A search for long-lived particles that stop in the CMS detector and decay to muons

339 Pages·2015·18.53 MB·English

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EARCH FOR ONG IVED
P S CMS
ARTICLES THAT TOP IN THE
D D M
ETECTOR AND ECAY TO UONS
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
' Copyright 2016 by Juliette Alimena
This dissertation by Juliette Alimena is accepted in its present form by
the Department of Physics as satisfying the
dissertation requirement for the degree of
Doctor of Philosophy
Date...................... ................................................
David Cutts, Advisor
Recommended to the Graduate Council
Date...................... ................................................
Meenakshi Narain, Reader
Date...................... ................................................
JiJi Fan, Reader
Approved by the Graduate Council
Date...................... ................................................
Peter M. Weber
Dean of the Graduate School
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Juliette Alimena
Physics Department [email protected] 203-362-7287 (cell)
Barus and Holley Build-
ing
Brown University
182 Hope Street
Providence, RI 02906
Education
Brown University, Providence, RI
Candidate for Doctor of Philosophy in Physics, Expected May 2016
Thesis: (cid:16)A Search for Delayed Muons in the CMS Experiment(cid:17)
Advisor: Prof. David Cutts
Master of Science in Physics, May 2010
University of Pennsylvania, College of Arts and Sciences, Philadelphia, PA
Bachelor of Arts in Physics with Honors, Math and English Mi-
nors, cum laude, May 2008
Awards
CMS Achievement Award, December 2012
For (cid:16)implementation of triggers for long-lived particles and outstanding contribu-
tions to the High Level
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Trigger (HLT) code and trigger menu integration.(cid:17)
Selected Publications
√
D0 Collaboration, (cid:16)Search for charged massive long-lived particles at s = 1.96 TeV(cid:17),
Phys. Rev. D 87 (2013) 052011.
D0 Collaboration, (cid:16)Search for charged massive long-lived particles(cid:17), Phys. Rev. Lett.
108 (2012) 121802.
Research Experience
Physics Research Assistantship, Brown University, September 2009 (cid:21) present
Primary analyst for long-lived exotica searches:
Search for Delayed Muons, Run I data, CMS Experiment, January 2012 (cid:21) present
Performed a search for long-lived particles predicted by theories beyond the Stan-
dard Model, which stop
in the detector material and decay to delayed and displaced muons
Created and maintained an analysis-speci(cid:28)c trigger for the 2012 run
Developed a new muon reconstruction for highly displaced muons, for o(cid:31)ine and
HLT
Search for Charged Massive Long-Lived Particles, Run II data, D0 Experi-
ment, May 2009 (cid:21) March 2013
Performed a search for long-lived particles with long time-of-(cid:29)ight and large ion-
ization energy loss (dE/dx)
Detector experience:
Trigger Convener, CMS Exotica, March 2011 (cid:21) December 2014
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Supervised the exotica analysts when developing their triggers within the opera-
tional limits of the HLT
Member of STORM, CMS Trigger Studies Group, March 2011 (cid:21) December 2014
Co-led integration all the HLT paths into the trigger menus for the 2011, 2012,
and 2015 runs
Research Details
Compact Muon Solenoid (CMS) Experiment
Analysis: Search for Delayed Muons
We search for long-lived exotic particles, which arise in many theories beyond
the Standard Model, that are stopped in the detector material and decay to muons
sometime after the bunch crossing. If a new particle were su(cid:30)ciently massive, slow-
moving, and long-lived, it could traverse part of the detector and stop somewhere
in the material and then decay between nanoseconds and days later. Using Run I
data, we search for long-lived particles, which have been stopped somewhere between
the inner tracker and the muon system and which decay to muons. We require
these delayed muons to be out-of-time with respect to the bunch crossing, and they
would typically not point back to the primary vertex. For this search, I created and
maintainedanewanalysis-speci(cid:28)ctriggerthatwasimplementedintheCMScollisions
trigger menu for the entire 2012 run. I also developed a new muon reconstruction
for highly displaced muons using only the muon system, which has been incorporated
into the CMS software and used by other long-lived exotica searches involving muons.
