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Title: Measurement of 1/σ dσ/dy for Z/γ* → e +e - at √s= 1.96 TeV

Abstract

The author presents the measurement of p$$\bar{p}$$ → Z/γ* → e +e - + X inclusive differential cross section as a function of boson rapidity. The data, which correspond to an integrated luminosity of 0.4 fb -1, were collected with D0 detector at Tevatron p$$\bar{p}$$ collider. At the Run II energy of √s = 1.96 TeV, Z bosons are produced with rapidity out to ± 3. The cross section is measured in a mass range between 71 to 111 GeV for the allowed kinematic range.

Authors:
 [1]
  1. Univ. of Maryland, College Park, MD (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
907792
Report Number(s):
FERMILAB-THESIS-2007-04
TRN: US0703310
DOE Contract Number:
AC02-07CH11359; FG05-97ER41015
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; BOSONS; CROSS SECTIONS; DIFFERENTIAL CROSS SECTIONS; FERMILAB TEVATRON; LUMINOSITY; PARTICLE RAPIDITY; Experiment-HEP

Citation Formats

Yan, Ming. Measurement of 1/σ dσ/dy for Z/γ* → e+e- at √s= 1.96 TeV. United States: N. p., 2007. Web. doi:10.2172/907792.
Yan, Ming. Measurement of 1/σ dσ/dy for Z/γ* → e+e- at √s= 1.96 TeV. United States. doi:10.2172/907792.
Yan, Ming. Thu . "Measurement of 1/σ dσ/dy for Z/γ* → e+e- at √s= 1.96 TeV". United States. doi:10.2172/907792. https://www.osti.gov/servlets/purl/907792.
@article{osti_907792,
title = {Measurement of 1/σ dσ/dy for Z/γ* → e+e- at √s= 1.96 TeV},
author = {Yan, Ming},
abstractNote = {The author presents the measurement of p$\bar{p}$ → Z/γ* → e+e- + X inclusive differential cross section as a function of boson rapidity. The data, which correspond to an integrated luminosity of 0.4 fb-1, were collected with D0 detector at Tevatron p$\bar{p}$ collider. At the Run II energy of √s = 1.96 TeV, Z bosons are produced with rapidity out to ± 3. The cross section is measured in a mass range between 71 to 111 GeV for the allowed kinematic range.},
doi = {10.2172/907792},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}

