Extra dimensions and black holes at the LHC

Transcription

1 Extra dimensions and black holes at the LHC R.M. Buckingham University of Oxford IOP half-day meeting - Black Holes, Extra Dimensions and Colliders Cavendish Laboratory, Cambridge Thursday 9th of December 2010 R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 1 of 15

2 Outline... What are the current limits? The LHC and ATLAS Gravitational signatures What can we look for at the LHC? Multiobject final states Results so far at s = 7 TeV Predictions for s = 14 TeV Two body final states... Results so far for dijets Summary R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 2 of 15

3 Results from previous collider experiments Experiment n Limit on M D (TeV) LEP CDF D0 lower limit 1.23 R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 3 of 15

4 The LHC ] Total Integrated Luminosity [pb ATLAS Online Luminosity LHC Delivered ATLAS Recorded 1 Total Delivered: 48.9 pb 1 Total Recorded: 45.0 pb s = 7 TeV 10 24/03 21/0419/05 16/06 14/07 11/0808/0906/10 03/11 Day in 2010 At the end of 2010, 45 pb 1 at s = 7 TeV Reached luminosity rate of 6 pb 1 day 1 Starting Feb 2011, possibility of s = 8 TeV Aim to collect 1-2 fb 1 R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 4 of 15

5 The ATLAS detector R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 5 of 15

6 The ATLAS detector R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 5 of 15

7 R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 6 of 15

8 Jets and Missing E T? What is a jet? A narrow cone of hadrons, and other particles produced by the hadronization of a quark or gluon also produced by an incident hadron. e.g. proton or neutron Jet algorithms reconstruct individual energy deposits into a jet object What is Missing E T (MET) For every calorimeter energy cell in the transverse plane, form E cell T = E cell ( x cell x detcenter ) Since there is initially zero transverse momentum, we can construct MET = cells E cell T Representing the energy of escaping neutrinos or gravitons R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 7 of 15

9 Gravitational signatures at the LHC We expect: Gravity to couple democratically to the degrees of freedom all SM particles quarks, gluons, leptons, neutrinos, W, Z, γ, (G) high multiplicity final states We measure: jets, electrons, muons, photons We can reconstruct: taus, W, Z, MET also low multiplicity final states for low mass threshold. e.g. QBH: 2 body final states - dijets, ll, jet +t, jet +Z, jet +W, jet +γ, t t,jet +l,... It is expected that cross sections could be large... Here we will look at some first results from new kinematic regime at the LHC R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 8 of 15

10 High multiplicity final states Calculate: pt = i p Ti, and M eff = p 2, where p = i p i + (E miss T and i are the measured objects., ETx miss, ETy miss, 0) Look for deviations from SM backgrounds: For this study: QCD is dominant for higher lumi: t t, W /Z + jets and more... The challenges: Large theoretical uncertainties Uncertainties due to jet energy scale (JES) Large uncertainty on background processes R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 9 of 15

11 ATLAS Results at s = 7 TeV ATLAS-CONF Select events with > 2 objects inc. leptons, photon and jets. pt > 300 GeV and 300 < M eff < 800 GeV for control region - used for normalisation of backgrounds pt > 700 GeV for signal region Control region to fit background: Signal region: No discrepancy between MC and data is observed - set limits! R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 10 of 15

12 The conclusions and implications... Previous limit for M D = 0.94 TeV for n = 6, means we do not expect to see semi-classical behaviour for this study... Upper limit % C.L on acceptance cross-section Detector Acceptance, A = 58%, - calculated using BlackMax & Charybdis MC generators Using BlackMax & Charybdis acceptance as illustation... upper limit on production cross-section for high invariant mass events above 800 GeV is 0.6 nb as a conservative limit for low scale gravity in high multiplicity final states R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 11 of 15

13 The conclusions and implications... Previous limit for M D = 0.94 TeV for n = 6, means we do not expect to see semi-classical behaviour for this study... Upper limit % C.L on acceptance cross-section Detector Acceptance, A = 58%, - calculated using BlackMax & Charybdis MC generators Using BlackMax & Charybdis acceptance as illustation... upper limit on production cross-section for high invariant mass events above 800 GeV is 0.6 nb as a conservative limit for low scale gravity in high multiplicity final states R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 11 of 15

14 The conclusions and implications... Previous limit for M D = 0.94 TeV for n = 6, means we do not expect to see semi-classical behaviour for this study... Upper limit % C.L on acceptance cross-section Detector Acceptance, A = 58%, - calculated using BlackMax & Charybdis MC generators Using BlackMax & Charybdis acceptance as illustation... upper limit on production cross-section for high invariant mass events above 800 GeV is 0.6 nb as a conservative limit for low scale gravity in high multiplicity final states R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 11 of 15

15 The conclusions and implications... Previous limit for M D = 0.94 TeV for n = 6, means we do not expect to see semi-classical behaviour for this study... Upper limit % C.L on acceptance cross-section Detector Acceptance, A = 58%, - calculated using BlackMax & Charybdis MC generators Using BlackMax & Charybdis acceptance as illustation... upper limit on production cross-section for high invariant mass events above 800 GeV is 0.6 nb as a conservative limit for low scale gravity in high multiplicity final states R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 11 of 15

16 Looking ahead to 100 pb 1 at s = 14 TeV ATL-PHYS-PUB pt > 2.5 TeV pt > 2.5 TeV with lepton of p T > 50 GeV R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 12 of 15

