Double Parton Scattering measurements at

LHCb

Vanya Belyaev ( ITEP/Moscow, Russia)On behalf of LHCb Collaboration

Vanya Belyaev, LHCb DPS measurements 2

Outline

• DPS measurements• LHCb detector and data set• Double charm analysis and

discussion• Z0+jets analysis• Conclusions

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LHCb DPS measurements

• Observation of J/y pair production in pp collisions at √s=7TeV Phys.

Lett. B 707 (2012) 52

• Observation of double charm production involving open charm in pp collisions at √s=7 TeV

JHEP 06 (2012) 141

• Measurement of jet production in Z0/g* →m+m- events at LHCb in √s=7TeV pp collisions

LHCb-CONF-2012-016

Not direct DPS measurements, but measurements that are interesting to discuss in context of DPS

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Vanya Belyaev, LHCb DPS measurements 4

Double Parton Scattering

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287k documents

Vanya Belyaev, LHCb DPS measurements 5

DPS: simple paradigm

scatters

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Two independent scattering processes

Relations through (unknown) 2PDFs

Assume factorization of 2PDFs

(Can’t be true for all x,Q2)

Easy to make predictions!

And the predictions are easy to test

Universal (energy and process independent) factor)

CDF, F.Abe et al., PDR 56 3811 (1997)

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How to test DPS ?

• For two species A and B one need to measure associative production s(A+B) as well as their inclusive productions s(A), s(B)• DPS contribution follows from identity: • Look for the correlations:

pT spectra, Df & Dy correlations, mass spectra, polarization effects, …. ?

• Inclusive production is well measured at LHCb for many speciesJ/y Z0 Open charm: D0, D+, Ds, Lc jetsand many-many others: y’, Y(nS), W±, cc, cb, B-hadrons, ...

Today 26 pairs: 2×J/y (1) J/y+open charm (4) 2×open charm (6+10) Z0+jets (1)

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Dedicated talk by Patrick Spradlin

Forward production studies at

LHCb

EJPC 71(2011) 1645

arXiv:1204.1620

CERN-LHCb-PAPER-2012-041

CERN-LHCb-CONF-2011-015

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LHCb experiment

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LHCb: beauty detector

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General purpose universal detector in forward region

2<h<5

4% of solid angle

40% of heavy quarks

pp-collisions

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VELO

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42×2 silicon strip planes

r-f geometry

40-100 mm pitch

7mm away from the beam

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Tracking system

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Two silicon stations upstream magnet

Dipole magnet 4Tm

Three stations downstream magnet

Inner: silicon

Outer: Straw tubes

Momentum resolution: 0.4-0.6%

J/y mass resoluton 13 MeV/c2

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Hadron ID

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Two RICH detectors

Good p/K separation up to ~100 GeV/c

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Calorimeter system

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Scintillating Pad Detector/SPD

Preshower Detector

Electromagnetic Shashlik Calorimeter

Hadron Tile Calorimeter

Important to trigger hadronic final states

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Muon system

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4(+1) stations

MWPC

0.7% p→mmisID

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LHCb in numbers

• Data taking efficiency > 90% •Working channels > 99%• Integrated Luminosity:

2k+10 37pb-1

2k+11 1fb-1

2k+12 >2fb-1 (not a final word yet)• Trigger efficiency :• for dimuon final states ~ 90%• for multihadron final states ~ 30%

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Inclusive signals

• Start from well reconstructed tracks• Utilize powerful particle ID:• muons from J/y, Z0→m+m- decays [MUON]• charged kaons, pions and protons from from

open charm [RICH]D0 →K-p+, D+→K-p+p+, Ds→K-K+p+, Lc →pK-p+

• Exploit the excellent vertex and momentum resolution: • Good quality common vertex• Narrow mass-peaks

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Dimuons: J/y and Z0

• Yields @ 7 TeV 1.5×108/fb-1

• Yields @ 7 TeV 5.5×104/fb-1

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arXiv:1204.1620 JHEP 06(2012) 141

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Open charm signals

N(D0) ≈ 2×108/fb-1 N(D+) ≈1×108/fb-1 N(Ds) ≈ 1×107/fb-1 N(Lc) ≈2×106/fb-1

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JHEP 06(2012) 141

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Event Selection

J/yС two charm with common vertex

2×Open charm hadrons

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m+

m-

K-

p+

D0

K-

p+

D0

D0

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Make a common vertex and refit

• Global c2/ndf from consistency refit:• Remove pileup, cascade and background

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JHEP 06(2012) 141

signal signalbackground

background

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Signal extraction

2×J/y : fit one mm-mass in bins of another mm-pair mass• 141±19 events• significance exceed 6s

• ~30 years after NA3(fixed target)

PLB 114 (1982) 457PLB 158 (1985) 85

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PLB707(2011) 52

pPt: 16±4 J/yJ/y

pPt: 13 J/yJ/y

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Signal extraction

• J/y + open charm• clear signals for all four modes• Significances > 7s

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JHEP 06(2012) 141

J/yD0

J/yD+

J/yDs J/yLc

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(open charm)2

D0 & open charm D+ & open charm

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For all cases significance > 5s,

2.5 sigma D+Lc

+

JHEP 06(2012) 141JHEP 06(2012) 141

D0

D0

D0

D+

D0

Ds D0Lc

D+

D+

D+

Ds

D+Lc

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Open charm + open anti-charm

D0 & open anti-charm D+ & open anti-charm

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For all cases significance >

8s

JHEP 06(2012) 141 JHEP 06(2012) 141

𝐃𝟎𝐃𝟎D

0D-

D𝟎D𝒔−

D𝟎𝚲𝐜−

D+

D- D+¿D 𝒔

−¿

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Cross-sections

• Use per-event efficiency, mainly from DATA: trigger, particle ID, background etc.

