angelo carbone infn bologna (on behalf of the lhcb collaboration) beauty 2006 oxford, uk

LHCbat prospects h'h B -0(s)

Angelo CarboneAngelo CarboneINFN BolognaINFN Bologna

(on behalf of the LHCb Collaboration)(on behalf of the LHCb Collaboration)

BEAUTY 2006BEAUTY 2006Oxford, UKOxford, UK

Angelo Carbone BEAUTY 2006 2

OutlineOutline

BBhh++h’h’-- channels and U-spin symmetric modes channels and U-spin symmetric modes Event selectionEvent selection Sensitivity on direct and mixing induced CP Sensitivity on direct and mixing induced CP

violation parametersviolation parameters Extraction of the Extraction of the angle of the unitarity triangle angle of the unitarity triangle ConclusionsConclusions


Why BWhy Bhh++h’h’-- decays decays interesting? interesting?

Since the original CLEO measurement that BR(BSince the original CLEO measurement that BR(BddKK++--) )

is is ~~4 times larger than BR(B4 times larger than BR(Bdd++--), it is well known that ), it is well known that penguin diagrams cannot be neglected in the two-body penguin diagrams cannot be neglected in the two-body B-decay amplitudesB-decay amplitudes This fact complicates considerably the extraction of CKM phases from

these decays However, a possibility to eliminate unknown hadronic quantities relies in

exploiting flavour symmetries, e.g. combining the measurements from U-spin related decay modes

TThis way, the presence of penguins can be transformed his way, the presence of penguins can be transformed from a problem to an opportunityfrom a problem to an opportunity New Physics contributions might show up inside the loops of the penguin

diagrams, and CKM quantities extracted from these modes can differ from the ones calculated from tree-level modes, which are basically unaffected from NP


U-spin (dU-spin (ds quark exchange) s quark exchange) symmetric modessymmetric modes

BBdd++-- B BssKK++KK--

T+P+PT+P+PCCEWEW+PA+E+PA+E T+P+PT+P+PCC

EWEW+PA+E+PA+E

BBd d ++-- BBss++KK--


EWEW

BBssKK++KK-- BBd d KK++--


EWEW

Not all exactly U-spin symmetric, E and PA contributions missing from flavour specific decays E and PA contributions expected to be relatively small, and can be experimentally probed by measuring the still unobserved Bs +- and BdK+K- branching ratios (BR~10-8)

T: treeP: penguinPC

EW: colour suppressed electroweak penguinPA: penguin annihilationE: exchange


BBhh++h’h’-- events eventsproduced at LHCbproduced at LHCb

Large beauty production Large beauty production cross section expected at 14 cross section expected at 14 TeV p-p collisionsTeV p-p collisions All b-hadron species produced

B hadrons are produced B hadrons are produced very likely with a small very likely with a small relative angle and in the very relative angle and in the very forward (backward) regionforward (backward) region LHCb uses just the forward

direction 1.8 < < 4.9

,.... 00bcsd Λ,B,B,B,B

~40% ~40% ~10% ~10%

At the nominal LHCb luminosity At the nominal LHCb luminosity LL=2x10=2x103232 cm cm-2-2ss-1 -1 aboutabout 10101212 B events B events are produced in 10are produced in 1077 s s Bh+h’- channels have typical branching

ratios in the range 10-5 - 10-6

Millions of such events produced per year!


Event simulationEvent simulation Event generation using Pythia 6.3 with dedicated LHCb tuningEvent generation using Pythia 6.3 with dedicated LHCb tuning Full GEANT4 simulation and Pattern RecognitionFull GEANT4 simulation and Pattern Recognition Problem: how to estimate combinatorial background-to-signal Problem: how to estimate combinatorial background-to-signal

ratios before data ratios before data comescomes?? Expected beauty production cross section is about 100 times less than visible

cross section in the detector (~0.5 mb vs ~65 mb), and branching ratios of interest at 10-5-10-6

The number of minimum bias events equivalent to signal events necessary to be generated and processed through GEANT4 is out of reach

