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WP1 – Physics Performance

WP1 – Physics Performance. Andrea Dainese (INFN Padova). Outline. WP1 plans for 2014 Beam pipe radius: first considerations pp running requirements for beauty measurements Impact of MFT service barrel. ITS WP1 plans for 2014. Complete the studies that were not mature enough for the TDR

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WP1 – Physics Performance

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  1. WP1 – Physics Performance Andrea Dainese (INFN Padova) ITS Plenary meeting, 20.01.14 Andrea Dainese

  2. Outline • WP1 plans for 2014 • Beam pipe radius: first considerations • pp running requirements for beauty measurements • Impact of MFT service barrel ITS Plenary meeting, 20.01.14 Andrea Dainese

  3. ITS WP1 plans for 2014 • Complete the studies that were not mature enough for the TDR • Lc->V0+h, b-jets, D-correlations, nuclei with charm … • Input to decision on beam pipe radius: 20 or 18 mm • Requirements for running in pp at 14 TeV (not foreseen in LOI) • Physics performance with final detector specs (resolution, material) • Something can be done with hybrid method; but ultimately requires full MC • Effect of more realistic experimental conditions, for example pile-up •  New full MC simulation with updated/improved geom and more realistic conditions • Assess physics perf of ITS+TRD+TOF • Try with hybrid method, but ultimately requires full MC (reco w/o TPC) • Trigger: does ALICE need a ITS-based trigger (FastOR-like)? • Eg for UPC, for pp, can something be needed/useful also for HF-jets? • Further explore the potential of extended acceptance • in particular for correlations, also considering the usage of MFT • Fast simulation tools to study reconstruction of rare signals (beauty) • First discussions towards an “Upgrade Physics Performance Report” (timeline not defined, not for 2014, but it is a big project) ITS Plenary meeting, 20.01.14 Andrea Dainese

  4. Beam pipe and inner barrel Reduced: TDR: Changed to 1.94 ITS Plenary meeting, 20.01.14 Andrea Dainese

  5. Input on beam pipe radius: first considerations • Effects of a smaller beam pipe: • Tracking resolution improves • Conversions in the beam pipe occur closer to the primary vertex • Increase of innermost layers occupancy in Pb-Pb • Effect on fake probability to be quantified • Consider two measurements: • Heavy flavour reconstruction (e.g. LcpKp and Lb or B+) • This should benefit from 1. How much, needs to be quantified. Could be done with the Hybrid method, using the LHC13d19 production. Note that this production used already the 18 mm beam pipe. • Low-mass dielectrons • This should be affected by both 1. and 2. (see next slide) ITS Plenary meeting, 20.01.14 Andrea Dainese

  6. Lmee and beam pipe radius (1) • In the Lmee analysis for the upgrade, a cut on impact parameter is applied to reject background from charm (mainly) and a (small) part of the conversions • E.g. reject 55% of the charm electrons, keeping 80% of the primary electrons (signals) • These efficiencies enter in quadrature when considering the e+e- background • If the resolution improves, the charm rejection should improve • Potentially a large effect • Plan: estimate the improvement (reduction of systematic error from charm subtraction), using the parametrization of the resolution for smaller pipe scenario ITS Plenary meeting, 20.01.14 Andrea Dainese

  7. Lmee and beam pipe radius (2) • In the Lmee analysis for the upgrade, a cut on impact parameter is applied to reject background from charm (mainly) and a (small) part of the conversions • The effect on rejection of conversions in the beampipe and innermost ITS layer should be small: • The rejection power is already very small (~5-10%) • The smaller distance of the conversion point from the primary vertex decreases the separation (d0 ~ rpipe), but this is to some extent compensated by the better resolution (~ rpipe), so that s(d0)/d0 should remain ~constant d0 ITS Plenary meeting, 20.01.14 Andrea Dainese

  8. First look at reduced R case • Effect on resolution looks small (~10%, as expected) • Almost no effect above 0.8 GeV (region relevant for Lc) • Give priority to test with Lmee (effect is quadratic) • If promising, assess impact on fakes and look at Lc • Consider case of smaller pipe and current detector radii? Strong motivation from the mechanical point of view? • But could deteriorate conversion rejection for Lmee (should be quantified) Gudda ITS Plenary meeting, 20.01.14 Andrea Dainese

  9. pp running: energy and Lint • For charm and charmonium measurements (low S/B and large significance): Lint ~ 6/pb to give pp relative statistical errors smaller by sqrt(2) wrt Pb-Pb • i.e. error on RAA 20% larger than error on PbPb yield • Energy should be the same as Pb-Pb, because charm has a large interpolation error with pQCD Relative theoretical uncertainty on D s(5.5)/s(14) 2e6 s at 200 kHz 4e5 s at 200 kHz 1e5 s at 200 kHz 50% unc. below 2 GeV/c FONLL, Cacciari et al., JHEP 1210 (2012) 137 ITS Plenary meeting, 20.01.14 Andrea Dainese

