b physics in lhcb

Introduction:LHCb physicsThe experimental challengeVertex reconstructionParticle IDTriggerFlavour taggingSystematic effects

Hugo Ruiz Winter meeting 2007 - Santiago

Hugo Ruiz Winter Meeting Santiago 2007

SM introduces CP violation through:the CKM matrix is complexphases switch sign under CP: Vij Vij*

After requiring unitarity and removing non-physical phases, the values of Vij are no longer independent3 magnitudes + 1 phase fix the matrix: 4 parameters

All measurements related with electroweak quark transitions are coherent with the CKM picture of the SM:BR, Dm and phases measured fit within a set of values of the 4 CKM parametersIn particular, unitarity triangle closes gently

31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*l = 0.22400.0036 A = 0.830.02 r = 0.1680.029 h = 0.3400.017Wolfenstein parameterization, values from UTFit


But there is room for NP in B meson decaysAnd after all, the CKM picture of CPV does not account for the presence of matter in the UniverseSome quantities very sensitive to NP are yet to be measured or lacking precise measurementFour examples accessible to LHCb in this talk:

c arg(Vts)-p via phase of Bs mixingCKM fit prediction is very preciseg -arg(Vub) from tree decaysTree processes assumed free of NPComparison with measurements from loop processes can reveal NPBranching ratios of rare decaysExpect large contributions from NP models which fit rest of dataAngular distributionsSensitive to non-SM operators in interactions

31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*


Prediction from a global fit to CKM measurements (UT fit):fs = -0.037 0.002 Very small, so very sensitive to NP!Recent D0 measurement:fs = -0.790.56(stat)+0.14-0.01(syst)Note: no Bs produced in B factoriesD0 used golden channel BsJ/y(m+m-)f(K+K-)

31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*The diagram for Bs oscillation in the SM isThe phase of the oscillation in the SM is given by:fsSM -2 arg (Vts) -2c = -2l2hVtsVts*up to o(l6)


31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007Bs(Bs)J/y(m+m-)f(K+K-) can proceed directly or through mixinghf = +, - 1 CP eigenstatesLifetime distributions of events with a Bs (Bs) at production show oscillation patternOscillation phase is opposite and different phase in time evolution ACP appears

Strong requirement on vertexing__Need flavour tagging2arg(Vts) is only weak phase


One nominal LHCb year (2 fb-1):BR=310-5 3K eventss(fs)= 0.023 ( UT fit value: -0.037)

The measurement can be interpreted via a parameterization of NP effects:M12 = (1 + hs e 2iss) MSM12MSM12= dispersive part of the BS mixing amplitude in the SM

Then Dms and fs can be used to constrain NP in the oscillation:31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*From Z. Ligeti et al hep-ph/0604112Allowed regions CL > 0.90, 0.32, 0.052006, After first Dms measurement fs= 0.040.030.1 0.3 0.5 hs0.5 1.5 2.5 hsssss 180o 180o 90o 90o0o0oLHCb, L=2fb-1Allowed region


g arg of (Vub) to o(l4)Measurement (tree dacays only): g = (83 19)oFrom global fit of CKM params. (incl. loop processes!): (64.1 4.6)o

One promising method for tree determination: measure BR of B- (K+p-)DK- and the charge-conjugated process2 diagrams (via D0 and via D0) contributing with similar amplitudes large interference effects hence large CPV in the decay

No flavour tagging neededNo need to measure B lifetime

31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*_arg(Vub) is the only weak phase involved


But too many unknowns: relative amplitudes and strong phases of each B, D decay31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*Strong requirement on PIdNeed to measure BRs from additional D decay modes to extract g (ADS, GLW)Current status: B- (K+p-)DK- not yet seen in B factoriesPresent g sensitivity from B decays with higher BR, but less sensitivityWith LHCb 10fb-1, expected 3.5 K eventsB+: 2500 with B/S ~1.5, B-: 1000 with B/S ~ 4.5*sg = 3.6o (2.4o if combined with other tree decays) Alternative method from ACP of BdK+K-, Bs p+p- with penguin contribution (NP?) gives sg = 4o

????


Status of g from tree processes now and in ~ 2013:31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*31/05/200731/05/2007Current from tree processes onlyggFrom BDK, Tree process, LHCb 10 fb-1|Vub/Vcb| from semileptonic BRsFrom UT fit, quantities affected by loopsThis is what we know about CKM if we suspect NP in loop processes!


Occurs via loops:Small BR in SM: (3.4 0.4) x 10-9Sensitive to NP!

Strongly enhanced by some SUSY modelsEx: up to x100 by CMSSM with parameters preferred by anomalous m mag. moment in BNL.

Limit from Tevatron at 90% CL:Current (1 fb-1) < 710-8Expected final (8 fb-1): < 210-8~ x10 higher than SM!

