LHCb results
description
Transcript of LHCb results
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LHCb resultsHugo Ruiz
On behalf of the LHCb Collaboration
Institut de Ciències del Cosmos
PLANCK‘2011, May-June 2011, Lisboa
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The LHCb physics scope
• ATLAS, CMS: direct search
• LHCb: look for effect of new massive particles in lower energy observables– Many low energy constraints NP will probably show up in loop processes
• New particles can distort the SM (CKM) picture of B decays by modifying:
– Phases CP violation– Amplitudes branching ratios– Lorentz Structure angular distributions
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LHCb: B physics at a pp collider
• And: not too many primary collisions design lumi 2·1032 cm-2s-1
• Signal-background separation:– Invariant mass– Secondary vertices, IP– Particle Id (p-K, etc)
<L> ~ 8 mm
IP
• CP violation studies:
– Event-by-event lifetime– B flavour @ production
Primary pp collision
~ 50 tracks
Signal B
Tagging Bm±K±
K±, p±, m±…
VELORICH
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MUON
CALORICH2
T
MAGNET
RICH1
VELO
TT
LHCb: B physics at a pp collider
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Data taking in 2010 (and 2011)
• CDF&D0 > 6000 pb-1
– But: x-sect (x3), acceptance, trigger, vertex resol., pID, flavour tagging
• LHCb prospects: – 1 fb-1 by end 2011 (2010 x 27)
2010: 42 pb-1 delivered 37 pb-1 collected (±10%) results in this talk
Design lumi since May 1st! But with ¼ of bunches
2011 : 150 pb-1 delivered 130 pb-1 collected
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Vertexing Tracking
Hit residuals
sm(J/ym+m-) = 13.3 MeV
(12.1 in MC)
s(IP
x) tr
ack
(mm
)
stB ~ 60 fs (~40 fs from MC), work in progressoscillation period Bd(Bs) ~12500(350) fs
s(Z)
ver
tex
(mm
)
# tracks
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Particle identification
fK+K- D K+p- from D*
Ksp+p- Lp+p-
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Production & spectroscopy
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Z production (16.5 pb-1)
LHCb-CONF-2011-012
x: fract. of pbeamcarried by colliding partonQ2: squared p transfer in partonic collision
ATLAS CMS
ds/dh
(pb)
hZ
Trigger: pT(m)>10GeV
Main syst: lumi LHCb preliminary
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W production (16.5 pb-1)
W-
W+
• Selection: lepton + global event (ΣM<20GeV, ΣPT<10GeV)
Acceptance of GPDsATLAS, CMS
Trigger: pT(m)>10GeV
LHCb-CONF-2011-012
Z&W data vs models:
LHCb preliminary
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J/y production (5.2 pb-1)
• Interesting: no model describes both dsJ/y/dpT
and J/y polarization from Tevatron
• LHCb: >0.5M J/y’s, no life-time bias @trigger• Measured both in 5 bins of h and 14 of pT
• Prompt and from-B separated using pseudo-lifetime
Eur. Phys. J. C 71 (2011) 1645
One bin!
Prompt J/y production
Main systs: lumi, J/y polarization, etracking
from bOne bin!
prompt
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sbb
• Method 1: from J/y – From “long-lived” component in J/y analysis– Extrapolated to 4p:
spp = 288 ± 4 ± 48 mb
• Method 2: through b→D0(→K-π+)Xμ-ν(uses BRs of B0D*-Xμ+ν D0Yμ+ν, B+ D0Xμ+ν, B0
s Ds*-Xμ+νD0Yμ+ν)
– Extrapolated to 4p:
spp = 284 ± 20 ± 49 mb
• Good agreement between both– though correlated errors: lumi, etracking, etc)
Phys. Lett. B 694 (2010) 209
Main systs: lumi, etracking
Black, violet: 2 subsamples with different triggerRed: combination
Theoretical error
(e.g. mb and μR,F)
Cacciari, et al., NL0 + resum of pT logs to NLO , e.g. hep-ph/9803400
(NLO, MCFM v5.8, Campbell, Ellis)
Eur. Phys. J. C 71 (2011) 1645
Additional syst.: BR(b→J/y X)
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fs/fd
• Required for normalizing new Bs BRs with precisely-measured Bd BRs from B factories, current uncertainty 13%
• Use decays of Bs and B0 with:– Precise theoretical prediction of ratio of BRs – same kinematics cancellation of systematics
LHCb-CONF-2011-013
Same particles in final stateTheo. uncert. 9%
Theo. uncert. 7%
Main syst: BR(Ds+KKp), 5%
B0 D-(K+p-p-)p+B0 D-(K+p-p-)K+ BsDs-(K+K-p-)p +
LHCb preliminary
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Mass of X(3872)• Mass far from expected from conventional charmonium state• Exotic alternatives: D*D0 molecule, tetraquark
Main systs: p scale, E loss correction, TT alignement
LHCb-CONF-2011-021
LHCb preliminary
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Towards CP violation
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CP violation
• Bd sector extensively studied at B factories– CKM is basically OK
• Lacking precise direct measurement of g
•Required modes too rare (B fact. yield 10-4LHCb)•g will provide many new tests of SM
• Bs sector only accessed by Tevatron– Lacking a precise measurement of the Bs mixing phase– Penguins unexplored!
