η and η'. In the γ(γρ<sup>0</sup>) final state, a broad structure is observed in the 1.4 GeV region. Although the measured angular distributions are consistent with the pseudoscalar predictions, the central mass of this structure is below that found for the ι in the KK̅π channels. Thus, with the present limited statistics, it is unclear whether this structure should be identified with the ι. Upper limits are obtained for ι → γφ and ι → γω. Measurements are also obtained for B(J/Ψ → γη') and B(J/Ψ → γη) using the γ(γπ<sup>+</sup>π<sup>-</sup> final state. These results are compared with theoretical predictions.</p>
<p>Measurements of the hadronic decays J/Ψ → φη, ωη, and ωπ<sup>0</sup>, as well as the observation of the isospin-violating decay J/Ψ → ρ<sup>0</sup>η, are presented.</p>
<p>Finally, the two- and three-body helicity formalisms are discussed in the Appendices.</p>https://thesis.library.caltech.edu/id/eprint/4119A Systematic Study of the Decays of Charmed D Mesons
https://resolver.caltech.edu/CaltechTHESIS:01312019-122402912
Authors: Hauser, Jay
Year: 1985
DOI: 10.7907/g0wf-ny80
<p>A large sample of D mesons, produced by the decay of the Ψ(3770) and observed by the Mark III detector at SPEAR, forms the basis for a study of the decays of charmed D<sup>+</sup> and D<sup>0</sup> mesons. Many Cabibbo-allowed and Cabibbo-suppressed decays are observed. When normalized by a new, absolute technique, the branching ratios appear significantly higher than those reported by previous experiments. No evidence is found for specific final states from D<sup>0</sup> decay which are indicative of non-spectator W-exchange diagrams: limits are quoted. Finally, the inclusive semileptonic branching fractions of charged and neutral D mesons are measured by observation of electrons in the recoil from fully reconstructed hadronic D decays of known charm. By neglecting the contribution of Cabibbo-suppressed decays to the total decay widths, the ratio of these branching fractions can be interpreted as the ratio of D<sup>+</sup> and D<sup>0</sup> lifetimes, thus confirming the inequality of lifetimes observed by direct decay length experiments. The observed pattern of hadronic decays appears to favor modification of the spectator model over non-spectator processes as the main source of the lifetime difference.</p>https://thesis.library.caltech.edu/id/eprint/11368The Properties of Semileptonic Decays of Charmed D Mesons
https://resolver.caltech.edu/CaltechTHESIS:08302019-143806077
Authors: Coffman, Daniel Mark
Year: 1987
DOI: 10.7907/4be7-sc20
<p>The MARK III collaboration has collected a large sample of D mesons produced at the Ψ(3770) resonance. The reconstruction of several thousand hadronic D decays makes possible for the first time the reconstruction of exclusive semileptonic D decays. Absolute branching ratios are measured for the nine decays D<sup>0</sup> → K<sup>-</sup> e<sup>+</sup> ν<sub>e</sub>, D<sup>0</sup> → K<sup>-</sup> π<sup>0</sup> e<sup>+</sup> ν<sub>e</sub>, D<sup>0</sup> → K̅<sup>0</sup> π<sup>-</sup> e<sup>+</sup> ν<sub>e</sub>, D<sup>+</sup> → K̅<sup>0</sup> e<sup>+</sup> ν<sub>e</sub>, D<sup>+</sup> → K<sup>-</sup> π<sup>+</sup> e<sup>+</sup> ν<sub>e</sub>, D<sup>0</sup> → π<sup>-</sup> e<sup>+</sup> ν<sub>e</sub>, D<sup>0</sup> → K<sup>-</sup> μ<sup>+</sup> ν<sub>μ</sub>, D<sup>0</sup> → K̅<sup>0</sup> π<sup>-</sup> μ<sup>+</sup> ν<sub>μ</sub>, and D<sup>+</sup> → K̅<sup>0</sup> μ<sup>+</sup> ν<sub>μ</sub>. The sums of the exclusive branching ratios are in good agreement with the inclusive semileptonic branching ratios measured by the MARK III. The rate of the Cabibbo-suppressed decays is consistent with the predicted rate. The contribution of the K<sup>*</sup>(892) to the K-π invariant mass spectrum for decays of the type D → K π e<sup>+</sup> ν<sub>e</sub> is found to be about 55%. The vector form factor in the decays D<sup>0</sup> → K<sup>-</sup> e<sup>+</sup> ν<sub>e</sub> and D<sup>0</sup> → K<sup>-</sup> μ<sup>+</sup> ν<sub>μ</sub> is measured and found to be consistent with a simple pole form.</p>https://thesis.library.caltech.edu/id/eprint/11781The Decay Properties of the ψ(3770)
