Preparations for Physics at the Large Hadron Collider using the CMS Detector
Preparations for Physics at the Large Hadron Collider using the CMS Detector
Darin Acosta
University of Florida
Hurricane Ivan, Sept. ‘04
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 2
CMS
The Large Hadron Collider
Atlas
R = 4.5 km
E = 7 TeV
Oct. 21, 2004 IIT Colloquium, Physics with CMS
CERN
Point 5 – CMS
2 proton rings housed in one tunnel
Completion: 2007…
Darin Acosta, University of Florida 3
Current Highest Energy Collider
Fermilab Tevatron
Proton beam energy is
1 TeV
In operation since 1985
Batavia, IL
LHC:
7-fold increase in beam energy
100-fold increase in collision rate!
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 4
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.
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 5
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
Oct. 21, 2004
Lots of possibilities that Dan Brown missed
IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 6
Fundamental Particles in the SM
Fermions Vector bosons m u,d
Proton recipe:
Take 2u, add 1d m t
= 174 GeV
EM m
= 0 m g
= 0
Strong
Hydrogen recipe:
Take 1p, add 1e
(net charge = 0) m e
= 0.511 MeV
Weak m
Z
= 91.188 GeV m
W
= 80.4 GeV
1 eV = 1.6
10
–19
J
Oct. 21, 2004
Nice picture, but why 3 families and these masses?
IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 7
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 (10 2 GeV) and the Planck energy scale (10 19 GeV)
Hierarchy problem
The Higgs mass must be fine-tuned to extremely high precision since it receives radiative corrections
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 8
Theoretical Higgs Mass Constraints
10 18
10 15
10 12
10 9
10 6
Excluded
10 3
0
Oct. 21, 2004
200 400
M
H
(GeV)
IIT Colloquium, Physics with CMS
600
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
800
Higgs mass measurement tells us the energy scale of new physics
Darin Acosta, University of Florida 9
Indirect Experimental Constraints
Direct m
W
, m t measurements
Indirect from electro-weak parameters
Consistent picture emerging from SM
SM predictions
PDG, 2002
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 10
Hints of Grand Unification
Coupling “constants” vary with the energy scale
Appear to unify at a very high energy scale (10 16 suggestively close to the Planck scale
GeV) that is also
EM
137
128 Gravity
Weak
Strong
10 2 GeV
Oct. 21, 2004 IIT Colloquium, Physics with CMS
10 16 GeV
M
Planck
10 19
=
GeV
Darin Acosta, University of Florida 11
Hints of Grand Unification II
Neutrinos have mass!
Neutrino oscillations observed
Atmospheric neutrinos
Solar neutrinos SNO
Very roughly speaking:
m 2 ~ 10 -4
10 -5 eV 2 for
e
,
m < few eV (beta-decay expts.)
But why are neutrinos so light? ( m e
=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 m
1
~M
GUT and another with mass m
2
~m 2 /M
GUT
For m~100 GeV, M
GUT
~10 16 GeV, m
2
~10 -3 eV m
1
IIT Colloquium, Physics with CMS Oct. 21, 2004 Darin Acosta, University of Florida m
2
12
Hints from Cosmology
Precise measurement of the cosmic microwave background anisotropy from WMAP
When combined with supernovae data, Big Bang nucleosynthesis, etc. the best fit yields:
1 (flat universe)
m
0.73 (dark energy)
0.27
b
CDM
0.04 (baryonic matter)
0.23 (dark matter)
Oct. 21, 2004 IIT Colloquium, Physics with CMS
What are these?
Darin Acosta, University of Florida 13
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
,
0
, , ,
, ~
At least two Higgs doublets (5 scalars):
h H
0
A H
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 ~
(10 11 GeV) 2
5 free parameters: m
0
, m
1/2
, A
0
, 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
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 14
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 3D “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 possible depending on the model
e.g. missing energy lost to other dimensions
3D brane
N th D brane
Another missed opportunity for Dan Brown…
Oct. 21, 2004 IIT Colloquium, Physics with CMS
Gravity weak Gravity strong
Darin Acosta, University of Florida 15
LHC Status
Construction of the LHC dipoles on schedule
Can monitor LHC progress: http://lhc-new-homepage.web.cern.ch/lhc-newhomepage/DashBoard/index.asp
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 16
The Compact Muon Solenoid Expt.
