|
Top Properties
|
An upper limit on the total width of the top quark at CDF
Speaker: Satomi Shiraishi (CDF Collaboration) PDF
Abstract: We present the first direct experimental upper limit on the total decay width of the top quark using 955 pb$^{-1}$ of the Tevatron's $p\bar p$ collisions taken by the CDF II Detector at the
Fermilab Tevatron. We identify 253 top-antitop pair candidate events. The distribution of reconstructed top quark mass from the candidate events is fitted to template representing different values of the top quark width. The Feldman-Cousins prescription is used to extract an upper limit on the
top quark width at 95$\%$ confidence level for an assumed top quark mass
of 175 GeV/c$^2$.
|
Measurement of the differential top cross section ($d\sigma$/$dM_{t\bar t}$) at CDF
Speaker: Alice Bridgeman (CDF Collaboration) PDF
Abstract: We present a measurement of the $t\overline{t}$
differential cross section, $d\sigma/dM_{t\overline{t}}$, at $\sqrt{s}= 1.96$~TeV using
approximately $1.9~fb^{-1}$ of data collected with the CDF II Detector at the
Fermilab Tevatron. We select events in the $W+\geq4$~jets sample
with displaced secondary vertices from jets with heavy-flavor
decays. We use a regularized unfolding technique to correct the
reconstructed invariant mass distribution back to the true
distribution. We see no evidence of inconsistency with the standard
model, with an observed p-value of 0.45.
|
Measurement of the top production cross section using events with large missing energy and bottom quark jets at CDF
Speaker: Gabriele Compostella (CDF Collaboration) PDF
Abstract: We present a $t\bar{t}$\ production cross section measurement in the
multi-jet final state channel from collisions of protons and
anti-protons at $\sqrt{s}$= 1.96 TeV at the CDF II Detector at the Fermilab Tevatron.
We study events with high missing transverse energy and we select those that contain jets that are identified in the silicon vertex detector as originating from b-quarks using a neural network algorithm.
|
Search for a scalar top quark at CDF
Speaker: Will Johnson (CDF Collaboration) PDF
Abstract:
For some regions of SUSY parameter space it is conceivable that the
supersymmetric partner of the top quark (stop squark) could be the
lightest squark, and could actually be less massive than the standard
model top quark. Also, depending on the mass hierarchy of SUSY, a stop
squark event might look nearly identical in the detector to that of a
top
quark event. The presence of such a light stop squark could easily go
unnoticed due to the much lower production cross section of the scalar
stop squark, as compared to the fermionic top quark. We present a
search
for the stop squark at CDF in the mass range 135 to 170 GeV. We look in
the dilepton decay channel, that is a final state with two leptons, at
least two jets, and large missing transverse energy. Using a weighting
technique, we reconstruct the mass of the under-constrained stop squark
events, and use the reconstructed mass to discriminate stop squark
events
from backgrounds. This new reconstruction technique provides a promising
avenue to search for the stop squark.
|
Search for Flavor Changing Neutral Currents in Top Quark Decays at CDF
Speaker: Jennifer Gimmell (CDF Collaboration) PDF
Abstract:
In the CDF~II detector at the Fermilab Tevatron, $t\bar{t}$ pairs are
produced in $p\bar{p}$ collisions at $\sqrt{s}$=1.96 TeV. We have performed a
search for the flavor-changing neutral current (FCNC) decay of the top
quark $t \rightarrow Zq$. This decay is extremely rare in the standard
model, and any signal at the Tevatron would be an indication of new
physics. For the summer 2007 conferences, using 1.12 fb$^{-1}$ of
data we presented the world's best limit on the branching fraction
$\mathcal{B} \left (t \rightarrow Zq\right)$ of 10.6\% at 95\% C.L.
