The LHCb Online System Design, Implementation, Performance, Plans
LHCb status and plans
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Transcript of LHCb status and plans
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1. LHCb status2. Physics highlights3. Plans
Roger Forty (CERN)on behalf of the LHCb Collaboration
Physics at the LHC, Vancouver, 4–9 June 2012
LHCb status and plans
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LHCb status and plans 2
• LHCb is the dedicated flavour physics experiment at the LHC• ATLAS & CMS search for the direct production of new states
LHCb is designed to see their indirect effect on charm and beauty decays via virtual production in loop diagrams:
• Such an indirect approach can be very powerful: e.g. B0–B0 mixing discovered at ARGUS (1987) → top quark unexpectedly heavy: m(t) > 50 GeV/c2
• Key topics for LHCb include: to check whether CP violation is due to a single phase in the quark mixing (CKM) matrix, as in the Standard ModelStudy rare decays: FCNC decays (e.g. Bs → m+m-) are strongly suppressed in SM, may be enhanced by Supersymmetry, or other new physics
Roger Forty
1. LHCb status
e+e- (4S) B0B0
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LHCb status and plans 3Roger Forty
Forward spectrometer
p p
10 – 300 mrad
[PYTHIA]
[CONF-2010-013]
Marco Adinolfi
See talk of
• Forward-peaked B production → LHCb is a forward spectrometer (operating in collider mode)
• bb cross-section = 284 ± 53 mb at the LHC (s = 7 TeV) [PLB 694 209]
→ ~ 100,000 bb pairs produced/second (104 B factories) Charm production factor ~20 higher!
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LHCb status and plans 4
Advantages
Roger Forty
[arXiv:1204.0079]
Lb*
Bc+
[arXiv:1205.3452]
B+ p+m+m-
[CO
NF-2012-006]
[CO
NF-2011-039]
ATLAS/CMSLHCb
W± charge asymmetry vs h
William Barter & Marianna Fontana
• Enormous production rate have overtaken B factories even for B0 and B+ decays– BR (B+ p+m+m-) = (2.4 ± 0.6stat ± 0.2sys) ×10-8
Previous limit < 6.9 × 10-8 (Belle PRD 78 011101)
Rarest B decay ever observed!• All b-hadron species are produced at the
high energy of the LHC – New states discovered
e.g. Lb*(5912/5920) orbitally-excited states
– New decay modes discovered e.g. Bc
+ J/y p+p-p+
– Bs physics is rich and little explored
• Large boost: B decay lengths ~ O (1 cm)• Complementary coverage for other physics
– Electroweak, QCD, exotics, …
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LHCb status and plans 5Roger Forty
Collaboration804
55
Added since PLHC-2011: Birmingham, Cincinnati, Lahore, Rostock
VELOMagnetMuondetector
Calorimeters
RICH
Tracker
16
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LHCb status and plans 6
• Dipole magnet, polarity regularly switched to cancel systematic effects
• New this year: beam optics changed to decouple crossing angles from LHC (V) and spectrometer magnet (H)
• Momentum resolution:Dp/p = 0.4 – 0.6 % (5–100 GeV/c)
Tracking performance
Roger Forty
Bs J/y fBeam optics at interaction point
s(mB) = 8 MeV/c2
cf ~ 16 MeV/c2 [CMS DPS-2010-040] 22 MeV/c2 [ATLAS CONF-2011-050]
[CO
NF-2012-002]
Real data!
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LHCb status and plans 7Roger Forty
Vertex detection[C
ON
F-2012-002]
Prompt J/y Bs J/y f
Beam
r
z
• VELO (Vertex Locator)21 modules of r-f silicon sensor disksRetracted for safety during beam injection
• Reconstructed beam-gas vertices (used for luminosity measurement)
• Impact parameter resolution ~ 20 mmProper-time resolution: st = 45 fscf CDF: st = 87 fs [PRL 97 242003]
VELO sensors
7 mm[PLB
693 69]Beam 2Beam 1
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RICH-1: dual radiator
Roger Forty
Particle identification• Charged hadrons identified with two
Ring-imaging Cherenkov detectors covering 2 < p < 100 GeV/c
• Hybrid Photon Detectors (HPDs) 500 tubes each with 1024 pixelsHigh efficiency, low noise
• New this year: gas-tight box for aerogelto avoid contamination by C4F10 gas
eKK > 90% for epK < 5%
Allows strong suppression ofcombinatorial background inhadronic decays e.g. f K+K-
RICH-1: dual radiator
Without RICH
With RICH
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LHCb status and plans 9Roger Forty
Calorimeters + Muon• ECAL: Shashlik Pb-scintillator
s(E)/E = 10% /√E 1%• HCAL: Tile Fe-scintillator
allows triggering on hadronic final states• Muon system: 5 stations MWPCs/Fe
[arXiv:1202.6267]
Giacomo Graziani
[arXiv: 1202.6579]
m+m-
Bs → f g
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LHCb status and plans 10
• Nominal LHCb luminosity = 2 × 1032 cm-2 s-1
Precision physics depending on vertex structure:easier in a low-pileup environment
• Continuous (automatic) adjustment of offset of colliding beams allows luminosity to be levelledThanks to LHC team for excellent collaboration!
