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U.GaspariniCorso SM, Dottorato, XX ciclo1 Parte II) La fisica dello Standard Model (escluso l’ Higgs, trattato successivamente) -misure di precisione di.

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Presentation on theme: "U.GaspariniCorso SM, Dottorato, XX ciclo1 Parte II) La fisica dello Standard Model (escluso l’ Higgs, trattato successivamente) -misure di precisione di."— Presentation transcript:

1 U.GaspariniCorso SM, Dottorato, XX ciclo1 Parte II) La fisica dello Standard Model (escluso l’ Higgs, trattato successivamente) -misure di precisione di M w e M top. - b- physics Prospettive di fisica a LHC

2 U.GaspariniCorso SM, Dottorato, XX ciclo2 Lo Standard Model a LHC 10 8 tt/anno (ad alta luminosità) LHC: una fabbrica di top quarks  (bb)= 500  b Possibili studi di processi rari (es. B s ->2 , studio di violazione di CP con alta statistica; Caveat: capacità di Trigger) misure di alta precisione di M W (goal:  M W  10 MeV, limitato dalla sistematica)

3 U.GaspariniCorso SM, Dottorato, XX ciclo3 Le misure di precisione a LHC: motivazioni Misure dirette Fit agli osservabili elettrodeboli Dipendenza da m t, m H nello SM  M W = 39 MeV  M t = 5.2 GeV consistenza?! 80.385 La predizione SM di M Higgs : incertezze attuali

4 U.GaspariniCorso SM, Dottorato, XX ciclo4 La fisica del top NNLO-NNNLL: Kidonakis, Vogt, PRD 68 (03) 114014  tt (th) =825±150 pb This means 8 millions tt pairs/year (1 pair/second) at “low” luminosity! gg->tt: 87%qq->tt: 13% Produzione di coppie di top: 10 33 cm -2 s -1 =1nb -1 s -1 quark annihilationgluon fusion

5 U.GaspariniCorso SM, Dottorato, XX ciclo5 La fisica del top 3.5 million semileptonic events corresponding to 10 fb -1 CMS analysis with hard cuts: 0.14% of the events kept (!!!) Goal:  Error on m t   1 GeV statistical error 250 MeV largest sys. errors: p T spectrum 400 MeV b-jet energy scale ? „easiest“ channel : tt  bb qq l (semi-leptonic) j1j1 j2j2 b-jet t W Measurements at 1 fb -1 initial mass determination total & diff. cross sections BR = 43 %

6 U.GaspariniCorso SM, Dottorato, XX ciclo6 La fisica del top tt  bb qq  event simulated in CMS

7 U.GaspariniCorso SM, Dottorato, XX ciclo7 Low Lumi HLT threshold 10 fb -1 > 70% efficiency in fiducial region, for typical HLT threshold Full L1 simulation + HLT reconstruction Top quark: capacita’ di trigger Off-line reconstruction 0.2 0.4 0.6 0.8 Efficienza di trigger

8 U.GaspariniCorso SM, Dottorato, XX ciclo8 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)-M top correlation to determine Mtop   m t   1.7 GeV La fisica del top: eventi di-leptonici

9 U.GaspariniCorso SM, Dottorato, XX ciclo9 La fisica del top Lepton + J/: 1000 events/year @ L=10 34 J/-> is a very clean signal. M lJ/ has a dependence on M t. Independent from jet scale Among the main sistematics: b fragmentation J/->J/->ee Metodo alternativo per la misura di M top

10 U.GaspariniCorso SM, Dottorato, XX ciclo10 M top da leptone + J/  : Per confronto: di-leptoni

11 U.GaspariniCorso SM, Dottorato, XX ciclo11 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 A= 0.311  0.035  0.028 (using 30 fb -1 ) Use double leptonic decays tt  bb l l La fisica del top tt spin correlation

12 U.GaspariniCorso SM, Dottorato, XX ciclo12 s-channel t-channel Wt-channel =10 pb =247 pb=56 pb Tevatron puts only an upper limit on  Directly related to |V tb | Sensitivity to new physics: FCNC (t-ch.), new gauge bosons (s-ch.), H ± ->tb … Background to tt and several searches (ttH, WH->lbb, …) Possibility to study top properties (mass, polarization, charge) with very little reconstruction ambiguities Main bkgs: ttbar, Wbb Produzione di top singolo

13 U.GaspariniCorso SM, Dottorato, XX ciclo13 Produzione di top singolo  245 pb  60 pb  10 pb Production mechanisms and cross sections: direct measurement of V tb observable by Tevatron in Run II LHC  t  1.5  t Selection: t  bW  b e (  ) b-jet + high p T lepton reconstruction of top mass Background from tt signal to bkgd. 3.5 : 1 Experimental determination of V tb to percent level (with 30 fb -1 )

