Muon endcap alignment for the CMS experiment and its effect on the search for Z′ bosons in the dimuon channel at
LHC
Samir Guragain
Dissertation Committee
Dr. Marcus Hohlmann (Advisor)
Dr. Debasis Mitra (Outside member)
Dr. László A. Baksay
Dr. Terry D. Oswalt
Dr. Ming Zhang
Department of Physics and Space Sciences,
Florida Institute of Technology
September 8, 2010

• Published paper on muon alignment in 2008 CRAFT exercise in J. of Inst.
– I am a principal co-author of muon endcap alignment
– Presented at Muon alignment meetings during CMS weeks and / or regular, South Eastern
Section meeting of American
Physical Society (SESAPS) in
2006 and 2007
– 2 nd journal publication with major Fl. Tech contributions on behalf of CMS collaboration
(1 st was CMS detector paper)
CRAFT = Cosmic Run At Four Tesla
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain
18 pp. w/o author list
2

• Published an analysis note on Z′ search in the dimuon channel with CMS expt.
– I am a principal author
– Full responsibility of work from the beginning to the final approval and endorsement of the analysis
– 1 st CMS physics analysis note publication from our research group at Florida Tech
– Presented at various CMS meetings (Exotica, EXOresonances, TeV muon, muon
POG, and muon alignment) and US CMS meeting 2010
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain
25 pages
3

• Motivations
• Compact Muon Solenoid (CMS) experiment at LHC and the Muon alignment system
• Muon endcap hardware alignment system
– Commissioning of the ME system at CERN
– Muon endcap alignment constants
• Physics analysis: Z′ → 
+

search
– Monte Carlo (MC) simulation
– Effect of muon misalignments
• CMS collision data analysis
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 4

Standard model &
Elementary particles
The
Standard Model (SM) current knowledge in particle physics . theory of strong interactions and unified theory of weak and electromagnetic interactions
These theories are called gauge theories, meaning that they model the forces between fermions by coupling them to bosons, called gauge bosons .
These gauge bosons are force carriers.
Fermions (spin ½, 3/2, 5/2, ..)
:
Leptons & Quarks (Spin ½) and Bosons (spin 0,1, 2..):
Known Force carriers (Spin 1)
Lack of gravitational interactions in the SM
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 5

Physics
• Many models predict new heavy force carrier particles
• An extended gauge model predicts a neutral and heavy gauge boson, Z'
• The cleanest signal is decay to opposite-signed muons
• Current mass limit is > 1030 GeV/c 2 (CDF)
• LHC is the first opportunity to search for Z' in a high-mass (TeV/c 2 ) range
• Z' → µ + µ is one of the most promising channel for its discovery (clear signature, low background)
• CMS discovery potential
Detector Implications
• Good benchmark channel for muon detector
• Importance of reconstruction of very-high-p
T
• Detector misalignment muons
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 6

Model: Z
SSM within the sequential standard model (SSM), which has the same coupling as the standard model Z.
pp → Z' → µ + µ -
Muon Tracks in the simulated event of a dimuon decay: pp → Z' → µ + µ -
Sept. 8, 2010
Table from H. Lee’s PhD defense talk on May 20, 2005
Z′ is a new (proposed) force carrier with spin 1.
Ph. D. Thesis Defense, S. Guragain 7

Current lower Z′ mass limits for various models
Collider Detector at Fermilab (CDF) result in 2009
Z′ Mass limit (TeV)
0.789
0.821
0.861
0.878
0.892
0.904
1.030
Z′
SSM
1.030
1.023
Sept. 8, 2010 lower mass limit Channel Collaboration
TeV in 2009 Dimuon CDF (Tevatron at Fermilab)
TeV in 2010 Dielectron D0 (Tevatron at Fermilab)
Ph. D. Thesis Defense, S. Guragain
From CDF collaboration, “Search for
High-Mass Resonances Decaying to
Dimuons at CDF”
Phys. Rev. Lett. 102 (2009) 091805
8

