Experimental preview ofLHCb results

PatrickRobbe,LALOrsay,5February 2017,

FortheLHCb Collaboration

• LHCb joined the LHC Heavy Ion program in 2013: pPb (1.1 nb-1) + Pbp (0.5 nb-1) collisions at 5 TeV, and performed several measurements from thesedata:

• J/y [JHEP 02 (2014) 72], y(2S) [JHEP 03 (2016) 133] and Y(nS) [JHEP 07 (2014) 094]

• Z [JHEP 09 (2014) 030], D0 [LHCb-CONF-2016-003], particle correlations [PLB 762C (2016) 473]

• The program continued in the Run 2 of the LHC and new collision data recorded:

• PbPb in 2015, for the first time• pPb + Pbp in 2016, with 10 times more statistics

• In parallel, development of a fixed target program2

LHCb andHeavyIons

TheLHCb experiment

3

~20m

~12m

10-300mrad

10-250mrad

VertexDetectorreconstructverticesdecaytimeresolution:45fsIPresolution:20μm

RICHdetectorsK/π/pseparationε(K→K) ~ 95 %, mis-ID ε(π→K) ~ 5 %

DipoleMagnetbendingpower:4Tm

Trackingsystem:TTandOTmomentumresolutionΔp/p=0.5%–1.0%(5GeV/c– 100GeV/c)

Calorimeters(ECAL,HCAL)energymeasuremente/γ identificationΔE/E=1%⨁10%/√E(GeV)

Muon systemμ identificationε(μ→μ)~97%,mis-IDε(π→μ)~1-3%

b𝑏" acceptance

[IJMPA30(2015)1530022][JINST3(2008)S08005]

LHCb andHeavyIons• LHCb is specialised in heavy flavour precision

physics, beauty and charm:• Optimised for low pile-up collisions (ie low multiplicity):

• Precise reconstruction of production and decay vertices: time dependent CP violation

• Correlations between particles: flavour tagging

• Some characteristics of the experiment make itattractive for measurements in Heavy ion physicstoo:

• Instruments fully the forward region: 2<h<5• Precise vertexing: separation of prompt production

from B decay products• Precise tracking: reconstruction down to pT=0• Particle identification: reconstruction of hadronic

decays4

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LHCb operates intwo modesUn

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LHCb

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nerg

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Collider mode:PbPb collisions(2015)• LHCb took part for the first time to a LHC PbPb run end of

2015, with emphasis on low multiplicity events.• Up to 54 colliding bunches, ie 10% of the luminosity provided

to the other LHC experiments, and a total of 3-5 µb-1 integratedluminosity recorded with the detector running in standard conditions (same as with proton-proton collisions)

• Centrality reach: up to 50%, where measurements of J/y, D0, Ks

0, L, … production can be done• No final measurement but latest news in presentation by

Michael Winn (7 February, session 4.3, 5:10 pm)

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]2) [MeV/cπM(K1800 1850 1900 1950

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= 5 TeVNNs

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K0S➝ p- p+

• pPb collisions at 5 TeV: « small » sample collected (~50% of the 2013 sample)

• pPb (~13nb-1) and Pbp (~17nb-1) collisions at 8.2 TeV: more than 10 times the 2013 statistics. Possibility to perform many new or improved measurements [LHCb-PUB-2016-011]

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Collider mode:pPb collisions(2016)

D+➝ K- p+p+

• Due to geometry of detector: when reverting beams, two different coverages: large statistics accumulatedin both configurations in 2016

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Collider mode:pPb collisions(2016)

pPb

Pbp

p

Pb

Pb

p

1.5<y*<4.5

-5.5<y*<-2.5 Measurement of Forward-Backward ratios in a commonrange (2<|y*|<4.5)y* = center of mass rapidity

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Collider mode:pPb collisions(2016)

For the first time for heavy ion collisions, we usedthe trigger scheme introduced in Run 2 for ppcollisions.

This scheme gives at the output of the trigger, fullyreconstructed and selected signal candidates (J/y, y(2S), D0, ….) using full detector information (PID, …) and with optimal alignment and calibration: no further reconstruction required.

This allows fast processing of the data: more details and previews of the LHCb pPb 2016 data for quarkonium, open charm and even open beauty in the presentation by Michael Winn(7 February, session 4.3, 5:10 pm))2) (MeV/c-µ+µMass(

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Fixed TargetPhysics With LHCb

• Gas can be injected inside the LHC vacuum, in the VELO detector.

• Used to determine the luminosity but since 2015 is used to also collect physics data. [JINST 7 (2012) P01010]

• Originally use Neon gas

• Other non-getterable noble gases can be used: in 2015 and 2016, we used also Ar and He

• The gas spreads in the beam pipe around LHCb: collision vertices over a range of ~1m (usable range)

• Physics events are collected by the LHCb detector, operated in standard configuration

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• The pressure in the LHC when the gas is injected is ~2x10-7 mbar (insteadof 10-9 mbar with no injection), between 1 day to 2 weeks.

• The pressure is so low that it does not interfere with the running of the LHC.

• Data samples collected during special runs in 2015 and 2016:• p (6.5 TeV) Ne during van der Meer scan [2015, 20h]• p (6.5 TeV) He during large b* run [2015, 8h] and van der Meer scan [2016, 16h]• p (6.5 TeV) Ar during large b* run [2015, 18h]• p (2.5 TeV) Ar during van der Meer scan of reference 5 TeV pp run [2015, 11h]

• Data were also collected in parallel to LHCb taking data in collision mode (during the Heavy Ion runs), injecting the gas continuously:

• Pb (6.37 Z TeV) Ar during the PbPb run (2 weeks) [2015, 50h]

• p (4 TeV) He during the pPb 5 TeV run (several days) [2016, 80h]11

Fixed TargetPhysics With LHCb

Fixed TargetPhysics With LHCb

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2015 pNe data

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2015 pNe data

J/y➝ µ+ µ-

inpNe

D0➝ K- p+inpNe

[https://twiki.cern.ch/twiki/bin/view/LHCb/LHCbPlots2015#SMOG_plots_pNe_collisions_approv]

Physics program is for the moment:• Measurement of p production

cross-section in pHe collisions (useful for understanding of cosmological p production)

• Measurement of heavy flavourproduction: first measurement of J/y to D0 production ratio in the pAr sample will be shown by Emilie Maurice (session 4.4, Feb 7 at 5:50 pm)

Conclusions

• Main news for the LHCb heavy ion program:• Large sample of pPb and Pbp collisions at 8 TeV collected in optimal

conditions: this will provide new precise results in the very near future• First result on heavy flavour from the fixed target program

• LHCb talks in parallel sessions:• Emilie Maurice, session 4.4 (Open Heavy Flavours), Tuesday 7 Feb, 5:50 pm

New high resolution measurements of open and hidden charm production in proton-nucleus collisions at sqrt(s) = 110 GeV with the LHCb detector

• Michael Winn, session 4.3 (Quarkonia), Tuesday 7 Feb, 5:10 pm Heavy flavour production in proton-lead and lead-lead collisions with LHCb

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