Last update at the RPVLL meeting: https://indico.cern.ch/event/276607 Search for (semistable) charged heavy particles using the ionization in the Pixel Detector A.Gaudiello1, C. Gemme1, G.Gagliardi1, E. Guido1, S. Passaggio1, L. Rossi1, C. Schiavi1 1INFN Genova Last update at the RPVLL meeting: https://indico.cern.ch/event/276607

Motivations for the searches with dE/dx The ATLAS Pixel detector is able to measure the particle ionization in the very first cm of the trajectory and to tag tracks that have high release due to low bg particles. The measurement is possible if the track is reconstructed and it is not sensitive to possible decays or interactions with material after the silicon layers.  CMS analysis only for stable, using ID only, ID+MS, MS only: doi:10.1007/JHEP07(2013)122 Bethe-Bloch empirical fit of low mass particles allows to measure the particle mass from its energy release and momentum measurement This calibration done in 2010 is very stable over the time. Proton mass

Pixel-only Analysis 2012 Benchmark signals: Stable squarks and gluinos R-hadrons, as in 2011, in extended mass range 200-1700 GeV; Metastable squarks and gluinos R-hadrons with lifetime 10,1,0.1,0.01, 0.001 ns and mass 400,600,800, 1000 GeV and decaying in a heavy or light neutralino. Stable (100-800 GeV) and metastable Charginos (same samples as kinked tracks analysis, lifetime 0.3-1 ns). Two main changes in 2012 wrt 2011 analysis: In the DESDM RPVLL stream, the online skimming of the JetTauEtmiss stream has raised the high-pT track threshold from 50 to 80 GeV. The un-prescaled triggers have changed wrt to 2011. EF_xe80T_tclcw_loose; // All data periods

Stable squarks and gluinos R-hadrons 49% 31% 20%

Trigger selection and Efficiency EF_xe80T_tclcw_loose triggers ~ 98% of the OR of the unprescaled MET triggers in signal events. We prefer to adopt one single trigger for the full data period to make the study of the systematics simpler. Trigger efficiency is ~17% on a wide range of masses (slightly larger than in 2011). 2012 2011

Event Selection Cuts have been revised to optimize S/√B and populate the bkg samples. Event level (after RPVLL filter and squeezing): GRL* offline confirmation of the MET trigger: Etmiss RefFinal > 130 GeV (was 80) at least 1 primary vertex (PV) with at least 5 tracks SUSY recommended event cleaning Track level (at least one track with) High-pT: pT>80 GeV, primary, n.Pixel hits >=3, nBLayer hits >=1 and n.SCT hits >=6 Isolated: no primary with pT>1 GeV in a cone of radius ΔR<0.25 Electron veto, p-cuts: p>150 GeV & Δp/p<50% (was p>100 GeV) High ionization: dE/dx > 1.800 - 0.055|η|+ 0.129|η|2 -0.037|η|3 MeV/g cm-2 * (A-G)data12_8TeV.periodAllYear_DetStatus-v54-pro13-04_DQDefects-00-00-33_PHYS_StandardGRL_All_Good.xml (H-L)data12_8TeV.periodAllYear_DetStatus-v61-pro14-02_DQDefects-00-01-00_PHYS_StandardGRL_All_Good.xml

Small sensitivity to Pile-up Period J Being the pixel detector at high granularity, it is not very sensitive to pile-up. Anyhow MC needs to be properly reweighted with PU: effect is mainly on the skimming of the track. high low Period J mu<16 Eff rel Eff tot mu>30 trigger&&mu 677802 127810 75836 MET 78912 0.12 1.2E-01 15931 8137 0.11 1.1E-01 PV 78838 1.00 15915 8128 skim 55096 0.70 8.1E-02 11240 0.71 8.8E-02 5377 0.66 7.1E-02 isolation 6307 9.3E-03 1354 1.1E-02 566 7.5E-03 electronVeto 4249 0.67 6.3E-03 896 7.0E-03 398 5.2E-03 pCut 1818 0.43 2.7E-03 393 0.44 3.1E-03 181 0.45 2.4E-03 ionization 29 0.02 4.28E-05 6 4.69E-05 2 0.01 2.64E-05 jetCleaning

Slight increase in signal efficiency (7.7% vs 5.8%) MC 2011 gluino 1000 GeV MC 2012 gluino 1000 GeV data 2012 (period J, ~3ifb) data 2011 (5ifb) * * Squeezed = Ef_xexx_yy and track pT>80 GeV, 2 pix, 6 SCT Slight increase in signal efficiency (7.7% vs 5.8%) Higher rejection for background (314 vs 40*5fib/3ifb candidates)

Outlook for stable We are studying and revising the definition of the background samples. Analysis cuts could slightly change to allow enough statistics in the bkg samples. Bkg1 (low ionization) as data but dE/dx <1.8 Bkg2 (low momentum) as data but p<150 GeV and pT>10 GeV Next-to-next: Study systematics. Move to analysis for stable charginos.

Metastable squarks and gluinos R-hadrons R-hadrons Decay in neutralinos (either close to the R-hadron mass or lighter). Current selection is pretty efficient on MET. Inefficiency comes if lifetime is too short to generate a reconstructable track.

“Reconstructable” charged R-hadrons Ratio of Charged R-hadrons associated (DR<0.01) to a track with pT>5 GeV (no other request!) and generated charged R-hadrons. Clearly no/poor efficiency for rest lifetimes < 1 ns independently of any selection optimization. In the next 2 slides, properties of the generated R-hadrons that are associated to reconstructed tracks. Not applied yet any selection cut.

