The Particle Physics Playbook

Konstantin Matchev

This talk will not contain• Predictions of what new physics CDF might discover• The latest new physics models

– See talks from LHC conference at Santa Barbara• The latest advances in NLO calculations

– See talks from LHC conference at Santa Barbara – Come to F. Petriello’s talk on Wednesday morning

• The model I have recently been working on– But in case you are interested:

UMSSM = NMSSM + U(1) + + exotica• Interesting features of UMSSM

– Z’ gauge boson and Z’-ino neutralino– Scalar LSP: right-handed sneutrino dark matter– TeV scale colored exotics– Z3 discrete symmetries

• B3 (leptophobic Z’), L3, M3

– R-parity violation– Stable proton

Lee,KM,Nasri 2007

Lee,KM,Wang 2007

Luhn,Lee,KM 2007

Kang,Langacker,Nelson 2007

This talk will contain• Jokes• Homework assignments• General classification of new physics signatures

– Bump hunting– Bean counting

• Review of (some) existing techniques for precision measurements at hadron colliders– Mass measurements– Spin measurements

• Opportunities to do such measurements with existing Tevatron data

• The discussion will be signature-based and largely model-independent

• Useful “theorems”

What do we do for a living?• Look for new particles. How?

- Full reconstruction (bump hunting)- Backgrounds can be measured from data- Easy to do mass, width measurements- More likely to be done with early data

- Excess of events (bean counting)- Prone to systematic errors- Difficult to measure particle properties- Less likely to be done with early data

• It is worth thinking about bump hunts first!• It is possible to give an exhaustive and systematic

classification of all resonance searches

Run IIV. Shary CALOR04

Classification of resonance searches

• How many resonances per event? (1 or 2)• How many objects does the resonance decay to? (2,3,4,…)• What are those objects?

Note the absence of a “Missing energy calorimeter”

List of all di-object resonances

• The scheme can be generalized to – three body decays etc.– pair-production etc.

e jet b Z’ LQ LQ W’

e Z’ LQ LQ W’

h

jet Z’ LQ

b h LQ

h W’

-

‘Z’, ‘t’, ‘W’…

• A single resonance decaying to 3 objects (inclusive)

• Pair production of resonances

• Such searches are very model-independent• To summarize - just ask:

– How many new resonances are present in each event?– What did each one decay to?

More complicated topologies

Homework • (Warm-up exercise) Classify all existing CDF new physics

(and Higgs) searches according to this scheme. • Notice if there are any remaining empty slots. Can you think

of any reason why such a resonance should not exist?– If “yes”, report to me and/or the Theory Group– If “no”, then proceed to next step.

• Think of a model where such a resonance would exist. (Ask your theory friends for help.)

• Is there a good reason why CDF is not looking for such a resonance? – If “Yes”, go back to previous step.– If “No”, proceed.

• Is D0 looking for it? If yes, talk to D0. If no, proceed. • Are ATLAS/CMS going to look for it? If yes, talk to them. If

no, proceed.• If you got here, talk to your physics coordinator.

Useful Theorems• Hinchliffe’s theorem:

If the title of a paper is in the form of a “Yes/No” question, the answer is always “No”– Corollary: “If the abstract of the paper claims the answer is “Yes”,

the paper is wrong and should be rejected”• Folk theorem:

If you ask a theorist a question starting with “Is it possible to have a model where [I get signature X]?” the answer is always “Yes”– Exception: Signature X violates some fundamental conservation law

(e.g. charge conservation, Lorentz invariance etc.)– Corollary: CDF should be on the lookout for all allowed signatures.

• Some “easy” examples– e resonance– trilepton resonance

SUSY and R-parity Violation• What is R-parity?

– SM particles: +1– Superpartners: -1

• Who needs R-parity?– Proton decay– Dark matter

• What if R-parity was violated?– Superpartners will still decay down to the LSP– The LSP will decay to SM particles (resonance?)– The LSP does not have to be neutral(ino)!