In order to study the combinatorial background we make the In order to study the combinatorial background we make the reasonable assumption that the dominant source comes from reasonable assumption that the dominant source comes from beauty events, thbeauty events, thus reducing by a factor 100 the number of us reducing by a factor 100 the number of simulated eventssimulated events Still a computing challenge, but affordable with currently available resources

on the LCG For this study about 300k signal events and 27M inclusive For this study about 300k signal events and 27M inclusive

beauty events have been used beauty events have been used


BBhh++h’h’-- s selection cutselection cuts

For each pair of charged For each pair of charged trackstracks we cwe cut onut on max (pT1, pT2) min (pT1, pT2) max (IP1/IP1, IP2/IP2) min (IP1/IP1, IP2/IP2) 2 of common vertex

B0(s)

, K

, KIP

IPIPB L

TheThen, the n, the B candidate isB candidate is selected with cuts onselected with cuts on pT

IP/IP

L/L

Parameters used Parameters used

for selectionfor selection

h,hh,h Smallest pSmallest pttGeV/cGeV/c >> 11

h,hh,h largest plargest pttGeV/cGeV/c >> 33

h,hh,h smallest IP/smallest IP/IPIP>> 66

h,hh,h largest IP/largest IP/IPIP>> 1212

h, hh, h vertex fit vertex fit 22 << 55

BB ppttGeV/cGeV/c >> 11

BB IP/IP/IPIP<< 2.52.5

BB L/L/LL>> 1818


Particle identification p/K/Particle identification p/K/Invariant mass of

selected events (no PID)

PID discriminants built as difference between log likelihoods of particle hypotheses

Efficient hadron PID crucial for the Bh+h’- channels Invariant masses one on top of the other kinematic separation possible but weak

Calibration of K/ PID on data will be performed using the D*+D0+, D0 K+- decay chain Large ”PID unbiased” samples of such D* decays

will be acquired with dedicated D* trigger chain(300 Hz bandwidth) - see talk by Raluca Muresan

K separationfor Bh+h’-

decays at LHCb

For true kaonsFor true pions


Performance of hadron PID: Performance of hadron PID: invariant mass spectrainvariant mass spectra

ππ

hypothesis

πK

hypothesis

KK

hypothesis

pK

hypothesis

pπ

hypothesis

πK

hypothesis

Every hEvery h++h’h’-- channel is potentially a background for the other channels… channel is potentially a background for the other channels… ……but impressive performance of RICH systems allowbut impressive performance of RICH systems allows to select very clean s to select very clean

samplessamples


Nominal mass resolution of =16 MeV/c2 allows for a clean separation between the two signals

Importance of goodImportance of goodmass resolutionmass resolution

Discrimination of Bs π+ K - from Bd K- π+ must rely on mass resolution only since they share exactly the same signature Bd K- π+ about 16 more abundant

4 times larger branching fraction, 4 times large hadronization fraction


Decay rate for BsK+K- events tagged as B at

LHCb(integrated luminosity

L=2fb-1)Δms 20 ps-1 in this simulation, a bit larger than the

truth…

Proper time resolutionProper time resolution

Proper time resolution

(from full GEANT4 simulation)

Excellent proper time resolution Excellent proper time resolution allows to perfectly resolve the fast Ballows to perfectly resolve the fast Bss oscillationsoscillations t = ~40 fs

almost 10 times less than the oscillation period actually

Calibration of proper time resolution Calibration of proper time resolution on data very important to achieve in on data very important to achieve in order not to be dependent on MC order not to be dependent on MC imperfectionsimperfections will be done in LHCb by disentangling

prompt J/+- from non-prompt component from B decays

The prompt component is affected just by the intrinsic resolution of the detector, hence can be used for calibration

“Lifetime unbiased” prompt J/ events will be acquired with dedicated high-mass di-muon trigger (600 Hz bandwidth)

=~~40 fs

Bkg


Selection performance Selection performance summarysummary

Yields are calculated for an integrated luminosity Yields are calculated for an integrated luminosity of 2 fbof 2 fb-1-1

107 seconds at nominal LHCb luminosity

Limited background-to-signal ratiosLimited background-to-signal ratios Both combinatorial and from the other Bh+h’- modes

(due to wrong particle ID

Hundreds of thousands of BHundreds of thousands of Bhh++h’h’-- decays decays triggered, reconstructed and selected per year of triggered, reconstructed and selected per year of running with high degree of purity!running with high degree of purity!

