| 41. |
- Abazov, V. M., et al.
(författare)
-
Search for pair production of second generation scalar leptoquarks
- 2009
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 671:2, s. 224-232
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a search for the pair production of second generation scalar leptoquarks (LQ) in p (p) over bar collisions at the center of mass energy root s- = 1.96 TeV using a data set corresponding to an integrated luminosity of 1.0 fb(-1) collected with the D empty set experiment at the Fermilab Tevatron Collider. Topologies arising from the LQ (LQ) over bar -> mu q nu q and LQ (LQ) over bar -> mu q mu q decay modes are investigated. No excess of data over the standard model prediction is observed and upper limits on the leptoquark pair production cross section are derived at the 95% C.L. as a function of the leptoquark mass and the branching fraction beta for the decay LQ -> mu q. These are interpreted as lower limits on the leptoquark mass as a function of beta. For beta = 1 (0.5), scalar second generation leptoquarks with masses up to 316 GeV (270 GeV) are excluded.
|
|
| 42. |
|
|
| 43. |
- Abazov, V. M., et al.
(författare)
-
Dependence of the t(t)over-bar production cross section on the transverse momentum of the top quark
- 2010
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 693:5, s. 515-521
-
Tidskriftsartikel (refereegranskat)abstract
- We present a measurement of the differential cross section for t (t) over bar events produced in p (p) over bar collisions at root s = 1.96 TeV as a function of the transverse momentum (p(T)) of the top quark. The selected events contain a high-p(T) lepton (l), a large imbalance in p(T). four or more jets with at least one candidate for a b jet, and correspond to 1 fb(-1) of integrated luminosity recorded with the D0 detector. Objects in the event are associated through a constrained kinematic fit to the t (t) over bar -> WbW (b) over bar -> lvbq (q) over bar' (b) over bar process. Results from next and next-to-next-to-leading-order perturbative QCD calculations agree with the measured differential cross section. Comparisons are also provided to predictions from Monte Carlo event generators using QCD calculations at different levels of precision. (C) 2010 Elsevier B.V. All rights reserved.
|
|
| 44. |
- Abazov, V. M., et al.
(författare)
-
Determination of the strong coupling constant from the inclusive jet cross section in pp collisions at s=1.96 TeV
- 2009
-
Ingår i: PHYS REV D. - 1550-7998 .- 1550-2368. ; 80, s. 111107-
-
Tidskriftsartikel (refereegranskat)abstract
- We determine the strong coupling constant alpha(s) and its energy dependence from the p(T) dependence of the inclusive jet cross section in pp collisions at s=1.96 TeV. The strong coupling constant is determined over the transverse momentum range 50 < p(T)< 145 GeV. Using perturbative QCD calculations to order O(alpha(3)(s)) combined with O(alpha(4)(s)) contributions from threshold corrections, we obtain alpha(s)(M-Z)=0.1161(-0.0048)(+0.0041). This is the most precise result obtained at a hadron-hadron collider.
|
|
| 45. |
- Abazov, V. M., et al.
(författare)
-
Double parton interactions in gamma+3 jet events in p(p)over-bar collisions at root s=1.96 TeV
- 2010
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 81:5, s. 052012-
-
Tidskriftsartikel (refereegranskat)abstract
- We have used a sample of gamma + 3 jets events collected by the D0 experiment with an integrated luminosity of about 1 fb(-1) to determine the fraction of events with double parton scattering (f(DP)) in a single p (p) over bar collision at root s = 1.96 TeV. The DP fraction and effective cross section (sigma(eff)), a process-independent scale parameter related to the parton density inside the nucleon, are measured in three intervals of the second (ordered in p(T)) jet transverse momentum p(T)(jet2) within the range 15 <= p(T)(jet2) <= 30 GeV. In this range, f(DP) varies between 0.23 <= f(DP) <= 0.47, while sigma(eff) has the average value sigma(ave)(eff) = 16.4 +/- 0.3(stat) +/- 2.3(syst) mb.
|
|
| 46. |
- Abazov, V. M., et al.
(författare)
-
Measurement of the t-channel single top quark production cross section
- 2010
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 682:4-5, s. 363-369
-
Tidskriftsartikel (refereegranskat)abstract
- The DO Collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb(-1) of p (p) over bar collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14(-0.80)(+0.94) pb for the t-channel and 1.05 +/- 0.81 pb for the s-channel. The measured t-channel result is found to have a significance of 4.8 standard deviations and is consistent with the standard model prediction.
|
|
| 47. |
- Abazov, V. M., et al.
(författare)
-
Measurement of the t(t)over-bar cross section using high-multiplicity jet events
- 2010
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 82, s. 032002-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a measurement of the t (t) over bar cross section using high-multiplicity jet events produced in p (p) over bar collisions at root s = 1.96 TeV. These data were recorded at the Fermilab Tevatron Collider with the D0 detector. Events with at least six jets, two of them identified as b jets, were selected from a 1 fb(-1) data set. The measured cross section, assuming a top quark mass of 175 GeV/c(2), is 6.9 +/- 2.0 pb, in agreement with theoretical expectations.
|
|
| 48. |
- Abazov, V. M., et al.
(författare)
-
Measurement of Z/gamma* plus jet plus X angular distributions in p(p)over-bar collisions at root s=1.96 TeV
- 2010
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 682:4-5, s. 370-380
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first measurements at a hadron collider of differential cross sections for Z/gamma* + jet + X production in Delta phi(Z. jet), vertical bar Delta y(Z, jet)vertical bar and vertical bar y(boost)(Z + jet)vertical bar. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.
|
|
| 49. |
- Abazov, V. M., et al.
(författare)
-
Search for a Resonance Decaying into WZ Boson Pairs in p(p)over-bar Collisions
- 2010
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:6, s. 061801-
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first search for an electrically charged resonance W' decaying to a WZ boson pair using 4.1 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron p (p) over bar collider. The WZ pairs are reconstructed through their decays into three charged leptons (l = e, mu). A total of 9 data events is observed in good agreement with the background prediction. We set 95% C.L. limits on the W'WZ coupling and on the W' production cross section multiplied by the branching fractions. We also exclude W' masses between 188 and 520 GeV within a simple extension of the standard model and set the most restrictive limits to date on low-scale technicolor models.
|
|
| 50. |
- Abazov, V. M., et al.
(författare)
-
Search for charged Higgs bosons in top quark decays
- 2009
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 682:3, s. 278-286
-
Tidskriftsartikel (refereegranskat)abstract
- We present a search for charged Higgs bosons in top quark decays. We analyze the e + jets, mu + jets, ee, e mu, mu mu, tau e and tau mu final states from top quark pair production events, using data from about 1 fb (1) of integrated luminosity recorded by the DO experiment at the Fermilab Tevatron Collider. We consider different scenarios of possible charged Higgs boson decays, one where the charged Higgs boson decays purely hadronically into a charm and a strange quark, another where it decays into a tau lepton and a tau neutrino and a third one where both decays appear. We extract limits on the branching ratio B(t -> H(+)b) for all these models. We use two methods, one where the t (t) over bar production cross section is fixed, and one where the cross section is fitted simultaneously with B(t -> H(+)b). Based on the extracted limits, we exclude regions in the charged Higgs boson mass and tan beta parameter space for different scenarios of the minimal supersymmetric standard model.
|
|
