R. Mureşan. University of Oxford On behalf of LHCb Collaboration. Prepared for the CERN Theory Institute "Flavour as a Window to New Physics at LHC"

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1 May 8 CERN Theory Institute Charm Physics at LHCb R. Mureşan University of Oxford On behalf of LHCb Collaboration Prepared for the CERN Theory Institute "Flavour as a Window to New Physics at LHC" R. Mureşan Charm Physics 1

2 May 8 CERN Theory Institute Outline LHCb and its charm physics trigger; CP violation searches in D decays at LHCb; Charm mixing measurements at LHCb; Summary. R. Mureşan Charm Physics

3 May 8 CERN Theory Institute LHCb VELO and RICH-es are the most important detectors for charm analysis. R. Mureşan Charm Physics 3

4 May 8 CERN Theory Institute LHCb Very high statistics; Outstanding vertexing and proper time resolution ~ 45 fs for secondary D ; Good tracking and momentum resolution ~ 6 MeV at D mass. VELO R. Mureşan Charm Physics 4

5 May 8 CERN Theory Institute LHCb Very high statistics; Outstanding vertexing and proper time resolution ~ 45 fs for secondary D ; Good tracking and momentum resolution ~ 6 MeV at D mass; Excellent K-π discrimination. RICH R. Mureşan Charm Physics 5

6 May 8 CERN Theory Institute Pile-up system Calorimeters Muon system stem Full detector Information (partial reco) LHCb trigger overview 4 MHz Level Hardware Favours bb events over prompt charm; # int/crossings E E p had T e, γ, π T μ, μμ T > > >.5 GeV 1GeV GeV 1 MHz HLT- Event filter farm Confirm L optional add IP cut parallel μ, e,h,γ alley Inclusive/exclusive selections khz Hz Exclusive B modes 3 Hz D* D (hh)π 6 Hz μ J/ψ, b J/ψ X 9 Hz 1 μ inclusive for b data mining R. Mureşan Charm Physics 6

7 May 8 CERN Theory Institute LHCb sources of charm B decays (B D (*) () X): + Favoured by LHCb triggers; + Potentially less background; - New techniques need to be developed no published measurements. Prompt production in primary interaction: + Triggered less efficiently but prolific production; - Potentially larger backgrounds random π s for D* ; + CDF has proved measurements possible in hadronic environment. R. Mureşan Charm Physics 7

8 May 8 CERN Theory Institute Estimated D* D (hh)π yields, events to fb -1 from b-hadrons: D K - π + 5 x 1 6 ; D K - K + 5 x 1 6 ; D K + π -. x 1 6 ; D π - π + x 1 6. Similar number of prompt D* are expected to pass the trigger and to be reconstructed. 1 8 potentially usable D* D (hh)π events per fb -1 are available for: Charm Physics studies RICH calibration The LHCb numbers in the following slides are obtained using exclusively the D* from the b-hadrons. R. Mureşan Charm Physics 8

9 May 8 CERN Theory Institute D* D (hh)π trigger stream Loose cuts on hadrons p t, min IP sign, D mass and (D*-D ) mass. Present values favour the D * coming from b hadrons. RICH information not used in the trigger HLT assumes Kπ, π K, KK, ππ, masses in turn. 18 K π KK ππ GeV R. Mureşan Charm Physics 9

10 May 8 CERN Theory Institute D* D (hh)π trigger stream Loose cuts on hadrons p t, min IP sign, D mass and (D*-D ) mass. Present values favour the D * coming from b hadrons. HLT assumes Kπ, π K, KK, ππ, masses in turn. RICH information not used in the trigger unbiased sample for MC - independent RICH calibration. K K, p All kaons and pions identified using MC truth (pt >1GeV) Kaons and pions from the MC independent calibration sample (pt >1GeV) π K, p P(GeV) R. Mureşan Charm Physics 1

11 May 8 CERN Theory Institute RICH information and various D decay modes No PID K - π With PID K + K - K + K - K - π M KK (MeV) M KK (MeV) PID RICH information very important to select clean samples of different D decay modes. R. Mureşan Charm Physics 11

12 May 8 CERN Theory Institute CP violation searches in the charm sector at LHCb The Standard Model (SM) predicts any CP violation (CPV) in charm decays to be very small. Observable CPV at the level 1% would be an unambigous sign of new physics (NP). Time integrated and time dependent CPV searches in as many charm channels as possible; Two body Kπ, K - K +, π π + modes; Three body charged and neutral decays: Amplitude analyses; D K s π + π, K s K + K -, K s K π, D + K + K - π +, K π π; Four body decays: Quantities odd under T; Amplitude analyses; D K + K π + π, K π π π. Main focus of this talk R. Mureşan Charm Physics 1

