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Spectroscopy at LHCb

Spectroscopy at LHCb. Benoit VIAUD, LAL-CNRS-IN2P3. (On behalf of the LHCb collaboration). HPC-Toronto, August 24 th , 2010. I. Motivations for Spectroscopy. Quarkonia are a unique laboratory to study QCD !.

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Spectroscopy at LHCb

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  1. Spectroscopy at LHCb Benoit VIAUD, LAL-CNRS-IN2P3 (On behalf of the LHCb collaboration) HPC-Toronto, August 24th, 2010

  2. I. Motivations for Spectroscopy

  3. Quarkonia are a unique laboratory to study QCD ! • Their production in high energy collisions, their hadronisation into bound states with non trivial properties (mass, spin, width) and their hadronic decays are ruled by QCD and involve all energy regimes. Our understanding of nonperturbative QCD and its interplay with perturbative QCD can be improved by testing many theoretical approaches (NRQCD, Potential Models, LQCD, pQCD). • Copious production at LHCb: study many states, some of them still poorly known • J/, (2S) (Production cross section) • cJ, hc, Y(nS), b (Production and hadronic decays) • X, Y and Z (Nature, mass, width) • Rare hadronic decay modes • Bc (mass and lifetime, in back-up)

  4. Quarkonia provides LHCb’s first major results • Measurement of (ppJ/ X) to better understand quarkonia prod. mechanisms • NRQCD at NNLO shows the important role of the Color Singlet mechanism. Agreement with CDF & RHIC: tot for J/,’,Y(nS) ; d/dPT for Y(nS) (and J/ at RHIC) • Still a puzzle for charmonia: need for other contributions. Role of the Color Octet ??  PT-differential cross sections leave room for CO (high PT) but disfavored since no transverse pol. in data. (c2)/(c1) ratio not explained so far without CO • Beauty hadrons decay to J/: Measuring (ppJ/ X) also provides (ppbb X). • Interesting for QCD • Useful ingredient to many LHCb analyses

  5. II. The LHCb Experiment

  6. The LHCb Experiment Seeks New Physics via the precision study of CP and B and D decays • Exploits large cross-sections in pp collisions with s=14 TeV (7TeV in 2010-11) Early measurements Pythia • Nominal luminosity: 21032 cm-2s-1. Reach 11032 cm-2s-1 in 2010. Int. luminosity: few dozens of pb-1 in 2010, 1 fb-1 in 2011  ~300 billions bb pairs by late 2011 ( 2 orders of magn. above B factories) • The Challenge: precise rare decays and time-dependent CP asymmetries in a high background environment. Needs highly performant vertexing, p and M reconstruction, particle-ID and very selective, polyvalent and configurable trigger.

  7. LHCb in 2010 • LHCb recorded L ~ 1400 nb-1 so far in 2010. • ~15nb-1 analysed so far to produce the first physics results • Also used to understand/calibrate the detector, and get close to LHCb’s nominal performance: • Charged tracks momentum: p/p=0.35-0.55% • Mass resolution: 7-50 MeV/c2 • ECAL: E/E=10%/E  1% (E in GeV) • muon-ID () = 94%, mis-ID rate()=1-3% • K- separation(KK) = 95%, mis-ID rate()=7% • Proper time: t~ 40 fs, z~ 60m (Prim. Vertex) z~ 150 m (Secondary Vertex) More detail in G. Carboni’s talk “Status of LHCb” (or in back-up)

  8. The LHCb Experiment Correlated bb production at low  • Forward geometry: 15 < < 300 mrad  RICHES: PID: K, separation Tracking Stations: p of charged particles VELO: Vertexing Muon System Trigger ! Hadr. and Electr. Calorim. PID: e,, 0 Trigger! Trigger Tracker: p for trigger and Ks reco

