Preparations for Physics at the Large Hadron Collider using the CMS Detector Darin Acosta University of Florida Hurricane Ivan, Sept. ‘04

Preparations for Physics at the Large Hadron Collider using the CMS Detector

Darin Acosta

University of Florida

Hurricane Ivan, Sept. ‘04

Oct. 21, 2004 IIT Colloquium, Physics with CMS 2Darin Acosta, University of Florida

Outline The LHC Issues in particle physics Status of the LHC and CMS construction The trigger & data acquisition system of CMS Sensitivity to the Higgs boson,

SuperSymmetry, and new forces Including benchmark mock analyses

Conclusions


The Large Hadron Collider

Point 5 – CMSCERN

2 proton rings housed in one tunnel

Completion: 2007…

R = 4.5 kmE = 7 TeV

CMS

Atlas


Current Highest Energy Collider

Fermilab Tevatron Proton beam energy is

1 TeV In operation since 1985

LHC: 7-fold increase in beam

energy 100-fold increase in

collision rate!

Batavia, IL


Facts about the LHC and CERN

Don’t rely on this novel! Yes, the LHC will create antimatter, but

we’ve been doing it since well before the LHC (antimatter was discovered in 1932)

Antimatter is very explosive, if we could create enough of it and if we could store it

The LHC is funded primarily by states, not private organizations, for basic research about particles and fields

About 0.5G$ contribution from U.S.


What we are really after… Not really a novel, sort of a non-fiction play!

Current theories of particle interactions, known as the “Standard Model”, are extremely successful for quantitative predictions

For example, the measured magnetic dipole moment of the muon (a heavy cousin of the electron) agrees with theory to >9 decimal places

The “Higgs mechanism” is a necessary ingredient to the Standard Model in order to introduce mass into our theories

Yields at least one scalar particle, the Higgs boson, which so far has escaped detection

But with the LHC, we are also looking for evidence of grand unification of the forces, new symmetries, and maybe even extra dimensions

Lots of possibilities that Dan Brown missed


Fundamental Particles in the SM

m = 0

mg = 0

mZ = 91.188 GeV

mW = 80.4 GeVme = 0.511 MeV

m >0

mu,d ~ 5 MeV

mt = 174 GeV

1 eV = 1.6 10–19 J

Fermions Vector bosons

Nice picture, but why 3 families and these masses?

Proton recipe:Take 2u, add 1d

Hydrogen recipe:Take 1p, add 1e (net charge = 0)

EM

Strong

Weak


Limitations of the Standard Model Large number of degrees of freedom

Quark and lepton masses are not predicted There is no explanation for why quarks and leptons are related

Specifically, the relationships between quark and lepton electroweak charges exactly cancel triangle anomalies in the Standard Model

Makes the Standard Model a renormalizable theory Does not incorporate gravity There is a vast gulf between the electroweak energy scale (102 GeV) and the Planck energy scale (1019 GeV)

Hierarchy problem The Higgs mass must be fine-tuned to extremely high precision since it receives radiative corrections


Theoretical Higgs Mass Constraints

Self consistency of the Standard Model places upper and lower bounds on the Higgs mass

Wide mass range up to ~1 TeV allowed if new physics comes in at scale of 1 TeV

Higgs mass measurement tells us the energy scale of new physics

200 400 600 8000

MH (GeV)

103

106

109

1012

1015

1018

Ma

ss

sc

ale

fo

r n

ew

ph

ys

ics

(G

eV

)

ExcludedEx

clu

ded


Indirect Experimental Constraints

PDG, 2002

SM predictions

Direct mW, mt measurements

Indirect from electro-weak parameters

Consistent picture emerging from SM


Hints of Grand Unification Coupling “constants” vary with the energy scale Appear to unify at a very high energy scale (1016 GeV) that is also

suggestively close to the Planck scale

EM

Weak

Strong1 /

co

up

ling

1016 GeVMPlanck = 1019 GeV

Gravity

102 GeV

137128


Hints of Grand Unification II Neutrinos have mass! Neutrino oscillations observed

