CP Violation Studies at DØ

Transcription

1 CP Violation Studies at DØ Bd Bs Bd Bs Rick Van Kooten Indiana University For the DØ Collaboration LHCP 13 Barcelona, Spain May 13?

2 CP Violation Three kinds: In mixing: Mass eigenstates in mesonic systems "Light" "Heavy" In interference of decay and mixing amplitudes mix mix Different Different In decay: (B Factories) (LHCb) 1

3 Outline Three kinds: In mixing: Mass eigenstates in mesonic systems "Light" "Heavy". Dimuon charge asymmetry More recent DØ results: 1. Semileptonic charge asymmetry from:. " " In interference of decay and mixing amplitudes Previous ~s Tevatron deviation from SM; LHCb shows consistency Different? In decay: 3. Asymmetry

4 Dimuon Charge Asymmetry Direct semileptonic decay Neutral B meson oscillation and then semileptonic decay Measure CP violation in mixing via Constrain backg. Reduce syst. Inclusive single muons Mostly background 3

5 Dimuon Charge Asymmetry Direct semileptonic decay Neutral B meson oscillation and then semileptonic decay Measure CP violation in mixing via Constrain backg. Reduce syst. Inclusive single muons Mostly background Phys. Rev. D 8, 31 (11) 3.9s deviation from SM prediction Asymmetry is a linear combination semileptonic charge asymmetries of and ; 4

6 Dimuon Charge Asymmetry a s sl. 3.9s SM -. Standard Model Prediction: -.4 DØ A b sl DØ Asl b 95% C.L. DØ, 9. fb a d sl arxiv:11.474, JHEP6, 7 (7) New predicted CP-violating source in dimuons, see backup slides 5

7 Dimuon Charge Asymmetry Entries To test origin of dimuon charge asymmetry, two complementary measurements with impact parameter (IP) requirements on muons: - IP > 1 mm Enriched in b's and larger - IP < 1 mm More background, smaller fraction Results consistent with default result Extract: DØ, 9. fb -1 Data MC MC, muons from fraction IP(m) [cm] a s sl correlation A b sl(ip <1 ) A b sl A b sl(ip >1 ) 68% and 95% C.L. regions are obtained from the measurements with IP selections DØ, 9. fb -1 68% C.L. SM 95% C.L asl d 6

8 Semileptonic Charge Asymmetry How? 7

9 Semileptonic Charge Asymmetry How? Use lepton charge to identify the B-meson flavor at time of decay 8

10 Semileptonic Charge Asymmetry How? Use lepton charge to identify the B-meson flavor at time of decay Correct for asymmetries of detector and physics backgrounds 9

11 Semileptonic Charge Asymmetry How? Use lepton charge to identify the B-meson flavor at time of decay Correct for asymmetries of detector and physics backgrounds Scale by the fraction of mixed/oscillated events (using Monte Carlo) Assume no production asymmetry, no direct CP violation in charged D-meson or B-meson semileptonic decay; only CP violation in mixing of B mesons 1

12 Tevatron / DØ Strengths Initial is CP invariant Excellent muon coverage out to h <, non-gaseous tracker Reverse polarities of solenoid and toroid reversed every ~ weeks Four roughly equal-sized samples Solenoid ~6.5 15l Toroid (55 tons Fe) Swap polarities Difference in reconstruction efficiency between positive and negative particles minimized helps cancel/reduce many detector charge asymmetries! (cancel to first order ~3% ~.1%) 11

13 Kaon Charge Asymmetry Once data split into magnet polarity-flip subsamples, largest contribution to (since detector made of matter) material than, therefore travel further in detector ; more chance to decay in flight to (%) -1 D Run II, 1.4 fb a K Kaon asymmetry, < h(k) <..7 < h(k) < 1. h(k) < p(k) (GeV/c) Measure in data using as a function of p and Residual muon reconstruction charge asymmetry and tracking asymmetry typically ~1 times smaller, also measured in data using and 1

14 via Full Run II data set Two channels: Find asymmetry in bins of visible proper decay length First two bins as control region to test corrections, osc F B Fraction of Oscillated B, g t DØ MC expect no mixing Visible Proper Decay Length(B) [cm] 13

15 via ) N(mD) / (4 MeV/c ) ) / (4 MeV/c + D - ) - N(m - N(m + D Sum -1 D Run II, 1.4 fb M(Kpp) (GeV/c ) 5-1 D Run II, 1.4 fb 4 Difference M(Kpp) (GeV/c ) Simultaneous fit to sum and difference Expect an asymmetry; correct for,, ) ) ) / (.5 MeV/c + ) - N(m - D* - N(m + D* N(mD*) / (.5 MeV/c D Run II, 1.4 fb DM = M(Kpp ) - M(Kp) (GeV/c ) D* -1 D Run II, 1.4 fb DM = M(Kpp ) - M(Kp) (GeV/c ) D* 14

16 via Asymmetry (%) DØ Run II, 1.4 fb Asymmetry (%) DØ Run II, 1.4 fb -1 - A - A BG osc F B asl d Visible Proper Decay Length(B ) (cm) -1 - A - A BG osc F B asl d Visible Proper Decay Length(B ) (cm) PRD 86, 79 (1) World's single most precise published measurement (BaBar preliminary update at Beauty 13) Correction: BaBar result (see p. 1) submitted May 1; arxiv: [hep-ex], accepted for publication in PRL May 15 15

