Status and expectations for first physics with LHCb. M. Needham On behalf of the LHCb collaboration Symmetries and Spin July 20 th - 26 th Prague

Transcription

1 Status and expectations for first physics with LHCb M. Needham On behalf of the LHCb collaboration Symmetries and Spin July 20 th - 26 th Prague

2 Outline Introduction to LHCb Tour of the detector First Physics in 2008 B s mixing phase: s (Key 2009 measurement) Rare B decays B s μ + μ (Key 2009 measurement) Angle Summary

3 Searching for New Physics Expect New Physics at the TeV scale Two complementary approaches to discovering it: Direct searches (ATLAS + CMS) Indirect searches (LHCb) Look for effect of virtual particles in loop processes Indirect searches very important in development of Standard Model Suppression of K L μ + μ - (GIM mechanism) charm New particles? New particles?

4 LHCb Dedicated B physics experiment at the LHC: bb pairs produced in the acceptance per year All B species produced: B d, B s, B u, B c, b B production correlated and peaked in the forward direction LHCb luminosity of cm -2 s -1 by focussing the beam less Maximizes probability of one interaction per crossing P T of B-hadron 100μ b Pythia 230μb of B-hadron pp interactions/crossing LHCb ATLAS/CMS b b

5 Key Ingredients Perform time dependent measurements Harsh enviroment of the LHC ~ 50 tracks per event from primary vertex B events 1 % of the visible cross-section Selective trigger needed LHCb Geant4 simulation Mass + pointing constraints to reduce background p B ~ 80 GeV Primary vertex ~1 cm Good primary + secondary vertexing to measure proper time b t K + B s K+ D s Flavour Tagging Example: B s D s K K Good K/ separation

6 The Detector Muon System RICH Detectors Vertex Locator VELO pp collision Point ~ 1 cm B Calorimeters Tracking System

7 The Detector Muon det Calo s RICH-2 OT+IT Magnet RICH-1 VELO Detector ready for physics

8 Tour of the Detector

9 MC Simulation Simulation software: Pythia+EvtGen GEANT4 simulation Detector response Reconstruction software: Event Reconstruction Decay Selection Trigger/Tagging Physics parameter fits Optimise the experiment+ test physics sensitivities

10 Vertex Locator 8.4 cm 21 stations Silicon Strip detectors Strips measuring r and Sensitive area ~ 8 mm from beam 5 μm hit resolution 30 μm impact parameter resolution Detector halves retracted/inserted each fill ~ 1 m Interaction point

11 Tracking System Large Silicon Detector before Magnet + 3 stations [straws + Silicon] after magnet Trigger Tracker 1.3 m 80 cm 4.7 m IT OT 5.6 m T stations Magnet B dl = 4 Tm

12 Tracking System dp/p: 3-4 per mille Efficiency ~ 95 % above 10 GeV ~4-5 particles in final state High tracking efficiency Good dp/p resolution Mass constraints Remaining background from B s D s after PID suppressed by good mass resolution

13 Particle Identification RICH2: 100 m3 CF4 RICH1: 5 cm aerogel 4 m 3 C 4 F 10 2 RICH detectors for K/ separation

14 Particle Identification 0 Cherenkov rings RICH1 y (cm) x (cm) Primary vertex B s D s K +,K + B s K + b t D K s K K : ± 0.06% K : 5.15 ± 0.02%

15 Calorimeters Calorimeter system : Preshower, ECAL, HCAL Detection of electrons, 0, Level 0 trigger: high E T electron and hadron, photon PreShower/SPD: 12k scintillator pads Shaslik ECAL: Pb/Scintillator, 25 X 0 6k cells /E ~ 10%/ E 1% Tile HCAL (only for trigger) Fe/Scintillator, k channels /E ~ 80%/ E 10%

16 Muon system: Level 0 trigger: High Pt muons Flavour tagging Muon System B s K + K + K Primary vertex b t D s muon tag Arranged in 5 stations; Inner part M1: 24 triple GEM chambers; Outer part M1, M2-M5: 1100 MWPCs

17 pt ~ 1 GeV μ pt ~ 3 GeV e,h 1000 box CPU farm 40 MHz 1 MHz Trigger HLT: L0 confirmation + high IP[software] then full reconstruction of event 2 khz Detector L0: high p T (μ, e,, h) [hardware] Storage (event size ~ 35 kb) L0, HLT and L0 HLT efficiency (normalized to offline selected) HLT rate Event type Physics 200 Hz Exclusive B candidates 600 Hz High mass dimuons B (core program) J/, b J/ X (unbiased) 300 Hz D* candidates Charm (mixing & CPV) 900 Hz Inclusive b (e.g. b μ) B (unbiased sample)

