Studies on Pseudoscalar Meson Bound States and Semileptonic Decays in a Relativistic Potential Model

In this thesis quark-antiquark bound states are considered using a relativistic two-body equation for Dirac particles. The mass spectrum of mesons includes bound states involving two heavy quarks or one heavy and one light quark. In order to analyse these states within a unified formalism, it is desirable to have a two-fermion equation that limits to one body Dirac equation with a static interaction for the light quark when the other particle's mass tends to infinity. A suitable two-body equation has been developed by Mandelzweig and Wallace. This equation is solved in momentum space and is used to describe the complete spectrum of mesons. The potential used in this work contains a short range one-gluon exchange interaction and a long range linear confining and constant potential terms. This model is used to investigate the decay processes of heavy mesons. Semileptonic decays are more tractable since there is no final state interactions between the leptons and hadrons that would otherwise complicate the situation. Studies on B and D meson decays are helpful to understand the nonperturbative strong interactions of heavy mesons, which in turn is useful to extract the details of weak interaction process. Calculation of form factors of these semileptonic decays of pseudo scalar mesons are also presented.

Measurement of the B-s(0) lifetime using semileptonic decays

We report a measurement of the B-s(0) lifetime in the semileptonic decay channel B-s(0)-> D-s(-)mu(+)nu X (and its charge conjugate), using approximately 0.4 fb(-1) of data collected with the D0 detector during 2002-2004. Using 5176 reconstructed D-s(-)mu(+) signal events, we have measured the B-s(0) lifetime to be tau(B-s(0))=1.398 +/- 0.044(stat)(-0.025)(+0.028)(syst) ps. This is the most precise measurement of the B-s(0) lifetime to date.

Measurement of the Lambda(0)(b) lifetime using semileptonic decays

We report a measurement of the Lambda(0)(b) lifetime using a sample corresponding to 1.3 fb(-1) of data collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron collider. The Lambda(0)(b) baryon is reconstructed via the decay Lambda(0)(b)->mu(nu) over bar Lambda X-+(c). Using 4437 +/- 329 signal candidates, we measure the Lambda(0)(b) lifetime to be tau(Lambda(0)(b))=1.290(-0.110)(+0.119)(stat)(-0.091)(+0.087)(syst) ps, which is among the most precise measurements in semileptonic Lambda(0)(b) decays. This result is in good agreement with the world average value.

Measurement of Bottom Versus Charm as a Function of Transverse Momentum with Electron-Hadron Correlations in p plus p Collisions at s=200 GeV

The momentum distribution of electrons from semileptonic decays of charm and bottom quarks for midrapidity |y|< 0.35 in p+p collisions at s=200 GeV is measured by the PHENIX experiment at the Relativistic Heavy Ion Collider over the transverse momentum range 2 < p(T)< 7 GeV/c. The ratio of the yield of electrons from bottom to that from charm is presented. The ratio is determined using partial D/D -> e(+/-)K(-/+)X (K unidentified) reconstruction. It is found that the yield of electrons from bottom becomes significant above 4 GeV/c in p(T). A fixed-order-plus-next-to-leading-log perturbative quantum chromodynamics calculation agrees with the data within the theoretical and experimental uncertainties. The extracted total bottom production cross section at this energy is sigma(bb)=3.2(-1.1)(+1.2)(stat)(-1.3)(+1.4)(syst)mu b.

Measurement of the Bottom Quark Contribution to Nonphotonic Electron Production in p plus p Collisions at root s=200 GeV

The contribution of B meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in p + p collisions at root s = 200 GeV has been measured using azimuthal correlations between nonphotonic electrons and hadrons. The extracted B decay contribution is approximately 50% at a transverse momentum of p(T) >= 5 GeV/c. These measurements constrain the nuclear modification factor for electrons from B and D meson decays. The result indicates that B meson production in heavy ion collisions is also suppressed at high p(T).