One of two large general purpose experiments at the LHC
4T magnet Muon chambers
Silicon Tracker
(200 m 2 )
PbWO
4
Oct. 21, 2004
Crystals
/ e detection Hadronic calorimeter
Jets, missing E
T
(
)
IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 17
CMS Construction in Assembly Hall
CMS 4T solenoid under construction
Nice EM problem:
B
2 stored energy = = 2.7 GJ
0
½ barrel of hadron calorimeter
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 18
Cathode Strip Chamber Muon System
2 endcaps
4 stations (disks) in z
2 or 3 rings in radius
540 chambers
6000 m 2 active area
2.5 million wires
0.5 million channels
Chambers overlap in
and
Oct. 21, 2004 IIT Colloquium, Physics with CMS
162 chambers installed (35%)
Darin Acosta, University of Florida 19
All CSC Chambers Produced
Oct. 21, 2004
Muon chambers stored in the tunnel of the
Intersecting Storage Ring
CERN’s first proton collider
(will the LHC suffer the same fate?)
IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 20
Detector “Slice Test”
or how I spent my summer vacation
CSC 2
CSC 1
CSC 3
CSC 4
RPC 1
Oct. 21, 2004
Integration test of electronics and software to prepare for commissioning
IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 21
Magnet Test in Assembly Hall
Slice tests will continue in Assembly Hall
Oct. 21, 2004
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 50 th Anniversary)
IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 22
Underground Cavern
Assembly hall
Everything gets lowered into the “pit” 100 m underground in about 1 year
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 23
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
Large switching network (~Tbit/s)
O(1000) node PC cluster
*n.b. by “trigger” we mean “filter”
Oct. 21, 2004 IIT Colloquium, Physics with CMS
100 MB/s
Darin Acosta, University of Florida 25
Beam Energy
Inst. Lumi. (cm -2 s -1 )
Bunch xing freq
L1 output rate
L2 output / HLT input
L3 output rate
Event size
Filter Farm
Quick Collider Comparisons
Tevatron / CDF
1 TeV
10 32
2.5 MHz (7.6 MHz clk)
25 kHz
400 Hz
90 Hz
0.2 MB
250 nodes
LHC / CMS
7 TeV
10 34
40 MHz
100 kHz
100 kHz
100 Hz
1 MB
O(1000) nodes
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 26
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 27
CMS Trigger Designed by Da Vinci !
Hmm… Maybe something for another Dan Brown novel
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 28
Level-1 Trigger Scheme
electrons, photons, jets, MET muons
Data flows in a pipeline with a 40 MHz heartbeat
Accept/reject decision reached in 3.2
s
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 29
Some Level-1 Trigger Hardware (U.S.)
Phase
ASIC
PHASE
ASICs
BSCAN
ASICs
Optical links
SRAM
Oct. 21, 2004
MLUs
RCT Receiver card
FPGA
EISO
Sort
ASICs
BSCAN
ASICs
SORT
ASICs
EISO
RCT Jet/Summary card
RCT Electron isolation card
CSC
Track-Finder • Custom chips (ASICs)
• Programmable logic
• RAM
• Gbit/s Optical links
• Dense boards
IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 30
Level1 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% P
T resolution for sufficient rate reduction
Highest quality candidates sent to Global Trigger, which filters events by selecting muons above a momentum threshold
TrackFinder prototype successfully triggered muon “slice test”
Optical links
SRAM
FPGA
Oct. 21, 2004 IIT Colloquium, Physics with CMS
Darin Acosta, University of Florida 31
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
Jets: resolution 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
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 32
L1 and HLT Muon Trigger Rates
Oct. 21, 2004 IIT Colloquium, Physics with CMS
Better resolution offers improved rate reduction
Isolation only yields minor gains for muons
but crucial for electrons
Darin Acosta, University of Florida 33
Muon HLT Simulation Results
Target 1 st year luminosity of L=2
10 33 s -1 cm -2 p
T
>20
30 Hz output rate
Efficiencies
H
ZZ *
98% for M=150 GeV
H
WW *
92% for M=160 GeV
Good efficiency for Higgs decay channels into muons
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 34
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 H
ZZ
4
channel
should be visible after one or two year’s running for
M
H
>200 GeV, but more challenging at low mass
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 36
H
→ ZZ → 4
Sensitivity
