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DOE OSTI2012

Search for New Physics in the B 0 2 →J/ΨΦ and B 0 2 →ΦΦ Decays at CDF

We present a search for physics beyond the standard model (SM) through a measurement of the violation of the charge-parity (CP) symmetry in two decays of the B 0 2 meson using data collected by the Collider Detector at Fermilab (CDF) in proton-antiproton collisions at the center-of-mass energy of 1.96TeV. We exploit the decays B 0 2 →J/Ψ(→ μ + μ - )(→ K + K - ) and B 0 2 →Φ (→ K + K - )Φ(→ K + K - ), for which the SM accurately predicts very small or vanishing CP violation; both decay modes are very sensitive to new sources of CP violation expected in a broad class of SM extensions. We analyze the time-dependent CP asymmetry of the B 0 2 →J/ΨΦ decays collected in the full CDF Run II dataset for providing the final measurement of the B 0 2 -¯B 0 2 mixing phase, 2β s , and we present the first measurement of CP violation in B 0 2 →ΦΦ decays, through the determination of two time-integrated CP asymmetries, A v and A u , using an original method developed in this work. We find: -0.06 < β s < 0.30 at the 68% confidence level; A v = (-12.0 ± 6.4(stat) ± 1.6(syst))%; and A u = (-0.7 ± 6.4(stat) ± 1.8(syst))%. In addition, we provide measurements of the decay width difference between the light and heavy mass eigenstates of the B 0 2 meson,ΔΓ s 0.068 ± 0.026(stat) ± 0.009(syst) ps -1 ; and of their mean lifetime, τ s = 1.528 ± 0.019(stat) ± 0.009(syst) ps. All results are among the most precise determinations from a single experiment and exhibit an excellent agreement with the SM predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Search for the Higgs Boson in the $ZH\to\mu^+\mu^- b\bar{b}$ Channel at CDF Using Novel Multivariate Techniques

We present a search for the Standard Model Higgs Boson using the process $ZH\to\mu^+\mu^- b\bar{b}$. We use a dataset corresponding to 9.2 fb$^{-1}$ of integrated luminosity from proton-antiproton collisions with center-of-mass energy 1.96 TeV at the Fermilab Tevatron, collected with the CDF II detector. This analysis benefits from several new multivariate techniques that have not been used in previous analyses at CDF. We use a multivariate function to select muon candidates, increasing signal acceptance while simultaneously keeping fake rates small. We employ an inclusive trigger selection to further increase acceptance. To enhance signal discrimination, we utilize a multi-layer approach consisting of expert discriminants. This multi-layer discriminant method helps isolate the two main classes of background events, $t\bar{t}$ and $Z$+jets production. It also includes a flavor separator, to distinguish light flavor jets from jets consistent with the decay of a $B$-hadron. Wit h this novel multi-layer approach, we proceed to set limits on the $ZH$ production cross section times branching ratio. For a Higgs boson with mass 115 GeV/$c^2$, we observe (expect) a limit of 8.0 (4.9) times the Standard Model prediction.

Pilot, Justin R.↗

DOE OSTI2012

Improving the Acceptance in the Single Top Quark Analysis using 7.5 fb$^{-1}$ of CDF data

The Top quark was observed at the Fermilab Tevatron by the CDF and D0 collaboration in 1995 via strong production of top quarks pairs at center-of-mass energy of $ \sqrt{s}=1.8 $ Tev, using 60 pb -1 of data [1]. Standard Model of elementary particles predicts top quark to be produced individually via electroweak interactions in three different channels (s, t and Wt). This is defined as ”single top” (from now on also ST). ST was observed by CDF collaboration in 2009 at center-of-mass energy of $ \sqrt{s}=1.96 $ Tev using 3.2 fb -1 of $ p\overline{p}\ $ collected data [2]. This thesis concerns the upgrade of this measurement using 7.5 fb -1 of data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Measurements of the Top Anti-Top Production Cross Section and Top Quark Mass in the Hadronically Decaying Tau + Jets Decay Channel at CDF