https://resolver.caltech.edu/CaltechTHESIS:10252013-112507352
Authors: Zhu, Yanong
Year: 1989
DOI: 10.7907/2c5y-sq13
The decays of the ψ(3770) resonance to final states that do not contain charmed D mesons are measured for the first time. Using a sample of 9.3pb⁻¹ of e⁺e⁻ annihilations at √s = 3.77 GeV, collected with the Mark III detector at SPEAR, we have measured the branching ratio for the decays ψ(3770) → J/ψπ⁺π⁻ and γχ<sub>J</sub>. These branching ratios together with the electronic widths of the ψ(3685) and ψ(3770) are used to determine the mixing angle between the 2³S₁ and 1³D₁ Charmonium states and are compared with a number of predictions. In addition, evidence is found for other non-DD̅ hadronic final states, such as 3π, 4π, and 5π, as well as η2π, η4π, p̅p2π and p̅p3π.https://thesis.library.caltech.edu/id/eprint/8010Resonant Substructure in Kπππ Decays of D Mesons
https://resolver.caltech.edu/CaltechETD:etd-06062007-122309
Authors: DeJongh, Don Frederic
Year: 1990
DOI: 10.7907/0wda-j731
<p>We determine the resonant substructure of D → K̅πππ decays using a five-dimensional maximum likelihood technique to extract the relative fractions and phases of the amplitudes contributing to the K⁻π⁺π⁺π⁻, K̅⁰π⁺π⁺π⁻, and K̅⁻π⁺π⁺π⁰ final states. We find that two-body decay modes account for about 75% of these decays. We obtain branching ratios for D → K̅a₁, D → K̅*ρ, D → K̅₁(1270)π, D → K̅₁(1400)π, and D⁰ → K̅⁰ω decay modes, as well as several three and four-body decay modes. In the case of D → K̅a₁ and D → K̅*ρ, we obtain the branching ratios for all three possible isospin combinations, enabling us to extract the isospin 1/2 and 3/2 amplitudes. This allows us to eliminate the ambiguity due to phase shifts between the isospin amplitudes when comparing our results with theoretical models. We find that the isospin 3/2 amplitudes are suppressed relative to the isospin 1/2 amplitudes, confirming that an understanding of the lifetime difference of the D⁰ and D⁺ depends on an understanding of two-body hadronic decays.</p>
<p>For the D → K̅*ρ decay modes, we obtain detailed information on the polarization of the K̅* and ρ. This enables us to obtain information on form-factors for D → K̅* and D → ρ transitions, within the context of the factorization hypothesis. Comparison of our results on D → K̅*ρ decays with recent results on semileptonic decays allows us to test the factorization hypothesis.</p>https://thesis.library.caltech.edu/id/eprint/2481Upper Limits on Inclusive Branching Fractions to Narrow States in Radiative J/ψ Decays
https://resolver.caltech.edu/CaltechTHESIS:08302011-160306362
Authors: Dubois, Gregory P.
Year: 1992
DOI: 10.7907/56qf-9005
The inclusive photon energy spectrum arising from J/ψ decays is studied in a sample of 4.83 x 10^6 produced J/ψ’s, with the very good energy resolution available through the observation of converted photons in the Mark III spectrometer. The spectrum is inspected for evidence of monochromatic lines due to two-body radiative J/ψ decays to narrow states. The decays J/ψ → γ + ή (958) and
J/ψ → γ + ι/X (1450) are observed with limited statistical significance. No evidence is found for any other statistically significant structure in the inclusive spectrum. Upper limits are set on the branching fractions for the observed decays, as well as for the decays
J/ψ → γ +ϕ/ϝο(1710) and J/ψ → γ + X(2230).