• Some hints of NP:– Like-sign di-m charge asymmetry hints for NP in mixing,
sin2b…
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Direct CP violation in B0/Bs K-p+
LHCb:
LHCb-CONF-2011-11
Bs
Not corrected for det. & prod. asymm.
We had to control potential sources of fake CP violation:• Detector: from many D decays, magnet up & down, using known CP violation
• Production: from B+J/y(m+m-)K- + MC correction for B+B0
Before LHCb
~9σ CP viol. not yet stablished
Bd
LHCb preliminary
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g from tree processes• Time-independent methods: same final state
through crossed D decay (GLW, ADS, GGSZ…)
– Main challenge: BRs in suppressed modes
• Enhancing statistics:
– Measured relative BRs withworld-best precisions!
– Proved we can do physics with 6 track decays
B-D0K-
+p+p-
LHCb-CONF-2011-07
LHCb preliminary
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Flavour tagging & Dmd
• Optimized using real data:
LHCb-CONF-2011-03LHCb-CONF-2011-10
Signal B
Tagging B
PV
lepton (m±, e±)
kaon (K±)
Dx
hadron from fragmentation or B** decay (K±, p±)
Same side (SS)
Opposite side (OS)
vertex charge
Channel eefftag
B0D*-μ+ν 2.87±0.32%
B+J/yK+ 2.38±0.33%
B0J/yK* 2.82±0.87%
Dmd fixed to pdg value
Main systs: z scale, p scale (to 0.1%, due to B, align.)
LHCb preliminary
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Dms• Used 1300 events:
• Fit with event-by-event values of st (36-44 fs) & mistag prob.– eeff
tag = 3.8 ± 2.1 % (OS only)– Mixing signal at 4.6s level
• CDF:• LHCb:
LHCb-CONF-2011-05
LHCb preliminary
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Towards fs with Bs J/yf• Golden channel:
• Acceptances are a key issue, benchmarked by measuring: a) B meson lifetimes b) Polarization amplitudes
Time-unbiased trigger only
Final state combines CP even-odd need to disentangle polariz. amplitudes angular analysis
All consistent with world valuesLHCb-CONF-2011-01 LHCb-CONF-2011-02
st 50 fs
LHCb preliminary LHCb preliminary
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fs: first results from Bs J/yf• 757±28 events (t>0.3ps)• 7D fit (m,t,tag,η,φ,ψ,θ)• No point-estimate yet• Include statistical uncertainty &
systematics from tagging and Δms
– All other systematycs << stat. uncert.
• Comparison with CDF:
Expect world-best fs measurement with 2011 data!
LHCb 36pb-1 CDF 5.2fb-1
Events 750 6500
st (fs) 50 100
OS eefftag (%) 2.2±0.5 1.2±0.2
SS eefftag (%) Not enough
stats to calib. 3.5±1.4
SM
LHCb preliminary
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1st observation of Bs decays
• Bs→J/ψf0(980) (33 pb-1 )– fs (as J/yf), no need for angular analysis
• Bs→K*0K*0
– fs & g through Bs penguin, Bd → fKs
• Bs→D0K*0
– Bckgrd for g from trees from BDK
• Bs→Ds2*(2573)+m-n (20pb-1)
– Start exploration of D reson. in Bs syst.