R-parity Violation• Baryon number violation:

WBV = ijk Ui D[j Dk]

• Lepton number violation:

WLV = ijk Li Qj Dk + ijk L[i Lj] Ek

iU~

jD

kDjD~ iU

kDkD~

iU

jD

iL~

jQ

kDjQ~ iL

kDkD~

iL

jQ

iL~

jL

kEjL~ iL

kEkE~

iL

jL

Signatures of R-parity Violation

• 2 LSP’s per event, large cross-sections• The leptons may be different flavor

LSP UDD LQD LLE

0 3j ljj,jj ll

gluino 3j ljj,jj jjll

squark 2j lj jll

slepton ljjj 2j l

sneutrino jj 2j ll

chargino* 3j ljj,jj 3l

Midpoint summary

• Look for all possible resonances

• R-parity violation: SUSY under the lamppost– Large rates from

squark/gluino production

– Resonances from LSP decays

– Hard leptons if LV• LQD, LLE

Missing energy signatures

• Motivated by the dark matter argument• Inevitable model dependence• No resonances• Follow the general classification:

– How long was the cascade?– What were the emitted SM particles?

• What can we measure? Mass? Spin?

Missing energy signatures

e jet b W W W

e

jet

b t t t

AB

a

C

b

a

b• Can be extended to longer cascades

• Two such cascades per event

• Repeat the previous homework

• Can we measure the mass/spin of A,B?

Mass measurements

• Single semi-invisibly decaying particle

• Use the transverse mass distribution

2222 ),( TeTTeTTW ppppemM

We

Mass measurements

• A pair of semi-invisibly decaying particles

• Use the “stransverse” mass (MT2)

2222 ),( TeTTeTTW ppppemM

W

e

W

Kong, KM• This formula is valid for m=0.

Lester,Summers 99Barr,Lester,Stephens 03

Homework

• Use MT2 to measure the W mass in dilepton W pair events

• Use MT2 to measure the top quark mass in dilepton tt-bar events

Cho,Choi,Kim,Park 2008

SUSY or UED?• Folk theorem:

Any signals of new physics can be explained with some SUSY model

• A more recent theorem

Any SUSY signature can be faked by some UED or Little Higgs model– Corollary: Any signal of

new physics can have alternative explanations unless we can measure spins

• KK masses at one-loop

Cheng,KM,Schmaltz 2002

Only the LKP is stable.The LKP is neutral (DM!)

Model discrimination/Spin determination

• What is the nature of A,B,C,D?– Find $N,000,000,000 and build an ILC– Find the momentum of A, fully reconstruct the event– Study m2 distributions of visible particles

• The distributions depend on– Spins of A,B,C,D– Masses of A,B,C,D– Chirality of couplings– Initial state (particles vs antiparticles)

• Most spin studies compare two sets of spin assignments, but fix everything else

• That is not a true measurement of the spin

Battaglia,Datta,DeRoeck,Kong,KM 05

Cheng,Engelhardt,Gunion,Han,McElrath 08Athanasiou et al 06, Kilic,Wang,Yavin 07,

Csaki,Heinonen,Perelstein 07, S. Thomas (KITP)

“SUSY” vs “UED”

• Mass spectrum {A,B,C,D}={1000,600,420,210} GeV

Burns,Kong,KM,Park 08

Homework• Consider dilepton WW events and try to

discriminate the following alternatives:– W pair -> 2 leptons + 2 neutrinos, – Slepton pair -> 2 leptons + 2 neutralinos– Chargino pair -> 2 leptons + 2 sneutrinos– KK lepton pair -> 2 leptons + 2 KK photons

• Consider dilepton top pair events and try to discriminate the following alternatives– t -> b W -> b+lepton+neutrino– t -> b H+ -> b+lepton+neutrino– stop -> b chargino -> b+lepton+sneutrino– KK top -> b KK W -> b+lepton+KK neutrino

A positive note• Clean multilepton + MET events in

SUSY– 3 leptons: gold plated mode– 4 leptons: platinum plated?– 8 leptons: ???

• What is the max number of leptons?

hino

qL

lL

lR

wino

bino

qL

q

wino

l

bino

l

lL hino

ll

lR

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• Check out the MC4BSM workshops– Fermilab 2006– Princeton 2007– CERN 2008

Summary

• Think about model-independent signature based searches.– Resonances– Missing energy

• Ask for the theory model later.• Think of ways to test the proposed

methods for precision measurements at the LHC (masses, spins etc.) with existing Tevatron data.

• Do the homework.

BACKUP SLIDES

How do we know LHC will find anything new or interesting?

• The X7 argument • Where is the Higgs?