Collider Detector At Fermilab Research Articles

New results of experiments at the Tevatron

The most important results obtained by the D0 and CDF collaborations in 2011–2012 on the search for the Higgs boson, studying the properties of the t-quark, measuring the W-boson mass, studying meson and baryon states with b-quarks, and a search for a New Physics beyond the Standard Model, are discussed. A comparison with the experimental results from the LHC is given.

Pseudorapidity Distribution of Charged Particles and Square Speed of Sound Parameter inp-porp-p-Collisions over an Energy Range from 0.053 to 7 TeV

Pseudorapidity distributions of charged particles produced in proton-proton (p-p) or proton-antiproton (p-p-) collisions over an energy range from 0.053 to 7 TeV are studied by using the four-component Landau hydrodynamic model. The results calculated by the model are in agreement with the experimental data of the UA5, PHOBOS, UA1, P238, CDF, ALICE, and CMS Collaborations which present orderly from low to high energies. According to the distribution widths of different components, the values and some features of square speed of sound parametercs2for “participant” and “spectator” quark components are obtained. It is shown that the speed of sound for “participant” quark components agrees approximately with that for “spectator” quark components in the error ranges. The present work is useful for studying nucleus-nucleus collisions in the related energy range.

Measurement of top quark properties at the Tevatron and LHC

Almost two decades after its discovery at Fermilab's Tevatron collider experiments, the top quark is still under the spotlight due to its connections to some of the most interesting puzzles in the Standard Model. The Tevatron has been shut down two years ago, yet some interesting results are coming out of the CDF and D0 collaborations. The LHC collider at CERN produced two orders of magnitude more top quarks than Tevatron's, thus giving birth to a new era for top quark physics. While the LHC is also down at the time of this writing, many top quark physics results are being extracted out of the 7 TeV and 8 TeV proton proton collisions by the ATLAS and CMS collaborations, and many more are expected to appear before the LHC will be turned on again sometime in 2015. These proceedings cover a selection of recent results produced by the Tevatron and LHC experiments.

Top cross-sections and single top

This paper summarizes top quark cross-section measurements at the Tevatron and the LHC. Top quark pair production cross-sections have been measured in all decay modes by the ATLAS and CMS collaborations at the LHC and by the CDF and D0 collaborations at the Tevatron. Single top quark production has been observed at both the Tevatron and the LHC. The t-channel and associated Wt production modes have been observed at the LHC and evidence for s-channel production has been reported by the Tevatron collaborations.

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 (ET) 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.

Flavor physics: past, present, future

In recent years, huge progress in flavor physics and in the physics of CP violation has been achieved by the BaBar, Belle, CDF, D0 and LHCb experiments. This led to a significant theoretical progress. In particular, the Kobayashi–Maskawa mechanism has been proven to be the dominant source of the observed CP violation, and the Cabibbo–Kobayashi–Maskawa mechanism has been proven to be a major player in the observed flavor changing neutral current (FCNC) processes. Two major questions in flavor physics remain however open. Firstly, the Standard Model flavor puzzle is the question of what is the source of the structure—smallness and hierarchy—in the charged fermion flavor parameters. The measurement of neutrino related flavor parameters only added to the complexity of this puzzle. Secondly, the New Physics flavor puzzle is the following question: if there is new physics at the TeV scale, why and how are its contributions to FCNC so strongly suppressed? The high pT experiments at the LHC, ATLAS and CMS, are likely to solve the latter puzzle, and may even provide hints to the solution of the former.

Charmonium production at the Tevatron and Large Hadron Collider in the Regge limit of QCD

Processes involving direct J/ψ-meson production in proton-antiproton and proton-proton collisions are studied under the assumption of gluon Reggeization in t-channel exchanges and with the aid of the formalism of nonrelativistic quantum chromodynamics. The present calculations are performed in the leading approximation in the strong coupling constant α s and in the relative quark velocity v. The octet nonperturbative matrix elements for the transition of a c \(\bar c\) pair to quarkonium are fixed in fitting the transverse-momentumspectra obtained by the CDF Collaboration for J/ψ mesons at the Tevatron collider. The spectra of J/ψ-meson production at the energies of the Large Hadron Collider are predicted, and the resulting predictions agree well with experimental data obtained by the ATLAS, CMS, and LHCb Collaborations at \(\sqrt S \) = 7 TeV.

