Charm physics at LHCb

Transcription

1 Charm physics at LHCb Alexey Dzyuba on behalf of the LHCb Collaboration 29th of August 2017, Moscow 18th Lomonosov Conference on Elementary Particle Physics

2 Charm quark Important properties: High mass [simplify QCD calcultions] Applications of charm physics: Spectroscopy of charmed baryons bridge between quarkonia spectroscopy and spectroscopy of light hadrons 2

3 Charm quark Important properties: High mass [simplify QCD calcultions] CP violation effects [discribed in Standard Model (SM) by complex phases of CKMmatrix elements ] are very small for charm arg(vcd) ~ 10 4 arg(vcs) ~ 10 5 Applications of charm physics: Spectroscopy of charmed baryons bridge between quarkonia spectroscopy and spectroscopy of light hadrons Search for New Physics Searches for CPV in charm 3

4 Charm quark Important properties: High mass [simplify QCD calcultions] CP violation effects [discribed in Standard Model (SM) by complex phases of CKMmatrix elements ] are very small for charm Suppressed flavor changing neutral current (FCNC) transitions Mixing neutral charm meson measured, but is not-intensive ( small mixing parameters x~δm, y ~ΔΓ ) arg(vcd) ~ 10 4 arg(vcs) ~ 10 5 Applications of charm physics: Spectroscopy of charmed baryons bridge between quarkonia spectroscopy and spectroscopy of light hadrons Search for New Physics (Searches for CPV in charm / rare charm decays driven by FCNC) Mixing / FCNC 4

5 LHCb as heavy quark fabrique (at s = 7 TeV) 5

6 LHCb as heavy quark fabrique Suitable angular acceptance for heavy quark pair production in pp-collisions (at s = 7 TeV) 6

7 LHCb as heavy quark fabrique Suitable angular acceptance for heavy quark pair production in pp-collisions (at s = 7 TeV) Exellent vertexing and tracking give access to decay time distribution / trigger for weak decays / promptsecondary separation 7

8 LHCb as heavy quark fabrique Exellent PID allows to supress background dramatically and explore many decay modes Suitable angular acceptance for heavy quark pair production in pp-collisions (at s = 7 TeV) Exellent vertexing and tracking give access to decay time distribution / trigger for weak decays / promptsecondary separation 8

9 LHCb as heavy quark fabrique Nice tagging, triggering & great potential to search for rare decays with di-muons Exellent PID allows to supress background dramatically and explore many decay modes Suitable angular acceptance for heavy quark pair production in pp-collisions (at s = 7 TeV) More about LHCb performance: Int. J. Mod. Phys. A 30, Exellent vertexing and tracking give access to decay time distribution / trigger for weak decays / prompt (2015) secondary separation 9

10 Luminosity and trigger Operated in constant instantanious luminosity mode 10

11 Luminosity and trigger Operated in constant instantanious luminosity mode Two stage trigger which is efficient for hadronic channels 11

12 Luminosity and trigger Operated in constant instantanious luminosity mode Two stage trigger which is efficient for hadronic channels Turbo stream for Run-II [Candidates reconstructed at the trigger level saved directly for offline analysis, huge acceped rates, a kind of revolution in experimental HEP] 12

13 Flavor tagging for charm Prompt tagging Primary vertex (PV) Secondary (semileptonic) h PV D0 D*+ D0 IP h = π±, K± X μ π+ Higher tagging rate B h h υμ More efficient triggering 13

14 Flavor tagging for charm Prompt tagging Secondary (semileptonic) h Primary vertex (PV) PV D0 D*+ B h D0 IP h = π±, K± X μ π+ Higher tagging rate h υμ More efficient triggering Mixing & CPV Right sign (RS) D*+ / K π+: 1.7M D0 Kπ with doubly-tagged sample RS appears when no-mixing AND Cabibbo-favorite (CF) decay PR D95 (2017)

15 Flavor tagging for charm Prompt tagging Secondary (semileptonic) h Primary vertex (PV) PV D0 D*+ B h D0 IP h = π±, K± X μ π+ Higher tagging rate h υμ More efficient triggering Mixing & CPV Right sign (RS) D*+ / K π+: 1.7M Wrong sign (WS) D*+ / K+π : 6.7k D0 Kπ with doubly-tagged sample RS appears when no-mixing AND Cabibbo-favorite (CF) decay WS either [mixing AND CF] OR [no-mixing and Doubly-Cabibbo suppresed decay] PR D95 (2017) Probe for all possible CPV scenarious (direct, in mixing, interference) 15

16 Mixing & CPV As mixing parameters (x' and y') are small the WS / RS ratio can be approximated as: h PV IP B π+ D*+ D0 X μ h υμ 16

17 h Mixing & CPV PV As mixing parameters (x' and y') are small the WS / RS ratio can be approximated as: IP B π+ D*+ D0 X μ h υμ PRL 111 (2013) Parameter DT+Prompt Prompt Result of all CPV allowed fit PR D95 (2017)

