135 Matching Results

Search Results

Advanced search parameters have been applied.

Randall-Sundrum membrane model with 7D anti-de Sitter space

Description: In the same sense that AdS{sub 5} warped geometries arise naturally from Type IIB string theory with stacks of D3 branes, AdS{sub 7} warped geometries arise naturally from M theory with stacks of M5 branes. We compactify two spatial dimensions of AdS{sub 7} to get AdS{sub 5} x {Sigma}{sup 2}, where {Sigma}{sup 2} is e.g. a torus T{sup 2} or a sphere S{sup 2}. The metric for {Sigma} inherits the same warp factor as appears in the AdS{sub 5}. Bulk fields generically have both Kaluza-Klein and winding modes associated with {Sigma}. In the effective 5d action these will contribute exotic new excitations. We analyze the 5d spectrum in detail for the case of a bulk scalar or a graviton in AdS{sub 5} x T{sup 2}, in a setup which mimics the first Randall-Sundrum model. The results display several novel features, some of which might be observed in experiments at the LHC. For example, we obtain TeV scale string winding states without lowering the string scale. This is due to the double warping which is a generic feature of winding states along compactified AdS directions. Experimental verification of these signatures of AdS{sub 7} could be interpreted as direct evidence for M theory.
Date: September 1, 2005
Creator: Bao, Ruoyu; /Chicago U., EFI /Chicago U.; Lykken, Joseph D. & /Chicago U., EFI /Chicago U. /Fermilab
Partner: UNT Libraries Government Documents Department

The Interval approach to braneworld gravity

Description: Gravity in five-dimensional braneworld backgrounds may exhibit extra scalar degrees of freedom with problematic features, including kinetic ghosts and strong coupling behavior. Analysis of such effects is hampered by the standard heuristic approaches to braneworld gravity, which use the equations of motion as the starting point, supplemented by orbifold projections and junction conditions. Here we develop the interval approach to braneworld gravity, which begins with an action principle. This shows how to implement general covariance, despite allowing metric fluctuations that do not vanish on the boundaries. We reproduce simple Z{sub 2} orbifolds of gravity, even though in this approach we never perform a Z{sub 2} projection. We introduce a family of ''straight gauges'', which are bulk coordinate systems in which both branes appear as straight slices in a single coordinate patch. Straight gauges are extremely useful for analyzing metric fluctuations in braneworld models. By explicit gauge fixing, we show that a general AdS{sub 5}/AdS{sub 4} setup with two branes has at most a radion, but no physical ''brane-bending'' modes.
Date: June 1, 2005
Creator: Carena, Marcela; /Fermilab; Lykken, Joseph D.; /Fermilab /Chicago U., EFI; Park, Minjoon & /Chicago U., EFI
Partner: UNT Libraries Government Documents Department

Revamped braneworld gravity

Description: Gravity in five-dimensional braneworld backgrounds often exhibits problematic features, including kinetic ghosts, strong coupling, and the vDVZ discontinuity. These problems are an obstacle to producing and analyzing braneworld models with interesting and potentially observable modifications of 4d gravity. We examine these problems in a general AdS{sub 5}/AdS{sub 4} setup with two branes and localized curvature from arbitrary brane kinetic terms. We use the interval approach and an explicit ''straight'' gauge-fixing. We compute the complete quadratic gauge-fixed effective 4d action, as well as the leading cubic order corrections. We compute the exact Green's function for gravity as seen on the brane. In the full parameter space, we exhibit the regions which avoid kinetic ghosts and tachyons. We give a general formula for the strong coupling scale, i.e. the energy scale at which the linearized treatment of gravity breaks down, for relevant regions of the parameter space. We show how the vDVZ discontinuity can be naturally but nontrivially avoided by ultralight graviton modes. We present a direct comparison of warping versus localized curvature in terms of their effects on graviton mode couplings. We exhibit the first example of DGP-like crossover behavior in a general warped setup.
Date: November 1, 2005
Creator: Bao, Ruoyu; /Chicago U., EFI /Chicago U.; Carena, Marcela; /Fermilab; Lykken, Joseph; /Chicago U., EFI /Chicago U. /Fermilab et al.
Partner: UNT Libraries Government Documents Department