31/05/2007SMLHCb: with L=2fb-1, 3s observation if SM valueYesterdays talk by Diego Martinez


It is a rare decay: BR(SM) = (1.22+0.38 -0.32) 10-6Decay seen in B factories, ~ no NP in BRAngular distributions can reveal NPEx: AFB(s) between + and B direction in the +- rest-frame as a function of mmm231/05/2007*Hugo Ruiz Winter Meeting Santiago 2007SM


31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007The LHCb collaboration: 619 scientists 46 institutes 14 countries Spain: Universidade de Santiago de CompostelaUniversitat de Barcelona - Universitat Ramon Llull


Tracking Stations:p of charged particlesCalorimeters:PID: e,, 0Muon SystemInteraction region31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007


Within LHCb acceptance: ~ 1012 b hadrons per year~104 more than in B factories but some disadvantages too

31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007pT (GeV)hDetector acceptances:angle to beam


31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*B meson 1B meson 2Primary Vertex (PV): pp interaction ~ 8 mmDh~1.4Dh~0.71 fmIPTriggerHard work for hadron final statesMass resolution:Distinguish Bs from BdReduce combinatorial bckgrdFlavour taggingB flavour at start of oscillation

A typical bb event:high pT, IP tracksVertex reconstruction: Selection of B candidates (IP of tracks & displaced vertex)Measurement of B lifetimeParticle identification: Background reductionDistinguish Bdpp, Bs KK


LHCb needs a lower luminosity:Chosen to maximize the probability of a single interaction: 2 5 1032 cm-2s-1 50 times lower than LHC design lumi

LHCb will probably reach its design luminosity before ATLAS and CMS31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007Luminous region (within 1 sigma):

With nominal LHC lumi (1034 cm-2s-1): 23 interactions per bunch crossing 23 PVsDifficult to find secondary vertices!5 cm~ 1 mm~ Maximum for detector radiationNum. of pp collisions


31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*


The closest to the beam, the less extrapolation distances, and the better IP and vertex resolution

But cannot go too close: at injection beams are separated, and VELO has to provide enough aperture

Solution: retractable detectorAt 3 cm at beginning of fillMoved to 8 mm when stable beams declared

Even though lower lumi, higher dose than ATLAS and CMS pixel detectorsWill have to replace in a few years31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*


31/05/2007*Hugo Ruiz Winter Meeting Santiago 20071/pT distribution for B tracksdIP 14mm 35 mm/pT Signal BPVIPFor trigger, VELO R-sensors allow for a fast search of high IP tracks in 2-D:


PV resol (~70 VELO tracks):z=47 m, x=8 m

31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*z coordinate:Dz


B physics require separation between final states with p and KBest example: extraction of g from ACP in BsK+K- and Bd p+p-. What happens if we are p-K blind?If all tracks considered to be pions:m(B0) = 5279 MeVm(Bs) = 5367 MeV31/05/2007*


Ring Imaging Cherenkov detectors measure angle of Cherenkov emission, a function of velocity of particlesDifferent radiating materials separate p-K in different ranges of momentumLHCb has 3 radiators in 2 different detectors31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007


*HPD arrays out of acceptance31/05/2007Hugo Ruiz Winter Meeting Santiago 2007RICH 1 structure:Typical event (RICH2):RICH2 in the pit:


Kaon identification:31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007Effect on Bdp+p-:Plot obtained using MC truth


PId performance will be calibrated without using MC

Use D*+D0 p+, D0 K-p+BR: 3.810-4 (K-p+~400 times smaller)Golden kinematics:(mD* - mD0) = 144.5 MeV

Purity on PId of each track is > 99% without using the RICH, by:Kinematical cuts and chargesVeto in muon chambers and ECAL

Dedicated D* line in trigger:300 Hz with 50Hz of signal

To compare tracks from this sample with any other only a pT binning is needed31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*p (GeV)D* calibration sample (300 s of data)

All tracks in bb eventsExample: 1GeV

Momentum is measured from curvature of tracks between VELO and main tracking stations The LHCb (warm) magnet:B dL = 4 TmField reversal to reduce syst. effects on CP asymmetries


31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*3 stations (T1 T3)Occupancy(in an arbitrary # of events):Next talk by Pablo Vzquez


Typical B track (p>12 GeV):20-50 hits98.7% correctly assignedEfficiency >95%Ghost rate

Momentum resolution:31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007Resolution dominated by multiple scattering (over detector resolution) up to 80 GeVp distribution for B tracksMass resolution:Bs m+m-sm=18 MeVN combinatorial background sm!CMS: 36 MeV (ms have large p)ATLAS: 77 MeV (lower BdL)

dp/p 0.35%0.55%Combinatorial background

Arbitrary scale!!


31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007Relevant rates: LHC: 40 MHz, 2 bunches full: 30 MHzAt least 2 tracks in acceptance 10 MHzbb: 100 KHz Decay of one B in acceptance: 15 KHzrelevant decays BR ~10-4 10-9Particles reconstructedTrigger an important issue!

