darren price – production of j/ at atlas :: quarkonium2011, vienna :: april 18 th ‘11 page 1...

Darren Price – Production of J/ at ATLAS :: Quarkonium2011, Vienna :: April 18th ‘11

Inclusive, prompt and non-prompt J/Inclusive, prompt and non-prompt J/ production in pp collisions at 7 TeVproduction in pp collisions at 7 TeVProbing QCD at the LHC, Quarkonium2011, ViennaProbing QCD at the LHC, Quarkonium2011, Vienna

Darren PriceDarren Price, , INDIANA UNIVERSITYINDIANA UNIVERSITY

on behalf of the ATLAS Collaborationon behalf of the ATLAS Collaboration


Introduction

In this talk is presented measurement of the:

Inclusive J/ production cross-section Fraction of J/ from B-decays Non-prompt J/ production cross-section Prompt J/ production cross-section

using the ATLAS detector with ~2.2 pb-1 data from 2010 running.

The measurements are presented both differentially as a function of J/ pT and rapidity, and integrated over the maximum span of these to provide integrated cross-sections

Experimental uncertainties are at the 10—15% level across the range of measured cross-sections, and the results are systematics limited over the bulk of the distributions

Results are compared to theoretical predictions from Colour Evaporation Model, Colour Singlet NNLO* and FONLL where appropriate.

arXiv:1104.3038


Dataset selection and trigger

Trigger selection:

Use single muon seeded trigger (and Minimum Bias Scintillator based trigger in very early data-taking) with open (~0 GeV), 4 GeV and 6 GeV thresholds as instantaneous luminosity increased (to keep rate under control)

B-fraction measurement uses a logical OR of all of these triggers, giving increased candidate events and (slightly) higher integrated luminosities

Event-based selection:

Has two reconstructed muons (with Inner Detector matched track).Three tracks associated to Primary Vertex (PV)Tracks associated to these muons/PV pass loose selection criteria of at least one pixel hit, and at least six hits in the Silicon tracker


Candidate selection

Combined muon

Muon spectrometer Calorimeters Inner DetectorTagged muon

Muons associated to J/ candidate may be:Combined (full Muon Spectometer & Inner Detector track measurement with fit between the two)Tagged (Inner Detector measurement associated to at least one hit in Muon Spectrometer)

Tagged increases chance of fake muon signature, so require at least one of muons in pair to be combined

At least one muon in pair must have been the object that fired the trigger.

Muons must have p>3 GeV, pT>1 GeV, ||<2.5, pixel hits >0, silicon hits>5


Event/candidate selection

2.2 pb-1

= 46 MeV = 111 MeV


Basic strategy of inclusive cross-section analysis method is:Reconstruct J/ candidates in pT-y binsCorrect candidate-by-candidate for efficiency, bin migrations, acceptances

Ncorr = w-1.Nreco

Fit resultant weighted yields to derive signal component NcorrNJ/corr

Extract resultant cross-section from NJ/corr in given analysis bin

Measurement of inclusive cross-section

Detector acceptance

Reconstruction efficiency

Trigger efficiency

Bin migration

ID reco efficiency (per muon track)


Spin-alignment and acceptance

ATLAS CMS LHCb

Graphic from C. Lourenco

Acceptance maps correct from offline reconstruction efficiency to total inclusive distributionModel-dependent on spin-alignment scenarioAlso correct for differences between prompt and non-prompt J/ spectra


Bin migration and track/vertex efficiencies

Bin migration effectsDue to finite detector resolution J/ candidate measured in one bin at reconstruction level may be identified with a different analysis bin before smearing.

Correct for by parameterising unfolded cross-section, smearing with muon resolution measured in ATLAS, and looking at change in yields in given bin

Effect varies from 0.1% to 3% across measured phase space

ID track reconstructionID track reco efficiency correction 99.5% per (muon) track with 0.5% uncertainty per track added linearly

Vertex requirementRequire di-muon pair to fit to common vertex. Determined that impact on (real) J/ candidates was below 0.1% and so correction is neglected.Requirement does reduce continuum background


Trigger efficiencies

Trigger efficiency maps derived from hybrid scheme of finely-binned Monte Carlo (needed to remove biases) reweighted using Tag & Probe data from J/ (low pT) and Z (high pT) decays

Significant charge dependence observed (and corrected for)Muon turn-on thresholds needed accurate handling Fine granularity needed to properly model features (even at high pT)

Efficiencies plateau at around 80-100% dependent on pseudorapidity


Reconstruction efficiencies

Reconstruction efficiency maps derived from Tag & Probe data from J/ supported by Z derived data at higher pT for improved precision in plateau region

Reconstruction efficiency for low pT from J/ decays

Reconstruction efficiency at high pT from Z data


Weighted fits and cross-section extraction

For inclusive cross-section measurement, a binned 2 fit was used

Was found to give stable unbiased weighted fit results w.r.t unbinned maximum likelihood fits once restricted to fine pT—y slices as in this analysis

low pT, central rapidity high pT, forward rapidity


Systematic studies: “acceptance”

Acceptance map MC statistics: Obtained from dedicated MC simulation. Statistical uncertainties on maps bin-to-bin propagated through to final result (contribution at level of 1-2%)

Bin migration effectsBin migration effects were studied, corrections applied (0.1—3%) and variation of bin migration within bin considered as systematic on correction

ID track reconstructionID track reco efficiency correction 99.5% per muon track with 0.5% uncertainty per track added linearly

