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Prospettive di fisica a LHC

Prospettive di fisica a LHC. Parte II) La fisica dello Standard Model (escluso l’ Higgs, trattato successivamente) -misure di precisione di M w e M top . - b- physics. Lo Standard Model a LHC. LHC: una fabbrica di top quarks. s (bb)= 500 m b Possibili studi di processi rari

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Prospettive di fisica a LHC

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  1. Prospettive di fisica a LHC Parte II) La fisica dello Standard Model (escluso l’ Higgs, trattato successivamente) -misure di precisione di Mw e Mtop. - b- physics Corso SM, Dottorato, XX ciclo

  2. Lo Standard Model a LHC LHC: una fabbrica di top quarks s(bb)= 500mb Possibili studi di processi rari (es. Bs->2m, studio di violazione di CP con alta statistica; Caveat: capacità di Trigger) misure di alta precisione di MW (goal: dMW10 MeV, limitato dalla sistematica) 108 tt/anno (ad alta luminosità) Corso SM, Dottorato, XX ciclo

  3. Le misure di precisione a LHC: motivazioni La predizione SM di MHiggs: DM t= 5.2 GeV incertezze attuali DMW= 39 MeV Misure dirette consistenza?! 80.385 Fit agli osservabili elettrodeboli Dipendenza da mt, mH nello SM Corso SM, Dottorato, XX ciclo

  4. La fisica del top Produzione di coppie di top: stt(th)=825±150 pb NNLO-NNNLL: Kidonakis, Vogt, PRD 68 (03) 114014 This means 8 millions tt pairs/year (1 pair/second) at “low” luminosity! 1033cm-2s-1=1nb-1s-1 qq->tt: 13% gg->tt: 87% quark annihilation gluon fusion Corso SM, Dottorato, XX ciclo

  5. j1 W j2 t b-jet La fisica del top • „easiest“ channel : • tt  bb qq l (semi-leptonic) BR = 43 % • 3.5 million semileptonic events • corresponding to 10 fb-1 • CMS analysis with hard cuts: • 0.14% of the events kept (!!!) • Goal: • Error on mt  1 GeV • statistical error 250 MeV • largest sys. errors: • pT spectrum 400 MeV • b-jet energy scale ? • Measurements at 1 fb-1 • initial mass determination • total & diff. cross sections Corso SM, Dottorato, XX ciclo

  6. La fisica del top tt  bb qq  event simulated in CMS Corso SM, Dottorato, XX ciclo

  7. Top quark: capacita’ di trigger Efficienza di trigger 0.8 0.6 0.4 Low Lumi HLT threshold 0.2 10 fb-1 Full L1 simulation + HLT reconstruction Off-line reconstruction > 70% efficiency in fiducial region, for typical HLT threshold Corso SM, Dottorato, XX ciclo

  8. La fisica del top: eventi di-leptonici • Both top quarks decay • semi-leptonically: • - BR  5% • - low background • - Mass determination free from • Jet-scale uncertainties • but two neutrinos in final state • Exploit M(ll)-Mtop correlation • to determine Mtop • mt  1.7 GeV Corso SM, Dottorato, XX ciclo

  9. La fisica del top Metodo alternativo per la misura di Mtop Lepton + J/y: 1000 events/year @ L=1034 J/y->mm J/y->ee J/y->mm is a very clean signal. MlJ/y has a dependence on Mt. • Independent from jet scale • Among the main sistematics: • b fragmentation Corso SM, Dottorato, XX ciclo

  10. Mtop da leptone + J/y: Per confronto: di-leptoni Corso SM, Dottorato, XX ciclo

  11. tt spin correlation La fisica del top • Very short lifetime, • no top bound states • Spin info not diluted by hadron formation • Distinguishes between • quark annihilation • A = -0.469 • and gluon fusion • A = +0.431 Use double leptonic decays tt  bb l l A= 0.311  0.035  0.028 (using 30 fb-1) Corso SM, Dottorato, XX ciclo

  12. Produzione di top singolo t-channel s-channel Wt-channel s=10 pb s=247 pb s=56 pb Main bkgs: ttbar, Wbb • Tevatron puts only an upper limit on s • Directly related to |Vtb| • Sensitivity to new physics: FCNC (t-ch.), new gauge bosons (s-ch.), H±->tb … • Background to tt and several searches (ttH, WH->lnbb, …) • Possibility to study top properties (mass, polarization, charge) with very little reconstruction ambiguities Corso SM, Dottorato, XX ciclo

  13. direct measurement of Vtb • observable by Tevatron in Run II • LHC t  1.5 t • Selection: • t  bW  b e () • b-jet + high pT lepton • reconstruction of top mass • Background from tt • signal to bkgd. 3.5 : 1 Production mechanisms and cross sections: Produzione di top singolo  245 pb  60 pb  10 pb Experimental determination of Vtb to percent level (with 30 fb-1) Corso SM, Dottorato, XX ciclo

  14. y = pseudorapidity DGLAP evolution qq  W  l Produzione di W e pdf • Fundamental processes at LHC are • the scattering of • Quark – Antiquark • Quark – Gluon • Gluon – Gluon Examples: gg  H • need precise of parton density Functions [ pdf(x,Q2) ] + QCD corrections (scale) Corso SM, Dottorato, XX ciclo

