Download ASearch FOR LONG-LIVED PARTICLES THAT STOP IN THE CMS DETECTOR AND DECAY TO ... PDF

TitleASearch FOR LONG-LIVED PARTICLES THAT STOP IN THE CMS DETECTOR AND DECAY TO ...
LanguageEnglish
File Size18.5 MB
Total Pages339
Table of Contents
                            Curriculum Vitae
Preface and Acknowledgments
Contents
List of Tables
List of Figures
1 INTRODUCTION
2 THE STANDARD MODEL AND BEYOND
	2.1 The Standard Model (SM)
		2.1.1 The Particle Content of the SM
			2.1.1.1 Fermions
			2.1.1.2 Bosons
			2.1.1.3 Mass and Gauge Eigenstates
		2.1.2 The Fundamental Forces
		2.1.3 Quantum Electrodynamics (QED)
		2.1.4 Weak Interactions
		2.1.5 Electroweak Unification
		2.1.6 Quantum Chromodynamics (QCD)
		2.1.7 The SM before the Higgs Mechanism
		2.1.8 Spontaneous Symmetry Breaking
			2.1.8.1 Discrete Spontaneous Symmetry Breaking
			2.1.8.2 Continuous Spontaneous Symmetry Breaking
			2.1.8.3 The Higgs Mechanism in an Abelian Theory
			2.1.8.4 The Higgs Mechanism in the the Electroweak Sector of the SM
		2.1.9 Measurements of the SM
		2.1.10 Summary of the Fundamental Forces
	2.2 Why the SM is Incomplete
		2.2.1 Unexplained Phenomena
			2.2.1.1 Gravity
			2.2.1.2 Neutrino Oscillations
			2.2.1.3 Dark Matter and Dark Energy
			2.2.1.4 The Baryon-Antibaryon Asymmetry
		2.2.2 Theoretical Problems
			2.2.2.1 Arbitrary Assumptions and Parameters
			2.2.2.2 The Hierarchy Problem, Naturalness, and Fine Tuning
			2.2.2.3 Strong CP Problem
	2.3 Theories Beyond the SM
		2.3.1 Supersymmetry (SUSY)
			2.3.1.1 SUSY Breaking
		2.3.2 Extra Dimensions
			2.3.2.1 Kaluza-Klein Theories
			2.3.2.2 Large Extra Dimensions
			2.3.2.3 Warped Extra Dimensions
		2.3.3 New Strong Dynamics and Little Higgs
		2.3.4 Hidden Valley Theories
		2.3.5 Grand Unified Theories and Theories of Everything
3 THE COMPACT MUON SOLENOID EXPERIMENT AT THE LARGE HADRON COLLIDER
	3.1 The Large Hadron Collider (LHC)
		3.1.1 The Proton Acceleration
		3.1.2 Luminosity, Vertices, and Pileup
		3.1.3 Data-Taking at the LHC
	3.2 The Compact Muon Solenoid Experiment (CMS)
		3.2.1 Particle Interactions in Matter
		3.2.2 The Coordinate System
		3.2.3 The Superconducting Magnet
		3.2.4 The Inner Tracker
			3.2.4.1 The Pixel Detector
			3.2.4.2 The Silicon Strip Tracker
		3.2.5 The Electromagnetic Calorimeter (ECAL)
			3.2.5.1 The ECAL Barrel
			3.2.5.2 The ECAL Endcaps
			3.2.5.3 The ECAL Preshower Detector
		3.2.6 The Hadronic Calorimeter (HCAL)
			3.2.6.1 The HCAL Barrel
			3.2.6.2 The HCAL Endcaps
			3.2.6.3 The HCAL Outer Calorimeter
			3.2.6.4 The HCAL Forward Calorimeter
		3.2.7 The Muon System
			3.2.7.1 The Drift Tubes
			3.2.7.2 The Cathode Strip Chambers
			3.2.7.3 The Resistive Plate Chambers
		3.2.8 The Trigger and Data Acquisition
			3.2.8.1 Level 1 Trigger
			3.2.8.2 High Level Trigger
			3.2.8.3 Data Acquisition
		3.2.9 The Detector Infrastructures
			3.2.9.1 Detector Powering
			3.2.9.2 Detector Cooling
			3.2.9.3 Detector Cabling
			3.2.9.4 Detector Safety System (DSS)
			3.2.9.5 Beam and Radiation Monitoring (BRM) Systems
		3.2.10 Computing
			3.2.10.1 MC Event Simulation
			3.2.10.2 Data Formats and Distribution
			3.2.10.3 Calibration and Alignment
			3.2.10.4 Data Quality Montioring and Certification
