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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Modelling nearest neighbour distributions of biased tracers using hybrid effective field theory

ABSTRACT We investigate the application of hybrid effective field theory (HEFT) – which combines a Lagrangian bias expansion with subsequent particle dynamics from N-body simulations – to the modelling of k-nearest neighbour cumulative distribution functions (kNN-CDFs) of biased tracers of the cosmological matter field. The kNN-CDFs are sensitive to all higher order connected N-point functions in the data, but are computationally cheap to compute. We develop the formalism to predict the kNN-CDFs of discrete tracers of a continuous field from the statistics of the continuous field itself. Using this formalism, we demonstrate how kNN-CDF statistics of a set of biased tracers, such as haloes or galaxies, of the cosmological matter field can be modelled given a set of low-redshift HEFT component fields and bias parameter values. These are the same ingredients needed to predict the two-point clustering. For a specific sample of haloes, we show that both the two-point clustering and the kNN-CDFs can be well-fit on quasi-linear scales (≳ 20h−1Mpc) by the second-order HEFT formalism with the same values of the bias parameters, implying that joint modelling of the two is possible. Finally, using a Fisher matrix analysis, we show that including kNN-CDF measurements over the range of allowed scales in the HEFT framework can improve the constraints on σ8 by roughly a factor of 3, compared to the case where only two-point measurements are considered. Combining the statistical power of kNN measurements with the modelling power of HEFT, therefore, represents an exciting prospect for extracting greater information from small-scale cosmological clustering.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Tests of factorization and SU(3) relations in B decays into heavy-light final states

Using data from the B factories and the Tevatron, we perform tests of how well nonleptonic B decays of the kind B{yields}D{sub (s)}{sup (*)}P, where P is a pion or kaon, are described within the factorization framework. We find that factorization works well--as is theoretically expected--for color-allowed, tree-diagram-like topologies. Moreover, also exchange topologies, which have a nonfactorizable character, do not show any anomalous behavior. We discuss also isospin triangles between the B{yields}D{sup (*)}{pi} decay amplitudes, and determine the corresponding amplitudes in the complex plane, which show a significant enhancement of the color-suppressed tree contribution with respect to the factorization picture. Using data for B{yields}D{sup (*)}K decays, we determine SU(3)-breaking effects and cannot resolve any nonfactorizable SU(3)-breaking corrections larger than {approx}5%. In view of these results, we point out that a comparison between the B{sub d}{sup 0}{yields}D{sup +}{pi}{sup -} and B{sub s}{sup 0}{yields}D{sub s}{sup +}{pi}{sup -} decays offers an interesting new determination of f{sub d}/f{sub s}. Using CDF data, we obtain the most precise value of this ratio at CDF, and discuss the prospects for a corresponding measurement at LHCb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Search for new heavy particles decaying to ZZ→llll, lljj in pp̄ collisions at √s=1.96 TeV

We report on a search for anomalous production of Z boson pairs through a massive resonance decay in data corresponding to 2.5–2.9 fb⁻¹ of integrated luminosity in pp̄ collisions at √s=1.96 TeV using the CDF II detector at the Fermilab Tevatron. This analysis, with more data and channels where the Z bosons decay to muons or jets, supersedes the 1.1 fb⁻¹ four-electron channel result previously published by CDF. In order to maintain high efficiency for muons, we use a new forward tracking algorithm and muon identification requirements optimized for these high signal-to-background channels. Predicting the dominant backgrounds in each channel entirely from sideband data samples, we observe four-body invariant mass spectra above 300 GeV/c² that are consistent with background. We set limits using the acceptance for a massive graviton resonance that are 7–20 times stronger than the previously published direct limits on resonant ZZ diboson production.

Aaltonen, T.↗
DOE OSTI2011

New color-octet axial vector boson revisited

In this paper we reexamine how to utilize the previous proposed color-octet axial-vector boson Z{sub C} to explain the 3.4{sigma} anomaly of tt forward-backward (FB) asymmetry A{sub FB} for m{sub tt}>450 GeV observed by CDF. Our numerical results indicate that the best-fit parameters are g{sub A}{sup q}=0.07, g{sub A}{sup Q}=3, and M{sub C}=440 GeV, which are obtained by fitting the mass dependent A{sub FB} and total cross section data provided by a recent CDF measurement. Here g{sub A}{sup q}(g{sub A}{sup Q}) and M{sub C} are the axial couplings among Z{sub C} with the first two (the third) generation quarks, and Z{sub C} mass, respectively. We also calculate one-side forward-backward asymmetry A{sub OFB} for top and bottom quark pair production at the LHC, focusing on the new contributions from Z{sub C}. Our studies show that A{sub OFB} can be utilized to measure the properties of new particle Z{sub C}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

