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Exotica at LHCb:
More on Long-Lived Particles
David Kaplan (Johns Hopkins U) and Matt Strassler (Rutgers U)
LHCb May 2009 M J Strassler
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Question: What didn’t we cover yet?

We’ve considered events with 2 highly displaced vertices
 From Higgs  X X with X long-lived
 From SUSY with LSP long-lived :
 LSP  visible, or LSP  visible + invisible

The importance of the Hidden Valley scenario, and related classes
of models, for LHCb is
 Additional 2-vertex examples in Higgs decays, SUSY decays
 Enhanced likelihood of new long-lived particles
 Enhanced likelihood of events with > 2 displaced vertices

In other words:
 more particles per model AND more particles per event
LHCb May 2009 M J Strassler
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Hidden Valley Scenario
MJS + Zurek hep-ph/0604261,hep-ph/0605193
MJS hep-ph/0607160,arXiv/0801.0629
We have very few limits on light particles that interact weakly with SM
Could an entire sector of such particles await us?
Such sectors easily generate neutral long-lived particles, often more than one
type, and often produced with multiplicity > 2.
If nature provides us with such phenomena, LHCb may scoop ATLAS/CMS
LHCb May 2009 M J Strassler
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Energy
A Conceptual Diagram
Entry into Valley
via
Narrow “Portal”
Slow Decay Back to
SM Sector
via
Narrow Portal
Multiparticle
Production
in Valley
Some Particles
Unable to Decay
Within Valley
LHCb May 2009 M J Strassler
Inaccessibility
4
General Predictions of HV Scenario

New neutral particles

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Often several of them in each model
Exhibiting many possible decay modes
Masses are usually of order (and above) the valley floor (mass gap)
Long-lived resonances



MJS + Zurek hep-ph/0604261
Displaced vertices common

Great opportunity for LHCb if rates are sufficiently high
Lifetimes for some new particles in the right range if barrier ~ TeV scale
Multiparticle production with unusual clustering

Valley dynamics can give events with of ~ 4, ~ 10, even ~ 30 vertices

Possibly highly correlated in direction

Possibly widely dispersed in direction
LHCb May 2009 M J Strassler
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Motivation for the HV scale

Why should nature set barrier and valley floor at these scales?


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Some dynamics generates the electroweak scale –

maybe SUSY breaking,

maybe the true Planck scale,

etc.
The same dynamics may easily generate similar scales in other sectors
and couplings to those scales in the TeV range
Developing models of this type is very easy (too easy!) for theorists
LHCb May 2009 M J Strassler
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HV: typical lifetimes are long
Examples: particles in 1 – 100 GeV range, coupled to SM by ~ (1 TeV) scale

Dimension 6 effective operator [e.g. two SM fermions, two valley fermions]
[ (20 GeV)5/(1 TeV)4 ] yb2 times phase space  10-10 sec lifetime

Dimension 8 effective operator [e.g. two gluons, two valley gauge bosons]
(100 GeV)9/(1 TeV)8 times phase space  10-10 sec lifetime

Dimension 4 effective operator with a 2-loop mixing angle
[e.g. photon mixing with valley gauge boson]
1 GeV * (mixing angle)2 times phase space  10-12 sec lifetime
Note the lifetimes are very sensitive to parameters;
may easily be too long or too short to observe … but …
LHCb May 2009 M J Strassler
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HV: multiple metastable particles

Consider:



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QCD has many hadrons which are long lived on QCD time-scales
against electromagnetic and weak decays

So may a hidden sector have particles with suppressed decays
The lifetimes of these hadrons span many orders of magnitude

So may a hidden sector have particles with many lifetimes
Many hadrons may be simultaneously produced

So may hidden sector particles be produced with high multiplicity
A hidden valley that is no more complicated than QCD itself can
easily put vertices into LHCb’s reach
LHCb May 2009 M J Strassler
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HV: production through decays/radiation
Cross sections for multiple vertices may well be high enough for LHCb