• Data taken with high efficiency > 90%Offline data quality rejects < 1%Detectors all with > 98% active channels
Roger Forty
Data takingLHCb
pp collisions/crossing (25ns)
2011 was a fantastic year! L dt = 1 fb-
1 (used for most results shown here) ~ 30 × more data than at PLHC-2011Data taking in 2012 at 4 × 1032 cm-2 s-1 ~ 0.4 fb-1 integrated so far
20112012
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• Trigger in two steps: Level-0 in hardware pT of e, m, and hadron (thresholds ~ 1–3 GeV) reduce rate to 1 MHz
• Then all detectors read out into large CPU farm (~1500 servers) High Level Trigger in software
• New this year: – Output rate increased to 4.5 kHz to provide
data sample for analysis during shutdown (events are relatively small ~ 60 kB)
– Deferred triggering: fraction of events writtento local storage of CPUs and processed during inter-fill gap ~10% increase in effective power
• O(1010) events recorded per year: centralized “stripping” selection to reduce to samples of < ~107 events for individual analysis: ~ 800 selections!
Roger Forty
Data processing
4.5 kHzStorage
Detector Output rate of single server vs time
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2. Physics highlights
Roger Forty
Miriam Calvo Gomez
• 56 physics publications to date, more in pipeline> 80 preliminary results submitted as Conference Papers [LHCb-CONF-xxx]
all available at www.cern.ch/lhcb • Can only give a selective taste of LHCb’s physics output
— for the full feast see the contributed talks and posters
• Tagging of production flavour (B/B) important for mixing & CP analysesPerformance calibrated using control channels such as B+→ J/y K+
• Tagging power: eeff = e (1-w)2 determined from mixing signals
• eeff = (3.2 ± 0.8) % (Opposite side)(1.3 ± 0.4) % (Same side) [CONF-2011-050]
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LHCb status and plans 13
Right-sign
Roger Forty
Particle-antiparticle mixing
B0
D0
Wrong-sign
Bs0 [CONF-2011-050][arXiv:1202.4979]
[CONF-2011-029]
B0 D*-m+n
• Studied for all neutral mesons B0 : now well-established• Bs
0 : studied using Bs0 Ds
+ p- decays
Dms = 17.725 ± 0.041 ± 0.026 ps-1 (world-best) cf : 17.77 ± 0.10 ± 0.07 ps-1 (CDF PRL 97 242003)
• D0 : “wrong-sign” decays D0 K+p- measured Time-dependent analysis in progress to separate mixing from DCS contribution
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• Phase of B0 mixing is well known: sin 2b = 0.67 ± 0.02 [PDG]
• Analogous phase in the Bs system is denoted fs Expected to be very small, precisely predicted: fs = -0.036 ± 0.002 rad (SM)
• First Tevatron results hinted at large value (discrepancy with SM up to ~3 s)• Golden mode for this study is Bs J/y f
• VV final state: mixture of CP-odd and -even components separated using angular analysis
Roger Forty
CP violation
[LHCb-CONF-2012-002]
Olivier Leroy
Transversity angle distributions [CONF-2012-002]
CP-evenCP-odd
[arXiv:1106.4041]
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LHCb status and plans 15Roger Forty
Results correlated with DGs = width difference of the Bs mass-eigenstates plotted as contours in (fs vs DGs) plane
Ambiguous solution excluded by study of phase vs KK mass
CPV in Bs mixing Sean Benson
[CONF-2012-002]
SM
Result presented at PLHC-2011[arXiv:1202.4717]
Update with 10 × data
• LHCb result consistent with Standard ModelFirst significant direct measurement of DGs = 0.116 ± 0.018 ± 0.006 ps-1
• fs also measured in a second mode: Bs J/y f0 Combined result: fs = -0.002 ± 0.083 ± 0.027 radStill room for new physics: increased precision required!