LHC detectors and accelerator are the most complex scientific instruments ever built.
LHCb
(beauty)
Genève,
Switzerland
A Toroidal LHC ApparatuS
/ LHC forward
Sept. 8, 2010
Cessy, France
ALICE
(A large Ion Collider Experiment)
TOTal Elastic and diffractive cross-section Measurement
Ph. D. Thesis Defense, S. Guragain 9

ME -
Compact Muon Solenoid (CMS)
• Tracker
• Calorimeters
• Magnet
• Muon
ME+4
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 10

Global Muon Track Standalone Muon Track
Muon in
Silicon
Tracker
Sept. 8, 2010
Muon Hits and
Track Segments
Ph. D. Thesis Defense, S. Guragain 11

Installation & commissioning of CMS ME system at CERN
Cross-hair laser adjustment to pass through four CCDs in
Digital CCD based Optical Positioning Sensors (DCOPS)
Fully instrumented ME+1 in 2006!
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 12

Z-sensors
Clinometers Transfer
Plate (TP)
Note: only small sample of analog sensors shown
R-sensors
TOTAL: 768 sensors and 60 lasers
Sept. 8, 2010
The system monitors the positions of CSCs relative to each other and to the central disk.
Straight Line Monitors (SLMs) and Transfer lines
Ph. D. Thesis Defense, S. Guragain 13

Ref.
DCOPS
2 Crosshair
Lasers (adjustable)
Z-tube
Z-sensors
Clinometer
Transfer
Plate 1
Transfer
Line
DCOPS
Mounting
Tower
R-sensor
Sept. 8, 2010
Z
CMS
Rphi
CMS
ME+2 SLM
Ph. D. Thesis Defense, S. Guragain 14

Relative displacements at fields using Z-sensor measurements
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 15

Basic strategy for reconstruction of chamber positions at B=3.8T
• Fit DCOPS data at B=0T and reconstruct
DCOPS and chamber positions using COCOA
( C MS O bject-oriented C ode for O ptical A lignment)
• Check B=0T reco results for one SLM against photogrammetry (PG) in full detail and with great care until we can trust the reconstruction
• Reconstruct chamber positions using DCOPS data and Z-sensor relative shifts at B=3.8T
• Apply lessons learned to reco of other SLMs
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 16

ME+3 SLM1-4 at 0T using
DCOPS & PG measurements
Fit residual ~ 50 µm
Sept. 8, 2010
Reconstructed chamber center position
Ph. D. Thesis Defense, S. Guragain 17

Sept. 8, 2010
345 µm
Ph. D. Thesis Defense, S. Guragain 18

ME+3 SLM1-4 at 3.8T using
DCOPS & Z sensor measurements
TP’s position from PG and relative shift from Z-sensor
Disk bending is reconstructed !
Fit residual ~ 50 µm
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 19

ME+2,3 CSC displacements using relative shift of TP from 0 to 3.8T
-12,86
-9,61
-10,89
-8,97
-10,59
-12,5
-5
-1,74
-3,13
-4,54
-2,15
-3,39
-12,85
-9,73
-10,86
-12,25
-8,74
-10,41
0
-5,14
-2,36
-3,13
-4,54
-2
-2,17
-3,4
-4
-6
-8
-10
-12
-14
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 20

ME-2,3 CSC displacements using relative shift of TP from 0 to 3.8T
13,25
12,39
13,46 13,32
11,45
12,25
4,8
4,24
5,04 5,07
3,77
4,1
12,55
11,96
12,19
12,73
10,74
11,25
6
4,65
4,21
4,81 4,8
3,39
3,95
4
2
0
16
14
12
10
8
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 21

Bending of YE2 disk due to magnetic field at 3.8T
10 - 14 mm YE2 bending towards the interaction point (IP) of CMS
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 22

1/6 of 468 CSCs are monitored and corrected individually.
Sept. 8, 2010
For the remaining unmonitored CSCs, average corrections are applied.
Ph. D. Thesis Defense, S. Guragain 23


