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Managing Multilepton Topologies: the Tau Trouble & a Concrete Proposal Sunil 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 Rutgers University, New Brunswick, NJ Sunil Somalwar 1 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 Thomas arXiv:0808.1605 (Scott Thomas yesterday) Rutgers University, New Brunswick, NJ Sunil Somalwar 2 “Channels” : Theory vs Expt •For experimentalists: Number of leptons 3, 4 or more Flavor of leptons e or mu Lepton 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 leptons Flavor of (parent) leptons (tau in particular) Rutgers University, New Brunswick, NJ Sunil Somalwar 3 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”.) Rutgers University, New Brunswick, NJ Sunil Somalwar 4 Now Need A Model Model for the “observed” signal (for PRL purposes…) (mSUGRA) PRL 101, 251801 (2008). t – tight lepton, l – loose lepton, T – (isolated) Track Rutgers University, New Brunswick, NJ Sunil Somalwar 5 Expt.Channels PRL (via a Rather Messy Scenario) sigma*BR vs Model Expectations Contours (1st mSUGRA) tan(beta) =3. CDF 2fb-1 Trilepton PRL 101, 251801 (2008) Rutgers University, New Brunswick, NJ Sunil Somalwar 6 Not a Pretty Scene Tom Banks: “Nice work, Sunil, but we already know that mSUGRA does not describe Nature.” Rutgers University, New Brunswick, NJ Sunil Somalwar 7 The 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?” Rutgers University, New Brunswick, NJ Sunil Somalwar 8 What We Did After CDF Trileptons Experimental [σB] is model-dependent because of acceptance. N [B] LA N : Observed signal (excess over SM in several experimental channels) L: Luminosity A: 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. Rutgers University, New Brunswick, NJ Sunil Somalwar 9 How does it help? The signal is spread across four t channels, and not always in a simple way. n N L Bi Ai i1 Rearrange: 1 n L Ai ( )Bi i1 N But, [σB]i = N/Lai, so 1 XM Rutgers University, New Brunswick, NJ Bi [B]i i Sunil Somalwar 10 How does it help? 1 XM Bi [B]i i 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 XM (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.) Rutgers University, New Brunswick, NJ Sunil Somalwar 11 An 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= 1t:(e/m)(e/m)t A1= 2t:(e/m) tt A2= 3t:ttt A3= 11% 5% 3% 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 . Rutgers University, New Brunswick, NJ Sunil Somalwar 12 Example (contd): Theorist Side Theorist 1: tan(beta) = 2 etc, has = 1.25 pb & BR’s B0=20%, B1=B2=B3=0 XM (1/XM) = (20%/0.27pb) + 0 + 0 + 0 XM = 1.35 pb 1 Bi [B]i i Compare to theory = 1.25 pb (Consistent) Theorist 2: tan(beta) = 8 etc, has = 5 pb & BR’s B0=10%, B1=30%, B2=30%, B3=20% (1/XM) = (10%/0.27pb) + (30%/0.6pb) + (30%/1.0pb) + (20%/2.1pb) XM = 0.8 pb Compare to theory = 5 pb (Ruled out) Rutgers University, New Brunswick, NJ Sunil Somalwar 13 Towards Model-independence Part 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.) Rutgers University, New Brunswick, NJ Sunil Somalwar 14 mSUGRA Simple Topology 1. 2. 3. 4. Approximations begin Having a variety of topologies will be extremely useful. Had to do some underhanded things at the Tevatron 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) Rutgers University, New Brunswick, NJ Sunil Somalwar 15 A 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) Rutgers University, New Brunswick, NJ Sunil Somalwar 16 A 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/pubarchive/0901 Good to 20-30% in the validity range Rutgers University, New Brunswick, NJ Sunil Somalwar 17 CDF Published vs “Model-Independent” CDF arXiv:0808.1605 1 XM Bi [B]i i & parameterized simplified topology Rutgers University, New Brunswick, NJ Sunil Somalwar 18 Turning 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. Rutgers University, New Brunswick, NJ Sunil Somalwar 19 A 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) COMMON SLHA 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 = (BA) (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. Rutgers University, New Brunswick, NJ Sunil Somalwar 20 How will a theorist use the results? Back-of-the-envelope Theorists Identify a published topology that is closest to your topology Input BR’s into the spreadsheet utility Compare theory and experimental cross section Enterprising (Simulation-Savvy) Theorists Run on published (simple) topologies SLHA 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. Rutgers University, New Brunswick, NJ Sunil Somalwar 21 Exclusive 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 … 1 Bi Monolepton Jets without leptons XM [B]i i (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 (Bi)’s. Rutgers University, New Brunswick, NJ Sunil Somalwar 22 Conclusions 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. Rutgers University, New Brunswick, NJ Sunil Somalwar 23