muon endcap alignment for the cms experiment and its effect on the search for z′ bosons in the...

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


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


Proposed new particle Z'Proposed new particle Z'


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


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


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)


• Tracker• Calorimeters• Magnet• Muon

ME+4ME -

Particle detection in CMS & Particle detection in CMS & muon reconstructionsmuon reconstructions


Global Muon Track Standalone Muon Track

Muon Hits and Track Segments

Muon in Silicon Tracker


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!


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


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



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


Reconstructed chamber center position

Fit residual ~ 50 µm

Comparison with PGComparison with PG


345 µm


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


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


Bending of YE2 disk due to Bending of YE2 disk due to magnetic field at 3.8Tmagnetic field at 3.8T


10 - 14 mm YE2 bending towards the interaction point (IP) of CMS

ME Alignment constantsME Alignment constants


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

Sept. 8, 2010 24Ph. D. Thesis Defense, S. Guragain



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)


MC samples and MC samples and event selectionevent selection


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


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


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.


ppTT resolution vs. resolution vs. ηηIdeal alignement & with 2mm BiasIdeal alignement & with 2mm Bias


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


• 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)


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


Asymmetric results

MC Mass SpectraMC Mass Spectra


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


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


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


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


Estimated data required for the expected Z′ signal with 5σ


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


Dimuon mass spectraDimuon mass spectrawith data taken through July 19with data taken through July 19


Z

J/ψ

Events

Up to date high-massUp to date high-massdimuon mass spectrumdimuon mass spectrum


Until September 3, 2010

Z

2.88 pb-1

A CMS collision event displayA CMS collision event display


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


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.


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


Contributed presentations = 63 + 10

AcknowledgementsAcknowledgements


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


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.

muon endcap alignment for the cms experiment and its effect on the search for z′ bosons in the...

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