Charmed baryons at LHCb · in predicting masses and mass splittings ... The ability to identify...

Charm 2016 (Bologna), 6 September 2016 1

Charmed baryons at LHCb

Paras Naik

on behalf of the LHCb collaboration

! 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)



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!



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)



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)



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



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.



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)



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)



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]



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



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



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



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.



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



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)

! 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)



Rare and forbidden Λc decays

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Babar, Phys. Rev. D840 072006 (2011)

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



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



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



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!



Additional Slides

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RICH performance plots

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Eur. Phys. J. C73 2431 (2013)

C4F10 radiator



Babar Ξcc+ search plots

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Charmed baryons at LHCb · in predicting masses and mass splittings ... The ability to identify...

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