Atmospheric neutrinos Solar neutrinos SNO

Very roughly speaking: m2 ~ 10-410-5 eV2

for e ,

m < few eV (beta-decay expts.) But why are neutrinos so light? (me=511,000 eV) One possibility is the “see-saw” mechanism:

In GUTs, unlike SM, can have right-handed neutrinos Mass matrix will give one neutrino with mass m1~MGUT

and another with mass m2~m2/MGUT

For m~100 GeV, MGUT~1016 GeV, m2~10-3 eVm1

m2


Hints from Cosmology

When combined with supernovae data, Big Bang nucleosynthesis, etc. the best fit yields:

1 (flat universe) 0.73 (dark energy)

m 0.27

b 0.04 (baryonic matter)

CDM 0.23 (dark matter)

Precise measurement of the cosmic microwave background anisotropy from WMAP

What are these?


A Possibility: SuperSymmetry Postulates a symmetry between bosons and fermions

Squarks/sleptons: scalar counterparts to the fermions

Charginos/neutralinos/gluinos: fermion counterparts to SM gauge bosons

At least two Higgs doublets (5 scalars): Avoids fine-tuning of SM, can lead to GUTs, prerequisite of

String Theories

Minimal Supersymmetric Models (MSSM) Usually assume that the lightest SuperSymmetric particle

(LSP) is stable (could explain to cold dark matter) But still 105 new parameters! Consider minimal Supergravity model (mSUGRA):

Universal gravitational interactions break SUSY at scale F ~ (1011 GeV)2

5 free parameters: m0, m1/2, A0, tan, Sign()Common scalar mass, common gaugino mass, common scalar trilinear coupling, ratio of v.e.v. of Higgs doublets, sign of Higgsino mixing parameter

~,~

q ~ , ~ , ~

, , , , 1 2 1 2 3 40 g

h H A H, , ,0


Another Possibility: Extra Dimensions? The apparent weakness of gravity compared to the

other forces is only because we observe gravity in 3 dimensions

In reality, perhaps gravity is strong in >3 dimensions (the “bulk”), but we (and the other forces) live on a 3-D “brane” Other dimensions are compactified and could be accessible at

the TeV energy scale LHC Might even create infinitesimal black holes at this energy

Variety of signatures possibledepending on the model e.g. missing energy lost

to other dimensions

Another missed opportunity for Dan Brown…

Nth Dbrane

3D brane

Gravity weak Gravity strong


LHC Status

Construction of the LHCdipoles on schedule

Can monitor LHC progress:http://lhc-new-homepage.web.cern.ch/lhc-new-homepage/DashBoard/index.asp


The Compact Muon Solenoid Expt.

PbWO4 Crystals / e detection

Muon chambers

Silicon Tracker(200 m2)

4T magnet

Hadronic calorimeterJets, missing ET ()

One of two large general purpose experiments at the LHC


CMS Construction in Assembly Hall

CMS 4T solenoid under construction

Nice EM problem:stored energy = = 2.7 GJ ½ barrel of hadron calorimeter

2

02

BV


Cathode Strip Chamber Muon System

2 endcaps4 stations (disks) in z2 or 3 rings in radius540 chambers6000 m2 active area2.5 million wires0.5 million channels

Chambers overlap in and 162 chambers installed (35%)


All CSC Chambers Produced

Muon chambers stored in the tunnel of the Intersecting Storage Ring CERN’s first proton collider(will the LHC suffer the same fate?)


Detector “Slice Test”

CSC 1

CSC 2

CSC 3

CSC 4

RPC 1

or how I spent my summer vacation

Integration test of electronics and software to prepare for commissioning


Magnet Test in Assembly Hall

Slice tests will continue in Assembly Hall

Scheduled for Fall ’05

Have slices of the detector record cosmic ray muons using produced chambers, electronics, and DAQ system

(In fact French President J.Chirac saw live cosmic muons Tuesday during CERN’s 50th Anniversary)


Underground Cavern

Everything gets lowered into the “pit” 100 m undergroundin about 1 year

Assembly hall

First Step toward Physics:Data Acquisition


CMS Trigger* & Data Acquisition LHC beam crossing rate is 40 MHz 1 GHz collisions CMS has a multi-tiered system to handle this:

Level-1 trigger reduces rate from 40 MHz to 100 kHz (max) Custom electronic boards and chips process

calorimeter and muon data to select objects High-Level triggers reduce rate from 100 kHz to O(100 Hz)

Filter farm runs online programs to select physics channels 40 TB/s

100 MB/s

Large switching network (~Tbit/s)

O(1000) node PC cluster

*n.b. by “trigger” we mean “filter”


Quick Collider Comparisons

Tevatron / CDF LHC / CMS

Beam Energy 1 TeV 7 TeV

Inst. Lumi. (cm-2s-1) 1032 1034

Bunch xing freq 2.5 MHz (7.6 MHz clk) 40 MHz

L1 output rate 25 kHz 100 kHz

L2 output / HLT input 400 Hz 100 kHz

L3 output rate 90 Hz 100 Hz

Event size 0.2 MB 1 MB

Filter Farm 250 nodes O(1000) nodes


The CMS Level-1 Trigger Reduces data rate from 40 MHz to <100 kHz

Provides 400X rejection while keeping important physics! Requires custom electronic hardware, some of which must be

radiation hard Only the muon and calorimeter systems participate

Select muons, electrons, photons, jets, and MET Silicon tracker data is unavailable until the High-Level Trigger

Significant handicap compared to previous collider experiments

Hardware and simulation results described in Level-1 Technical Design Report: CERN/LHCC 2000-038


CMS Trigger Designed by Da Vinci !

Hmm… Maybe something for another Dan Brown novel


Level-1 Trigger Scheme

Data flows in a pipeline with a 40 MHz heartbeat Accept/reject decision reached in 3.2 s

electrons, photons, jets, MET muons


Some Level-1 Trigger Hardware (U.S.)

BSCANASICs

PHASEASICs

MLUs

SORTASICs

EISO

EISO

SortASICs

BSCANASICs

PhaseASIC

RCT Receiver card RCT Jet/Summary card

RCT Electron isolation card

• Custom chips (ASICs)

• Programmable logic

• RAM

• Gbit/s Optical links

• Dense boards

Optical links SRAM

FPGA

CSC Track-Finder


Level-1 Muon “Track-Finding”

Track-Finder links local track segments into distinct tracks 2-D tracks for barrel region, 3-D tracks for endcaps

Standalone momentum measurement using B-field in iron yoke Require < 25% PT resolution for sufficient rate reduction

Highest quality candidates sent to Global Trigger, which filters events by selecting muons above a momentum threshold

Track-Finder prototype successfully triggered muon “slice test”

Optical links SRAM

FPGA


The CMS High-Level Triggers Reduces rate from 100 kHz to O(100 Hz)

Final rate will depend on data bandwidth, storage capability, and background rejection capability

Deployed as software filters running in an online computer farm (~1000 PCs)

Software is in principle the same as used for offline analyses Starts with a data sample already enriched in physics!

Level-1 already applied a factor 400 background rejection What can be done? Bring silicon tracker data into decision.

Electrons: require silicon track match to veto fakes from 0 , recover bremsstrahlung

Photons: veto tracks Muons: require silicon track match to improve momentum

resolution Jets: run standard jet algorithms (n.b. jet quark) Tracks: improve measurement of momentum, charge, and

vertex using silicon tracking detectors Apply isolation criteria to all leptons Apply topology and invariant mass cuts


L1 and HLT Muon Trigger Rates

Better resolution offers improved rate reduction

Isolation only yields minor gains for muons

but crucial for electrons


Muon HLT Simulation Results

30 Hz output rate Efficiencies

Target 1st year luminosity of L=21033 s-1cm-2

H ZZ* 98% for M=150 GeV

H WW* 92% for M=160 GeV

pT>20

Good efficiency for Higgs decay channels into muons

Next Step Toward Physics:Offline Analyses


Higgs Searches

Discovery of the Higgs boson, responsible for the origin of mass in the SM, is a high priority for the LHC

