Text Decays of heavy flavour hadrons measured by CMS and ATLAS M.
Outline Data collection and B-trigger strategies ID performance with increasing pileup Lifetimes B avg Bs, Bd Masses Λ b Bc Searches for rare decays B µµ Summary
ATLAS and CMS data taking 3 LHCb, ATLAS, CMS collected similar integrated luminosities - thus number of collected B- hadrons and Onia (in muon channels) roughly proportional to the production cross sections in respective fiducial volumes. ATLAS, CMS benefit from being able to collect data at increasing LHC instantaneous luminosity To benefit from higher integrated luminosity B-physics groups in ATLAS/CMS paid special attention to: B-physics triggers and stability of tracking, vertexing performance with growing pileup 3
ATLAS, CMS B-triggers in 4 In ATLAS, CMS di-muon triggers dominate B-trigger menus. Siingle muon triggers - prescaled CMS ATLAS low pt thresholds in a narrow mass windows events over whole mass region with a di-muon trigger with high pt thresholds "quarkonium" dimuon trigger during the first pb only pt thresholds 4&4 GeV or 4&6 GeV with masses in J/ψ (.5-4.3 GeV), B (4-8.5 GeV) and Υ (8 GeV) the combined range of all three (.54 GeV) a higher pt trigger ( GeV) di-muon events over whole mass region ATLAS, CMS di-muon triggers performed online tracking & vertexing, accepting only a good quality vertices. In ATLAS NO displaced vertex cuts applied at trigger level during whole in B-physics menu Events per MeV 6 5 4 3 Run, L =. fb J/! CMS s = 7 TeV!' $ % B s # trigger paths!' J/! - B " µ + s µ # low p double muon T high p double muon T Z dimuon mass [GeV] 4
Tracking-vertexing performance in pileup 5 Z Vertex Resolution [mm] ATLAS Preliminary Data, Random Trigger Minimum Bias MC CMS preliminary Transv.Impact Parameter Resolution (µm) 9 8 7 6 5 4 3 Data track! <.4 Simulation track! <.4 s = 7 TeV Excellent modeling of pixel hit resolution, multiple scattering, alignment 4 6 8 4 6 8 Track p (GeV/c) hia (Uni. Zürich) Heavy flavor physics with T the CM 4 CMS-PAS-TRK--5 CMS preliminary Vertex Eur.Phys.J. resolution C7 () important p.65 for precision B-physics s = 7 measurements: TeV lifetime, CPV, rare decays. Quality of vertexing monitored over as pileup increased. Data track! <.4 Vertex resolution vs. number of tracks and Simulation track! <.4 ATLAS (top average left) pt d of reconstructed track with respect to the PV for different number of pileups. The tails are sensitive to the rate of secondaries and fakes. No significant increase in the fake rate observed. Figure 6: Measured resolution of the track transverse (a) and longitudinal (b) impact parameter as a function of the track p T. Only central tracks with η <.4 are considered. Black and red symbols correspond to results from data and simulation, respectively. (b) (a) CMS (top right) excellent modelling of d resolution. Data / MC -.3...9.8 5 5 5 3 35 4 45 5 Number of tracks For each track passing these criteria, the unbiased position of the collision point is determined using all and only the other tracks in the event with the vertex fitter described in Section. The uncertainty on the position is estimated from the vertex fit and it is used to filter the newly reconstructed vertexes. If the errors on the x and y (z) coordinates of the vertex position are within 5 37 µm ( 36 µm), a vertex-track pair is created and used in the next step of the analysis. These cuts on the position error have been chosen as a trade-off between selecting vertexes that are very precisely reconstructed and having enough vertexes passing the selec- ATLAS,CMS d precision strongly improves as trigger thresholds lead to higher pt over. Good z-resolution of PV important at high luminosities. Figure : Primary vertex resolution in x (a), y (b), and z (c) as a f for different average transverse momentum p T. The Pythia8 Tu (c) 5