Analysis of the semileptonicΛb→Λℓ+ℓ−transition in the topcolor-assisted technicolor model

We comparatively analyze the flavor changing neutral current process of the $\Lambda_b \rightarrow \Lambda \ell^+ \ell^-$ in the standard model as well as topcolor-assisted technicolor model using the form factors calculated via light cone QCD sum rules in full theory. In particular, we calculate the decay width, branching ratio and lepton forward-backward asymmetry related to this decay channel. We compare the results of the topcolor-assisted technicolor model with those of the standard model and debate how the results of the topcolor-assisted technicolor model depart from the standard model predictions. We also compare our results on the differential branching ratio with recent experimental data provided by CDF and LHCb Collaborations.

Associative Memory for L1 Track Triggering in LHC Environment

The CDF Associative-Memory device (AM), proven technology developed for the Silicon-Vertex-Trigger at the CDF experiment, is one of the proposed solutions at the LHC for track reconstruction at level-1 in the HL-LHC upgrade, for very high-luminosity conditions (hundreds proton-proton collisions every 25 ns, at 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 2</sup> sec <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 1</sup> ). This luminosity requires a drastic revision of the existing trigger strategies. In the CMS experiment, one of the identified challenges for future upgrades is the capability of using already at L1 the tracker information to trigger events. Simulation studies show that this can be achieved by correlating hits on two closely spaced silicon strip sensors. This strategy requires massive computing power, to minimize the online execution time of complex tracking algorithms and the “combinatorial challenge.” The AM allows to compare the tracker information of each event to pre-calculated “expectations” (pattern matching) in a so short time that tracks can contribute to the trigger decision. One of the main challenges for the CMS tracker is the latency due to the tracker data distribution to the AM processors. A very parallelized readout architecture and a possible layout are discussed.

Combination of CDF and D0W-Boson mass measurements

We summarize and combine direct measurements of the mass of the $W$ boson in $\sqrt{s} = 1.96 \text{TeV}$ proton-antiproton collision data collected by CDF and D0 experiments at the Fermilab Tevatron Collider. Earlier measurements from CDF and D0 are combined with the two latest, more precise measurements: a CDF measurement in the electron and muon channels using data corresponding to $2.2 \mathrm{fb}^{-1}$ of integrated luminosity, and a D0 measurement in the electron channel using data corresponding to $4.3 \mathrm{fb}^{-1}$ of integrated luminosity. The resulting Tevatron average for the mass of the $W$ boson is $\MW = 80\,387 \pm 16 \text{MeV}$. Including measurements obtained in electron-positron collisions at LEP yields the most precise value of $\MW = 80\,385 \pm 15 \text{MeV}$.

Higgs boson studies at the Tevatron

We combine searches by the CDF and D0 Collaborations for the standard model Higgs boson with mass in the range 90--200 GeV$/c^2$ produced in the gluon-gluon fusion, $WH$, $ZH$, $t{\bar{t}}H$, and vector boson fusion processes, and decaying in the $H\rightarrow b{\bar{b}}$, $H\rightarrow W^+W^-$, $H\rightarrow ZZ$, $H\rightarrow\tau^+\tau^-$, and $H\rightarrow \gamma\gamma$ modes. The data correspond to integrated luminosities of up to 10 fb$^{-1}$ and were collected at the Fermilab Tevatron in $p{\bar{p}}$ collisions at $\sqrt{s}=1.96$ TeV. The searches are also interpreted in the context of fermiophobic and fourth generation models. We observe a significant excess of events in the mass range between 115 and 140 GeV/$c^2$. The local significance corresponds to 3.0 standard deviations at $m_H=125$ GeV/$c^2$, consistent with the mass of the Higgs boson observed at the LHC, and we expect a local significance of 1.9 standard deviations. We separately combine searches for $H \to b\bar{b}$, $H \to W^+W^-$, $H\rightarrow\tau^+\tau^-$, and $H\rightarrow\gamma\gamma$. The observed signal strengths in all channels are consistent with the presence of a standard model Higgs boson with a mass of 125 GeV/$c^2$.

