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The OPAL Collaboration,
G. Abbiendi,
C. Ainsley,
P. F. Åkesson,
G. Alexander,
G. Anagnostou,
K. J. Anderson,
S. Asai,
D. Axen,
I. Bailey, [......],
P. S. Wells,
T. Wengler,
N. Wermes,
G. W. Wilson,
J. A. Wilson,
G. Wolf,
T. R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: Hadronic event shape distributions from e+e− annihilation measured by the OPAL experiment at centre-of-mass energies between 91GeV and 209GeV are used to determine
the strong coupling α
S. The results are based on QCD predictions complete to the next-to-next-to-leading order (NNLO), and on NNLO calculations
matched to the resummed next-to-leading-log-approximation terms (NNLO + NLLA). The combined NNLO result from all variables
and centre-of-mass energies is
while the combined NNLO + NLLA result is
The completeness of the NNLO and NNLO + NLLA results with respect to missing higher order contributions, studied by varying
the renormalization scale, is improved compared to previous results based on NLO or NLO + NLLA predictions only. The observed
energy dependence of α
S agrees with the QCD prediction of asymptotic freedom and excludes the absence of running.
European Physical Journal C 04/2012; 71(9):1-21. · 3.63 Impact Factor
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The OPAL Collaboration,
G. Abbiendi,
C. Ainsley,
P. F. Åkesson,
G. Alexander,
G. Anagnostou,
K. J. Anderson,
S. Asai,
D. Axen,
I. Bailey, [......],
T. Wengler,
N. Wermes,
D. Wetterling,
G. W. Wilson,
J. A. Wilson,
G. Wolf,
T. R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: Data collected around
Ös=91\sqrt{s}=91
GeV by the OPAL experiment at the LEP e+e− collider are used to study the mechanism of baryon formation. As the signature, the fraction of Σ− hyperons whose baryon number is compensated by the production of a
[`(S-)],[`(L)]\overline{\Sigma^{-}},\overline{\Lambda}
or
[`(X-)]\overline{\Xi^{-}}
antihyperon is determined. The method relies entirely on quantum number correlations of the baryons, and not rapidity correlations,
making it more model independent than previous studies. Within the context of the JETSET implementation of the string hadronization
model, the diquark baryon production model without the popcorn mechanism is strongly disfavored with a significance of 3.8
standard deviations including systematic uncertainties. It is shown that previous studies of the popcorn mechanism with
L[`(L)]\Lambda \overline{\Lambda}
and
p\uppi[`(p)]\mathrm{p}\uppi \overline{\mathrm{p}}
correlations are not conclusive, if parameter uncertainties are considered.
European Physical Journal C 04/2012; 64(4):609-625. · 3.63 Impact Factor
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G. Abbiendi,
C. Ainsley,
P.F. Åkesson,
G. Alexander,
G. Anagnostou,
K.J. Anderson,
S. Asai,
D. Axen,
I. Bailey,
E. Barberio, [......],
T. Wengler,
N. Wermes,
G.W. Wilson,
J.A. Wilson,
G. Wolf,
T.R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic,
The OPAL Collaboration
[show abstract]
[hide abstract]
ABSTRACT: A study of Bose–Einstein correlations in pairs of identically charged pions produced in e+e- annihilations at the Z0 peak has been performed for the first time assuming a non-static emitting source. The results are based on the high statistics
data obtained with the OPAL detector at LEP. The correlation functions have been analyzed in intervals of the average pair
transverse momentum and of the pair rapidity, in order to study possible correlations between the pion production points and
their momenta (position–momentum correlations). The Yano–Koonin and the Bertsch–Pratt parameterizations have been fitted to
the measured correlation functions to estimate the geometrical parameters of the source as well as the velocity of the source
elements with respect to the overall centre-of-mass frame. The source rapidity is found to scale approximately with the pair
rapidity, and both the longitudinal and transverse source dimensions are found to decrease for increasing average pair transverse
momenta.
European Physical Journal C 04/2012; 52(4):787-803. · 3.63 Impact Factor
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S. Schael,
R. Barate,
R. Brunelière,
I. De Bonis,
D. Decamp,
C. Goy,
S. Jézéquel,
J.-P. Lees,
F. Martin,
E. Merle, [......],
G.W. Wilson,
J.A. Wilson,
T.R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic,
S. Heinemeyer,
A. Pilaftsis,
G. Weiglein,
The LEP Working Group for Higgs Boson Searches
[show abstract]
[hide abstract]
ABSTRACT: The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by
the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined
for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no
significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper
bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number
of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large
exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses
of neutral Higgs bosons.