  10. pp running: energy and Lint • For charm and charmonium measurements (low S/B and large significance): Lint ~ 6/pb to give pp relative statistical errors smaller by sqrt(2) wrt Pb-Pb • i.e. error on RAA 20% larger than error on PbPb yield • Energy should be the same as Pb-Pb, because charm has a large interpolation error with pQCD • Note: • One should keep in mind that the D measurements will be dominated by systematic errors: can we do with less than 6/pb? e.g. 3/pb? To be quantified. • These estimates are based on CDR performance; should be repeated with (better) TDR performance ITS Plenary meeting, 20.01.14 Andrea Dainese

  11. Need to consider also … • In the TDR we have shown that we can measure also • J/psiee from B decays • Fully reconstructed B and Lb decays in Pb-Pb • Jet physics not considered in the LOI estimate • Requirements being estimated (Mateusz) • MFT physics • To be discussed with MFT group ITS Plenary meeting, 20.01.14 Andrea Dainese

  12. pp reference: J/y from B • J/psi from B: <3/pbFiorella • Procedure: • Start from the statistical uncertainty at 7 TeV from 2010 data • Scale with statistics only (this is conservative, because also the better resolution reduces the error) • Compute Nevts needed to have stat. error = 3.5% (sqrt(2) times smaller than Pb-Pb error) ITS Plenary meeting, 20.01.14 Andrea Dainese

  13. pp reference: B and Lb • These measurements will have S/B >> 1 in pp, because the background is strongly reduced by the cuts and drops with 3rd power of multiplicity (three-track final state) • In addition, the S/ev is very small (much smaller than for charm measurements) • Therefore, they require significantly larger Lint, in order to have pp errors sqrt(2) times smaller than Pb-Pb ones • The positive aspect is that the pp reference can safely be measured at 14 TeV and scaled to 5.5 TeV Charm Beauty ITS Plenary meeting, 20.01.14 Andrea Dainese

  14. pp reference: Lb Cristina • Required integrated luminosity to make pp errors subdominant, calculated using the significance in each pT bin (larger value drives the requirement) • Calculated for the cases of pp 5.5 and pp 14 TeV • At 14 TeV the cross sections as larger by about x2.5  smaller Lint to get the same significance • These numbers have a larger unc. (being estimated) pT bin (pb-1) (pb-1) ITS Plenary meeting, 20.01.14 Andrea Dainese

  15. pp reference: B+ Johannes • Required integrated luminosity to make pp errors subdominant, calculated using the significance in each pT bin (larger value drives the requirement) • Calculated for the cases of pp 5.5 and pp 14 TeV • At 14 TeV the cross sections as larger by about x2.5  smaller Lint to get the same significance • These numbers have a larger unc. (being estimated) pT bin (pb-1) (pb-1) ITS Plenary meeting, 20.01.14 Andrea Dainese

  16. Summary on pp Lint requirements • *: from LOI, to be revised based on TDR performance • These numbers have sizeable uncertainty (being estimated) • Need to consider also: Jet Physics, MFT Physics ITS Plenary meeting, 20.01.14 Andrea Dainese

  17. Impact of MFT service barrel ITS Plenary meeting, 20.01.14 Andrea Dainese

  18. Impact of MFT service barrel • Multiple scattering: effect on pT resolution and matching eff • For electrons, additional effect due to bremsstrahlung • Production of conversions • For analyses that look for prompt electrons (Heavy Flavour electrons, Jpsiee, low-mass dielectrons): this will not be an issue, because hits in the innermost ITS layers are always required and this will reject all conversions at 50 cm • For analyses that use directly the conversions to measure direct photons, p0 and h: these analyses required a very accurate knowledge of the material details and positions. First estimate from experts: the material x/X0 between the vertex and the TPC should be know with accuracy of 2% for Run-3 (now it is 4%, but not very satisfactory). Implies that the ~1% x/X0 of the MFT barrel should be know to an accuracy of 3% See next slides ITS Plenary meeting, 20.01.14 Andrea Dainese

  19. MFT barrel: multiple scattering Need full MC to assess additional bremsstrahlung effect for electrons (probably dominant) ITS Plenary meeting, 20.01.14 Andrea Dainese

  20. MFT barrel: multiple scattering ITS Plenary meeting, 20.01.14 Andrea Dainese

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