Results and prospects for charm physics at LHCb Philip Hunt 1 on behalf of the LHCb collaboration 1 University of Oxford, Particle Physics Kruger 2010: Workshop on discovery physics at the LHC 5 th –10 th December 2010

Outline Introduction –Status of LHCb at end of 2010 run –Charm physics at LHCb Key results in charm physics in 2010 –J/ψ cross-section (covered by Patrick Robbe’s talk “Study of Prompt J/psi and b->J/psi X in pp collisions” on Tuesday) –Open charm cross-section Prospects for charm physics in 2011 and beyond –Mixing and CPV in neutral D –Direct CPV –Charmonium cross-sections Summary 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa2

Status of LHCb at end of 2010 running Recorded ~0.04fb -1 of data: ≈90% efficiency Plan to record 1fb -1 of data by end 2011 (½ design luminosity p.a.) Conditions much harsher than LHCb design –Multiple interactions/BX, much higher occupancy –Significant strain on trigger, but we’ve managed to cope so far 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa3

Charm physics at LHCb LHCb is primarily a b-physics experiment, but we have a very strong charm group Same aspects of LHCb that make us good for b-physics also aids charm physics –Low pileup –Great K-π discrimination –Excellent PV resolution Charm cross-section ~20x larger than b cross-section –Can do many competitive analyses in charm sector with early data –Harsh trigger conditions due to higher than expected pileup and occupancies mean we lose some efficiency in charm –Working hard to produce charm triggers that are optimised for multiple interactions 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa4

Open charm cross-section First measurements at √s = 7TeV Measurements down to p T =0 Current results: –Cross-sections for D 0, D *+, D s + and D + with 1.8nb -1 Work in progress: –Cross-sections for D 0, D *+, D s +, D + and Λ c + with larger statistics (14nb -1 ) 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa5

Measurement strategy 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa6

Prompt-secondary separation Remove/account for main background using sideband subtraction / mass fit Remaining background comes from decays of long-lived particles – secondary charm Measure secondary fraction from the D impact parameter distribution Similar technique will be used in some CPV and mixing measurements 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa7

Cross-section results: D 0 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa B.A. Kniehl, G. Kramer, I. Schienbein, and H. Spiesberger —— M. Cacciari, S. Frixione, M. Mangano, P. Nason, and G. Ridolfi σ(D 0 ;p T <8GeV/c,2<y<4.5)=1488±41(stat.) ±34(uncorr.) ±174(corr.) μb σ(D 0 ;p T <8GeV/c,2<y<4.5)=1488±182 μb PYTHIA prediction: σ(D 0 ;p T <8GeV,2<y<4.5)=1402±2 μb

Cross-section results: D *+ 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa9 σ(D *+ ;p T <8GeV/c,2<y<4.5)=676±64(stat.) ±21(uncorr.) ±119(corr.) μb σ(D *+ ;p T <8GeV/c,2<y<4.5)=676±137 μb PYTHIA prediction: σ(D *+ ;p T <8GeV,2<y<4.5)=653±1 μb

Cross-section results: D + 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa10 σ(D + ;p T <8GeV/c,2<y<4.5)=717±39(stat.) ±26(uncorr.) ±98(corr.) μb σ(D + ;p T <8GeV/c,2<y<4.5)=717±109μb PYTHIA prediction: σ(D + ;p T <8GeV,2<y<4.5)=509±1 μb

Cross-section results: D s + 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa11 σ(D s + ;p T <8GeV/c,2<y<4.5)=194±23(stat.) ±16(uncorr.) ±26 (corr.) μb σ(D s + ;p T <8GeV/c,2<y<4.5)=194±38μb PYTHIA prediction: σ(D s + ;p T <8GeV,2<y<4.5)=255±1 μb

Various cross-sections results are in agreement with MC and theory predictions Using published fragmentation fractions to calculate open charm cross-section for each analysis, and taking a least- squares fit, we find: –σ(pp→H c X,2<y<4.5,p T <8GeV/c)=1.23±0.19mb, χ 2 /ndf=2.28/3 Using PYTHIA to extrapolate to 4π, we obtain the following (preliminary) total open charm cross-section: –σ(pp→cc)=6.10±0.93mb Result for total cross-section in 4π consistent with expectations ( σ(pp→cc) ≈ 20×σ(pp→bb) ) Work ongoing to measure cross-sections with more data 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa Cross-section results

Mixing and CPV in neutral D sector Mixing implies two non-degenerate mass eigenstates: –D 1 = p|D 0 ＞ +q|D 0 ＞, D 2 = p|D 0 ＞ – q|D 0 ＞ CPV parameterized by relative magnitude |q/p| and phase φ≡Arg(q/p) of the eigenstates Two parameters used to quantify mixing x=Δm/Γ and y=ΔΓ/Γ ( Γ=(Γ 1 +Γ 2 )/2) First evidence for mixing from Babar and Belle in 2007 –no single analysis has 5σ separation from SM CPV in mixing small in SM, but can be enhanced by some BSM processes –Current measurements at upper end of SM predication Will also search for direct CPV in the charged D sector –CPV expected to be small in these modes 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa13 No mixing No CPV

