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Charm Physics @ LHCb

Charm Physics @ LHCb. Raluca Mure ş an Oxford University On behalf of LHCb collaboration. LHCb and its charm physics trigger RICH calibration using D* → D 0 (K p ) p events Charm Physics Mixing searches Direct CPV Rare decay D 0 → mm Summary. Unobserved phenomena.

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Charm Physics @ LHCb

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  1. Charm Physics @ LHCb Raluca Mureşan Oxford University On behalf of LHCb collaboration R. Muresan – Charm Physics @LHCb

  2. LHCb and its charm physics trigger RICH calibration using D*→ D0(Kp)p events Charm Physics Mixing searches Direct CPV Rare decay D0→mm Summary Unobserved phenomena Outline R. Muresan – Charm Physics @LHCb

  3. VELO and RICH-es are the most important detectors for charm analysis. For details on the LHCb detector see Lluis Garrido’s talk R. Muresan – Charm Physics @LHCb

  4. L0 hardware pt of m, e, h, g HLT software – confirm L0 , m, e, h, g alley. 2 kHz output rate 200 Hz Exclusive B specific final states 300 Hz D* → D0(hh)p 600 Hz Di-muon J/y, b → J/y X 900 Hz Single muon trigger for b data mining LHCb D* trigger • 108 potentially usable D* → D0(hh)pevents • per 2 fb-1, available for: • Charm Physics studies • RICH calibration Estimated D* → D0(hh)pyields, events to tape, @ 2 fb-1 from b-hadrons: D0 → K- p+ 50x 106 ; D0 → K- K+ 5x 106; D0 →p- p+ 2x 106; D0 → K+ p- 0.2x 106 . Similar number of prompt D* are expected. For details on the LHCb trigger see talk by Eduardo Rodrigues. R. Muresan – Charm Physics @LHCb

  5. D* → D0(hh)p trigger stream • RICH information not used in the trigger  unbiased sample for MC - independent offline RICH calibration. • HLT assumes Kp, pK, KK, pp,masses in turn. K p KK pp GeV D0 mass online/offline resolution 8.2 / 5.3 MeV R. Muresan – Charm Physics @LHCb

  6. HLT – D* stream Loose cuts on: • hadrons pt and min IP sign, • D0 mass and (D*-D0 ) mass Present values favour the D* coming from b hadrons. R. Muresan – Charm Physics @LHCb

  7. RICH calibration A method to calibrate and study the performance of the RICH detector completely independent of the MC truth information using the D*+  D0 p+, D0 Kp decay chain ”Golden” kinematics easy to supress the background in order to obtain a clean sample (MD* - MD0)=144.5 MeV . (D*-D0) mass (GeV) (D*-D0) mass resolution online/offline 0.61/0.45 MeV A kaon and two pions with different momenta from each event can be used for RICH calibration. R. Muresan – Charm Physics @LHCb

  8. 95% D0 selected are true D0 • b inclusive sample, 330 s data taking; • The cuts provide a very clean K and p sample (over 96% purity) . D* events selection cuts Offline SELECTION WITH KINEMATIC CUTS ONLY – NO RICH. Particles are attributed in turn K mass and p mass R. Muresan – Charm Physics @LHCb

  9. Pion P(GeV) Kaon P (GeV) PID performance of RICH as measured on D* sample (MC truth independent) compared with that from truth information on all tracks in b sample p->emp K->K, p p->K, p K->emp Possible discrepancies maybe related to hidden variables (pt, multiplicity…), will be investigated with much higher MC statistics in near future. R. Muresan – Charm Physics @LHCb

  10. Initial focus on D0 → h+ h- decays: Charm Physics @LHCb • CP Eigenstate Lifetime Difference comparing the CP even Singly Cabibbo Suppressed (SCS) decay D0→K+ K- (p+ p-) with non-eigenstate Right Sign (RS) decay D0→K-p+ • Oscillationstudies Wrong Sign (WS) decayD0→K+p- • Direct CP violation SCS decays D0→K+ K- (p+ p-) • Other interesting studies are possible: • investigation of D0→ 4h modes • search for D0→m+m- many others for which the potential has not yet been estimated…. R. Muresan – Charm Physics @LHCb

  11. mixing Indexes associated to the mass eigenstates . G av. width • sensitive to new particles in the box diagram loop • contributions from all the energy scales, sensitive to new physics • mixing through physical decay states (long range) • expected to be dominated by SM contributions tagged unambiguouslyat production using the slow p sign R. Muresan – Charm Physics @LHCb

  12. mixing SM expectations imprecise , several orders of magnitude possible, independent of discovery potential of NP precise measurement desirable. |x|,|y| are expected to be small . x enhancement ( |x| » |y| ) could signify NP. Petrov hep-ph/0311371 R. Muresan – Charm Physics @LHCb

