B PROPERTIES, LIFETIMES, AND B c DECAYS AT LHCb

Transcription

1 MIRCO DORIGO (CERN and INFN-TS on behalf of the LHCb collaboration B PROPERTIES, LIFETIMES, AND B c DECAYS AT LHCb BEAUTY 28 - LA BIODOLA, MAY

2 CONTENTS 2 B properties: focus on Bs lifetime. For other recent results on b hadron properties (baryons see Sheldon Stone s talk on Monday. Bc decays: two recent searches Using data from LCHb. Ideal for - lifetime measurement (large boost, precise FD and p measurements - Bc searches (large b production, all b hadron species σ IPx ~ 2μm σ p /p ~.5-.8% PID ε K = 95%, ε μ = 98%, misid π K = 5% misid K μ =.6%, misid π μ =.%

3 LIFETIMES Supporting measurements to sharpen our theoretical tools and to build confidence on experimental methods Test the heavy-quark expansion model: the best predictive tool for inclusive quantities in the dynamics of heavy mesons. τ(bs /τ(bd ! experiments τ(b s /τ(b has key discriminating power as corrections nearly vanish. Year [arxiv:6.777] theory Data value.99 ±.4 agree well with b x b the.9994 ±.25 prediction [JHEP 2 (27 68]. Want to improve data precision. q ȳ q = m b 2 m 2 b 2 m b 4 m 4 b 4...

4 SEMILEPTONIC 4 Semileptonic (SL decays B s! D s µ X µ provide huge sample. Reminder: with nonzero width-difference Bs lifetime is not uniquely defined. SL decays give access to the flavour-specific lifetime. Challenging. - Biased decay-time determination from the observed decay length. - Broad B mass, spoiling separation from background and between the various signals within the inclusive final state.

5 NOVEL METHOD K π ν 5 K τ s fs from change in Bs yield vs decay time, μ relative to the yield of B decays reconstructed in the same final state. D s or D B s! D s µ X µ ( ( Name of the game: minimize B s -to-b differences of the selection efficiency B s or B vs the decay-time. Extract Δ=/τ s fs /τ B. Precise value of τ B as input.

6 4K D candidates Figure : Candidates per SIGNAL SAMPLE Candidates per 2 MeV/c 2 4 LHCb [PRL 9 (27 8] Distributions of Dµ mass for (top panel reference candidates, formed by combining D! K K candidates with µ candidates, and (bottom panel signal candidates formed by D s! K K candidates combined with µ candidates. The inset shows the K K - mass distribution with vertical lines enclosing the D (D s candidates used to form the reference (signal candidates. The dark-filled histograms show same-sign candidate distributions K K π mass [GeV/c 2 ] validation of the approach, since the composition of this sample is known precisely from other experiments. The largest discrepancy observed among the individual fractional 47K D s candidates background (D ± μ ± combination 6

7 SAMPLE COMPOSITION 7 Candidates per 6 MeV/c LHCb B s sample Data B s B s D s µ ν µ * D µ s ν µ Physics backg. Combinatorics Fit Signal B sample serves also as validation: composition known from B-factories Candidates per 6 MeV/c LHCb Data B B D µ ν µ * D µ ν µ Physics backg. Combinatorics Fit m corr [GeV/c 2 ] [PRL 9 (27 8] [PRL 9 (27 8] m corr [GeV/c 2 ]

8 CORRECTING 8 THE DATA. Unreconstructed ν momentum biases the decay-time determination. Correct observed momentum for average missing momentum as determined in simulation: k = p(dμ/p(b [fermilab-thesis-26-8] 2. Want uniform signal-to-reference efficiency ratio as a function of decay time. Known 2x difference between 2% Ds and D lifetime introduces about 2% non uniformities. Equalise the D decay time distributions. [PRL 9 (27 8]