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LHCb status and plans Roger Forty 16
CPV in B decays[PR
L 108 201601]
0.011
B0 → K+ p- B0 → K- p+
Daniel Johnson
• Using the particle ID capability of LHCb, can isolate clean samples of the various decays that contribute to 2-body B → h+h- (h = p, K, p)
• B0 → K+p-: direct CP violation (in decay) clearly visible in raw distributions
• Corrections required for detector and production asymmetriescontrolled using D0 → K-p+, B0 → J/y K*0 samples: percent-level effectsACP = G(B0 → K- p+) – G(B0 → K+ p-) / sum = -0.088 ± 0.011 ± 0.008
in good agreement with world average: -0.098 ± 0.012
Bs → p+ K- Bs → p- K+
• Adjusting the selection to enhance the Bs → p+ K- contribution
ACP (Bs → p+ K-) = 0.27 ± 0.08 ± 0.02
→ First 3 s evidence for CP asymmetry in Bs decays
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LHCb status and plans 17
• Bs m+m- strongly suppressed in SMPredicted BR = (3.2 ± 0.2) 10-9 *
very sensitive to new physics• Analysis based on multivariate estimator
(BDT, combining vertex and geometrical information) & dimuon mass Mmm
• Their distributions calibrated using data: B → hh and dimuon resonances
• 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)
• Sensitivity (slightly) greater than CMS from 5 less integrated luminosity* Experimental BR is time-integrated, so prediction should be scaled by ×1.1 for comparison [arXiv:1204.1737]
Roger Forty
Mmm in sensitive region of BDT
Rare decays
[arXiv:1203.4493]
Setting limit on BR
Mitesh Patel
Cosme Adrover
[JHEP 1010 009]Bs m+m- candidate
mmm = 5.357 GeV, BDT = 0.90, Decay length = 11.5 mmTracks shown for pT > 0.5 GeV
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LHCb status and plans 18Roger Forty
Mmm in sensitive region of BDT
Rare decays
[arXiv:1203.4493]
Setting limit on BR
Mitesh Patel
Cosme Adrover
• Bs m+m- strongly suppressed in SMPredicted BR = (3.2 ± 0.2) 10-9 *
very sensitive to new physics• Analysis based on multivariate estimator
(BDT, combining vertex and geometrical information) & dimuon mass Mmm
• Not enough candidates to providesignificant 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 * Experimental BR is time-integrated, so prediction should be scaled by ×1.1 for comparison [arXiv:1204.1737]
[JHEP 1010 009]
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LHCb status and plans 19
[CONF-2012-008]
SM
[arXiv:1101.0470]
Roger Forty
B0 K*m+m- Cosme Adrover
-1.3
• Rare decay viab → s penguin:
• Forward-backward asymmetry sensitive to modification of the helicity structurePrevious results hinted at discrepancy
• LHCb has largest sample in the world: 900 events, as clean as the B factories!
• Zero-crossing point precisely predictedq2 (AFB= 0) = 4.0 – 4.3 GeV2/c4
• First measurement: 4.9 +1.1 GeV2/c4
Earlier discrepancies not confirmed• However, evidence seen for different BR
between B+ K+mm & B0 K0mm modes ( Additional slides)
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LHCb status and plans 20
• LHCb results provide strong constraints on possible models for new physicsComplementary to the direct searches at ATLAS/CMS
• Recent examples: limit on Bs m+m- constraining SUSY at high tan band combination of Bs m+m- and fs restricting various models:
Roger Forty
[D. Straub, arXiv:1107.0266][N. Mahmoudi, Moriond QCD]
Impact of results
• And then something unexpected…(fs)
Direct exclusion(CMS 4.4 fb-1)B s
m+m-
(LHCb 1 fb-1 )
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LHCb status and plans 21Roger Forty
CPV of charm Silvia Borghi
[PRL 108 111602]
D0 K+K-
1.4 × 106 signal
LHCb
• Expected to be small in the SM (< 10-3)• Enormous statistics available:
> 106 D0 K+K- from D*+ D0 p+
Charge of p from D* determines D0 /D0
• DACP = difference in CP asymmetry for D0 K+K- and D0 p+p-
Robust: detection and production asymmetries cancel (at first order)DACP = (-0.82 ± 0.21 ± 0.11)% Zero CPV is excluded at 3.5 s
• Before the LHCb result: “CP violation…at the percent level signals new physics” [Y. Grossman, arXiv:hep-ph/0609178] (and many others)
After: “We have shown that it is plausible that the SM accounts for the measured value… Nevertheless, new physics could be at play” [J.Brod et al, arXiv:1111.5000]
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LHCb status and plans 22
• New physics has not yet shown itself clearly at the LHC
• Essential to improve measurements of precisely-predicted quantities: fs, BR(Bs→ m+m), q2 (AFB= 0) …
Another example: the CP-angle gis the least well measured UT angle (depends on rare b → u decays)Uncertainty 10–12º [UTfit/CKMfitter]
