Giovanni Carboni Università degli studi di Roma “Tor Vergata” and INFN
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Transcript of Giovanni Carboni Università degli studi di Roma “Tor Vergata” and INFN
G. Carboni Spin 2012 Praha – Status of LHCb 1
Giovanni Carboni
Università degli studi di Roma “Tor Vergata” and INFN
On behalf of the LHCb Collaboration
Status of LHCb and recent results
2/7/20102
Symmetries and SpinPraha 2012
Charles University
22/7/20102
Outline of this talk
• Introduction• Detector performances• Selected physics results
• New states & decays• CP violation in b and c sectors• Rare decays• Electroweak
• Summary and outlook
Other LHCb Talks P. Naik Amplitude analysis for CP violation studies in LHCb I. Machikhiliyan Production and polarisation measurements in LHCb M. Ferro-Luzzi LHCb upgrade A. Shires Rare decays in LHCb
G. Carboni Spin 2012 Praha – Status of LHCb
The LHCb experiment
Aspen 2012 – Stefano de Capua New results from LHCb 3/17
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> 800 members59 institutes16 countries
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ComplementarityIn the search for New Physics Beyond the Standard Model the LHCb approach is complementary to the direct one of ATLAS and CMS If NP exists at the TeV scale its effects could be observed in decaysand CP asymmetries at much lower energies
This requires several high-precision tests of the SM and of the CKM framework we use to describe CP violation
• chart the known territory more accurately • explore new regions
Standard Model
t
s
s
Bs decay: “Penguin” diagram
W
W
W
b
B s
0
t
t
Bs–Bs oscillations: “Box” diagram
–
msSM |Vts
2|,s
SM = –arg(Vts2) = 2s
s
b
Bs0
s
s
s
b
Bs0
s
Strengths of indirect approach
Can access higher scales and therefore see effect earlier:— K0 mixing and decay hints to c-quark prediction (GIM, 1973)— Third quark family inferred by Kobayashi and Maskawa (1973) to explain
small CP violation measured in kaon mixing (1964), but only directly observed in 1977 (b) and 1995 (t)
— Neutral currents (+N +N) discovered in 1973, but real Z discovered in 1983
— B0 mixing (1987) hints to large t-quaks mass Can access the phases of the new couplings:
— NP at TeV scale must have a “flavor structure” to provide the suppression mechanism for already observed FCNC processes once NP is discovered, it is important to measure this structure (including new phases)
New Physics
? ???
ms s
? ?
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The LHCb Experiment
The LHCb Forward spectrometer layout efficiently exploits the large production cross-section for b-anti b pairs in the forward direction (2 < h < 5) at moderate PT
b 3.11.5 41)( uBTeV7@ s
within acceptancedoi:10.1007/JHEP04(2012)093 unprecedented number
of reconstructable b-hadronscreated per year
democratic production:mesons, baryons, charmedparticles
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Detector highlights• Excellent Impact Parameter (IP) and Vertex Resolution
• Si Vertex Locator (VELO) inside LHC beam pipe (8 mm from beam)
• Superior mass resolution • dipolar magnetic field (4 Tm)• high spatial accuracy of tracking• precise spatial alignment
• Particle identification• hadrons• muons • electrons
• powerful trigger• highly configurable• large rejection power
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The LHCb Detector
Forward Spectrometer
• Angular acceptance :15<θ<300 mrad
• Nominal luminosity:L = 4 x 1032cm-2s-1
(design 2 x 1032cm-2s-1)
Ds
Bs K
K
K
d≈1 cm
47 m 4 mPrimary vertex
Example
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• Silicon strip detector• 21 stations • Each station measures R and
Phi• Left-Right staggered in Z to
allow for overlapRetractable by ± 2.9 cm during injection
p
p
-sensors r-sensors
• 10o-20o stereo angle• Inner and outer region• 2048 strips• Pitch: 35 to 100 µm
• 4x45o sectors• 2048 strips• Pitch: 40 to 100 µm
42 mm
8 mm
3578
39
97 umpitch
~1m
Vertexing in the VELO
2/7/20102
[CO
NF-2012-002]
Prompt J/y Bs J/y
