Double Parton Scattering measurements at LHCb Vanya Belyaev

Double Parton Scattering measurements at LHCb Vanya Belyaev ( ITEP/Moscow, Russia) On behalf of LHCb Collaboration

Outline • DPS measurements • LHCb detector and data set • Double charm analysis and discussion • Z +jets analysis • Conclusions 0 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 2

LHCb DPS measurements • Observation of J/y pair production in pp collisions at √s=7 Te. V • Observation of double charm production Phys. Lett. B 707 (2012) 52 involving open charm in pp collisions at √s=7 Te. V • Measurement of jet production in Z /g →m m JHEP 06 (2012) 141 0 * + - events at LHCb in √s=7 Te. V pp collisions LHCb-CONF-2012 -016 Not direct DPS measurements, but measurements that are interesting to discuss in context of DPS 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 3

Double Parton Scattering 287 k documents 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 4

DPS: simple paradigm scatters Two independent scattering processes Relations through (unknown) 2 PDFs Assume factorization of 2 PDFs (Can’t be true for all x, Q 2) 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) 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 5

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: p. T spectra, Df & Dy correlations, mass spectra, polarization effects, …. ? • Inclusive production is well measured at LHCb for many species EJPC 71(2011) 1645 J/y Dedicated talk by 0 ar. Xiv: 1204. 1620 Patrick Spradlin Z Forward production Open charm: D 0, D+, Ds, Lc CERN-LHCb-PAPER-2012 -041 studies at LHCb CERN-LHCb-CONF-2011 -015 jets and many-many others: y’, Y(n. S), W±, cc, cb, B-hadrons, . . . Today 26 pairs: 2×J/y (1) J/y+open charm (4) 2×open charm (6+10) Z 0+jets (1) 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 6

LHCb experiment 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 7

LHCb: beauty detector General purpose universal detector in forward region pp-collisions 2<h<5 4% of solid angle 40% of heavy quarks 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 8

VELO 42× 2 silicon strip planes r-f geometry 40 -100 mm pitch 7 mm away from the beam 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 9

Tracking system Two silicon stations upstream magnet Dipole magnet 4 Tm Three stations downstream magnet Inner: silicon Outer: Straw tubes Momentum resolution: 0. 4 -0. 6% J/y mass resoluton 13 Me. V/c 2 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 10

Hadron ID Two RICH detectors Good p/K separation up to ~100 Ge. V/c 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 11

Calorimeter system Scintillating Pad Detector/SPD Preshower Detector Electromagnetic Shashlik Calorimeter Hadron Tile Calorimeter Important to trigger hadronic final states 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 12

Muon system 4(+1) stations MWPC 0. 7% p→mmis. ID 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 13

LHCb in numbers • Data taking efficiency > 90% • Working channels > 99% • Integrated Luminosity: 2 k+10 2 k+11 2 k+12 37 pb-1 1 fb-1 >2 fb-1 (not a final word yet) • Trigger efficiency : • for dimuon final states ~ 90% • for multihadron final states ~ 30% 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 14

Inclusive signals • Start from well reconstructed tracks • Utilize powerful particle ID: • • muons from J/y, Z 0→m+m- decays [MUON] charged kaons, pions and protons from open charm [RICH] D 0 →K-p+, D+→K-p+p+, Ds→K-K+p+, Lc →p. K-p+ • Exploit the excellent vertex and momentum resolution: • Good quality common vertex • Narrow mass-peaks 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 15

Dimuons: J/y and Z 0 • Yields @ 7 Te. V JHEP 06(2012) 141 ar. Xiv: 1204. 1620 1. 5× 108/fb-1 6 Dec 2 k+12 MPI@LHC 5. 5× 104/fb-1 Vanya Belyaev, LHCb DPS measurements 16

Open charm signals N(D 0) ≈ 2× 108/fb-1 N(D+) ≈1× 108/fb-1 N(Ds) ≈ 1× 107/fb-1 N(Lc) ≈2× 106/fb-1 JHEP 06(2012) 141 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 17

Event Selection 2×Open charm hadrons J/y. С two charm with common vertex K- K- m- p+ p+ D 0 m+ 6 Dec 2 k+12 MPI@LHC D 0 Vanya Belyaev, LHCb DPS measurements 18

Make a common vertex and refit • Global c /ndf from consistency refit: 2 • Remove pileup, cascade and background signal background JHEP 06(2012) 141 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 19

Signal extraction 2×J/y : fit one mm-mass in bins of another mm-pair mass 141± 19 events significance exceed 6 s • • • ~30 years after NA 3(fixed target) PLB 114 (1982) 457 PLB 158 (1985) 85 p. Pt: 13 J/y p. Pt: 16± J/y 16± 4 J/y PLB 707(2011) 52 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 20

Signal extraction • J/y + open charm • clear signals for all four modes • Significances > 7 s J/y. D 0 J/y. D+ J/y. Ds J/y. Lc JHEP 06(2012) 141 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 21

(open charm)2 D 0 & open charm D+ & open charm D 0 D 0 D+ D+ D+ D 0 Ds D 0 Lc D + Lc D+ Ds For all cases significance > 5 s, 2. 5 sigma D+Lc+ JHEP 06(2012) 141 6 Dec 2 k+12 MPI@LHC JHEP 06(2012) 141 Vanya Belyaev, LHCb DPS measurements 22