• Clean determination using B DK tree decays with theoretical uncertainty < 1º
• First constraints already achieved:Can profit from much higher statistics long term programme at LHCb
3. Plans
Roger Forty
Daniel Johnson & Sean Benson
g (r
ad)
rB
[PLB 712 203]
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LHCb status and plans 23Roger Forty
LHCb upgrade• Expect to double data-set by end of this year
After long shutdown, further doubling of data-set in 2015–17 (plus increase of cross-sections with higher energy): total of 5–7 fb-1
• Main limitation that currently prevents exploiting higher luminosity is the hardware trigger: keeping output rate < 1 MHz requires raising of thresholds hadronic yields reach plateau:
• Propose to remove the hardware trigger Read out LHCb at 40 MHz crossing rateFlexible software trigger in CPU farm increase in yields by factor 10–20 at 1–2 × 1033 cm-2 s-1 (25 ns is required)
• Requires replacing front-end electronicsPlanned for the long shutdown in 2018Running for ~10 years will give 50 fb-1
→ General-purpose detector for the forward region
Silvia Borghi
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LHCb status and plans 24
Detector modifications
Roger Forty
• Baseline detector modifications to allow 40 MHz readout
TORCH time-of-flightPixel VELO
e.g. Scintillating-fibre trackerR&D on possible detector upgrades
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LHCb status and plans 25
Upgrade status
Roger Forty
• Letter of Intent for upgrade submitted to LHCC last year Encouraged to proceed to Technical Design Report
• Framework TDR just submitted (25 May) schedules & cost of subsystems, and institute interests
• Update of physics case and expected performance:
[LHCC-2012-007]
Timeline (tight!)2011 Letter of Intent2012 Framework TDR
R&D ongoing2013 Subsystem TDRs2014-16 Tender & prodn
2017 Acceptance testing2018 Installation2019 Data taking
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LHCb status and plans 26Roger Forty
Conclusions• LHCb taking data with high efficiency and excellent detector performance
– Luminosity above design, 1.4 fb-1 recorded so far– Excellent mass and decay-time resolution, particle ID, etc.
• World-best measurements of many physics parameters– Dms, DGs, fs, BR(Bs m+m-), masses, lifetimes, etc.
First observations of new decays, evidence for CP violation of Bs
• So far almost all are in good agreement with the Standard Model → strong constraints on new physics in the flavour sector
• Possible hints of physics beyond the Standard Model require further study:– Evidence seen for CP violation in charm, unexpected– Isospin asymmetry for B → K m+m- is also puzzling
• Upgrade of LHCb in preparation for 2018: 10 × yield + software trigger
→ Much more to come: new collaborators welcome!
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LHCb status and plans 27
Additional slides
Roger Forty
• Signal for B0 → K 0∗ μ+μ-
• SM prediction for isospin asymmetry AI of K∗μ+μ-
[Feldmann &Maas, JHEP 01 074]
• LHCb result: consistent with SM expectation in this mode[arXiv:1205.3422]
A I (%
)
q2 (GeV2/c4)
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LHCb status and plans 28
• Compare B0 K0m+m- and B+ K+m+m- decays
• Isospin asymmetry AI defined as:G(B0 K0m+m-) - G(B+ K+m+m-) G(B0 K0m+m-) + G(B+ K+m+m-)
• Expect AI ~ zero in SM (< few %)Results from other experiments tended toward negative values
• Previous discrepancy with SM is supported by new LHCb result: AI < 0 with over 4s significance
• No asymmetry seen in closely-relatedB K*m+m- mode (K*+ K0p+)No clear interpretation, so far
Isospin asymmetry
Roger Forty
[arXiv:1205.3422]
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LHCb status and plans 29
g determination• Various methods used
Inputs mostly from B factoriesgcomb = (75.5 ±10.5)° [UTfit]
• Impact of LHCb results on the combination, for the ADS method (B+ → D0K+, D0 →K+p-)[D. Derkach, LHCb-TALK-2012-077]
Roger Forty
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LHCb status and plans 30Roger Forty
ASL• Strong interest in semileptonic (flavour-specific) asymmetry due to
D0 result for dimuon asymmetry (comparing # of m+m+ and m-m- events)ASL = (−7.87 ± 1.72 ± 0.93) × 10−3 [PRD 84 052007] (expect < 10-3 in SM)
• Same approach difficult at pp machine due to production asymmetriesInstead use semileptonic decays, B(s) → D+
(s) (K+K-p+) m- XResult from LHCb expected soon
• Note: if ASL is large, expected to see large fs in most models
[arXiv:0910.1032]
Projected LHCb precision (statistical, 1 fb-1)