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Fragmentation of quark and gluon jets in proton-antiproton collisions at center-of-mass energy of 1.8-TeV

Description: The author reports the first model independent measurement of charged particle multiplicities in quark and gluon jets, N{sub q} and N{sub g}, produced at the Tevatron in p{bar p} collisions with center-of-mass energy 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies 41 and 53 GeV by counting charged particle tracks in cones with opening angle of {theta}{sub c} = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = E{sub jet}{theta}{sub c} varies in the range from 12 GeV to 25 GeV. At Q = 19.2 GeV, the ratio of multiplicities r = N{sub g}/N{sub q} is found to be 1.64 {+-} 0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with re-summed perturbative QCD calculations and are consistent with recent e{sup +}e{sup -} measurements.
Date: May 1, 2005
Creator: Pronko, Alexandre P. & U., /Florida
Partner: UNT Libraries Government Documents Department

CDF Run II Monte-Carlo tunes

Description: Several CDF Run 2 PYTHIA 6.2 tunes (with multiple parton interactions) are presented and compared with HERWIG (without multiple parton interactions) and with the ATLAS PYTHIA tune (with multiple parton interactions). Predictions are made for the ''underlying event'' in high p{sub T} jet production and in Drell-Yan lepton-pair production at the Tevatron and the LHC.
Date: November 1, 2006
Creator: Field, Rick & U., /Florida
Partner: UNT Libraries Government Documents Department

Using Drell-Yan to probe the underlying event in Run II at Collider Detector at Fermilab (CDF)

Description: We study the behavior of charged particles produced in association with Drell-Yan lepton-pairs in the region of the Z-boson in proton-antiproton collisions at 1.96 TeV. We use the direction of the Z-boson in each event to define 'toward', 'away', and 'transverse' regions. For Drell-Yan production (excluding the leptons) both the 'toward' and 'transverse' regions are very sensitive to the 'underlying event', which is defined as everything except the two hard scattered components. The data are corrected to the particle level and are then compared with several PYTHIA models (with multiple parton interactions) and HERWIG (without multiple parton interactions) at the particle level (i.e. generator level). The data are also compared with a previous analysis on the behavior of the 'underlying event' in high transverse momentum jet production. The goal is to produce data that can be used by the theorists to tune and improve the QCD Monte-Carlo models of the 'underlying event' that are used to simulate hadron-hadron collisions.
Date: December 1, 2008
Creator: Kar, Deepak & U., /Florida
Partner: UNT Libraries Government Documents Department

Two-particle momentum correlation in jets at the Tevatron

Description: Presented are the measurements of two-particle momentum correlations in jets produced in p-pbar collisions at center of mass frame energy 1.96 TeV. Studies were performed for charged particles within a restricted opening angle of 0.5 rad around the jet axis and for dijet events with various dijet masses. Comparison of the experimental results to the theoretical predictions obtained for partons within the framework of the resummed perturbative QCD (Next-to-Leading Log Approximation) shows that the parton momentum correlations do survive the hadronization stage of jet fragmentation, thus, giving further support to the hypothesis of Local Parton-Hadron Duality.
Date: May 1, 2006
Creator: Jindariani, Sergo & U., /Florida
Partner: UNT Libraries Government Documents Department

Jet physics and the underlying event at the Tevatron

Description: Tevatron Run 2 results on the inclusive jet cross section (MidPoint and K{sub T} algorithm) and the b-jet and b{bar b}-jet cross section (MidPoint algorithm) are presented and compared with theory. The CDF b-jet {bar b}-jet {Delta}{phi} distribution is compared with theory and with the D0 jet No.1-jet No.2 {Delta}{phi} distribution. The understanding and modeling of the ''underlying event'' in Run 2 at the Tevatron is reviewed and new CDF results are presented.
Date: August 1, 2005
Creator: Field, Rick & U., /Florida
Partner: UNT Libraries Government Documents Department

Jet physics in Run 2 at CDF

Description: New CDF Run 2 results on the inclusive jet cross section (K{sub T} algorithm) and the b-jet cross section (MidPoint algorithm) are presented and compared with theory. We also study the ''underlying event'' by using the direction of the leading jet to isolate regions of {eta}-{phi} space that are very sensitive to the ''beam-beam'' remnants and to multiple parton interactions.
Date: January 1, 2005
Creator: Field, R. & U., /Florida
Partner: UNT Libraries Government Documents Department

Measurement of the inclusive jet cross section using the midpoint algorithm in Run II at CDF