+

-
• Unique contributions:
– Studied impact of muon misalignment systematics on
• High-p
T
Muon p
T resolution
• Z′ signal significance
– Provided first 7 TeV Monte Carlo samples (signal & DY background) for analysis using local CMS Tier-3 cluster
– Analyzed these MC samples and updated the CMS discovery potential for Z
′
SSM at 7 TeV center-of-mass energy pp collision
• Analysis note: CMS AN-2010/064
• 14 contributed presentations at Exotica Muon meetings
(since 4/1/09)
• Taken on responsibility for MC samples in Z ′→ 
+

group: https://twiki.cern.ch/twiki/bin/viewauth/CMS/ExoticaZprimeMumu
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 24

Alignment scenarios and corresponding global tags
• IDEAL (MC_31X_V5) : Ideal geometry of the detector
• STARTUP (STARTUP31X_V4): Based on CRAFT 2008 and
2009 data analysis for early phase and produced by randomly misaligning chambers with an RMS consistent with cross-checks
Uncertainty in chamber positions:
0.05 cm – 0.60 cm in (x,y,z) & 0.3 mrad – 2.3 mrad in (φ x
, φ y
, φ z
)
• 50 pb -1 (50PBMU31X_V1) : Assuming an alignment with tracks using 50 pb -1 data and produced by running the
Reference-Target algorithm on MC samples
Uncertainty in chambers:
0.05 cm – 0.18 cm (x,y,z) & 0.3 mrad – 0.6 mrad (φ x
, φ y
, φ z
)
Tracker misalignment scenarios in startup and 50 pb -1 are the same and based on CRAFT 2008 (tag TrackerCRAFTScenario310_mc)
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 25

MC samples and event selection
MC samples (50K events)
• Z′ signal samples with full Z ′/Z/γ interference for
M
Z ′
SSM
=1.0 TeV/c 2 , 1.2 TeV/c 2 , 1.3 TeV/c 2 , and 2.0 TeV/c 2
• Drell-Yan samples, one in the mass region (>500 GeV/c 2 ) around the Z ′ mass and another at lower mass(>200 GeV/c 2 )
Analysis Code
“Zprime2muAnalysis” package in CMSSW
Event selection:
• At least a pair of oppositely charged muons
• p
T of each muon track in a pair > 20 GeV/c
• Isolated muons: Σ track p
T
(ΔR < 0.3) < 10 GeV/c
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 26

Z'
SSM
Resolution study for 3 alignment scenarios using 1.2 TeV Z ′ MC sample at √s = 7TeV
→ µ + µ analysis
Muon Momentum resolution (endcap) for 3 misalignment scenarios with
M
Z′
= 1.2 TeV at 7 TeV CM energy
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 27

Summary: resolutions for 3 alignments and different Z ′ mass with √s=7TeV & 10TeV
50 pb -1 alignment scenario is validated.
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain
GR = Global Reconstruction
TK = Tracker only
FS = Tracker plus First Muon Station 28

Systematics study:
Muon endcap alignment
Method:
1. Muon Endcap was misaligned systematically with respect to ideal or startup muon geometry.
2. A signal sample (M
Z ′
=1.2TeV/c 2 or 2.0TeV/c 2 ) was fully reconstructed.
– The sample was reconstructed with a customized global tag by inputting a modified SQLite file, with a bias for the position(X
CMS
, Y
CMS
, Z
CMS
) up to 2 mm or a bias on rotation ( φ
Z
CMS
) up to 0.5 mrad of muon endcap stations together or individual ME stations
.
[For comparison: Current startup
ME disk misalignments are 0.5 -
1.0 mm in (∆x, ∆y, ∆z) & 0.1 mrad in ∆φ
Z
CMS
]
3. The analysis code was re-run over the resulting biased MC data set for each misalignment.
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 29

T
Ideal alignement & with 2mm Bias
Ideal alignment 2 TeV Z ′ Sample
Sept. 8, 2010
2 TeV Z ′ Sample
Ideal alignment + 2mm shift of muon endcaps
Ph. D. Thesis Defense, S. Guragain
No systematic bias applied to the Barrel and Trackeronly
30

