Mike Bisset / 毕楷杰 Tsinghua University Beijing, China
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Transcript of Mike Bisset / 毕楷杰 Tsinghua University Beijing, China
“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, ,
Tsinghua University
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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清华大学Return to Higgs boson decays
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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清华大学Concluding remarks
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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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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