Discovery Physics at the LHC Antonella De Santo

Discovery Physics at the LHC Antonella De Santo Royal Holloway, University of London YETI 08 Durham, January 9, 2008 YETI 08, Durham Jan'08 Antonella De Santo, RHUL

Foreword – LHC’s Main Goals Elucidate mechanism for EW symmetry breaking Search or Higgs boson in O(100 Ge. V)-O(1 Te. V) range If no light Higgs is found, study WW scattering at high mass Look for evidence of new physics at Te. V-scale Deviations from SM predictions SM only low-energy “effective theory” of more fundamental theory valid at higher energies YETI 08, Durham Jan'08 Antonella De Santo, RHUL 1

Outline Introduction The LHC ATLAS and CMS EW Symmetry Breaking Higgs boson Not an exhaustive list! Supersymmetry m. SUGRA Beyond SUSY Extra Dimensions YETI 08, Durham Jan'08 Antonella De Santo, RHUL 2

THE LHC

YETI 08, Durham Jan'08 Antonella De Santo, RHUL 4

The LHC – some basic facts LHC housed in former LEP tunnel 27 km circumference Design luminosity: Proton-proton machine “Low” = 1033 cm-2 s-1 (O(10 fb-1) / yr ) “High” = 1034 cm-2 s-1 (O(100 fb-1) / yr) Superconducting magnets 25 ns bunch crossing 40 MHz crossing frequency 2835 / 3564 “full” bunches B = 8. 4 T Limiting factor for total energy (Only 60% of circumference is magnetised) YETI 08, Durham Jan'08 Antonella De Santo, RHUL 5

Cross Sections Minimum Bias rate: O(109 Hz) !! Process (nb) #evts Rates(Hz) [10 fb-1] [ “high” L ] 500 mb 5 x 1012 14 Te. V YETI 08, Durham Jan'08 Antonella De Santo, RHUL 5 x 106 15 nb ~108 150 1. 5 nb ~107 15 800 pb ~107 10 ~1 pb ~104 10 -2 ~10 fb ~102 10 -4 “Needle in haystack” 6

sinel(pp)~70 mb Minimum Bias Non-single diffractive interactions (soft partons) “Operational” definition of “minimum bias” depends on experimental trigger LHC predictions CDF Measured at lower energies (Spp. S and Tevatron) Large uncertainties on extrapolation to LHC energies UA 5 YETI 08, Durham Jan'08 Antonella De Santo, RHUL 7

Minimum Bias and Pile-up At nominal high luminosity (L=1034 cm-2 s-1=107 mb-1 Hz), on average 23 minimum bias events superimposed on any rare discovery signal And ~1000 low-pt tracks per event ! Moreover, due to finite detector response time, out-of-time pile-up from different bunch crossings Event must be “time stamped” Important impact on detector design Fast electronics, high granularity, radiation hardness YETI 08, Durham Jan'08 Antonella De Santo, RHUL 8

The Challenge Rec. trks w/ pt>25 Ge. V H 4 m YETI 08, Durham Jan'08 Antonella De Santo, RHUL 9

The Challenge Rec. trks w/ pt>25 Ge. V H H 4 m 4 m YETI 08, Durham Jan'08 +30 Minimum Bias Antonella De Santo, RHUL 10

Collisions at a hadron collider d p u x 1 p d pu p u x 2 p p u Etot=? Ptot=? No constraint on total initial energy Broad range of √s good for discovery (All possible processes are “on” simultaneously) Typically x 1≠x 2 hard scatter boosted along beam direction YETI 08, Durham Jan'08 PDFs Antonella De Santo, RHUL 11

Event kinematics – p. T and h q h=0 h = -1. 0 h = -2. 5 Instead of polar angle q : beam axis Pseudo-rapidity h = +1. 0 Equivalent to rapidity for massless particles h = +2. 5 Invariant under boost beam axis YETI 08, Durham Jan'08 Antonella De Santo, RHUL 12

Event kinematics – Etmiss Assuming that the partons in the initial state move parallel to the proton beams, and that the total p. T of the unseen proton remnants (lost along the beam pipe) is ~0 : Total missing p. T approximated by vector sum of all energy deposits in calorimeters ( Etmiss) YETI 08, Durham Jan'08 Antonella De Santo, RHUL 13