CMS benchmark study
Full detector simulation with prototype reconstruction software to analyze mock data
Main Backgrounds
ZZ(*), tt, Zbb, Zcc
CMS
Full Simulation
Study of improving low mass sensitivity is ongoing
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 37
SuperSymmetry Signatures
Complex squark / gluino decay chains:
Many high-E
T
Leptons jets
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:
Oct. 21, 2004 m
0
= 1000 GeV m
1/2
> 0
= 500 GeV tan
= 35
A
0
= 0
IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 38
Inclusive SUSY Trigger Exercise
Consider several points in the m
0
m
1/2 plane near the Tevatron reach
(most difficult for LHC)
Possible triggers:
1 jet E
T
>180 GeV & MET>120
4 jets E
T
>110 GeV
~1 day of running
Overall efficiency to pass trigger:
=0.63, 0.63, 0.37
4 5 6
Background rate of ~12Hz @ L = 2
10 33 dominated by QCD jets
Further optimize SUSY over SM in offline analysis
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 39
Inclusive SUSY Reach vs. Luminosity
Oct. 21, 2004 IIT Colloquium, Physics with CMS
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 )
Tevatron reach
< 0.5 TeV
~1 week @ CMS with
L=10 33
(but 1 year or more to reconstruct masses)
Darin Acosta, University of Florida 40
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 41
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!
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 42
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 43
Comparison of SM and SUSY Kinematics
Significantly more energy in SUSY decays
“SUSY point #3”:
m
0
=149 GeV, m
1/2
=700 GeV, tan β = 10, A
0
= 0, sign μ > 0
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 44
Sensitivity for 10 fb
-1
(~1 year of LHC)
m
0
5000
10
4,6,8,10,11,19,20
18
6
8
4000
4
17
16
3000
7
9
15
14
19 20
2000
13
1000
2
12
0
0 500
1 3 5
1000 1500 2000 2500 m
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
11
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 45
SUSY Spectroscopy
If we DO observe an excess of events over the SM, the next step is to completely reconstruct a SUSY decay chain: p b
0
2
~ b b p
(~~, ~~, ~~ dominate)
Repeat the Particle
Data Book entries at
PostLEP Benchmarks for SUSY”
B: m
0
=100 GeV, m
1/2
=0
=250 GeV, tan
=10,
>0, A
0
TOT
(SUSY) = 58 pb
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 46
~
1
0
Di-Lepton Edge Reconstruction
BR=16%
~ b
0
Start with reconstructing (tan
not too large)
Two OS isolated leptons, P
T
>15 GeV, |
|<2.4
MET>150 GeV, E(ll)>100 GeV
Striking signature of
SUSY for low tan
Select 15 GeV window around di-lepton endpoint
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 47
Scalar b-quark Reconstruction
~ b
BR ~ 5%
Add most energetic b-jet to reconstruct b
E b-jet
>250 GeV, |
|<2.4
b-jet:
2 tracks with IP significance > 3
Require
MET>150 GeV
E(ll)>100 GeV
Result of fit:
M(b) = 500
~
M
7 GeV
= 42 GeV
Oct. 21, 2004
Generated masses:
~
M(b
L
) = 496 GeV
~
M(b
R
) = 524 GeV
BR dominates
IIT Colloquium, Physics with CMS
Mass (GeV)
Darin Acosta, University of Florida 48
Gluino Reconstruction
~ b
BR ~ 1%
Add another b-jet closest in
to reconstruct gluino
& 400 GeV
600 GeV
Result of fit:
M(g) = 594
~
M
7 GeV
= 42 GeV
Generated mass: Mass (GeV)
af ch
m
d i
:
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 49
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)
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 50
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 M
µµ likelihood values using an unbinned maximum
No constraints on the absolute background level: fit assumes only background shape is known
Use likelihood ratio significance estimator
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 51
Z′→µ
+
µ
−
: CMS Discovery Potential
“1 year”
“1 month”
Probe new territory in first month!
Tevatron reach
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 52
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
t
0
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 53
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
Noncollision 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!
Oct. 21, 2004 IIT Colloquium, Physics with CMS Darin Acosta, University of Florida 54
Higgs Sensitivity @ CMS
Low mass region tough for LHC
Oct. 21, 2004 IIT Colloquium, Physics with CMS
CMS Note
2003/033
Darin Acosta, University of Florida 55