In this thesis, we present the first exclusive observation of the t - t → hadronic τ + jets decay channel. Using these events, we measure the t - t pair production cross section and the top quark mass in 2.2 fb -1 of data collected with the Collider Detector at Fermilab (CDF). The Tevatron accelerator at Fermilab provides collisions of protons and anti-protons at a center-of-mass energy of √s = 1.96 TeV and is one of only two accelerators in the world with enough energy to produce top quarks. With a branching fraction of nearly 10%, the hadronic τ + jets decay channel is the third largest t - t decay mode, and it has only been minimally explored. This the first measurement of the t - t pair production cross section in this decay channel at CDF and the first measurement of the top quark mass in this decay channel in the world. The analysis introduces a new method to recover the total momentum of the ν produced in the τ decay and an artificial neural network to reduce the contribution from the largest background source, QCD multijet background. The t - t pair production cross section is extracted by minimizing a negative log likelihood function which compares the number of observed events to the number of expected events for a given t - t cross section. The top quark mass is extracted by minimizing a negative log likelihood function built from signal and ii background probabilities which are based on the matrix elements for t - t production and decay and W + 4 parton production, respectively. Using events selected with exactly 1 hadronically decaying τ, exactly 4 jets with at least 1 identified as having originated from a b quark, and large missing transverse energy, we measure the t - t pair production cross section to be 8.8 ± 3.3 (stat.) ± 2.2 (syst.) pb and the top quark mass to be 172.7±9.3 (stat.) ±3.7 (syst.) GeV. We find both values to be in good agreement with previous measurements in other t - t decay channels, and the cross section to be consistent with next-to-leading order theoretical predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Combined CDF and D0 Upper Limits on Standard Model Higgs Boson Production with up to 8.2 fb$^{-1}$ of Data

We combine results from CDF and D0's direct searches for the standard model (SM) Higgs boson (H) produced in p{bar p} collisions at the Fermilab Tevatron at {radical}s = 1.96 TeV. The results presented here include those channels which are most sensitive to Higgs bosons with mass between 130 and 200 GeV/c{sup 2}, namely searches targeted at Higgs boson decays to W{sup +}W{sup -}, although acceptance for decays into {tau}{sup |+} {tau}{sup -} and {gamma}{gamma} is included. Compared to the previous Tevatron Higgs search combination, more data have been added and the analyses have been improved to gain sensitivity. We use the MSTW08 parton distribution functions and the latest gg {yields} H theoretical cross section predictions when testing for the presence of a SM Higgs boson. With up to 7.1 fb{sup -1} of data analyzed at CDF, and up to 8.2 fb{sup -1} at D0, the 95% C.L. upper limits on Higgs boson production is a factor of 0.54 times the SM cross section for a Higgs boson mass of 165 GeV/c{sup 2}. We exclude at the 95% C.L. the region 158 < m{sub H} < 173 GeV/c{sup 2}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Search for rare SM processes in the MET+b-jets signature at CDF

The missing transverse energy (E{sub T}) plus b-jets signature is very promising for searches for the Higgs boson or new physics. Indeed, E{sub T} naturally arises from unidentified particles such as neutrinos, neutralinos, gravitons, etc., and b-quarks are the main decay products of a low mass Higgs boson as well as of several exotic particles. The main challenge is to identify and reject the numerous standard model (SM) backgrounds that mimic this signature. This is especially so for QCD multi-jet production, a large background due to mis-measurement (rather than undetectable particles). We present state-of-the-art data-driven and multivariate techniques to characterize and reject this instrumental background. These techniques make analyses in this signature as sensitive as those using lepton identification and allow probing for rare SM processes. We describe searches for electroweak single top production, a part of the observation of single top by CDF, and for a low mass SM Higgs boson, one of the most sensitive among low mass Higgs searches at CDF. We also present a measurement of the top pair cross-section in this signature, and discuss other analyses and future prospects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Combined CDF and D0 Searches for the Standard Model Higgs Boson Decaying to Two Photons with up to 8.2 fb^-1

We combine results from CDF and D0's direct searches for the standard model (SM) Higgs boson (H) produced in p{bar p} collisions at the Fermilab Tevatron at {radical}s = 1.96 TeV, focusing on the decay H {yields} {gamma}{gamma}. We compute upper limits on the Higgs boson production cross section times the decay branching fraction in the range 100 < m{sub H} < 150 GeV/c{sup 2}, and we interpret the results in the context of the standard model. We use the MSTW08 parton distribution functions and the latest theoretical cross section predictions when testing for the presence of a SM Higgs boson. With datasets corresponding to 7.0 fb{sup -1} (CDF) and 8.2 fb{sup -1} (D0), the 95% C.L. upper limits on Higgs boson production is a factor of 10.5 times the SM cross section for a Higgs boson mass of 115 GeV/c{sup 2}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Combined CDF and D0 upper limits on $gg\to H\to W^+W^-$ and constraints on the Higgs boson mass in fourth-generation fermion models with up to 8.2 fb$^{-1}$ of data