Search Strategy for Rare Processes High-p. T physics largely dominated by QCD processes, while interesting physics has EW cross sections Purely hadronic channels essentially hopeless Must rely on distinctive final state signatures leptons (e, mu and taus) photons b-jets missing ET Further signal suppression from branching ratios YETI 08, Durham Jan'08 Antonella De Santo, RHUL 14

Detector Requirements Excellent position and momentum resolution in central tracker b-jets, taus Excellent ECAL performance electrons, photons v. good granularity (energy and position measurements) Good HCAL performance jets, Etmiss (neutrinos, SUSY stable LSP, etc) good granularity (energy and position measurements) good h coverage (hermeticity for Etmiss measurements) Excellent muon identification and momentum resolution from “combined” muons in external spectrometer + central tracker YETI 08, Durham Jan'08 Antonella De Santo, RHUL 15

The Detectors CMS Muon System Calorimetry Magnet system Tracking ATLAS YETI 08, Durham Jan'08 Antonella De Santo, RHUL 16

ATLAS vs CMS ATLAS CMS Magnet system Air-core toroids + solenoid Calorimeter outside field B = 2 T (barrel) Solenoid Calorimeters inside field B=4 T Central tracker Si pixel + strips, TRT (e/had) (p. T)/p. T~5× 10 -4 p. T 0. 01 Si pixel+strips (p. T)/p. T~1. 5× 10 -4 p. T 0. 005 ECAL Pb + Liquid Ar (LAr) E/E~10%/√E (uniform) longitudinal segmentation HCAL m-Det YETI 08, Durham Jan'08 Fe-scintillator + Cu-LAr (10 l) E/E~50%/√E 0. 03 Air (p. T)/p. T~7% at 1 Te. V (standalone) Antonella De Santo, RHUL Pb. WO 4 crystals E/E~3 -5%/√E no longitudinal segmentation Cu-scintillator (5. 8 l + catcher) E/E~65%/√E 0. 05 Fe (p. T)/p. T~5% at 1 Te. V (“combined” muons) 17

Overview of the CMS and ATLAS Triggers 40 MHz input rate Detectors Lvl-1 L 1 Detectors (bunch crossing) Front end pipelines L 1 Lvl-1 Front end pipelines L 2 Lvl-2 Readout buffers O(100 k. Hz) L 1 rate Readout buffers Switching network HLT Switching network O(1 k. Hz) L 2 HLT rate (ATLAS only) Processor farms Lvl-3 EF Processor farms O(100 Hz) output rate (on tape) CMS – 2 levels L 1: Hardware based (calo+m’s) ATLAS – 3 levels ( L 2 + EF = HLT ) (HLT = High-Level Trigger) HLT: YETI 08, Durham Jan'08 Software based Antonella De Santo, RHUL Event size 18 1 -2 MBytes

Overview of the CMS and ATLAS Triggers 40 MHz input rate Detectors Lvl-1 L 1 Detectors (bunch crossing) Front end pipelines L 1 Lvl-1 Front end pipelines L 2 Lvl-2 Readout buffers Regions of Interest (Ro. Is) O(100 k. Hz) L 1 rate Readout buffers Switching network HLT Switching network O(1 k. Hz) L 2 HLT rate (ATLAS only) Processor farms Lvl-3 EF Processor farms O(100 Hz) output rate (on tape) CMS – 2 levels L 1: Hardware based (calo+m’s) ATLAS – 3 levels ( L 2 + EF = HLT ) (HLT = High-Level Trigger) HLT: YETI 08, Durham Jan'08 Software based Antonella De Santo, RHUL Event size 19 1 -2 MBytes

ATLAS YETI 08, Durham Jan'08 Antonella De Santo, RHUL 20

CMS YETI 08, Durham Jan'08 Antonella De Santo, RHUL 21

ATLAS CMS CERN, Building 40 YETI 08, Durham Jan'08 Antonella De Santo, RHUL 22

EW SYMMETRY BREAKING AND HIGGS BOSON

Constraints on Higgs Mass Direct LEP limit : MH >114. 4 Ge. V (95% C. L. ) mlimit = 144 Ge. V no perturbative unitarity unstable vacuum YETI 08, Durham Jan'08 From http: //lepewwg. web. cern. ch/LEPEWWG/ Antonella De Santo, RHUL 24