Some new results of the CDF and D0 experiments

New results obtained in experiments at the Tevatron and associated with t- and b-quark and W-boson physics are presented and are compared with respective Standard Model predictions. Prospects of improving the precision of D0 and CDF results after a complete treatment of the accumulated data sample are discussed.

Single Top Quark Measurements at the Tevatron

This paper reports the measurement of electroweak production of single top quarks in lepton plus jets final state by the DØ and CDF collaborations. At Fermilab's 1.96 TeV proton-antiproton collider, events are selected from several inverse femtobarns of data in the W+jets topology consistent with the signature of an isolated charged lepton (electron or muon), large missing transverse energy from the W boson decay and two or more jets, at least one of them is required to be identified as originating from a bottom quark. Sophisticated multivariate analysis techniques are employed to separate the small single top quark signal from background. Both experiments measure the single top production cross section in s-channel, t-channel and s + t-channel. The data is also used to extract limits on the CKM matrix element |Vtb|.

Next-to-leading-order nonrelativistic QCD disfavors the interpretation ofX(3872)asχc1(2P)

We study ${\ensuremath{\chi}}_{c1}(2P)$-inclusive hadroproduction at next-to-leading-order (NLO), both in ${\ensuremath{\alpha}}_{s}$ and ${v}^{2}$, within the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD), including the color-singlet $^{3}P_{1}^{[1]}$ and color-octet $^{3}S_{1}^{[8]}$ $c\overline{c}$ Fock states as well as the mixing of the latter with the $^{3}D_{1}^{[8]}$ state. Assuming the recently discovered $X(3872)$ hadron to be the ${J}^{PC}={1}^{++}$ charmonium state ${\ensuremath{\chi}}_{c1}(2P)$, we perform a fit to the cross sections measured by the CDF, CMS, and LHCb Collaborations. We obtain either an unacceptably high value of ${\ensuremath{\chi}}^{2}$, a value of $|{R}_{2P}^{\ensuremath{'}}(0)|$ incompatible with well-established potential models, or an intolerable violation of the NRQCD velocity rules. We thus conclude that NLO NRQCD is inconsistent with the hypothesis $X(3872)\ensuremath{\equiv}{\ensuremath{\chi}}_{c1}(2P)$.

Angular distributions at the Tevatron

We review measurements of angular distributions in top pair events by the CDF and D0 collaborations. The helicity of W bosons produced in top decays was measured, as was the correlation between the top quark and antiquark spins in pp̄ → tt̄ production. We also review the information available on top quark polarization in pp̄ → tt̄ production.

Signal modeling systematic uncertainties at Tevatron

An overview of the signal modeling systematic uncertainties in the top quark measurements at the Tevatron is given. We discuss approaches developed by the D0 and CDF collaborations for the estimation of these systematic uncertainties. Uncertainties related to the initial and final state radiation, higher order corrections, choice of the hadronization model, color reconnection and choice of the parton distribution functions set are considered in this contribution.

Search for Pair Production of Strongly Interacting Particles Decaying to Pairs of Jets inpp¯Collisions ats=1.96 TeV

We present a search for the pair production of a narrow nonstandard-model strongly interacting particle that decays to a pair of quarks or gluons, leading to a final state with four hadronic jets. We consider both nonresonant production via an intermediate gluon as well as resonant production via a distinct nonstandard-model intermediate strongly interacting particle. We use data collected by the CDF experiment in proton-antiproton collisions at √[s]=1.96 TeV corresponding to an integrated luminosity of 6.6 fb(-1). We find the data to be consistent with nonresonant production. We report limits on σ(pp[over ¯]→jjjj) as a function of the masses of the hypothetical intermediate particles. Upper limits on the production cross sections for nonstandard-model particles in several resonant and nonresonant processes are also derived.

