CP violation in mixing at LHCb CP violation in mixing at LHCb

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1 CP violation in mixing at CP violation in mixing at J.A. de Vries on behalf of the collaboration

2 OUTLINE Introduction asl d (5) asl s (new result) J.A. de Vries - CPV in mixing at - BEAUTY 6

3 CPV IN MIXING Neutral mesons: mass eigenstates vs flavour eigenstates B H,L i = p Biq B Mixing due to, m q q CP violation in mixing: P(B! B) 6= P( B! B) q/p 6= m 8 ps.5 ps (Bs system) So far only observed in kaon system: (εk =.%) PDG, Chin. Phys. C, 8, 9 (4) J.A. de Vries - CPV in mixing at - BEAUTY 6

4 on CPV IN MIXING ing means that the probability that a B mixes into a B is di erent that a B mixes into a B. The flavour specific or semileptonic P(Bq! B q ) 6= P(B q! Bq ) as CP Violation in mixing: aqsl P (B q! Bq ) P (Bq! B q ) =, P (B q! Bq ) + P (Bq! B q ) q/p 4 = 4 + q/p (q = d, s) q mq tan( () q ) Lenz, Nierste [JHEP 76:7 (7)] distinguishing the two species of neutral B mesons, namely the ndard Model predictions [, ] arefinal tiny state compared to the current Semileptonic inclusive (flavour specific) ty: adsl = ( 4..6) 4 and assl = (.9.) 5. This t of these asymmetries an excellent null test of the Standard Model. neutral B mesons: e dimuon asymmetry measured by D [] is sensitive adsl and assl + d B! D µ dard deviation discrepancy aslthe Standard Model. Dedicated µ X with d sand D [5]. An overview of past ave been by [4] Bsperformed! D s µ+ asl µx world average is provided by the Heavy Flavor Averaging Group d averages measurements as of Summer 5 (excluding adsl of = (pure 4.7asl.6) 4 metry) are assl = (..7) 5 metries= (+..)% adsl Artuso, Borissov, Lenz [arxiv:5.9466] J.A. de Vries - CPV in mixing at - BEAUTY 6 () 4

5 MEASURING asl Raw untagged asymmetry: Araw N (D µ+ ) N (D+ µ ) asl = = +... N (D µ+ ) + N (D+ µ ) Production asymmetry: N (B) N (B ) AP = N (B) + N (B ) Detection asymmetry: AD (D µ+ ) (D+ µ ) = (D µ+ ) + (D+ µ ) J.A. de Vries - CPV in mixing at - BEAUTY 6 5

6 TIME DEPENDENCE A raw (t) = N(f,t) N( f,t) N(f,t)+N( f,t) A D + ad sl + A P a d sl cos( m d t) Offset Amplitude Mixing oscillation For asl d : measure offset and amplitude to disentangle AP and asl d J.A. de Vries - CPV in mixing at - BEAUTY 6 6

7 asl d A raw (t) = N(f,t) N( f,t) N(f,t)+N( f,t) A D + ad sl + A P a d sl cos( m d t) AD + AP Asymmetry [%] ents / ps ) Events / (.4 MeV/c 4 Data Total fit Signal Comb m K ππ [MeV/c ] Data Total Signal t [ps] 8 85 Figure : Distribution of m K + D for * the µ B! D µ + µ X candidates in (left) 5data. Projections J.A. de Vries - CPV of the in mixing fitat function - BEAUTY are6 superimposed (blue continuous 7li ) Events / (.4 MeV/c, PRL 4 (5) 46 AP - asl d m K

8 THE STORY SO FAR SM: [%] Standard Model a d a s sl =( 4.7.6) 4 sl =(..7) 5 Artuso, Borissov, Lenz [arxiv:5.9466] a s sl - µνx Ds D µµ HFAG Fall '4 HFAG*: a d sl =(..) a s sl =(.48.48) HFAG [arxiv:4.755] *without D dimuon result [PRD 89, (4)] - - Ds µνx D D BaBar BaBar Belle ll D (*) µνx D (*) µνx D * lν ll ad sl [%] : a d a s sl =( sl =(..9(stat).(syst))%.6.5(stat).6(syst))% fb -, PRL 4, 46 (5), PLB 78C (4) 67 J.A. de Vries - CPV in mixing at - BEAUTY 6 8

9 -PAPER-6- asl s - /fb New result!