18 Flavour Tagging PV B 0 opposite B s 0 signal -, μ - + Same side Fragmentation K ± accompanying B s ± from B ** B (*) ± D K - Q vertex,q Jet Tag Opposite side High Pt leptons K ± from b c s Vertex charge Jet charge B d Figure of merit: D 2 = (1-2 ) 2 : tagging power : tagging efficiency : wrong tagging fraction Muon Electron Kaon opp.side Jet/ Vertex Charge Same side p / K Combined (Neural Net) ( p) ~ (K) ~9.5

19 Detector Commissioning Detector commissioning progressing with cosmics Time alignment of calorimeters, muons, Outer Tracker Regular readout of major components Ramp up to data taking with beam gas in August This data will allow first alignment + calibration Cosmic track Triggered by calorimeters Seen in the tracker

20 Physics Program

21 Physics Program 2008: Low luminosity ~10 31 cm -2 s days, 10 TeV Minimum bias +proto-hlt trigger, collect ~ 5 pb -1 Calibration + Alignment Minimum bias physics Charmonium production 2009: Luminosity cm -2 s days, 14 TeV L0 + HLT, collect ~ 0.5 fb -1 B Physics Run Calibration CP (sin2, m s,..) CP + rare decays Key measurements: s, Bs μμ 2010+: Luminosity cm -2 s days collect total of ~10 fb -1 Full Physics program ~2015: Upgrade? to run at luminosity cm -2 s Collect 100 fb -1

22 Physics Program with loops and trees B s mixing phase s B μμ, B K* μμ Radiative penguins: B K *, B s Key Measurements with B J/ K s with B B c and b physics Other rare B decays. Minimum bias physics Charm Physics W, Z, production [constrain PDF] Higgs search Exotics: Neutralino, Hidden valley particles Other B Physics More than B Physics

23 First Physics

24 First Physics Start "Physics" with first 10 TeV collisions 2 bunches on 2 bunches Increase luminosity gradually (zero external crossing angle) Target luminosities (for protons per bunch, * = 6m) Scheme coll. pairs non-coll. bunches Lumi at IP8 2x cm-2 s-1 43x x Expected integrated luminosity in 2008: ~5 pb -1

25 First Physics Minimum bias running 4 filled bunches L = 1.1 x cm -2 s -1 2 khz minimum bias to disk Collect events in 100 hours # min bias events needed to perform 10 % measurement Sample will contain ~500, 000 reconstructed K s and 2000 J/ Alignment, calibration of tracking/pid Studies of single particle production, generator tuning K s, production + polarization + hyperon production, Vector meson production (K*, )

26 J/ Production 5 pb-1 will have ~ 5 millon J/. Potential physics: Fraction of prompt J/ and from B [+ hence the B lifetime] Prompt J/ physics: Tests of the Color Octet Model pt spectra polarization (spin alignment) c production Extend to (2S), Upsilon μ lab direction + μ S/B ~ 4.8 J/ signal in 18.6 million min bias c J/ Combinatoric background from decays in flights

27 B Physics: First steps Significant samples should be available when high pt muon/hadron trigger are commissioned Angle Study background with B D(K ) Vertex, mass resolutions + lifetimes with B(D) hh For Bs μμ Methods for calibrating mass, PID demonstrated For B K*μμ Muon efficiency at low momentum understood Experience with angular fits of (2S) J/ Channel Yield / 5 pb -1 B D(K )X 31k B + D(K ) + 23k B D*μ 2.3k B J/ B s J/ 0.2 pb B K* 150 B K * Radiative Penguin decays Calibrate calorimeter First b s decays seen

28 Bs Mixing Phase: s

29 s with b ccs Key measurement for 2009 s, Bs oscillation mixing phase (analogue of sin 2 d ) s is small in the SM: s = -arg(v ts2 ) = -2 s = -2 2 ~ radian Sensitive probe for new physics: s = SM s + NP s Measure from time dependent asymmetry in b ccs transitions For measurement need m s as input Tevatron results: D0 2 s = with with 2.8 fb -1 CDF 2 s = 68%CL with 1.35 fb -1

30 s : Measurement B S J/ counter part of the golden mode B d J/ Ks High yield: 125 k signal events per 2fb -1 (before tagging) Vector-Vector final state: Admixture of CP eigenstates Angular analysis needed total flat background CP even CP odd Pure CP eigenstates (e.g. B S J/ ) can also be added No angular analysis needed but total statistics lower (27k 2fb -1 )

