D. Boutigny

Four-layer aerogel Cherenkov counter

Abstract A 4-layer design of aerogel threshold counters using two refractive indices was suggested for the particle identification in the forward region of the BaBar detector. Three prototypes filled with the high quality aerogel produced in Novosibirsk were tested at T10 beam at CERN. Monte Carlo code was developed for the simulation of the light collection in aerogel counters. Monte Carlo results based on measured PTFE reflection coefficient and aerogel absorption and scattering lengths are in agreement with experiment.

Performance of a prototype aerogel counter readout by fine mesh photo-tubes

Abstract The BaBar experiment, in order to achieve its physics program, requires pion/kaon identification capability up to 4.3 GeV/ c . The recent development of new processes has lead to the fabrication of low density silica aerogel with high optical quality. An aerogel threshold counter using the combination of two refractive indices (1.055 and 1.007) can be used to complete the angular coverage of the particle identification system in the forward region of the BaBar experiment. We present final test-beam results on a two-layer aerogel prototype, readout by Hamamatsu fine mesh photo-tubes, as required by the high magnetic field environment of the BaBar experiment. Several configurations have been tested, with different aerogels, photo-tubes and reflective materials. A comparison between data and a detailed Monte Carlo simulation is also presented. The result of the test shows that such a detector can achieve the desired performances.

Performance of an aerogel threshold particle identification detector readout by hybrid photon detectors

This paper describes an aerogel threshold particle identification detector developed for use in BABAR, the experiment to be run at the asymmetric e/sup +/e/sup -/ B-factory PEP-II under construction at the Stanford Linear Accelerator Center (SLAC). Results of extensive tests performed at the CERN PS indicate that this detector is capable of separating pions from below-threshold particles in a wide momentum range. The detector is read by a new version of a hybrid photon detector (HPD). The HPD has been chosen because of its excellent behavior in high magnetic fields, where it can be successfully exploited to preserve the required particle identification (PID) performance.

Recent results on prototype aerogel threshold counters for particle identification in the region 0.5–4.3 GeV/c

Abstract The recent development of new processes has led to the fabrication of small density silica aerogel with high optical quality. The BaBar experiment, in order to achieve its physics program, requires a good pion/kaon identification capability up to 4.3 GeV/ c able to work inside a 1.5 T magnetic field. An aerogel threshold counter using the combination of two refractive indices (1.055 and 1.007) can be used to complete the angular coverage of the particle identification system in the forward region. Different detector geometries read out by two photodetector types (fine mesh phototubes and hybryd photodiodes) have been considered and tested in a CERN beam test.

Observation of B{sup 0}{yields}K*{sup 0}K*{sup 0} and Search for B{sup 0}{yields}K*{sup 0}K*{sup 0}

We report the observation of the b{yields}d penguin-dominated decay B{sup 0}{yields}K*{sup 0}K*{sup 0} with a sample of 383.2{+-}4.2 million BB pairs collected with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} collider at the Stanford Linear Accelerator Center. The measured branching fraction is B(B{sup 0}{yields}K*{sup 0}K*{sup 0})=[1.28{sub -0.30}{sup +0.35}{+-}0.11]x10{sup -6} and the fraction of longitudinal polarization is f{sub L}(B{sup 0}{yields}K*{sup 0}K*{sup 0})=0.80{sub -0.12}{sup +0.10}{+-}0.06. The first error quoted is statistical and the second systematic. We also obtain an upper limit at the 90% confidence level on the branching fraction for B(B{sup 0}{yields}K*{sup 0}K*{sup 0})<0.41x10{sup -6}.We report the observation of the b -> d penguin-dominated decay B-0 -> K-*0(K) over bar (*0) with a sample of 383.2 +/- 4.2 million B (B) over bar pairs collected with the BABAR detector at the PEP-II asymmetric-energy e(+)e(-) collider at the Stanford Linear Accelerator Center. The measured branching fraction is B(B-0 -> K-*0(K) over bar (*0))=[1.28(-0.30)(+0.35)+/- 0.11]x10(-6) and the fraction of longitudinal polarization is f(L)(B-0 -> K-*0(K) over bar (*0))=0.80(-0.12)(+0.10)+/- 0.06. The first error quoted is statistical and the second systematic. We also obtain an upper limit at the 90% confidence level on the branching fraction for B(B-0 ->(KK*0)-K-*0)< 0.41x10(-6).

