Tracking developments for Long Living Particles at LHCb

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Tracking developments for Long Living Particles at LHCb

Sergio Jaimes Elles

Univeristat de València (IFIC-CSIC), Valencia, Spain November 24, 2022

XIV CPAN days, Bilbao, Spain.

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The LHCb detector ^|²

I Single arm forward spectrometer, pseudo-rapidity coverage2< η <5.

I Initially designed for heavy flavour physics studies of charm and beauty hadrons.

I During the Long Shutdown 2 (LS2) most of the sub-detectors systems have been upgraded for operation during Run 3 (2022-2025) onward.

I Increased instantaneous luminosity from4×10³²cm²s⁻¹ to

2×10³³cm²s⁻¹.

I Full detector readout at40MHz.

I Expected50fb⁻¹ before the end of Run 4.

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The LHCb detector ^|³ I Major changes include a new tracking system and the fully software-based

trigger system.

I Increased sensitivity to flavour physics channels of interest but also a capability for triggering on other signatures like Long Lived Particles (LLPs).

Turning the LHCb into a general purpose detector in the forward region.

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High Level Trigger at Run 3 ^|⁴

I Hardware trigger L0 has been completely removed.

I HLT1 implemented on GPUs.

• Rate reduction30MHz→1MHz (70−200GB/s).

• Partial reconstruction, real time calibration and alignment.

I HLT2 implemented on CPUs

• Output rate10GB/s.

• Trigger lines rely on offline quality reconstructed objects.

• Full Reconstruction and selection.

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Tracking at LHCb ^|⁵ I Long Tracks- VELO + SciFi hits,

optionally also UT. Best momentum resolution∼1%.

I Downstream tracks- UT + SciFi hits, have been used for physics analysis of Long Lived Particles at LHCb (ΛandK_s⁰).

I Upstream tracks- VELO + UT hits. In general low momentum tracks with a poor momentum resolution.

I VELO tracks- Only VELO hits, used for calibration. Useful for reconstruction of the Primary Vertex.

I TTracks- Only SciFi (T stations on Run 1/2). Lack of bending in the track makes the momentum resolution very poor∼25%.

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Tracking at LHCb ^|⁶

I Current HLT1 trigger

implementation only reconstructs Long tracks. This implies a limited sensitivity on LLP signals as it depends on the presence of Long tracks for triggering on signal.

I Only using Long and Downstream tracks for physics analysis limits the maximum decay length to around 2m.

I Downstream at HLT1 in developement.

I SciFi seeds standalone reconstruction.

Including TTracks on LHCb physics program can also set the possibility for Electric and Magnetic Dipole moment (EDM/MDM) measurement at LHCb and a increased sensitivity to LLP signatures. Eur. Phys. J. C 77, 181 (2017)

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Tracking at LHCb ^|⁷ Downstream and

TTracks have a huge potential for increasing efficiency of

reconstruction in a big range of SM and BSM decays of LLPs.

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Track reconstruction ^|⁸ Tracks that leave only hits after the magnet have never been used for physics analysis at LHCb.

I Poor momentum resolution.

I Long propagation distances in the magnet region make track extrapolation more difficult.

I Low vertex reconstruction efficiencies and resolution.

I Lack of RICH2 for TTracks in Run 1/2 makes background distinction harder.

Feasibility study usingΛb→ΛJ/ψ to explore the reconstruction using TTracks.

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Physics with TTracks ^|⁹

I Study on the physics capabilities of reconstruction with TTracks on Run2.

I Two SM benchmark channels considered

• Λb→J/ψΛ,Λ→pπ⁻

• B⁰→J/ψK⁰_s,K_s⁰→π⁺π⁻ I Reconstruction of the prompt

J/ψ→µ⁺µ⁻allows for a kinematically constrained fit of the decay chain.

I Motivated on the measurement of EDM/MDM of theΛbaryon exploiting the spin precession induced on the particles as they pass by the dipole magnet.

LHCb-DP-2022-001

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Physics with TTracks ^|¹⁰

I Momentum resolution improved using a kinematically constrained fit.

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Physics with TTracks ^|¹¹

I Overlapping of the mass peaks from Λ→pπ⁻andK_s⁰→π⁺π⁻makes it impossible to distinguish through mass cuts.

I As of Run 2, no RICH2 PID information is available for TTracks, developement ongoing.

I Armenteros-Podolanski (AP) technique to distinguish.

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Physics with TTracks ^|¹²

I Selection chain has one particular bottleneck, the vertex reconstruction.

I Extrapolation of TTracks over the magnet region combined with a poor momentum resolution makes vertex fitting prompt to failure.

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Physics with TTracks ^|¹³ I Closing tracks topology produces a ”ghost” vertex

I Large bias in the vertex position, that affects the resolution.

I Ghost vertices represent∼30%of events after selection.

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Physics with TTracks ^|¹⁴ I Closing tracks topology produces a ”ghost” vertex

I Large bias in the vertex position, that affects the resolution.

I Ghost vertices represent∼30%of events after selection.

I Improvements on the vertex fitter algorithms are under study.

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Physics with TTracks ^|¹⁵

∼6140signal events with a core mass resolution of(7.7±0.4)MeV/c² and (41±2)MeV/c²for theΛandΛbrespectively.

I Implementation of HLT2 lines for Run 3 will be key for LLP searches using TTracks at LHCb.

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Sensitivity on NP searches ^|¹⁶ I LHCb can perform very well for the reconstruction of hadronic signatures of

LLPs (XBSM →h⁺h⁻) including also muons.

I Sensitivity studies for searches involving a Higgs portal to Dark Matter.

B

⁺

→ K

⁺

H

⁰

(→ µ

⁺

µ

⁻

)

I Reconstructibility ofH⁰ decay vertex into (LL, DD, TT).

I Triggering on Downstream and TTracks at HLT1 level will be essential for these type of searches.

Front. Big Data 5:1008737

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Conclusions ^|¹⁷

I Upgrade of the LHCb detector will open a wide spectrum of

decays to study on Run 3.

I Triggering on different signatures will be key for LLPs in SM and BSM searches.

I Promising results from particle reconstruction downstream of the dipole magnet.

I Development of improved reconstruction algorithms will be key for reaching a larger sensitivity.

I Work in progress both in tracking and triggering algorithms for

Downstream and TTracks will be fundamental for the future of

LHCb physics program.

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Backup Slides

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SciFi Hybrid seeding ^|¹⁹

I Stand alone reconstruction algorithm for track seeds at the SciFi.

I Three stations arranged in x-u-v-x geometry. u-v layers at tilted by a±5^◦ stereo angle.

I Use of u-v layers for determining the y coordinate.

I x-z plane: parabolic trajectory projection.

I y-z plane: assume that trajectory is linear and that it comes from the origin (interaction point).