31 s : Physics Reach 2009: 0.5 fb -1 : sensitivity ~0.042 using B S J/ (cf SM value 2 s ~ ) Decay Mode Yield (2 fb -1 ) (2 s ) J/ ( ) 8.5 k J/ ( ) 3 k J/ ( ) 2.2 k J/ ( ) 4.2 k 0.08 c 3 k D + s D - s 4k All CP eigenstates J/ 130 k All Sensitivity with 2 fb -1 and m s = 17 ps -1, 2 s = -0.04, / = 0.15

32 Rare Decay Program

33 B s μ + μ - b t Z 0 μ B s s b W ± t Standard Model W ± μ μ Key measurement for 2009 Flavour Changing neutral current Highly suppressed in SM: BR(B s μμ) =(3.35±0.32) x10-9 B s B s s b s ± t t b W ± H 0 /A 0 SUSY μ μ μ μ Can be enhanced in SUSY BR(B s μμ) tan 6 /M 2 H Currents limits from Tevatron ~2 fb -1 : CDF BR < % CL D0 BR < % CL

34 B s μ + μ - 90% CL limit on BR (only bkgrd is observed) Expected final CDF+D0 limit High statistics + trigger efficiency Main issue is background rejection Largest background is b μ, b μ. Exploit good mass resolution ~ 20 MeV SM x10-8 (~0.05 fb -1 ) Exclusion 0.1 fb -1 BR < fb -1 < SM (2008) SM Branching ratio 2 fb 1 : 3 evidence 6 fb 1 : 5 evidence 5x10-9 (~ 0.5 fb -1 ) J. Ellis et al., arxiv: v1 [hep-ph]

35 B d K * μ + μ 2009: 0.5 fb-1 expect 2000 events B factories total ~ 1000 events by then Channel Yield (2 fb -1 ) BG (2 fb -1 ) Bs K*μ + μ (BR) A fb (s) 2 fb -1 Remove resonances s 0 (s 0 ) = 0.5 GeV 2 s = (m μμ ) 2 [GeV 2 ] Zero crossing point of forward-backward asymmetry A FB in l angle, as a function of m μμ precisely computed in SM: s SM 0 (C 7,C 9 )= GeV 2 35

36 B s A Probes the exclusive b s radiative penguin Measure time dependent CP asymmetry: CP () t ( s ) ( s ) ( Bs ) ( Bs ) B B Ad ir cos mt + Am ix sin mt = = + t t cosh + A sinh 2 2 Interference can only occur for final states with same photon polarization In SM b s is predominantly (O(m s /m b )) left handed Interference +hence mixing induced CP violation suppressed

37 B s SM: A dir 0, A mix sin2 sin2 A sin 2 cos2 tan = b s R / b s L, cos 2 1 Channel Yield (2 fb -1 ) B/S Bs 11k <0.55 Statistical precision after 1 year (2 fb -1 ) (A dir ) = 0.11, (A mix ) = 0.11 (requires tagging) (A ) = 0.22 (no tagging required) Measures fraction wrong polarization Suppressed in SM

38 Angle

39 Angle Measured values 90% CL Fit results 90% CL angle is least constrained Key measurement of LHCb Several independent strategies to extract

40 Angle From tree amplitudes : B s D s K 1 2 From tree amplitudes : B DK (ADS /GLW methods) 3 From penguins : B h h Sensitive to New Physics

41 from B s D s K Interference between tree level decays via mixing Insensitive to New Physics Determines in a clean way Measures + 2 s s from B s J/ Main background B s D s 10 times higher branching ratio Suppressed using Kaon identification by RICH (0) 0 B s e 2i B s 0 ( t) B 0 s ( t) B s0 { b s b i s + f e i s f e u s c s K + D s }K + }D s B u s s}k s0 { c s + K D s }D s + Channel Yield (2 fb-1) B/S (90% C.L.) Bs DsK 6.2 k [ ] Bs Ds 140 k [ ]

42 from B s D s K B s D s K, B s D s have same topology combine samples to fit m s, s and mistag rate together with CP phase + s years data: B s D s - + B s D s- K + ( m s = 20) t rec Sensitivity: 2 fb -1 ( + s ) = 9 o 12 o m s = ps -1