J/ψωdecay channel of theX(3872)charm meson molecule

Analyses of the $J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decay channel of the $X(3872)$ resonance by the CDF, Belle, and LHCb Collaborations have established its ${J}^{PC}$ quantum numbers as ${1}^{++}$. An analysis of the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ invariant mass distribution in the $J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decay channel by the BABAR Collaboration indicated a preference for ${2}^{\ensuremath{-}+}$ over ${1}^{++}$. We point out that a proper evaluation of the ${\ensuremath{\chi}}^{2}$ in that analysis increases the probability for ${1}^{++}$ from 7.1% to about 18.7%. In the case of quantum numbers ${1}^{++}$, where the $X$ has an $S$-wave coupling to $J/\ensuremath{\psi}\ensuremath{\omega}$, the proximity of the $J/\ensuremath{\psi}\ensuremath{\omega}$ threshold to ${D}^{*}\overline{D}$ thresholds and the narrow width of the $\ensuremath{\omega}$ suggest that the effects of scattering between $J/\ensuremath{\psi}\ensuremath{\omega}$ and charm meson pairs could be significant. We derive invariant mass distributions for $J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ and ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ that take into account $S$-wave scattering between the ${D}^{*0}{\overline{D}}^{0}$, ${D}^{*+}{D}^{\ensuremath{-}}$, and $J/\ensuremath{\psi}\ensuremath{\omega}$ channels. We also analyze the effects of scattering through the ${\ensuremath{\chi}}_{c1}(2P)$ charmonium resonance. We find that scattering effects are unable to produce significant changes in the shape of the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ invariant mass distribution.

Operational experience, improvements, and performance of the CDF Run II silicon vertex detector

The Collider Detector at Fermilab (CDF) pursues a broad physics program at Fermilab's Tevatron collider. Between Run II commissioning in early 2001 and the end of operations in September 2011, the Tevatron delivered 12fb−1 of integrated luminosity of pp¯ collisions at s=1.96TeV. The physics at CDF includes precise measurements of the masses of the top quark and W boson, measurement of CP violation and Bs mixing, and searches for Higgs bosons and new physics signatures, all of which require heavy flavor tagging with large charged particle tracking acceptance. To realize these goals, in 2001 CDF installed eight layers of silicon microstrip detectors around its interaction region. These detectors were designed for 2–5 years of operation, radiation doses up to 2Mrad (0.02Gy), and were expected to be replaced in 2004. The sensors were not replaced, and the Tevatron run was extended for several years beyond its design, exposing the sensors and electronics to much higher radiation doses than anticipated. In this paper we describe the operational challenges encountered over the past 10 years of running the CDF silicon detectors, the preventive measures undertaken, and the improvements made along the way to ensure their optimal performance for collecting high quality physics data. In addition, we describe the quantities and methods used to monitor radiation damage in the sensors for optimal performance and summarize the detector performance quantities important to CDF's physics program, including vertex resolution, heavy flavor tagging, and silicon vertex trigger performance.

PromptΥ(nS)production at the LHC in the Regge limit of QCD

We study prompt $\ensuremath{\Upsilon}(nS)$ hadroproduction ($n=1$, 2, 3) invoking the hypothesis of gluon Reggeization in $t$-channel exchanges at high energy and the factorization formalism of nonrelativistic quantum chromodynamics at leading order in the strong-coupling constant ${\ensuremath{\alpha}}_{s}$ and the relative velocity $v$ of the bound quarks. The transverse-momentum distributions of prompt $\ensuremath{\Upsilon}(nS)$-meson production measured by the ATLAS Collaboration at the CERN LHC are fitted to obtain the color-octet nonperturbative long-distance matrix elements, which are used to predict prompt $\ensuremath{\Upsilon}(nS)$ production spectra measured by the CMS and LHCb Collaborations. At the numerical calculation, we adopt the Kimber-Martin-Ryskin prescription to derive unintegrated gluon distribution function of the proton from its collinear counterpart, for which we use the Martin-Roberts-Stirling-Thorne set. We find good agreement with measurements by the ATLAS, CMS, and LHCb Collaborations at the LHC at the hadronic c.m. energy $\sqrt{S}=7\text{ }\text{ }\mathrm{TeV}$ as well as with measurements by the CDF Collaboration at the Fermilab Tevatron.