https://thesis.library.caltech.edu/id/eprint/6635Inclusive Weak Decays of Charmed Mesons
https://resolver.caltech.edu/CaltechTHESIS:01042013-100942921
Authors: Matthews, Christopher Gerald
Year: 1993
DOI: 10.7907/v7vw-np18
<p>Inclusive analyses provide a different insight into our understanding of weak decay
physics. In this thesis, I experimentally determine inclusive decay properties of charmed
D mesons. I also use exclusive decay predictions from a variety of theoretical models
to make predictions about inclusive properties. Both experimental and theoretical realms
benefit from the new techniques presented in this thesis.</p>
<p>Inclusive properties derived are the multiplicity distributions, average multiplicities
and inclusive branching ratios of charged particles, charged and neutral kaons, and
charged pions. The center-of-mass momentum spectra of charged and neutral kaons
are also obtained. Additionally, in the theoretical realm only, the inclusive properties of
neutral pions, and the center-of-mass momentum spectra of charged and neutral pions
are determined.</p>
<p>The experimental analysis, which uses data from the Mark III experiment at the
Stanford Linear Accelerator Center, employs an unfold technique utilizing fold matrices
to obtain the charged particle and kaon properties. A new, enhanced unfold technique
involving fold tensors obtains the first-ever results for the inclusive charged pion properties.
The average strange quark contents and the average charged lepton multiplicities
of the D<sup>+</sup>, D<sup>0</sup> , and D<sup>+</sup><sub>s</sub> are also presented.</p>
<p>In the theoretical analysis, the exclusive decay mode predictions from the factorization
model of Bauer, Stech and Wirbel; the quark diagram scheme of Chau and Cheng; and
the QCD sum rules model of Blok and Shifman are processed to determine inclusive
properties. It is hoped that an examination of a model's inclusive predictions will lead
to a better understanding of the model. I also derive inclusive predictions from the D
meson exclusive branching ratios compiled by the Particle Data Group.</p>https://thesis.library.caltech.edu/id/eprint/7368Doubly-tagged Ds decays at 4.03 GeV
https://resolver.caltech.edu/CaltechETD:etd-10122007-082523
Authors: Prabhakar, Ernest N.
Year: 1995
DOI: 10.7907/2ja4-ts17
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The [...] is a pseudoscalar meson composed of two second generation quarks, the heavy charm and the light strange. The bulk of our knowledge of the [...] comes from secondary production via B decays. These experiments have high statistics but are poorly suited to absolute branching fraction or production cross-section measurements. The best way to perform those is to use double-tagging of threshold pair production. Unfortunately, there is no strong resonance near [...] threshold, making it difficult to obtain sufficient statistics.
This thesis makes use of the [...] integrated luminosity collected by the Beijing Spectrometer from the Beijing Electron-Positron Collider at 4.03 GeV. This energy was chosen because the coupled-channel model of Eichten et al. predicts an enhancement there of the [...] cross section to somewhat below 1 nb. We attempt to fully reconstruct hadronic and semileptonic [...] pairs from six-prong events not containing any photons. We combine the [...] from kinematic fitting and particle identification to form a single value, the joint confidence level, for each event.
Using this in the analysis yields five hadronic events, with multiple combinations per event. Since the [...] principally decays to resonant moves, we preferentially select those combinations which lead to resonant two-body masses. This gives us a signal containing 7 resonant decays and 3 non-resonant [...] decays. We use Monte Carlo efficiencies and knowledge of the ratio [...] to estimate the production rates represented by these tags.
We perform a likelihood analysis using those numbers, together with the absolute branching fractions, to obtain a value of [...] one sigma below the coupled channel model. Using only relative [...] branching fractions, we fit to a value for the ratio [...] This is within one sigma of the current world average, and differs [...] noticeably from the model of Bauer, Stech, and Wirbel value of [...]
