Search Results (34 total)

We present a measurement of the mass difference m(D_s⁺)-m(D⁺), where both the D_s⁺ and D⁺ are reconstructed in the φπ⁺ decay channel. This measurement uses 11.6 pb^-1 of data collected by CDF II using the new displaced-track trigger. The mass difference is found to be m(D_s⁺)-m(D⁺)=99.41±0.38(stat)±0.21(syst) MeV/c².

Inclusive momentum distributions of charged particles in restricted cones around jet axes were measured in dijet events with invariant dijet masses in the range 80 to 600 GeV/c². Events were produced at the Fermilab Tevatron in pp̅ collisions with a center of mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The results were compared to perturbative QCD calculations carried out in the framework of the modified leading log approximation (MLLA) and assuming local parton-hadron duality. It was shown that the data follow theoretical predictions quite well over the whole range of the jet energies included in this analysis. We extracted the MLLA cutoff scale Q_eff and found a value of 230±40 MeV. The theoretical prediction of E_jetsin θ_c scaling, where θ_c is the cone opening angle, was experimentally observed for the first time. From the MLLA fits to the data, two more parameters were extracted: the ratio of parton multiplicities in gluon and quark jets, r=N_partons^g-jet/N_partons^q-jet=1.9±0.5, and the ratio of the number of charged hadrons to the number of predicted partons in a jet, K_LPHD^charged=N_hadrons^charged/N_partons=0.56±0.10.

We report the results of a search for a W^′ boson produced in pp̅ collisions at a center-of-mass energy of 1.8 TeV using a 106   pb^-1 data sample recorded by the Collider Detector at Fermilab. We observe no significant excess of events above background for a W^′ boson decaying to a top and bottom quark pair. In a model where this boson would mediate interactions involving a massive right-handed neutrino (ν_R) and have standard model strength couplings, we use these data to exclude a W^′ boson with mass between 225 and 536   GeV/c² at 95% confidence level for M_W^′≫M_νR and between 225 and 566   GeV/c² at 95% confidence level for M_W^′<M_νR.

We have performed a search for radiative b-hadron decays using events produced in pp̅ collisions at sqrt[s]=1.8 TeV and collected by the Collider Detector at Fermilab. The decays we considered were B_d⁰→K^*0(→K^-π⁺)γ, B_s⁰→φ(→K⁺K^-)γ, Λ_b⁰→Λ(→pπ^-)γ, and their charge conjugates. Two independent methods to identify photons from such decays were employed. In the first method, the photon was detected in the electromagnetic calorimeter. In the second method, the photon was identified by an electron-positron pair produced through the external photon conversion before the tracking detector volume. By combining the two methods we obtain upper limits on the branching fractions for the B_d⁰, B_s⁰, and Λ_b⁰ radiative decays which, at the 95% confidence level, are found to be B(B_d⁰→K^*0γ)<1.4×10^-4, B(B_s⁰→φγ)<1.6×10^-4, and B(Λ_b⁰→Λγ)<1.9×10^-3.

The exclusive γE̸_T signal has a small standard model cross section and is thus a channel sensitive to new physics. This signature is predicted by models with a superlight gravitino or with large extra spatial dimensions. We search for such signals at the Collider Detector at Fermilab, using 87   pb^-1 of data at sqrt[s]=1.8   TeV, and extract 95% C.L. limits on these processes. A limit of 221 GeV is set on the scale |F|^1/2 in supersymmetric models. For 4, 6, and 8 extra dimensions, model-dependent limits on the fundamental mass scale M_D of 0.55, 0.58, and 0.60 TeV, respectively, are found. We also specify a “pseudo-model-independent” method of comparing the results to theoretical predictions.

The inclusive cross section for J/ψ production times the branching ratio B(J/ψ→μ⁺μ^-) has been measured in the forward pseudorapidity region: B×dσ[p̅ +p→J/ψ(p_T>10 GeV/c,2.1<|η|<2.6)+X]/dη=192±9(stat)±29(syst) pb. The results are based on 74.1±5.2 pb^-1 of data collected by the CDF Collaboration at the Fermilab Tevatron Collider. The measurements extend earlier measurements of the D0 Collaboration to higher p_T^J/ψ. In the kinematic range where the experiments partially overlap, these data are in good agreement with previous measurements.