  9. Tracking and Vertexing OT • Trigger Tracker (TT), Inner Tracker (IT) • VELO Silicon R- microstrips. 21 stations. 2 upstream stations (pile-up) Pitch: 40-100m Silicon Microstrips. 4 planes (0o, +5o, -5o, 0o). Readout pitch 183 m, 198 m TT • Outer Tracker (OT) Straw tube (diameter = 5 mm) Four 2-layer planes (0o, +5o, -5o, 0o). IT

  10. X resolution Y resolution Tracking and Vertexing • Silicon Trackers • VELO hit resolution: 55m (TT) 54m (IT) Cluster finding efficiency 99.7%, Alignment better than 5% hit misalignment : 35m (TT) 16m (IT) Nominal hit resolution in OT: 250 m !  Mass reconstruction  Primary vertex reconstruction  Tracking eff. (Ks+-) L~100 nb-1 D0→ K x,y~15m (data) ~11m (MC) z ~90m (data) ~60m (MC) M(D) ~ 9 MeV (data) ~ 7 MeV (MC) Already close to expectation from MC and test beam. Will be improved with better alignment and material description.

  11. Particle ID: Muon System • Essential for -ID and L0-trigger • Five stations, Two technologies • MWPCs and GEMs

  12. Particle ID: Muon System • -ID algorithm • Tracks extrapolated to the Muon-system • “IsMuon” if associated to one 1 hit in • each of 2 to 5 Muon stations.

  13. Particle ID: Muon system • ID and mis-ID efficiency: “Tag and Probe” Candles: J/, KS+-,  K+K-, p Tracking system J/ µ tag (cut on PID) (2S) µ probe (to measure performance) J/   (decay in flight) p (Comb. in -stations) Average Eff: ()= 97.31.2%,()= 2.350.04%, (p)= 0.210.05%

  14. Trigger Level-0 High-pt objects in Calorimeters or in Muon system. -pt(e,)>2.5 GeV -pt(h)>3.5 GeV -pt()>1GeV 40 MHz Hardware L0 m L0 had L0 e, g 1 MHz HLT1 ECAL Alley Had. Alley Muon Alley Partial reconstruction to confirm L0 objects. Cuts on impact parameter w.r.t to primary vertex (IP) to select events with a displaced vertex. 30 kHz Global reconstruction HLT2 Inclusive selections: topological, m, m+track, mm, D→X, Φ Full detector information available. Look for inclusive signatures, augmented by exclusive selections in certain key channels. Exclusive selections 2 kHz Software (Event Filter Farm)

  15. Trigger in 2010 • Luminosity improving fast, but quite below 1032cm-2s-1 so far (71030 last week) • The L0 and HLT1 rates are reached with looser PT and IP cuts. • HLT2 not used in early data, then introduced progressively with loose cuts  Good early opportunity for Charm Physics ! • Typical efficiencies - D hadronic decays: >25%. - B decays: > 70% - Leptonic decays: >90%. (i.e. many quarkonia) J/ L0*HLT1 • Trigger-unbiased samples to check the trigger performance on real data

  16. III. J/ and bb Production Cross-Sections

  17. J/ Production: Introduction • Cross-sections in pp collisions with L=14.2 nb-1at s=7 TeV • Inclusive J/: σ( incl. J/, pTJ/ψ < 10 GeV/c, 2.5 <yJ/ψ < 4) Also d/dpT in 10 pT bins • J/from the decay of a b-hadron: σ( J/ from b, pTJ/ψ < 10 GeV/c, 2.5 <yJ/ψ < 4) • bb production cross-section in 4:σ( ppbbX) • J/ reconstructed via the J/ decay mode, extracted using 2 variables: • M(J/) Fraction of J/ from b • Pseudo proper time tz μ pJ/ψ PV z μ dz