9 KKπ s/b R(B gure : Candidates pe 6 m [GeV/c 2 ] 5 Dµ [PRL 9 (27 8] B s RESULT 9 Data Same-sign candidates LHCb B decay time [ps] 5% better than world s best. Halved the systematic of previous-best SL result. Agree with and improve previous determinations. Precision limited by the size of the reference sample. Ample chances for improvement with new data. Systematic dominated by the modelling in simulation of the Distributions of Dµ mass for (top panel reference candidates, formed by combining! K K candidates with µ candidates, and (bottom panel signal candidates formed signal. D s fs! K K candidates combined with µ candidates. The inset shows the K K - ass distribution =.547 ±. ±. ±.4( ps s with vertical lines enclosing the D (D s B candidates used to form the reference gnal candidates. The dark-filled histograms show same-sign candidate distributions. Method potential extends well beyond lifetimes. Method is lidation of the approach, since the composition of this sample is known precisely from her experiments. The largest discrepancy observed among the individual fractional suitable for other experiments too.

10 (SOME LHCb LIFETIMES Bs DμX [PRL 9 (27 8] Bs Dsπ [PRL (24 72] Bs J/ψf [PRL 9 (22 522] Bs J/ψφ [PRL 4 (25 48] Bs J/ψΚΚ [JHEP 8 (27 7] Bs ψ(2sφ [PLB 762 (26 25] See Greig Cowan s talk on Monday Bs J/ψη [PLB 762C (26 484] Bs DsDs [PRL 2 (24 82]

11 K K π BONUS DV μ BV ν PV Fit of composition in D decay time bin and then fit the resulting signal-to-reference yield ratio. Use precise D lifetime as input to obtain the Ds lifetime. KKπ s/b R(B [PRL 9 (27 8] LHCb Data Fit 2 4 D decay time [ps] Include a 4% relative acceptance correction and fs decay-time resolution Ds =.564 ±. ±.7 ±.7( D ps Improved by factor of 2 Agreement with world s average. the precision of the world s best result

12 ON THE B c SECTOR Bc first observation by CDF in 98 [PRL 8, 242]. Least studied of all B mesons. Only 6 decay modes established so far. Ratio of Bc yields w.r.t. B R(t/R"(t - -2 Candidates per LHCb 2 [PLB 742 ( ] LHCb 5.4 ±. ± 5.7 fs Small production, about O(.% of all b hadrons. Yet, several results from LHCb: - m Dµ [GeV/c Mass, PRL 9, 22 (22. Figure : Lifetime, PLB 742 ( ; EPJ C74 ( New decays: PRD 95, 25 (27; PRL 8, 8 (27; PRD 94, 92 (26; PLB 759, (26; PRL, 52 (24; JHEP 45 (24 48; JHEP (2 94; PRL, 88 (2; JHEP9(275; PRD 87, (2 22; PRD 87, 7 (2; PRL 8, 2582 (22. Will focus on two recent searches of Bc and Bc(2S decays. Distributions of Dµ mass for (top panel reference cand -4 D! K K candidates with µ candidates, and (bottom pa by D s! K K candidates combined with µ candidates. Th decay time [mm/c] mass distribution with vertical lines enclosing t the D (D [mm/c] s candida (signal candidates. The dark-filled histograms show same-sign ca validation of the approach, since the composition of this sam other experiments. The largest discrepancy observed amon contributions is. statistical standard deviations. The composition fit is su cient for the determination of corrections are needed since the final state is fully reconstruc through a least-squares fit of the ratio of signal Bs and refere

13 DECAYS INTO DD MESONS CP violation not observed yet in B c decays. B c D ( D ( decays, where D is D (s or D, proposed to measure γ [PRD 62, 575; PRD 65, 46]. Cabibbo-suppressed, colour-allowed Color-allowed Cabibbo-favoured, colour-suppressed Color-supressed Ratio of interfering suppressed and favoured amplitudes expected to be about. Enhanced [PRD 62 (2 575] CP asymmetries w.r.t. B DK decays. Attempt a first observation. Expectation of BRs are around -6 for most modes. [PRD 86 (22 749; arxiv:hep-ph/22; PLB 555 (2,89; PRD 7 (26, 5424]

