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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
Angelo Carbone BEAUTY 2006 3
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
Angelo Carbone BEAUTY 2006 4
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--
T+P+PT+P+PCCEWEW+PA+E+PA+E T+P+PT+P+PCC
EWEW
BBssKK++KK-- BBd d KK++--
T+P+PT+P+PCCEWEW+PA+E+PA+E T+P+PT+P+PCC
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
Angelo Carbone BEAUTY 2006 5
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!
Angelo Carbone BEAUTY 2006 6
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
Angelo Carbone BEAUTY 2006 7
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
Angelo Carbone BEAUTY 2006 8
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
Angelo Carbone BEAUTY 2006 9
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
Angelo Carbone BEAUTY 2006 10
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
Angelo Carbone BEAUTY 2006 11
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
Angelo Carbone BEAUTY 2006 12
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+-
Angelo Carbone BEAUTY 2006 13
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
Angelo Carbone BEAUTY 2006 14
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
Angelo Carbone BEAUTY 2006 15
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
Angelo Carbone BEAUTY 2006 16
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
Angelo Carbone BEAUTY 2006 17
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
Angelo Carbone BEAUTY 2006 18
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)
Angelo Carbone BEAUTY 2006 19
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
Angelo Carbone BEAUTY 2006 20
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