https://thesis.library.caltech.edu/id/eprint/4049Measurement of the Leptonic Branching Fraction of the Dₛ Meson and Determination of Its Decay Constant
https://resolver.caltech.edu/CaltechTHESIS:04202020-172701960
Authors: Kelsey, Michael Henderson
Year: 1996
DOI: 10.7907/x5qg-g497
<p>Between February 1992 and June 1994, the Beijing Spectrometer (BES) experiment collected 24.5 pb⁻¹ of data in e⁺e⁻ collisions at a center of mass energy of 4.03 GeV, above threshold for production of Dₛ⁺Dₛ⁻ meson pairs. In this thesis, these data are searched for Dₛ⁺Dₛ⁻ events by identifying sets of charged tracks consistent with the decay channels Dₛ → Φπ,Φ → K⁺K⁻; Dₛ → K*⁰K,K*⁰ → K⁺π⁻; or Dₛ → K⁰<sub>S</sub>K,K⁰<sub>S</sub> → π⁺π⁻. A global maximum-likelihood technique is used, which combines particle identification detector data and a kinematic fit to each decay hypothesis, for maximum sensitivity. A sample of 190 candidates is found in the mass range 1958.5-1978.5 MeV/c², of which 76.9 ± 13.8 are estimated (from a fit to 1097 combinations with 1800 < m < 2015 MeV /c²) to be true e⁺e⁻ → Dₛ⁺Dₛ⁻ events.</p>
<p>This event sample is searched for leptonic decays of the Dₛ meson in the channels Dₛ → µν<sub>µ</sub> and Dₛ → τν<sub>τ</sub> (with τ → µν̅<sub>µ</sub>ν<sub>τ</sub> → eν̅<sub>e</sub>ν<sub>τ</sub>, or τ → πν<sub>τ</sub>). Five candidate decays are found. A likelihood function is formed as a product over the candidate events, where each contributes a sum over all of the leptonic decay channels, weighted according to the likelihoods of the particle identifications and the kinematics of the decay. This likelihood function is maximized with respect to the branching fraction B(Dₛ → µν<sub>µ</sub>), or the Dₛ pseudoscalar decay constant f<sub>Dₛ</sub>, with the results</p>
<p>B(Dₛ → µν<sub>µ</sub>) = .75<sup>+1.23</sup><sub>-.47</sub> (stat) ± .06 (syst) %,</p>
<p>f<sub>Dₛ</sub> = 308<sup>+164</sup><sub>-189</sub> (stat) ± 12 (syst) MeV.</p>
<p>Comparison of the measured value of f<sub>Dₛ</sub> with other experimental determinations and with a variety of theoretical models is discussed, with implications for constraining those models.</p>https://thesis.library.caltech.edu/id/eprint/13678Dalitz Plot Analysis of the Decay B± → K±K±K∓
https://resolver.caltech.edu/CaltechETD:etd-03312006-135838
Authors: Dvoretskii, Alexei
Year: 2006
DOI: 10.7907/7HTG-0W17
We perform an analysis of the three-body charmless decay B+ -> K+K+K- using a sample of 226.0 +/- 2.5 million BB pairs collected by the BABAR detector and measure the total branching fraction and CP asymmetry to be B = (35.2 +/- 0.9 +/- 1.6) x 10-6 and A = (-1.7 +/- 2.6 +/- 1.5)%. We fit the Dalitz plot distribution using an isobar model and report the measured values of magnitudes and phases of the production coefficients. The decay dynamics is dominated by the K+K- S-wave, for which we perform a partial-wave analysis in the region m(K+K-) < 2 GeV/c2. We find no evidence of CP violation for individual components of the isobar model.https://thesis.library.caltech.edu/id/eprint/1226Radiative Leptonic B Decays
https://resolver.caltech.edu/CaltechETD:etd-01302007-083640
Authors: Chen, Edward Tann
Year: 2007
DOI: 10.7907/KNQF-1R30
We present the results of a search for B+ meson decays into gamma l+ nu, where l = e, mu. We use a sample of 232 million B Bbar meson pairs recorded at the Y(4S) resonance with the BaBar detector at the PEP-II B factory. We measure a partial branching fraction DeltaBF in a restricted region of phase space that reduces the effect of theoretical uncertainties, requiring the lepton energy to be in the range 1.875 and 2.850 GeV, the photon energy to be in the range 0.45 and 2.35 GeV, and the cosine of the angle between the lepton and photon momenta to be less than -0.36, with all quantities computed in the Y(4S) center-of-mass frame.https://thesis.library.caltech.edu/id/eprint/408Search for B → (ρ/ω)γ decays at BABAR
https://resolver.caltech.edu/CaltechETD:etd-08252008-225854