Scalar resonances in a unitary pi pi S-wave model for D(+)->pi(+)pi(-)pi(+)

We propose a model for D(+)->pi(+)pi(-)pi(+) decays following experimental results which indicate that the two-pion interaction in the S wave is dominated by the scalar resonances f(0)(600)/sigma and f(0)(980). The weak decay amplitude for D(+)-> R pi(+), where R is a resonance that subsequently decays into pi(+)pi(-), is constructed in a factorization approach. In the S wave, we implement the strong decay R ->pi(+)pi(-) by means of a scalar form factor. This provides a unitary description of the pion-pion interaction in the entire kinematically allowed mass range m(pi pi)(2) from threshold to about 3 GeV(2). In order to reproduce the experimental Dalitz plot for D(+)->pi(+)pi(-)pi(+), we include contributions beyond the S wave. For the P wave, dominated by the rho(770)(0), we use a Breit-Wigner description. Higher waves are accounted for by using the usual isobar prescription for the f(2)(1270) and rho(1450)(0). The major achievement is a good reproduction of the experimental m(pi pi)(2) distribution, and of the partial as well as the total D(+)->pi(+)pi(-)pi(+) branching ratios. Our values are generally smaller than the experimental ones. We discuss this shortcoming and, as a by-product, we predict a value for the poorly known D ->sigma transition form factor at q(2)=m pi(2).

Mesure du rapport d'embranchement des désintégrations B^0--> pi^- l^+v et B^+--> êta^(') l^+v, du spectre des facteurs de forme des désintégrations B^0--> pi^- l^+v et B^+--> êta l^+v, et extraction de |V_ub| dans l'expérience BABAR

Nous rapportons les résultats d'une étude des désintégrations semileptoniques non-charmées B^+--> êta^(') l^+v et B^0--> pi^- l^+v, mesurés par le détecteur BABAR avec une production d'environ 464 millions de paires de mésons BBbar issues des collisions e^+e^- à la résonance Upsilon(4S). L'analyse reconstruit les événements avec une technique relâchée des neutrinos. Nous obtenons les rapports d'embranchement partiels pour les désintégrations B^+--> êta l^+v et B^0--> pi^- l^+v en trois et douze intervalles de q^2, respectivement, à partir desquels nous extrayons les facteurs de forme f_+(q^2) et les rapports d'embranchement totaux B(B^+--> êta l^+v) = (3.39 +/- 0.46_stat +/- 0.47_syst) x 10^-5 et B(B^0--> pi^- l^+v) = (1.42 +/- 0.05_stat +/- 0.08_syst) x 10^-4. Nous mesurons aussi B(B^+--> êta' l^+v) = (2.43 +/- 0.80_stat +/- 0.34_syst) x 10^-5. Nous obtenons les valeurs de la norme de l'élément |V_ub| de la matrice CKM en utilisant trois calculs différents de la CDQ.

Dilepton mass spectra in p plus p collisions at root s=200 GeV

PHENIX has measured the electron-positron pair mass spectrum from 0 to 8 GeV/c(2) in p + p collisions at root s = 200 GeV. The contributions from light meson decays to e(+)e(-) pairs have been determined based on measurements of hadron production cross sections by PHENIX. Within the systematic uncertainty of similar to 20% they account for all e(+)e(-) pairs in the mass region below similar to 1 GeV/c(2). The e(+)e(-) pair yield remaining after subtracting these contributions is dominated by semileptonic decays of charmed hadrons correlated through flavor conservation. Using the spectral shape predicted by PYTHIA, we estimate the charm production cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) pb. which is consistent with QCD calculations and measurements of single leptons by PHENIX. (C) 2008 Elsevier BV. All rights reserved.

Search for anomalous heavy-flavor quark production in association with W bosons

We search for anomalous production of heavy-flavor quark jets in association with W bosons at the Fermilab Tevatron p(p) over bar Collider in final states in which the heavy-flavor quark content is enhanced by requiring at least one tagged jet in an event. Jets are tagged using one algorithm based on semileptonic decays of b/c hadrons, and another on their lifetimes. We compare e+jets (164 pb(-1)) and mu+jets (145 pb(-1)) channels collected with the D0 detector at root s = 1.96 TeV to expectations from the standard model and set upper limits on anomalous production of such events.