Open charm + open anti-charm D 0 & open anti-charm D+ & open anti-charm • D 0 D- • • • D+ D- • For all cases significance > 8 s JHEP 06(2012) 141 6 Dec 2 k+12 MPI@LHC JHEP 06(2012) 141 Vanya Belyaev, LHCb DPS measurements 23

Cross-sections • Use per-event efficiency, mainly from DATA: trigger, particle ID, background etc. • Major systematic: tracking (reducible) Br(Lc), Br(Ds), …. JHEP 06(2012) 141 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 24

Cross-sections Major systematic: tracking (reducible) and Br(Lc), Br(Ds), …. JHEP 06(2012) 141 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 25

Cross-sections A. Berezhnoy et al. , Phys Rev D 57 4385 (1998) S. P. Baranov. Phys Rev D 73 074021 (2000) J. -P. Lansberg. Eur. Phys. J. C 61 693 (2009) 6 Dec 2 k+12 MPI@LHC JHEP 06(2012) 141 Vanya Belyaev, LHCb DPS measurements 26

Event Properties: p. T J/y + open charm: 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 27

Slope parameter for p. T-spectra • 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 28

Df & Dy correlations No evident correlations 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 29

Df & Dy correlations Clear correlations! 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 30

Compare with CDF’ 2 k+6 • CDF: azimuthal correlations for D • Large gluon splitting contribution http: //www-cdf. fnal. gov/physics/new/bottom/060921. blessed-double-charm-corr / (0, +) D*- Very different kinematical region 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 31

Mass distributions The same shape for m>7 Ge. V/c 2 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 32

Z 0&jets • Good test of p. QCD • Sensitive to PDF for small x and large Q 2 • Poorly constrained by existing measurements … and also possible contribution from DPS 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 33

Z 0&jets • 2 k+11 data set: 1 fb -1 CERN-LHCb-CONF-2012 -016 6 Dec 2 k+12 MPI@LHC Jet reconstruction Particle Flow: tracks, V 0, g, p 0 and • unmatched HCAL clusters • Anti-k algorithm, R = 0. 5 T Vanya Belyaev, LHCb DPS measurements 34

Jet distributions p. T> 10 Ge. V/c clean-up 2<h<4. 5 CERN-LHCb-CONF-2012 -016 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 35

s(Z 0+jets)/s(Z 0) • Jet multiplicity Fraction on jet events: DATA: 0. 229 ± 0. 06 ± 0. 09 FEWZ/MSTW 08 0. 212 ± 0. 009± 0. 016 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 36

DPS @ LHCb summary • Processes, sensitive to DPS, and their properties have been studied at LHCb with 2 k+10 and (part of) 2 k+11 data • 2×J/y is in good agreement both with SPS/p. QCD and DPS • J/y+C strongly disagree with SPS/p. QCD, supports DPS dominance (and well consistent with see charm quark contributions) • DPS is only partially supported by (open charm) : if DPS dominates s would be factor 2 -3 larger • The pattern of p -distributions is difficult to interpret if only one mechanism dominates • Z +jets is nicely consistent with SPS picture 2 eff T 0 Still more data to analyse (including √s=8 Te. V) … and more processes to study 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 37

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 Mad. Onia • MPI@LHC organizers for the invitation and all of you for your kind attention 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 38

BACK UP 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 39

Per-event efficiencies: • as much as possible from data MC DATA Diff 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 40

Efficiencies II • • • eiacc&rec&sel from (single charm) Monte Carlo Simulation • • As function of p. T & y for D 0, D+, Ds, Lc As function of p. T, y & cosq* for J/y • As function of p&h and #Tracks e. K , ep and ep from DATA using L 0→p+p- and D*+ →(D 0 →K-p+) p+ e 2 m, J/y from DATA, using inclusive J/y peak • As function of J/y p. T&y • As function of p. T&y etrg(J/y) & eitrg from DATA using inclusive J/y, D 0, D+, Ds+, Lc+ e*track from detailed DATA/MC comparison • As function of track p. T&h 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 41

Predictions for LHCb A. Berezhnoy et al. , Phys Rev D 57 4385 (1998) S. P. Baranov. Phys Rev D 73 074021 (2000) J. -P. Lansberg. Eur. Phys. J. C 61 693 (2009) S = 0. 1 mb 6 Dec 2 k+12 MPI@LHC 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. B 705 116 (2011) A. Novoselov, ar. Xiv: 1105. 62076 M. Luszczak, R. Maciula, A. Szczurek, ar. Xiv: 1111. 3255 Vanya Belyaev, LHCb DPS measurements 42

Yields & Significances Yield 6 Dec 2 k+12 MPI@LHC Significance Goodness-of-fit[%] Vanya Belyaev, LHCb DPS measurements • 43

Cross-section • Use Weight/ Plot technique: s s • Each event i has weight wi from s. Weight • Probability event to be signal • This weight is corrected by 1/e. TOT The price: The inflation of “statistical” error Need good control over efficiency! 6 Dec 2 k+12 MPI@LHC Vanya Belyaev, LHCb DPS measurements 44