Authors: Piatenko, Timofei
Year: 2009
DOI: 10.7907/JFX3-1629
<p>We present the results of the search for the decays ß<sup>(0/±)</sup> ? ?<sup>(0/±)</sup>? (previously observed) and ß<sup>0</sup> ? ?? (for which currently only an upper limit exists). Together with ß ? K<sup>*</sup>? decays, B ? (?/?)? allow us to measure the ratio of CKM-matrix elements |V<sub>td</sub>/V<sub>ts</sub>|. The analysis is based on the full BaBar dataset of 424.35 fb<sup>-1</sup>, corresponding to 465 million BB pairs, and makes heavy use of multivariate classification techniques based on decision trees. We find ßR(B ? ?<sup>±</sup>? ) = (1.20+0.42-0.38±0.20)×10<sup>-6</sup>, ßR(B ? ?<sup>0</sup>?)= (0.95+0.23-0.21 ±0.06)×10<sup>-6</sup>, and ßR(B ? ??)=(0.51+0.27-0.24±0.10)×10<sup>-6</sup>, where the first error is statistical and the second is systematic. We do not observe a statistically significant signal in the latter channel and set an upper limit at ßR(B ? ??) < 0.9 × 10<sup>-6</sup> (90% C.L.). We also measure the isospin and SU(3)<sub>F</sub> violating quantities ?(B<sup>+</sup> ? ?<sup>+</sup>?)/2?(B<sup>0</sup> ? ?<sup>0</sup>?) - 1 = -0.43+0.25-0.22±0.10 and ?(B ? ??)/?(B<sup>0</sup> ? ?<sup>0</sup>?) - 1 = -0.49+0.30-0.27±0.10.</p>https://thesis.library.caltech.edu/id/eprint/3226Measurement of the Rare Transition b→sγ Using the Complete BABAR Data Set
https://resolver.caltech.edu/CaltechTHESIS:05312011-194358237
Authors: Doll, David Andrew
Year: 2011
DOI: 10.7907/E6S9-4D28
We present the results of a measurement of the total rate and photon energy spectrum in b -> sγ transitions using the entire BABAR data set, 429 fb<sup>-1</sup>. These results use a "sum of exclusives" approach in which we reconstruct a subset of the final states of the s-quark system and correct for the final states that are missing. We find B(B<sup>-</sup> -> X<sub>s</sub>γ)=(329 ± 19 ± 48)x10<sup>-6</sup> for Eγ>1.9 GeV. We also measure the mean and variance of the photon spectrum and find <E>=2.346 ± 0.018<sup>+0.027</sup><sub>-0.022</sub> and <E<sup>2</sup>> - <E><sup>2</sup> = 0.0211 ± 0.0057<sup>+0.0055</sup><sub>-0.0069</sub>. Finally we fit two classes of models for the photon spectrum and extract their respective HQET parameters.https://thesis.library.caltech.edu/id/eprint/6484Measurement of the Direct CP Asymmetry in b→sγ via Sum of Exclusive B Meson Decays Using the BABAR Detector
https://resolver.caltech.edu/CaltechTHESIS:05022013-152247133
Authors: Ongmongkolkul, Piti
Year: 2013
DOI: 10.7907/ZNVN-R508
We perform a measurement of direct CP violation in b to sγ A<sub>CP</sub>, and the measurement of a difference between Acp for neutral B and charged B mesons, Delta A_{X_s\gamma}, using 429 inverse femtobarn of data recorded at the Upsilon(4S) resonance with the BABAR detector. B mesons are reconstructed from 16 exclusive final states. Particle identification is done using an algorithm based on Error Correcting Output Code with an exhaustive matrix. Background rejection and best candidate selection are done using two decision tree-based classifiers. We found $\acp = 1.73%+-1.93%+-1.02% and Delta A_X_sγ = 4.97%+-3.90%+-1.45% where the uncertainties are statistical and systematic respectively. Based on the measured value of Delta A_X_sgamma, we determine a 90% confidence interval for Im C_8g/C_7gamma, where C_7gamma and C_8g are Wilson coefficients for New Physics amplitudes, at -1.64 < Im C_8g/C_7gamma < 6.52.https://thesis.library.caltech.edu/id/eprint/7655Measurement of R(D) and R(D*) Using Semileptonic Tags and Hadronic τ Decays
https://resolver.caltech.edu/CaltechTHESIS:01252019-144433241
Authors: Kim, Jae Hong
Year: 2019
DOI: 10.7907/KF89-DS18
