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LHCb RESULTS

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LHCb RESULTS Introduction B hh CP violation asymmetries EW gauge boson production New b,c spectroscopy and exclusive dimuons Some B rare decays and Majorana neutrinos – PowerPoint PPT presentation

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Title: LHCb RESULTS


1
LHCb RESULTS
  1. Introduction
  2. B? hh CP violation asymmetries
  3. EW gauge boson production
  4. New b,c spectroscopy and exclusive
    dimuons
  5. Some B rare decays and Majorana
    neutrinos

Main LHCb highlights by Guy Wilkinson BSM with
LHCb tomorrow
54 institutions, 15 countries
3 Spanish universities among them
2
The LHCb Apparatus
3
The LHCb Trigger Data acquisition
4
LHCb integrated luminosity
2011 7.0 TeV (1 fb-1 recorded)
High efficieny (lt90) good performance
2010 (37 pb-1 recorded)
5


CP-VIOLATION IN B? hh DECAYS
6
CP violation , the challenge
? Noninvariance of fundamental forces under the
combined action of charge conjugation (C)
and parity (P) transformations is well
established in the K0 and B0 meson
systems 1 ? Recent results from LHCb also
provided evidence of CP violation in the
decays of D0 meson R. Aaij et al. (LHCb
Collaboration) Phys. Rev. Lett. 108, 111602
(2012) ? Yet LHCb has found CP violation in
the only neutral heavy meson that remains,
the Bs R. Aaij et al. (LHCb Collaboration)
Phys. Rev. Lett. 108, 201601 , published 16
May 2012
1 J. H. Christenson, J.W. Cronin, V. L. Fitch,
and R. Turlay, Phys. Rev. Lett. 13, 138 (1964).
B. Aubert et al. (BABAR Collaboration), Phys.
Rev. Lett. 87, 091801 (2001). K. Abe et al.
(Belle Collaboration), Phys. Rev. Lett. 87,
091802 (2001).
7
CP violation , the challenge
? All current experimental measurements of CP
violation in the quark flavor sector are
generally well described by the Kobayashi-Maskawa
mechanism which is embedded in the
framework of the Standard Model (SM) 1 . ?
However, it is believed that the size of CP
violation in the SM is not sufficient
to account for the asymmetry between matter and
antimatter in the Universe 2 . Hence,
additional sources of CP violation are being
searched for as manifestations of physics
beyond the SM.
1 N. Cabibbo, Phys. Rev. Lett. 10, 531
(1963). M. Kobayashi and T. Maskawa, Prog.
Theor. Phys. 49, 652 (1973). 2 W.-S. Hou,
Chin. J. Phys. (Taipei) 47, 134 (2009),
http//psroc.phys.ntu.edu.tw/cjp/download.php?type
fullvol472page134.
8
Charmless Two-Body Decays Bs,d ?h h-
9
Bs,d ?h h- direct CP violation
10
Direct CP-asymmetry in Bs ? K p-
Phys. Rev. Lett. 108, 201601
11
Annihilation Diagrams
12
Effective Bs ?K K- Lifetime
13
Time Dependent B0 ? K p- Fit
14
Time Dependent CP Violation in B0 ? pp-
15
Time Dependent CP Violation in Bs ?K K-
t0 0.95 ps
16
Summary on CPV asymmetries in Bs,d ?h h-
(see Paula Alvarezs talk tomorrow)
17
Measurement of the Ds? Ds- production
asymmetry in 7 TeV pp collisions
LHCb-PAPER-2012-009 May 4, 2012
LHCb has determined the overall production
asymmetry of Ds? mesons produced directly in pp
collisions in the rapidity region 2.0 lt ? lt 4.5
and pT gt 2 GeV
Which is consistent with theoretical expectations
1 and , provides significant constraints on
models of Ds? production, and it is a key input
for CP violation measurements.
M. Chaichian and A. Fridman Phys. Lett. B298
(1993) 218. E. Norrbin and R. Vogt
arXivhep-ph/0003056 E. Norrbin and T. Sjostrand
Eur. Phys. J. C17 (2000) 137.
18
Ds? Ds- production asymmetry results
  • Subtle sources of production asymmetries
  • only c can form a charmed baryon
  • non-independent fragmentation process
  • even interference with S-waves ?
  • are they reduced at central rapidities?

