1 Rutgers University, New Brunswick, NJ Sunil Somalwar Managing Multilepton Topologies: the Tau...

1Rutgers University, New Brunswick, NJ Sunil Somalwar

Managing Multilepton Topologies: the Tau Trouble

& a Concrete Proposal

Managing Multilepton Topologies: the Tau Trouble

& a Concrete ProposalSunil Somalwar

with Sourabh Dube, Julian Glatzer, Richard Gray, Alex Sood and Scott Thomas

(Rutgers)

Characterization of New Physics @LHC Workshop

CERN Nov 5-6, 2010


Outline Outline

• Multilepton complications & an attempt at making CDF trilepton results model-independent• An LHC proposal from the lessons learnt: -- exclusive “theory” channels • Practical realities from working experience

“Addressing the Multi-Channel Inverse Problem at High Energy Colliders: A Model Independent Approach to the Search for New Physics with Trileptons”Sourabh Dube, Julian Glatzer, Sunil Somalwar, Alexander Sood, Scott ThomasarXiv:0808.1605

(Scott Thomas yesterday)


“Channels” : Theory vs Expt “Channels” : Theory vs Expt

• For experimentalists: Number of leptons 3, 4 or moreFlavor of leptons e or muLepton Reconstruction

High Quality: Tight e or mu (could be from a tau) Medium Quality: Loose e/m, 1-prong t as isolated track Low Quality: 3-prong tau’s, possibly jumbled up tau’s

• For Theorists:Number of leptonsFlavor of (parent) leptons (tau in particular)


Expt. Channels Give Observed Signals Expt. Channels Give Observed Signals

CDF 2fb-1 Trilepton PRL 101, 251801 (2008) Exclusive channels:

(t – tight lepton, l – loose lepton, T – isolated track)

Observed minus expected Nobserved signal in each channel• Limit or measurement – No distinction.• No Model so far (although signal now “observed”.)


Now Need A Model Now Need A Model

PRL 101, 251801 (2008). t – tight lepton, l – loose lepton, T – (isolated) Track

Model for the “observed” signal (for PRL purposes…)(mSUGRA)


Expt.Channels PRL(via a Rather Messy Scenario)

Expt.Channels PRL(via a Rather Messy Scenario)

CDF 2fb-1 Trilepton PRL 101, 251801 (2008)

sigma*BR vs Model Expectations Contours (1st mSUGRA)

tan(beta) =3.


Not a Pretty SceneNot a Pretty Scene

Tom Banks: “Nice work, Sunil, but we already know that mSUGRA does not describe Nature.”


The QuestionThe Question• Regardless of the motivation behind cuts, the analysis is done.• N(observed signal) /Luminosity written in stone (in many expt

channels).

• How to map the experimental result onto theory channels?• Theory tau’s show up as e, mu, clean isolated tracks, or as

dirty pencil jets.

• Experimental acceptance is model dependent (specific topology).

• Clean acceptance: kinematics: pt, eta, phi, met, angles..• Dirty acceptance: Isolation, resolution, tails, pileup…

“Just show sigma*BR. Why do you need models?”


What We Did After CDF TrileptonsWhat We Did After CDF Trileptons

Experimental [σB] is model-dependent because of acceptance.

[B] N

LA

N : Observed signal (excess over SM in several experimental channels) L: LuminosityA: Total acceptance = Clean A (kinematic) times Dirty A (isolation etc) Stay in the topology but factorize: Factorize out the “theory” channels

0t:(e/m) (e/m) (e/m) 1t:(e/m)(e/m)t 2t:(e/m)tt 3t:ttt Provide: [σB]0τ, [σB]1τ, [σB]2τ, and [σB]3τ, where,

[σB]0τ = N/LA0τ etc • Same observed signal N is used four times. The topology under consideration is split

into four sub-topologies AT THE GENERATOR LEVEL.• e/mu go together and are fine with the combined treatment.• No approximations so far.

10

Rutgers University, New Brunswick, NJ Sunil Somalwar

How does it help?How does it help?

The signal is spread across four t channels, and not always in a simple way.

