muon endcap alignment for the cms experiment and its effect on the search for z′ bosons in the...
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Muon endcap alignment for the CMS Muon endcap alignment for the CMS experiment and its effect on the search experiment and its effect on the search for Z′ bosons in the dimuon channel at for Z′ bosons in the dimuon channel at
LHCLHC
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
Ph. D. Thesis DefensePh. D. Thesis Defense
Major achievements (I)Major achievements (I)
• 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
– 2nd journal publication with major Fl. Tech contributions on behalf of CMS collaboration (1st was CMS detector paper)
18 pp. w/o author listSept. 8, 2010 2Ph. D. Thesis Defense, S. Guragain
CRAFT = Cosmic Run At Four Tesla
Major achievements (II)Major achievements (II)
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 3
• 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
– 1st CMS physics analysis note publication from our research group at Florida Tech
– Presented at various CMS meetings (Exotica, EXO-resonances, TeV muon, muon POG, and muon alignment) and US CMS meeting 2010
25 pages
OutlineOutline• 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 &Standard model & Elementary particles Elementary particles
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 5
The Standard Model (SM) current knowledge in particle physics. theory of strong interactions and unified theory of weak and electromagnetic interactions
Fermions (spin ½, 3/2, 5/2, ..): Leptons & Quarks (Spin ½)
and Bosons (spin 0,1, 2..): Known Force carriers (Spin 1)
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.
Lack of gravitational interactions in the SM
MotivationsMotivationsPhysics• 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/c2 (CDF)• LHC is the first opportunity to search for Z' in a high-mass (TeV/c2) 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-pT muons
• Detector misalignment
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Proposed new particle Z'Proposed new particle Z'
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Model: ZSSM within the sequential standard model (SSM), which has the same coupling as the standard model Z.
Table from H. Lee’s PhD defense talk on May 20, 2005
Muon Tracks in the simulated event of a dimuon decay:pp → Z' → µ+ µ- Z′ is a new (proposed) force carrier
with spin 1.
pp → Z' → µ+ µ-
Current lower Z′ mass limits Current lower Z′ mass limits for various modelsfor various models
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Z′ Mass limit (TeV)
0.7890.8210.8610.8780.8920.9041.030
From CDF collaboration, “Search for High-Mass Resonances Decaying to Dimuons at CDF” Phys. Rev. Lett. 102 (2009) 091805
Z′SSM lower mass limit Channel Collaboration1.030 TeV in 2009 Dimuon CDF (Tevatron at Fermilab) 1.023 TeV in 2010 Dielectron D0 (Tevatron at Fermilab)
Collider Detector at Fermilab (CDF) result in 2009
LHC at CERN LHC at CERN
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LHCb (beauty)
ALICE
(A large Ion Collider Experiment)
Cessy, France
Genève, Switzerland
LHC detectors and accelerator are the most complex scientific instruments ever built.
TOTal Elastic and diffractive cross-section Measurement
A Toroidal LHC ApparatuS/ LHC forward
Compact Muon Solenoid (CMS)Compact Muon Solenoid (CMS)
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• Tracker• Calorimeters• Magnet• Muon
ME+4ME -
Particle detection in CMS & Particle detection in CMS & muon reconstructionsmuon reconstructions
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Global Muon Track Standalone Muon Track
Muon Hits and Track Segments
Muon in Silicon Tracker
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Installation & commissioning Installation & commissioning of CMS ME system at CERNof 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!
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Full reconstruction modelFull reconstruction model
R-sensors
Z-sensors
Note: only smallsample of analog sensors shown
ClinometersTransfer Plate (TP)
DCOPS’s
Straight Line Monitors (SLMs)and Transfer lines
Lasers
Lasers
The system monitors the positions of CSCs relative to each other and to the central disk.