43 from B ± DK ± (ADS) Measure relative rates of B D(K ) K and B + D(K ) K + Two interfering tree B-diagrams, one colour-suppressed (r B ~0.077) D 0, anti-d 0 reconstructed in same final state (interference term accessing ) Two interfering tree D-diagrams, one Double Cabibbo-suppressed (r K D ~0.06) Colour allowed Double Cabbibo suppressed Colour suppressed Cabbibo favoured Reversed suppression of the D decays relative to the B decays results in more equal amplitudes Large interference effects Simple counting experiment (no tagging, no proper time) measure:

44 from B ± DK ± (ADS) favoured colour suppressed Channel Yield (2 fb -1 ) B/S B D(hh) K 7.8 k 1.8 B D(K ) K, Favoured 56 k 0.6 B D(K ) K, Suppressed 0.71k 2 B D(K3 ) K, Favoured 62k 0.7 B D(K3 ) K, Suppressed 0.8k 2 Also under study: ( ) B ± DK ± with D K s B ± DK ± with D KK 18 B 0 DK* 0 with D KK, K, 6 12 B ± D*K ± with D KK, K, (high background) Dalitz analyses ( ) = 5 o to 13 o depending on strong phases. Overall: expect precision of ( ) = 5 o with 2 fb -1 of data

45 from B hh B 0 + originally proposed for measurement of angle = - - But extraction of compromised by influence of penguin diagrams /K Measure time-dependent CP asymmetries for B 0 + and B s + A CP (t) = A dir cos( m t) + A mix sin( m t) Extract four asymmetries: A dir (B 0 + ) = f 1 (d,, ) de i = ratio of penguin and tree A mix (B 0 + ) = f 2 (d,,, ) amplitudes in B 0 + A dir (B s + ) = f 3 (d,, ) d e i = ratio of penguin and tree A mix (B s + ) = f 4 (d,,, s ) amplitudes in B s + Assume U-spin flavour symmetry (d s) d = d and = Take d from B d J/ Ks and s from B S J/ solve for 4 observables, 3 unknowns (can relax U-spin assumptions)

46 from B hh Invariant mass NO PID Counts WITH RICH PID B d B d B s B s Λ b Λ b - π + π + K π K K - π + K - p K - p π GeV/c Channel Yield (2 fb -1 ) B/S B 36k 0.5 B s KK 36k 0.15 ( ) ~ 10 o with 2 fb -1 ( ) ~ 5 o with 10 fb -1, free in the fit Assume d = d (at 20 % level)

47 Summary LHCb will collect high statistics samples of B hadrons Including B s and b baryons Detector installed and being commissioned for physics this summer First physics in 2008 with 5 pb -1 Alignment and detector calibration Particle multiplicities Ks and production Charmomium physics Preparation for B physics measurements in 2009

48 Summary Key measurements with 0.5 fb -1 in 2009: s [precision ~0.04] Bs μμ [exclusion down to SM model expectation] Full physics program in 2010+: aim to collect 10 fb -1 by ~ Angle precision ~ 5 o with 2 fb -1 Search for new physics in photon polarization in radiative penguin decays Precision measurement of forward-backward asymmetry in B K*μμ m s precision of 0.01 ps -1 sin2 precision of 0.01 with 10 fb -1 with B precision of 10 o Charm physics: D 0 mixing, direction CP violation in D 0 KK, D 0 μμ Z, W production at high rapidity And much more LHCb offers an excellent opportunity to spot New Physics signals beyond the Standard Model

49 Backup

50 sin2 with B 0 J/ K s Time dependent CP asymmetry in will one of the first CP measurements at LHCb. 236k signal events / 2 fb 1 B/S= 0.6 (bb) A CP (t) A CP (t) = N ( B 0 J/ K S ) NB 0 J/ K S N( B 0 J/ K S )+ NB 0 J/ K S ( ) ( ) stat (sin(2 )) = in 2 fb 1 cf ~0.019 expected from B-Factories with 2ab -1 2 fb 1 (fast MC, incl. bkg) Proper time t (ps) With 10 fb 1 : (sin(2 )) ~ Can also push further the search for direct CP violating term cos( m d t)

51 Charm Physics LHCb will collect large tagged D* D 0 sample Used for PID calibration Dedicated D* trigger for this purpose. Tag flavour with pion from D* ± D0 ± Interesting measurements: Time-dependent D 0 mixing with wrong-sign D 0 K + decays stat (x 2) ~0.14 x10 3, stat (y ) ~2 x10 3 with 2 fb 1 Direct CP violation in D0 K + K A CP < 10 3 in SM, up to 1% with New Physics Expect stat (A CP ) ~ with 2 fb 1 D 0 μ + μ - BR < in SM, up to 10 6 with New Physics Expect to reach ~ with 2 fb 1