18 h Mixing & CPV PV As mixing parameters (x' and y') are small the WS / RS ratio can be approximated as: IP B π+ D*+ D0 X μ h υμ PRL 111 (2013) Parameter DT+Prompt Prompt Result of all CPV allowed fit PR D95 (2017) Higher signal purity and complementary decay-time coverage allow to impove precision by 10-20% when adding few percents of doubly tagged data No evidence for CPV in mixing / decay 18

19 Direct CPV in charm Measured observable: to get access to CPV observable, it need to be corrected for production and detection asymmetries. For example for prompt tagging: 19

20 Direct CPV in charm Measured observable: PLB 767 (2017) 177 to get access to CPV observable, it need to be corrected for production and detection asymmetries. For example for prompt tagging: Combination of the results from prompt and semileptonic tagging (per-mile precision): 20

21 Direct CPV in charm Measured observable: PLB 767 (2017) 177 to get access to CPV observable, it need to be corrected for production and detection asymmetries. For example for prompt tagging: Combination of the results from prompt and semileptonic tagging (per-mile precision): Other decay modes are also under investigation: D±(s) η'π± D0 4π [ PLB 771 (2017) 21 ] [ PLB 769 (2017) 345 ] 21

22 Indirect CPV in charm sector Time integrated CP asymmetries as well as mixing parameters are small: CPV in decay closecpv in mixing / to-zero interference Expected to be less Inverse of effective lifetime 22

23 Indirect CPV in charm sector PRL 118 (2017) Time integrated CP asymmetries as well as mixing parameters are small: CPV in decay closecpv in mixing / to-zero interference Expected to be less AГ slope of linear fit Inverse of effective lifetime Prompt D* tagging D Kπ to keep production and detection asymmetries under control 23

24 Indirect CPV in charm sector PRL 118 (2017) Time integrated CP asymmetries as well as mixing parameters are small: AГ slope of linear fit CPV in decay closecpv in mixing / to-zero interference Expected to be less Inverse of effective lifetime Prompt D* tagging D Kπ to keep production and detection asymmetries under control Combination with semileptonic tagged sample [JHEP 04 (2015) 043] : Most precise CPV measurement for charm: 24

25 0 + + Rare decays: D h h μ μ (h = π, K) Goal: Probe New Physics in c u transitions, appears at short distances and very suppressed in SM ( < 10 9 ) Short range Long range 25

26 0 + + Rare decays: D h h μ μ (h = π, K) Goal: Probe New Physics in c u transitions, appears at short distances and very suppressed in SM ( < 10 9 ) Long range contribution from ρ, ω, φ due to decays into μ+μ pair (difficult to predict leakage of events from resonance tails into search region) Short range Long range 26

27 0 + + Rare decays: D h h μ μ (h = π, K) Goal: Probe New Physics in c u transitions, appears at short distances and very suppressed in SM ( < 10 9 ) Long range contribution from ρ, ω, φ due to decays into μ+μ pair (difficult to predict leakage of events from resonance tails into search region) Short range Long range Non-blinded mass bins 27 LHCb-PAPER / arxiv:

28 0 + + Rare decays: D h h μ μ (h = π, K) Goal: Probe New Physics in c u transitions, appears at short distances and very suppressed in SM ( < 10 9 ) Long range contribution from ρ, ω, φ due to decays into μ+μ pair (difficult to predict leakage of events from resonance tails into search region) Short range Long range Non-blinded mass bins The rarest charm-hadron decays ever observed! Branching fractions are consistent with SM expectations 28 LHCb-PAPER / arxiv:

29 Spectroscopy: five excited Ωc Single charmed baryons predicted from SU(3) multiplets: All ground states as well as excited Λc, Σc and Ξc states have been reported No exited Ωc states were observed before LHCb 29

30 Spectroscopy: five excited Ωc Single charmed baryons predicted from SU(3) multiplets: All ground states as well as excited Λc, Σc and Ξc states have been reported No exited Ωc states were observed before LHCb Many possible channels: Ref. to theory papers in backup 30

31 Spectroscopy: five excited Ωc Single charmed baryons predicted from SU(3) multiplets: All ground states as well as excited Λc, Σc and Ξc states have been reported No exited Ωc states were observed before LHCb Many possible channels: 3 fb 1 Run I fb 1 Run II pp collision data Decay chain: Cabibbo suppressed, but very suitable for LHCb (high selection efficiency) τ(ξc+) 45 ps detached from PV Ref. to theory papers in backup PRL 118 (2017)

32 Spectroscopy: five excited Ωc Ξc candidate combined with charged kaon Five narow peaks for Ξc+K No structures in Ξc+K+ invariant mass PRL 118 (2017)