Fossils of reionization in the local group

Description: We use a combination of high-resolution gas dynamics simulations of high-redshift dwarf galaxies and dissipationless simulations of a Milky Way sized halo to estimate the expected abundance and spatial distribution of the dwarf satellite galaxies that formed most of their stars around z {approx} 8 and evolved only little since then. Such galaxies can be considered as fossils of the reionization era, and studying their properties could provide a direct window into the early, pre-reionization stages of galaxy formation. We show that 5-15% of the objects existing at z {approx} 8 do indeed survive until the present in the MW like environment without significant evolution. This implies that it is plausible that the fossil dwarf galaxies do exist in the Local Group. Because such galaxies form their stellar systems early during the period of active merging and accretion, they should have spheroidal morphology regardless of their current distance from the host galaxy. We show that both the expected luminosity function and spatial distribution of dark matter halos which are likely to host fossil galaxies agree reasonably well with the observed distributions of the luminous (L{sub V} > 10{sup 6} Lsun) Local Group fossil candidates near the host galaxy (d<200 kpc). However, the predicted abundance is substantially larger (by a factor of 2-3) for fainter galaxies (L{sub V} < 10{sup 6} Lsun) at larger distances (d>300 kpc). We discuss several possible explanations for this discrepancy.
Date: January 1, 2006
Creator: Gnedin, Nickolay Y.; /Fermilab /KICP, Chicago /Chicago U., EFI; Kravtsov, Andrey V. & /KICP, Chicago /Chicago U., EFI /Chicago U., Astron. Astrophys. Ctr.
Partner: UNT Libraries Government Documents Department

Present Limits on the Precision of SM Predictions for Jet Energies

Description: We investigate the impact of theoretical uncertainties on the accuracy of measurements involving hadronic jets. The analysis is performed using events with a Z boson and a single jet observed in p{bar p} collisions at {radical}s = 1.96 TeV in 4.6 fb{sup -1} of data from the Collider Detector at Fermilab (CDF). The transverse momenta (p{sub T}) of the jet and the boson should balance each other due to momentum conservation in the plane transverse to the direction of the p and {bar p} beams. We evaluate the dependence of the measured p{sub T}-balance on theoretical uncertainties associated with initial and final state radiation, choice of renormalization and factorization scales, parton distribution functions, jet-parton matching, calculations of matrix elements, and parton showering. We find that the uncertainty caused by parton showering at large angles is the largest amongst the listed uncertainties. The proposed method can be re-applied at the LHC experiments to investigate and evaluate the uncertainties on the predicted jet energies. The distributions produced at the CDF environment are intended for comparison to those from modern event generators and new tunes of parton showering.
Date: August 1, 2010
Creator: Paramonov, A.A.; /Argonne; Canelli, F.; /Chicago U., EFI; D'Onofrio, M.; U., /Liverpool et al.
Partner: UNT Libraries Government Documents Department

A proposal to study hard hadron - hadron collisions

Description: We propose a novel technique to study hadron-hadron collisions in which a significant fraction of the available energy is carried off in directions transverse to the beam. The technique is independent of the details of the final state so is ideally suited to searching for the jet-like particle clusters predicted by the parton model. The detector consists of a small calorimeter and several planes of 1 meter square proportional chambers.
Date: June 1, 1973
Creator: Frisch, Henry J.; Shochet, M.; Pilcher, J.; Winstein, B. & /Chicago U., EFI
Partner: UNT Libraries Government Documents Department

BMSSM Higgs Bosons at the Tevatron and the LHC

Description: We study extensions of the Minimal Supersymmetric Standard Model (MSSM) with new degrees of freedom that couple sizably to the MSSM Higgs sector and lie in the TeV range. After integrating out the physics at the TeV scale, the resulting Higgs spectrum can significantly differ from typical supersymmetric scenarios, thereby providing a window Beyond the MSSM (BMSSM). Taking into account current LEP and Tevatron constraints, we perform an in-depth analysis of the Higgs collider phenomenology and explore distinctive characteristics of our scenario with respect to both the Standard Model and the MSSM. We propose benchmark scenarios to illustrate specific features of BMSSM Higgs searches at the Tevatron and the LHC.
Date: May 1, 2010
Creator: Carena, Marcela; /Fermilab /Chicago U., EFI; Ponton, Eduardo; U., /Columbia; Zurita, Jose & U., /Zurich
Partner: UNT Libraries Government Documents Department

First Dark Matter Search Results from a 4-kg CF$_3$I Bubble Chamber Operated in a Deep Underground Site