Description: A measurement is presented of the inclusive jet cross section using the Midpoint jet clustering algorithm in five different rapidity regions. This is the first analysis which measures the inclusive jet cross section using the Midpoint algorithm in the forward region of the detector. The measurement is based on more than 1 fb{sup -1} of integrated luminosity of Run II data taken by the CDF experiment at the Fermi National Accelerator Laboratory. The results are consistent with the predictions of perturbative quantum chromodynamics.
Date: December 1, 2006
Creator: Group, Robert Craig & U., /Florida
Partner: UNT Libraries Government Documents Department

Measurements of the Differential Cross Sections for the Inclusive Production of a Photon and Heavy Flavor Jet

Description: This thesis presents the first measurement of the differential production cross section of a heavy flavor (bottom or charm) jet and direct photon at the Fermilab Tevatron. These measurements were performed using data recorded with the D0 detector from proton-antiproton collisions at a center of mass energy of {radical}s = 1.96 TeV. These results probe a kinematic range for the photon transverse momentum of 30 < p{sub T}{sup {gamma}} < 150 GeV and rapidity of |y{sup {gamma}}| < 1.0 and for jet transverse momentum p{sub T}{sup jet} > 15 GeV and rapidity of |y{sup jet}| < 0.8. These results are compared to next-to-leading-order theoretical calculations.
Date: April 1, 2009
Creator: Duggan, Daniel & U., /Florida State
Partner: UNT Libraries Government Documents Department

Tevatron searches for excited and exotic leptons

Description: The Tevatron experiments, D0 and CDF, have searched for excited electrons and excited and exotic muons in Run II. Using 1 fb{sup -1} of data, D0 has searched for excited electrons. No excess above the standard model background is observed. Choosing the scale for contact interactions to be {Lambda} = 1 TeV, excited electron masses below 756 GeV are excluded at the 95% C.L. CDF has searched for excited and exotic muons using 371 fb{sup -1} of data. Using gauge mediated models with {Lambda}/f = m{sub {mu}*}, exotic muons are excluded for masses below 221 GeV. For compositeness models with {Lambda} = m{sub {mu}*}, masses below 853 GeV are excluded. Using a similar size data set, D0 get similar limits.
Date: April 1, 2008
Creator: Hagopian, Sharon & U., /Florida State
Partner: UNT Libraries Government Documents Department

New results on jet fragmentation at CDF

Description: Presented are the latest results of jet fragmentation studies at the Tevatron using the CDF Run II detector. Studies include the distribution of transverse momenta (Kt) of particles jets, two-particle momentum correlations, and indirectly global event shapes in p{bar p} collisions. Results are discussed within the context of recent Next-to-Leading Log calculations as well as earlier experimental results from the Tevatron and e{sup +}e{sup -} colliders.
Date: December 1, 2006
Creator: Jindariani, Sergo & U., /Florida
Partner: UNT Libraries Government Documents Department

Searches for new phenomena with lepton final states at the Tevatron

Description: Numerous searches for new phenomena have been carried out using data from proton-antiproton collisions at Fermilab's Tevatron. Final states with leptons give signatures which are relatively unique and generally have small backgrounds. We present many of the latest results from the CDF and D0 collaborations from 0.4-1.2 fb{sup -1} of data. Topics include supersymmetry, extra gauge bosons, Randall-Sundrum gravitons, excited electrons and neutral, long-lived particles.
Date: May 1, 2007
Creator: Adams, T. & U., /Florida State
Partner: UNT Libraries Government Documents Department

Physics at the Tevatron

Description: The theme of the XXXIV International Meeting on Fundamental Physics held in El Escorial, Spain on April 2-7, 2006 was ''From HERA and the TEVATRON to the LHC''. This is a summary of the four lectures I presented on ''Physics at the Tevatron''. Heavy quark production and the production of photons, bosons, and jets at the Tevatron are discussed. Also, a detailed study at the ''underlying event'' at CDF is presented together with a discussion of PYTHIA 6.2 tunes. A look back at the ''old days'' of Feynman-Field collider phenomenology is included.
Date: April 1, 2006
Creator: Field, Rick & U., /Florida
Partner: UNT Libraries Government Documents Department

First measurement of top quark pair production cross-section in muon plus hadronic tau final states

