what i aim for today

December 3rd, 2009

Single leptonic SUSY searchesRobert Schoefbeck (Hephy Vienna)

Physics in progress, March 4th, 2010

What I aim for today ...

• to update the non-analysts at our Institute on what we‘re currently working on

• to give an overview for our friends (who are analysts) at Budapest and Debrecen on what the Vienna Susy Group does.

just briefly ...

1.Intro – What are we looking for?

2.An example study: ABCD in kinematical MET-significance and HT2

3.Uncertainties in early leptonic SUSY

4.OSETs – a general tool for some fb-1

5.Plans

1. What are we looking for?Result of a systematic quantitative search (9 x Ω Moon): doi:10.1038/nature05497

• behaves like matter• interacts only weakly

Colliding cluster MACSJ0025Hubble/Chandra NASA/ESA“Weak lensing" A.Einsteinmiddle/pink: ordinary matterblue lobes: gravitationally int.

How can we see DM in the detector?SUSY-model

The simplest models with supersymmetry in accordance with experiment predict good dark matter candidates.

The details of the mass spectrum are not set, however.

large amounts of MET

The LSP interacts weakly in many

models!

Discovery reach for different

integrated luminosities(PTDR-II)

bird’s eye view: (early) SUSY at CMStotal SUSY production

cross section(PTDR-II)

varies over many magnitudes

LHC: startup due in November March

Early descoping: Bent Pyramid of Sneferu c. 2600 BCE (LeComte)

2 x 3.5TeV

(2 x 5TeV)

2 x 7TeV

you are here

future

Start-up & early data

Until startup: prepare for data-taking

SUSY is a possible early discovery

However, MC simulation of background in regions where SUSY is suspected suffers from high uncertainties, especially in the tails

Estimation of the background from data

is a vital necessity

Don’t be model-dependent, look for general signatures!

SUSY Hadronic Reference Analyses – Exclusive n-jet analyses Dijets + Multijets – Inclusive ≥3 jet analysis InclusiveJets– photon+MET analysis Diphoton+X– Diphoton+Jet+MET, Photon+JET+MET

SUSY Lepton Reference Analyses – Single-lepton analysis SingleLepton_e, SingleLepton_mu – Same-sign dilepton analysis (ee, emu, mu-mu, mu-tau)– Opposite-sign dilepton analysis– Trilepton analysis Trilepton – Dilepton + photon

Overview: early SUSY searches at CMS

lep. search: SUSY=JETS+MET and the lepton vetoes QCD

what are the backgrounds?t-tbar • 9.000 events in the first 100pb-1

• if one of the W decays leptonically, the bkg is irreducible

• W->tau decays and tau-conversions– different Bkg-physics in different MET-

regions

W+Jets• depending on pre-selection 10-50%• fewer jets, produced less centrally

QCD• is always there• small CS in the one-lepton mode but

not very well understood, especially the tails

Guiding principle is

*not* to optimize discovery reach.

t-tbar

signal

Summary: Typical event selection:

3 hard jets

1 Muon, no Electron

Large MET

physics objects: “as loose as possible, as tight as necessary”

jets at least three jets

pT > (50,50,50) GeV (corrected)

|η| < (2.4, 2.4, 2.4)

fem < (0.9, 0.9, 0.9)

Electron selection „eleIdRobLoose“ (rej. = 96.65%, eff = 26.0%)

pT>20 GeV and |η|<2.5

CaloRelIso < 0.1

Electron selection (veto)„eleIdRobTight“ (rej. = 99.76%, eff = 12.2%)


RelIso < 0.1

|d0|<0.2cm , w/ to the beam spot

Muon selection„GlobalMuonPromptTight“


RelIso < 0.1, ECalIso < 4 GeV,

HCalIso < 6 GeV, |d0|<0.2cm, Nhits>11

MET (missing transverse energy)

ET > 100 GeV , 200GeV<ET

mT (trans. mass of rec. W=lep+MET)

50<mT<100, 100<mT

mT: trans. mass (l,MET):

12

assumptions:

Bkg. dominates in A, B and C

possible problems:– signal contamination

in A, B and/or C – correlations

feature of leptonic searches:

few (>2) variables with some disc. power

control-

region A, C

signal-

region B, Dblue: predicted Bkg. in D

black: true Bkg.

Estimating the Background: the ABCD method

towards the real world

• Naive ABCD in early single-leptonic searches is not trivial due to correlations and signal contamination in most pairs of variables.

• For example, MET and mT discriminate very well but correlate, which is a hard to tackle problem with limited statistics.