  18. Selection • Two tracks identified as muons, Track quality 2 / ndof < 4 • pT() > 0.7 GeV/c • M() window: M( J/ )  390 MeV/c2 , -vertex p(2 )> 0.001% • At least one primary vertex in the event • If several candidates J/+1-1 & J/+2-2 remove clone tracks with cos(+1,+2) & cos(-1,-2) >0.9999 • Trigger on signal candidates for • L0: Single Muon line (pT> 320 MeV/c) • HLT1: Single Muon line or Dimuon line • pT> 1.3 MeV/c • M(  )>2500 MeV/c2 + vertex cut

  19. Signal Yield • Extended unbinned maximum likelihood fit to the M(J/) distribution • Signal Model: Crystal Ball function Background Model: linear function  N(J/) = 287273 M(J/) = 30880.4 MeV/c2 M=15.00.4 MeV/c2 N(bkg) =2273166

  20. Fraction of J/ from b: Simultaneous fit to tz and M(J/) • Signal J/ from b, Single exponential of pseudo lifetime b Prompt J/ Convoluted with a resolution function: double gaussian • Background: shape fixed by a fit to the J/ mass sideband • Results: fb = 11.1  0.8 % • 2 = 1.625 • Consistent results with a binned fit.

  21. Cross sections extraction determined in each pT bin from MC rec trig Total σ( incl. J/, pTJ/ψ < 10 GeV/c, 2.5 <yJ/ψ < 4) = (7.65 ± 0.19) μb σ( J/ψ from b, pTJ/ψ < 10 GeV/c, 2.5 <yJ/ψ < 4) = (0.81 ± 0.06 ) μb • bb cross-sections derived by extrapolating to the full solid angle (Pyhtia 6.421), by using the b-hadronisation fractions and B(bJ/X) from LEP σ( pp Hb X, 2<(Hb)<6) =(84.5  6.3) μb 2 σ( pp bbX ) =(319  24 ) μb

  22. Systematics Data driven evaluation for most of the systematic uncertainties • Tracking Efficiency: data/MC comparisons indicate 4% /track  8% • Muon ID efficiency via “Tag and Probe”  2.5% • Trigger Efficiency: difference between data and MC  3 to 9% nb of TIS&TOS eff = nb of TOS • TIS: “Trigger Independent of Signal” • event (triggers even if the signal is removed) • TOS: “Trigger On Signal” event.

  23. Systematics: Polarization • Efficiency depends strongly on angular distributions, thus on J/ polarization  J/ (lab frame) + J/ rest frame - Helicity frame, ignores azimuthal angular distribution. • J/ polarization unknown so far • Repeat the analysis for extreme cases • No polarization (=0) • Fully tranverse (=+1) • Fully longitudinal (=-1) •  Important variation in the result. •  Next step with more stat: • Full angular analysis.

  24. Summary of Systematic Uncertainties • Dominant ones: Luminosity, trigger and tracking uncertainties, knowledge of B(bJ/X)

  25. Results Polarization σ( incl. J/ψ, pTJ/ψ < 10 GeV/c, 2.5 <yJ/ψ < 4) = (7.65 ± 0.19 1.10 +0.87-1.27) μb σ( J/ψ from b, pTJ/ψ < 10 GeV/c, 2.5 <yJ/ψ < 4) = (0.81 ± 0.06  0.13) μb σ( pp Hb X, 2<(Hb)<6) = (84.5  6.3  15.6) μb 2 σ( pp bbX ) =(319  24  59) μb Consistent with another measurement of (bb) by LHCb: BD0X σ( pp bbX ) =(282  20  49) μb

  26. Short Term Prospects (50 pb-1, late 2010) • Measurement in 512 bins: (2.5<y<4.5) & (0<pT<12 GeV), 10% precision • Measurement of the polarization with a full angular analysis 260 nb-1 260 nb-1

  27. IV. Other Quarkonia

  28. (2S) • Measurement of the ratio (2S)/J/of in pT bins (prompt and from b) • Same performance for (2S)+-as for J/+- • Most of the systematics cancel in the ratio. Polarization requires a full angular analysis. • 22% uncertainty on the ratio of efficiencies if neglected • Observed on first data (260nb-1) • Nsignal = 423  50 • M = 3679.2 ± 0.3 MeV/c2 •  = 45.2 ± 8.4 MeV/c2 J/ (2S)  Very promising with 1 fb-1 (2011)