BR 10-6 Yield B/S

spec

B/S

bb

K spectrum selected from a sample of 27M bb MC events

Partially reco BK*+-

BdK+-


Flavour taggingFlavour tagging

DD22==(1-2(1-2))22: tagging power : tagging power

: tagging efficiency: tagging efficiency

: mistag probability : mistag probability

K+

Qvertex, QJet

Same

side

Opposite side

PV

e--

Bs0signal

D

KK

K-B0opposite

Opposite sideOpposite side High pHigh pTT leptons leptons KK±± from b from b → → c c →→ s s Vertex chargeVertex charge Jet chargeJet charge

Same sideSame side Fragmentation KFragmentation K±±

accompanying Baccompanying Bss

±± from B from B** ** → → BB(*)(*)±±

TagTag BBdd BBss

MuonMuon 1.11.1 1.51.5

ElectronElectron 0.390.39 0.690.69

Kaon opp.sideKaon opp.side 2.12.1 2.32.3

Jet/ Vertex ChargeJet/ Vertex Charge 1.01.0 0.970.97

Same side Same side / K / K 0.73 0.73 (())

3.5 (K)3.5 (K)

CombinedCombined 5.055.05 9.59.5

Tagging power in %

Work in continuous progress.See talk on LHCb tagging by Hugo Ruiz


Toy MC generation for CP Toy MC generation for CP sensitivity studiessensitivity studies

A toy MC is used in order to generate large samples of signal and background A toy MC is used in order to generate large samples of signal and background events for estimating sensitivities on CP parameters from time dependent events for estimating sensitivities on CP parameters from time dependent decay rate fitsdecay rate fits

Signal samples generated simulating CP violation, proper time acceptance, Signal samples generated simulating CP violation, proper time acceptance, proper time resolution and taggingproper time resolution and tagging For each event the toy MC generates mass, proper time, tagging response, PID response

according to the results from the full GEANT4 simulations Background mass and proper time spectra generated according to result from Background mass and proper time spectra generated according to result from

the full simulationthe full simulation

5

5

)(1

)()(

t

ttsig

5

5

)(1

)()(

t

tet t

bb

B0 +-

Proper time acceptancewill be calibrated on real data using event by event acceptance functions – studies going on in LHCb

Background proper timewill be well known from real data

using mass sidebands


Maximum likelihood fitMaximum likelihood fit

KK,fA

A

p

q

f

ff

CP sensitivities are then estimated with an extended unbinned maximum CP sensitivities are then estimated with an extended unbinned maximum likelihood fit to the toy MC samplelikelihood fit to the toy MC sample The likelihood fit is performed simultaneously to all the Bhh channels, including tagged and

untagged samples The various channels and background are then separated each-other in the fit by means of the

particle ID observables and invariant mass

In particular, the decay rate for BIn particular, the decay rate for Bdd++-- and B and BssKK++KK-- events tagged as B (q=+1) events tagged as B (q=+1) or B (q=-1) entering the likelihood is given byor B (q=-1) entering the likelihood is given by

The usual C and S coefficientsThe usual C and S coefficientsare related to are related to ff by by

LHCb can reach a sensitivity about 3LHCb can reach a sensitivity about 3times better than the current world averagetimes better than the current world averagein 10in 1077 s of running at nominal luminosity s of running at nominal luminosity

BBdd++-- BBssKK++KK--

(C)(C) 0.043 0.043 (0.10*)(0.10*) 0.0420.042

(S)(S) 0.037 0.037 (0.12*)(0.12*) 0.0440.044

BBddKK++-- BBss++KK--

(A(ACPCP)) 0.003 0.003 (0.015*)(0.015*) 0.020.02

mtsin)(m2mtcos121qt2

sinh)(e2t2

cosh1q,tF f

2

ff

2

f

2

f

ff2

f

2

ff

1

m2S

1

1C

Fit results corresponding to Int. L=2fb-1

(107 seconds at nominal LHCb luminosity)

*Current world average


Tree, penguins and… Tree, penguins and…

ii0 deeKBA

i2

2i

20s ed

1e'K

2/1KKBA

Relating by the U-spin symmetry the two amplitudes one Relating by the U-spin symmetry the two amplitudes one gets gets d=d’d=d’ and and ==’’ Using method and parametrization from