Description: New data are reported from the operation of a 4.0 kg CF{sub 3}I bubble chamber in the 6800 foot deep SNOLAB underground laboratory. The effectiveness of ultrasound analysis in discriminating alpha decay background events from single nuclear recoils has been confirmed, with a lower bound of >99.3% rejection of alpha decay events. Twenty single nuclear recoil event candidates and three multiple bubble events were observed during a total exposure of 553 kg-days distributed over three different bubble nucleation thresholds. The effective exposure for single bubble recoil-like events was 437.4 kg-days. A neutron background internal to the apparatus, of known origin, is estimated to account for five single nuclear recoil events and is consistent with the observed rate of multiple bubble events. This observation provides world best direct detection constraints on WIMP-proton spin-dependent scattering for WIMP masses >20 GeV/c{sup 2} and demonstrates significant sensitivity for spin-independent interactions.
Date: April 1, 2012
Creator: Behnke, E.; /Indiana U., South Bend; Behnke, J.; /Indiana U., South Bend; Brice, S.J.; /Fermilab et al.
Partner: UNT Libraries Government Documents Department

Implications of the Early X-Ray Afterglow Light Curves of Swift GRBs

Description: According to current models, gamma-ray bursts (GRBs) are produced when the energy carried by a relativistic outflow is dissipated and converted into radiation. The efficiency of this process, {epsilon}{sub {gamma}}, is one of the critical factors in any GRB model. The X-ray afterglow light curves of Swift GRBs show an early stage of flattish decay. This has been interpreted as reflecting energy injection. When combined with previous estimates, which have concluded that the kinetic energy of the late ({approx}> 10 hr) afterglow is comparable to the energy emitted in {gamma}-rays, this interpretation implies very high values of {epsilon}{sub {gamma}}, corresponding to {approx}> 90% of the initial energy being converted into {gamma}-rays. Such a high efficiency is hard to reconcile with most models, including in particular the popular internal-shocks model. We re-analyze the derivation of the kinetic energy from the afterglow X-ray flux and re-examine the resulting estimates of the efficiency. We confirm that, if the flattish decay arises from energy injection and the pre-Swift broad-band estimates of the kinetic energy are correct, then {epsilon}{sub {gamma}} {approx}> 0.9. We discuss various issues related to this result, including an alternative interpretation of the light curve in terms of a two-component outflow model, which we apply to the X-ray observations of GRB 050315. We point out, however, that another interpretation of the flattish decay--a variable X-ray afterglow efficiency (e.g., due to a time dependence of afterglow shock microphysical parameters)--is possible. We also show that direct estimates of the kinetic energy from the late X-ray afterglow flux are sensitive to the assumed values of the shock microphysical parameters and suggest that broad-band afterglow fits might have underestimated the kinetic energy (e.g., by overestimating the fraction of electrons that are accelerated to relativistic energies). Either one of these possibilities implies a lower {gamma}-ray efficiency, and ...
Date: January 17, 2006
Creator: Granot, Jonathan; /KIPAC, Menlo Park; Konigl, Arieh; /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI; Piran, Tsvi & U., /Hebrew
Partner: UNT Libraries Government Documents Department

The Hierarchical Build-Up of Massive Galaxies And the Intracluster Light Since z=1

Description: We use a set of simulation-based models for the dissipationless evolution of galaxies since z = 1 to constrain the fate of accreted satellites embedded in dark matter subhalos. These models assign stellar mass to dark matter halos at z = 1 by relating the observed galaxy stellar mass function (GSMF) to the halo+subhalo mass function monotonically. The evolution of the stellar mass content is then followed using halo merger trees extracted from N-body simulations. Our models are differentiated only in the fate assigned to satellite galaxies once subhalos, within which satellites are embedded, disrupt. These models are confronted with the observed evolution in the massive end of the GSMF, the z {approx} 0 brightest cluster galaxy (BCG)-cluster mass relation, and the combined BCG and intracluster light (ICL) luminosity distribution--all observables expected to evolve approximately dissipationlessly since z = 1. The combined observational constraints favor a model in which the vast majority ({approx}> 80%) of satellite stars from disrupted subhalos go into the ICL (operationally defined here as light below a surface brightness cut of {mu}{sub i} {approx} 23mag arcsec{sup -2}). Conversely, models that leave behind a significant population of satellite galaxies once the subhalo has disrupted are strongly disfavored, as are models that put a significant fraction of satellite stars into the BCG. Our results show that observations of the ICL provide useful and unique constraints on models of galaxy merging and the dissipationless evolution of galaxies in groups and clusters.
Date: March 19, 2007
Creator: Conroy, Charlie; U., /Princeton; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC; Kravtsov, Andrey V. & /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI
Partner: UNT Libraries Government Documents Department

