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1.
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D. S. Armstrong et al. G0 Collaboration
Show Abstract
We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2=0.15, 0.25 (GeV/c)2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state and generally agree with calculations with significant inelastic hadronic intermediate state contributions. An provides a direct probe of the imaginary component of the 2γ exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.
Phys. Rev. Lett. 99, 092301 (2007)
Cited 2 times
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2.
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A. Airapetian et al. HERMES Collaboration
Show Abstract
Precise measurements of the spin structure functions of the proton g1p(x,Q2) and deuteron g1d(x,Q2) are presented over the kinematic range 0.0041≤x≤0.9 and 0.18 GeV2≤Q2≤20 GeV2. The data were collected at the HERMES experiment at DESY, in deep-inelastic scattering of 27.6 GeV longitudinally polarized positrons off longitudinally polarized hydrogen and deuterium gas targets internal to the HERA storage ring. The neutron spin structure function g1n is extracted by combining proton and deuteron data. The integrals of g1p,d at Q2=5 GeV2 are evaluated over the measured x range. Neglecting any possible contribution to the g1d integral from the region x≤0.021, a value of 0.330±0.011(theo)±0.025(exp)±0.028(evol) is obtained for the flavor-singlet axial charge a0 in a leading-twist next-to-next-to-leading-order analysis.
Phys. Rev. D 75, 012007 (2007)
Cited 24 times
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3.
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A. Airapetian et al. HERMES Collaboration
Show Abstract
The first measurements of double-hadron production in deep-inelastic scattering within the nuclear medium were made with the HERMES spectrometer at DESY HERA using a 27.6 GeV positron beam. By comparing data for deuterium, nitrogen, krypton, and xenon nuclei, the influence of the nuclear medium on the ratio of double-hadron to single-hadron yields was investigated. Nuclear effects on the additional hadron are clearly observed, but with little or no difference among nitrogen, krypton, or xenon, and with smaller magnitude than effects seen on previously measured single-hadron multiplicities. The data are compared with models based on partonic energy loss or prehadronic scattering and with a model based on a purely absorptive treatment of the final-state interactions. Thus, the double-hadron ratio provides an additional tool for studying modifications of hadronization in nuclear matter.
Phys. Rev. Lett. 96, 162301 (2006)
Cited 6 times
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4.
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D. S. Armstrong et al. G0 Collaboration
Show Abstract
We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12≤Q2≤1.0 GeV2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, Q2 dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.
Phys. Rev. Lett. 95, 092001 (2005)
Cited 67 times
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5.
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Y. Chao et al. Belle Collaboration
Show Abstract
We report evidence for direct CP violation in the decay B0→K+π- with 253 fb-1 of data collected with the Belle detector at the KEKB e+e- collider. Using 275×106 BB̅ pairs we observe a B→K±π∓ signal with 2140±53 events. The measured CP violating asymmetry is ACP(K+π-)=-0.101±0.025(stat)±0.005(syst), corresponding to a significance of 3.9σ including systematics. We also search for CP violation in the decays B+→K+π0 and B+→π+π0. The measured CP violating asymmetries are ACP(K+π0)=0.04±0.05(stat)±0.02(syst) and ACP(π+π0)=-0.02±0.10(stat)±0.01(syst), corresponding to the intervals -0.05<ACP(K+π0)<0.13 and -0.18<ACP(π+π0)<0.14 at 90% confidence level.
Phys. Rev. Lett. 93, 191802 (2004)
Cited 60 times
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6.
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S.-K. Choi et al. Belle Collaboration
Show Abstract
We report the observation of a narrow charmoniumlike state produced in the exclusive decay process B±→K±π+π-J/ψ. This state, which decays into π+π-J/ψ, has a mass of 3872.0±0.6(stat)±0.5(syst) MeV, a value that is very near the MD0+MD*0 mass threshold. The results are based on an analysis of 152M B-B̅ events collected at the Υ(4S) resonance in the Belle detector at the KEKB collider. The signal has a statistical significance that is in excess of 10σ.
Phys. Rev. Lett. 91, 262001 (2003)
Cited 164 times
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7.