LHCb has reconstructed 771.031 Ds? mesons with 1
fb-1 , using both magnet polarities, and
determined the ?/ ?- detection asymmetries in
(p,pT) to 1 .
Key idea use the ratio of partial/full
reconstructed D? ? ?S? D0 decays . D0 ?
K-??(?-) 3-momentum determined from slow pion
?S? reconstruction
D?
RS
WS
19
Ds? Ds- production asymmetry
Then use reconstructed Ds? ? ??? ? ? K K-
decays to measure the production asymmetry. Note
no significant CP violation in decay is expected
1 being a Cabibbo favoured mode.
Overall production asymmetry AP (-0.33 ? 0.22
(stat.) ? 0.10 (syst.))
1 Y. Grossman, A. L. Kagan, and Y. Nir, Phys.
Rev. D75 (2007) 036008 S. Bergmann and Y. Nir
JHEP 09 (1999) 031.
20


W,Z BOSON PRODUCTION WITH LHCb
21

Electroweak boson production at LHCb
22

EW boson production and PDFs
23

EW boson production ratios
24

W? l? signal
25

Results Z production
26

W production and W/Z ratios
27

Results W- asymmetry
Differential W- asymmetry consistent with NNLO
predictions
Lepton pseudorapidity
28
Combined Electroweak Physics
29
b AND c SPECTROSCOPY
30
B spectroscopy
? Mesons consisting of LIGHT / HEAVY quarks are
an interesting laboratory to study QCD, just
as the hydrogen atom was to understand QED.
? The states with L0 and spin-parity 0- (B) and
1- (B) are well established. But precision
spectroscopy of orbitally excited B states is
still undone. Properties predicted by HQET
(Heavy Quark Effective Field Theory).
Key idea the spin of the heavy quark and the
total spin Jl of the light degrees of freedom
are separately conserved.
31
B spectroscopy
First precision measurement by CDF II
CDF 2009
Phys. Rev. Lett. 102 (2009) 102003.
32
B spectroscopy
How LHCb reconstructs B states


33
B spectroscopy
LHCb preliminary 2011 data, 336 pb-1

First observation
LHCb-CONF-2011-53
B2
B1
B2
B1
B0 ? B?-
B ? B0?
Fit signal 2 BWs for B 2 with fixed mass
difference 45.8 MeV for M(B)-M(B) (PDG) 1 BW for
B1. Fix yield ratio of two B 2 transitions to be
0.93?0.18 Phys. Rev. D64 (2001) 114004. Fix
B1/B2 width to be 0.9?0.2 Phys. Rev. D53(1996)
231. ?(B2) 20.6 ? 2.0 MeV/c2 Background WS
component 2 broad gaussians representing B0
and B1 states
34
B spectroscopy
BS1
BS2
?(BS1) 0.65 ? 0.07 MeV/c2 ?(BS2) 1.85 ?
0.13 MeV/c2


35
B spectroscopy


36
Charmonium-like exotics
37
Charmonium-like exotics
38
Charmonium-like exotics
39
Charmonium-like exotics
40
Charmonium-like exotics
41
Charmonium-like exotics
Physical Review D 85, 091103(R) (2012)
No confirmation of narrow J/?? state X(4140) no
evidence for X(4274)
42
Bc and b-baryons
43
Bc meson mass measurement
44
Bc cross-section
45
Bc ? J/? ? ?- ? mode
46
Bc ? J/? ? ?- ? results
47
Bc ? J/? ? ?- ? production
48
Masses of ? ?b , ?b
LHCb-CONF-2011-060
49
Masses of ? ?b , ?b
LHCb-CONF-2011-060
?bdsb , ?b ssb