Observation of the Semileptonic Decays B{yields}D*{tau}{sup -}{nu}{sub {tau}} and Evidence for B{yields}D{tau}{sup -}{nu}{sub {tau}}

We present measurements of the semileptonic decays B--> D-0 tau(-)(nu) over bar (tau), B--> D-*0 tau(-)(nu) over bar (tau), (B) over bar (0)-> D+tau(-)(nu) over bar (tau), and (B) over bar (0)-> D*+tau(-)(nu) over bar (tau), which are potentially sensitive to non-standard model amplitudes. The data sample comprises 232x10(6) Upsilon(4S)-> B (B) over bar decays collected with the BABAR detector. From a combined fit to B- and (B) over bar (0) channels, we obtain the branching fractions B(B -> D tau(-)(nu) over bar (tau))=(0.86 +/- 0.24 +/- 0.11 +/- 0.06)% and B(B -> D-*tau(-)(nu) over bar (tau))=(1.62 +/- 0.31 +/- 0.10 +/- 0.05)% (normalized for the (B) over bar (0)), where the uncertainties are statistical, systematic, and normalization-mode-related.

Observation of B{sup +}{yields}a{sub 1}{sup +}(1260)K{sup 0} and B{sup 0}{yields}a{sub 1}{sup -}(1260)K{sup +}

We present branching fraction measurements of the decays B{sup +}{yields}a{sub 1}{sup +}(1260)K{sup 0} and B{sup 0}{yields}a{sub 1}{sup -}(1260)K{sup +} with a{sub 1}{sup {+-}}(1260){yields}{pi}{sup {+-}}{pi}{sup {+-}}{pi}{sup {+-}}. The data sample corresponds to 383x10{sup 6} BB pairs produced in e{sup +}e{sup -} annihilation through the {upsilon}(4S) resonance. We measure the products of the branching fractions B(B{sup +}{yields}a{sub 1}{sup +}(1260)K{sup 0})B(a{sub 1}{sup +}(1260){yields}{pi}{sup -}{pi}{sup +}{pi}{sup +})=(17.4{+-}2.5{+-}2 = .2)x10{sup -6} and B(B{sup 0}{yields}a{sub 1}{sup -}(1260)K{sup +})B(a{sub 1}{sup -}(1260){yields}{pi}{sup +}{pi}{sup -}{pi}{sup -})=(8.2{+-}1.5{+-}1. = 2)x10{sup -6}. We also measure the charge asymmetries A{sub ch}(B{sup +}{yields}a{sub 1}{sup +}(1260)K{sup 0})=0.12{+-}0.11{+-}0.02 and A{sub ch}(B{sup 0}{yields}a{sub 1}{sup -}(1260)K{sup +})=-0.16{+-}0.12{+-}0.01. The first uncertainty quoted is statistical and the second is systematic.We present branching fraction measurements of the decays B(+)-->a(1)(+)(1260)K(0) and B(0)-->a(1)(-)(1260)K(+) with a(1)(+/-)(1260)-->pi(-/+)pi(+/-)pi(+/-). The data sample corresponds to 383 x 10(6) BB pairs produced in e(+)e(-) annihilation through the Upsilon(4S) resonance. We measure the products of the branching fractions B(B(+)-->a(1)(+)(1260)K(0)B(a(1)(+)(1260)-->pi(-)pi(+)pi(+))=(17.4+/-2.5+/-2.2) x 10(-6) and B(B(0)-->a(1)(-)(1260)K(+)B(a(1)(-)(1260)-->pi(+)pi(-)pi(-)) = (8.2+/-1.5+/-1.2) x 10(-6). We also measure the charge asymmetries A(ch)(B(+)-->a(1)(+)(1260)K(0) = 0.12+/-0.11+/-0.02 and A(ch)(B(0)-->a(1)(-)(1260)K+) = -0.16+/-0.12+/-0.01. The first uncertainty quoted is statistical and the second is systematic.

Measurement of the Absolute Branching Fraction of D{sup 0}{yields}K{sup -}{pi}{sup +}

We measure the absolute branching fraction for D0 → K−π+ using partial reconstruction of B0 → DXlν̄l decays. Only the charged lepton and the soft pion from the decay D ∗+ → D0π+ are used. Based on a data sample of 230 million BB pairs collected at the Υ (4S) resonance with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC, we obtain B(D0 → K−π+) = (4.025 ± 0.038 ± 0.098)%, where the first error is statistical and the second error is systematic.