Examination of Flavor SU(3) in B, Bs to Kpi Decays

Description: We update a discussion of the relation between the weak phase and the rates and CP asymmetries of several K{pi} decays of B{sup +}, B{sup 0}, and B{sub s}. We emphasize the impact of measurements of B{sub s} {yields} K{pi}. Current data indicate large SU(3) breaking in the strong phases or failure of factorization (including its application to penguin amplitudes) in K{pi} modes of B{sup 0} and B{sub s}. SU(3) and factorization only remain approximately valid if the branching ratio for B{sub s} {yields} K{sup -}{pi}{sup +} exceeds its current value of (5.00 {+-} 1.25) x 10{sup -6} by at least 50%, or if a parameter {zeta} describing ratios of form factors and decay constants is shifted from its nominal value by more than twice its estimated error.
Date: April 14, 2008
Creator: Chiang, Cheng-Wei; /Taiwan, Natl. Central U. /Taiwan, Inst. Phys.; Gronau, Michael; /SLAC; Rosner, Jonathan L. & /Chicago U., EFI /Chicago U.
Partner: UNT Libraries Government Documents Department

Supersymmetric Higgs Bosons and Beyond

Description: We consider supersymmetric models that include particles beyond the Minimal Supersymmetric Standard Model (MSSM) with masses in the TeV range, and that couple significantly to the MSSM Higgs sector. We perform a model-independent analysis of the spectrum and couplings of the MSSM Higgs fields, based on an effective theory of the MSSM degrees of freedom. The tree-level mass of the lightest CP-even state can easily be above the LEP bound of 114 GeV, thus allowing for a relatively light spectrum of superpartners, restricted only by direct searches. The Higgs spectrum and couplings can be significantly modified compared to the MSSM ones, often allowing for interesting new decay modes. We also observe that the gluon fusion production cross section of the SM-like Higgs can be enhanced with respect to both the Standard Model and the MSSM.
Date: August 26, 2010
Creator: Carena, Marcela; /Fermilab /Chicago U., EFI; Kong, Kyoungchul; /SLAC, /Fermilab; Ponton, Eduardo; U., /Columbia et al.
Partner: UNT Libraries Government Documents Department

Post-inflation increase of the cosmological tensor-to-scalar perturbation ratio

Description: We investigate the possibility that the amplitude of scalar density perturbations may be damped after inflation. This would imply that CMB anisotropies do not uniquely fix the amplitude of the perturbations generated during inflation and that the present tensor-to-scalar ratio might be larger than produced in inflation, increasing the prospects of detection of primordial gravitational radiation. It turns out, however, that the damping of density perturbations is hard to achieve.
Date: July 1, 2005
Creator: Bartolo, N.; /ICTP, Trieste; Kolb, Edward W.; /Fermilab /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI; Riotto, A. & /Padua U. /INFN, Padua
Partner: UNT Libraries Government Documents Department

Dark energy as a modification of the Friedmann equation

Description: Dark energy could actually be the manifestation of a modification to the Friendmann equation arising from new physics (e.g., extra dimensions). Writing the correction as (1 - {Omega}{sub M})H{sup {alpha}}/H{sub 0}{sup {alpha}-2}, they explore the phenomenology and detectability of such. They show that: (1) {alpha} must be {approx}< 1; (2) such a correction behaves like dark energy with equation-of-state w{sub eff} = -1 + {alpha}/2 in the recent past (10{sup 4} > z >> 1) and w = -1 in the distant future and can mimic w < -1 without violating the weak-energy condition; (3) w{sub eff} changes, dz/dw|{sub z {approx} 0.5} {approx} {Omicron}(0.2), which is likely detectable; and (4) a future supernova experiment like SNAP that can determine w with precision {sigma}{sub w}, could determine {alpha} to precision {sigma}{sub {alpha}} {approx} 2{sigma}{sub w}.
Date: January 1, 2003
Creator: Dvali, Gia; U., /New York; Turner, Michael S. & /Chicago U., Astron. Astrophys. Ctr. /KICP, Chicago /Chicago U., EFI /Fermilab
Partner: UNT Libraries Government Documents Department

