LHCb results and prospects

Transcription

1 LHCb results and prospects M. Witek (IFJ PAN Cracow, Poland) On behalf of the LHCb Collaboration Miami 2011 Conference Fort Lauderdale, Florida 800 physicists 15 countries 54 institutes CERN LHC Large Hadron Collider LHCb CMS Atlas Alice

2 Outline Introduction LHCb detector Hot measurements? Angels and demons Tara Shears from LHCb experiment indirect proof that LHCb deals with antimatter 2

3 CP symmetry C - q -q (paricle antyparticle) P - r -r (left right handed coord system) Do the processes in CP mirror look exactly the same? The CP symmetry violation (CPV) was observed for neutral kaons in 1964 (0.2%) Jim Cronin KS CP K S 0 KL 0 KS CP KL KL K L + events Val Fitch 3

4 CPV and Baryogenesis n n baryon baryon baryon 10 n n n ~ O 10 The source of current matter domination over antimatter is unknown. CPV is one of the three necessary conditions (Sacharow 1967) d' V The unique source of CPV in Standard Model is a s' V single phase in the CKM matrix b' V ud cd td V V V us cs ts V V V ub cb tb d s Vˆ b CKM d s b CPV predicted in SM gives Δn baryon /n γ ~O(10-20 ). It is too small. There must be come other CPV beyond SM 4

5 Two ways of search for New Physics Indirect searches Probe up to ~100 TeV Precision measurements of well predicted observables in SM, in particular these with small values, search for suppressed processes (LHCb approach). Size of the B mesons ~10-16 m. NP occurs at >10-19 m, But some processes with B or D mesons sensitive to m due to virtual effects in loop mediated processes predicted by theories beyond SM Examples of indirect discoveries: Prediction of third generation of quarks (b,t) to introduce CPV in SM c and t quarks first seen in FCNC processes in K and B mesons (ν+n ν+n) seen in 1973; direct Z observation 10 years later Direct observations Probe up to ~4 TeV Direct production of new objects at s =14 TeV LHC operates now at s =7 TeV only 5

6 The DNA of New Physics A. Buras arxiv: v1

7 B (s) 0 mesons Flavour eigenstates are not mass eigenstates, both are not CP eigenstates. Eigenstates differ by Δm i ΔΓ Large mixing, large CPV test SM CPV Fast mixing, small CPV test non SM CPV LHCb specialty 7

8 LHCb detector σ(pp bb) = 284 ± 53 mb dla (s = 7 TeV) [PLB ] ~ 100,000 bb pairs/sec b B q b B q Excellent particle identification π/p/k separation over GeV Powerful muon identification Efficient trigger Low PT thresholds for lepton, γ/π 0 and hadron Precise tracking Good mass and IP resolution to suppress background Good vertex resolution for time dependent analysis 8

9 VErtex LOcator - VELO B-decay displaced vertex K Most precise vertex detecor at LHC B s D s K K B-production at pp-collision primary vertex B b tag + Makro movements ~cm Micro precision ~μm Impact parameter Interaction vertex σ z ~70 μm 9

10 Multi level trigger system 1092 bunches, 3*10 32 /cm 2 /sek, 3.5*10 14 collisions in LHC in MHz: visible interactions 650 khz: L0 3.6 khz: HLT On-line charm physics Signal/background ratio used to inspect data quality 1fb -1 recorded in events on tape 10

11 Selected results on CPV and NP 1. ϕ s - the phase of B s mesons mixing 2. Rare decays B s,d μ + μ - 3. Asymmetries for K* μ + μ - 4. CPV in two body charm decays 11

12 ϕ s - the phase of B s mesons mixing 12

13 ϕ s - the phase of B s mesons mixing d s b V V V ud cd td V V V us cs ts V V V ub cb tb d s b B 0 s s V ts V ts s B 0 s SM prediction ϕ s - an analogue of 2β (phase of B 0 mixing) in the B s system is expected to be very small. First measurements from the Tevatron indicated large values for ϕ s discrepancy with SM reaching almost 3 σ at a certain moment. 13