An effective Z'

We describe a method to couple Z' gauge bosons to the standard model (SM), without charging the SM fields under the U(1)', but instead through effective higher-dimension operators. This method allows complete control over the tree-level couplings of the Z' and does not require altering the structure of any of the SM couplings, nor does it contain anomalies or require introduction of fields in nonstandard SM representations. Moreover, such interactions arise from simple renormalizable extensions of the SM—the addition of vectorlike matter that mixes with SM fermions when the U(1)' is broken. We apply effective Z' models as explanations of various recent anomalies: the D0 same-sign dimuon asymmetry, the CDF W+di-jet excess and the CDF top forward-backward asymmetry. In the case of the W+di-jet excess we also discuss several complementary analyses that may shed light on the nature of the discrepancy. We consider the possibility of non-Abelian groups, and discuss implications for the phenomenology of dark matter as well.

Fox, Patrick J.↗
DOE OSTI2012

Search for new phenomena in events with two Z bosons and missing transverse momentum in pp̄ collisions at √s=1.96 TeV

We present a search for new phenomena in events with two reconstructed Z bosons and large missing transverse momentum, sensitive to processes pp̄→X₂X₂→ZZX₁X₁, where X₂ is an unstable particle decaying as X₂→ZX₁ and X₁ is undetected. The particles X₁ and X₂ may be, among other possibilities, fourth-generation neutrinos or supersymmetric particles. We study the final state in which one Z boson decays to two charged leptons and the second decays hadronically. In data corresponding to an integrated luminosity of 4.2 fb⁻¹ from proton-antiproton collisions recorded by the CDF II detector at the Tevatron, with center-of-mass energy of 1.96 TeV, we find agreement between data and standard-model backgrounds. We calculate 95% confidence level upper limits on the cross section of the process pp̄→X₂X₂→ZZX₁X₁ ranging from 50 fb to 1 pb, depending on the masses of X₁ and X₂.

Aaltonen, T.↗
DOE OSTI2012

Measurement of the WZ cross section and triple gauge couplings in pp̄ collisions at √s=1.96 TeV

This article describes the current most precise measurement of the WZ production cross section as well as limits on anomalous WWZ couplings at a center-of-mass energy of 1.96 TeV in proton-antiproton collisions for the Collider Detector at Fermilab (CDF). WZ candidates are reconstructed from decays containing three charged leptons and missing energy from a neutrino, where the charged leptons are either electrons or muons. Using data collected by the CDF II detector (7.1 fb⁻¹ of integrated luminosity), 63 candidate events are observed with the expected background contributing 8±1 events. The measured total cross section σ(pp̄→WZ)=3.93 +0.60 –0.53 (stat) +0.59 –0.46 (syst) pb is in good agreement with the standard model prediction of 3.50±0.21. The same sample is used to set limits on anomalous WWZ couplings.

Aaltonen, T.↗
DOE OSTI2012

Diffractive dijet production in p̄p collisions at √s=1.96 TeV

We report on a study of diffractive dijet production in p̄p collisions at s√=1.96 TeV using the CDF II detector at the Fermilab Tevatron p̄p collider. A data sample from 310 pb⁻¹ of integrated luminosity collected by triggering on a high transverse energy jet, EjetT, in coincidence with a recoil antiproton detected in a Roman pot spectrometer is used to measure the ratio of single-diffractive to inclusive-dijet event rates as a function of x p̄ of the interacting parton in the antiproton, the Bjorken-x, x p̄ Bj , and a Q²≈(E jet T )² in the ranges 10⁻³ p̄ Bj <10⁻¹ and 10² p̄ <0.09 and a four-momentum transfer squared t p̄ >-4 GeV². The t p̄ dependence is measured as a function of Q² and x p̄ Bj and compared with that of inclusive single diffraction dissociation. We find weak x p̄ Bj and Q² dependencies in the ratio of single diffractive to inclusive event rates, and no significant Q² dependence in the diffractive t p̄ distributions.

