Th Lester PRAHA2003 1a

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

Motivation: 

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)

Production at the LHC: 

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

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: 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

Production cross section(2): 

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.

Black Hole Decay at LHC: 

Black Hole Decay at LHC

Event generators …: 

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” * To the best of my knowledge …

Grey-body Factors: 

Grey-body Factors

Grey-body factors; Effects: 

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 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: 

Relative Emission Probabilities Conclusion: (Harris) Grey-body factors should not be ignored when looking at small numbers of extra dimensions (“small”: n<6) .

Easy to reconstruct MBH !: 

Easy to reconstruct MBH !

Extract “n” from Wien’s Law?: 

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.

Problems?: 

Problems? Fitted value of “n” depends strongly on how you model the BH decay Example: Compare two models; BH decays “suddenly” at fixed temperature, 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? : 

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 …: 

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: 

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 events per 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 ...