Biomedical subjects

A Anastassov

Publications and source records attributed to A Anastassov.

At least 55 records · Page 3Linked to original sources

PubMed2005

First measurements of inclusive W and Z cross sections from run II of the fermilab tevatron collider.

We report the first measurements of inclusive W and Z cross sections times leptonic branching ratios for pp collisions at square root[s]=1.96 TeV, based on their decays to electrons and muons. The data correspond to an integrated luminosity of 72 pb(-1) recorded with the CDF detector at the Fermilab Tevatron. We test e-mu universality in W decays, and we measure the ratio of leptonic W and Z rates from which the leptonic branching fraction B(W-->lnu) can be extracted as well as an indirect value for the total width of the W and the Cabibbo-Kobayashi-Maskawa matrix element, |V(cs)|.

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PubMed2005

Measurement of Wgamma and Zgamma production in pp collisions at square root s=1.96 TeV.

The standard model predictions for Wgamma and Zgamma production are tested using an integrated luminosity of 200 pb(-1) of pp collision data collected at the Collider Detector at Fermilab. The cross sections are measured by selecting leptonic decays of the W and Z bosons, and photons with transverse energy ET>7 GeV that are well separated from leptons. The production cross sections and kinematic distributions for the Wgamma and Zgamma data are compared to SM predictions.

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PubMed2004

Search for doubly charged Higgs bosons decaying to dileptons in pp collisions at square root of s=1.96 TeV.

We present the results of a search for doubly charged Higgs bosons (H+/-+/-) decaying to dileptons (ll(')) using approximately 240 pb(-1) of pp collision data collected by the CDF II experiment at the Fermilab Tevatron. In our search region, given by same-sign ll(') mass m(ll('))>80 GeV/c(2) (100 GeV/c(2) for ee channel), we observe no evidence for H+/-+/- production. We set limits on sigma(pp -->H++H---->l(+)l('+)l(-)l('-)) as a function of the mass of the H+/-+/- and the chirality of its couplings. Assuming exclusive same-sign dilepton decays, we derive lower mass limits on H(+/-+/-)(L) of 133, 136, and 115 GeV/c(2) in the ee, mumu, and emu channels, respectively, and a lower mass limit of 113 GeV/c(2) on H(+/-+/-)(R) in the mumu channel, all at the 95% confidence level.

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PubMed2004

Measurement of the tt production cross section in pp collisions at sqrt[s]=1.96 TeV using dilepton events.

We report a measurement of the tt production cross section using dilepton events with jets and missing transverse energy in pp collisions at a center-of-mass energy of 1.96 TeV. Using a 197+/-12 pb(-1) data sample recorded by the upgraded Collider Detector at Fermilab, we use two complementary techniques to select candidate events. We compare the number of observed events and selected kinematical distributions with the predictions of the standard model and find good agreement. The combined result of the two techniques yields a tt production cross section of 7.0(+2.4)(-2.1)(stat)+1.6-1.1(syst)+/-0.4(lum) pb.

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PubMed2004

Observation of the narrow state X(3872)-->J/psipi+pi- in pp collisions at sqaure root of s=1.96 TeV.

We report the observation of a narrow state decaying into J/psipi+pi- and produced in 220 pb(-1) of p p-bar collisions at =1.96 Tesqaure root of sV in the CDF II experiment. We observe 730+/-90 decays. The mass is measured to be 3871.3+/-0.7(stat)+/-0.4(syst) MeV/c2, with an observed width consistent with the detector resolution. This is in agreement with the recent observation by the Belle Collaboration of the X(3872) meson.

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PubMed2004

Search for B0s-->micro+micro- and B0d-->micro+micro- decays in pp collisions at square root s = 1.96 TeV.

We report on a search for B(0)(s)-->micro(+)micro(-) and B(0)(d)-->micro(+)micro(-) decays in pp collisions at square root of s=1.96 TeV using 171 pb(-1) of data collected by the CDF II experiment at the Fermilab Tevatron Collider. The decay rates of these rare processes are sensitive to contributions from physics beyond the standard model. One event survives all our selection requirements, consistent with the background expectation. We derive branching ratio limits of B(B(0)(s)-->micro(+)micro(-))<5.8x10(-7) and B(B(0)(d)-->micro(+)micro(-))<1.5x10(-7) at 90% confidence level.

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PubMed2003

Measurement of prompt charm meson production cross sections in pp collisions at square root s = 1.96 TeV.

We report on measurements of differential cross sections dsigma/dp(T) for prompt charm meson production in ppmacr; collisions at sqrt[s]=1.96 TeV using 5.8+/-0.3 pb(-1) of data from the CDF II detector at the Fermilab Tevatron. The data are collected with a new trigger that is sensitive to the long lifetime of hadrons containing heavy flavor. The charm meson cross sections are measured in the central rapidity region |y|</=1 in four fully reconstructed decay modes: D0-->K-pi(+), D(*+)-->D0pi(+), D+-->K-pi(+)pi(+), D(+)(s)-->phipi(+), and their charge conjugates. The measured cross sections are compared to theoretical calculations.