We combine results from searches by the CDF and D0 Collaborations for a standard model Higgs boson (H) in the processes gg {yields} H {yields} W{sup +}W{sup -} and gg {yields} H {yields} ZZ in p{bar p} collisions at the Fermilab Tevatron Collider at {radical}s = 1.96 TeV. With 8.2 fb{sup -1} of integrated luminosity analyzed at CDF and 8.1 fb{sup -1} at D0, the 95% C.L. upper limit on {sigma}(gg {yields} H) x {Beta}(H {yields} W{sup +}W{sup -}) is 1.01 pb at m{sub H} = 120 GeV, 0.40 pb at m{sub H} = 165 GeV, and 0.47 pb at m{sub H} = 200 GeV. Assuming the presence of a fourth sequential generation of fermions with large masses, we exclude at the 95% Confidence Level a standard-model-like Higgs boson with a mass between 124 and 286 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Updated Search for $B_s \to \mu^+$ mu- at CDF

The decay B{sub s}{sup 0} {yields} {mu}{sup +}{mu}{sup -} is very sensitive to contributions from new physics processes. Thus the Tevatron and LHC experiments are hunting for an observation of a B{sub s}{sup 0} {yields} {mu}{sup +}{mu}{sup -} signal. In this article the updated search for B{sub s}{sup 0} {yields} {mu}{sup +}{mu}{sup -} and B{sup 0} {yields} {mu}{sup +}{mu}{sup -} by the CDF experiment is presented. The CDF result was received with great interest because an excess over the background expectation is seen, although of modest statistical significance and still consistent with the prediction of a standard model signal and other experimental results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Hadronic final states in high -pT QCD at CDF

The heavy quark content of gauge boson events is of great interest to studies of QCD. These events probe the gluon and heavy-quark parton distribution functions of the proton, and also provide a measurement of the rate of final state gluon splitting to heavy flavor. In addition, gauge boson plus heavy quark events are representative of backgrounds to Higgs, single top, and supersymmetric particle searches. Recent work with the CDF II detector at the Fermilab Tevatron has measured the cross-section of several gauge boson plus heavy flavor production processes, including the first Tevatron observation of specific charm process p{p bar} → W +c. Results are found to be in agreement with NLO predictions that include an enhanced rate of g → {cc bar}/bb splitting. Lastly, a new analysis promises to probe a lower pT (c) region than has been previously explored, by fully reconstructing D* → D0(Kπ)π decays in the full CDF dataset (9.7 fb-1).

Matera, Keith↗

DOE OSTI2016

Combination of the CDF and D0 Effective Leptonic Electroweak Mixing Angles

CDF and D0 have measured the effective leptonic weak mixing angle $sin^2 \theta^{lept}_{eff}$ , using their full Tevatron datasets. This note describes the Tevatron combination of these measurements, and the zfitter standard model-based inference of the on-shell electroweak mixing angle $sin^2 \theta_W$, or equivalently, the W-boson mass. The combination of CDF and D0 results yields: $sin^2 \theta^{lept}_ {eff}$ = 0.23179 ± 0.00035, and $sin^2 \theta_W$ = 0.22356 ± 0.00035, or equivalently, $M_W$(indirect) = 80.351 ± 0.018 GeV/$c^2$.

Source record↗

DOE OSTI2012

Rare decay searches at CDF

In the last decade the CDF experiment at the Tevatron clearly demonstrated that it is possible to study extensively heavy flavour physics in hadron collisions and achieve remarkable results, competitive and complementary to $B$-factories. In this paper we report on the indirect searches for physics beyond the standard model via measurements of rare $b$-hadron decays. The final limits, based on the analysis of the full CDF data set, on the branching fraction of the $B^0_{(s)}$ decay into a pair of muons are presented and discussed. Moreover we review the latest measurements, with 6.8 fb$^{-1}$ of collected data, of the total and differential branching fractions and angular observables of rare $b$-hadron decays proceeding via the flavour-changing neutral-current process $b \rightarrow s \mu^+ \mu^-$. PACS numbers: 13.20.He, 13.30.-a, 12.15.Mn

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Charm Physics at CDF

The study of the charm quark continues to have wide interest as a possible avenue for the discovery of physics beyond the Standard Model and can as well be used as a tool for understanding the non-perturbative aspects of the strong interactions. Owning to the large production cross-section available at the Tevatron collider and to the flexibility of a trigger on fully hadronic final states, the CDF experiment, in a decade of successful operations, collected millions of charmed mesons decays which can be used to investigate the details of the physics of the production and decay processes of the charm quark. Here we present a brief collection of new CDF results on this subject.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

