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Title: Precision Physics and Searches with Top and Bottom Quarks

Abstract

This report goes into detail about all of the topics that were worked on by the research group from July 2015 to July 2016. The topics are: Search for supersymmetry in the all-jets final state using α T, measurement of the $$t\bar{t}$$ differential cross section in CMS Run 2, B-physics leadership, CMS HCAL operations, CMS HCAL detector upgrade. In addition to detailing these topics, publications are listed which came from this research group.

Authors:
 [1]
  1. Univ. of Rochester, NY (United States). Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Univ. of Rochester, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1328431
Report Number(s):
DE-SC0006535
TRN: US1700350
DOE Contract Number:
SC0006535
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; T QUARKS; B QUARKS; DIFFERENTIAL CROSS SECTIONS; SUPERSYMMETRY; JETS; QUARK-QUARK INTERACTIONS; CMS DETECTOR; SHOWER COUNTERS

Citation Formats

Garcia-Bellido, Aran. Precision Physics and Searches with Top and Bottom Quarks. United States: N. p., 2016. Web. doi:10.2172/1328431.
Garcia-Bellido, Aran. Precision Physics and Searches with Top and Bottom Quarks. United States. doi:10.2172/1328431.
Garcia-Bellido, Aran. 2016. "Precision Physics and Searches with Top and Bottom Quarks". United States. doi:10.2172/1328431. https://www.osti.gov/servlets/purl/1328431.
@article{osti_1328431,
title = {Precision Physics and Searches with Top and Bottom Quarks},
author = {Garcia-Bellido, Aran},
abstractNote = {This report goes into detail about all of the topics that were worked on by the research group from July 2015 to July 2016. The topics are: Search for supersymmetry in the all-jets final state using αT, measurement of the $t\bar{t}$ differential cross section in CMS Run 2, B-physics leadership, CMS HCAL operations, CMS HCAL detector upgrade. In addition to detailing these topics, publications are listed which came from this research group.},
doi = {10.2172/1328431},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 9
}

Technical Report:

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  • Using the precision vertex detectors of the Mark 2 at the SLC, an impact parameter tag was developed to select a sample of hadronic Z{degree} decays enriched in its fraction of bottom quark events. The nominal tagging method requires that there be at least three tracks whose impact parameters are inconsistent with the track having originated at the electron-position interaction point. A tagging efficiency for b{bar b} events of 50% with a enriched sample purity of 85% was achieved. This impact parameter tag was used to measure the fraction hadronic Z{degree} decays which produce b{bar b} events, F{sub b}. Itmore » is found that F{sub b} = 0.232{sub {minus}0.045}{sup +0.053} (stat) {sub {minus}0.021}{sup +0.025} (syst). This result is consistent with those found using other tagging methods as well as the Standard Model prediction of 0.217. The b{bar b}-enriched event sample was also used to measure the difference between the average charged multiplicity of b{bar b} events and that of all hadronic Z{degree} decays, {delta}{bar n}{sub b} = 2.11 {plus minus} 1.82(stat) {plus minus} 0.57(syst). Using previous measurements of the total hadronic charged multiplicity, the corresponding total multiplicity for b{bar b} events is {bar n}{sub b}=23.05 {plus minus} 1.82 (stat) {plus minus} 0.60 (syst). Subtracting the contribution to the multiplicity from B hadron decays yields the multiplicity of the b{bar b} non-leading system, {bar n}{sub nl} = 12.04 {plus minus} 1.82 (stat) {plus minus} 0.63(syst). Comparing this non-leading multiplicity to the total hadronic multiplicity data at lower energy supports the hypothesis that the non-leading particle production is independent of the flavor of the initial quarks.« less
  • We use the precision vertex detectors installed in the Mark 2 detector to measure R{sub b}, the fraction of Z{sup 0} bosons decays into hadrons that include bottom quarks. The Z{sup 0} bosons were created via e{sup +}e{sup {minus}} annihilation at 91 GeV by the Stanford Linear Collider during the 1990 running. The Mark 2 tracking system, including the Silicon Strip Vertex Detector and Drift Chamber Vertex Detector, achieves a track position resolution of better than 20 microns for high momentum tracks at the collision point. We describe procedures used to obtain this resolution, including alignment of the Silicon Stripmore » Vertex Detector, and techniques used to quantify the achieved resolution. We can, for the first time, measure the impact parameters of tracks accurately enough to use the finite b quark lifetime to tag a sample of events containing b quarks. This is done by requiring events which contain at least three tracks with impact parameter greater than three times the calculated impact parameter error. The b quark tagging efficiency is 48% and 85% of the tagged sample events contain b quarks. Using the 29 events tagged out of a total of 220 identified hadronic Z{sup 0} decays, we measure R{sub b} {triple bond} Br(Z{sup 0} {yields} b{bar b})/Br(Z{sup 0} {yields} hadrons) = 0.230{plus minus}0. 048{plus minus}0.030 where the first error is statistical and the second is systematic. This value of R{sub b} is in good agreement with existing measurements made using other methods and the Standard Model prediction of 0.22 using a sin {sup 2}{Theta}{sub W} value of 0.225.« less
  • The studies performed by the principal investigator during the period of the grant constitute the ground work for search for new physics in channels including top and bottom quarks with the ATLAS detector at the Large Hadron Collider. The PI has been involved in search for heavy charged Higgs bosons decaying into top and bottom quark pairs, and top quark rare decays involving Higgs bosons and c-quarks. Both channels have the top quark pair production as their main background, which was studied in detail. The search for heavy charged Higgs and top quark rare decays requires signi cant amount ofmore » data accumulated by the experiment. In case no signal is observed in the present data sample collected by ATLAS (5 fb{sup -1} of integrated luminosity at proton-anti proton center-of-mass energy of 7 TeV and 20 fb{sup -1} at 8 TeV), data from the upgraded detector running at 14 TeV needs to be analyzed. The PI has been working on physics and performance studies at upgraded detector.« less
  • Searches for the decay of Z bosons into pairs of new quarks and leptons in a data sample including 455 hadronic Z decays are presented. The Z bosons were produced in electon-positron annihilations at the SLAC Linear Collider operating in the center-of-mass energy range from 89.2 to 93.0 GeV. The Standard Model provides no prediction for fermion masses and does not exclude new generations of fermions. The existence and masses of these new particles may provide valuable information to help understand the pattern of fermion masses, and physics beyond the Standard Model. Specific searches for top quarks and sequential fourthmore » generation charge--1/3(b{prime}) quarks are made considering a variety of possible standard and non-standard decay modes. In addition, searches for sequential fourth generation massive neutrinos {nu}{sub 4} and their charged lepton partners L{sup {minus}} are pursued. The {nu}{sub 4} may be stable or decay through mixing to the lighter generations. The data sample is examined for new particle topologies of events with high-momentum isolated tracks, high-energy isolated photons, spherical event shapes, and detached vertices. No evidence is observed for the production of new quarks and leptons. 95% confidence lower mass limits of 40.7 GeV/c{sup 2} for the top quark and 42.0 GeV/c{sup 2} for the b{prime}-quark mass are obtained regardless of the branching fractions to the considered decay modes. A significant range of mixing matrix elements of {nu}{sub 4} to other generation neutrinos for a {nu}{sub 4} mass from 1 GeV/c{sup 2} to 43 GeV/c{sup 2} is excluded at 95% confidence level. Measurements of the upper limit of the invisible width of the Z exclude additional values of the {nu}{sub 4} mass and mixing matrix elements, and also permit the exclusion of a region in the L{sup {minus}} mass versus {nu}{sub 4} mass plane.« less
  • I present brief descriptions of two top quark analyses performed using D0 data from p{bar p} collisions at {radical}s = 1.96 TeV: the search for flavor-changing neutral-current couplings (FCNC) of the top quark with a charm or an up quark with the exchange of a gluon, and the search for the standard model production of single top quarks. The search for FCNC couplings of a gluon to the top quark is the first such analysis at hadron colliders. I describe the application of the Bayesian approach for comparing our physics models to the observed data in both analyses and, inmore » one of them, to separate small signals from large backgrounds.« less