SM Higgs Couplings Different Feynman rules for fermions and gauge bosons, but in all cases Higgs couplings proportional to mass YETI 08, Durham Jan'08 Antonella De Santo, RHUL 25

SM Higgs Production at the LHC Gluon Fusion Higgs-strahlung YETI 08, Durham Jan'08 Vector Boson Fusion ttbar H (“associated” production) 26 Antonella De Santo, RHUL

SM Higgs Production Cross Sections YETI 08, Durham Jan'08 Antonella De Santo, RHUL 27

Standard Model Higgs Decays Heaviest quark (b-bbar) BR dominates at low masses, until there is enough energy to produce gauge boson pairs (WW, ZZ) But b-bbar very difficult due to huge QCD background and limited b-jet resolution (O(15%)) Despite much lower BR, H gg via intermediate ttbar loop has better Signal/Bkgd ratio for low Higgs mass YETI 08, Durham Jan'08 Antonella De Santo, RHUL 28

Low Mass Higgs (MH<140 Ge. V) – H gg Direct Higgs coupling to gg forbidden, as photon is mass less Low branching ratio (~10 -3), but nice mass peak thanks to excellent ECAL energy resolution (both ATLAS and CMS) S/B 1: 20 100 fb-1 CMS Physics YETI 08, Durham Jan'08 TDR, 2006 Resolution ~1 Ge. V at 100 Ge. V 29 Antonella De Santo, RHUL

H gg – Backgrounds Irreducible (from physics) – Intrinsically v. similar to signal q _ q gluon π0 γ γ Reducible (can be suppressed in principle) – e. g. increased. Antonella calo segmentation YETI 08, Durham Jan'08 De Santo, RHUL 30

High Mass Higgs (MH>2 MZ) – H 4 lep e+ q _ q H Z e- Z e+ e- H ZZ* l+l– =e, m) l+l– (l Very little background (ZZ, Zbb, t-ttbar) CMS Resolution <1 Ge. V at 100 Ge. V Antonella De Santo, RHUL YETI 08, Durham Jan'08 31

Vector Boson Fusion Tagging Forward Jets YETI 08, Durham Jan'08 Antonella De Santo, RHUL 32

Vector Boson Fusion Two tagging forward jets Higgs decay products in central region Lep-lep or lep-had signature for H tt High-p. T jet veto J 2 m. J 1 e- YETI 08, Durham Jan'08 H tt. Antonella emnn De Santo, RHUL 4 for 30 fb-1 CMS, H tt 33

SM Higgs – Discovery Potential Significance vs. MH CMS, 30 fb-1 YETI 08, Durham Jan'08 ATLAS, 30 fb-1 Antonella De Santo, RHUL 34

What If No Higgs? . . . If no Higgs boson is found at the Te. V scale, new mechanism is required to avoid divergencies at high energy Study of the WW cross section may hold the key in this case, as WW scattering becomes strong at the Te. V scale in the absence of a light Higgs YETI 08, Durham Jan'08 Antonella De Santo, RHUL 35

What If No Higgs? . . . If no Higgs boson is found at the Te. V scale, new mechanism is required to avoid divergencies at high energy Study of the WW cross section may hold the key in this case, as WW scattering becomes strong at the Te. V scale in the absence of a light Higgs y a od T t No YETI 08, Durham Jan'08 Antonella De Santo, RHUL 36

SUPERSYMMETRY

Why go Beyond the Standard Model? Despite its many successes, Standard Model is widely believed to be only an effective theory, valid up to a scale L << MPlanck Gravity not included in SM Hierarchy/naturalness problem: MEW << MPlanck Fine-tuning Unification of couplings Need a more fundamental theory of which SM is only a low-energy approximation YETI 08, Durham Jan'08 Antonella De Santo, RHUL 38

Supersymmetry (SUSY) Space-time symmetry that relates fermions (matter) and bosons (interactions) Further doubling of the particle spectrum Every SM field has a “superpartner” with same mass Spin differs by 1/2 between SUSY and SM partners Identical gauge numbers Identical couplings Superpartners have not been observed SUSY must be a broken symmetry But SUSY-breaking terms in Lagrangian must not re-introduce quadratic divergences in theory ! YETI 08, Durham Jan'08 Antonella De Santo, RHUL 39