Impact parameter resolution ~ 20 mProper-time resolution: t = 45 fscf CDF: t = 87 fs [PRL 97 242003] [PRL 97 242003]
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Tracking SystemSilicon + Straw TubesTT + 3 stations (T1,T2,T3) each with 4 stereo planes (0o,+5o,-5o,0o)
OT
T1T2
T3
TT
IT
Inner Tracker~0.5 m2 around beam pipe (130k ch)
Trigger Tracker~1.41.2 m2
(144k ch)
TT: 128 Modules(7 Si sensors)
IT: ladders with 1 or 2 sensors
Similar sensors for TT & IT:Si µ-strip with pitch ~ 200 µm
Outer TrackerStraw Tubes(56 k ch)Pitch 5.25 mmLength 2.4 ~ 4.9 m
dp/p = 0.4-0.6 %
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Excellent resolution + calibration of the mass scale
(dp/p)scale = 0.02 %
t> 0.3 ps
PLB 708 (2012) 241
σm = 9.0 ± 0.6 MeV/c2 σm = 7.0 ± 0.3 MeV/c2
Bs J/ψ φΛb J/ψ Λ
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ECAL: Shashlik Pb-scintillator (E)/E = 10% /√E 1%HCAL: Tile Fe-scintillator allows triggering on hadronic final statesMuon system: 5 stations MWPCs+3-GEM Fe filters
Bs→ g
Preshower
Lead and SPD
HCAL ECAL
MUON570
candidates
y(2S)and X(3872) →
Calorimeter and Muon Detectors
EPJC (2012) 72:1972
RICH2
23/08/2010G. Carboni HCP 2010 Toronto – Status of LHCb 14
Unique to LHCb: 2 RICH Detectors – 3 Radiators
RICH1196 HPDRICH2
288 HPD
HPD Readout83 mm 1024 Pixels
New this year: gas-tight box for aerogelto avoid contamination by C4F10 gas
2 < p < 100 GeV/ccoverage
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The LHCb Trigger
4.5 kHz
L0 e, g
40 MHz
1 MHz
L0 had
L0
ECALAlley
Had.Alley
Global reconstruction
30 kHz
MuonAlley
Inclusive selections:topological, ,
+track, ,D→X, ΦExclusive selections
Level-0
HLT1
HLT2
‘High-pt’ signals in calorimeter & muonsystems
Associate L0 signals withtracks, especially thosein VELO displaced from PV
Full detector information available.Global reconstruction similar tooffline (nclusive and exclusive).
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Triggering is a challenge! ~1/100 events contain
b interesting b branching
fractions ~10-3 or less
storage
Farm with 19000 CPUcoresHLT efficiency> 80%
Overall typical L0xHLT efficiency:30% (multibody hadron decays) to 90% (dimuons)
O(1010)events/y
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Data taking in 2012 running conditions: L = 4 1032 cm-2 s-1
L0 trigger 1 MHz saturating the bandwidth deferred HLT trigger (10% gain) magnet polarity regularly reversed (systematics!) tilted beam-crossing plane (systematics!)
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Periodical magnetic field reversal crucial to keep systematic asymmetries under control
PLB 713 (2012) 186
)%10.022.033.0( PAasymmetry production ss DD
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Flavor tagging
Important for oscillations and CP violation measurements
same side, uses or K emitted together with signal b-hadron
opposite side, detects flavor of partner b-hadron from decay
ϵeff =ϵtag(1-2ω)2=ϵtag D2
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Example: Same-Side K vs. Opposite Side tagging in B0s D-
s
SSK only ϵeff =(1.3±0.4)% OS only ϵeff =(3.2±0.8)%
Calibration performed using several self-tagging control channels EPJC (2012) 72:2022
LHCB
-CON
F-20
11-0
50
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2012
1.5 fb-1 goal for 2012
Integrated L in 2011 @ 7 TeV, 2012 @ 8 TeV
Excellent data taking performance
In 2012 larger physics
yield expected
(8 TeV vs. 7 TeV)
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LHC performanceLong fills with ~ 50 % time in stable beam.
• Thursday only bad day.
• Monday game over at 1pm: 90 m run/MD starting
New filling scheme from Fill 2734 on Friday (lost some bunches)
ATLAS, CMS, LHCb Luminosities
Automatic luminosity leveling
stable beams VELO close: 4 min stable beams L = 4 1032 cm-2 s-1: 7 min
Example week 24this year
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Physics results
Impossible to list all measurements
I will try to give a panoramic view, with emphasis on the capabilities of the experiment
For more details on quarkonia, CP violationin Bs and rare decays refer to dedicated talks.