Thesis/Dissertation:
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  • A study of events with Z/γ* bosons and hadronic jets produced at the Tevatron in pmore » $$\bar{p}$$ collisions at a center of mass energy of 1.96 TeV is presented. The data consist of approximately 14,000 Z/γ* → e +e - decay candidates from 343 pb -1 of integrated luminosity collected with the D0 detector. Cross sections and jet production properties have been measured for Z/γ* + ≥ 0 to 5 jet events. This measurement represents a significant improvement over previous measurements at the Tevatron, and it is the first at this center of mass energy with the D0 detector. The results are in good agreement with QCD predictions.« less
  • This Ph.D. thesis presents the measurement of inclusive jet cross sections in Z/γ*→ e +e - events using 1.7 fb -1 of data collected by the upgraded CDF detector during the Run II of the Tevatron. The Midpoint cone algorithm is used to search for jets in the events after identifying the presence of a Z/γ* boson through the reconstruction of its decay products. The measurements are compared to next-to-LO (NLO) pQCD predictions for events with one and two jets in the final state. The perturbative predictions are corrected for the contributions of non-perturbative processes, like the underlying event andmore » the fragmentation of the partons into jets of hadrons. These processes are not described by perturbation theory and must be estimated from phenomenological models. In this thesis, a number of measurements are performed to test different models of underlying event and hadronization implemented in LO plus parton shower Monte Carlo generator programs. Chapter 2 is devoted to the description of the theory of strong interactions and jet phenomenology at hadron colliders. Chapter 3 contains the description of the Tevatron collider and the CDF detector. The analysis is described in detail in Chapter 4. Chapter 5 shows the measurement of those observables sensitive to non-perturbative effects compared to the predictions from several Monte Carlo programs. Chapter 6 discusses the final results and the comparison with theoretical expectations. Finally, Chapter 7 is devoted to the conclusions.« less
  • The resonant production of tau-lepton pairs is as interesting for the study of Standard Model (SM) physics as the production of lighter leptons pairs. For new phenomena, such as Higgs boson production or in case new particles beyond the SM would arise, the detection of (resonant) pairs of tau leptons becomes much more interesting. This is due to the fact that tau leptons are much heavier than the other leptons, which increases the chance that these new phenomena would be observed first in this channel. Unfortunately their clean detection is far more difficult than that of muons or electrons. The cross section times branching ratio σ. Br for the process pmore » $$\bar{p}$$ → Z → τ +τ - was measured at √s = 1.96 GeV using 1.0 fb -1 of data collected by the D0 experiment. This measurement was performed in the channel in which one of the tau leptons decays to a muon and neutrinos, while the other decays either hadronically or to an electron and neutrinos. A set of 1511 events, of which about 20% estimated background, passed all selection criteria. The trigger and muon reconstruction efficiencies, as well as the efficiency for track reconstruction were obtained from data using the 'tag and probe' method on Z → μ +μ - events. The multijet background was estimated from the sample of events which passed all selection criteria but in which the muon and the tau candidate had the same charge. The W → μv + jets background was modeled by Monte Carlo simulations, but normalized to data. All the other backgrounds, as well as the efficiency for Z → τ +τ - events were estimated using simulated events normalized to the theoretical calculations of cross sections at next-to-leading order or next-to-next-to-leading order. The energy of the tau candidates was corrected for the estimated response of the charged pions in the calorimeter, which is of the order 50-80%. Since the charged pion response in data was not well reproduced by the default simulation of hadronic interactions (Geisha), a different simulation (gCALOR) was used to obtain an estimated charged pion response consistent with the one measured in data. This tau energy correction method makes use of the superior resolution of the track momentum measurement compared to the resolution of the tau candidate energy as measured by the calorimeter, which leads to a better data--simulation agreement and a decrease of 10% in the resolution of the visible mass peak. The result of this measurement is σ(p$$\bar{p}$$ → Z) • Br(Z → τ +τ -) = 240 ± 8(stat) ± 12(syst) ± 15(lumi) pb, in good agreement with the theoretical predictions of 241.6$$+3.6\atop{3.2}$$ pb [79] or 251.9$$+5.1\atop{-12}$$ pb [93-95], as well as with other measurements performed by the D0 and CDF experiments in all channels in which the Z boson decays leptonically [96-100]. This is the most precise Z boson cross section measurement to date performed in the tau lepton channel at hadron colliders. The analysis demonstrates the ability of the D0 experiment to identify tau leptons decaying hadronically with good efficiency and high purity, a challenging task in p{bar p} collisions where the number of jets resembling tau leptons is very high. This achievement forms a solid basis for other analyses using hadronic tau lepton decays, such as the search for the Higgs boson decaying into tau-lepton pairs, which was performed for the last part of this thesis.« less
  • In this thesis the first measurement of σ(pmore » $$\bar{p}$$ → Z 0 → τ$$\bar{τ}$$ with the D0 detector at the Tevatron is presented. The tau pair candidates are recorded by the D0 detector using p$$\bar{p}$$ interactions at a center-of-mass energy of 1.96 TeV. Events in which one tau decays into a muon and the other tau final state is hadronic with one charged particle are selected for this analysis. The selection criteria for the hadronic tau decay are based on the tau final state, hence for two channels of one-prong taus: single charged pion (τ π) and rho decays (τ ρ). The selection is based on simple cuts on a number of discriminating variables and the cut values have been optimized for the best cross section measurement. Of hadronic tau candidates that have been reconstructed as τ π candidates, 0.801 ± 0.017 ± 0.066 pass the selection cut; in the case of τ ρ taus, the selection efficiency is 0.676 ± 0.009 ± 0.009. Of all QCD jets that are reconstructed as hadronic tau candidates, 0.0093 ± 0.0002 pass the τ π selection cuts and 0.0122 ± 0.0002 the τ ρ cuts. The cross section has been measured to be 274 ± 121 ± 40 ± 27 pb in the μτ π channel and 273 ± 40$$+18\atop{-23}$$ ± 27 pb in the μτ ρ channel, resulting in a combined measurement of σ(p$$\bar{p}$$ → Z 0 → τ$$\bar{τ}$$) = 273 ± 38$$+19\atop{-23}$$ ± 27 pb which agrees with the SM prediction within errors. The errors are dominated by the statistical error as only the first data taken with the D0 detector in Run II was used. Due to the small set of tau candidates, the calorimeter energy scale could not yet be determined using data and this uncertainty is the largest systematic effect on the measurement. Another large contribution arises from the uncertainty of 10% on the luminosity measurement. This is expected to decrease significantly in the future. It was demonstrated that the currently available tools are sufficient to use tau leptons in the measurement of a SM process. This opens the door to the use of hadronic tau decays in the search for new particles, like SUSY particles, that decay preferentially to tau leptons in a number of models or the Higgs boson of either the SM or extended model. Doing physics at the Tevatron as the accelerator at the current energy frontier is our current best hope to find the yet elusive Higgs boson and will allow to either find proof of physics beyond the Standard Model or tighten the constraints on these models.« less
  • The cross-section of pmore » $$\bar{p}$$ → Z 0 γ+ X production at √s = 1.96 TeV using the CDF II detector at the Fermilab Tevatron is measured using 202 pb -1 of data from March 2002 to September 2003, collected with high P T lepton triggers. The number of events observed and their kinematic distributions are compared to the NLO Standard Model prediction in both the Z 0 → e +e - and Z 0 → μ +μ - channels. For a minimum lepton-photon separation of ΔR > 0.7, E$$γ\atop{T}$$ > 7 GeV and a dilepton invariant mass m(l,l) > 40 GeV/c 2, the cross-section times branching ratio is measured to be 4.6 ± 0.5(stat) ± 0.2(sys) ± 0.3(lumi) pb compared to the NLO Standard Model prediction of 4.5 ± 0.3(th) pb.« less