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**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

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**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

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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

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**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

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**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

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**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

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**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

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**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

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**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

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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

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**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

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**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

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

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**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

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**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

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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

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

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**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

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**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

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**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

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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

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