“Linear Collider” conference Tsinghua, July 17, 2005

Mike Bisset / 毕楷杰Tsinghua University

Beijing, China

plusa bit more

MUED’s Minimal universal extra dimensions

All SM fields propagate in a single compactified extra dimension

with compactification radius near the TeV scale

All SM particles have KK partners with similar couplings

The lowest KK level particles carry a conserved quantum numberKK-parity

The lightest KK particle is the stable LKP

The LKP is not detected, resulting in a missing energy signal.

(lowest energy states in the Kaluza-Klein towers)

Sounds a lot like the MSSM, no?

First consider something that is NOTNOT supersymmetry ---

H.-C. Cheng, Matchev & Schmaltz hep-ph/0205314

Distinctions between the MSSM and MUED’s

Sparticles have different spins from their SM partnerswhile KK particles have the same spin

This would certainly be testable at a LC, but at the LHC maybe not

There is no analog to the heavier MSSM Higgs bosons

The KK partners to the Higgs carry KK-parity, and so should be pair produced (behaving more like Higgsinos than like Higgs bosons)

Smillie & Webber hep-ph/0507171

Barr, hep-ph/0405052limited attempts:

So we see detection of the heavier MSSM Higgs bosons

is crucial for even being sure that we are seeing

SUPERSYMMETRY

How well can we do at the LHC?

ATLAS TDR

only detect h‘‘decouplingdecoupling regime’regime’

the

BUT depends on good

detection capabilities

for b’s and tau’s

only detect h

LEP II excluded

, ,A H H

signals

Depends on good

detection capabilities

for b’s and tau’s

only detect h

, muonsH A

Gold-plated signal

LEP II excluded

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the preceding does not take into account possible Higgs boson decays into sparticles

BUTBUT

0 0 *, , , , ,i j i jh H A 0 ,i jH

On the bad side…

On the good side…

decays to these channels reduce the rates of SM signal channels

new signals may be found

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0 0 0 02 2 1 1, i i j jH A

4 leptons + signatureE

But if such a signal is observed,But if such a signal is observed, is it really from this decay chain?is it really from this decay chain?

(assumption in several studies thus far)

(2 OS same-flavor pairs)

OneOne channel that has received some attention is:

M

(Ge

V)2

tan 5 , BR , 4 inPP H A H A N fb

1 20.5M Mfrom

gauginounification

400AM GeV

500AM GeV

600AM GeV

light sleptons

M

(Ge

V)2

tan 10 , BR , 4 inPP H A H A N fb 400AM GeV

500AM GeV

600AM GeV

2M

(G

eV

)

tan 20 , BR , 4 inPP H A H A N fb 400AM GeV

500AM GeV

600AM GeV

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Now what about non-Higgs boson ‘backgrounds’?

hello

in mSUGRA

, BR , 4 inPP H A H A N fb

1sign 0 0A

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Now what about non-Higgs boson ‘backgrounds’?

hello

Dependence on sleptons

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Now what about non-Higgs boson ‘backgrounds’?

hello

Now what about non-Higgs boson backgrounds?

SM backgrounds can be eliminated mainly through

TE cut coupled with 4 final state

Other SUSY processes?

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Now what about non-Higgs boson backgrounds?

Look at processes of the type

Let’s try to think more generally for a while …

1 1 2 2stuffp p X X f f f f

other stuff

Pair production of new heavy states

Decay to SM fermion pairs

Required by some new symmetry of the SM extension

e.g.’s: R-parity in SUSYconservation

ZZ22-symmetry in little Higgs models FCNC

KK-parity in MUED’s

?X T-parity

Hubisz & Meadehep-ph/0411264

MSSM with R-parity conservation

LSP is stable and invisible01

1 1 2 2stuffp p X X f f f f E other stuff

Here we take

a decaying neutralino X (-ino for short)

0 0 02 3 4, ,

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清华大学At LHC, can have

0 02 3

0 02 4 0 03 3

0 03 4

0 02 2 1 1 2 2production f f f f E other

stuff

but also

0 04 4

How much of each?