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PubMed2001

Search for the familon via B(+/-) --> pi+/-X(0), B(+/-) --> K(+/-)X(0), and B(0) --> K(0)(S)X(0) decays.

We have searched for the two-body decay of the B meson to a light pseudoscalar meson h = pi(+/-),K+/-,K(0)(S) and a massless neutral feebly interacting particle X(0) such as the familon, the Nambu-Goldstone boson associated with a spontaneously broken global family symmetry. We find no significant signal by analyzing a data sample containing 9.7x10(6) BBbar mesons collected with the CLEO detector at the Cornell Electron Storage Ring, and set 90% C.L. upper limits italicB(B(+/-) --> h(+/-)X(0)) = 4.9x10(-5) and italicB(B(0) --> K(0)(S)X(0)) = 5.3x10(-5). These limits correspond to a lower bound of approximately 10(8) GeV on the family symmetry breaking scale with vector coupling involving the third generation of quarks.

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PubMed2001

First measurement of gamma(D*(+)).

We present the first measurement of the D*(+) width using 9/fb of e(+)e(-) data collected near the Upsilon(4S) resonance by the CLEO II.V detector. Our method uses advanced tracking techniques and a reconstruction method that takes advantage of the small vertical size of the Cornell Electron-positron Storage Ring beam spot to measure the energy release distribution from the D*(+)-->D(0)pi(+) decay. We find gamma(D*(+)) = 96+/-4 (stat)+/-22 (syst) keV. We also measure the energy release in the decay and compute Delta m identical with m(D*(+))-m(D(0)) = 145.412+/-0.002 (stat)+/-0.012 (syst) MeV/c(2).

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PubMed2001

Rate measurement of D(0)-->K+pi(-)pi(0) and constraints on D(0) -- D(0) mixing.

We present an observation and time-integrated rate measurement of the decay D(0)-->K(+)pi(-)pi(0) produced in 9 fb(-1) of e(+)e(-) collisions near the Upsilon(4S) resonance. The signal is inconsistent with an upward fluctuation of the background by 4.9 standard deviations. We measured the time-integrated rate of D(0)-->K(+)pi(-)pi(0) normalized to the rate of D(0)-->K(+)pi(-)pi(0) to be 0.0043(+0.0011)(-0.0010) (stat)+/-0.0007 (syst). This decay can be produced by doubly Cabibbo-suppressed decays or by the D(0) evolving into a D(0) through mixing, followed by a Cabibbo-favored decay to K(+)pi(-)pi(0). We also found the CP asymmetry A = (9(+25)(-22))% be consistent with zero.

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PubMed2001

Experimental investigation of the two-photon widths of the chi(c0) and the chi(c2) mesons.

Using 12.7 fb(-1) of data collected with the CLEO detector at CESR, we observed two-photon production of the cc states chi(c0) and chi(c2) in their decay to pi(+)pi(-)pi(+)pi(-). We measured gamma(gammagamma)(chi(c))xB(chi(c)-->pi(+)pi(-)pi(+)pi(-)) to be 75+/-13(stat)+/-8(syst) eV for the chi(c0) and 6.4+/-1.8(stat)+/-0.8(syst) eV for the chi(c2), implying gamma(gammagamma)(chi(c0)) = 3.76+/-0.65(stat)+/-0.41(syst)+/-1.69(br) keV and gamma(gammagamma)(chi(c2)) = 0.53+/-0.15(stat)+/-0.06(syst)+/-0.22(br) keV. Also, cancellation of dominant experimental and theoretical uncertainties permits a precise comparison of gamma(gammagamma)(chi(c0))/gamma(gammagamma)(chi(c2)), evaluated to be 7.4+/-2.4(stat)+/-0.5(syst)+/-0.9(br), with QCD-based predictions.

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PubMed2001

Study of tau decays to six pions and a neutrino.

The tau decays to six-pion final states have been studied with the CLEO detector at the Cornell Electron Storage Ring. The measured branching fractions are B(tau(-)-->2pi(-)pi(+)3pi(0)nu(tau)) = (2.2+/-0.3+/-0.4)x10(-4) and B(tau(-)-->3pi(-)2pi(+)pi(0)nu(tau)) = (1.7+/-0.2+/-0.2)x10(-4). A search for substructure in these decays shows that they are saturated by intermediate states with eta or omega mesons. We present the first observation of the decay tau(-)-->2pi(-)pi(+)omega(nu)tau and the branching fraction is measured to be (1.2+/-0.2+/-0.1)x10(-4). The measured branching fractions are in good agreement with the isospin expectations but somewhat below the conserved-vector-current predictions.