In this talk, we show the updated analysis with 1.9 fb$^{-1}$ of
data. We discriminate signal from background by exploring kinematic
constraints present in FCNC events. We construct a mass $\chi^2$
variable and fit templates to the data, taking into account shape
systematic uncertainties of the $\chi^2$ distribution. Using a
Feldman-Cousins limit technique, we expect to set an improved limit on
the branching fraction $\mathcal{B} \left (t\rightarrow Zq \right)$.
|
Search for non-standard model top antitop resonance production in the all-hadronic channel at CDF
Speaker: Yuri Oksuzian (CDF Collaboration) PDF
Abstract: We present the first result of a novel search for resonant top-antitop
pair production and subsequent decay in the all-hadronic channel. We
examine the top-antitop invariant mass spectrum observed in CDF II
data from 1.9 TeV proton-antiproton collisions at Fermilab Tevatron. A narrow
resonance state decaying to a top-antitop pairs will appear as a
"bump" in the observed mass spectrum. We apply a powerful
reconstruction technique where the observed event kinematics are
constrained according to the full Standard Model top-antitop
production and decay matrix element. This technique provides excellent
mass resolution. Also, probability densities from the per-event
matrix element calculation are used as discriminants to reduce and
control the large backgrounds of the all-hadronic channel.
|
Measurement of the top production cross section rate from gluon-gluon fusion at CDF
Speaker:Jared Yamaoka (CDF Collaboration) PDF
Abstract: We present a measurement of the ratio of top-antitop production cross section via gluon-fusion to the total production cross section
in proton-antiproton collisions with $\sqrt(s)$ = 1.96 TeV at the Fermilab Tevatron. The data sample, recorded by CDF II, has an integrated luminosity of 955 pb$^{-1}$. Using an artificial neural network trained on the kinematics to discriminate the gluon-fusion events, we find the ratio of the gluon-fusion cross section to the total cross section to be < 0.33 at the 68$\%$ confidence level and < 0.61 at the 95$\%$ confidence level. Additionally, we combine this measurement with a complementary analysis using the charged particle multiplicity in top-antitop evens and find the ratio to be 0.07+0.15-0.07.
|
Search for charged Higgs in lepton+jets channel at CDF
Speaker: Geumbong Yu (CDF Collaboration) PDF
Abstract: We present a search for an anomalous boson in top decays
using pairly produced top events collected by CDF II detector at the Fermilab Tevatron.
Our search focuses on a boson which decays into two jets,
like hadronic $W$ decays in the leptop+jets $t\bar t$ decay processes.
With well identified lepton and $b$ jets, reconstructed di-jet mass
would represent higher mass than $W$ if there is another particle
produced from top. We especially concern about charged Higgs(MSSM)
in low tan$\beta$ plane near 1 with mass between 90 GeV/$c^2$
and 150 GeV/$c^2$. Here we will present the sensitivity of finding
such abnormal particle from top decays.
|
|
Single Top
|
Search for single top quark production optimized for s-channel production at CDF
Speaker: Koji Nakamura (CDF Collaboration) PDF
Abstract: We present a search for single top quark production using 1.7 fb$^{-1}$
of data accumulated with the CDF II detector at the Fermilab Tevatron. We select events with one high-$p_{T}$ lepton,
large missing transverse energy and two jets with $b$ tags. One jet must have a $b$ tag using
secondary-vertex information and the other jet's $b$ tag may use secondary-vertex or
impact-parameter information. The kinematic fitter and the background-separation technique
are designed to maximize the sensitivity to s-channel single top production.
|
Search for single top quark production at CDF using neural networks at CDF
Speaker: Ji-Eun Jung (CDF Collaboration) PDF
Abstract: We present a search for electroweak single top quark production in proton-antiproton collisions using 2~fb$^{-1}$ of data collected by the CDF II detector at the Fermilab Tevatron. Single top quarks are expected to be produced via virtual $W$ boson exchange in t-channel and s-channel processes. We select events with one charged lepton, missing transverse energy, and two or three jets, at least one of which is identified as containing a B hadron. Bayesian neural networks are used to further separate the signal from the backgrounds. Results are presented for s-channel and t-channel single top quark production as well as the combined process.