R. Fleischer, PLB 459 (1999) 306

Sensitivity to Sensitivity to from the from the interference of T interference of T and P amplitudesand P amplitudes d, d’: penguin-to-

tree ratios , ’: penguin-tree

strong phase differences

Sensitivity to doubly Cabibbo suppressed in

this mode


Extraction of Extraction of

),,,d(f)KKB(S

),,d(f)KKB(C

),,,d(f)B(S

),,d(f)B(C

s40s

30s

d20d

10d

Once the direct and mixing-induced CP-violating terms are measured, one has a system of 7 unknowns and 4 equations

However, the mixing phase d (s) is (will be) measured from BdJ/KS (BsJ/) 5 unknowns

Finally, relying on U-spin symmetry one eliminates two further unknowns 3 unknowns, system over-constrained, can be extracted unambiguously

2sinhA

2cosh

)Msin(S)Mcos(C)(Ath

CP


Sensitivity on Sensitivity on (for L=2fb(for L=2fb-1-1))

Extraction of Extraction of performed with a Bayesian approach in 3 different performed with a Bayesian approach in 3 different scenarios (in this exercise scenarios (in this exercise =65=65oo is assumed) is assumed) (1) Perfect U-spin symmetry

i.e. using the constraints d=d’ - = ’ (2) Weaker assumption: perfect U-spin symmetry just for d, d’

d=d’ - no constraint on , ’ (3) Even weaker: given U-spin breaking for d, d’

= d’/d = [0.8, 1.2] - no constraint on , ’

1 2 3

Sensitivity ranging from ~4o in case of perfect U-spin assumed, to 7°-10° partially releasing U-spin assumptions (but a secondary fake solution appears)


An exercise: using current world An exercise: using current world averages of Baverages of Bdd++-- and B and BddKK++--

(not using LHCb results)(not using LHCb results) Instead of using the BInstead of using the BssKK++KK-- one can make use of the B one can make use of the BddKK++--

It just differs for the spectator quark, but neglecting penguin annihilation and exchange diagrams which are not present in BdK+-

Assuming U-spin symmetry the cosine term of the time dependent asymmetry of BsK+K- is equal to the charge asymmetry of BdK+-, thus we can replace CKK with AK

However one observable is missing, since SKK is unaccessible, but still can solve system of contraints for Current world averages from HFAGCurrent world averages from HFAG

C = -0.37 ± 0.10 (BaBar/Belle) S = -0.50 ± 0.12 (BaBar/Belle) AK = -0.093 ± 0.015 (BaBar/Belle/CLEO/CDF)

p.d.f. for p.d.f. for obtained allowing for a U- obtained allowing for a U-spin breakingspin breaking = ’- = ±20o

= d’/d = [0.8, 1.2]

p.d.f. for

Unitarity Triangle fits expectation


ConclusionsConclusions LHCb will collect large samples of BLHCb will collect large samples of Bhh++h’h’-- decays decays

Its excellent vertexing and PID capabilities will allow to collect several hundreds of thousands of Bh+h’- events with very high purity

The CP sensitivity reachable in 10The CP sensitivity reachable in 107 7 s of data taking at the nominal LHCb s of data taking at the nominal LHCb luminosity of 2luminosity of 2·10·103232 cm cm-2-2ss-1-1 is estimated to be about 3 times better than is estimated to be about 3 times better than the current world averages from the beauty factories and the Tevatronthe current world averages from the beauty factories and the Tevatron

Besides the general interest of measuring CP violation for these Besides the general interest of measuring CP violation for these channels, especially for the still unmeasured Bchannels, especially for the still unmeasured Bss decays, the B decays, the Bhh++h’h’- -

modes can provide useful information to constrain the CKM angle modes can provide useful information to constrain the CKM angle This is accomplished by relating the Bd and Bs decay modes by means of the U-spin

flavour symmetry Even if the U-spin symmetry will result to be broken to some extent, we have shown

how it is still possibile to extract useful information on in scenarios where the U-spin breaking is taken into account

The extraction of The extraction of from these decays can reveal contributions from New from these decays can reveal contributions from New Physics inside the loops of the penguin diagrams, which contribute Physics inside the loops of the penguin diagrams, which contribute significantly to the Bsignificantly to the Bhh++h’h’-- modes modes obtained from these decay modes might thus be different from from tree level

modes, such as BDK, which can be assumed to be basically free of New Physics contributions

angelo carbone infn bologna (on behalf of the lhcb collaboration) beauty 2006 oxford, uk

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