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

04/21/23 F.Cerutti 1

Status report from the Status report from the

LEPSUSYwg: “The stau LEPSUSYwg: “The stau

excess”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 ?!?

2

The facts: combined excess

stau ADLO 189-202 GeV combined

Exchanged matrixes in the Mstau-Mchi

plane : Cand, Bkg, Eff

3

The facts: excess probability

Estimator used to quantify the excess

)(

)(;

)(

,i

iiiiEcmExp

obsi

obs

obsNoExcess

bL

bsLwwnO

OOPCL

4


5


E fraction of point with CLexcess<2%

Gedanken experiments (bkg only)

Pexcess = N(E>Edata)/Ntot =10-3 (6.8% A)

6

Mstau from xs

Find the stau mass comparing R vs

data excess (M<30):

MR = (86.7 ± 1.4) GeV (M~15-

35)

7

The reference point

Take as “reference point”

M=85 GeV M=20 GeV:

Cand = 226

Bkg = 179.5

P(Bkg,NNcand) = 5 x 10-4

A D L O Tot

Can 50 34 70 72 226

Bkg 36.8 28.2 55.8 58.7 179.5

Diff 13.27.1 5.8 5.8 14.2 8.4 13.38.5 46.515.1

40% 30% 25% 55% -

/Vb 6.6% 5.6% 3.3% 7.2% -

8

Compatibility with signal in the reference point : ALEPH

only

9

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,NNcand) = 3 x 10-3

Gedanken experiment full plane with

bkg sys (+1):

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

Proc A D L O

4f 92.4% 75.1% 78.3% 86.7%

ll 6.3% 11.3% 11.5% 5.7%

qq - - 7.4% -

() 1.3% 12.1% 1.7% 4.0%

ll() - 1.5% 1.1% 0.6%

other - - - 3.0%

10

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:

P1 P2 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 )

11

Comparison Data vs Bkg

Emax

Emin

M

Ptmiss

Acollinearity

Emax vs Emin

M1 vs M2

Tau ID1 vs Tau ID2

12

ALEPH: H+ vs stau (B.Fabbro)

H+ vs stau Large-dM (L-M.OR.S-M):

can bkg can bkg

189 20 15.5 20 15.5

192-202 36 35.5 30(46) 21.7(34.2)

(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-m)

selected by stau and NOT by H+ have a

NOT identified energetic lepton -> to

be checked !

13

Perspective for y2k run

Patrick performance for LEP y2k

14


Studied 18 configurations:

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

15


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 M=20

GeV)

16

M=87 GeV

17

M=85 GeV

M=89 GeV

18

Significance for Mstau = 89-85 GeVSignificance for Mstau = 89-85 GeV

11 22 weeks at 192 GeV 3.1-3.9 sigma 22 weeks at 192 GeV 3.1-3.9 sigma

22 “ 196 GeV 3.4-4.3 sigma “ 196 GeV 3.4-4.3 sigma

33 “ 198 GeV “ 198 GeV 3.5-4.3 sigma3.5-4.3 sigma

4 4 “ 200 GeV “ 200 GeV 3.6-4.3 sigma3.6-4.3 sigma




88 “ 204.6 GeV 3.5-4.0 sigma “ 204.6 GeV 3.5-4.0 sigma

99 “ 205.2 GeV 3.5-3.9 sigma “ 205.2 GeV 3.5-3.9 sigma


11 11 22 w 206.8 GeV 22 w 206.8 GeV 3.1-3.3 sigma3.1-3.3 sigma

12 12 22 w MiniRamp 1-step 22 w MiniRamp 1-step 3.4-3.8 sigma3.4-3.8 sigma

1313 22+24 w MR 22+24 w MR 3.8-4.5 sigma3.8-4.5 sigma

1414 22+24 w 200 GeV 22+24 w 200 GeV 4.1-5.3 sigma4.1-5.3 sigma

15 15 Status at LEPC in July mr Status at LEPC in July mr 3.2-3.5 sigma3.2-3.5 sigma

1616 MR up to LEPC+200 GeV (22+24) MR up to LEPC+200 GeV (22+24) 4.1-5.2 sigma4.1-5.2 sigma

1717 MR up to LEPC+200 GeV (22+2) MR up to LEPC+200 GeV (22+2) 3.5-4.2 sigma3.5-4.2 sigma

18 18 Status before 2000 run 2.9 sigmaStatus before 2000 run 2.9 sigma

19

Question:

can we exclude at 95% CL

85<M<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

Perspective for y2k run:No signal hypothesis

20

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 to L is given and 6 months extension is obtained

21

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)

22

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

+): switch from MR to optimal stau

run (large L at Elep~200)

Final decision on 6 months extension

should 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

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

Documents