Transcript No Slide Title

What prospects for Black Holes
at the Large Hadron Collider ?
•How might black holes be produced at the LHC?
•Discussion of recent developments in their simulation.
•Comments on recent attempts to extract physics.
Christopher.Lester @ cern.ch
Motivation
• Ancient History
It is widely accepted that particle collisions above the
fundamental scale of Gravitational Interactions should
lead to Black Hole production.
We observe (macroscopically) MP(4D)~1018 TeV
• New ingredient
Models with extra dimensions (“n”) now permit the
extra-dimensional Planck Scale to be many orders of
magnitude smaller than the above.
We may have (fundamentally) MP((4+n)D)~1 TeV
(n=1 and n=2 ruled out on astrophysical grounds)
July 03
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Production at the LHC
• Get more than ~ TeV of energy into a small enough
region … and Black Hole forms spontaneously!
• Characteristic size of maximal impact parameter is approx
the Schwarzschild radius of the resulting Black Hole
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Production cross section
• Geometrical arguments:
• This is consensus view, but not everyone
agrees; e.g. hep-ph/0111099 promotes
exponential suppression but is strongly
contested by gr-qc/0201034.
• rBH is itself a function of MBH:
hep-ph/0106295
•
•
MBH goes like √s, so cross section falls with
increasing MBH due to rapidly falling PDFs.
Plot, right, shows cross sections for n=4 extra
dimensions at the LHC for a variety of fundamental
Planck masses.
Total x-sec examples:
•
•
0.5 nb (MP=2 TeV, n=7)
120 fb (MP=6 TeV, n=3)
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Production cross section(2)
• If the BHs are
produced at all, they
are likely to be
produced in large
numbers.
• Plot, right, shows SM
background would be
orders of magnitude
lower than BH
production.
July 03
hep-ph/0106295
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Black Hole Decay at LHC
Stage
Need a
Quantum
Theory of
Gravity?
Scale
In Event
Generators?
Production
Yes and No
>MP
πr2
“Hair Loss”
No
>MP
No
Spin
Down
No
>MP
No
Hawking
Radiation
Yes and No
>MP
~MP
Yes
<MP
Many
options
Remnant
Decay
July 03
Yes
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Event generators …
Two main generators*
• TRUENOIR (Landsberg)
• First on the scene!
• BLACK
{Soon to be renamed CHARYBDIS}
(Harris & Richardson & HERWIG authors)
• Time dependent evolution
(BH can get hotter as it shrinks)
• Parametrised Grey-Body Factors
• “Remnant Handling” options
• BH Recoil
• Interfaces to HERWIG and
PYTHIA via “Les Houches Accord”
(image courtesy of flukestudio.com)
* To the best of my knowledge …
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Grey-body Factors
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Grey-body factors; Effects
• Principally affect low part of emission spectrum
• Particularly important for low values of “n”
• (High part always looks like Planck Spectrum)
• Depend on spin of emitted particle
spin-1
• In example (right) grey-body
factors accentuate photon
emission as “n” increases.
• Could try to use
to constrain “n”.
•
•
New result: Harris (in
preparation) calculates
grey-body factors
numerically in “n” extra
dimensions
Finds significant
disagreement with earlier
analytic attempts which
only extracted “first few
terms” in series
July 03
scalars
fermions
n=6
scalars
n=2
fermions
spin-1
n=0
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Relative Emission Probabilities
Extra Dims
s=0
s=1/2
s=1
n=0
1.00
0.37
0.11
n=2
1.00
0.77
0.69
n=6
1.00
0.73
0.99
Black Body
1.00
0.75
1.00
Conclusion: (Harris)
Grey-body factors should not be ignored when looking
at small numbers of extra dimensions (“small”: n<6) .
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Easy to reconstruct MBH !
Particle
Branching Ratio
Photons
~2%
(lower for n=0)
Charged
Leptons
~10%
Neutrinos
~5%
Quarks/Gluons
~70%
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Extract “n” from Wien’s Law?
• Approach of Dimopoulos
and Landsberg (hepph/0106295).
• At high energies, γ and e
spectrum looks like black
body, so try to reconstruct
TH from Wien’s Law.
• Attempt also to
reconstruct MBH in each
event.
• Recover “n” from
dependence of TH on MBH.
July 03
hep-ph/0106295
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Problems?
•
•
Fitted value of “n” depends strongly
on how you model the BH decay
Example:
Compare two models;
A. BH decays “suddenly” at fixed
temperature,
B. BH temperature grows as BH shrinks
•
Fit both models according to fixed
temperature model.
Recover wrong value of “n” for
model B. Effect more pronounced as
“n” increases.
Conclusion:
Community needs to decide upon
status of temperature evolution
during Black Hole decays !
July 03
A: Evaporation at fixed T
Fit: n=1.7±0.3
B: Evaporation at varying T
Fit: n=3.8±1.0
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Event shape variables?
• Two BHs of the same
mass, but living in
different numbers of
dimensions: one is hotter,
one cooler;
• The Hot BH emits mostly
energetic particles, with
low mutliplicity.
• The Cool BH emits mostly
soft particles, with high
multiplicity.
• So look for changes in
multiplicities and event
shape variables ….
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No easy answers …
• Those attempting to measure “n” at Cambridge
(Sabetfakhri & Harris) are not celebrating yet
• While BH discovery easy, the hunt for
observables that do not do not depend on
• The temperature model,
• The remnant decay model, &
• Presence of BH recoil
seems to be very hard.
• May have to retain substantial model
dependence in attempts to measure “n”.
July 03
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Conclusions
•
•
We can expect ATLAS and CMS to
• Discover extra-dimensions thorough
Black Hole events provided
fundamental Planck scale is accessible
by the LHC, i.e. MP~few TeV.
• Expect discovery to be easy due to
large predicted cross sections.
• Expect discovery to be largely model
independent as the parts of the decay
that are not well understood are at the
end of the decays (remnants …) not in
the cross sections.
Other areas of completed and ongoing research
which there was not time to discuss:
•
•
•
•
New physics (Higgs?) from BH events …
Should we worry about spin-down?
Does Quantum Gravity mess everything up ?
What about production BELOW Planck scale?
•
•
Would it dominate?
Everything else which I have forgotten ...
We can hope ATLAS and CMS might
• Tell us something about the number of
extra dimensions “n”
• Answer may depend on model
• Make precise measurements ?
• In some scenarios, 107 BH events
per year – comparable to
Z bosons at LEP!
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