Possible study after SUSY discovery at the ATLAS experiment March 27th, 2007, JPS-meeting @ Tokyo Metropolitan Univ. Naoko Kanaya (Kobe University) Shoji Asai (University of Tokyo / ICEPP)

Introduction  SUSY discovery is highly expected at the LHC experiments (if it exists). We don’t know almost nothing about SUSY so it should be searched by inclusive way to have sensitivity over wide parameter space as much as we can… Background should be estimated using real data. This is very crucial task for SUSY discovery (see talk by Okawa-san) Assume we see SUSY-like signature at ATLAS. What we can/should do next? This is main topics of this talk.

Outline   Possible inclusive study of SUSY signature SUSY discovery and inclusive measurement Possible inclusive study of SUSY signature Summary and Outlook  Effective mass distribution Effect of background Studied observable sensitive to signal characteristic Effect of background All studied shown in this talk is done by using fast simulation

SUSY Discovery @ ATLAS Several inclusive search are studied at the ATLAS experiment: 0-lepton mode 1-lepton mode di-lepton mode (opposite/same signed leptons) di-jet mode We may see some excess in some of (all?) analyses… 0-lepton mode analysis After background subtraction L=1fb-1 L=1fb-1

Effective mass distribution One of well-known inclusive studies : Effective mass (Meff) Meff = MissingET +  | pTjet | +  |pTlepton| Why Meff? Since Meff does not only have good sensitivity for SUSY discovery but also have good relation to SUSY mass scale, MSUSY=min(mg. mq ) ~ ~ Meff -> Msusy -> sigma

Effect of background Effective mass is very powerful observable, however it is not so easy in real life due to background. Effective Mass (1fb-1) : 0-lepton Bkg correctly estimation Over-estimation(30%) Under-estimation(30%) MSUSY~1TeV Uncertainty of ~30% is expected due to contamination of SUSY signal to control sample (depends on mass scale).

Inclusive study after discovery

Possible study after discovery Understanding detector and background estimation are very important, however we should think about next step after discovery. We believe that we must/can do some study on SUSY in an inclusive way before precise measurement (I.e. nominal luminosity). Assume : Background estimation is successfully done. See excess or peak in MissingET and/or Meff distribution. Meff gives information on SUSY mass scale. Try to find other observable sensitive to SUSY production and/or decay pattern. Following characteristics are studied in this talk. Lepton richness B-jet richness Multi-jet likeness

Once we see excess … L=1fb-1 m0=500GeV, m1/2=400GeV tan=10, >0, A=0 L=1fb-1 Assume we can estimate background level successfully. Signal (Msusy~1TeV) Need different cut optimization to know SUSY event topology to reduce dilution from background background Applying additional cut for better S/N After background subtraction Meff > 1.5TeV

Inclusive SUSY signature (A) Light sneutrinos/sleptons ~ ~ ~ ~ ~ qL -> 1+ / 20 -> +l / l +l >>Lepton rich event Major production qq ~~ (B) Direct decay cc ~~ ~ ~ qR -> 10+q >> Lepton poor event g->tt ~ ~ qg ~~ (C) Light Stop/Sbottom ~ ~ ~ ~ ~ g -> t+t -> 2++b -> 20+W / 1++Z gg ~~ >> Lepton/b-jet rich event (D) gluino production/decay ~ ~ ~ g -> n+ / n0 + qq >> Multi-jet like event

Lepton Richness <Rlep1/0> ( = N(=1)/N(=0) ) m1/2=300 GeV(Msusy~0.8TeV) m1/2=500 GeV(Msusy~1.3TeV) MSUSY~0.8TeV MSUSY~1.3TeV Meff > 1TeV Meff >1.5TeV ~ ~ ~ ~ Br (qL->1+ + q)~65% Br (1+ -> l1+ + l )~38% Br (qR->10 + q)~64% Br (1+ -> 1+ +  )~63% ~ ~ ~ ~ ~ ~ Br (g -> t + t )~95% With statistic errors of signal ONLY (L=30fb-1)

b-jet Richness <Rptb> ( = S |pT(b-jet)|/ S |pT(jet)| ) Atlfast btag : eb=60%, Rc=10, Ru=100 b-jet Richness <Rptb> ( = S |pT(b-jet)|/ S |pT(jet)| ) m1/2=300 GeV(Msusy~0.8TeV) m1/2=500 GeV(Msusy~1.3TeV) MSUSY~0.8TeV MSUSY~1.3TeV Meff > 1TeV Meff >1.5TeV Ambiguity of lepton source can be solved with help of b-jet information. With statistic errors of signal ONLY (L=30fb-1)

