Multiple Partonic Interaction measurements at LHCb

Multiple Partonic Interaction measurements at LHCb

Measuring Multiple Partonic Interactions at the LHC

Research Workshop of the Israel Science Foundation

14-18 October 2012, Tel Aviv, Israel

Raluca Muresan Horia Hulubei National Institute of Physics and Nuclear Engineering

On behalf of the LHCb collaboration

R. Muresan - MPI at LHCb 2

Disclaimer

This talk represents a collections of LHCb results:

soft-QCD, EW, charm production

relevant for the MPI models, rather than a collection of measurements of the MPI observables and their interpretation.

The list might not be exhaustive and some of the results presented

are flashed or only hinted at.

October 2012 - Tel Aviv


LHCb detector


Designed to look for physics beyond the SM by studies of CP violation and rare decays using b & c hadrons JINST 3 (2008) S08005.


LHCb detector


Forward coverage15-300(250) mrad, high precision tracking and vertexing, excellent PIDPerfect tool for a large variety of physics studies in the forward region

JINST 3 (2008) S08005.


Unique space coverage

LHCb fully instrumented in an h range from 2 to 5.

Forward region particularly sensitive to MPI and low Bjorken-x QCD dynamics


6

LHCb data

October 2012 - Tel Aviv R. Muresan - MPI at LHCb

0.9 TeV 0.31 nb−1; 2.76 TeV 100 nb−1; 37.5 pb−1 7 TeV (2010) pA data taking planed for the beginning of the next year


Large coverage in rapidity loss


0.9 TeV & 2.76 TeV farther from the beam in y;

7 TeV & 8 TeV, overlap in rapidity loss; probing energy scale violation.

R. Muresan - MPI at LHCb 8October 2012 - Tel Aviv

P. Skands


LHCb - soft QCD results

KS0 x-section @ 0.9 TeV, PLB 693 (2010) 69-80;

V0 ratios: baryon vs. meson suppression & baryon number transport at @ 0.9 TeV and 7 TeV; JHEP 1108 (2011) 034.

ϕ cross-section @ 7 TeV; PLB 703 (2011) 267-273. Charged particle multiplicities @ 7 TeV EPJC 72 (2012) 1947

Measurement of forward energy flow LHCb-CONF-2012-012 @ 7 TeV Particle ratios at 0.9 & 7 TeV, arXiv:1206.5160 (accepted EPJ. C)


http://cdsweb.cern.ch/record/1285983?ln=en




https://cdsweb.cern.ch/record/1428912?ln=en

http://arxiv.org/abs/arXiv:1206.5160


Multiplicity studies

Particles counted using the tracks in Vertex Locator:

high efficiency, minimal material interaction, partial backward coverage, but no momentum measurement.

Prompt charge particle production

e, μ, p ,K, p with sum average proper lifetimes of the ancestors < 10ps.

2 x 1.5 M events, both magnet polarities were used.


Eur. Phys. J. C 72 (2012) 1947


Multiplicity studies


Multiplicity distributions

Charged particle densities

Eur. Phys. J. C 72 (2012) 1947

Several generators & tune predictions were compared to the data; none are able to describe them fully; as a general trend the multiplicity and charged particle densities are underestimated


Forward energy flow Energy flow (EF) @ high η - directly sensitive to the amount of

parton radiation and Multiple Parton Interaction (MPI). EF measurements results useful both for the collision physics

and for the ultra-high energy cosmic-ray interaction models. EF defined as:


1

N inttotdE

ddEtot is the total energy of stable particles in the η binNint number of inelastic pp interactions

Experimentally determined for a Δη bin:

1

1

Nint

Ei ,i1

N part,

Ei,η energy of an individual particle

LHCb-CONF-2012-012


Data and event sample

Inclusive MB at least one track p >2 GeV/c

Hard scattering at least one track pT > 3 GeV/c

Diffractive enriched inclusive MB with no tracks in

−3.5<η<−1.5

Non-diffractive enriched

inclusive MB with at least one track in −3.5<η<−1.5


Correction for detector effects - bin-by-bin from simulation

Systematic uncertainties: tracking multiple interaction events (5% of events) simulation model

0.1 nb-1 low luminosity LHC run @7 TeV Events with at least one well reconstructed track

LHCb-CONF-2012-012


Total forward energy flow


Corrected total EF compared with PYTHIA generator predictions.

