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Status report from the LEPSUSYwg: “The stau excess” F Cerutti, G.Ganis, F.Holldorfer, K.Jakobs and M.Maggi. The facts: First look to the excess Studies going on … Perspectives for 2000 run Signal hypothesis Fluctuation hypothesis Possible strategy Conclusions ?!?.

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slide1
Status report from the LEPSUSYwg: “The stau excess”F Cerutti, G.Ganis, F.Holldorfer, K.Jakobs and M.Maggi
  • The facts:
    • First look to the excess
    • Studies going on …
  • Perspectives for 2000 run
    • Signal hypothesis
    • Fluctuation hypothesis
    • Possible strategy
  • Conclusions ?!?

F.Cerutti

the facts combined excess
The facts: combined excess
  • stau ADLO 189-202 GeV combined
  • Exchanged matrixes in the Mstau-Mchi plane : Cand, Bkg, Eff
the facts excess probability
The facts: excess probability
  • Estimator used to quantify the excess
the facts excess probability2
The facts: excess probability
  • E fraction of point with CLexcess<2%
  • Gedanken experiments (bkg only)
  • Pexcess= N(E>Edata)/Ntot =10-3 (6.8% A)
m stau from xs
Mstau from xs
  • Find the stau mass comparingstRvs data excess (Mc<30):
    • MtR = (86.7 ± 1.4) GeV (Mc~15-35)
the reference point
The reference point
  • Take as “reference point”

Mt=85 GeV Mc=20 GeV:

      • Cand = 226
      • Bkg = 179.5
      • P(Bkg,NNcand) = 5 x 10-4
bkg composit and systematics
Bkg composit. and systematics
  • Background composition in 85-20:
  • Systematics on bkg: ~2-4% dominated by MC statistics
  • If we add 4% to bkg in 85-20:

P(Bkg,NNcand) = 3 x 10-3

  • Gedanken experiment full plane with bkg sys (+1s):

Pexcess=N(E>Edata)/Ntot=1.2%

comparison data vs bkg
Comparison Data vs Bkg
  • Decided to exchange more info within ADLO to allow additional checks
  • For each event (Data, MC Bkg and MC signal) exchange:

Pt1 Pt2 Pmiss Weight(bkg) Bin-position, ...

  • For the 85-20 point check variables [Bkg vs Data] ADL(189-202)O(189)

DT=184

MC=146.

Excess = 38±14 (2.7 s)

comparison data vs bkg1
Comparison Data vs Bkg
  • Emax
  • Emin
  • Mtt
  • Ptmiss
  • Acollinearity
  • Emax vs Emin
  • Mt1 vs Mt2
  • Tau ID1 vs Tau ID2
aleph h vs stau b fabbro
ALEPH: H+ vs stau (B.Fabbro)
  • H+ vs stau Large-dM (L-dM.OR.S-dM):

can bkg can bkg

189 20 15.520 15.5

192-202 36 35.530(46) 21.7(34.2)

e(M=85) 38%39%

  • The two analyses are NOT incompatible
    • cand=16 bkg=17 dif=-1±4 H+ only
    • cand=10 bkg=4 dif=6±3 stau only
    • cand=20 bkg=18 dif=2±4 H+.AND.stau
  • Warning: 9 events(5 large-dm)selected by stau and NOT by H+ have a NOT identifiedenergetic lepton -> to be checked !
perspective for y2k run
Perspective for y2k run
  • Patrick performance for LEP y2k
perspective for y2k run1
Perspective for y2k run
  • Studied 18configurations:
      • 1 22 weeks at 192 GeV
      • 2 “ 196 GeV
      • 3 “ 198 GeV
      • 4 “ 200 GeV
      • 5 “ 202 GeV
      • 6 “ 203 GeV
      • 7 “ 204 GeV
      • 8 “ 204.6 GeV
      • 9 “ 205.2 GeV
      • 10 “ 206 GeV
      • 11 22 w 206.8 GeV
perspective for y2k run2
Perspective for y2k run
      • 12 22 w MiniRamp 1-step 4-bun.
      • 13 22 w MR + 24 w extens. MR
      • 14 22 w + 24 w extens. 200 GeV
      • 15 Status at LEPC in July MR
      • 16 MR up to LEPC+200 GeV 22+24
      • 17 MR up to LEPC+200 GeV 22+2
      • 18 Status before 2000 run
  • Results for signal hypothesis in the given for three stau masses: 85,87 and 89 GeV (mild dependence from Mc=20 GeV)
slide17