14 ϕ s - the phase of B s mesons mixing How to measure the phase ϕ s? Interference of two amplitudes B s J/y f - golden mode B s J/y f 0 - independent measurement ϕ s 14

15 ϕ s - the phase of B s mesons mixing 15

16 Measurements of ϕ s Results correlated with G s = width difference of the B s mass eigenstates plotted as contours in (f s vs G s ) plane [reference plots in backup] Ambiguous solution for (f s f s, G s G s ) LHCb result is consistent with Standard Model First significant direct measurement of G s = ± ± ps -1 f s also measured in a second mode: B s J/y f 0 (first observed in LHCb) with lower statistics but CP-odd final state, so no angular analysis required Combined result: f s = 0.03 ± 0.16 ± 0.07 Still room for new physics, will continue to improve precision. Expect 2 fb -1 by end of 2012 σ(f s ) ~ 0.07 from simple scaling. 16

17 Rare decays B s,d μ + μ - 17

18 B s,d μ + μ - BR(B s μ + μ - )=(3.2±0.2)x10-9 BR(B d μ + μ - )=(1.0±0.1)x10-10 Example of enhancement in MSSM Strongly suppressed in SM A.J.Buras, arxiv:

19 B s,d μ + μ - B 0 s μμ? Selection with signal region blinded Searching for a few events from ~10 14 collisions delivered by LHC MVA Boosted Decision Tree Dominant background: a combination of two well identified μ + μ - BDT based on kinematical and topological variables: B: impact parameter, flight distance, PT, isolation μ: impact parameter, PT, polarization, μμ vertex Calibrated on B s,d h + h - 19

20 B s,d μ + μ - LHCb results for 0.37 fb -1 B s μ + μ - Combination of 2010 (0.37 pb -1 ) and 2011 (0.37 fb -1 ) data BR(B s μ + μ - 95%C.L. BR(B d μ + μ - 95%C.L. 20

21 Slide from G. Punzi, INFN-Gruppo1, November nd. LHCb results: 2010 and EPS2011 CDF results upper limit and branching ratio CMS result LHCb has currently the best upper limits 6

22 B s,d μ + μ - prospects 22

23 Asymmetries for B 0 K * m m 23

24 B 0 K * m m Sensitive to NP in loops which modify angular distributions (SUSY, graviton exchange, extra dimension). Forward-backward asymmetry A FB sensitive to modification of the helicity structure. A FB (q 2 ) asymmetry in the m m rest frame, q 2 = m 2 mm q 2 at zero of A FB is a good probe of NP 303 signal events from ~0.3 fb -1 LHCb has largest sample in world, as clean as the B Factories! [LHCbCONF ] 24

25 B 0 K * m m Previous measurements indicated a discrepancy [arxiv: ] LHCb measurement consistent with Standard Model. [arxiv: ] 25

26 CPV in two body charm decays 26

27 CPV for charm decays D 0 mixing now established but CPV not yet seen experimentally In SM, indirect CP violation in charm is expected to be very small asymmetries A CP ~ O(10-5 ) Direct CP violation can be a bit larger in SM A CP ~ O(10-3 ) - O(10-4 ) Both direct and indirect CPV can be affected by New Physics A CP up to O(10-2 ) Measure difference between two asymmetries D *+ D 0 (K + K - )π + and D *+ D 0 (π + π - )π + Nearly all systematic effects cancel in the double difference CPV direct: in decays CPV indirect: in mixing or in interference between mixing and decays 27

28 D and D* signals Enormous statistics available: > 10 6 D 0 K + K from D *+ D 0 + Charge of from D * determines production state of the D 0 28

29 CPV for charm decays Statistical significance 3.5 σ Result based on ~0.5 fb -1 Half of the 2011 data. LHCb-CONF

30 Comparison with world average 30

31 Summary The LHCb is carrying on and intensive search for phenomena beyond the Standard Model No sign of New Physics discovered yet, hint at CPV in charm decays 67 results from LHCb have been submitted as Conference Papers available at (most will soon be out as journal publications) Some of the results are already the best world measurements at the fraction of data used in the analyses fb -1 used for results shown, 1 fb -1 collected in 2011, additional 1 fb -1 expected in