Benjamin Carron Mai 3rd, 2004

Transcription

1 Physics Motivations Reconstruction of B s J/ψ η Benjamin Carron Mai 3rd, 4 B s J/ψ (µ + µ ) η (γγ) and B s J/ψ (e + e ) η (γγ) Selection Cuts Resolutions BR of the η B/S Ratios Annual Signal Yields and Efficiences Difficulties with the sensitivity Conclusion Future plans

2 Physics Motivations CP violation studies can provide a profound understanding of quark flavour physics in the SM framework and reveal a sign of the physics beyond! An outstanding role is played by B s mesons decays into CP eigenstates (b ccs transitions), such as B s J/ψ η, B s η c φ, B s J/ψ φ. Physics model: B s b s W + Physics motivations: c c s s J/ψ η c φ η Quark transition b ccs dominated by only one CKM amplitude penguins are negligible No CP-violation in the decay amplitude Easy channels to look for CP-violation Bs decays into pure CP-even eigenstates for J/ψ η and η c φ Bs decays into an admixture of CP eigenstates for J/ψ φ angular analysis Measure the B s weak mixing phase φ s arg (V tsv tb ) - expected O(.4) in SM Extract B s B s mixing parameters M s and Γ s Larger value of φ s would be a clear signal for contributions from new physics

3 Selection Cuts (DaVinci v11r4) Cuts J/ψ µ + µ J/ψ e + e ln L µπ (µ +, µ )(e +, e ) > ln L eπ (e +, e ) > 1. ln L Kp (e +, e ) > -. ln L pπ (e +, e ) >. χ (J/ψ) < 1 8 PT min (l low ) [MeV/c] < 5 PT min (l high ) [MeV/c] < 15 M(J/ψ) [MeV/c ] ± 5 + 5, - 15 PT min (γ low ) [MeV/c] > 6 7 PT min (γ high ) [MeV/c] > Abs (p x,y (l+, l, γ, γ)) [MeV/c] < 8 5 M(η) [MeV/c ] ± 3 3 z d /σ zd > M(Bs) [MeV/c ] ± 9 1

4 η Mass Resolutions (m η = MeV/c ) J/ψ µ + µ case J/ψ e + e case ) Counts / (.6 MeV/c σ = 14 MeV/c ) Counts / (.6 MeV/c 5 15 σ = 17 MeV/c [MeV/c m η ] [MeV/c m η ] µ = 554 MeV/c σ = 14 MeV/c µ = 551 MeV/c σ = 17 MeV/c

5 J/ψ Mass Resolutions (m J/ψ = MeV/c ) J/ψ µ + µ case J/ψ e + e case ) Entries / (4 MeV/c σ = 11 MeV/c ) Entries / (4 MeV/c [MeV/c ] m J/ψ [MeV/c ] m J/ψ µ = 396 MeV/c σ = 11 MeV/c Energy lost: Brehmstrahlung! Dissymetrical mass window

6 B s Mass Resolutions (m B s = MeV/c ) J/ψ µ + µ case J/ψ e + e case ) Entries / (8 MeV/c 1 σ = 33 MeV/c 1 ) Entries / (8 MeV/c 5 σ = 61 MeV/c [MeV/c ] m Bs [MeV/c ] m Bs µ = 537 MeV/c σ = 33 MeV/c µ = 5337 MeV/c σ = 61 MeV/c

7 Proper Time Resolutions J/ψ µ + µ case J/ψ e + e case Counts / (1 fs) 1 8 σ µ = 45. fs = -7 fs Counts / (1 fs) σ = 44 fs µ = -1 fs Proper time resolution [fs] Proper time resolution [fs] µ = 7 fs σ = 45 fs µ = 1 fs σ = 44 fs

8 Visible Branching Ratios (PDG 3) η and η are defined as: η = η 8 cos θ P η 1 sin θ P η = η 8 sin θ P + η 1 cos θ P θ P is calculated (SM) to be 1 o where η 1 and η 8 are composed by the quarks: η 1 = 1 3 uu + dd + ss η 8 = 1 6 uu + dd ss Causiously we fixed: η = η 1 (θ P 9 o ) what leads to a BR of: BR ch vis ( B s J/ψ η ) = (7.6 ±.5) 1 6 With θ P 1 o, the BR would be estimated ( 1.76): BR ch vis ( B s J/ψ η ) = (13.4 ±.8) 1 6 Consequences on the B/S ratios and annual signal yields!

9 B/S Ratios Estimation The most dangerous source of background are bb events, i.e. events where at least a b-hadron is emitted forward in the acceptance region. For this study: 5k signal events were used to tune the selection for each channel, while 1M background events have been analysed. B/S 9% unified CL interval Decays BR ch vis (in 1 6 ) bb selected B/S µ + µ 7.6 [., 1.] e + e 7.6 [., 4.56] µ + µ (θ P = 1 o ) 13.4 [.,.69] e + e (θ P = 1 o ) 13.5 [.,.58]

10 Annual Signal Yield (No Tagging, No HLT, PDG 3) # B s Final state = (#B s mesons) BR ch vis # B s J/ψ (µ + µ ) η (γγ) = 1.5 M # B s J/ψ (e + e ) η (γγ) = 1.5 M # B s J/ψ (µ + µ ) η (γγ) (θ P = 1 o ) =.7 M # B s J/ψ (e + e ) η (γγ) (θ P = 1 o ) =.7 M The annual yield is calculated as: (#B s final state ) Total efficiency Efficiencies (in %) J/ψ µ + µ J/ψ e + e Geometrical acceptance Reconstruction Offline selection Trigger Total efficiency Annual yield [k] Annual yield (θ P = 1 o ) [k]