Mt=85 GeV

Mt=89 GeV

slide18
Significance for Mstau = 89-85 GeV
  • 1 22 weeks at 192 GeV 3.1-3.9 sigma
  • 2 “ 196 GeV 3.4-4.3 sigma
  • 3 “ 198 GeV 3.5-4.3 sigma
  • 4 “ 200 GeV 3.6-4.3 sigma
  • 5 “ 202 GeV 3.6-4.2 sigma
  • 6 “ 203 GeV 3.6-4.1 sigma
  • 7 “ 204 GeV 3.6-4.0 sigma
  • 8 “ 204.6 GeV 3.5-4.0 sigma
  • 9 “ 205.2 GeV 3.5-3.9 sigma
  • 10 “ 206 GeV 3.1-3.3 sigma
  • 11 22 w 206.8 GeV 3.1-3.3 sigma
  • 12 22 w MiniRamp 1-step 3.4-3.8 sigma
  • 13 22+24 w MR 3.8-4.5 sigma
  • 14 22+24 w 200 GeV 4.1-5.3 sigma
  • 15 Status at LEPC in July mr 3.2-3.5 sigma
  • 16 MR up to LEPC+200 GeV (22+24) 4.1-5.2 sigma
  • 17 MR up to LEPC+200 GeV (22+2) 3.5-4.2 sigma
  • 18 Status before 2000 run 2.9 sigma
perspective for y2k run no signal hypothesis
Perspective for y2k run:No signal hypothesis
  • Question:

can we exclude at 95% CL 85<Mt<89 with next year data alone ?

  • Answer:

YES but for configurations 10, 11, 15 and 17(89 GeV only) !

      • 10 Ecm=103
      • 11 Elep=103.6
      • 15 Status at LEPC with MR
      • 17 MR up LEPC then 198 GeV
conclusions
Conclusions ?!?
  • The facts:
    • An excess in the ADLO combined LEP data has been found
    • This excess corresponds to a probability ~10-3 without any bkg systematics
    • With the bkg systematics included it goes up to ~0.5-1% (not a discovery !)
    • To be better understood background systematics (A lepton ID)
  • Y2K run: signal hypothesis:
    • 4-5 sigma significance still reachable if emphasis toL is given and6 months extension is obtained
conclusions1
Conclusions ?!?
    • At the July LEPC significance could increase from the actual 2.9 to [3.3-3.5] sigma (assuming a successful MR run)
    • Significance [3.8-5] sigma could still be reached if, after LEPC, run is optimized for L (run at ~200 GeV) .AND. the 6 months extension is given
  • Y2K run: no signal hypothesis:
    • A [85-89] GeV stau mass can be excluded at 95% CL by next year run alone in all the run configurations but the run at the highest energy (103 GeV)
slide22
Y2K optimal stau strategy ?!?
  • Run with MR up to LEPC ~ 120pb-1 than:
    • Higgs exclusion (Kinematic limit ?)
    • Stau excess significance (+ or - ?)
  • If+ indication for stau AND- for H (and c+): switch from MR to optimal stau run (large L at Elep~200)
  • Final decision on 6 months extensionshould be taken later (and/or as soon as the 4 sigma are reached): August-September ?
  • Ongoing work:
    • Careful review of bkg systematics
    • Provide signal files and fit for Mstau-Mchi (xs plus shapes)
    • Schedule regular meetings during y2k run
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