Depends on parameters of the model

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LHC will also have lots of SM QCD backgrounds

a nice choice is to take &1f e2f

(assuming –ino leptonic BRs adequate)

Alternatives: 0, , ,b Z W

( , 1)

0 0 stuffi j

p p e e Ei j

other stuff

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清华大学Facts of life at the LHC:

At hadron collider, cannot set energy for the parton-level processunlike at a linear collider where one can scan up incrementally in to cross each threshold sequentially one at a time

e e

cmE0 0i j

0 0i j So just must deal with different states

being produced simultaneously at different rates

Need to disentangle these

Production modes:

‘direct’ Higgs-mediated colored-sparticle cascade decays

Rates generally small

Rates may be large if heavier MSSM Higgs bosons

are in the right zone

Largest potential ratesdue to strong production cross-sectionsEspecially if gluinos (and squarks) are relatively light.

0 0 0, (but not )H A h

400 500 GeVgm

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Study such processes at the LHC

via a technique reminiscent of

DalitzDalitzPlotsPlots

Though disappearing LSP precludes looking for resonance bumps, we can look for endpoints.

R.H. Dalitz Phil. Mag. 44 (1953) 1068 E. Fabri Nuovo Cimento 1 (1953) 479

Dalitz plotsDalitz plots

Originally designed to determine the spin and parity of newly-discovered mesons

by examining their decays into 3 pions

vector meson

Later modified for use in

Resonance hunting

M. Ferro Luzzi et al., Nuovo Cimento 36 (1965) 1101

Clearly see the resonance in scattering

p

(1385) baryon resonance(1385)

(1385)

Shafer et al. PRL 10 (1963) 176&

0seen in p K

e.g.,

And still in use today:

…until now?

But apparently not meaningfully applied to SUSY or beyond the SM applications

BABAR hep-ex/0507026

Crystal Ball hepex/9708025

BELLE,Belle-Conf-0410

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( )M e e

M

box-like shape0 0i i for production

0 0i j

wedge-like shapefor production

( )i j

for our process types

Possible Dalitz-like Plots:

Could be 0 02 2

0 03 3

0 04 4

or

or

Complications

Assumes0i e NONO

NONO

other stuff

0

0

i

j

e e

0 stuffi jp p

other stuff

just other stuff (no leptons)

Typically these decay modes are small to negligibly tiny.

Neglects charginosAlong with leptons from decaying top quarks that might happen to be produced.

stuffi jp p stuffi jp p

These chargino channels sub-leading at worst

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清华大学First consider production processes with the largest rates…

Gluino/squark pair production with cascade decays

Salient points about (c):

Produces jets, cannot be hadronically quiet

No fundamental vertex0 0i jS

each –ino produced independently

reduction in number of possible patterns

IF -ino pair production is only due to gluinos

possible on Dalitz-like plots

Know and rates know rate. 0 0i i 0 0

j j 0 0i j

But squarks can also contribute significantly!!

2ij i jr r r

(or only one kind of colored sparticle)

Beenacker et al., NPB 492 (1997) 51

EW gaugino unification

endpoints become bands

Sleptons relatively light to enhance leptonic BRs

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charginos!!!

Note: these are inclusive 4-lepton rates with no cuts ore

simulate signals and backgrounds

realistic calorimeter simulation package (recent CMS package)

with HERWIG 6.5 event generatorcoupled to

Now actually

From Table can determine relative rates for different –ino pairs

Point C: 22 33 44: : 131.5 :1.3 :1r r r

23 24 34: : 10.2 : 9.6 :1r r r

CUTS

Note: lose up to 90% of inclusive 4-lepton events mostly due to one or more leptons being too soft.