On cosmic acceleration without dark energy

Description: We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion. This invalidates the no-go theorem that there can be no acceleration in our local Hubble patch if the Universe only contains irrotational dust. We then study perturbatively the time behavior of general-relativistic cosmological perturbations, applying, where possible, the renormalization group to regularize the dynamics. We show that an instability occurs in the perturbative expansion involving sub-Hubble modes, which indicates that acceleration in our Hubble patch may originate from the backreaction of cosmological perturbations on observable scales.
Date: June 1, 2005
Creator: Kolb, E. W.; /Fermilab /Chicago U., Astron. Astrophys. Ctr. /Chicago U., EFI; Matarrese, S.; /Padua U. /INFN, Padua; Riotto, A. & /INFN, Padua
Partner: UNT Libraries Government Documents Department

The Supersymmetric origin of matter

Description: The Minimal Supersymmetric extension of the Standard Model (MSSM) can provide the correct neutralino relic abundance and baryon number asymmetry of the universe. Both may be efficiently generated in the presence of CP violating phases, light charginos and neutralinos, and a light top squark. Due to the coannihilation of the neutralino with the light stop, we find a large region of parameter space in which the neutralino relic density is consistent with WMAP and SDSS data. We perform a detailed study of the additional constraints induced when CP violating phases, consistent with the ones required for baryogenesis, are included. We explore the possible tests of this scenario from present and future electron Electric Dipole Moment (EDM) measurements, direct neutralino detection experiments, collider searches and the b {yields} s{gamma} decay rate. We find that the EDM constraints are quite severe and that electron EDM experiments, together with stop searches at the Tevatron and Higgs searches at the LHC, will provide a definite test of our scenario of electroweak baryogenesis in the next few years.
Date: December 1, 2004
Creator: Balazs, C.; /Argonne; Carena, M.; /Fermilab; Menon, A.; Morrissey, D. E. et al.
Partner: UNT Libraries Government Documents Department

Measurement of direct photon emission in the K(L) ---> pi+ pi- gamma decay mode

Description: In this paper the KTeV collaboration reports the analysis of 112.1 x 10{sup 3} candidate K{sub L} {yields} {pi}{sup +}{pi}{sup -}{gamma} decays including a background of 671 {+-} 41 events with the objective of determining the photon production mechanisms intrinsic to the decay process. These decays have been analyzed to extract the relative contributions of the Cp violating bremsstrahlung process and the CP conserving M1 and CP violating E1 direct photon emission processes. The M1 direct photon emission amplitude and its associated vector form factor parameterized as |{bar g}{sub M1}|(1 + a{sub 1}/a{sub 2}/(M{sub {rho}}{sup 2}-M{sub K}{sup 2}) + 2M{sub K}E{sub {gamma}}) have been measured to be |{bar g}{sub M1}| = 1.198 {+-} 0.035(stat) {+-} 0.086(syst) and a{sub 1}/a{sub 2} = =0.738 {+-} 0.007(stat) {+-} 0.018(syst) GeV{sup 2}/c{sup 2} respectively. An upper limit for the CP violating E1 direct emission amplitude |g{sub E1}| {le} 0.1 (90%CL) has been found. The overall ratio of direct photon emission (DE) to total photon emission including the bremsstrahlung process (IB) has been determined to be DE/(DE + IB) = 0.689 {+-} 0.021 for E{sub {gamma}} {ge} 20 MeV.
Date: April 1, 2006
Creator: Abouzaid, E.; /Chicago U., EFI; Arenton, M.; U., /Virginia; Barker, A.R.; U., /Colorado et al.
Partner: UNT Libraries Government Documents Department