Any new particle may decay wholly or in part into a hidden valley






Higgs or any new scalar
LSP (or LKP or LTP)
New colored particles
Quirkonium
Z’
[cross section ~ few pb]
[cross section ~ few pb]
[cross-section ~ few pb]
[cross-section ~ few pb]
[cross section ~ 10 - 100 fb]
Also possible to radiate hidden valley particles off new particles
LHCb May 2009 M J Strassler
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HV: Examples
2 high-multiplicity vertices, similar lifetimes
LHCb May 2009 M J Strassler
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HV: Examples
JetsPairs,
Pion
Kaon Pairs,
Taus,
Muons,
Electrons…
many low-multiplicity vertices, similar lifetimes
LHCb May 2009 M J Strassler
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HV: Examples
Dijets or Trijets
many high-multiplicity vertices, similar lifetimes
LHCb May 2009 M J Strassler
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HV: Examples
many vertices, different multiplicities and lifetimes
Et cetera
LHCb May 2009 M J Strassler
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A broad scenario, but…

The number of reasonable models is enormous

However, number of possible phenomena, while large, is smaller

Benchmark models, Monte Carlo tools appropriate for the range of
phenomena are still under development (stay tuned)


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Triggers, backgrounds are detector dependent  So are benchmarks
Discussions on this matter are welcome
But for immediate purposes, simple models, simple studies using
PYTHIA will probably suffice
LHCb May 2009 M J Strassler
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Simulation of Multiple Vertex Decays

For many purposes, can use standard Pythia with small adjustments
 Use a standard Pythia production process
 Alter only the decays using PYUPDA or PYSLHA calls to


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Then Pythia will generate kinematically consistent events
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Add new particles
Add new decays to old/new particles
Caution: Pythia often cannot calculate total cross section correctly
The new decays are distributed according to phase space
Topology of the events determined by decay chain kinematics
PYUPDA examples below; PYSLHA is better (newer, more stable)

Let’s try Higgs  multiple vertices, two very simple examples
LHCb May 2009 M J Strassler
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Example: Higgs decays to many particles
PYTHIA


h0  X X followed by X  Y Y, Y  fermions
h0  Y Y Y, etc.

PMAS(35,1)=140.D0 ! set H0 mass

MSUB(152)=1
! MSUB(171)=1
! MSUB(172)=1
! MSUB(173)=1
! MSUB(174)=1





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!
!
!
!
!
MJS & Zurek 06
See also
Chang, Fox & Weiner 05
gg  H0 [we use H0 because h0 is treated specially by Pythia]
Z H0
W H0
VBF of H0
VBF' of H0
OPEN (UNIT=60,FILE=‘demo.pyupda.in',STATUS='OLD')
CALL PYUPDA(3,60) ! upload new-particle records
CLOSE(60)
LHCb May 2009 M J Strassler
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The PYUPDA file [watch formatting!]
Mass
Change Old Particle
35
H0
1
0
0
0
0
0 0 0 140.00000
0
0
0
0
0
0.399800
0.300000
0.300000
0.000100
0.000100
6000111
6001022
6001022
6001022
21
Width
0.01000
Max Delta-E Lifetime
0.10000 0.00001E+00 2 1
6000111
0
0
6001022
0
0
6001022 6001022
0
6001022 6001022 6001022
21
0
0
0
0
Decaying particle
6000111 ~v_pion
0 0 0 4.00000 0.01000 0.10000 1.00000E-03 2 1
1 0 1.000000 6001022 6001022
0
0
0
6001022
1
1
1
~Uboson
0 0.400000
0 0.400000
0 0.200000
Add New Particles
11
13
211
0 0 0
-11
-13
-211
0.60000 0.01000
0
0
0
0
0
0
0
0
0
LHCb May 2009 M J Strassler
0.10000 5.00000E+00 2 1
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The PYUPDA file [watch formatting!]
v-pion
H0
U-boson
Mass
Change Old Particle
35
H0
Decay
flag
1
0
0
0
0
0 0 0 140.00000
0
0
0
0
0
0.399800
0.300000
0.300000
0.000100
0.000100
Branching Fraction
6000111
6001022
6001022
6001022
21
Width
0.01000
Max Delta-E Lifetime
0.10000 0.00001E+00 2 1
6000111
0
0
6001022
0
0
6001022 6001022
0
6001022 6001022 6001022
21
0
0
0
0
Decaying particle
Particles in Final State
6000111 ~v_pion
0 0 0 4.00000 0.01000 0.10000 1.00000E-03 2 1
1 0 1.000000 6001022 6001022
0
0
0
6001022
1
1
1
~Uboson
0 0.400000
0 0.400000
0 0.200000
11
13
211
0 0 0
-11
-13
-211
0.60000 0.01000
0
0
0
0
0
0
0
0
0
0.10000 5.00000E+00 2 1
Electrons
Muons
Pions
Add New Particles
LHCb May 2009 M J Strassler
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The PYUPDA file [watch formatting!]
U-boson
H0
Mass
Change Old Particle
35
H0
Decay
flag
0
0
1
0
0
0 0 0 140.00000
0
0
0
0
0
0.399800
0.300000
0.300000
0.000100
0.000100
Branching Fraction
6000111
6001022
6001022
6001022
21
Width
0.01000
Max Delta-E Lifetime
0.10000 0.00001E+00 2 1
6000111
0
0
6001022
0
0
6001022 6001022
0
6001022 6001022 6001022
21
0
0
0
0
Decaying particle
Particles in Final State
6000111 ~v_pion
0 0 0 4.00000 0.01000 0.10000 1.00000E-03 2 1
1 0 1.000000 6001022 6001022
0
0
0
6001022
1
1
1
~Uboson
0 0.400000
0 0.400000
0 0.200000
11
13
211
0 0 0
-11
-13
-211
0.60000 0.01000
0
0
0
0
0
0
0
0
0
0.10000 5.00000E+00 2 1
Electrons
Muons
Pions
Add New Particles
LHCb May 2009 M J Strassler
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In backup slides