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PubMed2001

Observation of B --> phiK and B --> phiK*.

We have studied two-body charmless hadronic decays of B mesons into the final states straight phiK and phiK(*). Using 9.7 million B&Bmacr; pairs collected with the CLEO II detector, we observe the decays B- --> phiK- and B0--> phiK(*0) with the following branching fractions: B(B--->phiK-) = (5.5(+2.1)(-1.8)+/-0.6)x10(-6) and B(B0--> phiK(*0)) = (11.5(+4.5+1.8)(-3.7-1.7))x10(-6). We also see evidence for the decays B0-->phiK0 and B---> phiK(*-). However, since the statistical significance is not overwhelming for these modes, we determine upper limits of <12.3x10(-6) and <22.5x10(-6) ( 90% confidence level), respectively.

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PubMed2001

Search for B --> tau(nu) and B --> K(nu)nu.

We report results of a search for B-->tau(nu) in a sample of 9.7 x 10(6) charged B meson decays. We exclusively reconstruct the companion B decay to suppress background. We set an upper limit on the branching fraction B(B-->tau(nu))<8.4 x 10(-4) at 90% confidence level. We also establish B(B+/--->K+/-nu(nu))<2.4 x 10(-4) at 90% confidence level.

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PubMed2001

First observation of the decays B(0) --> D(-)p_p pi+ and B(0) --> D(-)p_n.

We report the first observation of exclusive decays of the type B-->D(*)N_NX, where N is a nucleon. Using a sample of 9.7x10(6)B_B pairs collected with the CLEO detector operating at the Cornell Electron Storage Ring, we measure the branching fractions B(B0-->D(*-)p_p pi(+)) = (6.5(+1.3)(-1.2)+/-1.0)x10(-4) and B(B0-->D(*-)p_n) = (14.5(+3.4)(-3.0)+/-2.7)x10(-4). Antineutrons are identified by their annihilation in the CsI electromagnetic calorimeter.

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PubMed2001

Measurement of the relative branching fraction of upsilon(4S) to charged and neutral B-meson pairs.

We analyze 9.7x10(6) B_B pairs recorded with the CLEO detector to determine the production ratio of charged to neutral B-meson pairs produced at the Upsilon(4S) resonance. We measure the rates for B0-->J/psiK((*)0) and B+-->J/psiK((*)+) decays and use the world-average B-meson lifetime ratio to extract the relative widths f(+-) / f(00) = gamma(Upsilon(4S)-->B+B-) / gamma(Upsilon(4S)-->B0 B-0)) = 1.04+/-0.07(stat)+/-0.04(syst). With the assumption that f(+-)+f(00) = 1, we obtain f(00) = 0.49+/-0.02(stat)+/-0.01(syst) and f(+-) = 0.51+/-0.02(stat)+/-0.01(syst). This production ratio and its uncertainty apply to all exclusive B-meson branching fractions measured at the Upsilon(4S) resonance.

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PubMed2001

First observation of the sigma(+)(c) baryon and a new measurement of the sigma(+)(c) mass.

Using data recorded with the CLEO II and CLEO II.V detector configurations at the Cornell Electron Storage Rings, we report the first observation and mass measurement of the Sigma(*+)(c) charmed baryon, and an updated measurement of the mass of the Sigma(+)(c) baryon. We find M(Sigma(*+)(c))-M(Lambda(+)(c)) = (231.0+/-1.1+/-2.0) MeV, and M(Sigma(+)(c))-M(Lambda(+)(c)) = (166.4+/-0.2+/-0.3) MeV, where the errors are statistical and systematic, respectively.

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PubMed2001

Study of B Decays to Charmonium States: B-->eta(c)K and B --> chi(c0)K.

In a sample of 9.66x10(6)B&Bmacr; pairs collected with the CLEO detector we make the first observation of B decays to an eta(c) and a kaon. We measure branching fractions B(B+-->eta(c)K+) = (0.69(+0.26)(-0.21)+/-0.08+/-0.20)x10(-3) and B(B degrees -->eta(c)K degrees ) = (1.09(+0.55)(-0.42)+/-0.12+/-0.31)x10(-3), where the first error is statistical, the second is systematic, and the third is from the eta(c) branching fraction uncertainty. From these we extract the eta(c) decay constant in the factorization approximation, f(eta(c)) = 335+/-75 MeV. We also search for B decays to a chi(c0) and a kaon. No evidence for a signal is found and we set 90% C.L. upper limits: B(B+-->chi(c0)K+)<4.8x10(-4) and B(B degrees -->chi(c0)K degrees )<5.0x10(-4).

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