Preparations for Physics at the Large Hadron Collider using the CMS Detector Darin Acosta University...
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Transcript of Preparations for Physics at the Large Hadron Collider using the CMS Detector Darin Acosta University...
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 3Darin Acosta, University of Florida
The Large Hadron Collider
Point 5 – CMSCERN
2 proton rings housed in one tunnel
Completion: 2007…
R = 4.5 kmE = 7 TeV
CMS
Atlas
Oct. 21, 2004 IIT Colloquium, Physics with CMS 4Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 5Darin Acosta, University of Florida
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 6Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 7Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 8Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 9Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 10Darin Acosta, University of Florida
Indirect Experimental Constraints
PDG, 2002
SM predictions
Direct mW, mt measurements
Indirect from electro-weak parameters
Consistent picture emerging from SM
Oct. 21, 2004 IIT Colloquium, Physics with CMS 11Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 12Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 13Darin Acosta, University of Florida
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?
Oct. 21, 2004 IIT Colloquium, Physics with CMS 14Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 15Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 16Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 17Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 18Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 19Darin Acosta, University of Florida
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%)
Oct. 21, 2004 IIT Colloquium, Physics with CMS 20Darin Acosta, University of Florida
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?)
Oct. 21, 2004 IIT Colloquium, Physics with CMS 21Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 22Darin Acosta, University of Florida
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)
Oct. 21, 2004 IIT Colloquium, Physics with CMS 23Darin Acosta, University of Florida
Underground Cavern
Everything gets lowered into the “pit” 100 m undergroundin about 1 year
Assembly hall
First Step toward Physics:Data Acquisition
Oct. 21, 2004 IIT Colloquium, Physics with CMS 25Darin Acosta, University of Florida
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”
Oct. 21, 2004 IIT Colloquium, Physics with CMS 26Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 27Darin Acosta, University of Florida
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 28Darin Acosta, University of Florida
CMS Trigger Designed by Da Vinci !
Hmm… Maybe something for another Dan Brown novel
Oct. 21, 2004 IIT Colloquium, Physics with CMS 29Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 30Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 31Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 32Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 33Darin Acosta, University of Florida
L1 and HLT Muon Trigger Rates
Better resolution offers improved rate reduction
Isolation only yields minor gains for muons
but crucial for electrons
Oct. 21, 2004 IIT Colloquium, Physics with CMS 34Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 36Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 37Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 38Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 39Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 40Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 41Darin Acosta, University of Florida
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 42Darin Acosta, University of Florida
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 43Darin Acosta, University of Florida
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 44Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 45Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 46Darin Acosta, University of Florida
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!
Oct. 21, 2004 IIT Colloquium, Physics with CMS 47Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 48Darin Acosta, University of Florida
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%
Oct. 21, 2004 IIT Colloquium, Physics with CMS 49Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 50Darin Acosta, University of Florida
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 51Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 52Darin Acosta, University of Florida
Z′→µ+µ−: CMS Discovery Potential
“1 month”
“1 year”
Tevatron reach
Probe new territory in first month!
Oct. 21, 2004 IIT Colloquium, Physics with CMS 53Darin Acosta, University of Florida
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
Oct. 21, 2004 IIT Colloquium, Physics with CMS 54Darin Acosta, University of Florida
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!
Oct. 21, 2004 IIT Colloquium, Physics with CMS 55Darin Acosta, University of Florida
Higgs Sensitivity @ CMS
CMS Note 2003/033
Low mass region tough for LHC