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

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

ITS WP1 plans for ) Complete the studies that were not mature enough for the TDR Lc->V0+h, b-jets, D-correlations, nuclei with charm … 2) Input to decision on beam pipe radius: 20 or 18 mm 3) Requirements for running in pp at 14 TeV (not foreseen in LOI) 4) Physics performance with final detector specs (resolution, material) Something can be done with hybrid method; but ultimately requires full MC 5) Effect of more realistic experimental conditions, for example pile-up  New full MC simulation with updated/improved geom and more realistic conditions 6) Assess physics perf of ITS+TRD+TOF Try with hybrid method, but ultimately requires full MC (reco w/o TPC) 7) Trigger: does ALICE need a ITS-based trigger (FastOR-like)? Eg for UPC, for pp, can something be needed/useful also for HF-jets? 8) Further explore the potential of extended acceptance in particular for correlations, also considering the usage of MFT 9) Fast simulation tools to study reconstruction of rare signals (beauty) 10) First discussions towards an “Upgrade Physics Performance Report” (timeline not defined, not for 2014, but it is a big project) ITS Plenary meeting, Andrea Dainese 3

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

Input on beam pipe radius: first considerations Effects of a smaller beam pipe: 1.Tracking resolution improves 2.Conversions in the beam pipe occur closer to the primary vertex 3.Increase of innermost layers occupancy in Pb-Pb  Effect on fake probability to be quantified Consider two measurements: a.Heavy flavour reconstruction (e.g.  c  pK  and  b 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. b.Low-mass dielectrons  This should be affected by both 1. and 2. (see next slide) ITS Plenary meeting, Andrea Dainese 5

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, Andrea Dainese 6

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 (d 0 ~ r pipe ), but this is to some extent compensated by the better resolution (~ r pipe ), so that  d 0 )/d 0 should remain ~constant ITS Plenary meeting, Andrea Dainese 7 d0d0

First look at reduced R case Effect on resolution looks small (~10%, as expected) Almost no effect above 0.8 GeV (region relevant for  c ) Give priority to test with Lmee (effect is quadratic) If promising, assess impact on fakes and look at  c 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) ITS Plenary meeting, Andrea Dainese 8 Gudda

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

pp running: energy and L int For charm and charmonium measurements (low S/B and large significance): L int ~ 6/pb to give pp relative statistical errors smaller by sqrt(2) wrt Pb-Pb i.e. error on R AA 20% larger than error on PbPb yield Energy should be the same as Pb-Pb, because charm has a large interpolation error with pQCD ITS Plenary meeting, Andrea Dainese 10 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

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  b 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, Andrea Dainese 11

pp reference: J/  from B J/psi from B: <3/pb Fiorella 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, Andrea Dainese 12

pp reference: B and  b These measurements will have S/B >> 1 in pp, because the background is strongly reduced by the cuts and drops with 3 rd 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 L int, 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 ITS Plenary meeting, Andrea Dainese 13 Charm Beauty

pp reference:  b Required integrated luminosity to make pp errors subdominant, calculated using the significance in each p T 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 L int to get the same significance These numbers have a larger unc. (being estimated) ITS Plenary meeting, Andrea Dainese 14 p T bin (pb -1 ) Cristina

pp reference: B+ Required integrated luminosity to make pp errors subdominant, calculated using the significance in each p T 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 L int to get the same significance These numbers have a larger unc. (being estimated) ITS Plenary meeting, Andrea Dainese 15 p T bin (pb -1 ) Johannes

Summary on pp L int 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, Andrea Dainese 16 MeasurementAt 5.5 TeVAt 14 TeV D0D0 6/pb*Not possible cc 0.6/pb*Not possible J/psi from B3/pbNot assessed bb 60/pb20/pb B+80/pb40/pb

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

Impact of MFT service barrel 1. Multiple scattering: effect on p T resolution and matching eff For electrons, additional effect due to bremsstrahlung 2. Production of conversions a)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 b)For analyses that use directly the conversions to measure direct photons,  0 and  : 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% ITS Plenary meeting, Andrea Dainese 18 See next slides

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

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