  29. cJ and hc Production cross sections, R= c2/c1 and the fraction of J/ coming from cJ • cJ J/ : add to the J/ selection a  found in ECAL with pT()>500 MeV • Production and hadronic decay modes • hc could be measured with 100pb-1 • Measurement in bins of pT with 1fb-1 (2011) Assuming (hc)~(J/) and B(hcpp)= 0.12 % M(pp) (GeV/c2)

  30. Y(nS) & b2 Production cross sections and polarisation as a function of pT • Y(1S)+-selection based on • -ID and pT > 1.5 GeV/c • Similar performance for Y(1S), Y(2S) and Y(3S) Data (7TeV, 260nb-1) • b2 Y(1S)  by adding a photon with pT > 0.5 GeV/c LHCb MC (14TeV, 2fb-1) M=47 MeV/c2 M(b2)-M(Y(1S))

  31. X(3872) & Z(4430) • X(3872) discovered by Belle (2003), further studied by Babar, CDF and D0. • Nature not yet established: Charmonium ? D0-D* ? Tetraquark ? • Necessary to measure its JPC. Current data: 1++ or 2 -+ • Angular analysis at LHCb can solve the case 1++2 -+ B+X(3872)K+with X(3872)J/+- ~1800 events expected with 2fb-1 at s=14TeV Angular study at generator level. • A similar study can be done for B+Z(4430)K+: expect ~6200 events (2fb-1) (Assumes B(B0→Z(4430)+K-)∙B(Z(4430)+→ψ(2S)π+) = 4.1 10-5)  Can confirm Belle’s discovery with 100 pb-1

  32. Conclusions • Quarkonia can help us better understand Long Distance QCD • They provide LHCb with one of its first important measurement (L=14.2 nb-1 ) • J/ production cross sections for (y, pT)  [2.5; 4],[0, 10 GeV] • Inclusive J/ and J/ from a b-hadron • bb total production cross section • 10 bins in pT, extended to 12 pT bins and 5 y bins with 50pb-1 (late 2010) • Good prospects in 2010-2011 (0.1 to 1 fb-1) for several other states. • J/, (2S), cJ, hc, Y(nS), b, X(3872), Z(4430) • LHCb is in good shape • Getting close to its nominal performance • Good data/MC for tracking, ID and trigger efficiencies.

  33. Back-up

  34. Bc • Measurement of the production cross section, mass and lifetime • LHCb at s=7TeV with 1fb-1 • Bc+ J/()+ : ~310 signal events • Bc+ J/()+ : ~4700 signal events Production cross section measurement possible with 100 pb-1

  35. Color Singlet, cg(cc) + c + n gluons Color Singlet, gg(cc) + n gluons or + 2 quarks Color Octet

  36. Motivations Understand the production of heavy quarkonia (J/, ’, (nS),…) via NRQCD • Color Singlet Mechanism at LO, NLO & NNLO agrees with Tevatron & RHIC’s data • tot for J/,’,Y(1S) • d/dPT for (1S,3S) (and J/ at RHIC) • Still troubles with J/&’: Polarization too large and d/dPT too low at high PT w.r.t data • The Color Octet could fill the gap, but makes the polarization transverse at high PT ! • In all cases, large th. uncertainties ! Precise measurements at the LHC energy can help clarify the situation ! • Total and differential (PT, y) cross sections pp J/, ’, Y(nS) inclusive cross sections • Individual subprocesses to test the dominance of Color Octet: ppJ/D ; J/(cc); J/, …

  37. X(3872) & Z(4430) • X(3872) discovered by Belle (2003), further studied by Babar, CDF and D0. • Its nature is not yet established • Mass and decays like X(3872)J/ suggest a charmonium • But none predicted at this mass + forbids observed I-violating decays, e.g. XJ/ Charmonium ? D0-D* molecule ? Tetraquark ?