Total EF underestimated at high η by all the PYTHIA6 tunes used and for all event categories studied.

PYTHIA 8 describes well the total EF for diffractive enriched events.

Similar conclusions hold for charged energy flow

LHCb-CONF-2012-012


Total forward energy flow


Corrected total EF compared with cosmic ray generators predictions.

Cosmic-ray models overestimate the total EF.

SYBILL/EPOS gives the best description of the total EF for inclusive MB events.

QGSJETII-03 gives reasonable description of the total EF for hard scattering events.

LHCb-CONF-2012-012


Prompt hadron production ratios

0.3 nb-1 of data @0.9 TeV and 1.8 nb-1@7 TeV low int LHC run. Simulated events used to calculate efficiencies and estimate

systematic uncertainties. PID calibration using data samples of Corrections applied for:

effects of non-prompt contamination, geometrical acceptance losses, track finding inefficiency.

Systematic uncertainties: PID (most important – size of calibration sample) , interaction x-section & amount of material, tracking & non-prompt contamination.


K S0 , p , K K

arXiv:1206.5160


Same particle ratios


The ratios differ from unity especially at high pT and high η. The behaviour is well described by all the generator tunes.

arXiv:1206.5160

0.9 TeV 0.9 TeV7 TeV 7 TeV


Strange vs. up/down particles


Tendency for data to lie significantly higher than Perugia 0 and Perugia NOCR PYTHIA 6 tunes, excess strangeness being produced compared to some MCpredictions.

arXiv:1206.5160

0.9 TeV 7 TeV


Strange vs. up/down particles


φ cross-section measurement Phys.Lett. B703 (2011).

Tendency for measurements to lie significantly higher than Perugia 0 and Perugia NOCR tune, excess strangeness seems to be produced compared to some MC predictions.

arXiv:1206.5160

0.9 TeV 7 TeV


Baryon suppression


Data lie in most cases significantly higher than predictions – especially at high pT

and high η.

arXiv:1206.5160

0.9 TeV 7 TeV


Baryon suppression


JHEP 1108 (2011) 034

arXiv:1206.5160

0.9 TeV 7 TeV

Data lie in most cases significantly higher than predictions – especially at high pT and high η.


Baryon transport


At 0.9 TeV theratio from 0.8 to0.4 in the highest pT and η bin. Data usually below LHCb MC and Perugia 0 predictions closer to Perugia NOCR PYTHIA 6 tunes

arXiv:1206.5160

0.9 TeV 7 TeV

p / p


Baryon transport


At 0.9 TeV the ratio from around 0.8to around 0.4 in the highest pT and η bin. Data below LHCb MC and Perugia 0 predictions closer to Perugia NOCR

JHEP 1108 (2011) 034.

arXiv:1206.5160

0.9 TeV 7 TeV

p / p


Baryon transport vs. rapidity loss


LHCb results cover a larger rapidity loss than any other single experiment and significantly improve the measurement precision in the region Δy = yb-y< 6.5.

arXiv:1206.5160

JHEP 1108 (2011) 034


EW results


LHCb probes two x-Q2 regions:Medium Q2 (104 GeV2): Z,W measurements x= 1.6 x10-4; Low Q2 (~ 25 GeV2): Drell-Yan ( γ*) towards x= 8 x10-6


EW measurements @ 7 TeV


Central exclusive di-m production LHCb-CONF-2011-022, 37 pb-1.Z0 x-section using Z0 -> t+t- LHCb-CONF-2011-041, 248 pb-1 (an update to be released soon LHCb-PAPER-2012-029, see for the moment LHCb-TALK-2012-254)