We report on measurements of the branching ratios of the decays B⁺→χ_c1⁰(1P)K⁺ and B⁺→J/ψK⁺π⁺π^-, where χ_c1⁰(1P)→J/ψγ and J/ψ→μ⁺μ^- in pp̅ collisions at sqrt[s]=1.8 TeV. Using a data sample from an integrated luminosity of 110 pb^-1 collected by the Collider Detector at Fermilab we measure the branching ratios to be BR(B⁺→χ_c1⁰(1P)K⁺)=15.5±5.4(stat)±1.5(syst)±1.3(br)×10^-4 and BR(B⁺→J/ψK⁺π⁺π^-)=6.9±1.8(stat)±1.1(syst)±0.4(br)×10^-4 where (br) is due to the finite precision on BR(B⁺→J/ψK⁺), BR(χ_c1⁰(1P)→J/ψγ) is used to normalize the signal yield, and (syst) encompasses all other systematic uncertainties.

We present the results of a search in pp̅ collisions at sqrt[s]  =  1.8 TeV for anomalous production of events containing a photon and a lepton ( e or μ), both with large transverse energy, using 86 pb^-1 of data collected with the Collider Detector at Fermilab during the 1994–1995 collider run at the Fermilab Tevatron. The presence of large missing transverse energy ( E_T), additional photons, or additional leptons in these events is also analyzed. The results are consistent with standard model expectations, with the possible exception of photon-lepton events with large E_T, for which the observed total is 16 events and the expected mean total is 7.6±0.7 events.

We have measured the cross sections d²σ/dP_Tdη for production of isolated direct photons in pp̅ collisions at two different center-of-mass energies, 1.8 TeV and 0.63 TeV, using the Collider Detector at Fermilab. The normalization of both data sets agrees with the predictions of quantum chromodynamics for a photon transverse momentum (P_T) of 25 GeV/c, but the shapes versus photon P_T do not. These shape differences lead to a significant disagreement in the ratio of cross sections in the scaling variable x_T(≡2P_T/sqrt[s]). This disagreement in the x_T ratio is difficult to explain with conventional theoretical uncertainties such as scale dependence and parton distribution parametrizations.

We present an improved measurement of b-meson lifetimes using fully reconstructed B-decays produced in pp̅ collisions at sqrt[s]=1.8 TeV, using 114 pb^-1 of data collected at the Collider Detector at Fermilab. We obtain τ(B⁺)=1.636±0.058(stat)±0.025(syst) ps, τ(B⁰)=1.497±0.073(stat)±0.032(syst) ps and for the lifetime ratio τ(B⁺)/τ(B⁰)=1.093±0.066(stat)±0.028(syst).

The presence of a sizable CP-violating phase in B_s-B_s mixing would be an unambiguous signal of physics beyond the standard model. We analyze various possibilities to detect such a new phase considering both tagged and untagged decays. The effects of a sizable width difference ΔΓ between the B_s mass eigenstates, on which the untagged analyses rely, are included in all formulas. A novel method to find this phase from simple measurements of lifetimes and branching ratios in untagged decays is proposed. This method does not involve two-exponential fits, which require much larger statistics. For the tagged decays, an outstanding role is played by the observables of the time-dependent angular distribution of the B_s→J/ψ[→l⁺l^-]φ[→K⁺K^-] decay products. We list the formulas needed for the angular analysis in the presence of both a new CP-violating phase and a sizable ΔΓ, and propose methods to remove a remaining discrete ambiguity in the new phase. This phase can therefore be determined in an unambiguous way.

Various methods are discussed for obtaining the CKM angle γ through the interference of the charged B-meson decay channels B^-→K^-D⁰ and B^-→K^-D⁰ where the D⁰ and D⁰ decay to common final states. It is found that choosing final states which are not CP eigenstates can lead to large direct CP violation which can give significant bounds on γ without any theoretical assumptions. If two or more modes are studied, γ may be extracted with a precision on the order of ±15° given ∼10⁸ B-mesons. We also discuss the case of three body decays of the D where additional information may be obtained from the distribution of the D decay products and consider the impact of DD̅ oscillations.