58 physics publications to date, more in pipeline> 80 preliminary results submitted as Conference Papers
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Best measurements of B0s and Λ0
b masses
PDG
PLB 708 (2012) 241
Precision measurements
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Penguins
ss KJB y/0
important to evaluate the penguincontribution to the measurementof sin2 in B0 J/ψ Ks from future CPV measurement in B0
s J/ψ Ks
Most precise determination of the B0s J/ψ Ks branching fraction
In agreement with SU(3) expectations
0.42 fb-1
arXiv:1205:0934PLB (2012) in press
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Some firsts
test of QCD predictions
PRL 108, 251802 (2012)
0.8 fb-1
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Two new excited b-baryons
Ʌb*0 Ʌb
0
Ʌb0 Ʌc
predicted by quark modelJP = 1/2- , 3/2-
4.9 σ 10.1 σarXiv:1205.3452
Talk by I. Machikhiliyan
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Never seen before. B+ K++ (4.8 ± 0.4) 10-7 PDG
BELLE limit B < 6.9 10-8 (90% CL) with 8 108 B-antiB pairsSM prediction (1.96 ± 0.21) 10-8 (*)1.0 fb-1 usedAnalysis uses Boosted Decision Tree (BDT)
kinematics, vertex quality, track quality trained on simulated signal sample and bkgd from data PID selection applied separately vetos on B+ J/ψ (ψ(2S)) K+
(*) H.-Z.Song et al., Comm. Th. Phys. 50 (2008)
More penguins
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• Use B+→ J/ψ K+ events to define signal shape and, under π+μ+μ- hypothesis, shape of mis-identified events• Components for partial reconstructed B decays and combinatorial bkgd• Validate by separating B+→J/ψK+ and B+→J/ψπ+ decays
Fitting
5.2events 3.25 7.6
4.6
Preliminary: B (B+ ++-)= (2.4±0.6(stat)±0.2(syst)) 10-
8
LHCb-CONF-2012-006
dbFirst
transitionever observed
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still penguins: B0 K0*+–
Interference of the two diagramsPossible NP contributions
crossing measured 1st time 421.1
3.120 /GeV 9.4 cq
earlier hints at possible discrepancies not confirmed consistent with SM prediction
900 events @1 fb-1:larger than previousworld total!
LHCb-CONF-2012-008
Talk by A. Shires
PRELIMINARY
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I’VE NEVER SEEN A FEYNMAN DIAGRAM THAT LOOKS LIKE
YOU!
WHY THE HELL YOU CALL THEM PENGUIN
DIAGRAMS? THEY DON’T LOOK LIKE
PENGUINS
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Double charm production Higher order QCD
process?
Intrinsic charm?
Double Parton Scattering?
J/ψ pairs previously seen in NA3 (FT) in 1982
Talk by I. Machikhiliyan
A. Szczurek arXiv:1206.0274
33
• Standard simple selection of single J/y candidates in the +- decay mode.
• Background from 2 J/y produced in different pile-up collisions or in the decay of a B hadron removed requiring the 2 J/y come from a common vertex.
nb 1.10.11.5// yy JJ
Theoretical expectations in LHCb acceptance
LO CSM with Single Parton Scattering (including feeddown from y(2S)): 4.1 ± 1.2 nb. [A. V. Berezhnoy et al., Phys. Rev. D84 (2011) 094023]
Contribution from Double Parton scattering: 2 ± 1 nb [A. Novoselov, arXiv:1106.2184]
J/ψ pairs
PLB 707 (2012) 52
arXiv:1205.0975
34
• Combine hadron, with vertex requirement to remove contamination from pile-up and B hadron decays.