50
Production of ?0b ? ?c?- ? ?-
Phys. Rev. D84 (2011) 092001.
Phys. Rev. D84 (2011) 092001.
51
?0b and ?b in D0pK- mode preliminary
52
Observation of excited ?b0 baryons
First observation by LHCb, significance of 4.9 ?
and 10.1?
Appreciable mismatch with respect to existing
relativistic quarks models, reasonable
agreement with large Nc (spin-averaged)
approaches. arXiv1205.3452v1 hep-ex 15 May
2012
53
Measurements of b-hadron masses
Mesons and baryons are colourless objects formed
by quarks and gluons and bound by strong
interaction. Masses can be compared with lattice
QCD calculations.
LHCb has achieved world-best measurements of
the B-meson and baryon masses in exclusive
modes. The momentum is calibrated with J/?? ??-
decays and verified to a relative precision of
2 ? 10-4 using other 2-body decays.
54
Summary on b,c spectroscopy at LHCb
? Bsector
? LHCb has access to the
poorly explored Bsector, and will improve
the knowledge of
their properties and decays
? X,Y,Z states
? First studies of X(3872) and X(4140)
demonstrate potential of LHCb
to explore the exotic meson
sector. Future results on larger data sets.
? Bc studies at LHCb
? Mass and cross section
measured using 2010 data
? First observation of Bc? J/? ?
?- ? (6.8 ?) ? b
baryon studies at LHCb
? Mass and lifetime of ?b0 using 2010
data ?
world best measurement by LHCb
? Masses of ? ?b , ?b measured
using 2011 data
? world best measurement by LHCb
? Productions of ?b0 measured
with various decay modes
? first observation of ?0b ? D0pK-
(6.8 ?) and ?b ? D0pK- (2.6?)

55
FORWARD DIMUONS
56
Central Exclusive Dimuon Production
No backward tracks, two forward tracks, no
identified photon
Relative proportions ?c0 , ?c1, ?c2 very
sensitive to models that can potentially explore
gluon x ? 2 ? 10 -6
?c0, ?c1, ?c2
Previous result by CDF PRL 102 (2009) 242001
Consistent with 42 ? 1 pb (QED)
57
SOME RARE b-DECAYS AND SEARCH FOR MAJORANA
NEUTRINOS
58
Search for B ? ???-
First observation of a b? d ll- decay
Vtd/ Vts supression relative to b? s ll-
not necessarily applies for NP models
5.2 ? significance for B ? ???- signal yield
25.3-6.4 6.7 events, 1 fb-1 integrated
luminosity Normalisation to B ? J/? K
Branching ratio (2.4 ? 0.6 (stat.) ? 0.20
(syst.) ) ? 10-8 in good agreement with SM
expectation 1 (1.96 ? 0.21) ? 10-8
Best published limit lt 6.9 ? 10-8 at 90 CL by
Belle Collaboration Phys. Rev. D78 (2008) 011101
1 S. Hai-Zhen, L. Lin-Xia, and L. Gong-Ru, New
Physics Effects on rare decays B ? ???- and
B ? ???- in a top quark two-higgs-doublet
model, Communications in Theoretical Physics 50
(2008) 696.
59
Search for Bs (B0) ? ? ?- ? ?-
Non-resonant Bs ? 4µ decay highly suppressed in
SM 1 , BR lt 10-10. But may be enhanced by NP due
to FCNC mediated by new particles decaying into
µ µ- pairs 2
LHCb-CONF-2012-010
Using the full 1 fb-1 2011 data sample, in the
non-resonant window after unblinding, one Bs ?
µ µ- µ µ- event and no B0 ? µ µ- µ µ- evts
are observed.
Bs
Expected backgrounds are 0.38-0.17 0.23
(0.30-0.20 0.22 ) for Bs (B0 )
B0 non-resonant window
Seven Bs ? J/? ? events observed in the resonant
window (estimated BR (2.3 ? 0.9) ? 10-8 ))
95 CL upper limits B (Bs ? µ µ- µ µ- ) lt
1.3 ? 10-8 and B (B0 ? µ µ- µ µ- ) lt 5.4 ?
10-9
1 D. Melikhov and N. Nikitin, PRD 70, 114028
(2004) 2 S. Demodov and D. Gorbunov Flavor
violating processes with sgoldstino pair
production, arXiv1112.5230.
60
Search for Majorana neutrinos at LHCb
Searches for Majorana neutrinos in B- decays
(The LHCb Collaboration)
arXiv1201.5600v2 hep-ex 23 Mar 2012
Virtual Majorana neutrino
a)
b)
Resonant neutrino production
c)
Also resonant production
61
Majorana neutrinos B- ? D()?- ?-
a)
B- ? D?-?-
B- ? D?-?-
No signal evidence, background from side
bands BR (B- ? D?-?-) lt 6.9 ? 10-7 95
CL BR (B- ? D?-?-) lt 2.4 ? 10-6 95 CL
1
1 More stringent than previous Belle result ,
Phys. Rev. D84 (2011) 071106
62
Majorana neutrinos B- ? ??- ?-
and B- ? Ds?- ?-
Neutrino on-shell masses (m4) have been
searched for
No signal seen above backgrounds
b)
m4
m4
63
Mass and lifetime acceptance for on-shell
Majorana Neutrinos
Our search has ignored thus far the possibility
of a finite neutrino lifetime. All sensitivity is
lost for lifetimes longer than 10-10s to 10-11s.

