Lecture 1: b quarks at Hadron Colliders

Transcription

1 1/44 Lecture 1: b quarks at Hadron Colliders CTEQ Summer School Rhodes, Greece - July 2006 Franco Bedeschi, Istituto Nazionale di Fisica Nucleare Pisa, Italy

2 2/44 Discovery of b quark E288/CFS experiment at Fermilab Search of lepton pairs p+nucleusµ + µ + X 1977: narrow resonance in µ pair mass spectrum S. W. Herb et Al., Phys. Rev. Lett. 39, (1977). In analogy with the J/ψ case this new particle, ϒ, can be interpreted as a bb bound state ϒ µ - µ +

3 3/44 b-production around the world Active experiment Year Year Year 89-today Near future qwe KEKB (Japan): Belle (1999- active) TRISTAN (Japan): Topaz, Venus, Amy ( ) SLAC-SLC: SLD ( ) PEP-II: BaBar (1999- active) FNAL-TeV: CDF, D0 (1988- Active) FNAL-FT: E288 ( ) HERA: ZEUS,H1 DORIS:ARGUS (1992- active) ( ) CESR: CLEO (1979- attivo) LHC: CMS, ATLAS, LHC-B (2007?) CERN-SppS: UA1, UA2 ( ) PETRA: Mark-J, Tasso, Pluto, Jade ( ) CERN-LEP: Aleph, Delphi, Opal, L3 ( )

4 4/44 B-production at e+e- Production on ϒ(4s) resonance σ ~ 1.1 nb S/N ~ 1/5 B s are at rest or have small βγ in asymmetric B factories (~ 0.6) Produce only Bu or Bd in coherent QM state Don t know which is which until decay (Z resonance production: LEP) σ ~ 6.5 nb S/N ~ 1/5 B s have large boost and are monochromatic Produce all kinds of B s ϒ M(B B) M(Bs Bs) = B B

5 5/44 B-production in e+e- Typical event properties Low charged multiplicity ~11 Collisions/crossing <1

6 6/44 B-production at hadronic machines Tevatron ~ 1.96 TeV CM energy σ ~ 100 µb S/N ~ 1/1000 B s are boosted βγ ~ 1-4 Each B s produced in flavor specific state q Produce all kind of B s q Flavor Creation (annihilation) Flavor creation (annihilation) b b g g g Flavor Creation (gluon fusion) Flavor creation (gluon fusion) Production b b b b h B-hadron h h h q, g b-jet 1 h h Fragmentation b-jet 2 B-hadron q, g

7 7/44 B-production at hadronic machines Typical Tevatron event Large charged multiplicity ~ 40 Multiple interactions per crossing ~ 1-10 Very demanding trigger to exploit efficiently the large sample potentially available

8 8/44 Tevatron for Run II CDF New Main Injector: Improve p-bar production Recycler ring: Additional storage and cooling of p-bars Main Injector D0 Tevatron

9 Tevatron Run II /44 Tevatron parameters cm -2 s -1 = 10-4 pb -1 s -1 Recycler Run I Run II (low) Run II (high) Energy/beam 900 GeV 980 GeV 980 GeV Peak Luminosity 1.6x x x10 32 Number of bunches Bunch spacing 3500 nsec 396 nsec 396 nsec Interactions/crossing Run period Integral Luminosity 118 pb -1 2 fb -1 8 fb -1 Main Injector Photo courtesy of Fermilab Tevatron Photo courtesy of Fermilab

10 Tevatron performance 10/44 Tevatron delivered more than 1.5 fb -1 up to Feb 2006 Recorded 1.4 fb -1 (CDF) / 1.2 fb -1 (DØ) Now ~ 1.0 fb -1 reconstructed and under analysis D0 & CDF Run II Integrated Luminosity CDF Delivered (from February 9th 2002) D0 Delivered (from April 19th 2002) CDF Recorded (from February 9th 2002) D0 Recorded (from April 19th 2002) Expect 4 8 fb -1 by Oct through 18 February Feb-02 May-02 Aug-02 Nov-02 Feb-03 May-03 Aug-03 Nov-03 Feb-04 May-04 Aug-04 Nov-04 Feb-05 May-05 Aug-05 Nov-05 Feb-06 May fb L u m in o sity (fb -1 ) fb -1

11 Tevatron Detectors 11/44 CDF Excellent mass and impact parameter measurement Good ability of lepton identification Limited PID capability DØ Extended tracking and muon coverage Good electron/mu identification

12 12/44 CDF-II: isometric view New Old Partially new Central calorimeters Solenoid Central muon TOF Front end Trigger DAQ Offline Forward muon Endplug calorimeter Silicon and drift chamber trackers

13 D0: side view! 13/44! Front End Electronics Triggers / DAQ (pipeline) Online & Offline Software

14 14/44 Key detector features for b physics Electron/muon identification Identify semi-leptonic B decays or decays involving ψµ + µ - Secondary vertices Identify decay vertex Requires high resolution tracking (silicon vertex detector) Powerful tracker Find all decay tracks with high efficiency Trigger: Identify leptons and detached tracks in times ~ 5-20 µs Only way to collect large samples of hadronic B decays Currently implemented only at CDF

