1 / 17

SUSY Measurements w i th ATLAS: Hadron ic Signatures and Focus Point

SUSY Measurements w i th ATLAS: Hadron ic Signatures and Focus Point. Outline. Tommaso Lari Università and INFN Milano On Behalf of the ATLAS Collaborat ion. Reconstruct ion of glu i no , r ight-handed squar ks and 3 rd generat ion squar k s for some low-mass mSUGRA benchmar k po i nts

fancy
Download Presentation

SUSY Measurements w i th ATLAS: Hadron ic Signatures and Focus Point

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. SUSY Measurements with ATLAS:Hadronic Signatures and Focus Point Outline Tommaso Lari Università and INFN Milano On Behalf of the ATLAS Collaboration • Reconstruction of gluino, right-handed squarks and 3rd generation squarks • for some low-mass mSUGRA benchmark points • First study of gluino decays in the focus-point region

  2. Bulk and Focus Point regions tanb=10 A0=0 m>0 mt=175 GeV Green: Regions of mSUGRA parameter space that give an acceptably low density of relic neutralinos 1st part of the talk Bulk low-mass:Several well-studied benchmark points 2nd part of the talk Focus Point: Studies started more recently. M1/2(GeV) Coannihilation Focus Point Bulk M0(GeV) H. Baer and C. Balazs, arXiv:hep-ph/0303114 T. Lari SUSY measurements with ATLAS: hadronic signatures

  3. Possible SUSY timeline • Phase 1- Discovery: See excess of events with large missing energy, make sure they are from New Physics • Phase 2 - First SUSY masses: Reconstruction of leptonic decays, combine lepton with jets • G. Comune’s talk • Phase 3 - More SUSY masses: Combine with b-jets and reconstructed tops. Purely hadronic final states. • This talk T. Lari SUSY measurements with ATLAS: hadronic signatures

  4. p p ~ c01 ~ ~ ~ q ~ c02 l g q q l l lq edge llq edge 1% error (100 fb1) 1% error (100 fb-1) Phase 2: a typical decay chain Other possibilities: c02 → c01 l+l- c02→ c01 h→ c01bb ~ ~ ~ ~ ~ The invariant mass of each combination has a minimum or a maximum which provides one constraint on the masses of c01 c02l q ~ ~ ~ ~ LHCC Point 5 ATLAS TDR ATLAS TDR ATLAS TDR ATLAS TDR llq threshold ll edge T. Lari SUSY measurements with ATLAS: hadronic signatures

  5. Sparticle Expected precision (100 fb-1) qL 3% 02 6% lR 9% 01 12% ~ ~ ~ ~ Model-independent masses • Combine measurements from edges from different jet/lepton combinations to obtain ‘model-independent’ mass measurements. ~ ~ c01 lR ~ ~ ~ ATLAS ~ ~ ~ c02 qL T. Lari SUSY measurements with ATLAS: hadronic signatures

  6. Going up the decay chain ~ • Once the mass of the c01 is known, it is possible to get the momentum of the c02 using the approximate relation p(c02) = ( 1-m(c01)/m(ll) ) pll valid for lepton pairs with invariant mass near the edge. • The c02 can be combined with b-jets to reconstruct the gluino mass peak: g → bb → bbc02 ~ ~ ~ ~ ~ ~ ~ Example: SPS1a B.K.Gjelsten et al., ATL-PHYS-2004-007 M0 = 100 GeV M1/2 = 250 GeV Tan b = 10 A = -100 GeV m > 0 ~ M(g) = 611 GeV M(b1) = 515 GeV M(b2) = 539 GeV M(c02) = 177 GeV ~ ~ ~ ATLAS - ATL-PHYS-2004-007 T. Lari SUSY measurements with ATLAS: hadronic signatures

  7. Gluino and sbottom reconstruction ATLAS - ATL-PHYS-2004-007 Good combinations. m(g) and m(b) correlated (Dominant error from c02 Momentum affects both) ~ ~ ~ ~ Bad c02 b combinations (b-jet is from gluino decay) T. Lari SUSY measurements with ATLAS: hadronic signatures

  8. Gluino mass reconstruction ATLAS ATL-PHYS-2004-007 ATLAS ATL-PHYS-2004-007 Reconstructed gluino mass. Width dominated byc02 momentum. Gluino mass as a function of the assumedc01 mass. ~ ~ ~ ~ m(g)-0.99m(c01) = (500.0 ± 6.4) GeV with 300 fb-1 Error is statistical plus 1% uncertainty on jet energy scale Central value 10 GeV lower than nominal because b-jet energy underestimated T. Lari SUSY measurements with ATLAS: hadronic signatures

