Status report from the LEPSUSYwg: “The stau excess”
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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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The facts: First look to the excess Studies going on … Perspectives for 2000 run

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The facts first look to the excess studies going on perspectives for 2000 run

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 probability1

The facts: excess probability


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


Compatibility with signal in the reference point aleph only

Compatibility with signal in the reference point : ALEPH only


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)


  • The facts first look to the excess studies going on perspectives for 2000 run

    Mt=87 GeV


    The facts first look to the excess studies going on perspectives for 2000 run

    Mt=85 GeV

    Mt=89 GeV


    The facts first look to the excess studies going on perspectives for 2000 run

    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)


  • The facts first look to the excess studies going on perspectives for 2000 run

    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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