Paolo Meridiani - INFN Roma11 Physics with CMS Paolo Meridiani (INFN Roma1)

Paolo Meridiani - INFN Roma12 Outline Lecture 1 Is SM satisfactory? Open questions in the SM? LHC: the answer to unanswered questions? CMS Detector: a challenging detector for a challenging machine CMS Commissioning: how much time is required to make it work? Lecture 2 CMS early physics: what can be done at the beginning? SM physics with CMS: known physics can be done better in CMS? Higgs Physics with CMS: if it’s there we will catch it! Lecture 3 Beyond the SM physics at CMS: hunting new theories

Paolo Meridiani - INFN Roma13 Hunting new physics Recall: Why do we think about extending the SM? Gravity is not incorporated Hierarchy problem Unification of couplings (GUT) Flavour/ number of families beg for explanation... Many candidate theories: Supersimmetry Extradimensions..... I do not have the time to go deeply into all of them, but I would like you to have a feeling of the strategy and things to be controlled for new physics discoveries in CMS

Paolo Meridiani - INFN Roma14 Features of SuperSimmetry SuperSimmetry: achieved in theory where lagrangian is invariant with respect to What this brings: Cancellation of quadratic divergences Unification of couplings Provides a candidate for cold dark matter (in case of R-parity conservation) Easy to accomodate EW precision data

Paolo Meridiani - INFN Roma15 MSSM Minimal Supersimmetric extension of the SM Introduce super-partners  s = ½ for each SM particle Two Higgs doublets with and superpartners. After EW simmetry breaking 5 Higgs bosons: h, H, A, H  remain Supersimmetry should be broken: no superpartner observed to date Additional ingredient: R-parity a new conserved quantum number

Paolo Meridiani - INFN Roma16 MSSM physical spectrum Mass are not predicted but usually charginos and neutralinos are lighter than squarks/spletons/gluinos

Paolo Meridiani - INFN Roma17 Breaking SUSY In MSSM supersimmetry is broken with explicit terms (105 free parameters) then reduced to imposing phenomenological constraints Since SUSY cannot be broken spontaneously, idea is to postulate an hidden sector of interactions Most of the following analysis will be shown in the mSUGRA scenario

Paolo Meridiani - INFN Roma18 Producing LHC

Paolo Meridiani - INFN Roma19 SUSY signatures In the assumption that R-parity is conserved:

Paolo Meridiani - INFN Roma110 Search strategy

Paolo Meridiani - INFN Roma111 Benchmark points Basis of detailed studies in the mSUGRA context Low mass points for early LHC running but outside Tevatron reach High mass points for ultimate LHC reach

Paolo Meridiani - INFN Roma112 Inclusive search: jets + MET Most powerfull way to observe SUSY excess CMS Example: MET>200 GeV + Clean-up  3 jets: E T > 180, 110, 30 GeV Indirect lepton veto Cuts on  between jets and MET H T /M eff =E T1 +E T2 +E T3 +MET>500 GeV CMS Results: LM1 efficiency is 13%, S/B ~ 26 ~6 pb -1 for 5  discovery

Paolo Meridiani - INFN Roma113 Same sign muons Even cleaner signature with low background due to same-sign requirement Concentrate here on isolating the SUSY diagrams giving prompt muons with strong muon isolation & tight quality cuts Cuts LM1): 2 SS isolated muons pT > 10 GeV MET > 200 GeV  3 jets: ET1>175 GeV ET2>130 GeV ET3>55 GeV 65% efficient at identifying SUSY diagrams, 90% pure

Paolo Meridiani - INFN Roma114 Inclusive MET + Z 0 Catch Mostly from q, g decays Z 0 gives extra handle against non-resonant dilepton bkg Cuts ( LM4 ): MET > 230 GeV 2 OS SF leptons p T (e) > 17 GeV, or p T ( µ ) > 7 GeV 81 < M ll < 96.5 GeV  < 2.65 rad Background (10 fb -1 ) SM: 200  40 (t-tbar+diboson) Systematic uncertainty 20% LM4 Signal (10 fb -1 ) 1550  30 e+e–e+e– CMS Sensitive here

Paolo Meridiani - INFN Roma115 Convince yourself that you have observed something If SUSY is there should be relatively easy to get an excess of events over the SM But the real problem is convince yourself that this is a real excess MET: key signature for SUSY in the assumption of R-parity conservation But tuning MET will not be easy: Lesson from Tevatron: All the instrumental garbage go in MET Long and painstaking polishing phase is required