		3.2.11 The Event and Object Reconstruction
			3.2.11.1 Particle Flow Algorithm
			3.2.11.2 Muons
			3.2.11.3 Electrons and Photons
			3.2.11.4 Jets
			3.2.11.5 Taus
			3.2.11.6 Missing Transverse Energy
4 EXOTIC LONG-LIVED PARTICLES
	4.1 Motivation for LLP Searches
	4.2 Theoretical Models Predicting LLPs
		4.2.1 Minimal Supersymmetry
		4.2.2 Gauge Mediated Supersymmetry Breaking
		4.2.3 Anomaly Mediated Supersymmetry Breaking
		4.2.4 Split Supersymmetry
		4.2.5 R-Parity Violating Supersymmetry
		4.2.6 Models with Multiply or Fractionally Charged Particles
		4.2.7 Supersymmetric Left-Right Model
		4.2.8 Hidden Valley Models
		4.2.9 Untracked Signals of SUSY
		4.2.10 Magnetic Monopoles
	4.3 LLP Interactions in Matter
		4.3.1 Ionization of Electrically and Magnetically Charged LLPs
		4.3.2 Hadronization of LLPs
	4.4 Detector Signatures of LLPs
		4.4.1 Signature of Particles that Pass Through the Detector
		4.4.2 Signature of Particles that Decay in the Detector
		4.4.3 Signature of Particles that Stop in the Detector
		4.4.4 Signature of Monopoles
	4.5 Previous and Present Searches for LLPs
		4.5.1 Previous and Present Searches for CMLLPs
		4.5.2 Previous and Present Searches for Displaced Vertices
		4.5.3 Previous and Present Searches for Weird Tracks
		4.5.4 Previous and Present Searches for Stopped Particles
		4.5.5 Previous and Present Searches for Monopoles
5 A SEARCH FOR DELAYED MUONS
	5.1 Introduction and Motivation
	5.2 Data and Monte Carlo Samples
		5.2.1 Trigger
		5.2.2 Data Samples
			5.2.2.1 Search Sample
			5.2.2.2 Cosmic Muon Background Sample
		5.2.3 Signal Samples
			5.2.3.1 Models
			5.2.3.2 Signal Generation
			5.2.3.3 Stopping Probability
			5.2.3.4 Event Weight for Doubly Charged Higgs
		5.2.4 Cosmic Muon MC Simulation Sample
	5.3 Analysis Strategy and Techniques
		5.3.1 Displaced Standalone Muon pT
		5.3.2 DT Time of Flight
		5.3.3 RPC BX Assignments
	5.4 Event Selection
		5.4.1 Trigger and Reconstruction Efficiency
		5.4.2 Preselection Criteria
		5.4.3 Signal and Background Comparison
		5.4.4 Cosmic Muon TOF
		5.4.5 Final Selection Criteria
	5.5 Background Modeling
		5.5.1 ABCD Method
		5.5.2 Choice of Momentum Variable for Background Estimation
		5.5.3 Choice of Free-1 and p Cuts
		5.5.4 Background Closure Test
		5.5.5 Background Estimation
		5.5.6 Other Backgrounds
	5.6 Systematic Uncertainties
	5.7 Results
	5.8 Results with at Least One Upper Hemisphere DSA Track
	5.9 Preparation for 13 TeV
6 SUMMARY
A A SEARCH FOR CHARGED MASSIVE LONG-LIVED PARTICLES AT D0
	A.1 Motivation and Signal Samples
		A.1.1 Motivation and Models
		A.1.2 Signal Generation
		A.1.3 Detection of Top Squarks
	A.2 The D0 Experiment at the Tevatron Collider
		A.2.1 The Tevatron and the D0 Detector
		A.2.2 The Central Tracker
		A.2.3 The Calorimeter
		A.2.4 The Muon System
		A.2.5 The Trigger
	A.3 Analysis Strategy and Techniques
		A.3.1 Time-of-Flight Measurement
		A.3.2 dE/dx Measurement
	A.4 Event Selection
	A.5 Background Estimation
		A.5.1 Background Normalization
		A.5.2 Differences in Kinematic Distributions and Additional Event Weight
	A.6 Analysis Method
	A.7 Systematic Uncertainties
		A.7.1 Flat Systematic Uncertainties
		A.7.2 Shape Systematic Uncertainties
	A.8 Results
Bibliography
                        