11 Status on the Sensitivity Studies (with Luis) The B s B s system will serve to test the Standard Model description of CP violation, based on the CKM picture (talk of Luis at the SPS). Physics Motivations: measure the mixing parameters extract M s O() ps 1 and Γ s /Γ s O(1%) probe the B s B s weak mixing phase φ s, expected to be small in the SM O(.4) B s system represents a prime candidate for the discovery of New Physics The sensitivity of LHCb to the CP B s observables are assessed by the use of fast toy Monte Carlo experiments, using RooFit. No results for the moment, due to the following problems: The acceptance has not been implemented yet - convergence difficulties Important variation of the results between versions - not reliable Biases in the pulls - can t trust the results Normalisation problems These points are under investigation!

12 Conclusion B s mass resolutions Good for the decay with J/ψ µ + µ : 33 MeV/c Larger for the decay with J/ψ e + e : 61 MeV/c Proper time resolutions Excellent resolutions ( 45 fs) needed for the CP violation study As M s = O() ps 1, the resolution are precise enough to resolve the fast B s B s oscillations. B/S estimations - Good rejection of the background (no bb event selected) J/ψ µ + µ : [., 1.] [.,.69] J/ψ e + e : [., 4.56] [.,.58] Annual Signal Yields J/ψ µ + µ : 7.4 k 13.1 contribution to B s sensitivity studies??? J/ψ e + e :.8 k 1.46 negligeable??? Significant improvement of the yield and of the B/S ratio when θ P = 1 o

13 Future plans Data Challenge 4 Provide pre-selection algorithm to generate the stripped bkg Provide selection algorithm with tight cuts to confirm the TDR estimations Get ready to work on the HLT selections B s J/ψ η selection Study which BR to use for the η Decide if the J/ψ e + e contribution is significant enough to be added to the J/ψ µ + µ Sensitivity studies Solve the difficulties encoutered till now Provide a general toy which can be used by other selection - B s J/ψ φ, B s η c φ,...

14 Bkp slides BACKUP SLIDES

15 Bkp: Trigger System Aim of the L trigger stage: Rate reduction from 4 MHz (detector output) to 1MHz (L1 input) The L is implemented in hardware and makes use of the muon stations, ECAL and HCAL detectors using high-p T of leptons, photons, and hadrons combined with a pile-up veto Aim of the L1 trigger stage: rate reduction from 1 MHz (L output) to 4 khz (HLT input) such that 4% of the minimum bias events are retained The L1 is implemented in software and makes use of the Velo (VErtex LOcator), TT (Trigger Tracker) detectors, and the L information Requires two tracks with high transverse momentum (p T1 and p T ) and large impact parameter for the generic algorithm Bonus: The efficiency for some benchmark specific channels such as Bd µ+ µ K, Bd K γ, Bd π+ π, Bd J/ΨK s is enhanced, based on the L information Aim of the HLT trigger stage: Final software decision on whether or not to write the event to storage ( Hz foreseen)

16 Bkp: LHCb detector

17 Bkp: Cut in the Transverse Plane In the transverse plane, wrt the Bs direction, the J/ψ and the η are emitted back to back The cut applied is: ( ) Abs p γ 1 T,i + pγ T,i + pµ+ T,i + pµ T,i < 8MeV/c, i = x, y Transverse plane p T γ1 p T γ1,γ η Counts / (5 [MeV/c]) 3 Solid : Associated signal 5 Cut: > -8 MeV/c Dash : b b background Cut: < 8 MeV/c pt γ 15 p B s p T µ1 θ γ,µ 1 p T µ1,µ J/ψ p T µ Sum of p T,y of the γ s and µ s [MeV/c]

18 Bkp: Presentation of this Talk s Characters B s mesons composition: B s s b composition: B s s b mass : MeV/c width : MeV/c lifetime : s J/ψ mesons composition: c c mass : MeV/c width : 87 kev/c lifetime : s η mesons composition: 1 3 (u u + d d + s s) mass : MeV/c width : 1.18 kev/c lifetime : s

19 Bkp: Various Track Types A shematic illustration of the various track types: long, upstream, downstream, VELO, and T tracks. For reference, the main B- field components (B y ) is plotted above as a function of the z coordinate. By [T] z [m] Upstream track TT Long track T track Downstream track VELO VELO track T1 T T3

20 Bkp: Long Tracks Resolution (a) Momentum resolution with a single Gaussian fit, and (b) impact parameter precision, for B-decay tracks (Long tracks). a) σ=.37% 5 b) <δip> = 4 µm (p rec p true ) / p true IP mismatch [mm]

21 Particle Identification A good particle identification is required in the decay reconstruction difference in log-likelihood between the particles hypotheses 1 ln L Kπ = ln L K ln L π (a) kaons All tracks p < 5 GeV/c 1 ln L µπ = ln L µ ln L π (a) muons 5 5 Entries 4 (b) pions Entries 75 (b) pions ln L Kπ ln L Kπ from the RICH system for (a) kaons and (b) pions ln L µπ ln L µπ from the Muon system for (a) muons and (b) pions.