Comment on “dark photon” branching fractions

Comment on simulating SUSY decays

Comment on models for which a more advanced Monte Carlo is
needed, with examples (specific Z’ and quirkonium models)
LHCb May 2009 M J Strassler
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Conclusions

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Long-lived particles are very common in the theoretical literature
The Hidden Valley scenario illustrates that we may have underestimated the
likelihood of long-lived particles.
HV dynamics also can lead to a high multiplicity (per event) of such particles
Tevatron experiments have not been able to put strong limits on long-lived
neutral particles decaying in flight
ATLAS/CMS will not find it easy in many cases due to
 Triggering limitations
 Reconstruction challenges
LHCb therefore may have a special opportunity to discover new physics
HLT1 and secondary interactions appear to be the bottleneck
Theorists are available to provide benchmark models, MC assistance
LHCb May 2009 M J Strassler
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Backup Slides
LHCb May 2009 M J Strassler
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Lepton-Jets comment

Getting the branching fractions right, as a function of mass, for a
“hidden photon” (or “U-boson” or “dark photon”) requires careful use
of data on off-shell photon decays.

Software to get the branching fractions right will be available before
the LHC turns on
 Contact e.g. Matt Reece (Princeton) or others
LHCb May 2009 M J Strassler
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SUSY decays
Same idea as for Higgs
 Set a standard PYTHIA card for MSSM production
 Use PYUPDA/PYSLHA to add new hidden sector particles
 Change the LSP from stable to unstable, set lifetime, and add
decay modes to the new sector
 e.g. Neutralino  vpion vpion + invisible
 e.g. Stau  tau + vpion + invisible
 Add decay modes within the hidden sector and from the hidden
sector back to visible particles
 E.g. vpion  b quarks
 E.g. vpion  U U ; U  mu+ mu-
LHCb May 2009 M J Strassler
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More complex physical processes



Some processes cannot be simulated properly using phase-space cascade
decays
 Decay of particle into a parton shower has special kinematics
 Other production mechanisms (e.g. quirk relaxation and annihilation)
may produce multiple particles with odd distributions
For these, specialized software is needed
 Software for decays of a heavy particle to a v-quark pair in a QCD-like
hidden sector exists
 Software for decays to a v-quark pair in a higgsed hidden sector is more
or less available
However, for the immediate future this does not seem critical
 The clustering of the new particles’ momenta is more or less obtainable
from the PYUPDA approach
LHCb May 2009 M J Strassler
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HV: Effects on Narrow-Width Particles:

hep-ph/0604261
hep-ph/0605193
Possible big effect on Higgs

Long lived particles: H  XX, X decays displaced  new discovery mode


not unique to HV!!! Chang Fox Weiner 05 / Carpenter Kaplan Rhee 06
High multiplicity decays: H  XXX, XXXX, etc

not unique to HV!!! Chang Fox Weiner 05

Also Z’, other resonances…

Big effect on SUSY, UED, Little Higgs – any theory w/ new global charge

LSP (or LKP or LTP) of our sector can decay to the valley LSP/LKP/LTP



Plus SM particles or
Plus hidden particles which decay back to SM particles or
Plus both
hep-ph/0607160
Either the hidden particles or the LSP/LKP/LTP may be long-lived;

LSP may have high-multiplicity decays;

SUSY events have significantly reduced MET
Generalizes well known work from 90s [GMSB, Anomaly, Hidden Sector]

LHCb May 2009 M J Strassler
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The PYUPDA file [watch formatting!]
v-pion
H0
U-boson
Mass
Change Old Particle
35
H0
Decay
flag
1
0
0
0
0
0 0 0 140.00000
0
0
0
0
0
0.399800
0.300000
0.300000
0.000100
0.000100
Branching Fraction
6000111
6001022
6001022
6001022
21
Width
0.01000
Max Delta-E Lifetime
0.10000 0.00001E+00 2 1
6000111
0
0
6001022
0
0
6001022 6001022
0
6001022 6001022 6001022
21
Particles in Final State
0
0
0
0
Decaying particle
Warning: Need to keep H0  g g to not forbid g g  H0
6000111 ~v_pion
0 0 0 4.00000 0.01000 0.10000 1.00000E-03 2 1
1 0 1.000000 6001022 6001022
0
0
0
6001022
1
1
1
~Uboson
0 0.400000
0 0.400000
0 0.200000
11
13
211
0 0 0
-11
-13
-211
0.60000 0.01000
0
0
0
0
0
0
0
0
0
0.10000 5.00000E+00 2 1
Electrons
Muons
Pions
Add New Particles
LHCb May 2009 M J Strassler
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q q  Q Q : v-quark production
v-quarks
q
Q
Z’
q
Q
Same for g g  new neutral particles of spin 0 or 2
Analogous to e+e-  hadrons
LHCb May 2009 M J Strassler
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qqQQ
v-gluons
q
Q
Z’
q
Q
Analogous to e+e-  hadrons
LHCb May 2009 M J Strassler
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qqQQ
q
Z’
q
v-hadrons
Q
Q
Analogous to e+e-  hadrons
LHCb May 2009 M J Strassler
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qqQQ
Some v-hadrons are
stable and therefore
invisible
v-hadrons
q
q
Z’
Q
Q
But some vhadrons decay
in the detector
to visible
particles, such
as bb pairs, qq
pairs, leptons
etc.
Analogous to e+e-  hadrons
Same structure for gg  H 
v-quark
LHCb
May 2009 pairs
M J Strassler
31
Cross sections and lifetimes?




The basic idea of a new particle decaying to a shower of hidden
valley particles in a hidden sector is general
 If these particles are long lived, get a shower of clustered
displaced vertices
 If these particles decay promptly to b’s, get a shower of many B’s
 Could be highly collimated OR widely dispersed
Typically Z’ production rates are too small for LHCb
But other resonances (including Higgs) could have similar decays
So could the LSP, or even new exotic colored particles
 In these cases, cross sections could be very large (1 – 10 pb)
LHCb May 2009 M J Strassler
32
Quirks and v-glueballs
GeV-TeV–confinement quirk production/annihilation
MJS + Zurek hep-ph/0604261
Juknevich, Melnikov, MJS hep-ph/09……
YM glueball spectrum
Morningstar Peardon 99
Quirk: Matter charged under SM and hidden confining group…

Hidden confining string cannot break  Quirkonium

Quirk loops induce couplings of SM and hidden gauge bosons
See also Low-confinement-scale “quirks”:
Kang, [Nasri], Luty 2006, 2008
g
g
g
q
g
g
photon
Q
photon
q
Q
quirks
g
g
v-gluons
LHCb May 2009 M J Strassler
v-glueballs
g
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