The branching ratio B(Λ_c→pK^-π⁺) normalizes the production and decay of charmed and bottom baryons. At present, this crucial branching ratio is extracted dominantly from B̅ →baryons analyses. This paper questions several of the underlying assumptions and predicts sizable B̅ →D^(*)NN^′X transitions, which were traditionally neglected. It predicts B(Λ_c→pK^-π⁺) to be larger (0.07±0.02) than the world average. Some consequences are briefly mentioned. Several techniques to measure B(Λ_c→pK^-π⁺) are outlined with existing or soon available data samples. By equating two recent CLEO results, an appendix obtains B(D⁰→K^-π⁺)=0.035±0.002, which is somewhat smaller than the current world average.

Hybrid charmonium with mass ∼4 GeV could be produced via a cc̅ color-octet component in b→cc̅ s. These states could be narrow and could have a significant branching ratio to light hadrons, perhaps enhanced by glueballs. Decays to gluonic hadrons could make a sizable contribution to B→no charm decays. Experimental signatures and search strategies are discussed.

The Gronau-London-Wyler method extracts the Cabibbo-Kobayashi-Maskawa angle γ by measuring B^± decay rates involving D⁰/D̅ ⁰ mesons. CP violation can be greatly enhanced for decays to final states common to both D⁰ and D̅ ⁰ that are not CP eigenstates. Large asymmetries are possible for final states f such that D⁰→f is doubly Cabibbo suppressed while D̅ ⁰→f is Cabibbo allowed. The measurement of interference effects in such modes allows the clean extraction of γ.

We investigate the time evolutions of angular distributions for B_s decays into final states that are admixtures of CP-even and CP-odd configurations. A sizable lifetime difference between the B_s mass eigenstates allows a probe of CP violation in time-dependent untagged angular distributions. Interference effects between different final state configurations of B_s→D_s^*+D_s^*-, J/ψφ determine the Wolfenstein parameter η from untagged data samples, or, if one uses |V_ub|/|V_cb| as additional input, the notoriously difficult to measure CKM angle γ. Another determination of γ is possible by using isospin symmetry of strong interactions to relate untagged data samples of B_s→K^*+K^*- and B_s→K^*0K̅ ^*0. We note that the untagged angular distribution for B_s→ρ⁰φ provides interesting information about electroweak penguin diagrams.

We investigate decay constants of P- and D-wave heavy-light mesons within the mock-meson approach. Numerical estimates are obtained using the relativistic quark model. We also comment on recent calculations of heavy-light pseudoscalar and vector decay constants.

We use the heavy quark expansion to investigate the width difference ΔΓ_Bs between the B_s mass eigenstates. The corrections of O(Λ_QCD / m_b) and O(m_s / m_b) to the leading-order expression in the operator product expansion are derived and estimated to yield a sizable reduction of the leading result for ΔΓ_Bs by typically 30%. For completeness we also quantify small effects due to penguin operators and CKM-suppressed contributions. Based on our results we discuss the prediction for (ΔΓ / Γ)_Bs with particular emphasis on theoretical uncertainties. We find (ΔΓ / Γ)_Bs=0.16_-0.09^+0.11, where the large error is dominated by the uncertainty in hadronic matrix elements. An accuracy of about 10% in (ΔΓ / Γ)_Bs should be within reach, assuming continuing progress in lattice calculations. In addition, we address phenomenological issues and implications of a ΔΓ_Bs measurement for constraints on ΔM_Bs and CKM parameters. We further consider in some detail the lifetime ratio τ(B_s) / τ(B_d) and estimate that, most likely, |τ(B_s) / τ(B_d)-1|<1%.

A width difference of the order of 20% has previously been predicted for the two mass eigenstates of the B_s meson. The dominant contributor to the width difference is b→cc¯s transition, with final states common to both B_s and B¯_s. All current experimental analyses fit the time dependences of flavor-specific B_s modes to a single exponential, which essentially determines the average B_s lifetime. We stress that the same data sample allows even the measurement of the width difference. To see that, this article reviews the time-dependent formulas for tagged B_s decays, which involve rapid oscillatory terms depending on Δ mt. In untagged data samples the rapid oscillatory terms cancel. Their time evolutions depend only on the much more slowly varying exponential falloffs. We discuss in detail the extraction of the two widths, and identify the large (small) CP-even (-odd) rate with that of the light (heavy) B_s mass eigenstate. It is demonstrated that decay length distributions of some untagged B_s modes, such as ρ⁰K_S,ωK_S,D_s^(*)±K^(*)∓, can be used to extract the notoriously difficult CKM unitarity triangle γ. Sizable CP-violating effects may be seen with such untagged B_s data samples. Listing ΔΓ as an observable allows for additional important standard model constraints. Within the CKM model, the ratio ΔΓ/Δm involves no CKM parameters, only a hadronic uncertainty. Thus a measurement of ΔΓ(Δm) would predict Δm(ΔΓ), up to the uncertainty. A large width difference would automatically solve the puzzle of the number of charmed hadrons per B decay in favor of theory. We also derive an upper limit of (‖ΔΓ‖/Γ)_Bs≲0.3. Further, we must abandon the notion of branching fractions of B_s→f, and instead consider B(B_L(H)⁰→f), in analogy with the neutral kaons.