B-lifetime measurements 6 Candidates / (.45 cm ) Events / (. cm) 3 (b) CMS s = 7 TeV L = 4 pb CMS data Prompt J/! + non-peaking B + peaking B + signal -.5.5..5..5.3.35.4 ct (cm) 4 3 Bd J/ψ K S CMS Preliminary s=7 TeV, L=4pb Bs J/ψ φ -.5.5..5..5.3.35 ctau (cm) Time measurements already in consistent with PDG ATLAS, CMS well prepared to measure time-dependent CPV and rare decays - requiring good vertexing τ, ps PDG τ, ps Bd ATLAS-CONF--9 4 pb.5 ±.4 (stat) ±.4 (syst).55 ±.9 Bd CMS PR Lett. 6:5, 4 pb cτ = 479 ± μm 457 ± 3 μm Bs ATLAS-CONF--9 4 pb.4 ±.8 (stat) ±.5 (syst).47 ±.6 Bs CMS PRD84, 58() 4 pb cτ = 478 ± 6 μm 49. ±8.7 μm B-average ATLAS-CONF-45 35 pb.489 ±.6 (stat) ±.43 (syst).544 ±.4 ps *) B J/ψ X Bd J/ψ K * Bs J/ψ φ B 6
B-hadrons mass signals, updates 7 - masses of all B-hadrons measured in exclusive decays with J/ψ(µµ) Consistency with PDG - showed that pt scale well understood also down to low pt values covered by beauty Latest updates using data shown here for Λb (CMS, ATLAS) and Bc (ATLAS) Events / ( 7 MeV ) 8 6 4 ATLAS Preliminary Bc J/ψ π m Bc = 68 ± N Bc = 8 ± # = 36 ± 7 (stat.) 7 (stat.) 9 (stat.) MeV MeV $ Ldt = 4.3 fb s = 7 TeV ATLAS-CONF--8 58 6 6 64 66 68 (MeV) m J/"! Events / (. GeV ) 9 8 7 6 5 4 Λb J/ψ Λ Twiki BPH7 CMS preliminary s = 7 TeV L =.8 fb ATLAS-CONF-4 3 4 5 Figure : Invariant mass distribution of reconstructed B ± c J/ψπ ± candidates. The points with error bars are the data. The solid line is the projection of the results of the unbinned maximum likelihood fit to all candidates in the mass range 577 68 MeV. The dashed line is the projection for the background component on the same fit. References [] CDF Collaboration, F. Abe et al., Observation of the B c Meson in pp Collisions at s =.8 TeV, Phys. Rev. Lett. 8 (998) 43. [] CDF Collaboration, A. Abulencia et al., Evidence for the exclusive decay B ± c J/ψπ ± and measurement of the mass of the B c meson, Phys. Rev. Lett. 96 (6) 8. 3 6 7 8 9 [3] CDF Collaboration, Λb J/ψ T. ΛAaltonen et al., Measurement of the B c Lifetime in B ± c J/ψ + l ± + X Decays, Phys. Rev. Lett. (8) 8. [4] D Collaboration, V. M. Abazov et al., Measurement of the B c meson mass in the exclusive decay B c J/ψπ, Phys. Rev. Lett. (8). 5.3 5.4 5.5 5.6 5.7 5.8 5.9 m!b (GeV) 3 3 3 [5] LHCb Collaboration, Measurement of the B + c to B + production cross-section ratio at s = 7TeV in LHCb, LHCb-CONF--7 (). [6] E. Eichten, C. Quigg, Mesons with beauty and charm: Spectroscopy, Phys. Rev. D 49 (994) 5845. 33 34 35 [7] S. S. Gershtein et al., B c spectroscopy, Phys. Rev. D 5 (995) 363. [8] R. Roncaglia et al., Predicting the masses of heavy hadrons without an explicit Hamiltonian, Phys. Rev. D 5 (995) 48. 7