  9. sbottom mass ~ ~ m(c02 bb) and m(c02 b) strongly correlated : use the difference ATLAS ATL-PHYS-2004-007 ATLAS ATL-PHYS-2004-007 300 fb-1 300 fb-1 ~ ~ With 300 fb-1 it should be possible to separate the b1 and b2 peaks ~ ~ ~ ~ m(g)-m(b1) = (103.3 ± 1.8) GeV m(g)-m(b2) = (70.6 ± 2.6) GeV With lower statistics only measure the average T. Lari SUSY measurements with ATLAS: hadronic signatures

  10. Right-handed squark ~ qR does not couple to Wino c01 is nearly a Bino c02 is nearly a Wino ~ ~ ~ qR → q c01 ~ ATLAS ATL-PHYS-2004-007 Combine the transverse momentum of two leading jets with missing transverse momentum as follows: 30 fb-1 ~ ~ Maximum of this variable is m(qR)-m(c01) ~ ~ m(qR)-m(c01) = (424.2 ± 10.9) GeV ~ ~ Note: can reconstruct lL→ l c01 with same technique ~ ~ m(lL)-m(c01) = (106.1 ± 1.6) GeV T. Lari SUSY measurements with ATLAS: hadronic signatures

  11. Purely hadronic final states ~ ~ ~ ~ ~ ~ Aim is to reconstruct g → tt1 → tbc±1 or g → bb → bt c±1 ~ ~ ~ ~ tb invariant mass has a maximum function of the masses of g, b(or t) andc±1 Two closely spaced edges from the two decays: can measure a weighed average. ATLAS • Selections: • - total jet energy and missing energy • 2 b-jets • lepton veto • 4 to 6 non-b jets Reconstruction: - m(jj) close to m(W) - m(jjb) close to m(t) - W-sidebands to estimate and subtract combinatorial background See J. Hisano et al., Phys. Rev. D68, 035007 for details T. Lari SUSY measurements with ATLAS: hadronic signatures

  12. Focus Point region Large scalar mass: heavy squarks and sleptons. Relatively low gaugino mass. Low m, large Higgsino/Bino mixing  low density of relic neutralinos, compatible with WMAP limits. The FP region has an high neutralino- nucleon cross section, so it will be probed by direct searches for dark matter. M1/2 (GeV) Focuspoint • Problems: • Very sensitive to top mass • Large discrepancies between SUSY mass • calculators Selected point for detailed study m0 = 3000 GeV M1/2 = 215 GeV Tanb = 10 A0 = 0 - m>0 M(top) = 175 GeV M0 (GeV) No EWSB solution T. Lari SUSY measurements with ATLAS: hadronic signatures

  13. Mass spectrum • Heavy squarks and leptons. • Heavy Higgs (except h) • Lighter gluino (640 GeV) decays into charginos and neutralinos ISAJET 7.69 T. Lari SUSY measurements with ATLAS: hadronic signatures

  14. Production x-Section Meff = Jet energy + ETmiss ~ ~ ATLAS ~ ~ ~ ~ • Neutralino/chargino production • abundant but without jet/missing • energy signature (mass similar or • lower than top mass). • Gluino pair production followed by • decay into chargino/neutralino is • dominant after cuts to reject SM • squarks still visible with • enough luminosity The gluino decays to chargino or neutralino via three-body decays: ~ ~ g→ cqq T. Lari SUSY measurements with ATLAS: hadronic signatures

  15. Dilepton analysis ~ ~ ~ ~ ~ ~ c02 → c01 ll c03 → c01 ll Direct three-body decay c0n → c01 ll Edge gives m(c0n)-m(c01) Z0→ ll ~ ~ ATLAS ATLAS 30 fb-1 30 fb-1 Combination with jets to reconstruct the gluino mass is under study. T. Lari SUSY measurements with ATLAS: hadronic signatures

  16. Gluino to chargino decay ~ ~ g → ctb Direct three-body decay: ATLAS 30 fb-1 ~ ~ m(g)-m(c1) = 530 GeV T. Lari SUSY measurements with ATLAS: hadronic signatures

  17. Conclusions • After the mass of the LSP has been measured with kinematic edges, the mass peaks of heavier particles can be reconstructed. • A detailed analysis has been performed for point SPS1a: a large number of SUSY masses can be measured with a precision of 5 to 12 GeV with a statistics of 300 fb-1. • The same reconstruction techniques can be used for other regions of parameter space. • Most studies done with fast simulation (parameterized detector response) so far. Analysis with detailed detector simulation has been started. • New regions of parameter space, guided by relic density constraints, are also an hot topic. A detailed characterization of the selected point in the focus point region is being made. T. Lari SUSY measurements with ATLAS: hadronic signatures

More Related