• MET-significance and HT2 are uncorrelated (to a few %)• Signal contamination will dominate systematics

• I will nowgive a brief overview of the methodand how it depends on different systematic uncertainties.

14

Robert Schoefbeck (HEPHY Vienna)

MET-significance:“MET over the square-root of the total scalar sum of pT”

HT2 : “Scalar sum of pTs with hardest jet removed”

where I consider jets if |η|<2.4 and pT>40GeVand Vjet-muons with pT>10GeV (somewhat preliminary).

2. ABCD in MET-sig. and HT2

15Robert Schoefbeck (HEPHY Vienna)

HT2

HT2 of Bkg-Components

• The Bkg-samplesshow similar tails.

• SingleTop and QCD are small

• Limited statistics for the tail of WJets

16


MET-sig

MET-sig of Bkg-Components

The composition of TTbar/WJetsslightly varies overMET-sig but this variation is to some extent independent of HT2.

QCD&singleTop ~O(small)


Binned distributions of total Bkg., 10TeV

met-sig HT-2

Limited statistics in the (highest) tails, very well-tempered behaviour, though.More plots in the backup and in my talk on Dec. 3rd.


A

B

C

D

HT2

MET-sig

Total Background on a log-scale Independent exp. variables have parallel contour lines; Fulfilled quite well ( ).

Control:3<MET-sig<6150<HT2<300Signal:8<MET-sig350<HT2

quick check of robustness (see later):Include shaded area to B,D and C (red arrows)CUT-AB

CU

T-B

D


A C

D

HT2

MET-sig

example: LM2 on a linear scale

B

20Robert Schoefbeck (HEPHY Vienna)December 3rd, 2009

find a working point (axis = cut values, fixed excluded regions, LM1)

double ratio (A/B)/(C/D) on Bkg relative statistical error

signal events in D “significance” (est. Signal / sigmastat+sys)CUT-AB

CU

T-B

D

CUT-AB

CU

T-B

D


Samples true BG in D predicted BG in D

rel. stat.err.

True Signal

BG 13.1 13.6 ± 12.7% 0.0

BG+LM0 13.1 47.7 ± 9.3% 59.5

BG+LM1 13.1 17.6 ± 12.0% 25.9

BG+LM2 13.1 14.2 ± 12.6% 6.5

BG+LM3 13.1 16.9 ± 12.1% 22.7

BG+LM4 13.1 14.9 ± 12.5% 14.2

BG+LM5 13.1 13.9 ± 12.7% 5.5

BG+LM6 13.1 13.9 ± 12.7% 6.2

BG+LM7 13.1 14.0 ± 12.7% 2.2

BG+LM8 13.1 14.6 ± 12.5% 12.1

BG+LM9 13.1 15.4 ± 12.3% 5.4

Results at 100pb-1 True BG in D: 13.1 Events

Except for LM0

these variables

seem to work

quite well.

Sig.Cont. is the

main remaining

problem, of

course.

total Bkg LM1 LM0

total Bkg, log scale LM1 LM0

10TeV

7TeV

met-sig. met-sig. met-sig.

met-sig. met-sig. met-sig.

HT

-2

HT

-2

HT

-2

HT

-2

HT

-2

HT

-2


3. What are my uncertainties?


Robustness: Including dead areas in D

Example: LM2RED: true Bkg in D, Black: estimated background in DVarying region D according to the red arrows on the previous slided, there is only a very small dependence on the HT2 cut-value (left) and an almost constant term in the relative error as function of region-D cut on met-sig (right).

cut on HT2 in „D“ cut on met-sig in „D“

JES

signal contamination and JES

Signal contamination gives a bias for every signal hypothesis (Middle Bin).Conservative: Treat it as an sys. unc. for whichthe width of the band is a good measure.

Other Bins: Dependence on JESThe true Bkg changes but the estimationfollows nicely (slope is corrected).

same as left, with true background subtracted

Estimate sys. uncertainty from JES :from the variation of the width

sig.