  38. Particle ID Aerogel • Cerenkov Detectors C4F10 Must provide an excellent PID and K- separation all over the typical B and D decay momentum range. CF4 Silica Aerogel C4F10 RICH-1

  39. Particle ID Aerogel • Cerenkov Detectors C4F10 Must provide an excellent PID and K- separation all over the typical B and D decay momentum range. CF4 CF4 RICH-2

  40. Particle ID • Cerenkov Detectors Must provide an excellent PID and K- separation all over the typical B and D decay momentum range. No PID PID C4F10

  41. Particle ID • Calorimeter system Shashlik Pb+Scint e,, h separation via a longitudinal segmentation. Essential to the Trigger (fast PT reco) Fe+Scint RICH-2

  42. Particle ID • Calorimeter system 0  = 7.2 MeV Final states with photons or electrons clearly reconstructable. Mass resolution within expected range. Resolution on M(0) better than in MC. D0K0,  = 24MeV J/ee  = 110 MeV L~150 nb-1

  43. CALO T station TT Long Track VELO K→ Long Track ? VELO-CALO track Tracking Efficiency ICHEP, LHCb-Plenary talk Obtained using KS candidates: Tracks (VELO + IT/OT+CALO) Tracks (VELO + CALO) e = Efficiency as a function of pT • Similar method can be • used to evaluate the • efficiency of VELO • Other resonances can be • reconstructed as well 43 ICHEP, Paris 2010

  44. Tracking efficiency syst. ( DKp vs DK3p ) ICHEP, LHCb-Plenary talk Data: Min.Bias Trigger MC: Incl. charm e(Data) / e(MC) = 1.00 ± 0.03 44 ICHEP, Paris 2010

  45. Trigger in 2010: Golden Age of Charm Physics • The luminosity does not exceed a few 1030cm-2s-1 • The L0 and HLT1 rates are reached with looser PT and IP cuts. • HLT2 not used in early data, then introduced progressively with loose cuts  Typical efficiencies for D hadronic decays above 25%. Above 70% for B, leptonic decays above 90%. • Trigger-unbiased samples used to check the trigger performance on real data Eff-trigL0*HLT1(data) = 60 ± 4 % D*D(K-+) Single Hadron HLT1 Line MC expectation = 66 % LHCb preliminary Minimum bias sample.

  46. The LHCb Experiment Requirements… …For Flavor Physics in pp collisions • High rapidity correlated bb pair production • Forward detector geometry • Large backgrounds (high multiplicity) • Moderate # of interactions per bunch crossing • Many decays with similar f-state topology Ex: B-D0 K- vs B-D0 - (  meas’t ) • Precise P and M reconstruction K- ~8 mm + • Powerful PID K- separation B K+ • Time-dependent CP asymmetries Needs precise B decay time • Precise Vertexing • Highly selective, polyvalent and configurable Trigger • tot ~ 200 (bb) + not all bb events are interesting

  47. The LHCb Experiment In nominal conditions: Maximized the probability of  1 interaction per event • Moderate # interactions per event

  48. Signal Yield • Extended unbinned maximum likelihood fit to the M(J/) distribution • Signal Model: Crystal Ball function Background Model: linear function • Background Model: linear function • Fit parameters • N(J/) = 287273 • N(bkg) =2273166 • M(J/) =  = 30880.4 MeV/c2 • M = 15.00.4 MeV/c2 n &  account for the radiative tail. Very correlated to M. Fixed to n= -0.9+0.14, =2.6-0.0033 (MC)

  49. Signal Yield

  50. Fraction of J/ from b: Fit to tz • Signal Prompt J/ J/ from b, Single exponential Convoluted with a resolution function: double gaussian • Background: 4 components: 1 peaking + 3 long-lived (exponential, due to secondary vertices Parameters determined by a fit to the J/ mass sidebands. • 8 fit parameters:

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