lhcb status and plans

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

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

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!


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, …


Collaboration804

55

Added since PLHC-2011: Birmingham, Cincinnati, Lahore, Rostock

VELOMagnetMuondetector

Calorimeters

RICH

Tracker

16


• 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!


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


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


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


• 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


• 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


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]


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


• 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]


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!

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


• 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


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]


[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)


• 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 )


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]


• 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]


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


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


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


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!


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)


• 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]


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


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)

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