Simple set of

Resulting Dalitz-like plots

MSSM Point A

envelope-types

MSSM Point A

Hard edges

3-body decay0 02 142.8 GeV massdifference

0 02 1( ) 0.245BR

off-shell sleptons very important

MSSM Point A

Here sleptons on mass-shell

two-body decays

End points no longer -ino mass differences

0 * 01,i

“stripe”

MSSM Point A

Note change in event density around 85 GeV

0 02 3 production

or a 0 0 04 2 1 other

stuff

E22.8% of the time

MSSM Point A“maverick events”

These events cannot be accounted for within the framework of our modeling for the Dalitz-like plot

Study of the detailed HERWIG output for such generated events confirmed that leptons in these events come from charginos

in addition, there were other exceptional features of these points

MSSM Point B

envelope-types

MSSM Point B

Double the luminosity

Two heavy –inos very close in mass

MSSM Point B

Note: squark production is required to account for these events

0 02 4

Can get a clean sample of events only coming from squarks, not gluinos.

MSSM Point C

envelope-types

Try to reconstruct

production rate leptonic BRrates for different –ino pairs

MSSM Point C

from 6 observables:

, , , , ,

Assuming triangular population density distributions:

# of

ev

ents

Point C: 55

55

96

96

173

173

for :44re.g.,

(GeV)

( )M

'sijr

Modest agreement

22 23 24 33 34 44: : : : : 431:118 : 59 :15.5 : 9.4 :1r r r r r r Count events in simulation

22 33 44: : 431:15.5 :1r r r

23 24 34: : 12.3 : 6.3 :1r r r

23 24 34: : 10.2 : 9.6 :1r r r

2 3 4: : 12.3 :1.6 :1r r r

22 33 44: : 131.5 :1.3 :1r r r

just boxes:

just wedges:

Compare with earlier estimates:2ij i jr r r ?

2 3 4: : 12.6 : 4.7 :1r r r

2 3 4: : 11.47 :1.16 :1 22.00 : 2.404 :1r r r

23 34 22 24, & orr r r r

23 34 44, &r r r

2 3 4: : 19.00 :1.04 :1 22.03: 2.404 :1r r r boxes

wedges

Earlier estimates:

with gluinos only!

A

B

C

Traditional 1-Dim plots2-D

im D

alitz-like plo

ts

2-D plots give quick visual impression of which –ino pairs are being significantly produced

Obvious advantages over traditional 1-D plots

AlmostAlmost likelikeFingerprints!Fingerprints!

Tsinghua University

清华大学Trifurcate SUSY pheno studies into 3 classes ---Trifurcate SUSY pheno studies into 3 classes ---

inclusive studiesinclusive studies

Do not ask/care what specific decay chains combine to give signal

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Mass relation methodMass relation methodM. Nojiri, Polesello & Tovey hep-ph/0312317M. Nojiri, Polesello & Tovey hep-ph/0312317

M. Nojiri, hep-ph/0411127M. Nojiri, hep-ph/0411127

Example from cascade squark decay

Applied toApplied to 0 0 0 02 2 1 1, i i j jH A

among other processes

Assumes you know the processes/decay chainresponsible for the observed events.

Assumes 1 decay chain is responsible for observed events.

Kawagoe,M. Nojiri & Polesello hep-ph/041160Kawagoe,M. Nojiri & Polesello hep-ph/041160

Use 4-momenta from observed final state particles from several events to reconstruct masses in the decay chain

e.g.,

specific processesspecific processes --- guess what decay chain is responsible for the signal (based on an a priori choice of model parameters)

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Try to find out which decay chains are contributing (and how much each chain contributes) to observed signal in as model-independent a manner as possible.

This is the goal of the Dalitz-esque techniqueThis is the goal of the Dalitz-esque technique

(SUSY-breaking/high scale)(SUSY-breaking/high scale)

Can be used to confirm or refute assumptions made in using the mass relation method.

