FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London1 B-Physics at the LHC P J Dornan Imperial College, London

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London2 Why b-physics at the LHC Millions of b’s With full luminosity, 10 34, gives bb pairs per year - But events much too difficult to analyse, ~25 interactions per crossing - So - need to run at lower luminosities for most b-physics - In the early period max luminosity expected ~ ATLAS/CMS - but will eventually be able to exploit full luminosity for certain rare decays - LHCb currently plan to run at by detuning the beam Signal/Background improves with increasing energy  inel = 80 mb,  bb = 500  b All b-species produced, B +, B 0, B s, B c, b-baryons At these energies b’s are getting ‘light’ Thus bb pairs produced dominantly forward - backward - -

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London3 General Purpose ATLAS, CMS – 4  ‘standard’ colliding beam detectors Main aim to search for new states - Higgs and those from BSM so will always aim to run at maximum luminosity, > 10 34Specialised LHCb – forward spectrometer (10 – 300 mrads), designed specifically for b-physics. Will always run at low luminosity, nominally General Purpose and LHCb operate in complementary kinematic regions The Experiments b bb b No

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London4 Experimental Requirements An excellent vertex detector B-states identified by displaced secondary vertices Good K-  separation Difficult for general purpose detector - a weakness of ATLAS/CMS An essential feature of LHCb A good trigger for interesting b-physics Far too many b’s produced to trigger on all of them. Therefore trigger must reject many b-states and concentrate on those from which CP/CKM physics will result This is probably the greatest challenge for a hadronic b- experiment -- and has caused failures in the past

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London5 ATLAS

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London6 ATLAS Tracker Tracker Pixel Detector Pixel Detector designed for b-physics Radius of inner layer = 5 cm. 3 layers, but middle will not be available at start-up

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London7 ATLAS Pit Today

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London8 CMS

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London9 CMS Tracker CMS Silicon Tracker Pixel Detector All Silicon 2 Pixel Layers Radii 4 and 7 cm Low luminosity Radii 7 and 11 cm high luminosity

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London10 CMS Today Tracker being assembled In the pit

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London11 LHCb

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London12 LHCB – VELO

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London13 LHCb - VELO Proper time resolution ~ 40 fs

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London14 LHCb - RICH1 RICH1 detector Vertex locator

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London15 LHCb – RICH1&2

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London16 LHCb RICH performance

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London17 Triggers LHCb much better for hadronic B-decays All comparable for B -> J/  decays ATLAS/CMS better for Rare Decays ->  (X) Vital - Still Evolving - Algorithms depend upon important physics channels Basic philosophy

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London18 What physics channels? Must be interesting and extractable at the trigger level Unitarity Triangles B d 0     B d 0    B S 0  D S  B d 0  J/  K S 0 B d 0  DK *0 B S 0  D S K B d 0       B S 0  K + K - B d 0  D *  B S 0  J/  Rare Decays B s(d)  X, b  s 

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London19 Flavour Tagging In many cases need to know the flavour of the B when produced Use Decays of the other B state - Opposite Side tag Lepton b -> e,  Kaon b -> c -> s Or from the accompanying  /K with the signal B – Same Side tag Or use vertex charge l B0B0 B0B0 D   K-K- b b d u d u B0B0 ++ Prelim. LHCb with Opposite side only Obtain eD 2 = 6.4%

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London20 B s Oscillation -  m s With  m d yields V td Oscillation is fast (>14.4 ps -1 ) Need excellent momentum and position resolution, i.e. a fully resconstructable final state and excellent vertex resolution Use B s -> D s  (LHCb) Obtain ~80,000 fully reconstructed/year, S/B ~3. Proper time resolution ~40fs Expected unmixed B s  D s    sample in one year of data taking (fast MC) Expect to make a 5  measurement in 1 year to 68 ps -1

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London21 sin2  - B 0 -> J/  K s Classic channel for CP violation study Still important for LHC experiments to measure with the best possible precision. Measure time dependent asymmetry A mix yields sin2  A dir direct CP violation - BSM Assuming A dir = 0 ATLAS quote  (sin2  ) = after 3 years at LHCb quote  (sin2  ) = after 1 year at LHCb

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London22 Sin2  - B 0 ->  +  = Actually measure  -  -   a very good channel for LHCb High p T hadron to give trigger RICH is essential But Penguins complicate the analysis Can reach 5° <  (  ) < 10° in one year if P/T known to 10%

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London23 Sin2  - B 0 ->  Three final states                   Requires time dependent Dalitz plot analysis But needs detailed understanding of the acceptance An analysis is being developed -- looks promising

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London24  LHCb Will be a major result for LHCb - relies on the hadronic trigger Many ways But none are simple - involve measuring low decay rates, time dependent analyses in the B s system, theoretical uncertainties Many approaches necessary to check consistency 4 time dep rates yields  Relate with U-spin yields  4 time dep rates yields 2  6 decay rates yields 