  15. Esempio di “early physics” a LHC: produzione di W • pT and rapidity distributions are very sensitive to pdf • particularly sensitive variable: • ratio of W+/Wcross section measures u(x)/d(x) Example: study for 0.1 fb-1, i.e. 2·106 W produced Sensitive to small differences in sea quark distribution Corso SM, Dottorato, XX ciclo

  16. CDF W MW 2004: mW = 80 412  42 MeV 2007: mW  80 ...  20 MeV (2.5 ·10-4) LEP & Tevatron Run I from Tevatron Run II Improvement at the LHC to  10 MeV envisaged requires control of systematic error to 10-4 level “Traditional” method: mW from transverse mass distribution Corso SM, Dottorato, XX ciclo

  17. MW Corso SM, Dottorato, XX ciclo

  18. MW • General idea at LHC: • take Z   events • remove one  to fake Z   ““ • mZ = 91 187.5  2.1 MeV known Corso SM, Dottorato, XX ciclo

  19. MW • Example: • use Z   ““ data to create • transverse mass distribution for • arbitrary MX • compare MXTand compare to W data • statistical error from 1 fb-1 • mW  20 MeV • Systematic errors to be investigated: • small differences in W/ Z production • (pT &  distributions) • final state radiation • ( doesn‘t radiate!) • different backgrounds Corso SM, Dottorato, XX ciclo

  20. MW Corso SM, Dottorato, XX ciclo

  21. W/Z + jet(s) physics • An ideal physics final state to connect data to theoretical predications, and improve our understanding of event generation which is critical to many physics analysis: • Test perturbative QCD at large momentum transfer • Indirect measurement of PDF including heavy flavor • Very large cross section to reduce the statistical uncertainty and compare to NLO and NNLO calculations • Serious background process of new physics • Improve Reconstruction technique • Precise Luminosity measurement • Reliable Background normalization Results of W + jets in Tevatron Phys. Rev. Lett. 79, 4760 (1997) Corso SM, Dottorato, XX ciclo

  22. Minimum Jet Pt : 25 GeV (because of large amount of jets from pileup and underlying events below 25 GeV, see plots in later slide) • Minimum Jet-Jet distance : 0.5 • Jet Eta from –5.0 to 5.0 • W/Z semileptonic decay, fragmentation and hadronization, multiple parton scattering by Pythia W/Z + jet(s) physics Alpgen prediction @ LHC: sensitive to , e.g.: => Z+1 jet W+1 jet Z+2 jet W+2 jet Z+3 jet W+3 jet Z+4 jet Z+4 jet Corso SM, Dottorato, XX ciclo

  23. Leading Order Feynman diagrams: Only s-channel has three boson vertex Charged Couplings Allowed in the Standard Model WWW, WWZ, WW Neutral Couplings Forbidden in the Standard Model ZZZ, ZZ, Z What we might expect to see: Cross section enhancement Enhancement at high pT of V 1,2 Enhancement at high MT Production Angle Triple Gauge Boson (W,Z,) Couplings Corso SM, Dottorato, XX ciclo

  24. Triple Gauge Boson Couplings Test CP conserving anomalous couplings at the WW vertex  and  Sensitivity: pT spectrum SM couplings vs current limits at 1.5 TeV • Method: • W final states • W  e and  • pT spectrum of photon Corso SM, Dottorato, XX ciclo

  25. B physics • b physics topics at CMS: • inclusive b production • at 14 TeV and in  collsions • b decays • e.g. b J/ + X • rare b decays • e.g. FCNC in B0s + • CP violation in B0s J/ • B0soscillations • Bc studies Example: reconstruction of B0s J/  + K+K • Main difficulties: • Trigger (low pT thresholds needed) • background rejection Corso SM, Dottorato, XX ciclo

  26. B physics example: B0s decays Rare decay: Bsmm s(bb)= 500 mb ~ 103 Bs/s @ L=1031 SM BR ~ O(10-9 ) from FCNC b  s reachable in 1 year L= 1031 isorate trigger curves: Non-rare channel: 20 Hz Bs J/psi f  mmKK 30 Hz Trigger efficiencies for Bs mm ~ 8 104 decays/10 fb-1 feasable for CP violation studies Corso SM, Dottorato, XX ciclo

  27. Method: • reconstruct B0s • b  X on other side • Analysis: • single  trigger pT > 6.5 GeV (< 2.4) •  4500 signal events expected in 10/fb • Result from MonteCarlo study: • sensitivity (95% CL) to oscillation • frequency xs [ps-1] versus signal • purity fs (less sensitive) mass resolution: 18.5 MeV B physics example: Sensitivity to B0s Oscillations TRIGGER (not easy !) critically dependent on background rejection capability… Corso SM, Dottorato, XX ciclo

  28. B0s Oscillations Current status: Corso SM, Dottorato, XX ciclo

  29. B0s Oscillations Tevatron will certainly improve this result…: Corso SM, Dottorato, XX ciclo

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