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K. Abe et al. (Belle Collaboration)
Show Abstract
This article describes an observation of mixing-induced CP violation and a measurement of the CP violation parameter, sin 2φ1, with the Belle detector at the KEKB asymmetric e+e- collider. Using a data sample of 29.1 fb-1 recorded on the Υ(4S) resonance that contains 31.3 million BB̅ pairs, we reconstruct decays of neutral B mesons to the following CP eigenstates: J/ψKS0, ψ(2S)KS0, χc1KS0, ηcKS0, J/ψKL0 and J/ψK*0. The flavor of the accompanying B meson is identified by combining information from primary and secondary leptons, K± mesons, Λ baryons, slow and fast pions. The proper-time interval between the two B meson decays is determined from the distance between the two decay vertices measured with a silicon vertex detector. The result sin 2φ1=0.99±0.14(stat)±0.06(syst) is obtained by applying a maximum likelihood fit to the 1137 candidate events. We conclude that there is large CP violation in the neutral B meson system. A zero value for sin 2φ1 is ruled out by more than six standard deviations.
Phys. Rev. D 66, 032007 (2002)
Cited 21 times
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8.
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K. Abe et al. (Belle Collaboration)
Show Abstract
The lifetimes of the B̅ 0 and B- mesons are extracted from 29.1 fb-1 of data collected with the Belle detector at the KEK B factory. A fit to the decay length differences of neutral and charged B meson pairs, measured in events where one of the B mesons is fully reconstructed in several hadronic modes, yields τB̅ 0 = 1.554±0.030(stat)±0.019(syst) ps, τB- = 1.695±0.026(stat)±0.015(syst) ps, and τB-/τB̅ 0 = 1.091±0.023(stat)±0.014(syst).
Phys. Rev. Lett. 88, 171801 (2002)
Cited 8 times
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9.
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K. Abe et al. (Belle Collaboration)
Show Abstract
Using the Belle detector operating at the KEKB e+e- storage ring, we have measured the mean multiplicity and momentum spectrum of neutral pions from the decays of the Υ(4S) resonance. We measure a mean of 4.70±0.04±0.22 neutral pions per Υ(4S) decay.
Phys. Rev. D 64, 072001 (2001)
Cited 8 times
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10.
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K. Abe et al. (Belle Collaboration)
Show Abstract
We present a measurement of the standard model CP violation parameter sin2φ1 based on a 29.1 fb-1 data sample collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. One neutral B meson is fully reconstructed as a J/ψKS, ψ(2S)KS, χc1KS, ηcKS, J/ψKL, or J/ψK*0 decay and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we determine sin2φ1 = 0.99±0.14(stat)±0.06(syst). We conclude that we have observed CP violation in the neutral B meson system.
Phys. Rev. Lett. 87, 091802 (2001)
Cited 140 times
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11.
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K. Abe et al. (Belle Collaboration)
Show Abstract
We report a determination of the Bd0-B̅ d0 mixing parameter Δmd based on the time evolution of dilepton yields in ϒ(4S) decays. The measurement is based on a 5.9 fb-1 data sample collected by the Belle detector at KEKB. The proper-time difference distributions for same-sign and opposite-sign dilepton events are simultaneously fitted to an expression containing Δmd as a free parameter. Using both muons and electrons, we obtain Δmd = 0.463±0.008 (stat)±0.016 (syst) ps-1. This is the first determination of Δmd from time evolution measurements at the ϒ(4S). We also place limits on possible CPT violations.
Phys. Rev. Lett. 86, 3228 (2001)
Cited 51 times
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12.
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A. Abashian et al.
Show Abstract
We present a measurement of the standard model CP violation parameter sin2φ1 (also known as sin2β) based on a 10.5 fb-1 data sample collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. One neutral B meson is reconstructed in the J/ψKS, ψ(2S)KS, χc1KS, ηcKS, J/ψKL, or J/ψπ0 CP-eigenstate decay channel and the flavor of the accompanying B meson is identified from its charged particle decay products. From the asymmetry in the distribution of the time interval between the two B-meson decay points, we determine sin2φ1 = 0.58-0.34+0.32(stat)-0.10+0.09(syst).
Phys. Rev. Lett. 86, 2509 (2001)
Cited 43 times
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13.
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Charles M. Ankenbrandt et al. (Muon Collider Collaboration)
Show Abstract
The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3–4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay (π→μνμ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96 Workshop [R. B. Palmer, A. Sessler, and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].
Phys. Rev. ST Accel. Beams 2, 081001 (1999)
Cited 37 times
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