Rare B decays B µµ: search for New Physics 8 Rare decays highly suppressed in SM both FCNC and helicity suppression SM prediction is rather precise ( no hadronic uncertainties) BR(Bs µµ)= (3. ±.) x -9 BR(Bd µµ)= (. ±.) x - A.J.Buras: arxiv:.447, E. Gamiz et al: Phys.Rev.D 8 (9) 453 BR are sensitive to new physics In SM ratio: B b t Z, + + W, H d/s d/s b B s/d d/s 6 t H,h... + ~ + W, χ µ + ~ ~ t,c,u q l ν W ~, χ µ µ + µ ( ) #m d $ d ˆ ( ) #m s $ s ˆ r = BR B "µµ s BR B d "µµ B Bs SM B Bd % sensitive tester 8
Search for Bs µµ in ATLAS 9 ATLAS is presenting result on Bs μμ limit using.4 fb collected with di-muon triggers in data Method Selection based on Use a reference channel: ( ) = N B s " µµ BR B s "µµ 4 variables N J /#K ± Multivariate analysis (BDT) 5% of sideband events to model background 5% of other sideband events to optimise BDT Efficiencies & acceptances $ tot % J /#K ±& J /#K ± tot $ % Bs " µµ& Bs " µµ Derived from MC(calibrated on data) Reference channel (B ± J/ψK ± ) selected with as-closeas-possible selection Bs J/ψφ data used for MC validation f u $ BR( B ± "J /#K ± ) f s /(4.45±.38)! 3 [PDG + LHCb] Limit of BR is placed using CLs method (frequentist method optimal for setting exclusion limits) Stability of isolation I ΔR (one of the selection variables) at growing pileup. Isolation cut efficiency.9.8.7.6.5.4.3.. extended to all non- B daughters within R, and p T >.5 GeV B ± J/ψK ± M.C., isolation with PV association M.C., isolation without PV association Data, isolation with PV association Data, isolation without PV association ATLAS preliminary s = 7 TeV Ldt =.4 fb 4 6 8 SV PV P t (B s ) Number of primary vertices 9
ATLAS results on Bs µµ Events/6.5 + - B s µ µ MC ( ) preliminary s = 7 TeV Ldt =.4 fb.5 6 MeV resolution η < Sidebands 8 MeV resolution < η <.5.5 MeV resolution.5 < η <.5 48 5 5 54 56 58 m µ µ [MeV] Events/6 MeV 3.5 3.5 Data + - B s µ µ MC ( ) ATLAS preliminary s = 7 TeV Ldt =.4 fb Events/6 MeV 3.5 3.5 Data + - B s µ µ MC ( ) ATLAS preliminary s = 7 TeV Ldt =.4 fb Events/6 MeV 3.5 3.5 Data + - B s µ µ MC ( ) ATLAS preliminary s = 7 TeV Ldt =.4 fb.5.5.5.5.5.5 48 5 5 54 56 58 m µ µ [MeV] 48 5 5 54 56 58 m µ µ [MeV] 48 5 5 54 56 58 m µ µ [MeV] Optimised search window Figure 7: Invariant mass distribution of candidates in data. For each invariant mass category (top to bottom) each plot shows the invariant mass distribution for the selected candidates in data (dots), the signal (continuous line) as predicted by MC assuming BR(Bs µ + µ ) = 3.5 8, and two vertical lines corresponding to the optimized m cut. The grey areas correspond to the sidebands used in the analysis. unblinded di-muon invariant mass in 3 search windows 556 557 558 559 9 to 8 and the 95% expected limit is equal to.9 +.3.8 8, confirming the expectation for a more sensitive analysis when separate mass-resolution categories are used. The background counts found in odd-numbered events
ATLAS upper limit on Bs µµ.4 fb Expected and observed CLs as a function of BR(Bs µ+µ-) The 95% CL limit indicated by the red line. BR(Bs"μμ) <.! -8 @ 95% CLs The yellow and green bands: ±σ and ±σ fluctuations on the expectation (dashed line) based on pseudo experiments with setting the counts in the search window to the interpolated background + resonant background - before unblinding the region