T
Ideal alignment + 2mm shift of muon endcap
• Up to 200 GeV/c, no significant change due to bias but changes at higher p
T
• Muon alignment becomes prominent at higher p
T in all scenarios
• Demonstrates tracker-only does not change, as expected with or without bias on endcap stations
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain
LHC startup alignment (now)
31

Alignment Systematics Study:
Bias on ideal Endcap positions q/pT resolution in Endcap vs. bias in the disk rotations around beamline q/pT resolution in Endcap vs. bias in ideal disk positions
8
8
7,5
7
All stations
ME+1 only
ME-1 only
ME+2 only
ME-2 only
7,5
7
6,5
6,5
6
6
5,5 5,5
5 5
4,5 4,5
-3
4
-2 -1 0 1 2
Bias on the disk positions (X
CMS
) [mm]
3 -0,6
4
-0,4 -0,2 0 0,2
Bias on the disk rotation, φ
Z
CMS
0,4
[mrad]
0,6
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 32

Alignment Systematics Study:
Bias on startup Endcap positions
19
18
17
Asymmetric results
16
15
14
-2,5
Sept. 8, 2010
-2 -1,5 -1 -0,5 0 0,5 1 1,5
Bias on the disk positions X
CMS
,Y
CMS
, Z
CMS
[mm]
2
Ph. D. Thesis Defense, S. Guragain
2,5
X All stations
Y All stations
Z All stations
X ME+1 only
Y ME+1 only
X ME-1 only
Y ME-1 only
X ME+2 only
Y ME+2 only
33

Generated and reconstructed dimuon mass with 3 alignment scenarios
Ideal alignment
(MC_31X_V5)
M
Z ′
= 1.2 TeV
50 pb -1 alignment
(50PBMU31X_V1)
Startup alignment
(STARTUP31X_V4)
Better aligned detector narrows the signal peak; e.g. from startup to 50 pb -1
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 34

Sept. 8, 2010
Z ′ Mass Reach Analysis:
Signal and background samples
Z ′ signal sample with full
Z ′/Z/γ interference, reconstructed with startup alignment ; and the background samples, one in the mass region
(> 500 GeV/c 2 ) around the Z ′ mass and the other at lower mass (> 200 GeV/c 2 ).
For the significance calculation, the reconstructed background sample is the weighted sum of these two background datasets.
Ph. D. Thesis Defense, S. Guragain 35

Reconstructed Mass fits:
Significance with 200pb -1
Likelihood-ratio estimator has been used to evaluate the significance
1000 pseudo-experiments
Sept. 8, 2010
STARTUP align.
M
Z
′
= 1.2 TeV &
200pb -1
( S
L
)
Ph. D. Thesis Defense, S. Guragain
50 pb -1 align.
M
Z
′
= 1.2 TeV &
200pb -1
( S
L
)
36

int
Variation of signal significance for M
Z ′
= 1.0 TeV/c 2 for different alignments and integrated luminosities.
and 1.2 TeV/c 2
Sept. 8, 2010
Better alignment puts us over 5
 discovery threshold
Better alignment equals doubling the data set
Ph. D. Thesis Defense, S. Guragain 37

Estimated data required for the expected Z ′ signal with 5 σ
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 38

Z ′ signal significance with misaligned muon endcaps only
Sept. 8, 2010
Negligible effect with the bias on endcaps only
Ph. D. Thesis Defense, S. Guragain 39

Datasets: (pre-ICHEP 2010)
1. /MinimumBias/Commisioning10-CS_Onia-Jun14thSkim_v1/RAW-RECO
–
135740 events, Run range 131511-135802, March 30
– April 15, 2010
2. /Mu/Run2010A-CS_Onia-jun14thSkim_v1/RAW-RECO
–
79833 events, Run range 135821-137436, April 15
– June 10, 2010
3. /Mu/Run2010A-PromptReco-v4/RECO
– 1M events, Run range 137437-140399 (July 19),
(Updated with data until September 3, 2010)
Event selections:
• Official good runs & lumisections certified from DQM group
(Cert_132440-140399_7TeV_StreamExpress_Collisions10_JSON.txt)
• Scraping filter to remove beam background rejection requiring ≥ 25% of high purity tracks with more than 10 tracks
•
Primary vertex (not fake) with at least 4 tracks (ndof
≥ 4) and with the z-coordinate of the point of closest approach to the tracks to the z-axis, i.e. |Z|
≤ 15 cm & position.Rho ≤ 2 cm
•
Two opposite sign muons with p
T
• Isolation Σ track p
T
> 1 GeV/c (Std. 20 GeV/c)
(ΔR < 0.3 ) < 10 GeV/c
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 40