15 15/44 L2 SVT trigger 8 VME crates Find tracks in Si in 20 µs with offline accuracy Online track impact param. σ=48 µm Secondary VerTex L2 trigger Online fit of primary Vtx Beam tilt aligned Observed D resolution 48 µm (33 µm beam spot transverse size) Efficiency

16 16/44 Example of b production event

17 17/44 b quark interest b is only 3 rd generation particle being produced in abundance fundamental probe of SM CKM in particular (see later) Couplings to γ and Z extensively studied at LEP Strong coupling to SM Higgs M b >> Λ QCD improves accuracy of many theory predictions No time to explore all of them! This lecture: Production x-section/correlations Test QCD B 0 mixing, Γ, CPV in mixing Many new recent results

18 18/44 B production Big gluon x-section/flux large NLO contribution Large b-mass provides natural cut-off, but introduces additional scale (and potential divergences) in calculations (see Carlo s lectures)

19 19/44 B production From J/ψ sample (low pt) Sensitivity up pt=0 B-fractions from lifetime analysis Find consistency with FONLL (=NLO + NLL) after reanalysis of fragmentation From b-tagged jets (hi pt) Compatible also with QCD

20 20/44 B production correlations Double b-tagged semileptonic sample Consistent with significant higher order production

21 21/44 CKM matrix (1) CKM matrix describes flavor mixing in weak charged current transitions All up-type quarks (u, c, t) can couple with any downtype quarks with a strength modulated by the elements of the CKM matrix b Vub u W CKM matrix = CKM matrix must be unitary if there are only 3 generations Vud Vcd Vtd Vus Vcs Vts V ts = V ts e iβs β s very small Vub Vcb Vtb V ub = V ub e iγ Only 2 elements are complex * V td = V td e iβ * Only 1 phase needed, the two phases are related

22 22/44 CKM matrix (2) CKM can be expressed in powers of V us = λ = sin(θ Cabibbo ) ~ 0.22 Wolfenstein representation Measurement of CKM elements allows test of unitarity triangle is closed 1st, 3rd col.: V ud V ub *+V cd V cb *+V td V tb *=0 Other triangles less interesting Let: V ud = 1, V cd = -λ, V tb = 1 V ub *+ V td = λ V cb * O (3%) Divide by Aλ 3 = λ V cb * = -λ V ts 1 2 λ 2 λ 3 Aλ (1 ρ iη) λ V cb (ρ+iη) Charmless V ub * γ ρ α 1 λ 2 λ 2 2 Aλ (1+ i η 1 A ~ 0.8 ρ ~ 0.2, η ~ 0.4 V td 2 ) 3 Aλ ( ρ iη) β A Mixing 2 λ 1 λ V ts (1-ρ-iη) Angles: CP violation

23 23/44 Basic Theory (1) 1 state effective theory: 2 state effective theory: M, Γ hermitian CPT invariance: Μ 11 =M 22,Γ 11 =Γ 22 Solution reduces to 1 state case after diagonalization of H Eigenvalues: Eigenstates:

24 m 12 from box diagram Top quark dominant m 12 V 2 td(s) e -2iβ (s) Box diagrams New particles can run in loops besides W and quarks Assuming m 12 >>Γ 21 : B d,s B d,s b d, s b d, s Neutral B s can turn into their antiparticle MIXING W u c t 2 m 12 = m s(d) =[G F2 m t2 η F(m t2 /m W2 )/6π 2 ] m Bs(d) f 2 Bs(d)B Bs(d) V ts(d) V * tb 2 u c t W W u c t u c t W d, s b d, s b B d,s B d,s 24/44 Oscill. Freq. Known factors From lattice O(30 %) error ~ 1

25 25/44 Basic Theory (2) Time evolution of B(0)> and B(0)> Assume Γ 12 << m 12 Bd Bs

26 26/44 Mixing theory Neutral mesons time evolution with mixing can be easilty derived from the equations of previous slide: Bd mixing well established m d = ps -1 Measurements from LEP, Tevatron and B-Factories Accuracy dominated by BaBar and Belle Bs mixing much harder Less signal and much faster (~ x 1/λ 2 ) oscillation Tevatron has first results NOW!