CMS search for Bs µµ and Bd µµ Previous CMS results. fb, PRL, 7, 98. New result presented here is using 4.9 fb Measurement of Bs µ+µ relative to normalization channel: similar trigger and selection to reduce systematic uncertainties B(B s µ+ µ ; 95%C.L.) = N(n obs,n B,n S ; 95%C.L.) ε B s N B s = N(n obs,n B,n S ) ε B s L σ(pp B s ) = N(n obs,n B,n S ) N(B ± J/ψ K ± ) Calibration/validation of MC: Calibration/validation of MC: B ± J/ψK ± with high statistics Control sample Bs J/ψ φ validation of Bs signal MC Analysis in two subsets A B + ε A B s ana B + ε ana B s ε µ B + ε µ B s ε trig B + ε trig B s f u f s B(B + J/ψ [µ + µ ]K) barrel (both muons η <.4): better signal/background ratio good mass resolution (36 MeV) endcap (at least one muon with η >.4): add more statistics [σ(m) 7 MeV] Analysis is (still) cut-n-count Analysis was performed blind total amount of data: 4.9 fb
CMS results on Bs µµ, Bd µµ 3 Variable B µ + µ Barrel B s µ+ µ Barrel B µ + µ Endcap B s µ+ µ Endcap Signal.4 ±..7 ±.4. ±..3 ±.8 Combinatorial bg.4 ±.34.59 ±.5.76 ±.35.4 ±.53 Peaking bg.33 ±.7.8 ±.6.5 ±.3.8 ±. Sum.97 ±.35 3.47 ±.65. ±.35.45 ±.56 Observed 4 Candidates /.5 GeV CMS, 4.9 fb Preliminary s = 7 TeV 5 4 3 B s B Barrel signal window signal window Candidates /.5 GeV 4 3 CMS, 4.9 fb Preliminary s = 7 TeV 5 B s B Endcap signal window signal window 5 5. 5.4 5.6 5.8 [GeV] m µµ 5 5. 5.4 5.6 5.8 [GeV] unblinded di-muon invariant mass in the barrel (left) and endcap (right) m µµ 3
CMS upper limits on Bs µµ, Bd µµ 4 B B upper limit (95%CL) observed (median) expected B(B s µ+ µ ) 7.7 9 8.4 9 B(B µ + µ ).8 9.6 9 -values (for background-only hypotheses).4.3 CMS Preliminary 4.9 fb, s = 7 TeV Observed CLs+b Expected CLs+b - Median Expected CLs+b ± # Expected CLs+b ± # Expected and observed CLs as a function of BR(Bs µ+µ-) The 95% CL limit is indicated by the red line... SM expectation bands 4 6 8 B(B!µµ) s -9 " The yellow and green bands: ±σ and ±σ predictions on the expectation. A median expected limit of 8.4 x -9 at 95% CL determined from background + SM signal pseudoexperiments 4
Current status 5 LHCb fb @95%CL CMS 4.9 fb @95%CL ATLAS.4fb @95%CL CDF fb @95%CL CDF fb 95% double sided A. Cerri - LHC Seminar March 6th 5
Conclusions 6 good quality data of ~ 5 fb collected by each ATLAS/CMS allowed substantially increased statistics of B-hadrons with two muons in final states relative to Observed stable performance (tracking, vertexing) with increasing pileup - basic for good quality B-physics measurements B-lifetimes, masses consistent with PDG - excellent pt calibration vertexing and alignment - well equipped to measure CPV in particular in Bs J/ψφ Rare decays limits extracted: by CMS and ATLAS Upper limit at 95% CL Bs µ + µ Bd µ+µ CMS 4.5 fb 7.7 9.8 9 ATLAS.4 fb. -8 6
Backup 7 7
Current results 8 Upper limits 95% CL Bs μ + μ Bd μ+μ D ) 5. 8 CDF ) 3. -8 (.3 +.9 -.7 ) 8 4.6 9 CMS older 4).9-8 3.6 9 LHCb 3) 4.5-9.3 - ATLAS. -8 ) 6. fb, PL, B693, 539 ) fb P u b l i c N o t e i n p r o g r e s s --9 (previous result 7 fb, P R L, 7, 98 ) 3) fb, LHCb-PAPER--7 4). fb, PRL, 7, 98 CMS 7.7 9.8 9 8
CMS 9 CL s+b.4.3 B CMS Preliminary 4.9 fb, s = 7 TeV Observed CLs+b Expected CLs+b - Median Expected CLs+b ± # Expected CLs+b ± # CL s.4.3 CMS Preliminary 4.9 fb, s = 7 TeV Observed CLs Expected CLs - Median Expected CLs ± # Expected CLs ± #. SM expectation bands... 4 6 8 B(B!µµ) s -9 " 4 6 8 B(B!µµ) s -9 " Expected CLs as a function of BR(Bs µ+µ-) for Left: determined from background + SM signal pseudo-experiments RIght: background only 9