1. Extended LHC Reach in Focus Point Region of MSSM
Marie-Hélène Genest
with
Alexander Belyaev*, Claude Leroy, Rashid Mehdiyev
Université de Montréal
*Florida State University
Marie-Hélène Genest, Wien 2005

2. Searching for CDM at LHC
WMAP Results
Constraints on cold dark matter
Constraints on supersymmetric parameter space
What is the portion of this constrained parameter space accessible at LHC?
Monte Carlo generation of events in ATLAS
Analysis optimization and results
Marie-Hélène Genest, Wien 2005

3. WMAP
Wilkinson Microwave Anisotropy Probe measures anisotropies in the cosmic microwave background
The position and relative heights of the peaks in the multipole moment representation of these anisotropies give information about the geometry of the universe, its composition, …
Puts constraints on dark matter models
Marie-Hélène Genest, Wien 2005

4. Dark matter constrains
The non-baryonic cold dark matter component of the energy density in the universe :
Matter content
Baryonic content
Hubble constant (h = 0.71±0.04)
Marie-Hélène Genest, Wien 2005

5. Supersymmetric candidate
If the R-parity is conserved:
R = (-1)B+2L+S with B, L, S the baryon number, lepton number and spin
the lightest supersymmetric particle (LSP) can’t decay to SM particles (is stable)
In some models, the LSP is the lightest neutralino (c), a non-baryonic, electrically neutral, weakly interacting massive particle (WIMP) with 10 GeVc-2 < Mc< 1 TeVc-2 defined as the combination of the supersymmetric partners of the U(1) and SU(2) gauge bosons:
Marie-Hélène Genest, Wien 2005

6. SUSY parameter space Minimal Supersymmetric Standard Model (MSSM)
Most popular choice: minimal supergravity (mSUGRA) scenario of SUSY breaking in which MSSM is valid from weak scale up to GUT scale (~1016GeV), where gauge couplings unify
Universal parameters at GUT scale:
scalar masses (M0)
Gaugino masses (M1/2)
a-terms (A0) (tri-linear couplings in the soft-breaking Lagrangian)
Two other parameters to fix:
tanb (Ratio of the two Higgs vacuum expectation values)
Sign(m) (m is the mass parameter of the Higgs)
In most mSUGRA parameter space, the relic density obtained is way beyond the WMAP bound
Marie-Hélène Genest, Wien 2005

7. Neutralino relic density Calculated using ISARED (part of ISATOOLS package in ISAJET v.7.72)
Green regions in agreement with WMAP results:
1- Bulk annihilation region :
c pair annihilation at large rate via slepton exchange
2- Stau co-annihilation region
stau and c mass almost the same; co-annihilation between them in the early universe
3- Hyperbolic branch/focus point region (HB/FP)
c’s have a significant higgsino component which facilitates annihilations in WW and ZZ pairs
4- A-annihilation funnel (not shown here, only for very large tanb (>45))
mA~2mc  annihilation through A0 resonance into a fermion/antifermion pair
Excluded regions:
- Theoritical exclusion in red (no radiative electroweak symmetry breaking or charged LSP)
Too high relic density for WMAP in blue and unshaded
Too low relic density for in yellow
Marie-Hélène Genest, Wien 2005

8. The Large Hadron Collider
 s = 14 TeV p on p collider
Luminosity
“low” : 1033 cm-2 s-1, 10 fb-1 /year
“high”: 1034 cm-2 s-1, 100 fb-1 /year
25 ns bunch crossing (BC) (40 MHz)
High luminosity and large inclusive at LHC implies:
~ 23 minimum bias events per BC
~ 70 charged tracks/event with
pT > 1 GeV/c for || < 2.5
Detector response speed (t < 50 ns)
Radiation hardness
~ 100 Hz trigger rate
LHC is a factory of everything: t, b, Z, W,Higgs, SUSY, … etc.
Some processes at Low L
Mass reach up to  5 TeV
Precision measurements dominated by systematic errors
Process 
Events/year
W  l 
Z  ee
gg(m=1 TeV)
H(m=0.8TeV)
15 nb
1.5 nb
800 pb
500 b
1pb
108
107
1012
104
Marie-Hélène Genest, Wien 2005

9. The ATLAS Detector Tracking in 2T solenoid:
SCT  Si pixel + strips (3+4 layers)
TRT  particle id.
B = 2 Tesla
 / pT ~ 5 10-4 pT  0.001
EM calorimeter: Pb – liquid Argon
presampler + segmented EM calo.
 / E ~ 10% / E(GeV)
Had. Calorimeter:
Fe –scintillator (barrel)
 / E ~ 50% / E(GeV)  0.03
Cu/W – liquid Argon(endcaps/Forwd)
 / E ~ 60% / E(GeV)  0.03
Muons: instrumented large toroid magnet
 / pT ~ 10 % at 1 TeV/c
Marie-Hélène Genest, Wien 2005

