What prospects for Black Holes at the Large Hadron Collider ?

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

July 03 Prague2003 : Black Holes at the LHC : [email protected] 2

Motivation

• Ancient HistoryIt 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 ingredientModels 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)


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


• 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:

• 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)

Production cross section

hep-ph/0106295


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.

hep-ph/0106295


Black Hole Decay at LHC

StageNeed a

Quantum Theory of Gravity?

Scale

In EventGenerators

?

Production Yes and No >MP πr2

“Hair Loss” No >MP No

SpinDown No >MP No

HawkingRadiation

Yes and No>MP

~MP

Yes

Remnant Decay Yes <MP

Manyoptions


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 …

http://flukestudio.com/


Grey-body Factors


Grey-body factors; Effects

n=0

n=2

n=6

scalars

fermions

spin-1

scalars

spin-1

fermions

• 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• 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


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) .


Easy to reconstruct MBH !

ParticleBranching

Ratio

Photons~2%

(lower for n=0)

Charged Leptons ~10%

Neutrinos ~5%Quarks/Gluons ~70%


Extract “n” from Wien’s Law?

• Approach of Dimopoulos and Landsberg (hep-ph/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.

hep-ph/0106295


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 !

A: Evaporation at fixed T

B: Evaporation at varying T

Fit: n=1.7±0.3

Fit: n=3.8±1.0


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 ….


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”.


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.

• 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 eventsper year – comparable to Z bosons at LEP!

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 ...

CMS

What prospects for Black Holes at the Large Hadron Collider ?

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