The correlations between a B meson and a pion produced nearby in phase space should respect isospin reflection symmetry I₃→-I₃. Thus, one generally expects similar π⁺B⁰ and π^-B⁺ correlations (nonexotic channels), and similar π^-B⁰ and π⁺B⁺ correlations (exotic channels). Exceptions include (a) fragmentation processes involving the exchange of quarks with the producing system, (b) misidentification of charged kaons as charged pions, and (c) effects of the decay products of the associated B¯. All of these can affect the apaprent signal for correlations of charged B mesons with charged hadrons. The identification of the flavor of neutral B mesons through the decay B⁰→K^*0J/ψ requires good particle identification in order that the decay K^*0→K⁺π^- not be mistaken for K¯^*0→K^-π⁺, in which case the correlations of neutral B mesons with hadrons can be underestimated.

We reconsider the conflict between recent calculations of the semileptonic branching ratio of the B meson and the experimentally measured rate. Such calculations depend crucially on the application of ‘‘local duality’’ in nonleptonic decays, and we discuss the relation of this assumption to the weaker assumptions required to compute the semileptonic decay rate. We suggest that the discrepancy between theory and experiment might be due to the channel with two charm quarks in the final state, either because of a small value for m_c or because of a failure of local duality. We examine the experimental consequences of such solutions for the charm multiplicity in B decays.

It is usually assumed that the production of baryons in B decays is induced primarily by the process b→cu̅ d, where the charm quark hadronizes into a charmed baryon. Motivated by an examination of the Λ_c momentum spectrum in the transition B→Λ_cX, we consider the alternative hypothesis that the production of charmed baryons in B decays is in fact dominated by the transition b→cc̅ s, and is seen primarily in modes with two charmed baryons in the final state. The dominance of such a mechanism would have potentially important implications for the "charm deficit" in B decays.

We investigate the possibility of observing direct CP violation in self-tagging B-meson decays of the type b→dJ/ψ. The CP asymmetry can be generated due to strong or electromagnetic scattering in the final state, or due to long distance effects. The first two contributions give asymmetries of a few ×10^-3, in the standard model. The long distance effects are hard to estimate, but it cannot be excluded that they yield asymmetries of about 1%.

Large CP-violation effects can occur for time-evolved B⁰ decays into definite CP eigenstates. The rates into these unique CP eigenmodes are tiny. This article advocates the use of many additional modes that are not CP eigenstates because of mixtures of angular momenta. Naively, for those modes a partial and sometimes large cancellation of the CP asymmetry occurs. However, a detailed study of their angular correlations enables the projection onto definite CP eigenstates, and thus recovers the full CP asymmetry.

The B_d decay modes D̅ ⁰(D̅ ^*0)X⁰ generated by the quark process b̅ →c̅ +ud̅ have a large CP asymmetry within the Cabibbo-Kobayashi-Maskawa (CKM) model. Here X⁰ denotes a light, neutral meson with zero strangeness, such as π⁰, ρ⁰, ω, etc. This asymmetry depends only on a ratio of CKM matrix elements and not on final-state phases. The CKM model predicts (up to a sign) the same asymmetries for the D̅ ⁰(D̅ ^*0)X⁰, ψK_S, and D⁺D^- modes. Adding those modes might lower the required luminosity for observing CP violation within the CKM model. On the other hand, future high-statistics measurements could reveal violations of the CKM model simply by demonstrating that the modes ψK_S, D⁺D^- and D̅ ⁰(D̅ ^*0)X⁰ differ in their individual CP asymmetries.