• Major systematic: tracking (reducible)Br(Lc), Br(Ds), ….

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JHEP 06(2012) 141

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Cross-sections

Major systematic: tracking (reducible) and Br(Lc), Br(Ds), ….

Major systematic: tracking (reducible) and Br(Lc), Br(Ds), ….

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JHEP 06(2012) 141

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Cross-sections

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A.Berezhnoy et al., Phys Rev D57 4385 (1998)

S.P.Baranov. Phys Rev D73 074021 (2000)

J.-P.Lansberg. Eur.Phys.J. C61 693 (2009)

JHEP 06(2012) 141

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Event Properties: pT

J/y + open charm:

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Slope parameter for pT-spectra• Fit pT-spectra with

exponential function: ~ exp (b×pT)

• DPS: expected similarity between inclusive and

• Expected to be similar between J/yC and CC

• No reason to be the same for J/yC and inclusive

• Expected to be similar between and inclusive

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Df & Dy correlations

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No evident correlations

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Df & Dy correlations

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Clear correlations!

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Compare with CDF’2k+6

• CDF: azimuthal correlations for D(0,+) D*- • Large gluon splitting contribution

Very different kinematical region

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http://www-cdf.fnal.gov/physics/new/bottom/060921.blessed-double-charm-corr/

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Mass distributions

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The same shape for m>7 GeV/c2

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Z0&jets

• Good test of pQCD• Sensitive to PDF for small x and large Q2

• Poorly constrained by existing measurements

… and also possible contribution from DPS

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Z0&jets

• 2k+11 data set: 1fb-1 Jet reconstruction• Particle Flow: tracks, V0, g, p0

and unmatched HCAL clusters • Anti-kT algorithm, R = 0.5

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CERN-LHCb-CONF-2012-016

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Jet distributions

pT> 10 GeV/cclean-up

2<h<4.5

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CERN-LHCb-CONF-2012-016

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s(Z0+jets)/s(Z0)

• Jet multiplicity

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Fraction on jet events:

DATA: 0.229 ±0.06 ±0.09

FEWZ/MSTW08 0.212 ±0.009±0.016

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DPS @ LHCb summary

• Processes, sensitive to DPS, and their properties have been studied at LHCb with 2k+10 and (part of) 2k+11 data

• 2×J/y is in good agreement both with SPS/pQCD and DPS • J/y+C strongly disagree with SPS/pQCD, supports DPS dominance

(and well consistent with see charm quark contributions)• DPS is only partially supported by (open charm)2:

if DPS dominates seff would be factor 2-3 larger• The pattern of pT-distributions is difficult to interpret if only one

mechanism dominates • Z0+jets is nicely consistent with SPS picture

Still more data to analyse (including √s=8 TeV) … and more processes to study

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Vanya Belyaev, LHCb DPS measurements 38

Thanks to

• Anatoly Likhoded for inspiring efforts and stimulating discussions• Antoni Szczurek for useful discussions on DPS• Jean-Philippe Lansberg for the great help with MadOnia

• MPI@LHC organizers for the invitation and all of you for your kind attention

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BACK UP

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Per-event efficiencies: as much as possible from data

etot = eacc&rec&sel ×epid ×etrg ×e*track

eacc&rec&sel = e1acc&rec&sel ×e2

acc&rec&sel

epid = PeK × Pep ×Pep [ ×e2m,J/y ] e*track = P e*track

etrg(J/yC) = etrg(J/y) etrg(CC,) = 1 - ( 1 – e1

trg ) ( 1 – e2trg )

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MC

DATA

Diff

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Efficiencies II

• eiacc&rec&sel from (single charm) Monte Carlo Simulation

• As function of pT & y for D0, D+, Ds, Lc

• As function of pT,y & cosq* for J/y

• eK ,ep and ep from DATA using L0→p+p- and D*+ →(D0 →K-p+) p+ • As function of p&h and #Tracks

• e2m,J/y from DATA, using inclusive J/y peak• As function of J/y pT&y

• etrg(J/y) & eitrg from DATA using inclusive J/y, D0, D+, Ds

+, Lc+

• As function of pT&y

• e*track from detailed DATA/MC comparison • As function of track pT&h

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Predictions for LHCb

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S = 0.1mb

A.Berezhnoy et al., Phys Rev D57 4385 (1998)

S.P.Baranov. Phys Rev D73 074021 (2000)

J.-P.Lansberg. Eur.Phys.J. C61 693 (2009)

C.H.Kom, A.Kulesza & J.W.Stirling, Phys.Rev.Lett, 107 082002 (2011)

S.P.Baranov, A.M.Snigirev and N.P.Zotov, Phys.Lett. B705 116 (2011)

A.Novoselov, arXiv:1105.62076

M.Luszczak, R.Maciula, A.Szczurek, arXiv:1111.3255

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Yields & Significances

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>5s

4 J/yC

6 CC

7

Yield Goodness-of-fit[%]Significance

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Cross-section

• Use sWeight/sPlot technique:• Each event i has weight wi from sWeight• Probability event to be signal

• This weight is corrected by 1/eTOT

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The price:

The inflation of “statistical” error

Need good control over efficiency!

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Comparison with models

pQCD ()/MadOnia, DPS, Pythia, IC• pQCD is off by the factor ~20• Support for (factorization) DPS • excellent agreement for J/yC• factor ~3 off for CC • general support for “uncorrelated” production

• Pythia fails to reproduce all the cross-section ratios and spectra. • IC agrees on cross-section, but lack of well-

defined predictions on spectra, correlations, …

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Theory: double charm at LHCb

• Ff

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PYTHIA

State-of-art pQCD