Charmed baryons at LHCb · in predicting masses and mass splittings ... The ability to identify...
Transcript of Charmed baryons at LHCb · in predicting masses and mass splittings ... The ability to identify...
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Charm 2016 (Bologna), 6 September 2016 1
Charmed baryons at LHCb
Paras Naik
on behalf of the LHCb collaboration
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! In the last decade, considerable progresshas been made in measuring charm baryon spectra.
! Several Σc, Ωc, and Ξc states have been identified by the B-factories.
! Quark model has been very successful in predicting masses and mass splittings of singly charmed states
Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Overview - Experiment
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Phys. Rev. D86 010001 (2012)
Ωc(2770)0 at BaBar Phys. Rev. Lett 97 232001 (2006)
Ξc(2980) and Ξc(3077) at Belle Phys. Rev. Lett 97 162001 (2006)
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Overview - Theory
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Phys. Rev. D90 094507 (2014)
Predicted charm and beauty baryon states from lattice QCD
(Brown, Detmold, Meinel, Orginos)! Observed states shown in red
! Many states still yet to be found!
! Large number of HQET calculations! lifetimes! decay widths! masses
! Experiment needs to catch up!
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
LHCb Experiment: Tracking
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! Accurate decay time resolution from our vertex locator (VELO)! High muon reconstruction efficiency from muon stations! Good momentum resolution from tracking stations, Δp/p = 0.35% — 0.55%
Vertex Locator Tracking stations
Warm magnet can switch polarity
Muon system
Int. J. of Mod. Phys A30 1530022 (2015)
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
LHCb Experiment: Particle ID and Trigger
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! p/K/π separation provided by Ring Imaging Cherenkov (RICH) detectors
! The ability to identify particles at LHCb is critical to many of our analyses.! Excellent trigger allows us to trigger on tracks with lower pT! Charm trigger uses 33% (2011) - 40% (2012) of our trigger bandwidth
RICH1 RICH2 Eur. Phys. J. C73 2431 (2013)
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Trigger strategy evolution
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! Charm production very large at the LHC
! However we can only keep what we trigger! Several improvements made from Run 1 to Run 2
7 TeV13 TeV
Run 1 Run 2
Nucl. Phys. B871 1 (2013)
JHEP 03 159 (2016) Erratum-ibid JHEP 09 013 (2016)
See talk by Dominik Muller
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Trigger strategy evolution
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! New “Turbo stream” for Run 2.
! Reconstruct full signal candidates directly in the trigger (“Tesla”), and not offline.
! Analyses thus performed directly on the trigger output.
! Smaller event sizes lead to increased yields within a limited bandwidth.
! Real-time alignment and calibration makes “Turbo” possible.
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Doubly and Triply charged charm baryons
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! Still an open question if quark model calculations will work well on doubly and triply charged baryons.
! Numerous predictions for Ξcc+(+) masses and lifetimes, e.g.:! m(Ξcc+): 3500 - 3700 MeV/c2
! τ(Ξcc+): 100 - 250 fs! Production relative to Λc generally expected to be highly suppressed
Phys. Rev. D86 010001 (2012)
Phys. Rev. D70 094004 (2004)
Eur. Phys. J. A45 267 (2010)
e.g. Physics-Uspekhi 45 (no. 5) 455 (2012)
! Ground state baryons with u,d,s,c form SU(4) multiplets
! Three weakly decaying C = 2, JP = ½+ states:! Ξcc isodoublet
(ccu, ccd)! Ωcc singlet (ccs)
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Ξcc+
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! SELEX reported signals in Ξcc+ → Λc+K−π+, and also Ξcc+ → p+K−D+
! Consistent with some predictions
! Not confirmed by Belle, FOCUS, or BaBar
SELEX Ξcc+ → Λc+K−π+
Phys. Rev. Lett. 89 112001 (2002)
Belle - Phys. Rev. Lett 97 162001 (2006) FOCUS - Nucl. Phys. B115 33 (2003)
SELEX Ξcc+ → Λc+K−π+
Phys. Lett. B628 18 (2005)
(not shown) - Phys. Rev. D74 011103 (2006)
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
LHCb Ξcc+ search
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! LHCb searched for Ξcc+ → Λc+K−π+ using of 0.65 fb-1 of 7 TeV data from 2011
! Measure production cross-section ratio
! where Λc+ → p+K−π+ in all cases
! Define:
! Extracted signal yields via 2D fit to and , no observed excess
! Calculate 95% CLs ULs of as a function of for various lifetimes
JHEP 1312 90 (2013)0.65 fb-1 @ 7 TeV [2011]
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
LHCb Expanded Ξcc+ search
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! LHCb result is not incompatible with the SELEX result.! Different production environments; Ξcc+ lifetime very short (<100 fs).
! Search with full Run I data already underway. ! Many improvements expected, including improvements to trigger
selection, and the inclusions of new modes like Ξcc+ → p+K−D+
! High D+ lifetime can lead to more efficient selections ! Expect sensitivity to increase by around a factor of 10
! Production cross-section should roughly double during Run 2! Would expect even a short lifetime Ξcc+ to be observable in Run 2 data
! Simultaneously looking for Ξcc++ (by searching for an extra charged pion).
Ongoing Analysis
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Λc+ → phh' branching fractions
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! Λc+ → phh' decays had imprecisely measured branching fractions, e.g.:! !