14 * Bc D D, D sd s Candidates / ( DECAYS INTO DD MESONS * Bc D D s 4 Use fb of data collected at 7 and 8 TeV. Reconstruct Ds KK π, D K ππ and D K π, K ππ π. 5 4 Data LHCb D Total fit B B Bc K π Bc Bc 2 Ds D K K πd Ds D * D D, D sd s * Ds D c2 m(ds D LHCb 2 D D D m(dd [MeV/ c2] [arxiv:72.472] s Data Data Total fit fit Total DD B B Ds D DD B B c K K π D * DDs DD, D D BBcc * * D B Bcc Ds DD, Ds D * Bc Ds D K π m m((d Ds D D [MeV/ [MeV/cc22]] [MeV/ c2] c K D D, 2.5K DsD, 2 modes: 4K DsD, Candidates Candidates // ( ( MeV/ MeV/cc22 Candidates / ( MeV/c2 Normalise to the B

15 DECAYS INTO DD MESONS 5 No signal found, extract limits at 9% [95%] CL. [arxiv:72.472] f c B(B c! D s D f u B(B! D s D =(. ±.7 4 [<.9(. ], f c B(B c! D s D f u B(B! D s D =(.8 ± [<.7(4.7 4 ], f c B(B c! D D f u B(B! D D =( 8. ± 7.5 [<.9(2.2 2 ], f c B(B c! D D f u B(B! D D =( 2.9 ± 5. [<.2(.4 2 ]. f c B(B c! D s D f u B(B! D s D =(.2 ± 4. [<.(. 2 ], f c B(B c! D s D f u B(B! D s D =( 7. ± 9.2 [< 2.(2.4 2 ], f c B(B c! D D f u B(B! D D =(.4 ± 2. [< 6.5(7. ], f c B(B c! D D f u B(B! D D =( 4. ± 9. 2 [<.(.6 ]. Upper limits also for combination of decays into a DsD * and Ds*D final states. Assuming fc/fu about %, extract limits on the B c decays BRs: far above the predictions e.g. BR(B c D D < 6.x 4 at 9% CL.

16 SEARCH FOR EXCITED B c 6 A rich mass spectrum predicted by various QCD potential models and Lattice QCD. States below BD threshold can only! " 2% # 2 undergo radiative or hadronic transitions to the ground state B c t! " # [PRD 7 (24 547] which decays weakly. ATLAS observed B c (2S using ~ B c J/ψπ decays. No discrimination between o B c (2 S B c π π o B c (2 S B c * ( B c γ π π g [PRL (24 24]

17 SEARCH M(B π π [MeV/c FOR 2 c ] EXCITED M(B π π [MeV/c B 2 c ] c 7 (a MLP category: (.2,.2 (b MLP category: [.2,.4 Candidates / (28 MeV/c 2 Use 2 fb collected at 8 TeV. Candidates / (8 MeV/c 2 6 Reconstruct 5 s = 8 TeV about B c J/ψπ decays, selected with a BDT 4 exploiting vertex displacement and kinematics of daughter particles Figure 2 : LHCb 2 fb LHCb 2 fb s = 8 TeV Data Total fit J/ψ π B c B c M(B π π [MeV/c 2 c ] (c MLP category: [.4,.6 M(J/ψ π [MeV/c 2 ] J/ψ K Combinatorial : Invariant mass distribution of the selected B c! J/ candidates. The points with Candidates / (28 MeV/c LHCb 2 fb s = 8 TeV π π [MeV/c 2 ] M(B c (d MLP category: [.6,.] The M(B c distributions in the same-sign (darkgreen shaded areas and data (points with error bars samples in the range [66, 7] MeV/c 2 with the background model (blue solid line overlaid, for the four MLP categories. The areas between the two vertical red lines are the signal regions. [JHEP (28 8] Attach π π pairs to form the excited state candidates. Categorise them with a MLP exploring angles between B c and B c (2S candidates. No signal found.

18 SEARCH FOR EXCITED B c 8 2 Put limits on R = B( c (2S B(B c ( (2S! B c ( B c and compared with the ATLAS measurement. p s =7TeV p s =8TeV ATLAS (.22 ±.8 (stat/" 7 (.5 ±.6 (stat/" 8 LHCb < [.4,.9] [PRL (24 24] [JHEP (28 8] ε7,8 is the efficiency to reconstruct B c (2S w.r.t. the Bc signals. It s, but much larger than that of LHCb. LHCb upper limits at 95% CL in the vicinity of the ATLAS peak at ~6842 MeV/c. The LHCb and ATLAS measurements are compatible in case of large values of ε7,8.