Golden HZZ4 channel should be visible after one or two year’s running for MH>200 GeV, but more challenging at low mass


H → ZZ → 4 Sensitivity CMS benchmark study

Full detector simulationwith prototype reconstructionsoftware to analyze mock data

Main Backgrounds ZZ(*), tt, Zbb, Zcc

Study of improving low mass sensitivity is ongoing

CMS

Full Simulation


SuperSymmetry Signatures Complex squark / gluino

decay chains: Many high-ET jets Leptons

From decays of sleptons, charginos, W, Z, and b-jets

Missing transverse energy (MET) From undetected particles

such as neutrinos and the LSP

Heavy-flavor “Long lifetime” particles such

as and b

CMS event simulation:

m0 = 1000 GeVm1/2 = 500 GeVtan = 35 > 0A0 = 0


Inclusive SUSY Trigger Exercise Consider several points

in the m0 m1/2 plane near the Tevatron reach (most difficult for LHC)

Possible triggers: 1 jet ET>180 GeV & MET>120

4 jets ET>110 GeV

Overall efficiency to pass trigger: =0.63, 0.63, 0.37

Background rate of ~12Hz @ L = 21033 dominated by QCD jets Further optimize SUSY over SM in offline analysis

4 5 6

~1 day of running


Inclusive SUSY Reach vs. Luminosity

Will rapidly explore the parameter space for Supersymmetry beyond Tevatron reach in the first few months of the LHC

Squarks/gluinos probed to ~1.5 TeV with 1 fb-1

Up to 2.5 TeV at design luminosity (100 fb-1)

~1 week @ CMS with L=1033 (but 1 year or more to reconstruct masses)

Tevatron reach < 0.5 TeV


CMS Squark and Gluino Reach

Jets+MET search without lepton requirement gives greatest sensitivity

Without realistic detector uncertainties folded in however…

Opposite-sign lepton signature useful for sparticle reconstruction

Same-sign lepton signature has low background

Nucl. Phys. B547 (1999) 60


Detailed Study of Same-Sign Muon Signature

Previous SUSY performance plots were based on a simple model of the CMS detector performance

In the last several years, we have significantly improved upon this with the following developments: A detailed detector simulation package to describe the

interactions of particles in the detector and the response of the active detector components

Exact emulation of the Level-1 trigger hardware validated against real prototypes at beam tests and slice tests

Physics reconstruction software applicable to real data On top of this, prototype “grid” computing models

have been developed in order to harness the CPU resources required to make use of these tools e.g. simulating one SUSY event requires 20 min CPU time!


Same-Sign Muon SUSY Signature

Signal: Background:

Motivation: Clean objects to select with trigger (muons) Reduced detector uncertainties compared to pure Jets + MET Low background

Perform mock data analysis with detailed detector and trigger simulation and prototype reconstruction software


Comparison of SM and SUSY Kinematics

“SUSY point #3”: m0=149 GeV, m1/2=700 GeV, tanβ = 10, A0 = 0, signμ > 0

Significantly more energy in SUSY decays


0

1000

2000

3000

4000

5000

6000

0 500 1000 1500 2000 2500 3000

Sensitivity for 10 fb-1 (~1 year of LHC)

Many points will be visible with ∫L<<10 fb-1

Reach is similar to earlier naïve study Significance for many points >> 5 std. deviations for ∫L=10 fb-1

m1/2

m0

18

15

12

14

17

97

16

5

4,6,8,10,11,19,20

2

1 3

13

4

68

10

1119 20


SUSY Spectroscopy If we DO observe an excess of events over the SM, the

next step is to completely reconstruct a SUSY decay chain:

CMS Study (naïve simulation though) Investigate Points B & G of “Proposed

Post-LEP Benchmarks for SUSY” (hep-ph/0106204)

B: m0=100 GeV, m1/2=250 GeV, tan=10, >0, A0=0

TOT(SUSY) = 58 pb

p

p

g~

b~

b

b

01

~

02

~ ~

q~

(~~, ~~, ~~qg qq gg dominate)

Repeat the Particle Data Book entries at the TeV scale!