Kinematic dependenceVariation of MC spectra to make acceptance maps, and correction for slight differences in non-prompt/prompt acceptance assigned as systematic (max 1.5%)

Final state radiationCentral result is corrected back to J/ kinematics rather than final state muon kinematics, systematic due to FSR is <0.1% (NB: taking effect of FSR on/off is overestimate)


Systematic studies: other components

Spin alignment Spin-alignment uncertainty is maximum envelope of cross-section re-casted under different spin-alignment hypothesis

LuminosityQuoted 3.4% uncertainty from Van der Meer scans

Muon reconstruction efficiencyUncertainties on J/ reco. efficiency maps from data and uncertainties on MC/data scale factors propagated through to final result (5—10%)

Fit uncertaintyDerived via pseudo-experiments – approx. 1—3% contribution

Trigger efficiencySimilarly, uncertainties from data maps propagated through to final result (~5% effect)

J/ vertex finding and primary vertex efficienciesBoth these efficiencies retain more than 99.9% signal, no uncertainty assigned


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Inclusive cross-section results

arXiv:1104.3038


Integrated inclusive cross-sections

We also sum up the measured differential inclusive cross-sections in two regions and quote the integrated cross-sections (taking into account correlations in the uncertainties)

For pT>7 GeV, |y|<2.4 (maximum rapidity span)

For pT>1 GeV, 1.5<|y|<2.0 (maximum transverse momentum span)


Measurement of non-prompt fraction

Perform simultaneous unbinned maximum likelihood fit on invariant mass and pseudo-proper time distribution (used as discriminant for prompt/non-prompt J/) to determine fraction in pT—y bins

Mass fit: signal – gaussian with per-event errorbackground – Chebyshev polynomial

Lifetime fit:signal – delta function plus exponential convoluted with

gaussian with per-event error to account for resolutionbackground – symmetric positive/negative exponentials plus

positive exponential convoluted with gaussian with per-event error for resolution


Simultaneous mass/lifetime fit projections


Systematic uncertainties for B-fraction

Many systematics cancel fully or partially in taking the ratio. Effects studied include:

Impact of acceptance, muon reconstruction, trigger efficiencies on fraction

Cancellation within statistical uncertainties for efficiency Correction for non-prompt/prompt acceptance and uncertainty

assigned

Background model variationsPer-event convolution function changed to per-event double GaussianChebyshev polynomial of degree 2 changed to 1 and 3 to test stability

Spin alignment uncertainty of prompt/non-prompt components propagated

Multiple primary vertices: No significant variation seenMass region: wider mass, include/exclude (2S): Stable; no systematic assignedSimultaneous fit: mean invariant mass plotted as function of lifetime

Found to be flat, no correlation systematic assigned


Non-prompt fraction results

arXiv:1104.3038


Prompt and non-prompt cross-sections

From inclusive cross-section and non-prompt fraction we can derive the prompt and non-prompt cross-sections

Take into account uncertainty correlations that exist between the two measurements (overlapping data samples!) and merge analysis bins where required

For the prompt cross-section we compare to predictions fromNLO/NNLO* pQCD (Colour Singlet) [J.P.Lansberg]Colour Evaporation Model [R. Vogt]

For the non-prompt cross-section we compare to predictions fromFixed Order Next-to-Leading-Log (FONLL) [M. Cacciari]


Non-prompt cross-sections

Integrated cross-sections again provided in two regions:

Assume isotropic distribution for spin-alignment central value (for consistency with inclusive and prompt results)

Spin-alignment envelope for non-prompt covers possible variation from isotropic i = 0 to = ~±0.1 as measured by CDF/Babar (only * angle dependence!)


Non-prompt cross-section

arXiv:1104.3038


Prompt cross-sections

Integrated cross-sections again provided in two regions:

Assume isotropic distribution for spin-alignment central value (for consistency with inclusive and prompt results)

Spin-alignment envelope here covers maximal envelope of possible variation of result due to spin-alignment configurations in both angles * and *


Prompt cross-section results

arXiv:1104.3038


Summary

Measurement of inclusive cross-section of J/ in four rapidity bins from pT

1—70 GeV (span rapidity-dependent) [arXiv:1104.3038]

Measurement of non-prompt production fraction and derivation of prompt and non-prompt production cross-sections from these two measurements

Highest reach in pT of any previous such measurement

Complementary results to other LHC measurements (rapidity and pT), good agreement with CMS where measurements overlap

Non-prompt FONLL predictions do good job of describing non-prompt production within scale uncertainties

Description of prompt production more problematic, but clearly represent a step forward over historical predictions

Expect many more results from quarkonia sector from ATLAS in future!


Additional slides


Di-muon invariant mass distribution

Combined + combined di-muon pair, 15,2.5 GeV


Charge-dependence of muon reco./trigger

Due to the toroidal magnetic field of the ATLAS Muon Spectrometer, muons with positive (negative) charge are bent towards larger (smaller) .

Introduces a charge dependence of the muon reconstruction/trigger efficiencies, particularly relevant at very large ||, where muons of one charge may be bent outside the detector geometrical acceptance, and at low pT, where muons of one charge may be bent back before reaching spectrometer stations


Charge-dependence of muon reco./trigger

Reconstruction efficiency of Combined (CB) + Tagged (ST) muons as a function of charge*pseudorapidity in MC and data

Low pT High pT

darren price – production of j/ at atlas :: quarkonium2011, vienna :: april 18 th ‘11 page 1...

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