Testing the Standard Model: A History and Rationale for Signature-based Searches

1
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
2
Brief History

• Run I- eeggmet event led to search for cousins
  in ggX and lgX
• Run I- Dave Toback Ph.D thesis on ggX
  Jeff Berryhill Ph.D thesis on lgX (2.7s)
• Run I- Ray Culbertson gbjmet- ???
• Run II Andrei Loginov Ph.D thesis on lgX
• Run II ggX- GMSB-optimized search Eunsin Lee
  thesis Dave Toback, Ray Culbertson, Sasha
  Pronko, Max Goncharov
• Run II- Irina Shreyber lgbX ttbarg
• 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
  arXiv0712253402 (Industrial Strength sig.
  searches)

3
SOME OF OUR COMMUNITY HAVE DISCOMFORT WITH HAVING
NO BSM MODEL AS MOTIVATION- cite SOMETHING,
ANYTHING

• Examples from recent b-quarkgamma 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?
4
Rationale(s) for SM emphasis

1. Have a robust and predictive hypothesis to test-
   the Standard Model- testing it is classic
   science.
2. 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 )
3. 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)
4. Particle theorists do it better- experimentalists
   should concentrate on communicating results to
   them and working together
5. Students learn the wrong lessons from
   poorly-motivated limit setting- complacency on
   ,time

5
HEP Searches
One of the best young CDF physicists asked me
How are discoveries made? Ive never seen one

1. J/Psi at BNL (LML,PJL story)
2. Neutral Currents at BNL (twice)
3. Neutral Currents at E1A Fermilab
4. Top at UA1
5. SUSY at UA1
6. J/Psi at Wideband Photon at Fermilab
7. And many others (young CDFers dont know what
   theyre missing!)

Point is to discover, not to set limits- so, what
are the right strategies? Me too- KL-gtmm
6
Finding what you expect, and not finding what you
dont
Lederman and 1971 J/Psi
Rubbia and the 1984 Top Discovery
Unexpected and so Not Found
Expected and so Found
7

Announcement of the 1986 UA1 SUSY Discovery
(Aspen 1986)
Expected and so Found (?!)
Shot down by Steve Ellis- cocktail of SM
processes
8
Our Own Saga at CDF Run I
Unexpected- but fired gt30 (?) triggers- electron,
met, photon, Z, .
First explicit signature-based search at CDF grew
out of one event-the eeggmet event
9
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 BRs)
• Two obvious ways to slice the eeggmet signature-
• 2 gammas X (2 neutral parents)
• Electron-gammaX (1 neutral 1 charged)
• Look in these signatures, as well as mmggmetX

first explicit signature-based searches at cdf
10
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
11
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.
12
Run II eeggmet Event Followup lgX
In g-lX 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 its 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
13
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
14
Run II-Searching for SM ttbar g
Irina Shreyber and Andrei added the requirement
of a b-quark e or m, g, bX (nice channel for
BSM)
Then ask for gt3 jets large Ht to look for SM
radiative top decays ttbar g
15
TtbarGamma Adding a b-quark, gt3 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
16
Run I Eeggmet event and the gbjmet signature
Gordy Kane suggested looking for C2N2-gt
stopbgN1-gtbcgmet

• This was a priori- selected cone1.0 for dijet
  mass from UA2 W -gtjj detection
• We got excited (even Gordy)- but data not robust
  to changing cuts, and too little statistics to be
  sure

BUMP
17
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)
18
Run II- the gbjmet signature

• Dan Krop, Shin-Shan Yu, Carla Pilcher, Scott
  Wilbur, Ray Culbertson, HJF
• Look at the same 2 plots with gt20 times the data

NO BUMP
As Sasha Paramonov would say, Alas (worse than
losing a girl-friend)
Just submitted to PRD
arXiv0905.0231
19
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
20
Run I Other Odd Events with Photons and Leptons
Just one example
2 legs of the Z (!)
200 Gev Photon

• Z-boson to mu-mu balanced by a 200 GeV-Pt photon
  (presumably)

21
Run II Search High Pt ZX
Look at a central Z X, for Pt gt 0, 60, 120 GeV,
and at distributions Need SM predictions even
for something as simple as this (not easy-ask
Rick)
22
Signature-Based High Pt ZX Searches
PTZgt0
PTZgt60
PTZgt 60
PTZgt120
Njets for PTZgt0, PTZgt 60, and PTZgt120 GeV Zs vs
Pythia (Tune AW)- this channel is the control for
MetJets at the LHC (excise leptons replace
with neutrinos).
23
Signature-Based High Pt ZXY
ZXanything
Simple Counting Expt- ask for a Z one object,
or Z 2objects
Two Objects
One Object
ZXYanything
ZXanything
24
Signature-based W/ZNjets 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
(WNjets)/(ZNjets). Systematics at few level
(PRD68,033014hep-ph/030388
25
Return to Rationale(s)

1. Have a robust and predictive hypothesis to test-
   the Standard Model- testing it is classic
   science.
2. 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 )
3. 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)
4. Particle theorists do it better- experimentalists
   should concentrate on communicating results to
   them and working together
5. Students learn the wrong lessons from
   poorly-motivated limit setting- complacency on
   ,time

26
Return to Rationale(s)

• Rationale 1- Testing the SM- a trigger-persons
  view.
• Have a perfectly good model to test!

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
Dont assume you know what it looks like here
27

• Rationale 2- Improving Detector Performance

Tuning MC, Sim
Rick Field UEV- Willis Sakumoto pttune lt20
Amazing agreement
W,Z to e,mu (Sasha)
28
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
29
Return to Rationale(s)

• Rationale 3- Experimental papers that are built
  on a specific model and parameter values- dont
  age well.
• I didnt want to cite specific examples- youre
  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

30
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.D65052006,2002.
hep-ex/0106012)- Appendix A
3 Ways A. Object Efficiencies (give cuts and
effic. for e, mu, jets,bs. met,. B. Standard
Model Calibration Processes (quote Wg, Zg, Wgg in
lgmet,e.g..) C. Public Monte Carlos (e.g. John
Conways 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 gammab-quarkmetx (good technisig)
31
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,

32
Return to Rationale(s)

• Rationale 5- Passing on the culture of time is

33
The End-
Thank you, and apologies for some
curmudgeonliness
34
BACKUP