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London25 Features of LHCb for  Determination Vertex Resolution - Time Dependent B s Asymmetries Separation B s -> D s  /B s - > D s K - RICH particle ID and mass cuts BsDsKBsDsK BsDsBsDs BsDsKBsDsK BsDsBsDs

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London26 B d  D 0 K *0 signal RICH minimises background B s  KK Separation With RICH

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London27 LHCb Expected performance for  2400 events per year 3° <  ) < 16 ° 5000 events per channel per year 3° <  ) < 16° ~500,000 events per year.  ) ~ 10 Some BR’s very small, >  ) ~ 10 ° per year

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London28 B s Mixing phase  s = -2  Use B s -> J/   B s analogue of golden channel, B 0 -> J/  K s Asymmetry very small in SM,  s ~ so very sensitive to new physics But two vectors in final state therefore need a time dependent angular analysis Sensitivity depends on  m s For  m s = 20, Expect  ) ~ 2° per year Analysis also yields  s and  s

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London29 B s,d ->  X Atlas/CMS can here use the high luminosity, so can do better than LHCb Full Tracker  = 46 MeV CMS – Mass resolution Need 30 fb -1 for a 5  observation B s ->  B s ->  X B d 0     x10 -6 B d 0  K *  B d 0     BGsignalBRchannel ATLAS statistics with 30 fb -1 F-B Asymmetry sensitive to some SUSY scenarios

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London30 BcBcBcBc Production less peaked forward Better for ATLAS/CMS For B c -> J/  p (GeV) ATLAS,  (M(B c ) = 74 MeV Expect between 5 – 10K B c -> J/  for each of ATLAS, CMS & LHCb per year Also B c -> J/  gives V bc

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London31 An Event in LHCb

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London32 The major problem - Triggering B-rates at the LHC are very high The final states of interest are a very small proportion For highest efficiency, the High Level Triggers (HLT)) must focus very directly on the predicted properties of the final states of interest and aim to distinguish them from the predicted backgrounds using the predicted properties of the detector Predictions in the forward area depend upon knowledge of the pdf’s at very low x where they are least reliable The simulation will not be perfect! The performance of the trigger is key to the success of the experiment Planned on the simulation Too loose -> low efficiency Too tight -> potential bias

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London33 Triggering LHCb Dimuon Triggers Much physics, J/  X decays, rare decays Strong signature, low rates Safe for LHCb and ATLAS & CMS, Triggers for hadronic final states Much of the physics is here - quite probably any new physics will at the few % level - probing this is the justification for LHCb But rates are low - or very lowNeed Statistical precision -> highly efficient trigger Systematic precision -> minimal biases and these must be accurately quantified Highly demanding for the trigger

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London34 The Problem Crossing rate at LHC = 40 MHz Running at and a 25 nsec bunch spacing expect crossings with interactions at 10 MHz - of which 200kHz will have bb pairs! But those useful for CP/CKM physics and having all decay products in the detector is very much less e.g. For B 0  J/  (  )Ks(    - ) it is 0.02 Hz – or 1 per minute. For B s 0   it is ~1 per week

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London35 Current LHCb Plan 3 Level Trigger Level 0 - reduce rate from 10 Mhz to 1 Mhz Pile-up veto, a high p t hadron, electron, muon, photon Increases b purity from 1% to 3% Level 1 – reduce rate from 1 Mhz to 40 kHz Demand tracks with finite impact parameter and high p t Divide bandwidth between generic and specific, cuts for special channels, electron, photon, dimuon b-purity now at 9% High Level trigger – reduce rate from 40 kHz to 200 Hz to tape Fast reconstruction, using all detectors except RICH – so far Bandwidth Division at Level1 To maintain efficiency at this rate, HLT must use tight ‘offline’ type cuts. Efficiency for channels not used to define HLT can be low

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London36 Possible Improvement Keep present philosophy but add a new inclusive stream with simple cuts and a high output rate To be based on detection of just a single muon with minimal p t and impact parameter cuts - small modification of level 1 bandwidth This would be Inclusive - trigger on the ‘other’ b Yields tagged events Robust Use to reduce/estimate systematic uncertainties Access to states not chosen for HLT optimisation  K s …. Output rate- whatever can be handled - would be 2 – 5 kHz with ~50% events with bb Under active investigation - Current 200 Hz stream would be preserved - now Hot Stream Inclusive stream to be reconstructed at many sites Possible future Level 1 bandwidth

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London37 The LHC Status Delays due to problems with the cryolines Poor quality control by the company charged with installation of work by its sub- contractors First collisions are still scheduled for ‘summer’ 2007 Great pressure to maintain this dateComponents Almost all ontime Cryodipoles, which were a problem now stacking up on the surface waiting for the repair of the cryolines

FPCP04, Daegu, 9 Oct 2004P J Dornan - Imperial College London38 Summary The LHC has great potential to make major advances in precision CPV b-physics All species of b-hadron state are produced Thousands of events for many important channels with small branching ratios make measurements at the few % level possible. But The hadronic environment will be difficult still a lot of background - mostly from uninteresting b-states Efficient, well understood triggering will be all important