Isolating Triggered Star Formation

Description: Galaxy pairs provide a potentially powerful means of studying triggered star formation from galaxy interactions. We use a large cosmological N-body simulation coupled with a well-tested semi-analytic substructure model to demonstrate that the majority of galaxies in close pairs reside within cluster or group-size halos and therefore represent a biased population, poorly suited for direct comparison to 'field' galaxies. Thus, the frequent observation that some types of galaxies in pairs have redder colors than 'field' galaxies is primarily a selection effect. We use our simulations to devise a means to select galaxy pairs that are isolated in their dark matter halos with respect to other massive subhalos (N= 2 halos) and to select a control sample of isolated galaxies (N= 1 halos) for comparison. We then apply these selection criteria to a volume-limited subset of the 2dF Galaxy Redshift Survey with M{sub B,j} {le} -19 and obtain the first clean measure of the typical fraction of galaxies affected by triggered star formation and the average elevation in the star formation rate. We find that 24% (30.5 %) of these L* and sub-L* galaxies in isolated 50 (30) h{sup -1} kpc pairs exhibit star formation that is boosted by a factor of {approx}> 5 above their average past value, while only 10% of isolated galaxies in the control sample show this level of enhancement. Thus, 14% (20 %) of the galaxies in these close pairs show clear triggered star formation. Our orbit models suggest that 12% (16%) of 50 (30) h{sup -1} kpc close pairs that are isolated according to our definition have had a close ({le} 30 h{sup -1} kpc) pass within the last Gyr. Thus, the data are broadly consistent with a scenario in which most or all close passes of isolated pairs result in triggered star formation. The ...
Date: September 12, 2007
Creator: Barton, Elizabeth J.; Arnold, Jacob A.; /UC, Irvine; Zentner, Andrew R.; /KICP, Chicago /Chicago U., EFI; Bullock, James S. et al.
Partner: UNT Libraries Government Documents Department

A Proposal to Continue Measurements of Direct Muon Production in the Forward Direction

Description: The authors recently have measured the direct muon production in the forward direction at small p{perpendicular} and find a large direct muon to pion ratio. At x = 0.3 the ratio is {mu}{sup -}/{pi}{sup -} = 1.83 {+-} 0.43 x 10{sup -4} for negatives and {mu}{sup +}/{pi}{sup +} = 6.4 {+-} 1.3 x 10{sup -5} for positives. The direct production of {mu}{sup +} and {mu}{sup -} are equal although the {pi}{sup +}/{pi}{sup -} ratios is large. They propose to continue these measurements and extend them to higher x. These new measurements would also include the A dependence of the {mu}/{pi} ratio. Based on their experience with this apparatus, they believe it is possible to extend these measurements of single lepton production to production by incident pions and kaons.
Date: October 20, 1975
Creator: Buchholz, D.; U., /Northwestern; Frisch, H.J.; Shochet, M.J.; /Chicago U., EFI; Johnson, Rolland P. et al.
Partner: UNT Libraries Government Documents Department

Observation of the Omega(b)- Baryon and Measurement of the Properties of the Xi(b)- and Omega(b)- Baryons

Description: The authors report the observation of the bottom, doubly-strange baryon {Omega}{sub b}{sup -} through the decay chain {Omega}{sub b}{sup -} {yields} J/{psi}{Omega}{sup -}, where J/{psi} {yields} {mu}{sup +} {mu}{sup -}, {Omega}{sup -} {yields} {Lambda}K{sup -}, and {Lambda} {yields} p {pi}{sup -}, using 4.2 fb{sup -1} of data from p{bar p} collisions at {radical}s = 1.96 TeV, and recorded with the Collider Detector at Fermilab. A signal is observed whose probability of arising from a background fluctuation is 4.0 x 10{sup -8}, or 5.5 Gaussian standard deviations. The {Omega}{sub b}{sup -} mass is measured to be 6054.4 {+-} 6.8(stat.) {+-} 0.9(syst.) MeV/c{sup 2}. The lifetime of the {Omega}{sub b}{sup -} baryon is measured to be 1.13{sub -0.40}{sup +0.53}(stat.) {+-} 0.02(syst.) ps. In addition, for the {Xi}{sub b}{sup -} baryon they measure a mass of 5790.9 {+-} 2.6(stat.) {+-} 0.8(syst.) MeV/c{sup 2} and a lifetime of 1.56{sub -0.25}{sup +0.27}(stat.) {+-} 0.02(syst.) ps.
Date: May 1, 2009
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Adelman, Jahred A.; /Chicago U., EFI; Akimoto, T.; U., /Tsukuba et al.
Partner: UNT Libraries Government Documents Department