33 Spectroscopy: five excited Ωc Ξc candidate combined with charged kaon Five narow peaks for Ξc+K No structures in Ξc+K+ invariant mass Sidebands for Ξc candidate do not produce peaking structures PRL 118 (2017)

34 Spectroscopy: five excited Ωc Ξc candidate combined with charged kaon Five narow peaks for Ξc+K No structures in Ξc+K+ invariant mass Sidebands for Ξc candidate do not produce peaking structures Feed-down contribution missed PRL 118 (2017)

35 Spectroscopy: five excited Ωc Ξc candidate combined with charged kaon Five narow peaks for Ξc+K No structures in Ξc+K+ invariant mass Sidebands for Ξc candidate do not produce peaking structures Feed-down contribution missed Fit quality improves when including a broad structure or multiple states around 3200 MeV PRL 118 (2017)

36 Spectroscopy: five excited Ωc PRL 118 (2017) Properties of observed peaking structures: Ref. to theory papers in backup Spectroscopy of system containing one heavy (c) and two intermedate mass squarks Spin-parity information is requided to match observed peaks with theory prediction Options: 1) Three body decays 2) Decays of heavier baryons 36

37 Spectroscopy: discovery of Ξcc Two SU(3) triplets are predicted as a parts of two SU(4) baryons 20-plets Weak force driven decays expected ++ EM / strong decays expected Many predictions: M(Ξcc+,++) in [ ] GeV, M(Ωcc) M(Ξcc) GeV Few MeV difference expected between Ξcc+ and Ξcc++ 37 Ref. to theory papers in backup

38 Spectroscopy: discovery of Ξcc Two SU(3) triplets are predicted as a parts of two SU(4) baryons 20-plets Weak force driven decays expected ++ EM / strong decays expected Many predictions: M(Ξcc+,++) in [ ] GeV, M(Ωcc) M(Ξcc) GeV Few MeV difference expected between Ξcc+ and Ξcc++ Lattice QCD: M(Ξcc+,++) 3.6 GeV, M(Ωcc) 3.7 GeV HQET: core from heavy diquark Lifetime expectations: Doubly heavy baryon expected to be similar to a heavy Qq meson 38 Ref. to theory papers in backup

39 Spectroscopy: discovery of Ξcc ++ Use Run-II pp data 1.7 fb 1, exclusive high efficent trigger (Turbo) Run-I (2012) 2 fb 1 for cross-check Expected up to 10% branching fraction for decay of interest 39

40 Spectroscopy: discovery of Ξcc ++ Use Run-II pp data 1.7 fb 1, exclusive high efficent trigger (Turbo) Run-I (2012) 2 fb 1 for cross-check Expected up to 10% branching fraction for decay of interest Invariant mass for: Right sign (RS) combination: Wrong sign (WS) : Sidebands LHCb-PAPER / arxiv:

41 Spectroscopy: discovery of Ξcc ++ Use Run-II pp data 1.7 fb 1, exclusive high efficent trigger (Turbo) Run-I (2012) 2 fb 1 for cross-check Expected up to 10% branching fraction for decay of interest Invariant mass for: Right sign (RS) combination: Wrong sign (WS) : Sidebands LHCb-PAPER / arxiv:

42 Spectroscopy: discovery of Ξcc ++ Signal yield: 313 ± 33 events Mass resolution: 6.6 ± 0.8 MeV Local significance > 12σ Sub-MeV precision for observation! Obtained value are consistent with many theoretical calculations (including LQCD) LHCb-PAPER / arxiv:

43 Spectroscopy: discovery of Ξcc ++ Signal yield: 313 ± 33 events Mass resolution: 6.6 ± 0.8 MeV Local significance > 12σ Sub-MeV precision for observation! Obtained value are consistent with many theoretical calculations (including LQCD) Signal peak for Run-I data has > 7σ local significance (113 ± 21 events) LHCb-PAPER / arxiv:

44 Spectroscopy: discovery of Ξcc ++ Signal yield: 313 ± 33 events Mass resolution: 6.6 ± 0.8 MeV Local significance > 12σ Sub-MeV precision for observation! Obtained value are consistent with many theoretical calculations (including LQCD) Signal peak for Run-I data has > 7σ local significance (113 ± 21 events) Peaking structure remains significant after requiring minimum decay time [ t > 5σt ] Week force driven decay indeed. LHCb-PAPER / arxiv:

45 Summary LHCb performs excellent Wide physics program in the charm sector including - spectroscopy studies ( five new Ωc* and Ξcc++), - search for New Physics in rare decays ( D hhμμ ) - and in CP violation ( WS / RS, time-int. ACP, AГ ) A lot of new results and many analyses ( Run-I & II ) in the stack Thank you! 45

46 Backup 46

47 Mass Ξcc 47

48 Lifetimes Ξcc 48

49 Theory references for Ωc* 49

50 Theory references for Ωc* 50