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Testing the Standard Model: A History and Rationale for Signature-based Searches Henry J. Frisch Enrico Fermi Institute OUTLINE • Some History (CDF-centric) • Rationale(s) • 4. My goal- thoughtful discussion of issues • 5. Exptl and Theoretical Consequences Apologies- Something of a rant after just getting 3 papers through the CDF Godparenting process- there is a deep diffence in opinion of how we (we_all) should spend our time. BUT still the best game in town…
Brief History • Run I- eeggmet event led to search for `cousins’ in gg+X and lg+X • Run I- Dave Toback Ph.D thesis on gg+X Jeff Berryhill Ph.D thesis on lg+X (2.7s) • Run I- Ray Culbertson gbj+met- ??? • Run II – Andrei Loginov Ph.D thesis on lg+X • Run II – gg+X- GMSB-optimized search Eunsin Lee thesis; Dave Toback, Ray Culbertson, Sasha Pronko, Max Goncharov • Run II- Irina Shreyber lgb+X; ttbar+g • Run II- Shin-Shan Yu, Dan Krop, Ray Culbertson, Carla Pilcher, Scott Wilbur, HJF- gbj +X • Run II- Georgios Choudalakis, Ray Culbertson, Conor Henderson, Bruce Knuteson- VistaSleuth: arXiv:0712:253402 (`Industrial Strength’ sig. searches)
SOME OF OUR COMMUNITY HAVE DISCOMFORT WITH HAVING NO BSM MODEL AS MOTIVATION- ``cite SOMETHING, ANYTHING” • Examples from recent b-quark+gamma +met “Is consistent with possible BSM signature”? HUH? ”One would hope that there are some models for new physics that.. could place limits on..” SOME?
Rationale(s) for SM emphasis • Have a robust and predictive hypothesis to test- the Standard Model- testing it is classic science. • Emphasis should be on understanding and improving the detector performance on SM predictions- time spent elsewhere is very costly (zero sum game for time and $ ) • Exptl papers dependent on a model do not age well- 20 years later one could use the data, but the comparisons with models are junk, and diminish the paper (e.g Trion-ProtoDynamics) • Particle theorists do it better- experimentalists should concentrate on communicating results to them and working together • Students learn the wrong lessons from poorly-motivated limit setting- complacency on $,time
HEP Searches* One of the best young CDF physicists asked me `How are discoveries made? I’ve never seen one…’ • J/Psi at BNL (LML,PJL story) • Neutral Currents at BNL (twice) • Neutral Currents at E1A Fermilab • Top at UA1 • SUSY at UA1 • J/Psi at Wideband Photon at Fermilab • And many others (young CDF’ers don’t know what they’re missing!) Point is to discover, not to set limits- so, what are the right strategies? * Me too- KL->mm
Finding what you expect, and not finding what you don’t Lederman and 1971 J/Psi Rubbia and the 1984 Top Discovery Unexpected and so Not Found Expected and so Found
Announcement of the 1986 UA1 SUSY Discovery (Aspen 1986) Expected and so Found (?!) Shot down by Steve Ellis- `cocktail’ of SM processes
Our Own Saga at CDF Run I Unexpected- but fired >30 (?) triggers- electron, met, photon, Z, …. First explicit signature-based search at CDF grew out of one event-the `eeggmet’ event
Are There Cousins to the eeggMet Event?(with D. Toback, J. Berryhill, R. Culbertson) • Idea- likely other related signatures from other decay chains- e.g. if this is due to C2C2, maybe there is C2N2 production ending in 2 gammas+ 1 lepton, or N2N2 ending in 2 gammas +met (hence `cousins’- signatures related by BR’s) • Two obvious ways to slice the eeggmet signature- • 2 gammas +X (2 neutral parents) • Electron-gamma+X (1 neutral 1 charged) • Look in these signatures, as well as mmggmet+X first explicit signature-based searches at cdf
The eeggmet event and the ggmet signature Observed SM expect. D. Toback Ph.D Thesis Univ. of Chicago Dec. 1997 PRL 81, 1791 (1998) PRD D59,092002 (1999) Plot of Data vs SM expect. Limits on models Which are more useful now? Eeggmet event
The eeggmet event and the lgmet signature J. Berryhill Ph.D thesis Univ. of Chicago Dec, 2000 PRL 89,041802 (2002) Phys Rev D66, 12004 (2002) Observed SM expect.