19 CONCLUSION 9 LHCb reports a novel data-driven method for competitive B-lifetime measurements with SL decays: precision improved by 5% in Bs FS lifetime and 2x in Ds lifetime [PRL 9 (27 8]. LHCb contributed with a number of new Bc decays observed. Keep searching: - no signal of Bc DD decays yet [arxiv:72.472]. - no signal of excited Bc(2S states [JHEP (28 8]. - see Patrick Owen s talk, LFU test with Bc J/ψ τν and Bc J/ψ μν decays [PRL 2, 28 (28]. Full Run 2 data set soon ready to explore new avenues and observations.

20 BACKUP

21 SEARCH FOR EXCITED B c 2 Categorise them with a MLP exploring angles between B c and B c (2S candidates. Candidates / (28 MeV/c 2 5 LHCb 2 fb s = 8 TeV Candidates / (28 MeV/c LHCb 2 fb s = 8 TeV [JHEP (28 8] π π [MeV/c 2 ] M(B c π π [MeV/c 2 ] M(B c (a MLP category: (.2,.2 (b MLP category: [.2,.4 Candidates / (28 MeV/c LHCb 2 fb s = 8 TeV π π [MeV/c 2 ] M(B c Candidates / (28 MeV/c LHCb 2 fb s = 8 TeV π π [MeV/c 2 ] M(B c (c MLP category: [.4,.6 (d MLP category: [.6,.]

22 SEARCH FOR EXCITED B c 22 2 R = B( c (2S B(B c ( (2S! B c ( [JHEP (28 8] B c = N B ( c (2S N B c " B c " B ( c (2S, e ciency " B c is determined to be.9 ±.5, MLP category (.2,.2 [.2,.4 [.4,.6 [.6,.] E ciencies in % B c (2S.48 ±.6.4 ±.6. ± ±.8 B c (2S.8 ±..4 ±.4.44 ± ±.5

23 SEARCH FOR EXCITED B c 2 Scan over different mass hypotheses for overlapping B c (2 S and B c (2 S and put limits on 2 [JHEP (28 8] upper limit on R Reconstructed M(B S [MeV/c 2 c (2 ] LHCb 2 fb s = 8 TeV B c (2 S B c (2 S B c (2 S B c (2 S CL 9% CL 95% upper limit on R M(B S [MeV/c 2 c (2 ] M(B [MeV/c 2 c (2 S ] (a M =MeV/c 2 (b M = 5 MeV/c 2 Reconstructed M(B S [MeV/c 2 c (2 ] LHCb 2 fb s = 8 TeV B c (2 S B c (2 S B c (2 S B c (2 S CL 9% CL 95% CL 9% CL 95% Reconstructed M(B S [MeV/c 2 c (2 ] Reconstructed M(B S [MeV/c 2 c (2 ] R = B( c (2S B c B(B c ( (2S! B c ( upper limit on R LHCb 2 fb s = 8 TeV B c (2 S B c (2 S B c (2 S B c (2 S CL 9% CL 95% CL 9% CL 95% upper limit on R LHCb 2 fb s = 8 TeV B c (2 S B c (2 S B c (2 S B c (2 S CL 9% CL 95% CL 9% CL 95% M(B S [MeV/c 2 c (2 ] M(B [MeV/c 2 c (2 S ] (c M = 25 MeV/c 2 (d M = 5 MeV/c 2

24 SEARCH FOR EXCITED B c 24 2 [JHEP (28 8] R = B( c (2S B c = N B ( c (2S N B c B(B c ( (2S! B c ( " B c " B ( c (2S, p s =7TeV p s =8TeV ATLAS (.22 ±.8 (stat/" 7 (.5 ±.6 (stat/" 8 LHCb < [.4,.9] Table : Summary of the predictions for the R values. Ref. for B prediction R Bc (2S R B c (2S Bcvegpy with listed settings [5].2.4 [7].2.5 Production according to Ref. [5] [5].2.4 Production according to Ref. [6] [5].4.9 [7].5.2