17 via Full Run II data set 16

18 via Kaon charge asymmetry mostly cancels out (small correction due to interference) Belle: PRL 18, 7181 (1) 17

19 via Sum 1 3 Diff. )/6 MeV/c D s N(m 3-1 DØ Run II, 1.4 fb Bs (Bs) Æ m D s n (weighted) N(D ) = s N(D ) = Signal Fit Background Fit )/1 MeV/c + D s - )-N(m - D s 5-1 DØ Run II, 1.4 fb 1 N(m + -5 Signal Fit 1.8. M (fp ) [GeV/c ] 1.8. M (fp ) [GeV/c ] Simultaneous fit, correct for small residual detector asymmetries (from data) PRL 11, 1181 (13) World's single most precise published measurement (LHCb preliminary LHCb-CONF-1-) 18

20 Comparison & Combination Compare with DØ dimuon result sl a s. DØ Dimuon DØ Semileptonic charge asymmetries consistent with SM and DØ dimuon result DØ SM s DØ asl DØ a b A (IP sl ) 68% C.L. >1 A b sl (IP d sl ) 68% C.L. <1 Standard Model asl d 19

21 Comparison & Combination Combine all three DØ measurements (including correl.) sl a s. DØ Dimuon DØ SM DØ -. s DØ asl d DØ asl p-value(sm) =.33% (.9 standard deviations) -.4 A A b (IP sl b sl (IP ) 68% C.L. >1 ) 68% C.L. <1 Combination is 3.1 standard deviations from zero Standard Model asl d

22 Comparison & Combination Compare to other measurements sl a s. BaBar prel. update DØ Dimuon DØ LHCb: LHCB-CONF-1- BaBar: Beauty 13 Babar update: submitted May 1, arxiv: [hep-ex], accepted for publication in PRL May 15 LHCb prel. DØ -. SM s DØ asl See backup slide for world average combination(s) -.4 d DØ asl A A b (IP sl b sl (IP ) 68% C.L. >1 ) 68% C.L. <1 Combination Standard Model asl d 1

23 via Full Run II data set Direct CP violation Correct using SM prediction: tree and penguin contributions have the same weak phase for so no direct CP violation expected (max asymmetry of ~.3%) Clean test of direct CP violation decays could have CP-violating effects of a few percent

24 via Full Run II data set Direct CP violation Sum: )/1 MeV/c N(J/y h D 1.4 fb Total B Æ J/y K B Æ J/y p B X Æ J/y h X Combinatorial M (J/y h ) [GeV/c ] Diff.: )/1 MeV/c + ) - N(J/y h - N(J/y h -1 D 1.4 fb Total M (J/y h ) [GeV/c B Æ J/y K B Æ J/y p B X Æ J/y h X Combinatorial ] arxiv:/ [hep-ex], submitted to PRL World's single most precise measurement 3

25 via World Average = (.8.55)% Uncertainty scaled by 1.8 Confidence Level.33 c DØ 13.7 Belle World Average = ( )% c DØ LHCb 1. Belle 7 BaBar 4.4 BaBar 5.5 Cleo J/yK A (%) 6.8 Belle J/yp A.87 (%) World averages following PDG procedure Both consistent with zero 4

26 Summary & Prospects Continuing to probe CP violation: Exclusive semileptonic charge asymmetries and measurements updated using the full DØ Run II data set most precise published values consistent with both the SM and DØ dimuon charge asymmetry Clean direct CP violation asymmetry measured using the full DØ Run II data set most precise single value; consistent with SM Prospects DØ dimuon charge asymmetry being updated to full Run II data set, including: more bins in muon impact parameters additional methods to estimate kaon asymmetry better optimized track quality requirements improved MC samples for estimating Unleash same tools to test CP violation in charm decays 5

27 Backup Slides

28 Interference between Mixing and Decay LHCb 1. fb 1 + CDF 9.6 fb 1 + D 8 fb 1 + ATLAS 4.9 fb 1 D LHCb Combined HFAG April 13 68% CL contours ( ).5 CDF SM ATLAS A1

29 Additional Source of CPV in Like-Sign Dimuons Borissov, Hoeneisen, arxiv: v1 [hep-ex], Understanding the like-sign dimuon charge asymmetry in pp(bar) collisions e.g., but due to interference between mixing and decay in B system: additional Deviation from SM not as large, but still well above 3s A

30 Comparison & Combination From Iain Bertram, DØ: sl a s. DØ Dimuon WA average of results from: DØ: PRL 11, 1181 (13) LHCb: LHCB-CONF-1- WA SM -. average of results from: s World average asl d World average asl DØ: PRD 86, 79 (1) B-factories: HFAG BaBar: Beauty A A b (IP sl b sl (IP ) 68% C.L. >1 ) 68% C.L. <1 Combination Standard Model Combine with DØ like-sign dimuon asymmetry: asl d p-value(sm) = 1.6%.4 s.d. A3