W & Z production: x-sections; differential x-sections; x-section ratios and lepton charge asymmetry arXiv:1204.1620 – accepted in JHEP (Z0 ->m+m-, W±-> m± ), n 37pb-1.x-section for Z0->e+e- production LHCb-CONF-2012-011, 945 pb-1.Jet production in Z0/g* events LHCb-CONF-2012-016, 1.02 fb-1. Low mass Drell Yan production LHCb-CONF-2012-013, 37pb-1.





http://cdsweb.cern.ch/record/1428904




Z0


Compared to NNLO and NLO predictions with different PDF for the proton. PDF uncertainty, evaluated at the68% CL.

Differential x-section in yZ alsoavailable spares & arXiv:1204.1620

arXiv:1204.1620, LHCb-CONF-2011-041, LHCb-CONF-2012-011


W&Z


Z0 ->m+m-

W+-> m+n

W--> m-n

Rw

(W++W-)/Z0

W+/Z0

W-/Z0

arXiv:1204.1620


W&Z


W differential x-section & RW as function of hm

also available spares & arXiv:1204.1620

arXiv:1204.1620


W&Z


Theory using DYNNLO + MSTW08 @NNLO LHCB-TALK-2012-254


Z0/g* +jet production

Z0/g*-> mm channel measurement, normalised to the total inclusive Z0/g*->mm x-section;

2.0 <h (μ)< 4.5, pT(μ) ≥ 20 GeV/c; dimuon 60 ≤M≤ 120 GeV/c2


Jets : reconstructed using the anti-kT algorithm with R = 0.5, and corrected to the hadron level. 2.0 <h < 4.5 and pT >10 GeV/c separated from μ of the Z0/g* by a distance R(μ, jet) ≥ 0.4 in η – φ space.

LHCb-CONF-2012-016

Event display

x-section ratio 0.229 ± 0.011 consistent with SM predictions




LHCb-CONF-2012-016

NLOprediction




LHCb-CONF-2012-016


Inclusive low mass Drell-Yan production

2 m final states: 2< h < 4.5 & 5 < M < 120 GeV/c2. pm

>10 GeV/c and pmT >3 GeV/c. For M>40 GeV/c2

pmT >15 GeV/c.


Extraction of signal yield uses a fit of the minimum muon isolation of the two muons i.e. fraction of the pT of the muon jet carried by the m.

LHCb-CONF-2012-013




LHCb-CONF-2012-013


Selected charm results @ 7 TeV

Cross-section measurements:

e.g J/ψ EPJ.C 71 (2011) 1645. Ratio of prompt χc to J/ψ production: arXiv:1204.1462. Production asymmetry measurements: e.g. Ds- anti Ds:

PLB 713 (2012) 186-195.

J/ψ pair production: PLB 707 (2012) 52–59, 37 pb-1. Double charm production involving open charm: JHEP

06 (2012) 141, 355 pb-1.











J/ψ pair production


Production of J/ψ pairs has been observed with a statistical significance in excess of 6 σ

Only statistical uncertainties

Theoretical prediction fromPRD 84 (2011) 094023

PLB 707 (2012)


Double charm production


Measured cross-sections, charged conjugate modes are included

Hatched areas: PRD 57 (1998) 4385 PRD 73 (2006) 074021.

Shaded area: EPJC 61 (2009) 693

JHEP 06 (2012)


Double charm production


Measured ratioscharged conjugate modes are included

Expectations from DPS using the x-section measured at Tevatron for multijet events

Properties of J/ψC, CC and C-anti C events were studied: pT,, slope parameters of pT spectra, difference in azimuthal angleand y etc. see spares and JHEP. 06 (2012) 141.