Typep25K10m0.5g (pT>2.5GeV)~1


31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*10 MHz1 MHzCalo+ Muon systemPileup systemL0: hight pT + not too busy On custom boards Fully synchr. (40 MHz), 4ms latency


Fast search for high pT particles

Calorimeter: look for high ET candidates in three categories: e, g and p0In regions of 2x2 cellsParticle identification fromECAL / HCAL energyPS and SPD information

Muons:Straight line search in M2-M5Look for compatible hits in M1Momentum measurement 20%

31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*Scintillator Pad Detector (SPD)Pre-Shower DetectorECALHCALInteraction region


31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007Bandwidth share:Efficiency (off-line selected evts):LHCb onlye ~ 50 % L0 is the bottle-neck for hadronic channels


31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007Muon alleyHadr. alleyECAL alleyHLT1MHz8KHz2KHzDisk


L0 hadron: 700 KHzReconstruct Velo, match to L0 object, IP cut (~75mm): 250 kHz (~2 cands.)Reconstruct T tracker, match VELO track, pT>2GeV: 40 kHz (~1.2 cands.)Select VELO tracks with IP forming good vertex with 1st candidateMatch them to T stations and cut at pT>1 GeV: 5-8 kHz (~1 cand. vertex)Then enter ex(in)clusive selections (rate reduced by a factor 100)


31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*Calibration and evaluation/reduction of systematics


Overall efficiencies (on offline reconstructed evts):31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*Unbiased BPVTrigger m (BR xx)The inclusive B sample:900 Hz of B mX, 550 Hz trueFrom the accompanying B meson: ~ 1.5109 fully contained, m-tagged and decay-unbiased B mesons / 2fb-1Tagging enhanced: eeff ~ 0.15

This trigger only: factor of ~10 higher yield in BB than B-factories for data mining (but worse backgrounds)

TypeExampleEfficiencyHadronicB h+h- 25 35 %RadiativeB K*g30 40%DimuonBsJ/y(m+m-)f(K+K-)60 70 %


Flavour tagging: determination of the flavour of the signal B at productionNeeded for all measurements involving oscillationsAt a hadron collider, information can be obtained from:Signal BTagging BPVm, eKDxhadron from fragmentation or B** decay (K, p)Same side (SS)Opposite side (OS)vertex charge (weighted on track pT)31/05/2007*High pT, low IP, close to signal BHigh pT, high IPSelectionDisplaced vertex


Flavour tagging algorithms are not perfect!Backgrounds in tagger selectionsThe tagging B can oscillate incoherently (unlike in B-factories):40% B, 10% baryons : no oscillation 40% Bd: Dmd ~ Gd oscillated 17.5%10% Bs: Dms >> Gs oscillated 50%

Characterization of tagging algorithms: etag: fraction of events with a tagw NW/(NW+NR): wrong tag fraction eeff etag(1-2w)2: effective tagging efficiencyIndicates the reduction in number of events that would account for the same statistical degradation as the fraction of wrong tags31/05/2007Hugo Ruiz Winter Meeting Santiago 2007*Average mixing probability: 13%


Typical performance for hadronic decays:

31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007Babar/BELLE: ~ 30%

B0 (B0 p+p-)Bs (Bs DsK)etag (%)w (%)eeff (%)etag (%)w (%)eeff(%)OSm8.7321.14 0.0713331.47 0.12e3.6330.39 0.044.2300.69 0.08K28362.09 0.7327362.27 0.15Vertex22391.01 0.0725400.97 0.10SSK/p15390.73 0.0633343.50 0.19Total51345.050.2265319.50 0.42


is a first order correction to CP asymmetries:

ACPmeas = Dtag Dres ACP true(1-2w)exp [-(m t)2/2], only relevant for Bs 31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007dw dACP uncertainty on the physics parameter that we want to extract we need small w and dw!Required precision: imposing that dACP induced by w is half the statistical error for 2fb-1:fs from BsJ/yf: dw/w < 15%g from BsDsK: dw/w < 2% MC cannot be used to reach such calibration of w (unlike in B factories) because of several effects: Uncertainty on bb production mechanismAsymmetry in interaction with matter, B(*,**) hadron composition


Idea: accumulate high statistics in flavour-specific modesw can be extracted by:B: just comparing tagging with observed flavourBd and Bs: fitting known oscillation31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007B/S~0.20.8


But MC studies show 5% differences in w between signal and control channels (> 2% target! )Reason: trigger and offline selections bias in different manner the distribution of 3-momentum of the signal BIt is solved by re-weight the events to get the same 3-momentum distribution of the signal-BBsJ/fBsDspBeforepT reweighting on signal B pT of tagging B pT of tagging BAfter pT of tagging B


Measurements from the B meson system in LHCb can reveal physics beyond the SMThe search is complementary to that at high pT in ATLAS and CMS

LHCb will be ready on time to exploit LHC as a B factoryThis year, LHCb plans to produce its physics book, in which the key analysis will be presentedWith treatment of calibrations and systematic effects using control channels from dataLooking forward for data taking!31/05/2007*Hugo Ruiz Winter Meeting Santiago 2007


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b physics in lhcb

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different phase