10. SUSY reach of CERN LHC
Can explore (Baer, H. et al., JHEP06 (2003) 54.)
all the bulk region
all the funnel region
all the stau co-annihilation corridor (unless tanb is really large)
Up to M1/2 ~ 700 GeV via conventional SUSY search channels
for the HB/FP region
The HB/FP region extends indefinitely to large M1/2, M0 values ultimately well beyond LHC reach.
A careful study can extend the LHC reach into this region…
Marie-Hélène Genest, Wien 2005

11. Actual LHC reach (Baer, H. et al)
M1/2/M0 is observable if (for 100fb-1):
the significance S>5, where S = Signal/sqrt(Background)
the number of signal events left >10
Monte Carlo generation method:
Signal & BG events: ISAJETv7.64
CMSJET v4.801 to model the CMS detector
Analysis:
Best cut combination for cuts on:
Number of jets, missing transverse energy, transverse energy of two most energetic jets, circularity, muon isolation and
Region in this study to improve actual limit
Marie-Hélène Genest, Wien 2005

12. SUSY Monte Carlo Generation
For each SUSY point (i.e. M1/2/M0 value) 5x x105 signal events were generated with ISAJETv7.72 (PDF CTEQ-5L, mtop=175 GeV) taking into account all SUSY subprocesses
ATLFAST code to simulate the experimental condition prevailing at LHC for ATLAS detector. Detector dependent parameters tuned to values expected from full simulation
Signal signature:
SUSY in FP/HB region dominated by production of gluino, neutralino and chargino one isolated lepton (from W decay in chargino decay chain) associated with multi-jet production and a large missing transverse energy
Marie-Hélène Genest, Wien 2005

13. SUSY points studied
With production cross section ranging from 36 to 699 fb
Marie-Hélène Genest, Wien 2005

14. Background Monte Carlo Generation
Various types of SM background can mimic SUSY signature
(1 lepton+multi-jet+large ET,miss) :
top quark pairs, single top quark production, W+jets, WW, QCD jets events.
These BG were generated using PYTHIA, the significant ones turning out to be top quark pairs and W+jets events (1.5x108 events generated for each with sprod= and 34.1 pb respectively for partonic transverse momentum cut used)
Marie-Hélène Genest, Wien 2005

15. Optimizing the analysis
To separate signal from background:
Pre-selection cuts:
1 lepton
At least one jet with a minimum transverse momentum pT(jet)>20 GeV
A minimum transverse missing energy ET,miss>200 GeV in the event
Cuts to tune to get the best significance while maintaining at least 10 signal events:
minimum number of jets Nj
minimum transverse mass of lepton and missing energy given by MT2 = 2pT(lepton)ET,miss(1-cosf)
maximum transverse momentum of the lepton
minimum transverse missing energy ET,miss
Cuts tuned first on point M0 ,M1/2: 3500,600
(which allows direct comparison with previous study)
correlation
Marie-Hélène Genest, Wien 2005

16. Number of jets cut
For all values of other cuts (maximum pT(l), MT, ET,miss)
The significance always go up with the number of jets
Chosen cut value to maximize significance while keeping reasonable number of
events
Marie-Hélène Genest, Wien 2005

17. MT and pT(l) cuts
Nj>9
Marie-Hélène Genest, Wien 2005

18. Different sets of cuts for parts of the HB/FP region
For reachable points, the observability criterion (S>10, S/sqrt(B)>5) was fullfilled using those optimized sets of cuts:
M0 , M1/2 Nj
pT(l)
(GeV) MT
ET,miss
3500,600  4670,880 9
160
200
4670,930  4850,1050
260
130
250
A significance greater than 5 can be achieved for some other points, having a number of signal events 5<S<10 by fine-tuning the cut values for each point.
Marie-Hélène Genest, Wien 2005

19. Cut efficiency example
SUSY point M0,M1/2: 4500,900
Top quark pair events
W + jets events
Fraction passing preselection (%)
4.8
4.7x10-1
3.8x10-2
Fraction of preselected events passing the Nj≥9 cut (%)
13.3
14.8
8.0
Fraction of events passing the Nj cut that pass the MT≥160 GeV cut (%)
23.7
2.5x10-2
1.1
Fraction of all events passing all cuts (%)
1.5x10-1
1.7x10-5
3.3x10-5
Marie-Hélène Genest, Wien 2005

20. New preliminary LHC reach
Blue x:
S/sqrt(B)>5, S>10
White dots:
S/sqrt(B)>5, 10>S>5
(3<S<5 for 4850,935 and 5000,1080)
Red cross:
S/sqrt(B)<5 or S<3
For now, reach seems to be extended and competitive with LC1000 to some extent
preliminary
Marie-Hélène Genest, Wien 2005

21. Future prospects
Results are encouraging, but more work is in progress to check the validity of this analysis by performing a direct comparison using the previous study cuts on point 3500,600 in ATLAS detector, with ISAJETv7.64
Marie-Hélène Genest, Wien 2005