! New result from BES III improves these considerablyPhys. Lett. B524 33 (2002)
Z. Phys. C48 29 (1990)
arXiv:1608.00407See talk by Binlong Wang
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Λc+ → phh' branching fractions
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! Copious samples of Cabibbo-suppressed decays in Run 1, O(105)! Λc+ → p+K−π+ Cabbibo-favored yield: 8.18 × 105 in 0.65 fb-1
! Compare to 6 × 103 Λc+ → p+K−π+ at BES III
! Studies of the LHCb Run 1 sample are well underway
30 pb-1 of Λc+ → pKπ
Ongoing Analysis
~5% of the 2011 data sample JHEP 1312 90 (2013)
arXiv:1608.00407
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
CPV in charm baryons
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! Several weakly decaying baryons: Λc, Ξc0, Ξc+, Ωc0
! As in charmed mesons, direct CP asymmetries can be measured:
! where Δs (Θ) is a difference between strong (weak) phases of SM and NP
! SM backgrounds are lower than in the meson sector
! Experimentally we can measure:
! To get the CP asymmetry we need to disentangle relevant production and detection asymmetries.
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
ΔACP in SCS Λc+ decays
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! Production and detector asymmetries mostly cancel by taking the difference:
! Expectation for SCS modes in SM is close to O(10-4)! First studies with Run 1 data are well underway! Limiting factor is our understanding of proton asymmetries
! Work in progress using several decays! Asymmetry scales down with luminosity
! Longer term:! CPV in DCS decays - SM predicts even smaller CP asymmetry than
SCS - Possible window to NP?! Examine local asymmetries in the phase space of the decay.
! e.g. “Miranda” method! Local asymmetries potentially stronger than global ones.
Phys. Rev. D80 096006 (2009)
Ongoing Analysis
PRL 117 011801 (2016) See talk by Kiyoshi Tanida of Belle
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Production and asymmetries
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! Λc decays contributed to our 7 TeV charm cross sections measurement
! Opportunity to study Λc production and Λc production asymmetry in Run 2
! Perform asymmetry measurements in bins of transverse momentum and pseudorapidity.
! Fit log10(χIP2) spectrum, apply prompt-secondary separation procedure
Ongoing Analysis
7 TeV Λc+ → p+K−π+ results Nucl. Phys. B871 1 (2013)
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! Analogies exist between rare tau and rare Λc decay! τ→3μ (LFV) :: Λc →3μ (B-L)! τ→pμ+μ− (B-L) :: Λc →pμ+μ− (FCNC)! τ→pμ̅+μ+ (B-L) :: Λc →pμ̅+μ+ (B-L)
! Constraints! B(Λc→3μ) : none! B(Λc→pμ+μ−) < 4.4 × 10-5 (90% CL) ! B(Λc→pμ̅+μ+) < 9.4 × 10-6 (90% CL)
! With Run 1 data set, LHCb is expected to probe Λc → pμ+μ− to O(10-7)! After Run 3 down to O(10-8)
Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Rare and forbidden Λc decays
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Babar, Phys. Rev. D840 072006 (2011)
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2260 2280 2300 2320m(pK�p+) [MeV/c2]
0
2
4
6
8
10
12
14
Can
dida
tes
/(1
MeV
/c2 )
⇥103
LHCb preliminaryps = 13TeV
L+c data
Turbo Stream 2016 Data
Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Possibility of amplitude analysis
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! Opportunity to perform amplitude analyses charm baryon decays ! O(106) Λc+ → pKπ recorded at LHCb in 2011 alone! E791 performed amplitude analysis with 103 events.
! BES III studied Λc+ → phπ decays to estimate detection efficiencies
! Experimentally challenging since baryons carry spin! Need two two-particle invariant masses and three helicity angles to
fully describe the phase space of the decay.
! Potential to analyze CF and SCS modes with existing LHCb data sample.
! Huge body of amplitude analysis expertise at LHCb.
Phys. Lett. B471 449 (2000)
arXiv:1608.00407
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Ongoing Analyses Summary
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! More analyst time has been invested in 2016, and several Run 1 analyses are in final stages of review.
! Analyses imminent/soon:! Λc+ → phh' branching fractions! ΔACP in SCS Λc+ decays! Expanded Ξcc searches
! Analyses planned and in progress:! Rare Λc decays! Amplitude analysis in Λc decays! Local CPV in Λc+ → phh’! Absolute Λc+ → pKpi branching fraction! Ξc branching fractions! 13 TeV Λc production asymmetry ! Excited charm spectroscopy
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Conclusion
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! The LHCb detector has worked “like a charm.” ! LHCb in its first run has published a modest number of charm baryon
physics results.
! LHCb is continuing to exploit its unique data set to investigate the relatively unexplored field of the physics of charmed baryons.
! New analyses are on the horizon; datasets at LHCb are becoming vast.! Several Run 1 analyses are in the final stages ! Expect LHCb charm baryon results from Run 2 very soon!
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Additional Slides
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
RICH performance plots
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Eur. Phys. J. C73 2431 (2013)
C4F10 radiator
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Searches for CP violation in charm at LHCb
Paras Naik, University of Bristol Charm, 6 September 2016
Babar Ξcc+ search plots
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