10 OVERVIEW Inclusive B s! D + s µ µ X Untagged, time-integrated analysis: A raw A D + as sl + Adding backgrounds: a s sl = f bkg (A raw A D f bkg A bkg ) A P a s sl Z cos( m s t)dt O( -4 ) m 8 ps.5 ps J.A. de Vries - CPV in mixing at - BEAUTY 6

11 DS SELECTION -PAPER-6- Dalitz regions Various levels of backgrounds in M(Ds - ). Regions treated separately. /c 4 ] π ) [GeV.5.5 φπ preliminary D s NR K K π m(kπ) in [86, 986] MeV m (K * K K.5 m(kk) in [, 4] MeV m (K K ) [GeV /c 4 ] Figure : Dalitz plot of the D s! K + K decay for selected D s µ + candidates, selection regions indicated. In addition, a invariant mass of the D s candidates is between 95 J.A. and de Vries 99 - CPV MeV/c in mixing. at - BEAUTY 6

12 DS YIELDS -PAPER-6- / (.5 MeV) Candidates * 6 K K 85 - M 9 inv (K 95 4 M inv (K K + π + )_PhiPi (MeV) 8 NR preliminary φπ D s D Comb. K + π + )_KStarK (MeV) m(k + K π ) [MeV/c ] 899 x 4 x 8 x 4 Figure : Invariant mass distributions for D s candidates in the three Dalitz regions, summed over - both Select magnet(ds polarities - μ + ), and fit data-taking Ds - mass periods. peaks Overlaid is the result of the fit, with signal and background components as indicated in the legend. - Directly produced Ds is removed - Raw yield contains peaking backgrounds approximated as A det A track + A PID + A trig, (4) J.A. de Vries - CPV in mixing at - BEAUTY 6

13 -PAPER-6- PEAKING BACKGROUNDS Peaking backgrounds dilute and bias the measurement a s sl = f bkg (A raw A D f bkg A bkg ) B +! D ( ) D s ( )+ X B! D D s ( )+ X B! D D ( )+ s B s! D ( ) s X D ( )+ s b! + c D s ( )+ X B! D s + K µ X B! D s + K S µ X double-d DsK f bkg =(8.4 6.)%, X fbkga i i bkg = f bkg A bkg =(.45.)% Taken into account: i fbkg: branching ratios (PDG) and efficiency Abkg mainly from production asymmetries:, JHEP 9 77 (4), PRL 4, 46 (5), Chin.Phys.C 4,, (6) J.A. de Vries - CPV in mixing at - BEAUTY 6

14 DETECTION ASYMMETRIES Tracking PID Triggering J.A. de Vries - CPV in mixing at - BEAUTY 6 4

15 T-stations (b) VELO (a) -PAPER-6- TRACKING ASYMMETRY Largest systematic in previous analysis Combine methods: - J/ψ tag-and-probe - D * partially reconstructed + simulation studies J/ψ method (π ) [%] A track J.A. de Vries - CPV in mixing at - BEAUTY 6 Magnet down essentially perfect momentum resolution and the detector that would not be measured with this p [GeV/c] Detection asym Figure 7: Tracking asymmetry as function of momentum p. The weighted av methods described Figure in the : text Theis two shownproposed in each bin signal with its statistical decays with uncertainty D + ) [%] A PID (K method has already been used at to me D! K + +. An attempt to apply the sa but using D + with a muon tag in order to con in Ref. [6]. This method is limited by the rela probe particle and poor separation of signal a the possibility to require that the probe parti 4 suggested in [6], preliminary thus restricting the problem to t Magnet up the direction of the probe particle fixed, the p mass peak. This also allows us to use the D! though this will only be possible with a dedicat In Sect., we study the expected level of nu from simulation. Sect. describes the selection yields. (right) D! K +. Primary vertex D * method D decay vertex Magnet up Magnet down F ) [%] A PID (K K - π +? π + π - π + U pi P as Ma Ma S st 5

16 PID & TRIGGER -PAPER-6- ) [%] A PID (K preliminary Magnet up Magnet down ) [%] A PID (K.4 preliminary Magnet up.8 Magnet down.6 K K & NR PID p T [GeV/c] p T [GeV/c] Figure 8: Asymmetry of the PID requirements on the kaon as a function of transverse momentum, p T, for (left) the 6region, and (right) the K K and NR regions. The 6 asymmetry is measured from a large sample of D +! D (K + ) + decays Magnet selected up without PID requirements. Magnet up 4 Magnet down 4 Magnet down Average Average Trigger A det(µ ) [%] A det(µ ) [%] - -4 preliminary p T [GeV/c] - -4 preliminary p T [GeV/c] J.A. de Vries - CPV in mixing at - BEAUTY 6 6

17 RESULTS -PAPER-6- ) - ( a s sl preliminary φπ,,up φπ,,down φπ,,up K K,,Down K K,,Up K K,,Down K K,,Up φπ,,down * * * * NR,,Down NR,,Up NR,,Down NR,,Up Source Value Stat. uncert. Syst. uncert. A raw..9. A track (K + K )... A track ( µ + )..5.4 A PID... A trig (hardware)... A trig (software)... f bkg A bkg.5 -. f bkg Total a s sl (%) J.A. de Vries - CPV in mixing at - BEAUTY 6 7

18 RESULTS -PAPER-6- New result! (preliminary) a s sl =(.45.6(stat).(syst))% [%] Standard Model a s sl D s µνx D D s µνx preliminary D µµ D (*) µνx D D (*) µνx BaBar D * lν BaBar ll Belle ll 4 ad sl [%] J.A. de Vries - CPV in mixing at - BEAUTY 6 8