European Physical Journal C 04/2012; 47(3):547-587. · 3.63 Impact Factor
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G. Abbiendi,
C. Ainsley,
P.F. Åkesson,
G. Alexander,
G. Anagnostou,
K.J. Anderson,
S. Asai,
D. Axen,
I. Bailey,
E. Barberio, [......],
T. Wengler,
N. Wermes,
G.W. Wilson,
J.A. Wilson,
G. Wolf,
T.R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic,
The OPAL Collaboration
[show abstract]
[hide abstract]
ABSTRACT: Hadronic final states with a hard isolated photon are studied using data taken at centre-of-mass energies around the mass
of the Z boson with the OPAL detector at LEP. The strong coupling αs is extracted by comparing data and QCD predictions for event shape observables at average reduced centre-of-mass energies
ranging from 24GeV to 78GeV, and the energy dependence of αs is studied. Our results are consistent with the running of αs as predicted by QCD and show that within the uncertainties of our analysis event shapes in hadronic Z decays with hard and
isolated photon radiation can be described by QCD at reduced centre-of-mass energies. Combining all values from different
event shape observables and energies gives αs(MZ)=0.1182±0.0015(stat.)±0.0101(syst.).
European Physical Journal C 04/2012; 53(1):21-39. · 3.63 Impact Factor
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G. Abbiendi,
C. Ainsley,
P.F. Åkesson,
G. Alexander,
G. Anagnostou,
K.J. Anderson,
S. Asai,
D. Axen,
I. Bailey,
E. Barberio, [......],
T. Wengler,
N. Wermes,
G.W. Wilson,
J.A. Wilson,
G. Wolf,
T.R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic,
The OPAL Collaboration
[show abstract]
[hide abstract]
ABSTRACT: Data from e+e- annihilation into hadrons at centre-of-mass energies between 91GeV and 209GeV collected with the OPAL detector at LEP,
are used to study the four-jet rate as a function of the Durham algorithm resolution parameter ycut. The four-jet rate is compared to next-to-leading order calculations that include the resummation of large logarithms. The
strong coupling measured from the four-jet rate is
a\textS(M\textZ0)=0.1182±0.0003(\textstat.)±0.0015(\textexp.) ±0.0011(\texthad.)±0.0012(\textscale)±0.0013(\textmass),\alpha_{\text{S}(M_{\text{Z}^0})}=0.1182\pm0.0003(\text{stat.})\pm0.0015(\text{exp.}) \pm0.0011(\text{had.})\pm0.0012(\text{scale})\pm0.0013(\text{mass}),
in agreement with the world average. Next-to-leading order fits to the D-parameter and thrust minor event-shape observables
are also performed for the first time. We find consistent results, but with significantly larger theoretical uncertainties.
European Physical Journal C 04/2012; 47(2):295-307. · 3.63 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Thermodynamic measurements of an organic spin liquid compound of κ-(BEDT-TTF)2Cu2(CN)3 where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene were performed by the ac calorimetry technique using a microchip device of TCG3880. This technique is effective to measure relative temperature and magnetic-field dependences of heat capacity for tiny single crystal samples less than 1μg. Broad hump structures in Cp vs T which are known as so-called 6 K anomaly were observed in κ-(BEDT-TTF)2Cu2(CN)3 and its deuterated compound. The hump temperatures are evaluated as 5.7 K in both compounds. This result demonstrates that the TCG3880 is useful for performing thermodynamic investigations of such kind of organic charge transfer complexes with much reduced sample quantity than the conventional techniques and that the existence of hump structure is intrinsic for κ-(BEDT-TTF)2Cu2(CN)3. The in-plane angular dependence of the magnetic field of 7 T applied parallel to the two dimensional layer is also studied and absence of in-plane anisotropy of the hump structure is discussed in both pristine and deuterated compounds.
Journal of Physics Conference Series 09/2011; 320(1):012027.