Ithenimplementedanonlineversionofthisnewreconstructionforthedelayedmuons
triggers, which will be used in the HLT in 2015. I have also developed algorithms
to measure the time-of-(cid:29)ight of the muons, which can help distinguish the primary
background, cosmic ray muons, from the signal. Furthermore, I have customized
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the Monte Carlo (MC) for this search, generating stopped long-lived particles that
decay to muons, using MC simulations of long-lived particles as input. I doubled the
stopping e(cid:30)ciency of the benchmark model with several simulation improvements. I
have developed the event selection, estimated the background, and will obtain the
results for this search.
Detector Experience: Trigger Studies Group
The CMS High Level Trigger (HLT) performs the (cid:28)nal online selection of events
thatarerecordedforphysicsanalyses. WithintheHLTTriggerStudiesGroup(TSG),
I had three separate tasks:
I was a Trigger Convener for the Exotica Physics Analysis Group, primarily work-
ing with the Long-Lived Particle Sub-Group. This task involves communicating
between the long-lived exotica trigger developers and the TSG, to ensure that the
physics analysis requirements are met within the operational limits. I worked with
the analysts to develop and maintain their trigger paths for the 2012 and 2015 runs.
For my work within the HLT Software, Tools, Online Releases and Menus
(STORM) group, I integrated trigger paths into the master HLT trigger menu and
then validated this menu. The two conveners of STORM and I integrated all the
changes to the HLT menu, which consists of approximately 400 trigger paths and
goes through about (cid:28)ve major and 25 minor revisions per year. I did this task for the
HLT menus in 2011, 2012, and in preparation for the 2015 run. This task involves
maintaining an intimate knowledge of the current state of the HLT trigger paths and
of confDB, the tool used to work on the HLT con(cid:28)guration database.
I designed code that I used to study and monitor any di(cid:27)erences between online
and o(cid:31)ine HLT results. In general, whether or not an event passed a trigger path
(the HLT results) should be reproducible o(cid:31)ine, but various di(cid:27)erences in online and
o(cid:31)ine code and release conditions occasionally produce discrepancies that need to be
studied.
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In addition to my trigger tasks, I also took about 20 online trigger shifts in the
Point 5 control room during the 2012 run.
D(cid:216) Experiment
Analysis: Search for Charged Massive Long-Lived Particles
We performed a search for charged massive long-lived particles (CMLLPs), using
Run II data collected with the D0 detector. We searched for events in which one or
more particles are reconstructed as muons but have speed and ionization energy loss
(dE/dx) inconsistent with muons produced in beam collisions. I developed data cor-
rections and Monte Carlo (MC) smearing for our key variables, studied and applied
event selection criteria, and modeled the background with a data-driven technique.
I used a multivariate technique known as Boosted Decision Trees (BDTs) to further
separate the signal from background, studied the systematic uncertainties, and ob-
tainedcon(cid:28)dencelevels(CLs)cross-sectionlimitsforourdi(cid:27)erentsignalmodels. This
work was published in PRL, with a longer article in PRD. The latter describes this
analysis, an analysis our group performed in parallel for a pair of CMLLPs, and an
earlier version of this analysis, in more detail.
Presentations and Posters
Brown Astrophysics Seminar Series, (cid:16)Search for Stopped Particles from Decays
to Delayed Muons(cid:17), October 2015.
Large Hadron Collider Physics Conference, ColumbiaUniversity, (cid:16)Performance
of Muon-Based Triggers at the CMS High Level Trigger(cid:17), June 2014.
Division of Particles and Fields Conference, American Physical Society, "A
Search for Single Charged Massive Long-Lived Particles at the Fermilab Tevatron",
August 2011.
April Meeting, American Physical Society, "A Search for Single Charged Massive
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Long-Lived Particles at the Fermilab Tevatron", May 2011.
Brown Astrophysics Journal Club, (cid:16)A Search for Charged Massive Long-Lived
Particles at D0(cid:17), April 2011.
Teaching Experience
Physics Teaching Assistantship, Brown University, September 2008 (cid:21) Decem-
ber 2009
TA for undergraduate introductory physics labs for physics and engineering concen-
trators (Phys 0050/0070,
Fall 2008; Phys 0160, Spring 2009)
TA for undergraduate introductory physics drop-in sections (Phys 0030, Fall 2009)
Additional Training and Skills
Fermilab-CERN Hadron Collider Physics Summer School, August 2012.
Knowledge of ROOT, C++, Python, UNIX shell, LATEX, Maple, Mathematica.
Conversational French.
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