Observation of Single Top Quark Production and Measurement of |Vtb| with CDF

Description: We report the observation of electroweak single top quark production in 3.2 fb{sup -1} of p{bar p} collision data collected by the Collider Detector at Fermilab at {radical}s = 1.96 TeV. Candidate events in the W+jets topology with a leptonically decaying W boson are classified as signal-like by four parallel analyses based on likelihood functions, matrix elements, neural networks, and boosted decision trees. These results are combined using a super discriminant analysis based on genetically evolved neural networks in order to improve the sensitivity. This combined result is further combined with that of a search for a single top quark signal in an orthogonal sample of events with missing transverse energy plus jets and no charged lepton. We observe a signal consistent with the standard model prediction but inconsistent with the background-only model by 5.0 standard deviations, with a median expected sensitivity in excess of 5.9 standard deviations. We measure a production cross section of 2.3{sub -0.5}{sup +0.6}(stat + sys) pb, extract the CKM matrix element value |V{sub tb}| = 0.91{sub -0.11}{sup +0.11}(stat + sys) {+-} 0.07(theory), and set a lower limit |V{sub tb}| > 0.71 at the 95% confidence level, assuming m{sub t} = 175 GeV/c{sup 2}.
Date: April 1, 2010
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Adelman, J.; /Chicago U., EFI; Alvarez Gonzalez, B.; Phys., /Cantabria Inst. of et al.
Partner: UNT Libraries Government Documents Department

Observation of exclusive charmonium production and gamma gamma ---> mu+mu- in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: We have observed the reactions p + {bar p} {yields} p + X + {bar p}, with X being a centrally produced J/{psi}, {psi}(2S) or {chi}{sub c0}, and {gamma}{gamma} {yields} {mu}{sup +}{mu}{sup -}, in proton-antiproton collisions at {radical}s = 1.96 TeV using the Run II Collider Detector at Fermilab. The event signature requires two oppositely charged muons, each with pseudorapidity |{eta}| < 0.6, with M{sub {mu}{mu}} {element_of} [3.0; 4.0] GeV/c{sup 2} and either no other particles, or one additional photon, detected. The J/{psi} and the {psi}(2S) are prominent, on a continuum consistent with the QED process {gamma}{gamma} {yields} {mu}{sup +}{mu}{sup -}. Events with a J/{psi} and an associated photon candidate are consistent with exclusive {chi}{sub c0} production through double pomeron exchange. The exclusive vector meson production is as expected for elastic photoproduction, {gamma} + p {yields} J/{psi}({psi}(2S)) + p, which is observed here for the first time in hadron-hadron collisions. The cross sections d{sigma}/dy|y = 0 for p + {bar p} {yields} p + X + {bar p} with X = J/{psi},{psi}(2S) or {chi}{sub c0} are 3.92 {+-} 0.62 nb, 0.53 {+-} 0.14 nb, and 76 {+-} 14 nb respectively. The cross section for the continuum, with |{eta}({mu}{sup {+-}})| < 0.6, M{sub {mu}{mu}} {element_of} [3.0, 4.0] GeV/c{sup 2}, is {integral} d{sigma}/dM.d{eta}{sub 1}.d{eta}{sub 2} = 2.7 {+-} 0.5 pb, consistent with QED predictions. We put an upper limit on the cross section for odderon exchange in exclusive J/{psi} production: d{sigma}/dy|y = 0(J/{psi}{sub OIP}) < 2.3 nb at 95% C.L.
Date: February 1, 2009
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Adelman, J.; /Chicago U., EFI; Akimoto, T.; U., /Tsukuba et al.
Partner: UNT Libraries Government Documents Department

Observation of Exclusive Dijet Production at the Fermilab Tevatron p-pbar Collider

Description: The authors present the first observation and cross section measurement of exclusive dijet production in {bar p}p interactions, {bar p}p {yields} {bar p} + dijet + p. Using a data sample of 310 pb{sup -1} collected by the Run II Collider Detector at Fermilab at {radical}s = 1.96 TeV, exclusive cross sections for events with two jets of transverse energy E{sub T}{sup jet} {ge} 10 GeV have been measured as a function of minimum E{sub T}{sup jet}. The exclusive signal is extracted from fits to data distributions based on Monte Carlo simulations of expected dijet signal and background shapes. The simulated background distribution shapes are checked in a study of a largely independent data sample of 200 pb{sup -1} of b-tagged jet events, where exclusive dijet production is expected to be suppressed by the J{sub z} = 0 total angular momentum selection rule. Results obtained are compared with theoretical expectations, and implications for exclusive Higgs boson production at the pp Large Hadron Collider at {radical}s = 14 TeV are discussed.
Date: December 1, 2007
Creator: Aaltonen, T.; Phys., /Helsinki Inst. of; Adelman, J.; /Chicago U., EFI; Akimoto, T.; U., /Tsukuba et al.
Partner: UNT Libraries Government Documents Department