27 27/44 Mixing measurements Steps needed to measure mixing: Select signal in flavor specific final states Identify B type at production: FLAVOR TAG Measure proper decay time and its resolution Parameterize background contributions Fit time dependence Significance from Fourier like analysis #signal #background Tagging power cτ resolution

28 28/44 CDF Signal Sample for m s D s : D s πππ Semileptonic Modes D s : D s φπ 32 K D s : D s K*K 11 K ~53 K events 10 K oscill. fit range Hadronic Modes B s D s π (φπ) B s D s π (K * K) B s D s π (3π) B s D s 3π (φ π) B s D s 3π (K * K) Total Yield

29 29/44 Huge Control Signals Hadronic decays: B + (J/ψK +, D 0 π, D 0 3π): ~ 50 k events B 0 ( J/ψK*, D - π, D* - π, D - 3π, D* - 3π ): ~ 60 k events Semileptonic decays: ld 0 (D 0 Kπ): ~ 540 k events ld* - (D* - D 0 π): ~ 74 k events ld - (D - Kππ): ~ 300 k events

30 Flavor tagging 30/44 Taggers charaterized by: Efficiency (ε) Dilution (D) = 1-2w w = prob. wrong tag Observed time evolution Use combined same side and opposite side tags Opposite side: electrons, muons, jet charge Same Side: tag with selected track (kaon) close to reconstructed (signal) B

31 31/44 OST tagger calibration Dilution calibration Use the large control samples of B+ and B0 Works only for OST SST different for every B type. Must use MC B + B 0 Bd mixing by-product and cross-check hadronic: m d = ± (stat) ± (syst) ps -1 semileptonic: m d = ± (stat) ± (syst) ps -1 world average: m d = ± ps -1

32 32/44 SSKT Particles closer to B in fragmentation carry information on B type at production Bs likely to have a K Use TOF/dE/dx for K/π separation Tune MC: Reproduce B+, Bd Determine systematics Apply to Bs

33 33/44 Flavor tag summary Opposite side: use combination of tags Total εd 2 5% Same side/ost combination assumes independent tagging information

34 Measuring proper time 34/44 σ L cτ = = γβ σ 0 p ct = σ ct ct p L M xy p T B Vertex resolution (~constant) Momentum resolution (proportional to ct) For fully reconstructed (hadronic) modes σ ct ~ O(30 µ ) (c.f. ct ~ 450 µ ) For semileptonic modes, missing neutrino causes σ p p ~ O(15%) => Resolution poor at large decay time

35 35/44 Bs proper time resolution Average σ t ~ 87 fs Good sensitivity for m s 20 ps -1

36 36/44 Amplitude scan Fit e -t/τ (1A(ω) Dcos ωt) G(t) for various values of ω A(ω) = 1 for ω = m Similar to a Fourier transform Putting all together Test amplitude scan on Bd A=1 at the correct value Shape consistent with model expectations

37 37/44 CDF Bs result A/σ A (17.31 ps -1 ) = 3.7

38 38/44 CDF Bs result m s = (stat) ± 0.07(sys) D0 consistent but lower sensitivity Probability of background fluctuation = 0.2% ~ 3σ Resolution dominated by hadronic decays

39 39/44 Γ 12 ρ f is phase space factor Γ 12 from common final states B d dominated by D + D -, π + π -,, Γ 12 ~ O(λ 4 ), Γ/Γ ~ 3x10-3 Γ = 2Re{Γ 12 / m 12 } m 12 = 2 Γ 12 cos φ Γ 12 / m 12 ~ 5x10-3 in SM B b d λ W - λ d D - c c d D + B b d λ 3 W - 1 d π u u d π + B s dominated by D s+ D s - Γ 12 ~ O(λ 2 ), Γ/Γ ~ 0.10 Γ 12 /m 12 mostly real: φ ~ arg(m* 12 ) ~ β s B b s λ W - 1 s c D s - c s D s +

40 40/44 Measurements of Γ/Γ Γ d very hard Limits from LEP and B-factories consistent with SM value Γ s feasible at Tevatron with several techniques: Combined lifetime/transversity (angular) analysis of Bsψφ decay Found to be ~ 19% CP-odd Measurement of BR(BsD s +(*) D s -(*) ) Mostly CP-even (theory expectations > 95%) Combination of flavor specific and CP specific lifetime measurements (e.g. BslνDs and BsK+K-)

41 DØ transversity analysis 41/44 Update of published analysis with 800 pb -1 τ Bs Γ s = 1.53± = 0.15 ± ps ps -1

42 42/44 Combined s Results Theoretical prediction (Nierste) Γ s = 0.10 ± 0.03 ps Unofficial world average Γ τ s s = = 1 Γ s f B s 250 MeV ps -1 = 1.461± ps 2

43 43/44 p/q 1 CPV Measure asymmetry Expect: CPV in mixing SM prediction: Bd: 9x10-4, Bs: 1x10-5 Bd avg: ± (LEP, CLEO, Belle, BaBar) Bs avg: ± (D0 2006) p/q =1 Mass eigenstates = CP eigenstates

44 44/44 Summary of lecture 1 B-quark hadrons have been studied for about 30 years e+e- storage rings and hadronic machines have complemented each other Now B-factories and Tevatron b-hadron production and their basic properties are now known with an unprecedented level of detail Their study has helped develop and test QCD, even in nonperturbative regimes Detailed measurements of neutral B meson mixing have become recently available for both species Find overall consistency with Standard Model In conjunction with CP violation measurements (next lecture) further confirm SM and limit possible new physics