Study of B{yields}{xi}{sub c}{lambda}{sub c}{sup -} and B{yields}{lambda}{sub c}{sup +}{lambda}{sub c}{sup -}K decays at BABAR

We report measurements of B-meson decays into two- and three-body final states containing two charmed baryons using a sample of 230×106 Υ(4S)→BB decays. We find significant signals in two modes, measuring branching fractions B(B-→Λc+Λ c-K-)=(1.14±0.15±0.17±0.60)×10-3 and B(B-→Ξc0Λ c-)×B(Ξc0→Ξ-π+)=(2.08±0.65±0.29±0.54)×10-5, where the uncertainties are statistical, systematic, and from the branching fraction B(Λc+→pK-π+), respectively. We also set upper limits at the 90% confidence level on two other modes: B(B 0→Ξc+Λ c-)×B(Ξc+→Ξ-π+π+)<5.6×10-5 and B(B 0→Λc+Λ c-K 0)<1.5×10-3. We observe structure centered at an invariant mass of 2.93  GeV/c2 in the Λc+K- mass distribution of the decay B-→Λc+Λ c-K-.We report measurements of B-meson decays into two- and three-body final states containing two charmed baryons using a sample of 230x10{sup 6} {upsilon}(4S){yields}BB decays. We find significant signals in two modes, measuring branching fractions B(B{sup -}{yields}{lambda}{sub c}{sup +}{lambda}{sub c}{sup -}K{sup -})=(1.14{+-}0.15{+-}0.17{+-}0.60)x10{sup -3} and B(B{sup -}{yields}{xi}{sub c}{sup 0}{lambda}{sub c}{sup -})xB({xi}{sub c}{sup 0}{yields}{xi}{sup -}{pi}{sup +})=(2.08{+-}0.65{+-}0.= 29{+-}0.54)x10{sup -5}, where the uncertainties are statistical, systematic, and from the branching fraction B({lambda}{sub c}{sup +}{yields}pK{sup -}{pi}{sup +}), respectively. We also set upper limits at the 90% confidence level on two other modes: B(B{sup 0}{yields}{xi}{sub c}{sup +}{lambda}{sub c}{sup -})xB({xi}{sub c}{sup +}{yields}{xi}{sup -}{pi}{sup +}{pi}{sup +})<5.6x10{sup -5} and B(B{sup 0}{yields}{lambda}{sub c}{sup +}{lambda}{sub c}{sup -}K{sup 0})<1.5x10{sup -3}. We observe structure centered at an invariant mass of 2.93 GeV/c{sup 2} in the {lambda}{sub c}{sup +}K{sup -} mass distribution of the decay B{sup -}{yields}{lambda}{sub c}{sup +}{lambda}{sub c}{sup -}K{sup -}.We report measurements of B-meson decays into two- and three-body final states containing two charmed baryons using a sample of 230×106 Υ(4S)→BB¯¯¯ decays. We find significant signals in two modes, measuring branching fractions B(B−→Λ+cΛ¯¯¯−cK−)=(1.14±0.15±0.17±0.60)×10−3 and B(B−→Ξ0cΛ¯¯¯−c)×B(Ξ0c→Ξ−π+)=(2.08±0.65±0.29±0.54)×10−5, where the uncertainties are statistical, systematic, and from the branching fraction B(Λ+c→pK−π+), respectively. We also set upper limits at the 90% confidence level on two other modes: B(B¯¯¯0→Ξ+cΛ¯¯¯−c)×B(Ξ+c→Ξ−π+π+)

Search for the rare charmless hadronic decay B{sup +}{yields}a{sub 0}{sup +}{pi}{sup 0}

We present a search for B decays to a charged scalar meson a{sub 0}{sup +} and a {pi}{sup 0} where the a{sub 0}{sup +} decays to an {eta} meson and a {pi}{sup +}. The analysis was performed on a data sample consisting of 383x10{sup 6} BB pairs collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We find no significant signal and set an upper limit on the product branching fraction B(B{sup +}{yields}a{sub 0}{sup +}{pi}{sup 0})xB(a{sub 0}{sup +}{yields}{eta}{pi}{sup +}) of 1.4x10{sup -6} at the 90% confidence level.We present a search for B decays to a charged scalar meson a0+ and a π0 where the a0+ decays to an η meson and a π+. The analysis was performed on a data sample consisting of 383×106 BB pairs collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We find no significant signal and set an upper limit on the product branching fraction B(B+→a0+π0)×B(a0+→ηπ+) of 1.4×10-6 at the 90% confidence level.