13 May 8 CERN Theory Institute CPV in D K + K - (π + π ) Occurs when the absolute value of the D decay amplitude to a final state is not equal to the CP conjugate amplitude. Γ ( D KK( ππ)) Γ ( D KK( ππ)) Γ ( D KK( ππ )) + Γ ( D KK( ππ )) ACP = D, D tagged using the slow pion sign Singly Cabibbo Supressed (SCS) decay, easy to modify its topology to get a penguin. R. Mureşan Charm Physics 13

14 May 8 CERN Theory Institute CPV in D K + K - (π + π ) In SM A CP 1-3 for SCS decays. Possible NP enhancements to 1% from, e.g., penguin diagram A N(K + - N(π + - cp (%) K ) π ) Data set BaBar.6 ±.36 ± fb -1 Belle.1 ±.3 ± fb -1 HFAG.13 ±.48 LHCb ~.4 % order (stat) 8 x x fb -1 Belle and BaBar calculate the asymmetries using τ(k + K - ) rather than Γ(K + K - ). CDF direct CPV search in K + K -,ππ Phys.Rev.Lett.94:11, 5 A cp (K + K - )(%) =. ± 1. ±.6 A cp (π + π - )(%) = 1. ± 1.3 ±.6 N (K + K - ) =16 for 13 pb -1. Entrie es/3 MeV/c CDF II CDF II *+ - D D π + [K K + ]π + *+ - D D π + [π π + ]π + + charge conjugate + charge conjugate 5 M KK (GeV) 5 M ππ (GeV) KK Mass [GeV/c ] R. Mureşan Charm Physics 14 ies/4 MeV/c Entri ππ Mass [GeV/c ]

15 May 8 CERN Theory Institute D D m 1 m x = Γ mixing Γ 1 y = Γ Γ Indexes associated to the mass eigenstates, Γ av. width. sensitive to new particles in mixing through physical the box diagram loop; decay states (long range) ; contributions from all the expected to be dominated by energy e scales, sensitive s e to NP. SM contributions. o D, D tagged unambiguously at production using the slow π sign. R. Mureşan Charm Physics 15

16 May 8 CERN Theory Institute Charm mixing studies at LHCb Precise mixing measurements: Measure CPV in mixing dominant mixing process. WS D π K + mixing analysis: BaBar 3.9 σ evidence, confirmed by CDF 3.8 σ evidence; Require measurement of strong phase δ by CLEO/BES-III to relate the Cabibbo Favoured (CF) amplitude to the Double Cabibbo Suppressed one (DCS). CP Eigenstate Lifetime Difference measurement Comparing the CP even SCS D K + K - (π + π - ) with non-eigenstate Right Sign (RS) D K - π +. Belle 3. σ evidence, confirmed by BaBar 3 σ evidence. Amplitude analysis of D K s π + π : Powerful technique demonstrated by CLEO and Belle. Mixing measurements in D 4h. R. Mureşan Charm Physics 16

17 May 8 CERN Theory Institute D production and decay vertices D lifetime measurement necessary input for mixing studies; Need good resolution for both the production and the decay vertex. cand / 53 μm bin χ / ndf / 67 Normalization 7.118e+4 ± 198 Core fraction.7164 ±.337 Mean.4313 ± Core sigma 56.8 ± 1. Second sigma ± 87.3 D lifetime τ =.411 ±.15 ps D flight distance 6 GeV βγcτ 4 mm 4 D decay vertex resolution.57 mm z D - z MC D (μm) R. Mureşan Charm Physics 17

18 May 8 CERN Theory Institute D production and decay vertices bin -4 cand / Lab Frame D daughter angle Lab Frame D -π+ s angle D and π s almost colinear χ / ndf / 6 1 Normalization 1.391e+6 ± Core fraction.765 ±.9 1 Mean ± Core sigma 43 ± 1.8 Second sigma 1.693e+4 ± 15 cand / 1 μm bin cosθ 1, Poor resolution of the D production vertex = 4.3 mm to be compared to 4 mm Proper time resolution =.465 ps to be compared to.41 ps For p D =6GeV z D *+ - z MC D *+ (μm) R. Mureşan Charm Physics 18

19 May 8 CERN Theory Institute Birth vertex improvement Use additional tracks at the production vertex; 76% of D* from B's have at least one charged sister; 63% have reconstructed sister tracks that pass some basic criteria; Use one additional track to partially reconstruct parent B parent. D D* B parent x y z Vertex resolutions (μm) cand /.1 ps bin.6 ps bin cand / D lifetime, reconstructed τ (ps) τ D,rec D,gen D lifetime, generated -1 1 D lifetime (ps) Proper time resolution =.4545 ps (bef..465 ps ); New technique factor of 1 improvement. R. Mureşan Charm Physics 19