Con

t.

sig

.Co

nt.

estim

ated

Bkg

.-ev

ents true Bkg. subtracted

measure efficiency of lepton-isolation cut (1)

Monitoring lepton-iso efficiency with tag and probe using Z+Jets• tag a RA4 muons• Select looser probe-muon (RA4-preselection without rel-iso cut) and

require opposite muon-charges and M(mu,mu) = MZ +/- 10GeV• measure efficiency of rel.iso-cut binned in pt, eta and njets• extrapolate to higher jet-multiplicites and compare with generator efficiency• done by Gregor Kasieczka, more info e.g. in talk by A.J. Richards, Nov.,

19th

mass[GeV]

T&P results: predicting iso-cut efficiency (2)

Example: prediction for iso-efficiency in the low-lepton-pT (10GeV < pT < 30GeV) range and extrapolation to high jet-multiplicities. Error bars for 100pb-1. Extrapolation works well. The model fitted is εn = ε0 pn . Mainly serves as a sanity check.

njets

Extraploation


• Take each jet• get its resolution• raise it by some factor• smear with the

additional contribution• reorder Jets• recalculate MET

Jet-Smearing

-> Jet smearing has practically no effect (only SM/SUSY scale)

Signal contaminationdefinitely the largest issue. Although it is a bias known under a signal hypothesis, I (for now) treat it as an sys. uncertainty in statistics (~3.1 Evts@100pb-1)

Jet-energy scalesecond largest, but ABCD subtracts leading term (~1Evts)

lepton-efficiencymonitoring Lepton Iso. Efficiency with T&P in Z-Eventsexpect only very small effect (see my talk on Dec. 3rd)

jet-efficiency and systematics in the low jet-pt range 30 to 50GeVneeds a close look, monitor jet-efficiency with T&P in Dijets (in the making)

jet-resolutionre-smearing Jets with worsened resolution has very small effect (talk on Dec. 3rd)

muon-trigger efficienciesThe muon-trigger efficiencies with Mu5, Mu7 and Mu9are constant over my ABCD regions within the statistical error

more on uncertainties

Sig. true BG in D pred.Bg. stat. sys.(sig.) JES JSM all Ev. in D

LM1 14.3 16.6 ± 2.3 ± 3.1 ± 1 ± 0.1 38.3LM2 14.3 13.6 ± 1.9 ± 3.1 ± 1 ± 0.1 20.6

mean significance of deviation from SM at 7TeV, including statistics + systematics, signal.cont. of (LM1-LM10) taken as systematic error

used roostats::ProfileLikelyhoodCalculator, preliminary

LM0 not seen100pb-1 probably is too littleroostat sometimes crashes,cause not yet known

ABCD regions:2.5 < met-sig < 4.5 and 4.5 < met-sig 250<HT-2<350 and 350<HT-2

• some points (LM1,LM3,...) much easier than others (LM2, LM7)

4. OSets: disentangle branchings and masses

mSUGRA LM2

(incomplete)

455 465

468

- 777

746 -

724

671

580

748

827

141

264 267

42%

t

12%

t

46% q

13% b 26% b15% t

38%

b

24% t

46% t

12% t

53%

q

30%

q

85 % τν 15% W

Z

15%

q

OSET LLM

mqmg

mN

mC

100

% →

ν τ

1

00%

→ tb

100

% →

q LM1: mq 550, mg 600, ∼ ∼ mC 180, mN 100∼ ∼

LM2: mq 760, mg 830, ∼ ∼ mC 270, mN 140∼ ∼

LM8: mq 800, mg 740, ∼ ∼ mC 230, mN 120∼ ∼

well modeled!

5. What to do next

tasks I ommitted:Vertexing, secondary vertex finding efficiency , also related to

(W.Waltenberger, D.Liko, C. Thomay) b-Tagging (W.Adam)maintenance of SUSY-PAT recipe and patification for the SUSY group

37


BACKUP

38


MET-sig MET-sig

met-sig. for signals (only lower cut)

typically, expect at least signal ~ O(Bkg) in signal region; (Note that this is summed over HT2-regions, as indicated)

A+B C+D A+B C+D

39


HT2 HT2

HT2 for signals (only lower cut)

A+C B+D A+C B+D

Again, this is summed over met-sig.-regions,Thus a small signal (e.g. LM2) in this plot need not be a problem (details->backup)

40


MET for different Backgrounds

MET

Cuts applied:

preselectionMET-Sig > 3HT2 > 150(lower region-cuts)


HT2 for Bkgs in AB and CD

HT2 HT2

A B C D

42


MET-sig MET-sig

MET-Sig for Bkgs in AC and BD

A C B D

43


HT2 HT2

HT2 for total Bkg. & signals in A,B & C,D

A B C D

44


MET-sig for total Bkg. & signals in A,C & B,D

MET-sig MET-sig

A C B D

what i aim for today

Documents

early susy searches

jets met

early singleleptonic

vienna susy group

early leptonic susyosets

susymodelthe simplest

5tev2 x 5tev2 x

sign dilepton analysis