Dimuon mass spectra with data taken through July 19
J/ ψ
Sept. 8, 2010
Z
Ph. D. Thesis Defense, S. Guragain
Events
41

Z
Up to date high-mass dimuon mass spectrum
2.88 pb -1
Until September 3, 2010
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 42

µ η= 0.46, p
T
=86 GeV
µ + η=-0.18, p
T
=87 GeV
M
µ+µ-
= 181 GeV
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 43

• CMS muon endcap alignment system is commissioned
• Entire muon endcap geometrical model is built and validated with independent survey and photogrammetry measurements using cosmic data at 0 Tesla (T)
• CARFT 2008 data are analyzed and CSC positions are reconstructed at 3.8T precisely
• Precisions ~300 µm in z
CMS and 200 µrad in φ
Z
& error < 500 µm
CMS
• Muon endcap alignment constants are delivered to CMS
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 44

• Samples for M
Z′
= 1.0 TeV, 1.2 TeV, 1.3 TeV, & 2 TeV and Drell-Yan at √s=7 TeV with the ideal, startup & 50 pb -1 alignment scenarios are generated, analyzed and published in CMS Database Bookkeeping System [hosted by FLTECH T3].
• The transverse momentum (p
T
) resolutions and dimuon mass resolutions are studied for various scenarios with the aforementioned samples. Typical dimuon mass resolutions are ~3% for ideal (MC), 6% for 50 pb -1 & 10% for startup.
• The muon p
T resolution in Endcaps is sensitive to the disk misalignment in position as well as rotation and the resolution is quantified for various misalignment scenarios.
• Simulation results for discovery potential for M
Z′SSM
= 1.0 TeV & 1.2 TeV with different muon alignments and integrated luminosities are studied.
– Effect of muon (mis)alignment on mass spectra
– Expect to observe the Z′ (M = 1.2 TeV) with 5σ significance at √s=7 TeV and integrated luminosity of 250pb -1 with the 50pb -1 alignment or better
– Negligible effect of muon endcap (only) misalignments upto 2 mm in translation or
0.5 mrad in rotation on Z ′ signal significance
Analyzed 7 TeV collision data up to run 140399 (July 19, 2010) and the dimuon mass spectra are shown and compared with simulated events of Z → µ + µ around Z mass region. The dimuon mass spectrum is updated. The search is in progress.
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 45

• Published a paper on muon alignment in CRAFT08 exercise in J. of Inst.
(Led, completed, and co-authored Muon Endcap alignment system )
– Commissioned CMS ME alignment system at CERN
– Delivered muon endcap alignment constants to CMS
• Published a CMS physics analysis note on muon misalignment systematics and expected Z′ signal significance using 7 TeV MC samples
• Analyzed CMS early collision data taken through
July 19 ( 250-300 nb -1 ) and updated with 2.88 pb -1
• Got approval / endorsement of my Ph.D. thesis by CMS on August 3 rd , 2010
Contributed presentations = 63 + 10
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 46

Thank you !
&
Drs. Baksay, Hohlmann, Mitra, Oswalt, and Zhang
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 47

• Is there something special about that day?
Dr. Oswalt’s question by email on input to fix defense date
Apparently! Yes
Today is
औसी
(New moon)
२०६७ भाद्र २३
(2067/5/23)
September
8
2010
बुवाको मुख हेर्ने दिर्न
Father ’s face see day
(Father ’s day)
This work is dedicated to his memory.
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 48