Minimal Supersymmetric Standard Model Particles and Fields Symbol YETI 08, Durham Jan'08 Name Supersymmetric Partners Interaction Eigenstates Symbol Name Mass Symbol Eigenstates Name quark squark lepton slepton neutrino sneutrino gluon gluino W-boson wino charged Higgs boson charged higgsino B-field bino W 0 -field wino neutral Higgs boson neutral Antonella De Santo, higgsino RHUL chargino neutralino 40

R-parity MSSM contains L- ad B-violating terms, which could in principle allow proton decay via sparticle diagrams: This can be prevented by introducing a new symmetry in theory, called R-parity: R=+1 (SM particles), R=-1 (SUSY particles) Two important consequences: LSP (=Lightest SUSY Particle) is stable – typically neutralino Sparticles can only be produced in pairs (in scattering of SM particles) YETI 08, Durham Jan'08 Antonella De Santo, RHUL 41

R-parity In the following, assume R-parity conservation Stable LSP (neutralino) YETI 08, Durham Jan'08 Antonella De Santo, RHUL 42

Neutralino as Dark Matter Constituent WMAP 0. 094 < WCDMh 2 < 0. 136 (95% CL) Neutralino LSP is a good DM candidate stable electrically neutral weakly and gravitationally interacting YETI 08, Durham Jan'08 Antonella De Santo, RHUL 43

m. SUGRA (or CMSSM) Soft SUSY breaking mediated by gravitational interaction at GUT scale Only five parameters: m 0 — universal scalar mass m 1/2 — universal gaugino mass A 0 — trilinear soft breaking parameter at GUT scale tanb — ratio of Higgs vevs sgn(m) — sign of SUSY Higgs mass term (|m|determined by EW symmetry breaking) Useful framework to provide benchmark scenarios YETI 08, Durham Jan'08 Antonella De Santo, RHUL 44

RGE Evolution Universal boundary conditions at some high scale (GUT) Evolution down to EW scale through Renormalisation Group Equations (RGE) gluino, squarks Universal gaugino mass charginos, neutralinos, sleptons YETI 08, Durham Jan'08 Universal scalar mass Antonella De Santo, RHUL 45

m. SUGRA Parameter Space Four regions compatible with WMAP value for Wh 2, different mechanisms for neutralino annihilation: (Ge. V) 3000 100 250 YETI 08, Durham Jan'08 350 (Ge. V) Antonella De Santo, RHUL 46

m. SUGRA Parameter Space Four regions compatible with WMAP value for Wh 2, different mechanisms for neutralino annihilation: bulk neutralino mostly bino, annihilation to ff via sfermion exchange (Ge. V) 3000 100 250 YETI 08, Durham Jan'08 350 (Ge. V) Antonella De Santo, RHUL 47

m. SUGRA Parameter Space Four regions compatible with WMAP value for Wh 2, different mechanisms for neutralino annihilation: bulk neutralino mostly bino, annihilation to ff via sfermion exchange (Ge. V) 3000 focus point neutralino has strong higgsino component, annihilation to WW, ZZ 100 250 YETI 08, Durham Jan'08 350 (Ge. V) Antonella De Santo, RHUL 48

m. SUGRA Parameter Space Four regions compatible with WMAP value for Wh 2, different mechanisms for neutralino annihilation: bulk neutralino mostly bino, annihilation to ff via sfermion exchange (Ge. V) 3000 focus point neutralino has strong higgsino component, annihilation to WW, ZZ co-annihilation pure bino, small NLSP-LSP mass difference, typically coannihilation with stau 100 250 YETI 08, Durham Jan'08 350 (Ge. V) Antonella De Santo, RHUL 49

m. SUGRA Parameter Space Four regions compatible with WMAP value for Wh 2, different mechanisms for neutralino annihilation: bulk neutralino mostly bino, annihilation to ff via sfermion exchange (Ge. V) 3000 focus point neutralino has strong higgsino component, annihilation to WW, ZZ co-annihilation pure bino, small NLSP-LSP mass difference, typically coannihilation with stau 100 Higgs funnel 250 YETI 08, Durham Jan'08 350 (Ge. V) Antonella De Santo, RHUL decay to fermion pair through resonant A exchange – high tanb 50

stot (pb) SUSY Cross-Sections Cross-section dominated by production of coloured particles m (Ge. V) YETI 08, Durham Jan'08 Antonella De Santo, RHUL 51

