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. cern.ch

July 03 Prague2003 : Black Holes at the LHC : 2 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) M P(4D) ~10 18 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) M P((4+n)D) ~1 TeV (n=1 and n=2 ruled out on astrophysical grounds)

July 03 Prague2003 : Black Holes at the LHC : 3 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

July 03 Prague2003 : Black Holes at the LHC : 4 Geometrical arguments: This is consensus view, but not everyone agrees; e.g. hep-ph/ promotes exponential suppression but is strongly contested by gr-qc/ r BH is itself a function of M BH : M BH goes like √s, so cross section falls with increasing M BH 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/

July 03 Prague2003 : Black Holes at the LHC : 5 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/

July 03 Prague2003 : Black Holes at the LHC : 6 Black Hole Decay at LHC Stage Need a Quantum Theory of Gravity? Scale In Event Generators? ProductionYes and No >M P πr2πr2 “Hair Loss” No>M P No Spin Down No>M P No Hawking Radiation Yes and No >M P ~M P Yes Remnant Decay Yes<M P Many options

July 03 Prague2003 : Black Holes at the LHC : 7 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)flukestudio.com * To the best of my knowledge …

July 03 Prague2003 : Black Holes at the LHC : 8 Grey-body Factors

July 03 Prague2003 : Black Holes at the LHC : 9 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

July 03 Prague2003 : Black Holes at the LHC : 10 Relative Emission Probabilities Extra Dimss=0s=1/2s=1 n= n= n= Black Body Conclusion: (Harris) Grey-body factors should not be ignored when looking at small numbers of extra dimensions (“small”: n<6).

July 03 Prague2003 : Black Holes at the LHC : 11 Easy to reconstruct M BH ! ParticleBranching Ratio Photons ~2% (lower for n=0) Charged Leptons ~10% Neutrinos ~5% Quarks/Gluons ~70%

July 03 Prague2003 : Black Holes at the LHC : 12 Extract “n” from Wien’s Law? Approach of Dimopoulos and Landsberg (hep- ph/ ). At high energies, γ and e spectrum looks like black body, so try to reconstruct T H from Wien’s Law. Attempt also to reconstruct M BH in each event. Recover “n” from dependence of T H on M BH. hep-ph/

July 03 Prague2003 : Black Holes at the LHC : 13 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

July 03 Prague2003 : Black Holes at the LHC : 14 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 ….

July 03 Prague2003 : Black Holes at the LHC : 15 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 Prague2003 : Black Holes at the LHC : 16 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. M P ~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, 10 7 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... CMS