Document Text Contents
Page 2

A SEARCH FOR LONG-LIVED

PARTICLES THAT STOP IN THE CMS

DETECTOR AND DECAY TO MUONS

by

Juliette Alimena

M.Sc. in Physics, Brown University, 2010

B.A. in Physics, University of Pennsylvania, 2008

A dissertation submitted in partial fulfillment of the requirements

for

the Degree of Doctor of Philosophy

in the Department of Physics at Brown University

Providence, Rhode Island

May 2016

Page 169

../plots/BDToutput-stau250.eps: Final Variable Canvas


data at

s = 8 TeV, are on Higgs bosons that decay to a pair of long-lived neutral

X bosons, which decay to dileptons (e+e− or µ+µ−); the 95% CL cross section limits

are between 0.1 and 5 fb for X bosons with lifetimes between 0.01 and 100 cm. The

limits from CMS on a pair of squarks that decay to a long-lived neutralino, which

decays to e+e−ν or µ+µ−ν, are between 2 and 5 fb for neutralino lifetimes between

0.1 and 100 cm and squark masses above 350 GeV. CMS has also started a search for

displaced muons using only the muon system, in order to expand their sensitivity to

LLPs with a transverse impact parameter greater than 40 cm [196].

There have been several searches for displaced jets, including CDF and D0 searches

for metastable particles decaying to b-quark jets [197,198], an LHCb search [199], the

ATLAS searches mentioned above [188�190, 192], and a CMS analysis [200]. The

CMS search uses 2012 data at

s = 8 TeV and looks for Higgs bosons that decay to

long-lived neutral X bosons. For Higgs boson masses between 400 and 1000 GeV, X

boson masses between 50 and 350 GeV, and X boson lifetimes between 0.1 and 200

cm, the upper limits are typically 0.3 to 100 fb. These are the most stringent limits

to date in this channel.

There has been a search for displaced lepton-jets at ATLAS [201]. They use the

2012,

s = 8 TeV data set to put limits on non-prompt lepton-jet models. Assuming

the SM gluon fusion production cross section for a 125 GeV Higgs boson, they �nd its

branching ratio to hidden-sector photons to be below 10%, at 95% CL, for a hidden

photon in the 14 mm ≤ cτ ≤ 140 mm range for the H→ 2γd + X model and in the

15 mm ≤ cτ ≤ 260 mm range for the H→ 4γd +X model.

A few searches for displaced photons have been performed. CDF performed a

search using MET [202], and CMS performed searches using converted photons and

MET [203, 204]. All other searches for photons in some SUSY scenario have been

with prompt photons. Currently, a search is being performed at CMS for displaced

photons using ECAL time measurements [205], and another search using photon

135

Page 170

../plots/BDToutput-stau250.eps: Final Variable Canvas


conversions [206]. The most stringent limits on displaced photons use 2011 data at


s = 7 TeV; CMS excludes neutralinos with masses below 220 GeV, for lifetimes of

500 mm [204].

There have also been searches for RPV SUSY, such as one search that looks for

slightly displaced, pair-produced stops [207]. This search has been performed at CMS

with 2012 data at

s = 8 TeV, and it looks for an electron and a muon in the �nal

state, which are displaced transversely from the LHC luminous region. No excess is

observed above the estimated number of background events for displacements up to

2 cm. For a lifetime of 2 cm, stops masses are excluded up to 790 GeV.

4.5.3 Previous and Present Searches for Weird Tracks

ATLAS has conducted a few searches for disappearing tracks [208, 209]. CMS is

currently performing a search for disappearing tracks using 2012 data at

s = 8

TeV [210]. The benchmark signal process for this search is AMSB where there is a

small mass splitting between the lightest chargino and neutralino, and the chargino

decays to a neutralino and a soft pion, which will not be reconstructed. If the chargino

decays within the tracker volume, a disappearing track will be produced. The most

stringent limits are from the CMS search, which for a mean lifetime of 1 ns, charginos

with masses below 443 GeV at 95% CL are excluded.

A search for kinked tracks in the CMS tracker is also in progress. This search

uses a coNLSP SUSY model in which mass degenerate selectrons and smuons decay

to their SM counterparts and a nearly massless gravitino. The tracks of the mother

NLSP (selectron or smuon) and of the daughter particle (electron or muon) create

the kinked track that could be observed.

