MR%20draft

1
MR draft

• SUSY Hadronic/GMSB Meeting 26-08-10
• Christopher Rogan
• California Institute of Technology

2
The Search for SUSY

• Here we re-introduce a new set of variables for
  a fully-inclusive SUSY search
• See talks in SUSY meeting 6-5-2010, H?WW
  meeting 28-5-10 or
• backup slides or
• In general, an analysis using these variables,
  relative to a canonical SUSY search looking in a
  MET/MHT/HT tail for an excess
• Yields higher signal efficiency w.r.t. the
  inclusive SUSY x-section
• More control over background distributions
• Distinctive signature tail search becomes bump
  hunt

arXiv1006.2727v1 hep-ph
BKG
Log(N)
BKG
BKG
Log(N)
SIG
SIG
SIG
x
x
3
Kinematic Variables for SUSY
? Two variables designed to be used together for
discovery ? and characterization of SUSY
arXiv1006.2727v1 hep-ph

• Doesnt involve MET
• Uses both transverse and longitudinal
  information
• Invariant under long. boosts

• Peaks for signal

• Dimension-less variable used for S/B
  discrimination
• Not only suppresses backgrounds, but also shapes
  their distributions in the variable in a
  predictable and well-understood way - the Razor

3
4
Selection/Sample Details

• For everything shown in this talk
• 7 TeV MC (see back-up slide for list of samples)
• 7 TeV Data (up to run 140387 right now 318
  nb-1)
• OR of HT200 and Jet110 triggers (for the moment)
• PF MET used (tcMET or corrected caloMET fine
  too)
• Require di-jets satisfying (parallel analyses)
• NO explicit lepton/photon reco or ID in
  constructing these variables
• If gt 2 reco jets, form two hemispheres by
  minimizing invariant masses added in quadrature
  (see back-up slides)

Corrected PF jets
Uncorrected Track jets
Corrected Calo jets
Only high quality tracks w/ vertex consistent
with reco PV considered for clustering
Loose jet ID
Loose jet ID
5
The Razor in practice
PF jets
LM1 MC
QCD MC (ALPGEN)

• Cut on R gives many orders of magnitude
  suppression of QCD background
• More importantly, cut on R dictates the shape of
  the surviving background events (QCD and others)
  in the variable MR (see next slide)

6
The Razor and MR
DATA behaves as expected
PF jets
Backgrounds fall exponentially after exceeding
relevant scale (set by process scaletrigger/reco
requirements) - slope set by R cut
7
MC Search Expectations
PF Jet Analysis
Normalized to 10 pb-1
Here, LM1 largest bkgs
There are two exclusive classes of events -
analogous variables to R and MR defined also in
the primed case (see arXiv1006.2727v1
hep-ph)
See back-up for all signal and bkg tables

• Assuming reasonable precision for bkg estimates
  (see following slides) we should be sensitive to
  LM1 with 10 pb-1 in PF jet analysis

8
MC Search Expectations
Calo Jet Analysis
Normalized to 10 pb-1
Here, LM1 largest bkgs
See back-up for all signal and bkg tables

• Assuming reasonable precision for bkg estimates
  (see following slides) we should be sensitive to
  LM1 with 10 pb-1 in Calo jet analysis

9
MC Search Expectations
Track Jet Analysis
Normalized to 10 pb-1
Here, LM1 largest bkgs
See back-up for all signal and bkg tables

• Assuming reasonable precision for bkg estimates
  (see following slides) we should be sensitive to
  LM1 with 10 pb-1 in Track jet analysis

10
Towards Background Estimations

• To zero-th order, we can use low MR region to
  predict high MR background yield
• Can even go further by defining mutually
  exclusive boxes defined using lepton ID/tracker
  isolation (independent of definition of MR and R)
• As of now, 9 exclusive boxes
• For a given bkg type, exponential slope in MR
  the same in each box (physics object final state
  independent)

Two ? at least one ISO
Two ?, no ISO
One e, one ? ISO
One e, one ? non-ISO
One ? ISO
One ? non-ISO
Two e
One e
Other
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Towards Backgrounds Estimations

• Using a loose R-cuts we have a QCD dominated
  sample which we can use to measure the QCD slope,
  as a function of R-cut, in the low MR region
• Can do this in any box with QCD population in
  low MR

12
Towards Backgrounds Estimations

• Using a loose R-cuts we have Wjets dominated
  samples (single lepton boxes) which we can use to
  measure the W slope, as a function of R-cut, in
  the medium MR region (range depending on R-cut)
• Can do this in several different boxes, with
  several different R-cuts
• MC predicts same exponential slope for W/Z/topX
  - dont need to assume this though

13
Towards Backgrounds Estimations

• Using a loose R-cuts we have top dominated
  samples (opposite flavor lepton boxes) which we
  can use to measure the ttbar slope, as a function
  of R-cut, in the medium MR region (range
  depending on R-cut)
• Can do this in different boxes, with several
  different R-cuts

14
Discovery Potential
3? Observation
5? Discovery
Here, we look at estimated sensitivity for a PF
Jets based search, doing a counting experiment
and estimating systematic uncertainty assuming
ratios of events in control regions to signal
region (conservative estimate) Sensitivity
comparable for each jet type considered
14
14
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Outlook

• SUSY search using variables MR and R appears to
  have good potential for SUSY discovery -
• Simple analysis defined in a fully inclusive way
  (with variables that are independent of certain
  topological considerations)
• Construction of variables allows us to control
  background shapes - can easily evolve analysis as
  a function of integrated luminosity
• Work on background estimation techniques
  underway - with mutually exlusive box definitions
  we will be able to over-constrain the relevant
  backgrounds
• Immediate TODO
• Analysis note nearly complete
• Additional jet types and MET types also (JPT,
  uncorrected jets, calo MET, tcMET) to be added
  for parallel analyses/cross-checks
• Analyze full available data-set
• Sensitivity estimations to be updated with
  final analysis when converged