Di-Lepton Edge Reconstruction

Start with reconstructing (tan not too large) Two OS isolated leptons, PT>15 GeV, ||<2.4 MET>150 GeV, E(ll)>100 GeV

Select 15 GeV window around di-lepton endpoint

p

p

g~

b~

b

b

01~

02~ ~

q~

p

p

g~

b~

b

b

01~

02~ ~

p

p

g~

b~

b

b

01~

02~ ~

q~q~

BR=16%

02

Striking signature of SUSY for low tan


Scalar b-quark Reconstruction

Add most energetic b-jet to reconstruct b Eb-jet>250 GeV, ||<2.4 b-jet: 2 tracks with IP significance > 3

Require MET>150 GeV E(ll)>100 GeV

Mass (GeV)

Result of fit:

M(b) = 5007 GeV M = 42 GeV

Generated masses:

M(bL) = 496 GeV

M(bR) = 524 GeV

~ ~

~

BR dominates

p

p

g~

b~

b

b

01~

02~ ~

q~

p

p

g~

b~

b

b

01~

02~ ~

p

p

g~

b~

b

b

01~

02~ ~

q~q~ BR ~ 5%


Gluino Reconstruction

Add another b-jet closest in to reconstruct gluino

&

Mass (GeV)Result of fit:

M(g) = 5947 GeV M = 42 GeV

Generated mass:

M(g) = 595 GeV~ ~

p

p

g~

b~

b

b

01~

02~ ~

q~

p

p

g~

b~

b

b

01~

02~ ~

p

p

g~

b~

b

b

01~

02~ ~

q~q~BR ~ 1%

400 GeV 600 GeVM b

m g m b m~ ~ ~af ch d i is independent of :10


New Gauge Bosons and Extra Dimensions

New Forces: Obligated to look for signatures of new gauge bosons since

the LHC crosses a new energy frontier e.g. Z’ with couplings similar to Z boson

but higher mass Di-lepton mass spectrum is a very clear signature

Little Higgs Theories: Solves problem of quadratic divergences in Higgs mass

without SUSY by introducing more gauge bosons with opposite couplings to known ones

But no explanation of where these new forces come from Extra Dimensions:

“Kaluza-Klein Towers” give resonance signatures like Z’ (but several states)


CMS Evaluation of Z’ Sensitivity Detailed detector simulation & current reconstruction software Require that there are at least two µ’s of opposite charge sign Generate ensembles of pseudo-experiments In each experiment, fit Mµµ values using an unbinned maximum

likelihood No constraints on the absolute background level: fit assumes only

background shape is known Use likelihood ratio significance estimator


Z′→µ+µ−: CMS Discovery Potential

“1 month”

“1 year”

Tevatron reach

Probe new territory in first month!


Summary The LHC will be the first collider to probe a new energy

scale in over 20 years The LHC and detectors are nearing reality

t0 3 years and counting Discovery of SuperSymmetry, if it exists, is almost

assured at the LHC Difficult part will be measuring masses and determining

particle spins But this is the sort of “problem” you dream of

Discovery of the Higgs may not come so quickly, but sensitivity to full mass range looks promising at LHC

But stranger things could happen New forces, extra dimensions, ?

CMS Collaboration is preparing for commissioning of its detector and for analysis of its data


Future Studies Still more to do to understand how realistic detector

uncertainties affect the CMS physics capability at start-up: Missing (unfinished) detector components Calibration uncertainties Uncertainty in the alignment of tracking detectors Uncertainty in the magnetic field Non-collision backgrounds (beam halo muons, cosmics,…)

CMS plans to incorporate such realistic scenarios and publish a report on the physics capability as well as the procedures to prepare for physics Will survey all physics “parameter-space” and report on

sensitivity to various theoretical models Get ready for data!


Higgs Sensitivity @ CMS

CMS Note 2003/033

Low mass region tough for LHC

Documents

Preparations for Physics at the Large Hadron Collider using the CMS Detector Darin Acosta University of Florida Hurricane Ivan, Sept. ‘04