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[show abstract]
[hide abstract]
ABSTRACT: A low-temperature thermodynamic investigation on an organic superconductor κ-(BEDT-TTF)2Ag(CN)2H2O is performed under pressure and with magnetic fields. Using the ac-modulation technique available under pressures, we have succeeded to detect the thermal anomaly being associated with the superconducting transition. The thermal anomaly was found to be sensitive to the external magnetic fields at ambient pressure. We have observed that this anomaly disappears under pressure of 0.4 GPa which suggests that the superconducting ground state is transformed into the normal metallic state by the application of the pressure. The observed feature is consistent with the scenario of Mott-Hubbard physics realized due to the strong electron correlations in the dimerized BEDT-TTF salts.
Journal of Physics Conference Series 10/2008; 132(1):012010.
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G. Abbiendi,
C. Ainsley,
P.F. Åkesson,
G. Alexander,
G. Anagnostou,
K.J. Anderson,
S. Asai,
D. Axen,
I. Bailey,
E. Barberio, [......],
T. Wengler,
N. Wermes,
G.W. Wilson,
J.A. Wilson,
G. Wolf,
T.R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic,
The OPAL Collaboration
[show abstract]
[hide abstract]
ABSTRACT: From a total data sample of 701.1pb-1 recorded with e+e- centre-of-mass energies of Ös =\sqrt{s} =161–209GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected. These data are used to obtain measurements
of the W-pair production cross sections at 10 different centre-of-mass energies. The ratio of the measured cross sections
to the standard model expectation is found to be:
\textdata/\textSM = 1.002±0.011 (\textstat.) ±0.007 (\textsyst.) ±0.005 (\texttheory){\text{data}}/{{\text{SM}}} = 1.002\pm0.011 ({\text{stat.}}) \pm0.007 ({\text{syst.}}) \pm0.005 ({\text{theory}}), where the uncertainties are statistical, experimental systematics and theory systematics respectively. The data are used
to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current
interaction. Assuming lepton universality, the branching ratio to hadrons is determined to be 67.41±0.37(stat.)±0.23(syst.)%,
from which the CKM matrix element |Vcs| is determined to be 0.969±0.017(stat.)±0.012(syst.). The differential cross section as a function of the W- production angle is measured for the qqeν and qqμν final states. The results described in this paper are consistent with
the expectations from the standard model.
European Physical Journal C 11/2007; 52(4):767-785. · 3.63 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We have proposed a novel structure of one dimensional spatial light phase modulator (SLPM) that consists of a micromirror array on an SOI wafer and ITO (Indium Tin Oxide) electrodes on a glass plate. Each micromirror can exhibit bidirectional single-axis rotation, as well as up- and down- translation motion. We have fabricated the device, and confirmed its motion experimentally.
Solid-State Sensors, Actuators and Microsystems Conference, 2007. TRANSDUCERS 2007. International; 07/2007
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[show abstract]
[hide abstract]
ABSTRACT: SUMMARY1. The antiarrhythmic properties of 5–(3-tert-butylarnino-2-hydroxy)propoxy-3,4-dihydrocarbostyril hydrochloride (OPC-1085) were compared with those of propranolol and pindolol using various kinds of preparations for experimental arrhythmia in dogs.2. Although OPC-1085 was the most potent drug to antagonize adrenaline-induced arrhythmia in animals anaesthetized with either pentobarbitone sodium or halothane, it was scarcely effective on ouabain-induced arrhythmia in pentobarbitone sodium anaesthetized animals.3. When these compounds were administered intravenously to conscious dogs 24 h after two-stage ligation of the anterior descending artery, ectopic ventricular beats of coronary ligation-induced arrhythmia were reduced while regular sinus beats were simultaneously increased.4. OPC-1085 was very effective on aconitine-induced arrhythmia in dogs anaesthetized with pentobarbitone sodium. The effective dose was similar to that of propranolol but about fifteen times less than that of pindolol.5. It is concluded that different potencies among these β-adrenoreceptor antagonists against various kinds of experimental arrhythmias cannot be simply deduced from any one of the following properties; β-adrenoreceptor antagonism, intrinsic myocardial stimulation, local anaesthetic and so-called quinidine-like effects.