16
BACK-UP SLIDES
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SUSY dijets

• Lets consider a SUSY di-jet final state
  topology where two squarks are produced and each
  decay to a quark and an LSP

x
z
For the moment we neglect any potential
transverse boost to the entire di-squark system
(from ISR for example)
18

• We define the variable MR as ( j1 and j2 are
  quark jets from previous slide)
• It is like a 1D analogue of the invariant mass,
  along the z-axis
• It is invariant under longitudinal boosts
• See paper for more details on its derivation

arXiv1006.2727v1 hep-ph
19
Properties of

• Returning to the di-squark example, if
  (the squarks are produced exactly
  at threshold) then
• We find that, even if deviates
  from 1 (which it will in practice) that MR still
  peaks
• For QCD di-jets (assuming no
• mis-measurements, no pt to dijet
• system etc.)
• Conceptually, we expect to see a
• peaking signal over a steeply falling
• background

20
The Razor

• Unfortunately, the rate of QCD (even at high
  ) is prohibitively high such that we will not
  be able to observe this signal without some
  additional discriminating variable(s)
• Such a variable is the Razor, denoted and
  defined as( )
• behaves similarly to the stransverse
  mass or , such that if .
  Then has a kinematic
  endpoint at
• Hence, similarly to or , we take the
  ratio of two variables with dimension mass (or
  energy if you prefer) and cut on a scale-less
  variable.

21
Properties of

• As defined, MR is very robust against jet
  mis-measurements, especially catastrophic
  under-measurements of jets energy
• This is because it is, in a sense, a geometric
  average of the two jets momentum
• The large transverse momentum imbalance that can
  result from jet mis-measurements or jets falling
  outside of phase-space acceptance, or unclustered
  energy - which can result in potentially large
  missing ET - is largely protected against by the
  use of the Razor. MTR and MR measure the same
  scale, but are also largely uncorrelated
• Rather than demonstrating this analytically, we
  will see some of these properties illustrated in
  these slides

22
Generalizing to an inclusive environment

• Up until this point, we restricted ourselves to
  a 2 jet final state. For a number of reasons we
  would like to generalize to a multi-jet (or even
  fully inclusive) final state
• final state radiation will occur, and is
  something we dont really capture in our current
  MC samples
• For better or worse, if nature includes SUSY
  then we shouldnt restrict ourselves to looking
  for right-handed squarks decaying directly to
  LSPs
• To do this, we will take all the jets (or all
  the objects) in our final state and group them
  into two mega-jets, or hemispheres
• In the following examples, we do this my
  minimizing the invariant masses of the two
  hemispheres
• We have studied several other hemisphere
  algorithms, and find that these results are not
  sensitive to this choice (since all the
  algorithms get the assignments often wrong anyway)

23
Toy examples

• What were our two jets are now two hemispheres,
  and MR is defined as before with this
  substitution (hemisphere masses set to zero, like
  jets)
• To understand what should happen to MR in a more
  general class of scenarios, we consider 3 toy
  examples
• (A) production of two different heavy particles
  with
• (B) production of two identical heavy particles,
  with one decaying through the lighter massive
  particle and then to jetLSP
• (C) Both identical heavy particles decaying like
  this

A
C
B
24
Pythia vs. ALPGEN QCD Modeling
DATA
Pythia QCD
ALPGEN QCD

• For multi-jet analyses - especially those which
  rely on the angular correlations between jets -
  Pythia is NOT reproducing the observed data,
  qualitatively OR quantitatively

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Calo Jet Analysis
Normalized to 10 pb-1
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Calo Jet Analysis
Normalized to 10 pb-1
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Calo Jet Analysis
Normalized to 10 pb-1
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Calo Jet Analysis
Normalized to 10 pb-1
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Calo Jet Analysis
Normalized to 10 pb-1
30
Calo Jet Analysis
Normalized to 10 pb-1
31
Calo Jet Analysis
Normalized to 10 pb-1
32
Track Jet Analysis
Normalized to 10 pb-1
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Track Jet Analysis
Normalized to 10 pb-1
34
Track Jet Analysis
Normalized to 10 pb-1
35
Track Jet Analysis
Normalized to 10 pb-1
36
Track Jet Analysis
Normalized to 10 pb-1
37
Track Jet Analysis
Normalized to 10 pb-1
38
Track Jet Analysis
Normalized to 10 pb-1
39
PF Jet Analysis
Normalized to 10 pb-1
40
PF Jet Analysis
Normalized to 10 pb-1
41
PF Jet Analysis
Normalized to 10 pb-1
42
PF Jet Analysis
Normalized to 10 pb-1
43
PF Jet Analysis
Normalized to 10 pb-1
44
PF Jet Analysis
Normalized to 10 pb-1
45
PF Jet Analysis
Normalized to 10 pb-1
46
MC samples

• NLO x-sections from https//twiki.cern.ch/twiki/b
  in/viewauth/CMS/StandardModelCrossSections used
  when available for backgrounds, otherwise LO
  x-sections returned from generator
• Samples those listed in
• https//twiki.cern.ch/twiki/bin/view/CMS/Product
  ionSummer2009at7TeV
• PYTHIA QCD, LM signal points, di-bosons, QCD
  di-photons
• MADGRAPH Single top (s-chan,t-chan, tW), ttbar,
  W(l?)jets, Z(ll)jets, Z(??)jets, ?jets
• ALPGEN QCD (beginning to look at other bkg)