Multi-jet likeness <R12> ( = pT(2nd)/ pT(1st) in each hemisphere ) Hemisphere Algorithm(HA) : reconstructed objects are assigned to each initially-produced particle (hemisphere) Usage of HA in iclusive study More information available in hemisphere than in event. Objects coming from upstream of SUSY decay chain are assigned to correct mother by good efficiency multi-jet like : R12 ->1 g -> 1+ + qq mono-jet like : R12 ->0 qR -> 10+q

Multi-jet likeness <R12> ( = pT(2nd)/ pT(1st) in each hemisphere ) m1/2=300 GeV(Msusy~0.8TeV) m1/2=500 GeV(Msusy~1.3TeV) MSUSY~0.8TeV MSUSY~1.3TeV gluino-gluino production is dominant With statistic errors of signal ONLY (L=30fb-1)

Lepton Richness + background Of course it is not easy in real life due to background... <Rlep1/0> ( = N(=1)/N(=0) ) m1/2=300 GeV(Msusy~0.8TeV) m1/2=500 GeV(Msusy~1.3TeV) MSUSY~0.8TeV MSUSY~1.3TeV + cut + cut + background S/B < 1 Not loose information on SUSY event with cut (Meff>1.5TeV) With statistic errors of signal + bkg (L=30fb-1)

b-jet Richness , R12 + background... Need to optimize cut for better S/B. m1/2=500 GeV(Msusy~1.3TeV) <Rptb> ( = S |pT(b-jet)|/ S |pT(jet)| ) <R12> ( = pT(2nd)|/ pT(1st) ) + cut + cut + background S/B < 1 Not loose information on SUSY event with cut (Meff>1.5TeV) With statistic errors of signal + bkg (L=30fb-1)

Summary and Outlook ~~ qq ~~ cc ~~ qg ~~ gg Meff is very good observable which is sensitive to SUSY mass scale. Background easily smears the peak. It is very important to estimate background using real data. Search good variables sensitive to SUSY production and decay pattern as Meff has good relation to SUSY mass scale Lepton richness, b-jet richness and multii-jet likeness are tested. Effect of background should be suppressed by optimizing cut or subtracting background with help of MC information Try to find better observable and think about how to remove/suppress of background effect. qq ~~ cc ~~ qg ~~ gg ~~

Backup Slides

Lepton Richness (3) <Rlep2/0> ( = N(=2)/N(=0) ) m1/2=500 GeV MSUSY~1.3TeV MSUSY~0.8TeV BR(UPL->W1SS+UP)~65% BR(W1SS->SLEP+L)~38% BR(UPL->W1SS+UP)~64% BR(W1SS->STAU+NUT)~63% BR(GLSS -> ST + T)~95% Signal ONLY (L=10fb-1) with statistic errors

Lepton Richness + background Of course it is not easy in real life due to background... <Rlep1/0> ( = N(=1)/N(=0) ) with MET>400GeV m1/2=500 GeV(Msusy~1.3TeV) m1/2=300 GeV(Msusy~0.8TeV) MSUSY~0.8TeV MSUSY~1.3TeV + cut + cut + background With statistic errors of signal + bkg (L=30fb-1) together including systematic uncertainties of bkg estimation

b-jet Richness , R12 + background... Need to opimize cut for better S/B. m1/2=500 GeV(Msusy~1.3TeV) with MET>400 GeV <Rptb> ( = S |pT(b-jet)|/ S |pT(jet)| ) <R12> ( = pT(2nd)|/ pT(1st) ) + cut + cut + background With statistic errors of signal + bkg (L=30fb-1) together including systematic uncertainties of bkg estimation