Clinical and Experimental Pharmacology and Physiology 06/2007; 4(6):545 - 559. · 1.85 Impact Factor
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G. Abbiendi,
C. Ainsley,
P.F. Åkesson,
G. Alexander,
G. Anagnostou,
K.J. Anderson,
S. Asai,
D. Axen,
I. Bailey,
E. Barberio, [......],
T. Wengler,
N. Wermes,
G.W. Wilson,
J.A. Wilson,
G. Wolf,
T.R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic,
The OPAL Collaboration
[show abstract]
[hide abstract]
ABSTRACT: This paper describes a topological search for an invisibly decaying Higgs boson, H, produced via the Bjorken process (e+e-→HZ). The analysis is based on data recorded using the OPAL detector at LEP at centre-of-mass energies from 183 to 209GeV
corresponding to a total integrated luminosity of 629pb-1. In the analysis only hadronic decays of the Z boson are considered. A scan over Higgs boson masses from 1 to 120GeV and
decay widths from 1 to 3000GeV revealed no indication for a signal in the data. From a likelihood ratio of expected signal
and standard model background we determine upper limits on cross-section times branching ratio to an invisible final state.
For moderate Higgs boson decay widths, these range from about 0.07pb (MH=60GeV) to 0.57pb (MH=114GeV). For decay widths above 200GeV the upper limits are of the order of 0.15pb. The results can be interpreted in
general scenarios predicting a large invisible decay width of the Higgs boson. As an example we interpret the results in the
so-called stealthy Higgs scenario. The limits from this analysis exclude a large part of the parameter range of this scenario
experimentally accessible at LEP 2.
European Physical Journal C 12/2006; 49(2):457-472. · 3.63 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: This paper describes construction of the M-CubITS pedestrian WYSIWYAS navigation system both in outdoor and indoor areas, toward realization of the M-CubITS pedestrian WYSIWYAS navigation environment. In outdoor navigation, we construct the experimental Saitama University campus outdoor navigation system "CamNavi" using ordinary mobile phone terminals as users' terminals and the i-application platform provided by Japanese NTT DoCoMo. Here, our studies on the outdoor system are mainly based on image processing for outdoor M-CubITS elements and a user interface for the mobile phone terminals. On the other hand, in indoor navigation, we also introduce the route guidance using the Dijkstra method and study databases. Then, we construct an experimental system at the seven-storied buildings in the faculty of engineering, Saitama University, and check the system operation
Intelligent Transportation Systems Conference, 2006. ITSC '06. IEEE; 10/2006
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[show abstract]
[hide abstract]
ABSTRACT: SOFCs have a potential of showing extraordinarily high electric conversion efficiency. Thus they are considered as promising candidates for future distributed generators. However operations of SOFCs are not simple compared with the other generators such as gas engines or gas turbine since SOFCs have to be operated at a high temperature. It is difficult to start up SOFCs rapidly and thus they are not suitable for situations where there is a large fluctuation of demand. This limits the application of SOFCs and the introduction is restricted within a narrow market. In order to promote the introduction of SOFCs to a market, how to make use of SOFCs is a very significant factor. Techniques to operate and control SOFCs are key factors to draw the potential of SOFCs. Therefore information technologies are expected as a powerful tool to improve the total performance of SOFCs.
Industrial Informatics, 2006 IEEE International Conference on; 09/2006
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[show abstract]
[hide abstract]
ABSTRACT: An (n,1,p)-quantum random access (QRA) coding, introduced by Ambainis et al (1999 ACM Symp. Theory of Computing p 376), is the following communication system: the sender which has n-bit information encodes his/her information into one qubit, which is sent to the receiver. The receiver can recover any one bit of the original n bits correctly with probability at least p, through a certain decoding process based on positive operator-valued measures. Actually, Ambainis et al shows the existence of a (2,1,0.85)-QRA coding and also proves the impossibility of its classical counterpart. Chuang immediately extends it to a (3,1,0.79)-QRA coding and whether or not a (4,1,p)-QRA coding such that p > 1/2 exists has been open since then. This paper gives a negative answer to this open question. Moreover, we generalize its negative answer for one-qubit encoding to the case of multiple-qubit encoding
New Journal of Physics 08/2006; 8(8):129. · 4.18 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: In a partially reconfigurable FPGA, arbitrary portions of its logic resources and interconnection networks can be reconfigured without affecting the other parts. Thus, several tasks can be mapped and executed concurrently in the FPGA. In order to execute the tasks efficiently using the limited resources of the FPGA, resource management becomes very important. Although some online FPGA placement methods have, recently, been proposed, they cannot handle I/O communications of the tasks. Taking such I/O communications into consideration, we introduce a new approach to online FPGA placement. We present a task placement algorithm which uses I/O routing information of each empty area to select a suitable area for each task. The algorithm uses a combination of two new fitting strategies and modified versions of two existing strategies.