Production Mechanisms Squark/Gluino Production YETI 08, Durham Jan'08 Antonella De Santo, RHUL Direct Gaugino Production 52

Possible Final States YETI 08, Durham Jan'08 Antonella De Santo, RHUL 53

Inclusive Searches p p q g~ ~ q ~ c 02 q ~ c 01 ~ l l l Complex long decay chains to undetected Inclusive search: high multiplicity of high-p. T jets large ETmiss (from escaping LSP) ≥ 0 (high-p. T) leptons YETI 08, Durham Jan'08 Antonella De Santo, RHUL 54

Inclusive Searches p p q g~ ~ q ~ c 02 q ~ c 01 ~ l l l Complex long decay chains to undetected Inclusive search: high multiplicity of high-p. T jets large ETmiss (from escaping LSP) ≥ 0 (high-p. T) leptons YETI 08, Durham Jan'08 Antonella De Santo, RHUL 55

The “Needle in the Haystack”… YETI 08, Durham Jan'08 Antonella De Santo, RHUL 56

… a SUSY event in ATLAS… Multi-jet event in Bulk Region 6 jets 2 high-pt muons Large missing ET YETI 08, Durham Jan'08 Antonella De Santo, RHUL 57

… and one in CMS Multi-jet event with large missing ET YETI 08, Durham Jan'08 Antonella De Santo, RHUL 58

SUSY Mass Scale ds/d. Meff (mb/400 Ge. V) SUSY mass scale defined as cross-section weighted mean of masses of initial SUSY particles produced in pp collision Effective SUSY mass scale Meff. SUSY takes into account mass of undetected LSP (neutralino) Meff a good estimator for Meff. SUSY Meff (Ge. V) YETI 08, Durham Jan'08 Antonella De Santo, RHUL 59

10 fb-1 reach — tanb=10, m>0, A=0 g(2500) m 1/2 (Ge. V) ATLAS m. SUGRA Reach Etmiss signature — tanb=10, m>0, A=0 g(2500) q(2500) g(1000) q(1000) YETI 08, Durham Jan'08 q(1000) m. Antonella 0 (Ge. V) De Santo, RHUL m 0 (Ge. V) 60

10 fb-1 reach — tanb=10, m>0, A=0 g(2500) m 1/2 (Ge. V) ATLAS m. SUGRA Reach Etmiss signature — tanb=10, m>0, A=0 g(2500) For ideal case of perfectly understood backgrounds and detector effects !! q(2500) g(1000) q(1000) YETI 08, Durham Jan'08 q(1000) m. Antonella 0 (Ge. V) De Santo, RHUL m 0 (Ge. V) 61

If Only Life Were That Easy… Significant discrepancy observed between PS (e. g. Pythia) and ME (e. g. ALPGEN) calculations of multiparton emission amplitudes Background rate larger in ME generator, which also predicts a more similar shape to that of signal Reliance on MC simulated events must be minimized and backgrounds estimated using datadriven techniques Also need good understanding of detector response YETI 08, Durham Jan'08 Antonella De Santo, RHUL 62

Example of Data-Driven Bkgd Estimation Z+jets (Z nn) background from Drell-Yan (Z ee, mm) m YETI 08, Durham Jan'08 Antonella De Santo, RHUL m 63

Example of Data-Driven Bkgd Estimation Z+jets (Z nn) background from Drell-Yan (Z ee, mm) n YETI 08, Durham Jan'08 Antonella De Santo, RHUL n 64

Example of Data-Driven Bkgd Estimation m n Red: Z nn Blue: Estimated YETI 08, Durham Jan'08 Antonella De Santo, RHUL 65

Dilepton Edge can undergo chain two-body decay to : Sharp Same-Flavour Opposite-Sign (SFOS) dilepton invariant mass edge sensitive to sparticle mass differences YETI 08, Durham Jan'08 Antonella De Santo, RHUL 66