Rearrange:

N L Bi Aii1

n

1

(

L AiN

)Bii1

n

But, [σB]i = N/Lai, so

1

XM

Bi

[B]ii

11


How does it help?How does it help?

1. Run a topology 4 times (with generator level cuts) through analysis, calculate acceptances & publish [σB]0τ, [σB]1τ, [σB]2τ, & [σB]3τ.

2. A theorist has her own BR’s (=Bi) (Maybe it is a different tan(beta))

3. Use the equation to combine the experiment and theory to get sXM

(Experimentally measured cross section for the theorist’s model.)

No approximations so far and we took care of the branching ratios.

Branching ratios just an example.

We mapped the experimental result onto theory channels. (Basis or eigen channels that can be recombined with weights.)

1

XM

Bi

[B]ii

12


An Example: Experimental SideAn Example: Experimental Side

Luminosity = 0.1 fb-1, SM expectation=6, observed=9 Observed signal = 3 N/L = (3)/(0.1fb-1) = 30fb [=(σB)A ]

Pick the topology. It has four exclusive “theory” channels. Get acceptances, selecting the channels at generator level.

0t:(e/m) (e/m) (e/m) (generator level) : Full acceptance A0= 11%

1t:(e/m)(e/m)t A1= 5%

2t:(e/m)tt A2= 3% 3t:ttt A3= 1.4%

[σB]0 = (N/L)/A0 = (30fb)/ (11%) = 0.27 pb [σB]1 = (N/L)/A0 = (30fb)/ (5%) = 0.6 pb [σB]2 = (N/L)/A0 = (30fb)/ (3%) = 1.0 pb [σB]3 = (N/L)/A0 = (30fb)/(1.4%) = 2.1 pb

Publish [σB]0, [σB]1, [σB]2, and [σB]3 .

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Example (contd): Theorist SideExample (contd): Theorist Side

Theorist 1: tan(beta) = 2 etc, has s = 1.25 pb & BR’s B0=20%, B1=B2=B3=0

(1/sXM) = (20%/0.27pb) + 0 + 0 + 0

sXM = 1.35 pb Compare to stheory = 1.25 pb (Consistent)

Theorist 2: tan(beta) = 8 etc, has s = 5 pb & BR’s B0=10%, B1=30%, B2=30%, B3=20%

(1/sXM) = (10%/0.27pb) + (30%/0.6pb) + (30%/1.0pb) + (20%/2.1pb)

sXM = 0.8 pb Compare to stheory = 5 pb (Ruled out)

1

XM

Bi

[B]ii

14


Towards Model-independenceTowards Model-independencePart A : Exclusive theory channels

Define (experimental) channels, selection, SM expectations, N(Obs Signal), full acceptance (clean and dirty) for theory channels, and publish (for a given topology):

• [σB]i’s for exclusive theory channels.

• A spreadsheet utility for combining [σB]i‘s and theory BR’s.

Part B: Simplify/generalize topology

• No general solution, approximations and scatter-shot at best.• Cover as many topologies as possible (We didn’t, but LHC can.)

• [σB]i’s get extra mileage out of each topology.

The emphasis here is on Part A: [σB]i’s for exclusive theory

channels. Our topology efforts were rudimentary (but worked out alright.)

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mSUGRA Simple TopologymSUGRA Simple Topology

1. Approximations begin2. Having a variety of topologies will be extremely useful.3. Had to do some underhanded things at the Tevatron4. It is great that we are doing it in an organized/legal fashion

@LHC (Thank you, organizers!)

Here is the simplified model we used for CDF trileptons:• Three mass parameters

• M (Lowest state mass)

• ΔM1 (Upper minus

intermediate mass)

• ΔM2: (Upper minus

lowest state mass)

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A Simple Topology ParameterizationA Simple Topology Parameterization

(M = lowest, ΔM1 =upper – middle, ΔM2: upper – lowest)

• Dependence on M factors out: fi(M)

• No intermediate particle case: [σB]i)-1 = fi(M) * gi(ΔM2)

• One intermediate particle case: [σB]i)-1 = fi(M)*hi(ΔM1,ΔM2)

