Prospects for New Physics at the LHC Michael Schmitt Northwestern University PANIC 08 Eilat, ISRAEL 10 – Nov – 2008 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) This is a vast topic. And I have just 20 minutes! I will discuss just three analyses, and - hopefully - give some real content… Z' → m+m- H → gg jets and missing energy intro: CMS and ATLAS concluding remarks 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) CMS LHC-b ALICE ATLAS Drs. Funk and Morettini will have discussed this in the prior session. 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) CMS 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) ATLAS 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Z' → m+m- Many theories of new physics predict a new gauge boson which will decay to fermion pairs, like the usual Z boson. Also, in extra-dimensional theories, spin-2 excited states of SM gauge bosons can decay to fermion pairs. Masses, couplings, cross sections, branching ratios are all unknown a priori (there are some theory constraints). We can observe these new bosons as resonances in di-fermion invariant mass distributions. The best result comes when the peak is narrow. This means electrons and muons are best. 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Elements of the Analysis: ATLAS & CMS have endcap muon systems – good acceptance. select a pair of high-pT opposite-charge leptons make sure kinematics are well measured Drell-Yan continuum, boson pairs, top quarks, fake leptons in jets none of these gives a peak in di-lepton invariant mass fake leptons can be strongly suppressed by demanding that the selected leptons not fall inside a jet – “isolation” Main background will be continuum di-lepton pairs. Look for a peak on top of a smooth background. CMS 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Results / Sensitivity : Assume resonance is relatively narrow. Test: are the data compatible with a peak at an arbitrary mass? Since couplings are indeterminate, take some benchmarks. CMS What can we see with 100 pb-1? Surpass the Tevatron… 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Discussion : Assume resonance is relatively narrow. → Then the width of the bump comes from detector resolution; a narrower peak means better signal/background. linear For muons, this means primarily alignment: point errors translate into curvature, ie, pT errors. “Prospects for Discovery” → getting a good alignment early! 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Alignment Methodology: 0) use photogrammetry to get excellent starting point. use lasers and sensors to refine this, and to track movements of gross structures 2) use reconstructed tracks for ultimate precision cosmic rays ATLAS 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) H → gg This is a SM process – that has never been observed… Theoretically novel – decay proceeds only through a loop, which could reveal new particles indirectly (in principle). In the SM, the rate is firmly predicted (as function of MH). And in SUSY, variations are small – lightest Higgs is SM-like. Main production is from gluons (another loop!) with important contributions from VBF and ttH production. BR, however, is very small, typically 0.002. (MH < 140 GeV) eff. cross-section = (30 – 50 pb) x 0.002 = 60 – 100 fb. 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Elements of the Analysis: As before, look for a narrow peak on top of a continuum. two well-reconstructed photons, high ET > 25, 40 GeV The background is huge!! irreducible – direct production of 2 photons w/o Higgs reducible – one of the photons is from p0 or is fake Use isolation and shower shape to suppress bad photons. photon ATLAS jet fraction outside core strip width 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Interesting Extension: Really try to remove all background – pull out all the stops! Combined kinematic quantities in an artificial neural network: polar decay angle scaled photon energies difference in h longitudinal momentum of di-photon pair Standard “cut-based” analysis simply looks for a peak; - hence, is lett model-dependent; This approach assumes the model and exploits all features wisely. → sensitivity improved by about 30% The two approaches are complimentary. 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Results / Sensitivity : Although signal is fairly well “known” the background is not, so discovery potential estimates comes with a lot of uncertainty. CMS NN Fortunately, sidebands are a ready source of background events → directly measure the rate, and kinematic characteristics 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Energy Resolution : CMS comparison test-beam and CR: 1.5% (need 0.5%) Again – we want as narrow a peak as possible. EM calorimeter must be well-calibrated. basic calibration done with test beam inter-channel calibration done with inclusive p0’s and muons (cosmic rays!) absolute scale will be set from W → en and Z peak 2) The amount of material in front of calorimeter is crucial more than one X0 ! 40% of the photons in H → gg convert. quality degrades when shower is spread out laterally recuperation is possible – not fully developed yet divide samples according to photon quality. 10-Nov-2008 New Physics at the LHC (Schmitt)

Jets and Missing Energy Supersymmetry = theorist’s best guess about BSM. LHC might turn out to be the machine that finds SUSY. Characteristic feature: LSP is weakly-interacting & neutral. Best place to find SUSY is probably in a sample of Jets+MET. Signatures vary widely, difficult to specify and hence most analyses pick one possibility and optimize for it: two jets and MET three or more jets, and MET jets and one lepton, and MET etc. 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Elements of the Analysis: Reconstruct jets from calorimeter energy clusters. demand at least 3: ET > 30 GeV and | h | < 3 MET > 200 GeV ET1 > 180 GeV, ET2 > 110 GeV, HT > 500 GeV Event Cleanup: vertex reconstructed from charged tracks fractions of “electromagnetic” and “charged” energy not too large. CMS cosmic ray data! 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Veto events with leptons (loose criteria). QCD 3-jet events have large MET usually due to one badly mis-measured jet: MET vector should not point close to any jet. CMS SUSY QCD 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Results / Sensitivity : Even though the selection is fairly straight-forward, the expected signal varies greatly. Here are two “benchmarks scenarios” : 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) Interesting Model-Independent Approach : Promising ATLAS study* looks for statistical excess anywhere in a predefined kinematic space. Kinematic quantities should be well suited to the generic channel. Construct a sphere around a given data point and compare number of data events to expectation (simul’n). No use of signal simulation at all. Performance appears to be as good as “targeted” analyses, yet much less model-dependent. 10-Nov-2008 New Physics at the LHC (Schmitt) (* E. Duchovni et al., Weizmann Institute)

New Physics at the LHC (Schmitt) Concluding Remarks You have seen a brief overview of three selected analysis – they are already quite advanced; others, too. Prospects for discoveries will be good since so much is being done in advance of collisions… 10-Nov-2008 New Physics at the LHC (Schmitt)

New Physics at the LHC (Schmitt) 10-Nov-2008 New Physics at the LHC (Schmitt)