An Artificial neural network based $b$ jet identification algorithm at the CDF Experiment

We present the development and validation of a new multivariate $b$ jet identification algorithm ('$b$ tagger') used at the CDF experiment at the Fermilab Tevatron. At collider experiments, $b$ taggers allow one to distinguish particle jets containing $B$ hadrons from other jets. Employing feed-forward neural network architectures, this tagger is unique in its emphasis on using information from individual tracks. This tagger not only contains the usual advantages of a multivariate technique such as maximal use of information in a jet and tunable purity/efficiency operating points, but is also capable of evaluating jets with only a single track. To demonstrate the effectiveness of the tagger, we employ a novel method wherein we calculate the false tag rate and tag efficiency as a function of the placement of a lower threshold on a jet's neural network output value in $Z+1$ jet and $t\bar{t}$ candidate samples, rich in light flavor and $b$ jets, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

Exploiting the full information carried by jets for reconstructing the mass of the hadronically decaying Z in WZ/ZZ events with a lepton, missing transverse energy and 3 jets at CDF

Observing WZ/ZZ production at the Tevatron in the final state with a lepton, missing transverse energy and two jets is extremely difficult because of the low signal rate and the very large background. In the attempt to increase the acceptance in the analysis of the data collected by the CDF experiment, we study the sample with 3 high-energy jets, where according to simulations about 1/3 of the diboson events are expected to be. Rather than choosing always the two jets of largest transverse energy ( E T ) to reconstruct the Z mass, we make use of the information carried by all jets. We describe in detail how to better combine the jet information, and introduce a method of interest in every experiment searching for hadronic resonances in the W/Z + jets channel, including measurements of Higgs boson production associated with a W or Z.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2012

Standard model Higgs boson searches at CDF

We present recent results from searches for a standard model Higgs boson by the CDF experiment at the Tevatron $p\bar{p}$ collider with the full Run II data set. An excess of events above the expected background is observed and is the strongest in the associated production search channels where the Higgs is produced together with a W or Z boson, and then decays to a bottom-antibottom quark pair, with a global significance of 2.5$\sigma$. Both limits and best fit values of the Higgs production cross section are presented. For a Higgs mass of 125~GeV/c$^2$, the best agreement with data in the $(\sigma_{WH}+\sigma_{ZH})\times Br(H\rightarrow b\overline{b})=291\pm^{118}_{113}$~fb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

sin 2 θ eff lept and M W (indirect) extracted from 9 fb -1 μ + μ - event sample at CDF

Here, we report on the extraction of $\sin^2\theta^{\rm lept}_{\rm eff}$ and indirect measurement of the mass of the W boson from the forward-backward asymmetry of $\mu^+\mu^-$ events in the $Z$ boson mass region. The data sample collected by the CDF detector corresponds to the full 9 fb$^{-1}$ run II sample. We measure $\sin^2 \theta^{\rm lept}_{\rm eff} = 0.2315 \pm 0.0010$, $ \sin^2 \theta_W = 0.2233 \pm 0.0009$ and $M_W ({\rm indirect}) = 80.365 \pm 0.047 \;{\rm GeV}/c^2$, where each uncertainty includes both statistical and systematic contributions. Comparison with the results of the D0 collaboration are presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of low-$p_T$ $D^+$ meson production cross-section at CDF II

In this paper I report on a measurement of the low- p T D + -meson production cross-section in proton-antiproton collisions at 1.96 TeV center-of-mass energy, using the full data set collected by the CDF experiment at the Tevatron collider during Run II. The measurement is performed in a yet unexplored low transverse momentum range, down to 1.5 GeV/ c . The actual QCD theory cannot predict the behavior of the strong interactions in the low transferred-four-momentum region because in these kinematic conditions the strong coupling constant is of the order of the unity. Thus, a perturbative expansion is not useful. At present, several phenomenological models have been proposed, but they are able to describe only a few aspects of the observed physical quantities and not the full complexity. Experimental results in these conditions are then crucial to test new QCD models. The measurement of the differential cross section at low p T plays an important role in this context allowing refinement of current knowledge. While these results lie within the band of theoretical uncertainty, differences in shape suggest that theoretical predictions can benefit from further refinement taking account of them.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