Needs far fewer events since it does not relay on end-point determinations so need not adequately fill 2-D space

Also fitting algorithms to whole set of MSSM parameters,But these results are perhaps not so intuitive.

at high speedat high speed

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Lower rates: Dalitz-like plot shapes less well-defined with available luminosity

Separate from gluino/squark cascade decays by cuts on jets?

Depends on jet properties in production, ,bb H A gg bb H A

at high tan .

currently under study

1100 fb 1200 fbint int

2400 200

tan 5 200AM GeV M GeV

GeV

/ 800 /1000g qm GeV

/150 / 250m GeV

Depends on good

detection capabilities

for b’s and tau’s

only detect h

, muonsH A

Gold-plated signal

LEP II excluded

new signal

0 02 2

dominated by

MSSM Point A1

MSSM Point A1 new

signal

dominated by

0 02 2

500AM GeVtan 20

2 180M GeV500GeV

/250m GeV

/ 1000g qm GeV

Significantly larger than previously found

Depends on good

detection capabilities

for b’s and tau’s

only detect h

, muonsH A

Gold-plated signal

LEP II excluded

MSSM Point B1

new signal

mostly NOT from

0 02 2

MSSM Point B1

mostly NOT from

new signal

0 02 2

600AM GeV

tan 35 2 200M GeV

200GeV /

150 / 250m GeV

/ 800 /1000g qm GeV

Non-log plots:

MSSM Point A1

MSSM Point B1

Can also look for charged Higgs bosons

0 0 01 1i j i i j jt H t t

3 Ttop E signature

2 210M GeV

135GeV

/110 / 210m GeV

/ 800 /1000g qm GeV

Set A :Set A :

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SUSY-decays of heavier Higgs bosons may well be a major discovery channel.

A complete picture of this requires inclusion of all the possible –ino pair decay states, …not just 0 0

2 2 !This may push up the searchable mass range considerably.AM

Discovery of heavier MSSM Higgs bosons is crucial.Discovery of heavier MSSM Higgs bosons is crucial.

Let me go!!! Dalitz-esque technique resurrected for use at the LHC

Have shown can extract substantial information on the MSSM –ino mass spectrum

But beware of assuming hard edges = -ino mass differences

Sleptons must also be considered as key players

Detailed study of the distribution of the events in the various regions of the Dalitz-like plot can also indicate the presence or absence

of squark-induced production modes.

e e Undoubtedly, will still require a ~TeV scale linear collider to fully sort things out and do better precision measurements.

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清华大学““complimentarity”complimentarity” between the LHC & the ILC between the LHC & the ILC

Favorite buzz-word for high energy physicistsFavorite buzz-word for high energy physicists who obviously want both machines builtwho obviously want both machines built

Perhaps a bit over-used, but still truePerhaps a bit over-used, but still true ……but do ourbut do our fundersfunders believe it?believe it?Another important word I think:

confirmationconfirmationMust this be lost in the big $$$’s?

Only 1 detector at the ILC?

How truly independent are two very similar detectors build and run 1 km apart?

Remember LSND ?

We should not give up on squeezing more information out of We should not give up on squeezing more information out of the LHC just because it is harder to extract than at the ILC.the LHC just because it is harder to extract than at the ILC.

---overlap and redundancy ---overlap and redundancy maybe as important as complimentaritymaybe as important as complimentarity

Studies done in collaboration with

Nick KerstingNick KerstingJun LiJun Li (H/A discovery plots)

Q.L XieQ.L Xie

(Sichuan U.)(Sichuan U.)

(Tsinghua U.)(Tsinghua U.)

(Sichuan U.)(Sichuan U.)

Filip MoortgatFilip Moortgat (CERN)(CERN)

Stefano MorettiStefano Moretti (Southampton U.)(Southampton U.)

The End

Thank you for listening!!!

End of Talk

Beenacker et al., NPB 492 (1997) 51

MSSM Point A

MSSM Point B

MSSM Point C

envelopes

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