<p>We present a measurement of R(D<sup>(*)</sup>) = B(B → D̅<sup>(*)</sup> τν<sub>τ</sub>)/B(B → D̅<sup>(*)</sup> ℓν<sub>ℓ</sub>) using semileptonic tagging and hadronic τ decays on the 433 fb<sup>-1</sup> of data collected at the Υ(4S) resonance using the BaBar detector at the PEP-II collider. We obtain a high statistics data sample using loose selection criteria. The signal is extracted by performing a 2-dimensional fit of the component densities to the kernel density estimate of the data, which is made computationally tractable by algorithmic improvements and speedups provided by graphics processing units. We obtain two distinct central values based on the model used to represent the BB̅ background densities: R(D) = 0.231 ± 0.028 ± 0.028 and R(D<sup>*</sup>) = 0.127 ± 0.019 ± 0.031 with a correlation of 0.06 and R(D) = 1.454 ± 0.028 ± 0.028 and R(D<sup>*</sup>) = 1.507 ± 0.019 ± 0.031 with a correlation of 0.06. The region encompassed by the two results are consistent with both the Standard Model prediction and the world average.</p>https://thesis.library.caltech.edu/id/eprint/11364Search for Beyond Standard Model Physics at BaBar
https://resolver.caltech.edu/CaltechTHESIS:05232022-144829107
Authors: Li, Yunxuan
Year: 2022
DOI: 10.7907/tz7n-d662
<p>This thesis reports searches for beyond Standard Model physics in <span class="math inline"><em>e</em><sup>+</sup><em>e</em><sup>−</sup></span> collisions in two directions.</p>
<p>We report the first search for a dark matter bound state. The existence of dark matter bound states could arise in a simple dark sector model in which a dark photon (<span class="math inline"><em>A</em>′</span>) is light enough to generate an attractive force between dark fermions. We report herein a search for a <span class="math inline"><em>J</em><sup><em>P</em><em>C</em></sup> = 1<sup> − −</sup></span> darkonium state, the <span class="math inline"><em>Υ</em><sub><em>D</em></sub></span>, produced in the reaction <span class="math inline"><em>e</em><sup>+</sup><em>e</em><sup>−</sup> → <em>γ</em><em>Υ</em><sub><em>D</em></sub>, <em>Υ</em><sub><em>D</em></sub> → <em>A</em>′<em>A</em>′<em>A</em>′</span>, where the dark photons subsequently decay into pairs of leptons or pions, using data collected with the BaBar detector. No significant signal is observed, and we derive limits on the <span class="math inline"><em>γ</em> − <em>A</em>′</span> kinetic mixing (<span class="math inline"><em>ϵ</em></span>) as a function of the dark sector coupling constant for <span class="math inline">0.001 < <em>m</em><sub><em>A</em>′</sub> < 3.16</span> GeV and <span class="math inline">0.05 < <em>m</em><sub><em>Υ</em><sub><em>D</em></sub></sub> < 9.5</span> GeV. Bounds on the mixing strength <span class="math inline"><em>ϵ</em></span> down to <span class="math inline">5 × 10<sup> − 5</sup> − 10<sup> − 3</sup></span> are set for a large fraction of the parameter space.</p>
<p>We also report a measurement of <span class="math inline"><em>R</em>(<em>D</em>) = <em>B</em>(<em>B</em> → <em>D̄</em><em>τ</em><em>ν̄</em><sub><em>τ</em></sub>)/<em>B</em>(<em>B</em> → <em>D̄</em>ℓ<em>ν̄</em><sub>ℓ</sub>)</span> and <span class="math inline"><em>R</em>(<em>D</em><sup>*</sup>) = <em>B</em>(<em>B</em> → <em>D̄</em><sup>*</sup><em>τ</em><em>ν̄</em><sub><em>τ</em></sub>)/<em>B</em>(<em>B</em> → <em>D̄</em><sup>*</sup>ℓ<em>ν̄</em><sub>ℓ</sub>)</span>, where <span class="math inline">ℓ</span> refers to either an electron or muon. We select samples by reconstructing tag-side <span class="math inline"><em>B</em></span> mesons in semileptonic decays and signal-side <span class="math inline"><em>τ</em></span> in a purely leptonic decay. Using data collected with the BaBar detector, we measure <span class="math inline"><em>R</em>(<em>D</em>) = 0.316 ± 0.062(stat) ± 0.019(syst)</span> and <span class="math inline"><em>R</em>(<em>D</em><sup>*</sup>) = 0.226 ± 0.022(stat) ± 0.012(syst)</span>, which agree with the Standard Model expectations by <span class="math inline">0.26<em>σ</em></span> and <span class="math inline">1.10<em>σ</em></span>, respectively. Taken together, the results are in agreement with the Standard Model within <span class="math inline">1.51<em>σ</em></span> level.</p>https://thesis.library.caltech.edu/id/eprint/14598