TOTAL: 768 sensors and 60 lasers
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A part of CMSA part of CMS
2 Crosshair Lasers (adjustable)
Ref. DCOPS
Chamber DCOPS’s
Transfer Line DCOPS
Z-tube
Z-sensors
Transfer Plate 1
Clinometer
MountingTower
ME+2 SLM
BackChamber
R-sensor
Laser beam
Laser on !ZCMS
RphiCMS
Relative displacements at fields Relative displacements at fields using Z-sensor measurements using Z-sensor measurements
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Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 16
Basic strategy for reconstruction of Basic strategy for reconstruction of chamber positions at B=3.8Tchamber positions at B=3.8T
• Fit DCOPS data at B=0T and reconstruct DCOPS and chamber positions using COCOA (CMS Object-oriented Code for Optical Alignment)
• 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
ME+3 SLM1-4 at 0T using ME+3 SLM1-4 at 0T using DCOPS & PG measurementsDCOPS & PG measurements
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Reconstructed chamber center position
Fit residual ~ 50 µm
Comparison with PGComparison with PG
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345 µm
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ME+3 SLM1-4 at 3.8T using ME+3 SLM1-4 at 3.8T using DCOPS & Z sensor measurementsDCOPS & Z sensor measurements
TP’s position from PG and relative shift from Z-sensor
Disk bending is reconstructed !
Fit residual ~ 50 µm
ME+2,3 CSC displacements using ME+2,3 CSC displacements using relative shift of TP from 0 to 3.8Trelative shift of TP from 0 to 3.8T
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ME-2,3 CSC displacements using ME-2,3 CSC displacements using relative shift of TP from 0 to 3.8Trelative shift of TP from 0 to 3.8T
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Bending of YE2 disk due to Bending of YE2 disk due to magnetic field at 3.8Tmagnetic field at 3.8T
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10 - 14 mm YE2 bending towards the interaction point (IP) of CMS
ME Alignment constantsME Alignment constants
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1/6 of 468 CSCs are monitored and corrected individually.
For the remaining unmonitored CSCs, average corrections are applied.
Physics: ZPhysics: Z′→ ′→ ++- - searchsearch• Unique contributions:
– Studied impact of muon misalignment systematics on• High-pT Muon pT 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
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Alignment scenarios and Alignment scenarios and corresponding global tagscorresponding 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 (φx,φy,φz)
• 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 (φx,φy,φz)
Tracker misalignment scenarios in startup and 50 pb-1 are the same and based on CRAFT 2008 (tag TrackerCRAFTScenario310_mc)
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MC samples and MC samples and event selectionevent selection
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MC samples (50K events)• Z′ signal samples with full Z′/Z/γ interference for
MZ′SSM=1.0 TeV/c2, 1.2 TeV/c2, 1.3 TeV/c2, and 2.0 TeV/c2
• Drell-Yan samples, one in the mass region (>500 GeV/c2) around the Z′ mass and another at lower mass(>200 GeV/c2)
Analysis Code
“Zprime2muAnalysis” package in CMSSW
Event selection:• At least a pair of oppositely charged muons
• pT of each muon track in a pair > 20 GeV/c
• Isolated muons: Σ track pT (ΔR < 0.3) < 10 GeV/c
Resolution study for 3 alignment scenarios Resolution study for 3 alignment scenarios using 1.2 TeV Zusing 1.2 TeV Z′′ MC sample at MC sample at √s = 7TeV√s = 7TeV
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Muon Momentum resolution (endcap)
for 3 misalignment scenarios with
MZ′ = 1.2 TeV at 7 TeV CM energy
Z'SSM → µ+ µ- analysis
Summary: resolutions for 3 alignmentsSummary: resolutions for 3 alignmentsand different Zand different Z′′ mass with mass with √s=7TeV & 10TeV√s=7TeV & 10TeV
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50 pb-1 alignment scenario is validated. GR = Global ReconstructionTK = Tracker onlyFS = Tracker plus First Muon Station
Systematics study:Systematics study:Muon endcap alignment Muon endcap alignment
Method:
1.Muon Endcap was misaligned systematically with respect to ideal or startup muon geometry.