More Decay Chains (and edges) lq edge Decay chains originating from squarks: lq edge Consider invariant mass combination of lepton and jets YETI 08, Durham Jan'08 Antonella De Santo, RHUL 67

More Decay Chains (and edges) llq edge Decay chains originating from squarks: llq edge Consider invariant mass combination of lepton and jets Combine constraints from different decay chains to extract information of individual sparticle masses YETI 08, Durham Jan'08 Antonella De Santo, RHUL 68

SUSY Trilepton Signal from Gaugino Pair Decays Total SUSY cross-section strong function of m 1/2 Gaugino production dominant at Focus Point (large m 0) Total SUSY cross section [pb] Gaugino contribution 90% ~0. 1 pb ~100 pb CMS 20% CMS SUSY 07 YETI 08, Durham Jan'08 Antonella De Santo, RHUL 69

Trileptons from Direct Gaugino Pairs 2 SFOS leptons Heavy scalars – No intermediate sleptons missing ET another lepton SM bkgd from ZW, ZZ, ttbar, Z/W+jets Relatively low-p. T leptons due to small mass differences YETI 08, Durham Jan'08 Antonella De Santo, RHUL 70

Trileptons from gaugino pairs in ATLAS and CMS s BR(3 lep) [pb] A 0=0, tanβ=50 Hi 0. 01 pb Discovery potential essentially equivalent for ATLAS and CMS, differences mostly due to phenomenology of selected points in parameter space s gg CMS [LM 9 point] 0. 1 pb 0. 2 pb NO EWSB CMS Excluded by LEP m 0=1450, m 1/2=175, tanβ=50 A 0=0, m>0 N 3 lep/fb-1 = 130 O(30 fb-1) ATLAS [SU 2 point] m 0=3550, m 1/2=300, tanβ=10 A 0=0, m>0 N 3 lep/fb-1 = 30 O(100 fb-1) SUSY 07 YETI 08, Durham Jan'08 Antonella De Santo, RHUL 71

Trileptons +jets (+ Etmiss) signature Jets 1, 2 >=3 leptons+ Etmiss (x 2) (+Etmiss) More relevant for “low-mass” SUSY (i. e. not in Focus Point region) An interesting channel for mass edges, but largest background is from SUSY itself explore discovery potential of inclusive 3 -lep search ! YETI 08, Durham Jan'08 Antonella De Santo, RHUL 72

Inclusive Trileptons Signal = any decay originating from SUSY particles that gives 3 leptons (+ jets + Etmiss) in the final state Simple cut flow: 3 isolated leptons (including e, m from taus) – not necessarily SFOS at least 1 high-pt jet (>200 Ge. V) high Etmiss requirement not crucial SUSY 07 ATLAS preliminary Signal only (SU 3) Preliminary results for 5 s discovery reach: SU 2 (“focus point”) : O(10 -15 fb-1) SU 3 (“bulk”) : O(1 -2 fb-1) SU 4(“low-mass”) : O(100 -150 pb-1) YETI 08, Durham Jan'08 Antonella De Santo, RHUL theoretical endpoint 73 OSSF Dilepton Edge (Ge. V)

BEYOND SUSY – EXTRA DIMENSIONS

Models of Extra Dimensions Plenty of models on the market cannot possibly discuss all of them in detail Two “popular” examples: ADD (Arkani-Hamed, Dimopoulos, Dvali) [Phys Lett B 429 (98)] RS (Randall-Sundrum) [Phys Rev Lett 83 (99)] YETI 08, Durham Jan'08 Antonella De Santo, RHUL 75

Motivations The hierarchy problem (MEW /MPlanck~10 -17) can also be addressed by exploiting the geometry of space-time The three spatial dimensions in which we live could be a three-spatialdimensional “membrane” embedded in a much larger extra dimensional space Observed hierarchy between gravitational and EW scale generated by geometry of additional dimensions (and not by an intrinsically small gravitational coupling constant!) YETI 08, Durham Jan'08 Antonella De Santo, RHUL 76

Motivations – Cont’d Weak and strong force probed down to ~(100 Ge. V)-1 ~O(10 -15 m) Gravitational force only probed down to ~1 mm (e. g. Cavendish expt), Not implausible that gravity may diverge from Newton’s law at much smaller distances Matter and non-gravitational forces “confined” to our 3 -dim space (“brane”), while gravity propagates throughout the full n+3 spatial volume of a higher dimensional (D=3+n+1) volume, the “bulk” YETI 08, Durham Jan'08 Antonella De Santo, RHUL 77