J/yD0 J/yD+
J/yDs+
J/yLc+
J/ψ + open charmopen charm pairs
D0 D0 D0 D+
D0 Ds+ D0 Lc
+
arXiv:1205.0975
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CP Violation
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First evidence (3.3) of CP violation in Bs
0080080270sum/)]()([ 00...KBKBA ssCP
PRL 108, 201601 (2012)
008001100880sum/)]()([ 00...KBKBACP
Most precise single measurement
byproduct
0
sB 0sBBs → K Bs → K
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CP violation in Bs mixing
Small SM phase, good place to look for NP effects
Phys. Rev. D84 (2011) 033005,
More in talk by P. Naik
0016.00015.0*
*
0363.0arg22
cbcs
tbtsDM
SMs VV
VV
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PRL 108, 101803 (2012)
Two-fold ambiguity ΔΓs -ΔΓs resolved by measuring ΔΓs
0.37 fb-1
8500 candidates
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Latest combined measurements of
Preliminary combined result using 1 fb-1
ϕs = -0.002 ± 0.083 ± 0.027 rad
LHCb-CONF-2012-002
still statistics dominatedroom for improvement
Details in Talk by P. Naik
arXiv:1204.5675 ϕs from Bs J/ψ φ 21200 evs. ϕs from Bs J/ψ f0(980) and J/ψ f0(1370) 7400 evs ΔΓs = ΓL-ΓH = 0.116 ± 0.018 ± 0.006 ps-1
CDF finds consistent result with11000 decays
(CDF Note 10778)
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Towards the g measurement
KKD ,0 CP mode
ADS mode
5.8 σ CP asymmetry observed 1 fb-1
KD 0 KD 0
PLB 712, (2012), 203
More in Talk by P. Naik
B+ [+K-]DK+B- [-K+]DK-
B- [-K+]Dπ- B+ [+K-]Dπ+
[Phys. Rev. D, 63 (2001), p. 036005]
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D0 mixing now established at % level
CP Violation expected to be small in SM since relevantdiagrams are dominated by the two first generations
Indirect CP Violation (in mixing) expected to be universal and of O(10-4)
Direct CPV expected to be negligible in Cabibbo-
allowed decays
up to O(10-3) in Single-Cabibbo-suppressed decays
CP in charm sector
LHCb-PAPER-2012-006
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Huge statistics available
)()()()()( *raw
DAAfAfAfA PsDDCP
Detector and production asymmetries cancel in the difference)()( rawraw
AKKAACP
use s charge to tag D0/D0
or KKf
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Lots of recent theory papers on the subject motivated by the ACP measurement.
However new calculations suggest that large hadronic enhancements in the SM could account for the result (e.g J. Brod et al., arXiv:1111.5000).
Stay tuned for more data…
0.62 fb-1zero CPV excludedat 3.5 σ level
ΔaCPdir = (−0.656 ± 0.154 )%
PRL 108, 111602 (2012)
world average result
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Bs +–
• Bs strongly suppressed in SMPredicted BR = (3.2 ± 0.2) 109 *
very sensitive to new physics• Analysis based on multivariate estimator
(BDT, combining vertex and geometrical information) & dimuon mass M
At the moment not enough candidates to provide significant measurement of BR
• World-best limit set:BR < 4.5 × 10-9 (at 95% CL)cf < 7.7 × 10-9 (CMS arXiv:1203.3976) < 22 × 10-9 (ATLAS CONF-2012-010)
• Large enhancement of BR relative to SM expectation is ruled out
PRL 108, 231801 (2012)
Talk by A. Shires
(arXiv:1005.5310)
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• LHCb results provide strong constraints on possible models for new physicsComplementary to the direct searches at ATLAS/CMS
• Recent examples: limit on Bs constraining SUSY at high tan and combination of Bs and s restricting various models: [D. Straub, arXiv:1107.0266[N. Mahmoudi, Moriond QCD]
(s)
Direct exclusion(CMS 4.4 fb-1)
B s
(LHCb 1 fb-
1 )
Impact of LHCb measurements
2/7/20102
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W & Z
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2.7 TeV/c Z0: probably the fastest ever made (by man)
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W and Z physics in the forward region has unique characteristics
one parton at high, one at low Bjorken-x
LHCb uniquely probes PDF down to x ~ 810-6
Q2 defined by +- mass
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Z μ+μ-
37 pb-1arXiv:1204.620accepted by JHEP
W μ ν
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Cross-section measurements
LHCb-CONF-2012-011
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LHCb-PAPER-2012-008
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Z + jet production
LHCb-CONF-2012-016
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ConclusionsLHCb is in great shape
The detector is more than 99% operational and routinely working at x2 its design luminosity
• today more than 1.6 fb-1 on disk– Improved on Tevatron and B-factories
spectroscopy, masses, lifetimes– Several world-best meaurements
s, ms, Bs → μμ, s etc.– Settled the Bs→J/ψϕ, Bd→K*μμ anomalies– CPV established in charm– Not only CP and rare ecays: also EW, quarkonia, exotic states
• strong constraints on NP in the flavor sector• possible hints of NP require further study (2012 and
beyond)
Upgrade in preparation for 2018: 10x yields, software trigger talk by Max Ferro-Luzzi
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...stay tuned!