Run II eeggmet Event Followup: lg+X In g-l+X we found a 2.7s excess over SM. What to do? Decided to repeat the analysis in Run II with the SAME (published) cuts so it’s A PRIORI. Only way to test. Note- NOT optimized for GMSB, etc.. (!). CDF Run I PRL: ..”an interesting result, but … not a compelling observation of new physics. We look forward to more data…”
Run II eeggmet Event Followup Andrei Loginov repeated the lgmet analysis- same cuts (no optimization- kept it truly a priori. Run II: 929 pb-1 at 1.96 TeV vs Run I: 86 pb-1 at 1.8 TeV
Run II-Searching for SM ttbar+ g Irina Shreyber and Andrei: added the requirement of a b-quark: e or m, g, b+X (nice channel for BSM) Then ask for >=3 jets+ large Ht to look for SM radiative top decays: ttbar+ g
Ttbar+Gamma: Adding a b-quark, >=3 jets, and large Ht No suprises- nothing really heavy, wild, or odd- to be submitted to PRD shortly: Consistent with ttbargamma =0.15+-0.08 pb (tiny!) Small cross-section
Run I: Eeggmet event and the gbjmet signature Gordy Kane suggested looking for C2N2-> stopbgN1->bcgmet • This was a priori- selected cone=1.0 for dijet mass from UA2 W ->jj detection • We got excited (even Gordy)- but data not robust to changing cuts, and too little statistics to be sure… BUMP
Run I: gbjmet signature cont. Different cone sizes: a) not robust; b) kinematic edge? D3-body vs 2-body mass- bump and outliers- odd? (or not)
Run II- the gbjmet signature • Dan Krop, Shin-Shan Yu, Carla Pilcher, Scott Wilbur, Ray Culbertson, HJF • Look at the same 2 plots with >20 times the data NO BUMP As Sasha Paramonov would say, `Alas’ (`worse than losing a girl-friend’) Just submitted to PRD arXiv:0905.0231
Run II- the gbjmet signature We observe 617 Events- expect (SM) 607 (too good) Can tighten selection beyond Run I to go to smaller crosssections
Run I: Other Odd Events with Photons and Leptons Just one example • Z-boson to mu-mu balanced by a 200 GeV-Pt photon (presumably) 2 legs of the Z (!) 200 Gev Photon
Run II: Search High Pt Z+X Look at a central Z +X, for Pt > 0, 60, 120 GeV, and at distributions… Need SM predictions even for something as `simple’ as this… (not easy-ask Rick)
Signature-Based High Pt Z+X Searches PTZ>0 PTZ>60 PTZ> 60 PTZ>120 Njets for PTZ>0, PTZ> 60, and PTZ>120 GeV Z’s vs Pythia (Tune AW)- this channel is the control for Met+Jets at the LHC (excise leptons – replace with neutrinos).
Z+X+anything Signature-Based High Pt Z+X+Y Simple Counting Expt- ask for a Z + one object, or Z+ 2objects Two Objects One Object Z+X+Y+anything Z+X+anything
Signature-based W/Z+Njets Search Crossection vs number of jets in W and Z events % uncertainty vs number of jets in W and Z events So, switch to a measurable that is more robust: look for new physics by precise measurements of (W+Njets)/(Z+Njets). Systematics at few % level (PRD68,033014;hep-ph/030388
Return to Rationale(s) • Have a robust and predictive hypothesis to test- the Standard Model- testing it is classic science. • Emphasis should be on understanding and improving the detector performance on SM predictions- time spent elsewhere is very costly (zero sum game for time and $) • Exptl papers dependent on a model do not age well- 20 years later one could use the data, but the comparisons with models are junk, and diminish the paper (e.g Trion-ProtoDynamics) • Particle theorists do it better- experimentalists should concentrate on communicating results to them and working together • Students learn the wrong lessons from poorly-motivated limit setting- complacency on $,time
Return to Rationale(s) Can hide all kinds of physics here … 60mb X 4 fb-1 = 2.4 1013 SM events- looking for ~10. Parts per 1012 Factor of 105 is rejected before data even go to tape Rationale 1- Testing the SM- a trigger-person’s view. Have a perfectly good model to test! Don’t assume you know what it looks like here
Tuning MC, Sim Rationale 2- Improving Detector Performance Rick Field UEV- Willis Sakumoto pttune <20 Amazing agreement W,Z to e,mu (Sasha)
Return to Rationale(s) Rationale 2- Improving Detector Performance from comparisons with SM control samples, single particles, etc. (vs time spent on limit-setting) Fake muons (Sasha) Fake photons (Andrei) Developing Tools
Return to Rationale(s) Rationale 3- Experimental papers that are built on a specific model and parameter values- don’t age well. I didn’t want to cite specific examples- you’re welcome to find your own among the SUSY limits from the early days. There are of course exceptions- we shot down the Constituent Interchange Model, and very general or well-tested models (e.g. the SM model) are of course worth testing NUF SAID
Communicating results of signature-based searches to Theorists Proposal (R. Culbertson et al, Searches for new physics in events with a photon and b-quark jet at CDF. Phys.Rev.D65:052006,2002. hep-ex/0106012)- Appendix A: 3 Ways: A. Object Efficiencies (give cuts and effic. for e, mu, jets,b’s. met,…. B. Standard Model Calibration Processes (quote Wg, Zg, Wgg in lgmet,e.g..) C. Public Monte Carlos (e.g. John Conway’s PGS) True Acceptnce Ratios to True (ABC) Comparison of full MC with the 3 methods: Conclusion- good enough for most applications, e.g. limits… Case for gamma+b-quark+met+x (good technisig)
Return to Rationale(s) Rationale 4- Particle Theorists can often test their own models more productively than some student, and should. My main point is that there are exptl tasks that need doing, including exploring other channels and making other measurements; running the detector, inventing new detectors,… Many consequences (needs discussion by PTB)- including funding particle theory separate from string theory, supplementing funding particle theory from exptl funds,…
Return to Rationale(s) Rationale 5- Passing on the culture of time is $
The End- Thank you, and apologies for some curmudgeonliness