Aaltonen, T.↗
DOE OSTI2011

Search for High Mass Resonances Decaying to Muon Pairs in {radical}(s)=1.96 TeV pp Collisions

We present a search for a new narrow, spin-1, high mass resonance decaying to {mu}{sup +}{mu}{sup -}+X, using a matrix-element-based likelihood and a simultaneous measurement of the resonance mass and production rate. In data with 4.6 fb{sup -1} of integrated luminosity collected by the CDF detector in pp collisions at {radical}(s)=1960 GeV, the most likely signal cross section is consistent with zero at 16% confidence level. We therefore do not observe evidence for a high mass resonance and place limits on models predicting spin-1 resonances, including M>1071 GeV/c{sup 2} at 95% confidence level for a Z{sup '} boson with the same couplings to fermions as the Z boson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Search for Heavy Bottomlike Quarks Decaying to an Electron or Muon and Jets in pp Collisions at {radical}(s)=1.96 TeV

We report the most sensitive direct search for pair production of fourth-generation bottomlike chiral quarks (b{sup '}) each decaying promptly to tW. We search for an excess of events with an electron or muon, at least five jets (one identified as due to a b or c quark), and an imbalance of transverse momentum by using data from pp collisions collected by the CDF II detector at Fermilab with an integrated luminosity of 4.8 fb{sup -1}. We observe events consistent with background expectation, calculate upper limits on the b{sup '} pair-production cross section ({sigma}{sub bb-bar}{sup '} < or approx. 30 fb for m{sub b}{sup '}>375 GeV/c{sup 2}), and exclude m{sub b}{sup '}<372 GeV/c{sup 2} at 95% confidence level assuming a 100% branching ratio of b{sup '} to tW.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Invariant Mass Distribution of Jet Pairs Produced in Association with a W Boson in pp Collisions at {radical}(s)=1.96 TeV

We report a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb{sup -1}. The observed distribution has an excess in the 120-160 GeV/c{sup 2} mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this Letter, we report studies of the properties of this excess.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Search for a Very Light CP-Odd Higgs Boson in Top Quark Decays from pp̄ Collisions at √s=1.96 TeV

We present the results of a search for a very light CP-odd Higgs boson a 0 1 originating from top quark decays t→H ± b→W ±(*) a 0 1 b, and subsequently decaying into τ⁺τ⁻. Using a data sample corresponding to an integrated luminosity of 2.7 fb⁻¹ collected by the CDF II detector in pp̄ collisions at 1.96 TeV, we perform a search for events containing a lepton, three or more jets, and an additional isolated track with transverse momentum in the range 3 to 20 GeV/c. Observed events are consistent with background sources, and 95% C.L. limits are set on the branching ratio of t→H ± b for various masses of H ± and a 0 1 .

Aaltonen, T.↗
DOE OSTI2011

QCD Resummation for Jet Substructures

We provide a novel development in jet physics by predicting the energy profiles of light-quark and gluon jets in the framework of perturbative QCD. Resumming large logarithmic contributions to all orders in the coupling constant, our predictions are shown to agree well with Tevatron CDF and Large Hadron Collider CMS data. We also extend our resummation formalism to the invariant mass distributions of light-quark and gluon jets produced in hadron collisions. The predicted peak positions and heights in jet mass distributions are consistent with CDF data within uncertainties induced by parton distribution functions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement of Polarization and Search for CP Violation in B{sub s}{sup 0}{yields}{phi}{phi} Decays

We present the first measurement of polarization and CP-violating asymmetries in a B{sub s}{sup 0} decay into two light vector mesons, B{sub s}{sup 0}{yields}{phi}{phi}, and an improved determination of its branching ratio using 295 decays reconstructed in a data sample corresponding to 2.9 fb{sup -1} of integrated luminosity collected by the CDF experiment at the Fermilab Tevatron collider. The fraction of longitudinal polarization is determined to be f{sub L}=0.348{+-}0.041(stat){+-}0.021(syst), and the branching ratio B(B{sub s}{sup 0}{yields}{phi}{phi})=[2.32{+-}0.18(stat){+-}0.82(syst)]x10{sup -5}. Asymmetries of decay angle distributions sensitive to CP violation are measured to be A{sub u}=-0.007{+-}0.064(stat){+-}0.018(syst) and A{sub v}=-0.120{+-}0.064(stat){+-}0.016(syst).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement of the B s 0 Lifetime in Fully and Partially Reconstructed B s 0 →D s - (Φπ⁻)X Decays in pp̄ Collisions at √s=1.96 TeV

We present a measurement of the BB s 0 lifetime in fully and partially reconstructed B s 0 →D s - (Φπ⁻)X decays in 1.3 fb⁻¹ collected in pp̄ collisions at √s=1.96 TeV by the CDF II detector at the Fermilab Tevatron. We measure τ(B s 0 )=1.518±0.041(stat)±0.027(syst) ps. The ratio of this result and the world average B⁰ lifetime yields τ(B s 0 )/τ(B⁰)=0.99±0.03, which is in agreement with recent theoretical predictions.

Aaltonen, T.↗