Description: This dissertation presents the first measurement of top quark pair production cross-section in events containing a muon and a tau lepton. The measurement was done with 1 fb{sup -1} of data collected during April 2002 through February 2006 using the D0 detector at the Tevatron proton-antiproton collider, located at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois. Events containing one isolated muon, one tau which decays hadronically, missing transverse energy, and two or more jets (at least one of which must be tagged as a heavy flavor jet) were selected. Twenty-nine candidate events were observed with an expected background of 9.16 events. The top quark pair production cross-section is measured to be {sigma}(t{bar t}) = 8.0{sub -2.4}{sup +2.8}(stat){sub -1.7}{sup +1.8}(syst) {+-} 0.5(lumi) pb. Assuming a top quark pair production cross-section of 6.77 pb for Monte Carlo signal top events without a real tau, the measured {sigma} x BR is {sigma}(t{bar t}) x BR(t{bar t} {yields} {mu} + {tau} + 2{nu} + 2b) = 0.18{sub -0.11}{sup +0.13}(stat){sub -0.09}{sup +0.09}(syst) {+-} 0.01(lumi) pb.
Date: November 1, 2007
Creator: Sumowidagdo, Suharyo & U., /Florida State
Partner: UNT Libraries Government Documents Department

Studying the underlying event at CDF

Description: A study of ''underlying event'' in Run 2 at CDF is presented. Several PYTHIA 6.2 tunes (with multiple parton interactions) are examined and compared with HERWIG (without multiple parton interactions) and with the ATLAS PYTHIA tune (with multiple parton interactions) and they are extrapolated to the LHC.
Date: October 1, 2006
Creator: Field, R.D. & U., /Florida
Partner: UNT Libraries Government Documents Department

Search for Large Extra Dimensions via Single Photons Plus Missing Energy Final States at s^(1/2) = 1.96 TeV

Description: This dissertation presents a search for large extra dimensions in the single photon plus missing transverse energy final states. We use a data sample of approximately 2.7 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV (recorded with the D{sup -} detector) to investigate direct Kaluza Klein graviton production and set limits, at the 95% C.L., on the fundamental mass scale M{sub D} from 970 GeV to 816 GeV for two to eight extra dimensions.
Date: December 1, 2008
Creator: Carrera, Edgar Fernando & U., /Florida State
Partner: UNT Libraries Government Documents Department

Min-Bias at the Tevatron

Description: As illustrated in Fig. 1, the total proton-antiproton cross section is the sum of the elastic and inelastic components, {sigma}{sub tot} = {sigma}{sub EL} + {sigma}{sub IN}. The inelastic cross section consists of three terms; single diffraction, double-diffraction, and everything else (referred to as the 'hard core'), {sigma}{sub IN} = {sigma}{sub SD} + {sigma}{sub DD} + {sigma}{sub HC}. For elastic scattering neither of the beam particles breaks apart (i.e. color singlet exchange). For single and double diffraction one or both of the beam particles are excited into a high mass color singlet state (i.e. N* states) which then decays. Single and double diffraction also corresponds to color singlet exchange between the beam hadrons. When color is exchanged the outgoing remnants are no longer color singlets and one has a separation of color resulting in a multitude of quark-antiquark pairs being pulled out of the vacuum. The 'hard core' component, {sigma}{sub HC}, involves color exchange and the separation of color. However, the 'hard core' contribution has both a 'soft' and 'hard' component. Most of the time the color exchange between partons in the beam hadrons occurs through a soft interaction (i.e. no high transverse momentum) and the two beam hadrons 'ooze' through each other producing lots of soft particles with a uniform distribution in rapidity and many particles flying down the beam pipe. Occasionally there is a hard scattering among the constituent partons producing outgoing particles and 'jets' with high transverse momentum.
Date: October 1, 2007
Creator: Field, Rick & U., /Florida
Partner: UNT Libraries Government Documents Department

Measurement of gamma + c + X and gamma + b + X production cross sections at s**(1/2) = 1.96-TeV

Description: The photon plus heavy-flavour quark (b, c) final state provides a unique and valuable window into both the sea quark content of the proton and the splitting of gluons into heavy-flavour quark pairs. A new combination of experimental techniques has provided the basis for the first measurements of the differential {gamma} + c + X and {gamma} + b + X production cross sections at {radical}s = 1.96 TeV. The measurements use {approx} 1 fb{sup -1} of data from p{bar p} collisions collected with the D0 detector.
Date: June 1, 2009
Creator: Duggan, Daniel & U., /Florida State
Partner: UNT Libraries Government Documents Department

Searches for Charginos and Neutralinos with the D0 Detector

Description: Within the framework of supersymmetry, charginos and/or neutralinos are often the preferred topics of searches for experimental evidence. This is due to the facts that in much of parameter space they are the lightest supersymmetric partners and they offer unique final states to separate from standard model backgrounds. The D0 experiment has performed several recent searches including the traditional trilepton final state and a decay chain involving dark photons.
Date: October 1, 2009
Creator: Adams, T. & U., /Florida State
Partner: UNT Libraries Government Documents Department