14 U.GaspariniCorso SM, Dottorato, XX ciclo14 Produzione di W e pdf Fundamental processes at LHC are the scattering of Quark – Antiquark Quark – Gluon Gluon – Gluon gg  H  need precise of parton density Functions [ pdf(x,Q 2 ) ] + QCD corrections (scale) Examples: qq  W  l y = pseudorapidity DGLAP evolution

15 U.GaspariniCorso SM, Dottorato, XX ciclo15 Esempio di “early physics” a LHC: produzione di W Sensitive to small differences in sea quark distribution p T 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. 2·10 6 W  produced

16 U.GaspariniCorso SM, Dottorato, XX ciclo16 MWMW 2004: m W = 80 412  42 MeV 2007: m W  80...  20 MeV (2.5 ·10 -4 ) “Traditional” method: m W from transverse mass distribution Improvement at the LHC to  10 MeV envisaged requires control of systematic error to 10 -4 level CDF W  LEP & Tevatron Run I from Tevatron Run II

17 U.GaspariniCorso SM, Dottorato, XX ciclo17 MWMW

18 U.GaspariniCorso SM, Dottorato, XX ciclo18 MWMW General idea at LHC: take Z   events remove one  to fake Z   “ “ m Z = 91 187.5  2.1 MeV known

19 U.GaspariniCorso SM, Dottorato, XX ciclo19 MWMW Example: use Z   “ “ data to create transverse mass distribution for arbitrary M X compare M X T and compare to W data statistical error from 1 fb -1  m W  20 MeV Systematic errors to be investigated: small differences in W/ Z production (p T &  distributions) final state radiation ( doesn‘t radiate!) different backgrounds

20 U.GaspariniCorso SM, Dottorato, XX ciclo20 MWMW

21 U.GaspariniCorso SM, Dottorato, XX ciclo21 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)

22 U.GaspariniCorso SM, Dottorato, XX ciclo22 W/Z + jet(s) physics Z+1 jet Alpgen prediction @ LHC: (1)Minimum Jet Pt : 25 GeV (because of large amount of jets from pileup and underlying events below 25 GeV, see plots in later slide) (2)Minimum Jet-Jet distance : 0.5 (3)Jet Eta from –5.0 to 5.0 (4)W/Z semileptonic decay, fragmentation and hadronization, multiple parton scattering by Pythia Z+2 jet Z+3 jet Z+4 jet W+3 jet W+2 jet W+1 jet sensitive to, e.g.: =>

23 U.GaspariniCorso SM, Dottorato, XX ciclo23 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

24 U.GaspariniCorso SM, Dottorato, XX ciclo24 Test CP conserving anomalous couplings at the WW  vertex  and Method: W  final states W  e and  p T spectrum of photon Sensitivity: p T spectrum SM couplings vs current limits at 1.5 TeV Triple Gauge Boson Couplings

25 U.GaspariniCorso SM, Dottorato, XX ciclo25 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 B 0 s   +   CP violation in B 0 s  J/   B 0 s oscillations B c studies Example: reconstruction of B 0 s  J/     +   K + K  B physics Main difficulties: -Trigger (low p T thresholds needed) - background rejection

26 U.GaspariniCorso SM, Dottorato, XX ciclo26 B physics example: B 0s decays Bs  J/psi    KK Trigger efficiencies for B s   isorate trigger curves: 30 Hz 20 Hz L= 10 31  (bb)= 500  b ~ 10 3 B s /s @ L=10 31 SM BR ~ O(10 -9 ) from FCNC b  s reachable in 1 year Non-rare channel: ~ 8  10 4 decays/10 fb -1 feasable for CP violation studies Rare decay: B s  

27 U.GaspariniCorso SM, Dottorato, XX ciclo27 Method: reconstruct B 0 s b   X on other side Analysis: single  trigger p T > 6.5 GeV (  < 2.4)  4500 signal events expected in 10/fb Result from MonteCarlo study: sensitivity (95% CL) to oscillation frequency x s [ps -1 ] versus signal purity f s (less sensitive) mass resolution: 18.5 MeV B physics example: Sensitivity to B 0s Oscillations TRIGGER (not easy !) critically dependent on background rejection capability…

28 U.GaspariniCorso SM, Dottorato, XX ciclo28 B0s Oscillations Current status:

29 U.GaspariniCorso SM, Dottorato, XX ciclo29 B0s Oscillations Tevatron will certainly improve this result…:

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