20 May 8 CERN Theory Institute Oscillation Search with WS Kπ D can arrive to a WS hadronic final state (K + π - ) via: DCS decay D K + π - Oscillating to D DCS + + CF decay D K π D Oscillat + πk - K + π illation D CF 3 contributions Γ WS exp( t )[R D + y t + 1 / 4( x ( Strong gphase difference between CF and DCS amplitudes ( x, y ) ( x, y ) R D is the ratio of DCS decay rate to the CF decay rate. R D + y R. Mureşan Charm Physics )t ]

21 May 8 CERN Theory Institute Oscillation Search with WS Kπ Toy MC study x y Investigate sensitivity to and 1D fit to proper time; 1 fb -1 simulated signal events/toy; Exponential background exp( t / τ D Acceptance and resolution effects included. ) Events /.3 ps bin Log 4 1 Data Signal + Background DCS Signal Background 3 1 Interference Mixing Proper Time (ps) 3 contributions Γ WS exp( t )[R D + R D y t + 1 / 4( x + y )t ] For more information CERN-LHCb-7-49 R. Mureşan Charm Physics 1

22 May 8 CERN Theory Institute Oscillation Search with WS Kπ Toy MC study Investigate sensitivity to and 1D fit to proper time; x y 1 fb -1 simulated signal events/toy; Exponential background: exp( t / τ D ) ; Acceptance and resolution effects included. Log Events /.3 ps bin Data Signal + Background DCS Signal Background Interference Mixing 1 Proper Time (ps) Data set N(K + π - ) Belle 4 fb BaBar 384 fb ±.3 ± ± 4.4 ± 3.1 CDF 1.5 fb ± ±7.6 B factories ab -1 x ±.15 y ±.5 LHCb 1 fb -1 x ±.64(stat) y ±.87 (stat) x 1 3 y 1 3 R. Mureşan Charm Physics

23 May 8 CERN Theory Institute Lifetime ratio Lifetime splitting, y CP can be measured by comparing the CP non-eigenstate decay D K - π + to CP even decay D K + K - (π + π ). y CP τ ( D D K K K = + + τ ( + π, π ) π _ ) 1 = y cos Φ x sin Φ R m 1 ( x y ) 1 R m + = y and y cp differ by CP violating phase Φ R. Mureşan Charm Physics 3

24 May 8 CERN Theory Institute Lifetime ratio Toy MC study 1 fb -1 simulated signal events/toy; Exponential background: ; Acceptance and resolution effects included. d exp( t / τ D N (K + K - ) Data set y CP (%) BaBar* fb ±.33±.19 Belle* fb ±.3 ±.5 HFAG average* 1.13 ±.66 B factories** ab -1 y cp ±.3 LHCb** 8 x fb -1 y cp ±.5 (stat) * both KK and ππ pairs were used. ** only KK pairs ) cand / bin ca and /.1 ps bin χ / ndf 6.48 / 7 Asymptote, A ± 6.47 Intercept, r i.6779 ±.148 Γ acc.481 ± D proper time (ps) Acceptance τ (ps) τ D,rec D,gen Resolution R. Mureşan Charm Physics 4

25 May 8 CERN Theory Institute Summary of LHCb at 1 fb -1 y Central Value WS 1 Sigma WS Sigma WS 3 Sigma y 1 sigma CP y sigma CP y 3 sigma CP x -3 Sensitivities (1 fb -1 ) from the WS study and the y CP study. Contours correspond to 1,, and 3 confidence levels from the WS study. Horizontal bands correspond to 1,, and 3 confidence levels from the y CP study. R. Mureşan Charm Physics 5

26 May 8 CERN Theory Institute Summary The LHCb experiment has an exciting potential for charm physics studies. A dedicated D* trigger will provide 1 8 flavour tagged D hh per fb -1, giving unprecedented sensitivity in searches for D mixing and CP violation. Multihadron D decay studies are also envisaged: D K s π + π, K s K + K -, K s K π, D + K + K - π +, K π π, D K + K π + π, K π π π. We have only begun to tap the potential of our charming experiment. R. Mureşan Charm Physics 6

27 May 8 CERN Theory Institute The looking-glass world Alice entered would indeed be a very different place. Not only will the books be written from right to left, but you must walk in the opposite direction to reach your goals and the White Queen, first bandages her finger, then begins to bleed, then screams, and finally pricks her finger. Also, as Alice suggested to her kitten, looking-glass milk would almost certainly not be good to drink. LHCb Holding a mirror to physics LHCb Holding a mirror to physics R. Mureşan Charm Physics 7