Transcript Slide 1
MR draft
SUSY Hadronic/GMSB Meeting 26-08-10
Christopher Rogan
California Institute of Technology
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, HWW meeting 28-5-10 or
backup slides or
arXiv:1006.2727v1 [hep-ph]
Log(N)
Log(N)
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
SIG
x
SIG SIG
x’
Christopher Rogan - SUSY All Hadronic/GMSB Meeting 26-08-10
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Kinematic Variables for SUSY
Two variables designed to be used together for discovery
and characterization of SUSY
arXiv:1006.2727v1 [hep-ph]
Doesn’t 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 wellunderstood way - the Razor
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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):
Corrected Calo jets
Loose jet ID
Corrected PF jets
Loose jet ID
Uncorrected Track jets
Only high quality tracks
w/ vertex consistent
with reco PV considered
for clustering
NO explicit lepton/photon reco or ID in constructing these variables
If > 2 reco jets, form two hemispheres by minimizing invariant masses
added in quadrature (see back-up slides)
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PF jets
The Razor in practice
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)
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PF jets
The Razor and MR
DATA behaves as
expected
Backgrounds fall ~exponentially after exceeding relevant scale (set by process
scale+trigger/reco
requirements) - slope set by R cut
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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
arXiv:1006.2727v1 [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
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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
Christopher Rogan - SUSY All Hadronic/GMSB Meeting 26-08-10
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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
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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:
Two at least one ISO
One e, one ISO
One ISO
Two e
Other
Two , no ISO
One e, one non-ISO
One non-ISO
One e
For a given bkg type, exponential
slope in MR the same in each box
(physics object final state independent)
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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
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Towards Backgrounds Estimations
Using a loose R-cuts we
have W+jets 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/top+X - don’t need to
assume this though
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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
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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
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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
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BACK-UP SLIDES
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SUSY dijets
Let’s 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)
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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 it’s derivation:
arXiv:1006.2727v1 [hep-ph]
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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
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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
Then
has a kinematic endpoint at
)
, such that if
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.
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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
jet’s 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
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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 don’t really capture
in our current MC samples
For better or worse, if nature includes SUSY then we shouldn’t restrict
ourselves to looking for right-handed squarks decaying directly to LSP’s
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)
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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 jet+LSP
(C) Both identical heavy particles decaying like this
A
B
Christopher Rogan - SUSY All Hadronic/GMSB Meeting 26-08-10
C
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Pythia vs. ALPGEN QCD Modeling
Pythia QCD
ALPGEN QCD
DATA
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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Normalized to 10 pb-1
Calo Jet Analysis
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Normalized to 10 pb-1
Calo Jet Analysis
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Normalized to 10 pb-1
Calo Jet Analysis
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Normalized to 10 pb-1
Calo Jet Analysis
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Normalized to 10 pb-1
Calo Jet Analysis
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Normalized to 10 pb-1
Calo Jet Analysis
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Normalized to 10 pb-1
Calo Jet Analysis
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Normalized to 10 pb-1
Track Jet Analysis
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Normalized to 10 pb-1
Track Jet Analysis
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Normalized to 10 pb-1
Track Jet Analysis
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Normalized to 10 pb-1
Track Jet Analysis
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Normalized to 10 pb-1
Track Jet Analysis
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Normalized to 10 pb-1
Track Jet Analysis
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Normalized to 10 pb-1
Track Jet Analysis
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Normalized to 10 pb-1
PF Jet Analysis
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Normalized to 10 pb-1
PF Jet Analysis
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Normalized to 10 pb-1
PF Jet Analysis
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Normalized to 10 pb-1
PF Jet Analysis
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Normalized to 10 pb-1
PF Jet Analysis
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Normalized to 10 pb-1
PF Jet Analysis
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Normalized to 10 pb-1
PF Jet Analysis
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MC samples
NLO x-sections from
https://twiki.cern.ch/twiki/bin/viewauth/CMS/StandardModelCrossSecti
ons used when available for backgrounds, otherwise LO x-sections
returned from generator
Samples those listed in:
https://twiki.cern.ch/twiki/bin/view/CMS/ProductionSummer2009at7TeV
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)
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