|
Search for single top quark production at CDF using a multivariate likelihood method
Speaker: Sarah Budd (CDF Collaboration) PDF
Abstract:
The electroweak production of single top quarks has been sought after since the discovery of the top quark more than 10 years ago. The measurement of the cross section for single top quarks provides sensitivity to the CKM element $V_{tb}$ and is sensitive to various models of physics beyond the standard model. We present new results from the search for single top quark production using 2 fb$^{-1}$ of data accumulated with the CDF detector. We select events with one charged lepton, large missing transverse energy, and two jets, where one jet is identified as a $b$-quark jet using displaced secondary-vertex information from the CDF silicon detector at the Fermilab Tevatron. Results are given using a multivariate likelihood function, used to search for s-channel and t-channel single-top production as well as the combined process.
|
Search for single top quark production at CDF using a matrix element method
Speaker: Peter Dong (CDF collaboration) PDF
Abstract: We present recent results from searches for single-top-quark production
using 2 fb$^{-1}$ of data accumulated with the CDF detector at the Fermilab Tevatron.
We select events with one charged lepton, large missing transverse
energy, and two jets, where one jet is identified as a b-quark jet using
displaced secondary-vertex information from the CDF silicon detector.
We employ a matrix-element analysis technique and a neural-network jet-flavor separator to improve separation of signal and background and greatly improve the sensitivity of our search.
|
|
Optimizing the search for single top quark and $WH$ production at CDF
Speaker: Bruno Casal (CDF collaboration) PDF
Abstract: We report new searches for single top quarks and $WHiggs$ production in a lepton+jets channel using 2 fb$^{-1}$ of data accumulated with the CDF detector at the Fermilab Tevatron. We present ways to increase the acceptance of candidate events using complementary trigger paths. The sensitivity of our search is further improved by employing a boosted decision tree together with a neural-network jet-flavor separator to better classify signal and background events in the analysis.
|
|
Top Mass
|
Measurement of the top quark mass in the lepton+jets channel using quantities that are independent of the jet energy scale at CDF
Speaker: Ford Garberson (CDF collaboration) PDF
Abstract: We will present two techniques for measuring the top quark mass in the lepton plus jets channel using quantities independent of the jet energy scale. One technique exploits the correlation of the transverse decay length of $b$-tagged jets with the top quark mass, and the other exploits the correlation of the transverse momentum of the lepton in the same events with the top quark mass. While these results are still statistically limited, their precision will improve with added data at the Tevatron and the LHC. Further, since their correlation to more conventional top quark mass measurement techniques is small, they will help to reduce the overall uncertainty on the top mass in combination with other results.
|
Meaurement of the top quark mass in the lepton+track sample at CDF
Speaker: Marco Trovato (CDF Collaboration) PDF
Abstract: We report on a measurement of the top quark mass in the lepton+track sample of $t\bar t$ events at CDF. This new selection was applied to $t\bar t$ candidates in the dilepton channel in order to increase the acceptance by relaxing the cuts on one lepton. To constrain the event kinematics the azimuthal angles of the two neutrinos are assumed as known and the top quark mass is reconstructed accordingly. The full neutrino phase space is scanned and $chi^2$-dependent weights are given to the solutions in order to build a preferred mass for each event. The integrated luminosity of the data sample is 2.1 fb$^{-1}$. 236 candidate events were reconstructed and fitted as a superposition of signal and background. In a constrained fit with 105.8 $\pm$ 12.9 background events as determined in the production cross section studies we measure $m_t$ = 167.7 + 4.2 - 4.0 (stat) $\pm$ 3.1 (syst.) GeV/c^2
If the background is left unconstrained we measure $m_t$ = 167.7 + 4.5 - 4.3 (stat) $\pm$ 3.1 (syst.) GeV/$c^2$.
|
Meaurement of the top quark mass in the lepton+jets channel using jets with large cone size at CDF
Speaker: Maria d'Enrico (CDF Collaboration) PDF
Abstract: A measurement of the top quark mass in the lepton + jets decay channel
$t\bar{t}\to W^+b + W^-\bar{b} \to l^+\nu b + q\bar{q}'\bar{b}$ is
performed on a selected sample of top event candidates, named ``clean events''.
This is a kinematical selection based on jet shape analysis. Clean events
are selected comparing two jet reconstructions, implemented with Cone
Algorithm of 0.4 or 0.7 radius, by requiring jets reconstructed within
a radius R = 0.4 to be uniquely linked to jets reconstructed with R = 0.7.