19 -PAPER-6- CLOSING STATEMENTS Measured asl s with full Run dataset (/fb) a s sl =(.45.6(stat).(syst))% New result! (preliminary) Most precise value of CPV in mixing in the Bs system Result compatible with Standard Model prediction Statistics limited! J.A. de Vries - CPV in mixing at - BEAUTY 6 9

20 BACKUP

21 /c ] obtained independently. The production and detection asymmetries are expec 4.5 Magnet up Magnet down simulation + Average D µ.5 ected in the SM. It is noted that the experimental 8 limits on these asymmetr 6 e muon trigger and PID selection in bins of muon for (left) data.95 and (right) simulation data. k M(µ + µ ) [MeV/c ]! µ + µ candidates, (left) where the positive muon etry can be written as he negative muon is accepted or rejected by the trigger the fits are overlaid, where the dashed lines show the lds obtained from these fits are used to determine the "(f,f) is the e /c] A D(µ ) [%] ciency to detect a f or f final state. Hence, the observed, un A meas (t) = N(f,t) N(f,t) N(f,t)+N(f,t) A D + ad sl + p(µ ) [GeV/c] Entries / (. ) es / (. ) k / k A P simulation + 8 D * µ J.A. de Vries - CPV in mixing at - BEAUTY 6 a d sl cos( m d t), to a good approximation all higher-order asymmetry terms and the lifetime n the B system, d, have been neglected. The production asymmetry c inedmuon simultaneously detection inasymmetry a time-dependent analysis, Time correction but the detection (k-factor) asymmet d on the kinematics of the final state, but a d sl is expected to be universal. We a igible level of direct CP violation in Cabibbo-favoured tree decays of charm h t the percent level. See e.g. Ref. []. Experimental approach asl d ecay time of the B meson is calculated as t = M(B )L, PRL 4 (5) 46

22 /c ] obtained independently. The production and detection asymmetries are expec 4.5 Magnet up -.5 (a) -.5 (b) Magnet down simulation + 5Average 5D µ ected in the SM. It is noted that the experimental 8 limits on these asymmetr 6 e muon trigger and PID selection in bins of muon for (left) data.95 and (right) simulation data. k M(µ + µ ) [MeV/c ]! µ + µ candidates, (left) where the positive muon etry can be written as he negative muon is accepted or rejected by the trigger the fits are overlaid, where the dashed lines show the lds obtained from these fits are used to determine the "(f,f) is the e /c] A D(µ ) [%] ciency to detect a f or f final state. Hence, the observed, un A meas (t) = N(f,t) N(f,t) N(f,t)+N(f,t) A D + ad sl + A(t).5 p(µ ) [GeV/c] Entries / (. ) es / (. ) k / k A P simulation + 8 D * µ J.A. de Vries - CPV in mixing at - BEAUTY 6 a d sl cos( m d t), to a good approximation all higher-order asymmetry terms and the lifetime n the B system, d, have been neglected. The production asymmetry c inedmuon simultaneously detection inasymmetry a time-dependent analysis, Time correction but the detection (k-factor) asymmet d on the kinematics of the final state, but a d sl is expected to be universal. We a igible level of direct CP violation in Cabibbo-favoured tree decays of charm h t the percent level. See e.g. Ref. []. Experimental -.5 (c) approach 5 asl d ecay time of the B meson is calculated as (d) t = M(B )L 5 [arxiv:64.475] t [ps]

23 "(f,f) is the e ciency to detect a f or f final state. Hence, the observed, un etry can be written as A meas (t) = N(f,t) N(f,t) N(f,t)+N(f,t) A D + ad sl + obtained independently. The production and detection asymmetries are expec Data + Data D µ Total Signal + Total D µ + B bkg. Signal Comb. bkg. B + bkg. 5 Comb. bkg. ected in the SM. It is noted that the experimental limits on these asymmetr 6 + D * µ 4 Experimental approach M(D 9, D ) [MeV/c ] Events / (.8 MeV/c ) : Mass distributions after weighting of (top) D candidates in the D µ + sample and of ) D candidates in the D µ + sample, with fit results overlaid., PRL 4 (5) 46 Data + Total J.A. de Vries - CPV in mixing at - BEAUTY 6 D * µ Signal Events / ps Asymmetry [%] ents / ps A P a d sl cos( m d t), to a good approximation all higher-order asymmetry terms and the lifetime n the B system, d, have been neglected. The production asymmetry c D ined simultaneously (*)- mass time dependence in a time-dependent analysis, but the detection asymmet d on the kinematics of the final state, but a d sl is expected to be universal. We a igible level of direct CP violation in Cabibbo-favoured tree decays of charm h t the percent level. See e.g. Ref. []. asl d ecay time of the B meson is calculated as t = M(B )L t [ps]

24 -PAPER-6- ASLS PEAKING BKG DETAILS Mode B [%] B(c! µ) [%] " sig /" bkg f bkg /f sig [%] A bkg [%] B +! D ( ) D s ( )+ X B! D D s ( )+ X B! D D s ( )+ X B s! D ( ) s D ( )+ s b! + c D ( )+ s X B! D + s K µ X B! D + s K S µ X J.A. de Vries - CPV in mixing at - BEAUTY 6 4