• Taylor expansions:

fi(M) = 1 + a1(M) + a2(M)2

gi(ΔM2) = b0 + b1(ΔM2) + b2(ΔM2)2

hi(ΔM1,ΔM2) = c0 + c1(ΔM2) + d1(ΔM1) + c2(ΔM2)2 + d2(ΔM1)2 + e2(ΔM1*ΔM2)

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A Simple Topology ParameterizationA Simple Topology Parameterization

(M = lowest, ΔM1 = upper–middle, ΔM2: upper–lowest)

[σB]i)-1 = fi(M) * gi(ΔM2) or fi(M)*hi(ΔM1,ΔM2)

f0(M)

An Excel spreadsheet at:http://www.physics.rutgers.edu/pub-archive/0901

Good to 20-30% in the validity range

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CDF Published vs “Model-Independent”CDF Published vs “Model-Independent”

CDF

1

XM

Bi

[B]ii

& parameterized simplified topology

arXiv:0808.1605

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Turning to LHCTurning to LHC

Scott Thomas and Richard Gray

Also, Sanjay Padhi earlier.

More complicated, but the exclusive theory channel approach, coupled with(possibly parameterized) simplified topology approach, should work.

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A Concrete Proposal for Disseminating ResultsA Concrete Proposal for Disseminating Results

THEORISTS Provide topologies (and sub-topologies). Identify exclusive

channels for each topology (start with Feynman diagrams for subtopologies, or generator level jets, met, # leptons… exclusive signatures)

COMMONSLHA files, possibly LHE.Generation Level Kinematic (Clean) Acceptances (pt, eta, met,

angles…)

EXPERIMENTALISTS(experimental) channels, selection, SM expectations, N(Obs

Signal),full acceptances (clean and dirty) for theory channels, and

publish • Publish N(Obs Signal)/L = (sBA) (very little effort) (Scott)

• [σB]i’s for exclusive theory channels.

• Generation-level clean acceptances (see Common above).

• A spreadsheet utility for combining [σB]i’s and theory BR’s.

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How will a theorist use the results?How will a theorist use the results?

Back-of-the-envelope TheoristsIdentify a published topology that is closest to your

topologyInput BR’s into the spreadsheet utilityCompare theory and experimental cross section

Enterprising (Simulation-Savvy) TheoristsRun on published (simple) topologiesSLHA files Events Generator level cuts Verify the

experimental values of Clean Acceptance Normalize to experiment: Conclude the dirty

acceptance (resolution, isolation etc) and use it as a correction factor

Switch to topology of interest, not necessarily a simple one.

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Exclusive Channels: an Ambitious ExampleExclusive Channels: an Ambitious Example

At the generator level, split the entire SUSY signal of a model 5 or more leptons (e, mu and tau’s), then 4 leptons (0,1,2,3,4 tau’s), then 3 leptons (0,1,2,3 tau’s), then … Same-sign e/mu’s (additional leptons too soft to be above.),

then … Monolepton Jets without leptons(Works short of interference effects) MET, HT, # jets used along the way to build up

signal/background Also: Define sub-channels just for individual lepton/jet

searches Complicated color chains: Each chain a channel (no

interference)

ATLAS and CMS (with theorists) can identify these channels and then each generate channel-tagged MC (CTMC) samples. Multiple analysis groups within both ATLAS and CMS can then produce combinable results in form of exclusive (sBi)’s.

1

XM

Bi

[B]ii

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ConclusionsConclusions

Identify exclusive channels in a model at the generator level. Channel-tagged MC (CTMC) will identify (simpler) constituent topologies within a complicated model and track them all the way through publication and follow-up pheno analyses.

Get much more mileage out of a model/topology by providing sigma*Br’ s for exclusive internal channels.

Doing so makes it easy to combine pieces within and between experiments.

At the very least, easily factorize branching ratios from the multidimensional parameter space for models.

Experiments will always have to deal with the dirty acceptance, but providing generator-level clean acceptance separately will allow enterprising theorists to tune their simulation tools better.

Unrelated: Organizing analyses within the experiment along exclusive (experimental) channels is advantageous.

1 Rutgers University, New Brunswick, NJ Sunil Somalwar Managing Multilepton Topologies: the Tau...

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