(of course this does not apply for virtual
Majoranas)
Mass dependent upper limits on BR
B- ? ??-?-
b)
Neutrino mass acceptance
64
Summary of Majorana neutrinos
b)
  • ? Using B- ? ??-?- , neutrino mass dependent
    upper limits were established
  • on the couplings V?4 of a heavy Majorana N
    to a muon and virtual W using
  • matrix elements from 1.
  • A model dependent calculation 2 was used for
    B- ? D0 ??-?- , but the mode
  • ??-?- is more sensitive.
  • For the B- ? D()?- ?- , upper limits on
    the coupling cannot be extracted until
  • there is theoretical calculation of hadronic
    form factor (as there is for 0??? decay) .

1 A. Atre, T. Han, S. Pascoli, and B. Zhang,
JHEP 05 (2009) 030, arXiv0901.3589. 2 D.
Delepine, G. Lopez Castro, and N. Quintero, Phys.
Rev. D84 (2011) 096011, arXiv1108.6009.
65
Conclusion
  • LHCb has shown powerful performance as a
    forward detector in pp collisions
  • at ?s 7 TeV for precision b and c physics,
    with very good mass and proper
  • time resolution, and excellent K/?
    separation
  • ? observation of asymmetries in forward
    production of EW bosons
  • ? first observation of new resonances and
    decay modes
  • ? great potential for exploring rare decays,
    including lepton flavor violation
  • CP-violation has been observed for the first
    time in D0 and Bs mesons,
  • and a wide range of measurements is forseen,
    with potential new physics
  • discovery, both in CP-violation and very
    rare decays
  • (see G. Wilkinsons talk tomorrow)

66
BACKUP
67
Lifetime distributions B0 and Bs
B0 ? pp-
Bs ?K K-
68
Charm spectroscopy


69
Charm spectroscopy

Feed-down states DJ ?D?(D?D?,D?0)
70
(No Transcript)
71
Lifetime of ?b preliminary
72
Mass of ?b
Phys. Lett. B 708 (2012) 241.
73
Production of ?0b semi-leptonic decays

Phys. Rev. D85 (2012) 032008.
Phys. Lett. B 708 (2012) 241.
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