Update from the Photons + MET Group

Bruce Schumm

UC Santa Cruz / SCIPP

11 March 2010

11 March 2010 2

Background Info

Since the SUSY/ETMiss Kick-Off, group has expanded a bit

• Photon(s) + leptons (U. Michigan)• Constraining MET with data (U. Victoria)Plus prior Photons + MET (GMSB) group• DESY• Liverpool• Santa Cruz

11 March 2010 3

100 pb-1 Analyses

Plan to have two baseline analyses, both GMSB-inspired, but concerned about model indpendence

• Photon(s) plus MET– Subject of this presentation

• Photons(s) plus leptons plus MET– Subject of later presentation by U Michigan

11 March 2010 4

Photons plus MET Analysis

We’ve been asked to think about

• Baseline analysis– Possible hard/medium/soft scenario

• What we can do with 10 pb-1 for summer conferences– Should support progress towards baseline

100 fb-1 analysis

11 March 2010 5

Prior Studies

10 TeV / 200 pb-1 analysis with

• Two photons and hard (160 GeV) MET cut (SCIPP)

• Two photons and NJET cut; soft MET cut (DESY)

e.g. Two Photon plus MET Result

11 March 2010 6

New Thinking I: Production and Decay Scales

Very roughly, two scales in problem• Production scale; heavier mass SUSY

partner sets overall Pt scale of event• Decay scale: NLSP (0) sets scale for

MET

So: use two independent discriminating variables:

• MET• HT (sum of ET of all objects in event,

excluding MET)

(But how independent are these really?)

Production

Decay

11 March 2010 7

Baseline Analysis

Proposal for Baseline Analysis

• Require two photons (powerful background suppression)

• Optimize cuts on MET and HT based on SPS8 trajectory (“analytic continuation” of GMSB1 to higher neutralino mass)

Is underway and should be available soon.

11 March 2010 8

Further Thinking II: Strong vs. Electroweak Production

Initial production can be “strong” (two squarks/gluinos), “electroweak” (two gaugino), or mixed (one of each)

• Still two photons from final decay, but signature quite different otherwise

• Electroweak production dominates at 2 TeV (Tevatron)

11 March 2010 9

Relative Percentages of the Types

• Breakdowns for 10k points

• Key:– Bin 0 = Weak– Bin 1 = Mixed– Bin 2 = Strong

• About ~30% for Λ=90 TeV and ~10% Λ=120 TeV

• Total production cross sections:

– Λ=90 TeV : 0.51pb– Λ=100 TeV : 0.29 pb– Λ=110 TeV : 0.17 pb– Λ=120 TeV : 0.11 pb

• Strong production has effective x-section of ~11 fb for Λ=120

7 TeV SPS8 rates

WeakStrong

11 March 2010 10

HT (sum of all ET except MET) vs. MET for full GMSB Sample

11 March 2010 11

HT (sum of all ET except MET) vs. MET for “Strong” GMSB Sample

Optimal cut from MET analysis

11 March 2010 12

HT (sum of all ET except MET) vs. MET for “Weak” GMSB Sample

Optimal cut from MET analysis

11 March 2010 13

HT vs. MET for ttbar (e background; require one SL decay)

11 March 2010 14

HT vs. MET for QCD (JF17, 7 TeV MC09)

11 March 2010 15

Baseline Analysis and Strong vs. Electroweak Producion

Possibility: “Hard” analysis selects strong component with low backgrounds; “Soft” analysis sensitive to weak component but with higher backgrounds

Note that production was almost exclusively weak at Tevatron

But: weak-sensitive is more sophisticated analysis, perhaps not for first pass…?

Proposal is to start with single, “hard” analysis.

11 March 2010 16

10 pb-1 Plans

Unlikely to set new limits or discover GMSB SUSY (although strong channel is turning on, with clear signature)

11 March 2010 17

Can we

11 March 2010 18

Three Categories of Events

• Seems to be three main categories of events classified by the sparticles coming out of the hard scatter– Weak production

• Events with two: neutralinos, charginos, sleptons

– Strong production• Events with two: sqaurks or gluinos

– Mixed• Take one particle each from the two other categories

• All three types of events have different characteristics• The ‘mixed’ type are basically intermediary of the two• Used 7 TeV SPS8 atlfastII sample

11 March 2010 19

Effect of Photon Selection• Using the normal

selection cuts for photons from past analysis (pt, isolation, etc)

• Looking at weak versus strong, the weak production events seem to have greater proportion of events with 2 photons

• Photons being lost because the strong prod. events are busier?

• This plus all remaining plots are using Λ=90TeV

11 March 2010 20

Photon PT Spectrum

• Pt spectrum seems to have longer tail for the strong prod events

– Seems to be a lot of the tail (plot needs better zoom)

• Though current pt cuts (or slightly higher even) shouldn’t bias us against one or the other prod mechanism

11 March 2010 21

Missing Et Spectrum

• Definitely different shapes as we thought

• Strong production is most of the tail

• MET > 160 GeV cut - definitely cut out most of the weak production as was speculated

11 March 2010 22

Number of Jets

• Jets (sorta random):– Et > 20 GeV– Eta < 2.5– Removed overlap

with photons + electrons (deltaR cut)

• Strong and weak production fairly different in terms of number of jets

• Mixed typed are intermediary

11 March 2010 23

“Meff” – no Missing Et

• Sum of the et of the four highest et selected jets (that weren’t removed by overlap)

• Double structure indeed comes from what we though it did

• Strong production peak is already pretty small at Λ=90 for 7 TeV

11 March 2010 24

“Meff” – w/ Missing Et

• Shifts spectrum to the right

• Strong production peak moves further – though that’s expected from the met distributions

11 March 2010 25

HT

• Everything added together – nothing surprising here

11 March 2010 26

Summary

• The strong and weak production mechanisms contribute as we had come to suspect

• There is a third intermediary type of events, but its cross section is very small

• Strong production component is already pretty small at Λ=90 for 7 TeV and drops off quite quickly from there

• No real revelations here but at least it conforms what we had suspected was going on