PLB 698 (2011) 115
LHCb-CONF-2011-019
PLB 698 (2011) 14
LHCb-CONF-2011-08
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Rare B decays
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Bd K*m+m-
• Golden observable:
•LHCb:
–Good data-MC agreement–Expect to be competitive with 300 pb-1
Rarest decay seen: B±K ±m+m- (BR 5 · 10-7)
BR 10-6
Useful to test SM prediction of BR(BKee) / BR(K Kmm)
Nσ = 5.5
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B0/Bs m+m-
• Double suppression: FCNC & helicity• Precise SM prediction:
Bsμ+μ- = (3.2±0.2)×10-9
B0μ+μ- = (1.0±0.1)×10-10
A.J.Buras, arXiv:1012.1447, E.Gamiz et al. Phys.Rev.D 80 (2009) 014503
• Sensitive to NP in scalar/pseudo-scalar sector: MSSM, large tanβ approximation
BR(Bs,dμ+μ- ) ∝ tan6β/M4A
• Results are competitive with world bests:
Phys. Lett. B 699 (2011) 330
BR(Bs→μμ) < 4.3 (5.6)×10-8 at 90% (95%) CLCDF BR(Bs→μμ) < 4.3×10-8 at 95% CL
3.7 fb-1 Public note 9892 (2009)D0 BR(Bs→μμ) < 5.1×10-8 at 95% CL
6.1 fb-1 Phys. Lett. B 693 (2010)
BR(B0→μμ) < 1.2 (1.5)×10-8 at 90% (95%) CLCDF BR(Bd→μμ)<0.76×10-8 at 95% CL
3.7 fb-1 Public note 9892 (2009)
Bs m+m-
B0 m+m-
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Bs m+m-: prospects
LHCb will either find signs of NP orexclude large regions of SUSY parameters with 2010/11 data
NUMH1 (O. Buchmuller et al, EPJ C64 (2009))
Compatible regions
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Conclusions• LHCb has successfully:
– Started exploration of terra incognita:• Proton PDFs• Flavour production• Spectroscopy• Bs and Bd BRs
– Produced world-class measurements• Dms
• Limits on BR(Bmm)– Demonstrated its capability to find NP with 2010/11 data:
• g• fs
• BR(Bmm)• B0K*mm• ...
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Back-up
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U production
CMSLHCb
Main systs: etrigger, U polariz.
Um+m-
LHCb-CONF-2011-017
• Interesting for QCD because heavy-quark state, challenging because fc 0.2 %
• Total of 2.2K candidates (in 3 modes) from Tevatron
• 43±13 in LHCb…
Bc±J/yp ±
Bc+ production
Main systs: Bc
± lifetime
LHCb-CONF-2011-016
• In addition: double J/y
LHCb-CONF-2011-009
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1st observation of Cabibbo-suppressed decays
• BR’s measured relative to Cabibbo-favoured modes:
LHCb-CONF-2011-24
Expect dg/g 5 with 2011/12 data
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Rare decays• Interesting decays at the limit of statistical reach of B factories
and Tevatron• Some examples:
BsfgBR NP affects:
Right-handed operators g polarization CP viol. in mixing appears
Bsm+m-TeVatron @90%CL (2fb1)
< 4510-9
SM: dBR/BR 10% sensitive to new scalar & pseudoscalar interactions
MSSM: BR tan6β/MA4
5·10-5
g gZ, Z,m+
m-
m+
m-
m+
m-t
B0K*m+m- 10-6Angular distributions sensitive to several new operators
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Branching ratios Production studies
• B factories @ U(4s) measured Bd BRs with precisions 2.5-5%– Could count numbers of produced B
• At Tevatron, LHC: non-straight-forward production mechanisms use B-factory measured BRs for nomalization
• To normalize Bs using Bd one needs ratio of b quarks hadronizing to Bs over Bd (fs/fd)– CDF (La Thuile 2011): fs/fd = 0.269 ±
0.033– HFAG (ALL): fs/fd = 0.270 ± 0.034
13% relative error
• h coverage complementary to that of ATLAS and CMS
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Running conditions
• LHCb prefers moderate luminosity to avoid multiple pp interactions / crossing– They complicate handling of secondary vertices
• 2010 and 2011 conditions far beyond nominal:
Design
m
# in
tera
ction
s/cr
ossin
g
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D0 flavor-specific asymmetry
• Inclusive method not fit for LHC, with expected production asymmetry 1%.
• Solution: measure difference, where this and other effects cancel
D0
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Fragmentation functions: semileptonic 3pb-1
• Uncertainties:• Branching ratio BR(Ds)
• Bs detection eff• BR(Bs→D0KXμν)• Tracking, PID, Trigger efficiency
Updated results expected soon
D0
D+
Ds+
N(D0) from b: 28474±190
N(D+) from b: 9406±105
N(Ds+) from b: 2208±61
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fs at Tevatron