ADD Model Modified Newton’s law ruled out for large ED, but not excluded for sufficiently small, “compactified” ED of size R <<r : effective Planck scale for n extra dim. Intrinsically strong gravitational force diluted by bulk volume For n>1, fundamental Planck scale could be as low as 1 Te. V (n=2 disfavoured by cosmological arguments): YETI 08, Durham Jan'08 R = radius of compactified Antonella De Santo, RHUL dimension 78

ADD Collider Signatures – Real Graviton Emission G Graviton emitted in association with jet or gauge boson Jet +Etmiss YETI 08, Durham Jan'08 Antonella De Santo, RHUL g, q jet, V 79

ADD Collider Signatures – Virtual Graviton Emission G g, q f, V Excess over dilepton continuum from SM processes such as q-qbar, gg l+l- YETI 08, Durham Jan'08 Antonella De Santo, RHUL 80

RS Models A small, highly curved (“warped”, e-2 kr ) extra dimension connects the SM brane (at O(Te. V)) to the Planck scale brane Gravity small in our space because warped dimension decreases exponentially between the two branes Series of narrow, high-mass resonances: 400 600 800 1000 Resonance width determined by ratio k/MPl Spin analysis to distinguish spin-2 G from spin-1 Z’ resonance YETI 08, Durham Jan'08 d /d. M (pb/Ge. V) (only first peak visible at LHC, due to PDFs) Mll (Ge. V) 700 -4 Ge. V KK Graviton at the 10 Tevatron 1 -6 = 1, 0. 7, 0. 5, 0. 3, 0. 2, 0. 1 from k/M 10 Pl 0. 5 0. 1 top to bottom -8 10 Drell-Yan at the LHC 0. 05 10 -10 0. 01 Antonella De Santo, RHUL 10 -2 1000 3000 5000 81 Mllmass (Ge. V) Dilepton

*** REALLY*** Parton i RS Exotics – Black Holes Parton j If the impact parameter of a head-on collision is smaller than the Schwarzschild radius Rs corresponding to the centre-ofmass energy √s (Rs=2 G √s/c 2), then a black hole of mass MBH= √s can be formed “Black disk” approximation: ~ p. RS 2 ~ 1 Te. V -2 ~ 10 -38 m 2 ~ 100 pb BH “evaporate” semi-classically in a time t~10 -27 s and emit black body radiation at a characteristic “Hawking temperature”, TH n = # of EDs (Mini-BH are “hot” (~100 Ge. V) Hawking radiation) YETI 08, Durham Jan'08 Antonella De Santo, RHUL 82

Mini-BH – Event Selection High multiplicity of high-p. T final state particles “Democratic” production of particles (all d. o. f. at ~100 Ge. V, at roughly equal rates) -- summing over spin and colour: 75% quarks, gluons 10% charged leptons 5% neutrinos 5% g, W/Z Hence hadronic activity is dominant -- jet trigger Large Etmiss -- from escaping n’s and gravitons Events tend to be spherical (but sphericity depends significantly on number of EDs) YETI 08, Durham Jan'08 Antonella De Santo, RHUL ATLAS simulation 83

… AND A LOT MORE… YETI 08, Durham Jan'08 Antonella De Santo, RHUL 84

More Physics at the LHC Standard Model B-physics Heavy Ions Diffractive physics YETI 08, Durham Jan'08 Antonella De Santo, RHUL 85

More Physics at the LHC Standard Model B-physics Heavy Ions y a od T t No Diffractive physics YETI 08, Durham Jan'08 Antonella De Santo, RHUL 86

CONCLUSIONS YETI 08, Durham Jan'08 Antonella De Santo, RHUL 87

With the LHC turn on, physics at the Te. V scale will become accessible experimentally at an accelerator for the first time High expectations to be able to shed light on the origin of mass and the mechanism for EW symmetry breaking Serious possibility to observe “dark matter in a laboratory”, and even to test gravity And 2008 is the year! YETI 08, Durham Jan'08 Antonella De Santo, RHUL 88