Mixing and CPV from lifetime ratios using CP eigenstates 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa14 A M =½(|q/p|–|p/q|) y CP =y if no CPV Can use other CP eigenstate in denominator e.g. D 0 ➝ π + π - Babar’s most recent measurement (Phys.Rev.D80:071103,2009) dominates world average result –2.7M D 0 ➝ K - π + and 260k D 0 ➝ K - K + untagged –0.73M Kπ, 70k KK and 31k ππ tagged –384fb -1 data analysed

Mixing and CPV from lifetime ratios using CP eigenstates 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa15 Require that the D 0 comes from a D *+ in order to tag the flavour of the neutral D Babar and Belle’s results both have very large uncertainties Babar (Phys.Rev.D78:011105,2008) : –0.73M Kπ, 70k KK and 31k ππ –384fb -1 data analysed Belle (Phys.Rev.Lett.98:211803,2007) : –1.2M Kπ, 110k KK and 49k ππ –540fb -1 data analysed

Mixing and CPV from “wrong-sign” (WS) Kπ 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa16 CP conserving strong phase (see Aurelian’s talk: “Study of hadronic b-decays at LHCb”, Tuesday)

Events yields: D 0 →K + K - from D *+ 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa17 Results for simultaneous fit of reconstructed D 0 mass (y) and difference between reconstructed D *+ and D 0 masses (x) Fitted signal yield in 22pb -1 = (62.3±0.5)k Already comparable yield with sample used in Babar’s A Γ measurement with <60% of full 2010 statistics

Events yields: D 0 →hh from D *+ 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa18 N Kπ =862k, N KK =96.7k, N ππ =31.2k Higher statistics than Babar for D 0 →Kπ and D 0 →KK, and same statistics for D 0 →ππ in 34pb -1 Enough statistics for competitive measurement of y CP and A Γ in 2010!

Mixing and CPV in D 0 →K S hh Time-dependent Dalitz analysis –Can directly extract mixing parameters x and y, as well as CPV parameters |q/p| and φ –Longer-term analysis: ~10 resonances, so fitting is complex, and requires much work on the Dalitz model and understanding of data 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa19

Mixing and CPV in K + π - π + π - Similar to the WS Kπ analysis, with different strong phase δ K3π –Multiple resonances, and 5D Dalitz space, so need good understanding of models –Initial analysis will use a “pseudo two-body” method Add a coherence factor to two-body equation for proper time distribution that quantifies the resonance structure of the decay Coherence factor measured by CLEO-c collaboration (see Lowrey et. al., (Phys.Rev.D80,(2009)031105) To use this method, we need to show that the coherence factor is uniform over the LHCb acceptance 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa20

Direct CPV in D (s) + →K s 0 h + Time-integrated production rate study Requires correction for both production and detection asymmetries –Need three very carefully chosen control modes to extract all parameters 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa21

Direct CPV in D + (s) →h + h - h + Time-integrated Dalitz analysis Model-independent (anisotropy) method: –See Bediaga et. al. (Phys.Rev.D80(2009),096006) –Split Dalitz space into CP-conjugate bins –Consider local CP asymmetry in each Dalitz bin –This technique is largely independent of production asymmetries Main search channels: –D + →K + K - π + (Singly Cabibbo supressed (SCS)) –D + → π + π - π + (SCS) Secondary search channels: –D s + →K + π - π +, D s + →K + K - K + (SCS) Primary control channels: –D + →K - π + π + (SCS), D + →K + π - π + (DCS), D + →K + K - K + (DCS) 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa22

Event yields for D + (s) →K - K + π + 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa23

Direct CPV in T-odd moments 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa24

Charmonium cross-section See many charmonium decays in LHCb –“Rediscovered” X(3872) –With full 2010 statistics, measurements of ψ(2S) and χ c cross-sections should be possible 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa25

Summary Measured J/ψ and open charm cross-sections –Expect updates in these analyses in coming months Have enough statistics in 2010 data for competitive measurements y cp and A Γ, and ψ(2S) and χ c cross- section Hope to have results from direct CPV searches with 2011 data Lots more to follow in 2011 and beyond 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa26

Backup 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa27

Overview of LHCb 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa28 VELO Excellent vertex resolution RICH1, RICH2 Excellent K-π identification Tracking system Good tracking efficiency and momentum resolution MUON system Good μ PID

9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa29 Event yields for D + (s) → π + π + π -

Event yields for D + →K - π + π + 9/12/2010Results and prospects for Charm physics at LHCb Kruger2010, South Africa30