By this request the contribution of events with jets due to gluon
radiation is reduced.
The top mass value is obtained using the standard template method. Monte
Carlo generated signal and background events are reconstructed using an
event-by-event $\chi^2$ kinematics fit, determining distributions of the
reconstructed top mass corresponding to the lowest $\chi^2$ value. A likelihood
fit is used to compare the data mass distribution with the Monte Carlo templates.
The results show that the clean selection combined with requesting exactly 4 jets
allows obtaining an improved systematic uncertainty on the top mass measurement.
|
Top quark mass measurement in the lepton+jets and dilepton channels at CDF using a template method
Speaker: Hyun Su Lee (CDF Collaboration) PDF
Abstract:
We present a measurement of the top quark mass using the CDF detector at the Fermilab Tevatron in a 2 fb$^{-1}$ data sample observed in the lepton+jets and two leptons final states. In the lepton+jets channel, we determine the reconstructed top quark invariant mass in each event by minimizing a $chi^2$ for the overconstrained kinematic system. At the same time, we measure the mass of the hadronically decaying $W$ boson in the same event sample, that provides an in situ improvement in the determination of the jet energy scale. In the dilepton channel, the reconstruction of the top quark mass involves an under-constrained system due to two neutrinos in each event. We integrate undetermined kinematic variables and produce a probability distribution which gives the relative likelihood of different values of the top quark mass. We extract the top quark mass and the jet energy scale by comparing representative distributions constructed from simulated events to the data distribution. We simultaneously fit for the top quark mass and the jet energy scale using two observables in the lepton + jets and dilepton channels with a single likelihood.
|
Top quark mass measurement in the lepton+jets channel at CDF using a mulitvariate template method
Author: Paul Lujan (CDF Collaboration) PDF
Abstract: We present a preliminary measurement of the top quark mass using data collected by the CDF II detector at the Fermilab Tevatron from $p\bar p$ collisions at $\sqrt(s)$ = 1.96 GeV. We reconstruct $t\bar t$ events in the lepton + jets channel using the Multivariate Template Method (MTM), which uses a matrix element integration with transfer functions relating jet and parton momentum to build a likelihood function for each event as a function of top mass. An additional likelihood cut is used to reject background and poorly-modeled signal events, improving our overall resolution in constructing the final likelihood function to determine the overall top quark mass value.
|
Top quark mass measurement in the dilepton channel at CDF using a neural network event selection and matrix element method
Speaker: Ravi Shekhar (CDF Collaboration) PDF
Abstract: We present a measurement of the top quark mass using events in the dilepton decay channel. The events used in this analysis are selected using a genetically-evolved artificial neural network that is optimized directly for precision in the top quark mass measurements. This is the first application of this method in high energy physics. We extract the top quark mass from a probability that a given event is consistent with $t\bar{t}$ decay in the dilepton channel. The probability is evaluated using the differential cross-section for ttbar production and decay. The effect of background events in the sample is accounted for by evaluating differential cross sections for major background processes. Using 2 $fb^{-1}$ of $p\bar{p}$ data collected at the CDF II detector, we measure $m_{t} = 171.2 \pm 2.7(\textrm{stat.}) \pm 2.9(\textrm{syst.}) \mathrm{~GeV}/c^2$. We discuss the gain in sensitivity due to the use of the evolving neural network.
|
Measurement of the top quark mass using the matrix element analysis technique in the lepton + jets channel with in situ W calibration at CDF
Speaker: Daryl Hare (CDF Collaboration) PDF
Abstract:
We present a top quark mass measurement from $p\bar p$ collisions at $\sqrt{s}$=1.96 TeV at CDF. We use events from $p\bar p$ to $t\bar t$ in the lepton+jets channel requiring one charged lepton, high missing transverse energy and at least 4 jets, at least one of which must be identified as a $b$-jet. The top quark mass is extracted with a 2D unbinned likelihood fit using per-event probabilities calculated using leading-order signal ($t\bar t$) and background ($W$+jets) matrix elements. The probabilities are a function of both the top quark mass and the energy scale of the calorimeter jets (JES) which is measured in-situ by constraining the invariant mass of two hadronic jets to the $W$ boson mass.
|