Combined D0 measurements constraining the CP-violating phase and width difference in the B-s(0) system

We combine the D0 measurement of the width difference between the light and heavy B-s(0) mass eigenstates and of the CP-violating mixing phase determined from the time-dependent angular distributions in the B-s(0)-> J/psi phi decays along with the charge asymmetry in semileptonic decays also measured with the D0 detector. With the additional constraint from the world average of the flavor-specific B-s(0) lifetime, we obtain Delta Gamma(s)equivalent to(Gamma(L)-Gamma(H))=0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=0.70(-0.47)(+0.39) or Delta Gamma(s)=-0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=2.44(-0.39)(+0.47). The data sample corresponds to an integrated luminosity of 1.1 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron Collider.

Measurement of the Lambda(0)(b) lifetime in the decay Lambda(0)(b)-> J/psi Lambda(0) with the D0 detector

We present measurements of the Lambda(b)(0) lifetime in the exclusive decay channel Lambda(b)(0)-> J/psi Lambda(0), with J/psi ->mu(+)mu(-) and Lambda(0)-> p pi(-), the B-0 lifetime in the decay B-0-> J/psi K-S(0) with J/psi ->mu(+)mu(-) and K-S(0)->pi(+)pi(-), and the ratio of these lifetimes. The analysis is based on approximately 250 pb(-1) of data recorded with the D0 detector in p (p) over bar collisions at root s = 1.96 TeV. The Lambda(b)(0) lifetime is determined to be tau(Lambda(b)(0))=1.22(-0.18)(+0.22)(stat)+/- 0.04(syst) ps, the B-0 lifetime tau(B-0)=1.40(-) (+0.11)(0.10)(stat)+/- 0.03(syst) ps, and the ratio tau(Lambda(b)(0))/tau(B-0)=0.87(-) (+0.17)(0.14)(stat)+/- 0.03(syst). In contrast with previous measurements using semileptonic decays, this is the first determination of the Lambda(b)(0) lifetime based on a fully reconstructed decay channel.

Measurement of the lifetime difference in the B-s(0) system

We present a study of the decay B-s(0)-> J/psi phi. We obtain the CP-odd fraction in the final state at time zero R-perpendicular to = 0.16 +/- 0.10 (stat) +/- 0.02(syst), the average lifetime of the (B-s(0), (B) over bar (0)(s)) system, (tau) over bar (B-s(0)) = 1.39(-0.16)(+0.13)(stat)(-0.02)(+0.01)(syst) ps, and the relative width difference between the heavy and light mass eigen-states, Delta Gamma/(Gamma) over bar = (Gamma(L) - Gamma(H))/(Gamma) over bar = 0.24(-0.38)(+0.28)(stat)(-0.04)(+0.03)(syst). With the additional constraint from the world average of the B-s(0) lifetime measurements using semileptonic decays, we find (tau) over bar (B-s(0)) = 1.39 +/- 0.06 ps and Delta Gamma/(Gamma) over bar = 0.25(-0.15)(+0.14). For the ratio of the B-s(0) and B-0 lifetimes we obtain (tau) over bar (B-s(0))/tau(B-s(0)) = 0.91 +/- 0.09(stat) +/- 0.003(syst).

