First Performance studies of jet rejection using a pixel based detector Michele Pioppi* on behalf of PRIN 2003024739_005 group *Università degli studi di Perugia & INFN Perugia 7th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detectors Firenze, 05 October 2005 RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Michele Pioppi-Univ.&INFN Perugia Outline Motivations Pixel detector overview Pixel performances Trigger strategies Results Plans & Conclusions RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Michele Pioppi-Univ.&INFN Perugia Motivations I LHC p-p collider Low luminosity L = 2x1033 cm-2s-1 -> ~108 events/s High Luminosity L = 1034 cm-2s-1 Mostly due to QCD background processes RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Michele Pioppi-Univ.&INFN Perugia Motivations II Main goal of LHC and CMS: Discovery of Higgs boson DAQ rate ~ 100 Hz 4*105 rejection power 2 trigger levels: L1 (40 MHz  100 kHz) HW Use of fast subdetectors HLT (100 kHz  100 Hz) SW Calorimetry Hgg CMS Muon chambers H4 m No L1trigger for multi hadronic jets final states ttH8 jets PIXEL COULD HELP!!! RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Michele Pioppi-Univ.&INFN Perugia Pixel Overview 3 barrel layers : r ~ 4.4cm r ~ 7.3 cm r ~ 10.2 cm |h|<1.6 endcap barrel 53cm ROC 8x8 mm2 Each ROC is a matrix of 52x80 pixel units(150x100 mm2) arranged in 26 doublecolumns. ROC has a fast output that provides: ROC address # hit doublecolumns # clusters of doublecolumns 16 x RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Pixel performanceses at full granularity How to build Pixel Jets : Pt measurement from pixel tracks 1)Pixel tracks from fit to triplets of pixel hits Good Pt meas. for Pt<10GeV 2) Vertex reconstruction 3) Pixel jets with at least 5 tracks Leading track (seed for jet) r Pixel tracks Rejected track ()jet=  Σi i·Pti Σi Pti z ()jet=  Σi ηi·Pti Σi Pti ZV (Pt)jet = Σi Pti RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Full granularity L1 calo/pixel jets comparison Studies performed on bb 100 GeV sample Test sample used to exploit algorithm performances pt f <Njet>=2,2 h Pixel Jet   PixelJet L1 calo jet <Njet>=1,7 Et f h L1 reconstruction: + cone algorithm 0.5 + Et>10 GeV + eta, phi bin = 0.087 RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Full granularity resolutions Geometrical associations between b partons and pixeljets Dz vtxrec-vtxsim Dh pixeljet-parton Df pixeljet-parton sh ~ 50 mrad sf ~ 50 mrad sz ~ 47 mm To be compared to 120 mrad spatial resolution of L1calo jet Improvement of jet finding & fake jet rejection RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Full granularity selection performances + Try to combine calorimetric and pixel information + Evaluate selection power on the ttH VS direct QCD production Fully hadronic final state (t->b, W->qq’ H->bb) 8 jets in the final state Soft jet (20-30 GeV) The pixel jet could help All events that can be considered not-signal from pp interaction We expect best performance on 3 and 4 jet-stream L1 selection RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Full granularity combining calo and pixel trigger L1 QCD rate (Low luminosity) 3 jets stream Ncaljet(E>Etr) >1,2,3,4 (Ncaljet(E>Etr) >1,2,3,4) && (Npixjet(E>Etr) >1,2,3,4) Considering the same QCD rate, the ttH efficiency gain is 20-40% Each pixel jet with at least 5 tracks RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Full granularity Pileup rejection Primary vertex finding is an essential tool to reduce secondary p-p interaction Approach: L1 calo/ pixel jet association Consider for L1 calo trigger, only jets that can be associated to a PV built with pixel RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Full granularity pixel vertex Jets vtx in 22mm PV window Jets vtx out of 22mm PV window Vertex width~22 mm 10*ptqual (PVpixel-PVtracker) before cuts (PVpixel-PVtracker) after cuts Selection: Ptqual>0.9 Dr(cal,pix)<0.5 RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Reduced granularity Idea: Use fast output of PixelROC to determine a L1 decision Worst scenario: At L1 only 52x80 pixel(8x8 mm2) geometry is available . RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Reduced granularity hit selection and track reconstruction ROCi= ROC of ith layer ROCHit selection #DoubleColumnROC1>1 #DoubleColumnROC2-3>0 ROCTrack preselection |fROC1 –fROC2 | <0.3 |Z0| from ZROC1 and ZROC2<15 cm |Z0| from ZROC1 and ZROC3<15 cm ROCTrack construction Linear and circular fit (Pt,h,f,Zv,) Tracks c2-ordered Only ROC1 could belong to more than 1 track <ROCHit>qcd80120 ~ 800 <ROCTracks>qcd80120 ~ 120 RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Reduced granularity Validation and angular resolution Study performed with a tighter preselection x-y plane Pixel jets ROC Hits ROC Tracks L1 Calo Jet sf =142 mrad bb jet 100 Gev events RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Reduced granularity Vertex reconstruction Algorithm: Histogram of Zv of all ROCtracks (Width of the bin = 1cm) Ntr(Pt>0.3GeV)>4 PVz =<Zroctk> of the most populated bin # vertices Primary Vertex resolution tth qcd5080 qcd80120 sz ~ 1.6 cm cm RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Reduced granularity ROCtracks in L1 trigger L1 trigger efficiency @ Etresh ~ 70 GeV Effqcd <0.1% Tth qcd5080 qcd80120 New L1 request: Ncalo (Et>Etresh) > 3 && Npixtr>90 Next step: Build ROCjets pointing at PV and use them at L1 RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Reduced granularity what is needed? Module trigger chip to combine fast output from all the ROC HW to build ROC tracks Pattern recognition (Associative memory) Histogramming vertex finder RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Reduced granularity alternative approach - strategy From ROC -> seed in f -> region finder Regional full granularity (DR=0.2) reconstruction Tracks are used for direction, PVz and IPz sf ~ 100 mrad qcd80-120 75% of events: 2 seeds found in DR<0.5 wrt MC RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Reduced granularity alternative approach - resolution s ~ 140 mm 80% Pv finding efficiency Good resolution on IPz For b-trigger application RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia

Michele Pioppi-Univ.&INFN Perugia Plans and conclusions Plans: Timing evaluation HW feasibility Conclusions: Pixel could contribute to L1 trigger especially for multihadronic jets final states At full granularity pixel can increase significantly ttH8jets efficiency maintaining the same QCD rate Reduced granularity: In the worst scenario (8x8 mm2) <ROChits>qcd80-120 ~800 Each ROChit is characterized by position(layer,phi,z), #doublecolumns and #clusters Tracks ~120 and vertices can be reconstructed at L1 L1 trigger efficiency for QCD reduced ROC could provide a seed in f for a regional full reconstruction RD05-Firenze, 5 Oct 2005 Michele Pioppi-Univ.&INFN Perugia