  13. Lifetime splitting, yCP can be measured by comparing the non-eigenstate decay D0→ K-p+toCP even decay D0→ K+ K- (p+ p-) . Lifetime ratio y and ycp differ by CP violating phase LHCb ~ 5x106 potentially useful tagged D0→ K+ K- events per 2 fb-1 R. Muresan – Charm Physics @LHCb

  14. RICH information and D0→ K+ K- p+K- No PID With PID K+K- K+K- p+K- MKK(MeV) MKK(MeV) PID RICH information essential for eliminating the background R. Muresan – Charm Physics @LHCb

  15. D0 can arrive to a WS hadronic final state (K+ p-) via: DCS decay Oscilating to+CF decay Oscillation Search with WS Kp 3 contributions assuming CP Strong phase difference between CF and DCS amplitudes LHCb - 0.2x 106 potentially useful tagged D0→ K+ p- events per 2 fb-1. R. Muresan – Charm Physics @LHCb

  16. WS decay time dependent mixing - K+ p- WS is the more challenging channel to pick out: BR ( K+ p- ) = ( 1.43  0.04 ) x 10-4 BR ( K+ p- ) / BR ( K- p+ ) = 3.76 x 10-3. D0, tagged using slow pion sign. Work in progress to further suppress the background peaking in mKπ: right sign decays mistagged by combination with a random pion. RICH particle ID effectively eliminates the background peaking in Δm: double misidentification of right sign decay Preliminary Monte Carlo lifetime fitting and sensitivity studies are underway R. Muresan – Charm Physics @LHCb

  17. D0 production and decay vertices • D0 lifetime measurement necessary input for mixing studies. • Need good resolution for both the production and the decay vertex D0 lifetime t = 0.41010.0015 ps D0 flight distance 60 GeV bgct  4 mm D0 decay vertex resolution 0.225mm R. Muresan – Charm Physics @LHCb

  18. D0 production and decay vertices Slow pion – very low momentum → D0 and ps almost colinear Poor resolution of the D0 production vertex = 4.270 mm to be compared to 4 mm Proper time resolution = 0.591 ps to be compared to 0.410 ps R. Muresan – Charm Physics @LHCb

  19. D0 production vertex reconstruction • Use additional tracks at production vertex 1. Prompt D* for primary vertex 2. Partially reconstruct parent Bparent • Preliminary work on 2 promising, for 1 MC not yet available. • 70% of D* from B’s have at least one charged sister, 45% have sister tracks which are reconstructed and pass some basic criteria Vertex resolutions (mm) Proper time resolution = 0.059ps R. Muresan – Charm Physics @LHCb

  20. Occurs when the absolute value of the D decay amplitude to a final state is not equal to the CP conjugate amplitude. D0, tagged using the slow pion sign Direct CPV in D0→ K+ K- (p+ p-) SCS decay, easy to modify its topology to get a penguin R. Muresan – Charm Physics @LHCb

  21. Direct CPV in D0→ K+ K- (p+ p-) In SM ACP≤ 10-3 for SCS decays. Possible NP enhancements to 1% from, e.g., penguin diagram • LHCb ~ 5x106 potentially usable flavour tagged D0→K+ K- events per 2 fb-1. • Statistical precision ~10-3 . • Normalize against initial state asymmetries through Kp mode. • Baseline measurement requires no lifetime estimation → all D* from B can be used. R. Muresan – Charm Physics @LHCb

  22. Rare decay D0→mm • D0→mm strongly suppressed in SM -- 10-18 - 10-13. • In some SUSY models, enhancements up to 10-6 possible. • Current best branching ratio limit BaBar: BR < 1.3 x 10-6 (122 fb-1). Oscillation Search with WS Kppp • A possible implementation of D*+→ p+ D0(→4h) in the HLT is under study. • Large branching fraction B (Kppp) ~ 2 x B (Kp) • Important sample for complementing K+p- mixing study • Sample for calibrating D decay model for 4-body Dalitz analyses in B → DK g measurement (see Yuehong Xie’s talk). LHCb large potential sample ~ 25 x 106 tagged Kppp events to tape per 2 fb-1 LHCb BR(D0→mm ) < 5 x 10 – 8 R. Muresan – Charm Physics @LHCb

  23. The LHCb experiment has an exciting potential for charm physics studies. A dedicated D* trigger will provide 108 flavour tagged D0→hh per 2 fb-1, giving unprecedented sensitivity in searches for D0 mixing, CP violation and rare decays. The same sample provides an invaluable calibration signal for LHCb performance, in particular the RICH detector. We have only begun to tap LHCb’s potential for charm physics. Summary Our beauty is also charming R. Muresan – Charm Physics @LHCb

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