2.A signal sample (MZ′=1.2TeV/c2 or 2.0TeV/c2) was fully reconstructed. – The sample was reconstructed with a customized global tag
by inputting a modified SQLite file, with a bias for the position(XCMS, YCMS, ZCMS) up to 2 mm or a bias on rotation (φZ
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 ∆φZ
CMS]
3. The analysis code was re-run over the resulting biased MC data set for each misalignment.
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ppTT resolution vs. resolution vs. ηηIdeal alignement & with 2mm BiasIdeal alignement & with 2mm Bias
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2 TeV Z′ Sample
2 TeV Z′ Sample
No systematic bias applied to the Barrel and Tracker-only
Ideal alignment
Ideal alignment + 2mm shift of muon endcaps
Comparison: pComparison: pTT resolution resolution
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• Up to 200 GeV/c, no significant change due to bias but changes at higher pT
• Muon alignment becomes prominent at higher pT in all scenarios
• Demonstrates tracker-only does not change, as expected with or without bias on endcap stations
Ideal alignment + 2mm shift of muon endcap
LHC startup alignment (now)
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Alignment Systematics Study: Alignment Systematics Study: Bias on ideal Endcap positionsBias on ideal Endcap positions
Alignment Systematics Study: Alignment Systematics Study: Bias on startup Endcap positionsBias on startup Endcap positions
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Asymmetric results
MC Mass SpectraMC Mass Spectra
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Ideal alignment(MC_31X_V5)
50 pb -1 alignment (50PBMU31X_V1)
Startup alignment(STARTUP31X_V4)
Generated and reconstructed dimuon mass with 3 alignment scenarios
MZ′ = 1.2 TeV
Better aligned detector narrows the signal peak; e.g. from startup to 50 pb -1
ZZ′ ′ Mass Reach Analysis:Mass Reach Analysis:Signal and background samplesSignal and background samples
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Z′ signal sample with full Z′/Z/γ interference, reconstructed with startup alignment ; and the background samples, one in the mass region (> 500 GeV/c2) around the Z′ mass and the other at lower mass (>200 GeV/c2).
For the significance calculation, the reconstructed background sample is the weighted sum of these two background datasets.
Reconstructed Mass fits: Reconstructed Mass fits: Significance with 200pbSignificance with 200pb-1-1
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Likelihood-ratio estimator has been used to evaluate the significance
STARTUP align.
MZ′ = 1.2 TeV & 200pb-1
MZ′ = 1.2 TeV & 200pb-1
50 pb -1 align.
1000 pseudo-experiments
(SL ) (SL )
Signal significance vs. Signal significance vs. LLintint
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Variation of signal significance for MZ′ = 1.0 TeV/c2 and 1.2 TeV/c2 for different alignments and integrated luminosities.
Better alignmentequals doublingthe data set
Better alignmentputs us over 5 discovery threshold
Int. luminosity for 5Int. luminosity for 5σσ
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Estimated data required for the expected Z′ signal with 5σ
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Negligible effect with the bias on endcaps only
ZZ′ signal significance with ′ signal significance with misaligned muon endcaps onlymisaligned muon endcaps only
7 TeV collision data analysis7 TeV collision data analysisDatasets: (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
1. Two opposite sign muons with pT > 1 GeV/c (Std. 20 GeV/c)
2. Isolation Σ track pT (ΔR < 0.3 ) < 10 GeV/c
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Dimuon mass spectraDimuon mass spectrawith data taken through July 19with data taken through July 19
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Z
J/ψ
Events
Up to date high-massUp to date high-massdimuon mass spectrumdimuon mass spectrum
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Until September 3, 2010
Z
2.88 pb-1
A CMS collision event displayA CMS collision event display
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µ- η= 0.46, pT=86 GeVµ+ η=-0.18, pT=87 GeV
Mµ+µ- = 181 GeV
Summary (I)Summary (I)• 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 zCMS and 200 µrad in φZCMS
& error < 500 µm
• Muon endcap alignment constants are delivered to CMS
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 44
Summary (II & III)Summary (II & III)• Samples for MZ′ = 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 (pT) 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 pT 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 MZ′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
ConclusionsConclusions• 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 3rd, 2010
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Contributed presentations = 63 + 10
AcknowledgementsAcknowledgements
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Thank you !&
A question!A question!• Is there something special about that day?Dr. Oswalt’s question by email on input to fix defense date
Apparently! Yes
Today is
Sept. 8, 2010 Ph. D. Thesis Defense, S. Guragain 48
औसी� (New moon)२०६७ भाद्र २३ (2067/5/23)
September 8 2010
बु�वाको� मु�ख हे�र्ने� दि�र्नेFather’s face see day
(Father’s day)This work is dedicated to his memory.