17 Looking ahead to s = 14 TeV ATL-PHYS-PUB Discovery reach: If semi-classical estimated are valid: BH can be discovered above a 5 TeV threshold with pb 1 1 fb 1 would allow discovery for production threshold at 8 TeV R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 13 of 15

18 R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 14 of 15

19 The χ Variable χ = exp y 1 y 2 where y = 1 2 ln ( E+pL E p L ) : Rapidity For E << p, we have y = η = ln tan(θ/2) This gives (to leading order) χ = 1+ cos ˆθ 1 cos ˆθ 1 1 cos ˆθ ŝˆt where ŝ and ˆt are the Mandelstam variables. For a t-channel process, we have d ˆσ dˆt α2 s ˆt 2 leading to d ˆσ dχ α2 s ŝ (For const. ŝ) QCD dominated by t-channel (Rutherford like) flat χ New physics isotropic excess at low χ χ distributions also binned in M jj and plotted for each mass bin R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 15 of 15

20 Dijet final states - ATLAS Results so far... ATLAS-CONF QBH model parameters mainly influence production cross-section and threshold - little effect on angular distributions. Limit set on θ = σ(signal) A(signal) σ(qcd) A(QCD) using QBH (M Pl = 600 GeV) template θ < 8% at the 95% C.L. for 520 < M jj < 680 GeV Uncertainties: Theoretical: NLO k-factors, PDF, scale Experimental: Jet Energy Scale (JES) (1/χ)dσ/dχ removes uncert. on lumi. χ significantly reduces systematics R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 16 of 15

21 Summary The LHC had already allowed us to: Explore a new kinematic region where we expect the effects of extra-dimensions to be evident Set limits on gravitational processes which would decay to multi-object final states Set limits on QBH processes which occur at the Plank scale In the future, it will be possible to: Set further limits on processes occurring at the Plank scale Set limits on semi-classical BH and string-ball processes Set limits on a further range of models Set limits using a wider range of experimental signatures R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 17 of 15

22 Summary The LHC had already allowed us to: Explore a new kinematic region where we expect the effects of extra-dimensions to be evident Set limits on gravitational processes which would decay to multi-object final states Set limits on QBH processes which occur at the Plank scale In the future, it will be possible to: Set further limits on processes occurring at the Plank scale Set limits on semi-classical BH and string-ball processes Set limits on a further range of models Set limits using a wider range of experimental signatures R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 17 of 15

23 Many thanks for listening and thank-you to Cigdem Issever for her help preparing this talk R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 18 of 15

24 BACK-UP SLIDES R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 19 of 15

25 Cross-sections for micro-bh LHC Production: R S = 2G L n M c 2 M = sx a x b = ŝ The production cross-section ˆσ ab BH (ŝ) = kπr 2 S σ pp BH+X (ŝ) = a,b 1 M 2 /s dx a 1 M 2 /x as dx bf a (x a )f b (x b )ˆσ ab BH (ŝ) R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 20 of 15

26 Cross-sections for micro-bh LHC Production: R S = 2G L n M c 2 M = sx a x b = ŝ The production cross-section ˆσ ab BH (ŝ) = kπr 2 S σ pp BH+X (ŝ) = a,b 1 M 2 /s dx a 1 M 2 /x as dx bf a (x a )f b (x b )ˆσ ab BH (ŝ) R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 20 of 15

27 Cross-sections for micro-bh LHC Production: R S = 2G L n M c 2 M = sx a x b = ŝ The production cross-section ˆσ ab BH (ŝ) = kπr 2 S σ pp BH+X (ŝ) = a,b 1 M 2 /s dx a 1 M 2 /x as dx bf a (x a )f b (x b )ˆσ ab BH (ŝ) R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 20 of 15

28 Cross-sections for micro-bh LHC Production: R S = 2G L n M c 2 M = sx a x b = ŝ The production cross-section ˆσ ab BH (ŝ) = kπr 2 S σ pp BH+X (ŝ) = a,b 1 M 2 /s dx a 1 M 2 /x as dx bf a (x a )f b (x b )ˆσ ab BH (ŝ) R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 20 of 15

29 Looking ahead to s = 14 TeV ATL-PHYS-PUB Determination of model parameters: After discovering extra dimensions at LHC, need to determine: M D - method using cross-section and highest p T objects 1 n - closely related to T H. - Energy emissions near m BH /2 give measure of initial T H 2 T H = 1 c 2 M D 1 8π k B M BH = 1+n M 1/(1+n) BH 1 C.M. Harris et al. arxiv:hep-ph/ and J. Tanaka et. al. arxiv:hep-ph/ C.M. Harris et al. arxiv:hep-ph/ R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 21 of 15

30 Looking ahead to 100 pb 1 at s = 14 TeV ATL-PHYS-PUB Model dependent event properties - larger n gives higher Hawking temp. leading to fewer, higher-energy particles study does not include graviton emission inclusion would result in 9% average energy loss R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 22 of 15

31 Looking ahead to 100 pb 1 at s = 14 TeV ATL-PHYS-PUB Prodominant backgrounds: t t and hadronic decay modes QCD dijet production W lν + jets production Z ll + jets production γ(γ) + jets production R.M. Buckingham, University of Oxford Extra dimensions and black holes at the LHC 23 of 15