Update from the Photons + MET Group
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Update from the Photons + MET Group
Bruce Schumm
UC Santa Cruz / SCIPP
11 March 2010
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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
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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
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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
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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
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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
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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.
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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)
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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
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11 March 2010 10
HT (sum of all ET except MET) vs. MET for full GMSB Sample
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11 March 2010 11
HT (sum of all ET except MET) vs. MET for “Strong” GMSB Sample
Optimal cut from MET analysis
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11 March 2010 12
HT (sum of all ET except MET) vs. MET for “Weak” GMSB Sample
Optimal cut from MET analysis
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11 March 2010 13
HT vs. MET for ttbar (e background; require one SL decay)
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11 March 2010 14
HT vs. MET for QCD (JF17, 7 TeV MC09)
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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.
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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)
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11 March 2010 17
Can we
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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
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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
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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
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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
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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
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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
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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
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11 March 2010 25
HT
• Everything added together – nothing surprising here
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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