Paolo Meridiani - INFN Roma116 MET in CMS Sum mom. over calorimeter towers MET is magnitude of imbalance MET Resolution Measure from data Use min-bias and prescaled jet triggers to measure resolution CMS stochastic term ~0.6–0.7 Jet calibration crucial to improve resolution and reduce systematic uncertainty Variety of techniques possible  -Jet balancing, di-jet balancing, W mass constraint in tt events CMS GOAL: Achieve 50 GeV with 1–10 fb -1 QCD Minbias

Paolo Meridiani - INFN Roma117 Example: MET SM Bkg normalization Idea: use Z  µµ + jets (>2) in data to normalize the Z  (invisible) contribution and calibrate MET spectrum

Paolo Meridiani - INFN Roma118 Capability of observing a SUSY like excess in CMS with inclusive searches

Paolo Meridiani - INFN Roma119 The fun begins... Assuming (hoping) to have observed an excess within 10 fb -1 what happens? Need to demonstrate that: Every particle has a superpartner with  s=1/2 and same gauge quantum numbers Mass relations predicted by SUSY holds Observables: Masses BR’s Production cross-sections Angular decay distributions

Paolo Meridiani - INFN Roma120 SUSY spectroscopy With stable  1 0 cannot fully reconstruct squark or gluino decay chains in general Kinematical endpoints in invariant mass distributions give access on sparticle masses Start from dileptons from  2 0 (m ll ) Add quark jet to get squark (m llq ) Add another jet to get gluino (m llqq ) These and other combinations (e.g. m lq ) have endpoints that are functions of the sparticle masses p p b b q ~ Kinematic end points (MC) in Dalitz plot of Mll and Mllq

Paolo Meridiani - INFN Roma121 Endpoint analysis

Paolo Meridiani - INFN Roma122 Example m(l+l-) at CMS Measure invariant mass distribution of same-flavor opposite-sign (SFOS) leptons as evidence for or Striking signature: probably first and clearest signal of SUSY LM1 with 1 fb -1, fit result: Subtract different flavor leptons

Paolo Meridiani - INFN Roma123 Alternative SUSY models: GMSB Actual phenomenology depens on neutralino life-time

Paolo Meridiani - INFN Roma124 And apart from SUSY? 1976 Nobel Discovery of the J/Psi Ting 1984 Nobel Discovery of W&Z Rubbia & Van der Meer Di-something resonances:

Paolo Meridiani - INFN Roma125 Di-something resonances Leptons and photons are the cleanest signature

Paolo Meridiani - INFN Roma126 Extended gauge simmetries

Paolo Meridiani - INFN Roma127 The Randall-Sundrum model

Paolo Meridiani - INFN Roma128 Experimental facts in reconstructing high energy objects in CMS Very High Energy Electrons and Photons Saturation in CMS ECAL (limited electronics range) above 1.7 TeV barrel, 3 TeV endcaps; mass resolution barrel 0.6 % (7%) with (without) saturation correction (based on non saturating adjacent crystals) Very High Energy Muon Misalignment + multiple scattering dominate Muon bremsstrahlung In general resolution of high energy electrons/photons better than muons  E/E  constant  0.5%  p/p  p

Paolo Meridiani - INFN Roma129 Searching for Z’ resonances Discovery potential even with less than 1fb -1

Paolo Meridiani - INFN Roma130 RS gravitons

Paolo Meridiani - INFN Roma131 Distinguishing RS graviton from Z’ Angular distribution of lepton in the boosted rest frame of the heavy mass particle

Paolo Meridiani - INFN Roma132 Not only resonances but also continuum...

Paolo Meridiani - INFN Roma133 ADD model M D << M Pl Constraints: M D <10 TeV n>1 (Newton law tested up to 200  m)

Paolo Meridiani - INFN Roma134 ADD graviton Signature: Single high p T  in central region High missing p T back-to-back photon Main SM bkg: Z+  → +  Normalization from Z+  →  +  Discovery reach M D < 3 TeV for 30fb -1

Paolo Meridiani - INFN Roma135 High multiplicity/spherical events

Paolo Meridiani - INFN Roma136 Black Holes hunting...

Paolo Meridiani - INFN Roma137 Do not forget that... Before any discovery we need to understand SM background that we know is there + control well our detector

Paolo Meridiani - INFN Roma138 CMS discovery path

Paolo Meridiani - INFN Roma139 THE END