Search for large extra dimensions in the exclusive photon + missing energy channel in p anti-p collisions

Description: A search was conducted for evidence of large extra dimensions (LED) at Fermi National Accelerator Laboratory's Tevatron using the D0 detector. The Tevatron is a p{bar p} collider at a center of mass energy of 1.96 TeV. Events with particles escaping into extra dimensions will have large missing energy. The search was carried out using data from a total luminosity of 197 {+-} 13 pb{sup -1} with an observable high transverse momentum photon and a large transverse missing energy. The 70 observed events are consistent with photons produced by standard known reactions plus other background processes produced by cosmic muons. The mass limits on the fundamental mass scale at 95% confidence level for large extra dimensions of 2, 4, 6 and 8 are 500 GeV, 581 GeV, 630 GeV, and 668 GeV respectively.
Date: April 1, 2006
Creator: Lazoflores, Jose A. & U., /Florida State
Partner: UNT Libraries Government Documents Department

Reco level Smin and subsystem Smin: improved global inclusive variables for measuring the new physics mass scale in MET events at hadron colliders

Description: The variable {radical}s{sub min} was originally proposed in [1] as a model-independent, global and fully inclusive measure of the new physics mass scale in missing energy events at hadron colliders. In the original incarnation of {radical}s{sub min}, however, the connection to the new physics mass scale was blurred by the effects of the underlying event, most notably initial state radiation and multiple parton interactions. In this paper we advertize two improved variants of the {radical}s{sub min} variable, which overcome this problem. First we show that by evaluating the {radical}s{sub min} variable at the RECO level, in terms of the reconstructed objects in the event, the effects from the underlying event are significantly diminished and the nice correlation between the peak in the {radical}s{sub min}{sup (reco)} distribution and the new physics mass scale is restored. Secondly, the underlying event problem can be avoided altogether when the {radical}s{sub min} concept is applied to a subsystem of the event which does not involve any QCD jets. We supply an analytic formula for the resulting subsystem {radical}s{sub min}{sup (sub)} variable and show that its peak exhibits the usual correlation with the mass scale of the particles produced in the subsystem. Finally, we contrast {radical}s{sub min} to other popular inclusive variables such as H{sub T}, M{sub Tgen} and M{sub TTgen}. We illustrate our discussion with several examples from supersymmetry, and with dilepton events from top quark pair production.
Date: August 11, 2011
Creator: Konar, Partha; U., /Florida; Kong, Kyoungchul; /SLAC; Matchev, Konstantin T.; Park, Myeonghun et al.
Partner: UNT Libraries Government Documents Department

Dark Matter Particle Spectroscopy at the LHC: Generalizing M(T2) to Asymmetric Event Topologies

Description: We consider SUSY-like missing energy events at hadron colliders and critically examine the common assumption that the missing energy is the result of two identical missing particles. In order to experimentally test this hypothesis, we generalize the subsystem M{sub T2} variable to the case of asymmetric event topologies, where the two SUSY decay chains terminate in different 'children' particles. In this more general approach, the endpoint M{sub T2(max)} of the M{sub T2} distribution now gives the mass {tilde M}p({tilde M}{sub c}{sup (a)}, {tilde M}{sub c}{sup (b)}) of the parent particles as a function of two input children masses {tilde M}{sub c}{sup (a)} and {tilde M}{sub c}{sup (b)}. We propose two methods for an independent determination of the individual children masses M{sub c}{sup (a)} and M{sub c}{sup (b)}. First, in the presence of upstream transverse momentum PUTM the corresponding function {tilde M}p({tilde M}{sub c}{sup (a)}, {tilde M}{sub c}{sup (b)}, P{sub UTM}) is independent of P{sub UTM} at precisely the right values of the children masses. Second, the previously discussed MT2 'kink' is now generalized to a 'ridge' on the 2-dimensional surface {tilde M}p({tilde M}{sub c}{sup (a)}, {tilde M}{sub c}{sup (b)}). As we show in several examples, quite often there is a special point along that ridge which marks the true values of the children masses. Our results allow collider experiments to probe a multi-component dark matter sector directly and without any theoretical prejudice.
Date: April 3, 2012
Creator: Konar, Partha; U., /Florida; Kong, Kyoungchul; /SLAC; Matchev, Konstantin T.; Park, Myeonghun et al.
Partner: UNT Libraries Government Documents Department