Information Sciences and Systems, 2006 40th Annual Conference on; 04/2006
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[show abstract]
[hide abstract]
ABSTRACT: Abnormal phenomenon of output voltage is observed in a paralleled N+1 redundant DC-DC converter (DDC) system. The phenomenon is caused by a current sharing control under the condition of periodic load change, resulting in output-voltage increase. The mechanism of the phenomenon is analyzed with a circuit simulator and confirmed by experiment. A new type of current sharing circuit is proposed to solve the problem
Telecommunications Conference, 2005. INTELEC '05. Twenty-Seventh International; 10/2005
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[show abstract]
[hide abstract]
ABSTRACT: We measured the specific heat Cp of an annealed sample of CePt3Si in magnetic fields B up to 10 T and confirmed two conspicuous anomalies in the temperature range where no apparent magnetic anomalies were found in the susceptibility. The lower-temperature anomaly at 2.2 K was depressed with increasing B and seemed to get absorbed around 4 T into the other one around 2.8 K. The latter anomaly continues to grow into a solid peak with increasing B. These features imply that neither of these transitions is due to long-range antiferromagnetism (AF) as originally proposed, but they are reminiscent of quadrupolar transitions found in certain Ce-based Kondo compounds, in which two distinct anomalies were also observed in Cp and identified as a quadrupolar transition followed by an AF transition at a slightly lower T. In the case of CePt3Si, the lower-T anomaly is not due to AF but to a new phase transition of yet-unknown nature, and in this new phase the superconductivity emerges at 0.8 K. We thereby hypothesize that the superconductivity could be mediated by magnetic or other electronic excitations under the influence of the quadrupolar-like order induced around 2.8 K and that CePt3Si would be the first example of an unconventional superconductor coexisting with electric-multipolar order.
Journal of Physics Condensed Matter 05/2005; 17(23):L231. · 2.55 Impact Factor
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G. Abbiendi,
C. Ainsley,
P. F. Åkesson,
G. Alexander,
J. Allison,
P. Amaral,
G. Anagnostou,
K. J. Anderson,
S. Asai,
D. Axen, [......],
P. S. Wells,
T. Wengler,
N. Wermes,
G. W. Wilson,
J. A. Wilson,
G. Wolf,
T. R. Wyatt, S. Yamashita,
D. Zer-Zion,
L. Zivkovic
[show abstract]
[hide abstract]
ABSTRACT: Anomalous quartic couplings between the electroweak gauge bosons may contribute to the νν̅ γγ and qq̅ γγ final states produced in e+e- collisions. This analysis uses the LEP2 OPAL data sample at center-of-mass energies up to 209 GeV. Event selections identify νν̅ γγ and qq̅ γγ events in which the two photons are reconstructed within the detector acceptance. The cross section for the process e+e-→qq̅ γγ is measured. Averaging over all energies, the ratio of the observed e+e-→qq̅ γγ cross section to the standard model expectation is R(data/SM)=0.92±0.07±0.04, where the errors represent the statistical and systematic uncertainties respectively. The νν̅ γγ and qq̅ γγ data are used to constrain possible anomalous W+W-γγ and ZZγγ couplings. Combining with previous OPAL results from the W+W-γ final state, the 95% confidence level limits on the anomalous coupling parameters a0Z, acZ, a0W and acW are found to be -0.007 GeV-2<a0Z/Λ2<0.023 GeV-2, -0.029 GeV-2<acZ/Λ2<0.029 GeV-2, -0.020 GeV-2<a0W/Λ2<0.020 GeV-2, -0.052 GeV-2<acW/Λ2<0.037 GeV-2, where Λ is the energy scale of the new physics. Limits found when allowing two or more parameters to vary are also presented.
Phys. Rev. D. 08/2004; 70(3).
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[show abstract]
[hide abstract]
ABSTRACT: We demonstrate passive mode-locking of short-cavity (/spl sim/2 cm) fiber Fabry-Perot laser by incorporating carbon nanotubes as a saturable absorber. Stable pulses are generated with pulsewidth as short as 0.68 ps and repetition rate as high as 5.18 GHz.
Lasers and Electro-Optics, 2004. (CLEO). Conference on; 06/2004