136

Page 338

[253] M. Eads and D. Hedin, �A Search for Charged Massive Stable Particles at

D0,� D0Note 4965 (2005) . [link].

[254] M. Eads, A Search for Charged Massive Stable Particles at D0. PhD thesis,

Northern Illinois University, 2005. [link].

[255] S. P. Martin, S. Moretti, J. Qian, and G. W. Wilson, �Direct investigations of

supersymmetry: subgroup summary report,� CERN Conference Note

CERN-TH-2001-343. DCPT-2001-114.

FERMILAB-CONF-2001-371-T. IPPP-2001-57 (2001) . [link].

[256] J. Alimena, S. Banerjee, S. Cho, D. Cutts, M. Eads, S. Park, and Y. Xie,

�Stable Stop Quark Production,� D0Note 6075 (2011) . [link].

[257] http://pythia6.hepforge.org/examples/main78.f.

[258] R. Mackeprang, Stable Heavy Hadrons in ATLAS. PhD thesis, University of

Copenhagen, 2007. [link].

[259] P. D. Grannis and M. J. Shochet, �The Tevatron Collider Physics Legacy,�

Annual Review of Nuclear and Particle Science 63 (2013) no. 1, .

http://www.annualreviews.org/doi/pdf/10.1146/annurev-nucl-102212-170621.

[260] S. Holmes, R. S. Moore, and V. Shiltsev, �Overview of the Tevatron collider

complex: goals, operations and performance,� JINST 6 (2011) T08001.

[link].

[261] D0 Collaboration, �The upgraded D0 detector,� Nucl. Instrum. Methods A

565 (2006) 463�537. [link].

[262] J. Alimena, S. Banerjee, S. Cho, D. Cutts, M. Eads, S. Park, and Y. Xie, �p20

SingleMuonOR Trigger Study for the Charged Massive Long-lived Particle

Search,� D0Note 6069 (2010) . [link].

304

http://www-d0.fnal.gov/d0pub/d0_private/4965/m_d0note4965_cmsp_analysis_v1.2.pdf
http://www-d0.fnal.gov/results/publications_talks/thesis/eads/thesis.pdf
http://www.slac.stanford.edu/econf/C010630/papers/P346.PDF
http://www-d0.fnal.gov/d0pub/d0_private/6075/m_stable_stop_quarks_v1.01.pdf
http://pythia6.hepforge.org/examples/main78.f
http://cds.cern.ch/record/1385016/files/CERN-THESIS-2007-109.pdf
http://arxiv.org/abs/http://www.annualreviews.org/doi/pdf/10.1146/annurev-nucl-102212-170621
http://stacks.iop.org/1748-0221/6/i=08/a=T08001
http://www.sciencedirect.com/science/article/pii/S0168900206010357
http://www-d0.fnal.gov/d0pub/d0_private/6069/m_CMSP_Trigger_v1.02.pdf

Page 339

[263] J. Alimena, S. Banerjee, S. Cho, D. Cutts, M. Eads, M. Klein, E. Teich, and

Y. Xie, �A study of dE/dx for the charged massive long-lived particle search,�

D0Note 6033 (2011) . [link].

[264] O. Brandt, S. Cho, M. Cooke, M. Eads, D. Hedin, A. Santos, B. Tuchming,

Y. Yatsunenko, and S. Youn, �Muon Identi�cation Certi�cation for the

Summer 2009 Extended Dataset (Run IIb-1 and -2),� D0Note 6025 (2010) .

[link].

[265] A. Hoecker, P. Speckmayer, J. Stelzer, J. Therhaag, E. von Toerne, and

H. Voss, �TMVA 4: Toolkit for Multivariate Data Analysis with ROOT,�

arXiv e-print physics/0703039 (2009) . [link].

[266] W. Fisher, �Collie: A Con�dence Level Limit Evaluator,� D0Note 5595 (2010)

. [link].

[267] D0 Collaboration, �The D0 experiment's integrated luminosity for Tevatron

Run IIa,� Fermilab Preprint FERMILAB-TM-2365 (2007) . [link].

305

http://www-d0.fnal.gov/d0pub/d0_private/6033/m_cmsp-dedx-v1-3.pdf
http://www-d0.fnal.gov/d0pub/d0_private/6025/m_6025_MuonCertification_p20_Summer2009Extended.pdf
http://tmva.sourceforge.net/docu/TMVAUsersGuide.pdf
http://www.desy.de/~titov/CollieDocumentation.pdf
http://inspirehep.net/record/750852

Similer Documents