Direct limits on the B-s(0) oscillation frequency

We report results of a study of the B-s(0) oscillation frequency using a large sample of B-s(0) semileptonic decays corresponding to approximately 1 fb(-1) of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider in 2002-2006. The amplitude method gives a lower limit on the B-s(0) oscillation frequency at 14.8 ps(-1) at the 95% C.L. At Delta m(s)=19 ps(-1), the amplitude deviates from the hypothesis A=0 (1) by 2.5 (1.6) standard deviations, corresponding to a two-sided C.L. of 1% (10%). A likelihood scan over the oscillation frequency, Delta m(s), gives a most probable value of 19 ps(-1) and a range of 17

Measurement of associated W plus charm production in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

QCD-Strahlungskorrekturen zu Polarisationsobservablen in semileptonischen Zerfällen schwerer Quarks

In dieser Arbeit werden die QCD-Strahlungskorrekturen in erster Ordnung der starken Kopplungskonstanten für verschiedene Polarisationsobservablen zu semileptonischen Zerfällen eines bottom-Quarks in ein charm-Quark und ein Leptonpaar berechnet. Im ersten Teil wird der Zerfall eines unpolarisierten b-Quarks in ein polarisiertes c-Quark sowie ein geladenes Lepton und ein Antineutrino im Ruhesystem des b-Quarks analysiert. Es werden die Strahlungskorrekturen für den unpolarisierten und den polarisierten Beitrag zur differentiellen Zerfallsrate nach der Energie des c-Quarks berechnet, wobei das geladene Lepton als leicht angesehen und seine Masse daher vernachlässigt wird. Die inklusive differentielle Rate wird durch zwei Strukturfunktionen in analytischer Form dargestellt. Anschließend werden die Strukturfunktionen und die Polarisation des c-Quarks numerisch ausgewertet. Nach der Einführung der Helizitäts-Projektoren befaßt sich der zweite Teil mit dem kaskadenartigen Zerfall eines polarisierten b-Quarks in ein unpolarisiertes c-Quark und ein virtuelles W-Boson, welches weiter in ein Paar leichter Leptonen zerfällt. Es werden die inklusiven Strahlungskorrekturen zu drei unpolarisierten und fünf polarisierten Helizitäts-Strukturfunktionen in analytischer Form berechnet, welche die Winkelverteilung für die differentielle Zerfallsrate nach dem Viererimpulsquadrat des W-Bosons beschreiben. Die Strukturfunktionen enthalten die Informationen sowohl über die polare Winkelverteilung zwischen dem Spinvektor des b-Quarks und dem Impulsvektor des W-Bosons als auch über die räumliche Winkelverteilung zwischen den Impulsen des W-Bosons und des Leptonpaars. Der Impuls und der Spinvektor des b-Quarks sowie der Impuls des W-Bosons werden im b-Ruhesystem analysiert, während die Impulse des Leptonpaars im W-Ruhesystem ausgewertet werden. Zusätzlich zu den genannten Strukturfunktionen werden noch die unpolarisierte und die polarisierte skalare Strukturfunktion angegeben, die in Anwendungen bei hadronischen Zerfällen eine Rolle spielen. Anschließend folgt eine numerische Auswertung aller berechneten Strukturfunktionen. Im dritten Teil werden die nichtperturbativen HQET-Korrekturen zu inklusiven semileptonischen Zerfällen schwerer Hadronen diskutiert, welche ein b-Quark enthalten. Sie beschreiben hadronische Korrekturen, die durch die feste Bindung des b-Quarks in Hadronen hervorgerufen werden. Es werden insgesamt fünf unpolarisierte und neun polarisierte Helizitäts-Strukturfunktionen in analytischer Form angegeben, die auch eine endliche Masse und den Spin des geladenen Leptons berücksichtigen. Die Strukturfunktionen werden sowohl in differentieller Form in Abhängigkeit des quadrierten Viererimpulses des W-Bosons als auch in integrierter Form präsentiert. Zum Schluß werden die zuvor erhaltenen Resultate auf die semi-inklusiven hadronischen Zerfälle eines polarisierten Lambda_b-Baryons oder eines B-Mesons in ein D_s- oder ein D_s^*-Meson unter Berücksichtigung der D_s^*-Polarisation angewandt. Für die zugehörigen Winkelverteilungen werden die inklusiven QCD- und die nichtperturbativen HQET-Korrekturen zu den Helizitäts-Strukturfunktionen in analytischer Form angegeben und anschließend numerisch ausgewertet.