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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 0 + jets analysis Conclusions. LHCb DPS measurements. - PowerPoint PPT Presentation
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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
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 3
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
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 4
Double Parton Scattering
6 Dec 2k+12 MPI@LHC
287k documents
Vanya Belyaev, LHCb DPS measurements 5
DPS: simple paradigm
scatters
6 Dec 2k+12 MPI@LHC
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)
Vanya Belyaev, LHCb DPS measurements 6
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)
6 Dec 2k+12 MPI@LHC
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
Vanya Belyaev, LHCb DPS measurements 7
LHCb experiment
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 8
LHCb: beauty detector
6 Dec 2k+12 MPI@LHC
General purpose universal detector in forward region
2<h<5
4% of solid angle
40% of heavy quarks
pp-collisions
Vanya Belyaev, LHCb DPS measurements 9
VELO
6 Dec 2k+12 MPI@LHC
42×2 silicon strip planes
r-f geometry
40-100 mm pitch
7mm away from the beam
Vanya Belyaev, LHCb DPS measurements 10
Tracking system
6 Dec 2k+12 MPI@LHC
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
Vanya Belyaev, LHCb DPS measurements 11
Hadron ID
6 Dec 2k+12 MPI@LHC
Two RICH detectors
Good p/K separation up to ~100 GeV/c
Vanya Belyaev, LHCb DPS measurements 12
Calorimeter system
6 Dec 2k+12 MPI@LHC
Scintillating Pad Detector/SPD
Preshower Detector
Electromagnetic Shashlik Calorimeter
Hadron Tile Calorimeter
Important to trigger hadronic final states
Vanya Belyaev, LHCb DPS measurements 13
Muon system
6 Dec 2k+12 MPI@LHC
4(+1) stations
MWPC
0.7% p→mmisID
Vanya Belyaev, LHCb DPS measurements 14
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%
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 15
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
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 16
Dimuons: J/y and Z0
• Yields @ 7 TeV 1.5×108/fb-1
• Yields @ 7 TeV 5.5×104/fb-1
6 Dec 2k+12 MPI@LHC
arXiv:1204.1620 JHEP 06(2012) 141
Vanya Belyaev, LHCb DPS measurements 17
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
6 Dec 2k+12 MPI@LHC
JHEP 06(2012) 141
Vanya Belyaev, LHCb DPS measurements 18
Event Selection
J/yС two charm with common vertex
2×Open charm hadrons
6 Dec 2k+12 MPI@LHC
m+
m-
K-
p+
D0
K-
p+
D0
D0
Vanya Belyaev, LHCb DPS measurements 19
Make a common vertex and refit
• Global c2/ndf from consistency refit:• Remove pileup, cascade and background
6 Dec 2k+12 MPI@LHC
JHEP 06(2012) 141
signal signalbackground
background
Vanya Belyaev, LHCb DPS measurements 20
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
6 Dec 2k+12 MPI@LHC
PLB707(2011) 52
pPt: 16±4 J/yJ/y
pPt: 13 J/yJ/y
Vanya Belyaev, LHCb DPS measurements 21
Signal extraction
• J/y + open charm• clear signals for all four modes• Significances > 7s
6 Dec 2k+12 MPI@LHC
JHEP 06(2012) 141
J/yD0
J/yD+
J/yDs J/yLc
Vanya Belyaev, LHCb DPS measurements 22
(open charm)2
D0 & open charm D+ & open charm
6 Dec 2k+12 MPI@LHC
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
Vanya Belyaev, LHCb DPS measurements 23
Open charm + open anti-charm
D0 & open anti-charm D+ & open anti-charm
6 Dec 2k+12 MPI@LHC
For all cases significance >
8s
JHEP 06(2012) 141 JHEP 06(2012) 141
𝐃𝟎𝐃𝟎D
0D-
D𝟎D𝒔−
D𝟎𝚲𝐜−
D+
D- D+¿D 𝒔
−¿
Vanya Belyaev, LHCb DPS measurements 24
Cross-sections
• Use per-event efficiency, mainly from DATA: trigger, particle ID, background etc.
• Major systematic: tracking (reducible)Br(Lc), Br(Ds), ….
6 Dec 2k+12 MPI@LHC
JHEP 06(2012) 141
Vanya Belyaev, LHCb DPS measurements 25
Cross-sections
Major systematic: tracking (reducible) and Br(Lc), Br(Ds), ….
Major systematic: tracking (reducible) and Br(Lc), Br(Ds), ….
6 Dec 2k+12 MPI@LHC
JHEP 06(2012) 141
Vanya Belyaev, LHCb DPS measurements 26
Cross-sections
6 Dec 2k+12 MPI@LHC
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
Vanya Belyaev, LHCb DPS measurements 27
Event Properties: pT
J/y + open charm:
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 28
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
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 29
Df & Dy correlations
6 Dec 2k+12 MPI@LHC
No evident correlations
Vanya Belyaev, LHCb DPS measurements 30
Df & Dy correlations
6 Dec 2k+12 MPI@LHC
Clear correlations!
Vanya Belyaev, LHCb DPS measurements 31
Compare with CDF’2k+6
• CDF: azimuthal correlations for D(0,+) D*- • Large gluon splitting contribution
Very different kinematical region
6 Dec 2k+12 MPI@LHC
http://www-cdf.fnal.gov/physics/new/bottom/060921.blessed-double-charm-corr/
Vanya Belyaev, LHCb DPS measurements 32
Mass distributions
6 Dec 2k+12 MPI@LHC
The same shape for m>7 GeV/c2
Vanya Belyaev, LHCb DPS measurements 33
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
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 34
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
6 Dec 2k+12 MPI@LHC
CERN-LHCb-CONF-2012-016
Vanya Belyaev, LHCb DPS measurements 35
Jet distributions
pT> 10 GeV/cclean-up
2<h<4.5
6 Dec 2k+12 MPI@LHC
CERN-LHCb-CONF-2012-016
Vanya Belyaev, LHCb DPS measurements 36
s(Z0+jets)/s(Z0)
• Jet multiplicity
6 Dec 2k+12 MPI@LHC
Fraction on jet events:
DATA: 0.229 ±0.06 ±0.09
FEWZ/MSTW08 0.212 ±0.009±0.016
Vanya Belyaev, LHCb DPS measurements 37
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
6 Dec 2k+12 MPI@LHC
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
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 39
BACK UP
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 40
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 )
6 Dec 2k+12 MPI@LHC
MC
DATA
Diff
Vanya Belyaev, LHCb DPS measurements 41
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
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 42
Predictions for LHCb
6 Dec 2k+12 MPI@LHC
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
Vanya Belyaev, LHCb DPS measurements 43
Yields & Significances
6 Dec 2k+12 MPI@LHC
>5s
4 J/yC
6 CC
7
Yield Goodness-of-fit[%]Significance
Vanya Belyaev, LHCb DPS measurements 44
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
6 Dec 2k+12 MPI@LHC
The price:
The inflation of “statistical” error
Need good control over efficiency!
Vanya Belyaev, LHCb DPS measurements 45
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, …
6 Dec 2k+12 MPI@LHC
Vanya Belyaev, LHCb DPS measurements 46
Theory: double charm at LHCb
• Ff
6 Dec 2k+12 MPI@LHC
PYTHIA
State-of-art pQCD