JHEP 06 (2012)


Stay tuned !for our future

resultsexploiting also the

data @ 2.76 & 8 TeV &pA


LHCb is not only a b&c-physics experiment but provides also an excellent environment for forward physics studies impacting on the MPI models

Have a look to the full list of the LHCb papers & LHCb conference contributions

http://cdsweb.cern.ch/collection/LHCb%20Papers?ln=en

http://cdsweb.cern.ch/collection/LHCb%20Papers?ln=en

http://cdsweb.cern.ch/search?ln=en&cc=LHCb+Conference+Contributions&sc=1&as=1&m1=o&p1=LHCb&f1=&op1=n&m2=a&p2=tbc&f2=title&op2=a&m3=a&p3=&f3=&action_search=Search&dt=&d1d=&d1m=&d1y=&d2d=&d2m=&d2y=&sf=&so=a&rm=&rg=10&of=hb

http://cdsweb.cern.ch/search?ln=en&cc=LHCb+Conference+Contributions&sc=1&as=1&m1=o&p1=LHCb&f1=&op1=n&m2=a&p2=tbc&f2=title&op2=a&m3=a&p3=&f3=&action_search=Search&dt=&d1d=&d1m=&d1y=&d2d=&d2m=&d2y=&sf=&so=a&rm=&rg=10&of=hb


Spares



Forward charged energy flow


Corrected charged energy flow compared with PYTHIA generator predictions.

All PYTHIA 6 tunes used underestimate the charged EF at high η for all the type of events studied.

PYTHIA 8 describes the best the charged EF for diffractive enriched events. LHCb-CONF-2012-012


Forward charged energy flow


Corrected charged EF vs. cosmic ray generators predictions.

Cosmic-ray models overestimate the charged EF.

SYBILL/EPOS best description of the inclusive MB charged EF.

QGSJETII-03 reasonable description of the charged EF in hard scattering.

Diffractive charged EF is underestimated by the cosmic-ray models

LHCb-CONF-2012-012


LHCb-MC & Perugia tunes

• PYTHIA6 generates pp interactions up to hadronization; the CTEQ6L parametrisation for the PDFs.

EvtGen to generates the decay and evolution of all particles, B hadrons, generic and user/signal.

delegate to PYTHIA when decay not present in decay table

delegate to Photos for QED radiative corrections



LHCb-MC & Perugia tunesLHCb PYTHIA tune:

I. Belyaev et al., Handling of the generation of primary events in Gauss, the LHCb simulation framework, Nuclear Science Symposium Conference Record (NSS/MIC) IEEE (2010) 1155.

PYTHIA used with P. M. Nadolsky et al., Implications of CTEQ global analysis for

collider observables, Phys. Rev. D78 (2008) 013004, arXiv:0802.0007.

M. Bengtsson and T. Sjostrand, Parton showers in �Leptoproduction Events, Z. Phys. C37 (1988) 465.

Tuning Monte Carlo Generators: The Perugia Tunes, Peter Zeiler Skands; Phys.Rev. D82 (2010) 074018



Protons vs. kaons


Agreement with simulationgenerally good, but results hard to interpret.

arXiv:1206.5160

0.9 TeV 7 TeV


Theory prediction for the EW – W&Z production

• The results are compared to theoretical predictions calculated at NNLO with the program DYNNLO (Phys. Rev. Lett. 98 (2007) 543 222002) for the NNLO PDF sets of MSTW08 (EPJC63 (2009) 189), ABKM09 (Phys. Rev. D81 (2010) 567 014032), JR09 (Phys. Rev. 569 D79 (2009) 074023), HERA15 (JHEP 01 (2010) 109) and NNPDF21 (Nucl. Phys. B838 (2010) 136) and at NLO for the NLO PDF set CTEQ6M (Phys. Rev. D78 (2008) 013004).



Z


Consistent to each other and to NNLO predictions.

arXiv: 1204.1620LHCb-CONF-2012-011


W


arXiv: 1204.1620

R. Muresan - MPI at LHCb 52October 2012 - Tel Aviv

Lepton charge asymmetry in bins of hm

Am=(W+-W-)/(W++W-)

arXiv: 1204.1620


Double charm



Double charm


JHEP 06 (2012)

Multiple Partonic Interaction measurements at LHCb

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