“Reconstructable” charged R-hadrons: Properties I pT nSCT 1 ns R-hadrons are reconstructed also at lower SCT hits than normal. p 1 ns R-hadrons are reconstructed if they are more boosted

“Reconstructable” charged R-hadrons: Properties II dE/dx mass 1 ns R-hadrons has broader mass distribution, Consequence of the high-p boost selection.

Event Selection Cuts have been revised to optimize S/√B and populate the bkg samples. Event level Trigger: EF_xe80T_tclcw_loose GRL* offline confirmation of the MET trigger: Etmiss RefFinal > 130 GeV (was 80) at least 1 primary vertex (PV) with at least 5 tracks SUSY recommended event cleaning (A-G)data12_8TeV.periodAllYear_DetStatus-v54-pro13-04_DQDefects-00-00-33_PHYS_StandardGRL_All_Good.xml (H-L)data12_8TeV.periodAllYear_DetStatus-v61-pro14-02_DQDefects-00-01-00_PHYS_StandardGRL_All_Good.xml

Metastable R-hadrons: MET@generation gluino 600 Neutralino 500: Met ~ 90 GeV All the energy of the neutralinos escape, but there are 2 gluinos back-to-back. When the neutralino is very light, there is ymuch more MET, because there are high pt jets coming out at random angles, and the escaping pt does not cancel on the two sides. gluino 600 Neutralino 100: Met ~ 220 GeV

Metastable R-hadrons: MET@afterTrigger gluino 600 Neutralino 500: Met ~ 90 GeV 600->500 stable 10 ns 1 ns EF_xe80T_tclcw_loose 0.25 0.47 0.60 MET>130 0.73 0.52 gluino 600 Neutralino 100: Met ~ 220 GeV 600->100 stable 10 ns 1 ns EF_xe80T_tclcw_loose 0.25 0.84 0.91 MET>130 0.73 0.82 0.86

Event Selection Cuts have been revised to optimize S/√B and populate the bkg samples. Event level Trigger: EF_xe80T_tclcw_loose GRL* offline confirmation of the MET trigger: Etmiss RefFinal > 130 GeV (was 80) at least 1 primary vertex (PV) with at least 5 tracks SUSY recommended event cleaning Track Level (at least one track with) High-pT: pT>80 GeV, primary, n.Pixel hits >=3, nBLayer hits >=1 and n.SCT hits >=4 (was 6 in stable) Isolated: no primary with pT>1 GeV in a cone of radius ΔR<0.25 Electron veto, p-cuts: p>150 GeV & Δp/p<50% (was p>100 GeV) High ionization: dE/dx > 1.800 - 0.055|η|+ 0.129|η|2 -0.037|η|3 MeV/g cm-2

Metastable R-hadrons: pT of skimmed tracks gluino 600 Neutralino 500: Lower momentum if gluino is unstable because R-hadron is not reconstructed. Close only if lifetime is 10 ns, mainly is X0 is light (there might be other high-p charged tracks in the decay) gluino 600 Neutralino 100:

Metastable R-hadrons: dE/dx of skimmed tracks gluino 600 Neutralino 500: Visible that for short lifetime there is less contribution of R-hadrons (high ionization) gluino 600 Neutralino 100:

Cut flow for 600 GeV (meta) stable Rhadrons 600->500 STABLE 10 ns 1 ns 0.1 ns 0.01 ns 0.001 ns generated 20000   9400 10000 9999 GRL 1.00 cleaning 19925 8503 0.90 9979 9980 9983 9984 trigger 5005 0.25 3985 0.47 6020 0.60 6153 0.62 6193 6163 MET>130 3662 0.73 2070 0.52 3125 3350 0.54 3561 0.58 3649 0.59 PV 3659 2060 3111 3326 0.99 3527 3634 skim SCT 4 1919 915 0.44 332 0.11 163 0.05 175 isolation 1637 0.85 817 0.89 184 0.55 1 0.01 2 electronVeto 1622 814 pCut 150 1593 0.98 729 114 0.50 ionization 1160 499 0.68 61 0.00 jetCleaning 0.058 0.0531 0.0061 0.0001 600->100 9900 9000 9500 8133 0.82 8954 9465 9960 9964 6827 0.84 8174 0.91 8706 0.92 9149 9182 5602 7058 0.86 7695 0.88 8269 8322 5522 7023 7613 8171 8214 2104 0.38 472 0.07 266 0.03 790 0.10 1061 0.13 1904 318 0.67 11 21 0.02 1900 8 15 0.71 1747 187 4 7 1282 120 0.64 0.1295 0.0133

Matching with Jets or muon MS 10 ns 600 100 1 ns Rhadron 600 Stable 10 ns 600500 1 ns MuSpectro: candidate track geometrical matched with a muid Jets only: candidate track geometrical matched with a Jet but not with a muid Others: candidate track geometrical not matched with a Jet or with a muid  For 10 (1) ns lifetimes the pixel-only analysis is the dominating (only) search method.

Outlook for metastable As for the stable case, study and revise the definition of the background samples mainly to populate the samples sufficiently. Bkg1 (low ionization) as data but dE/dx <1.8 Bkg2 (low momentum) as data but p<150 GeV and pT>10 GeV Next-to-next: Generate several lifetime samples, as in the disappearing tracks search, http://arxiv.org/pdf/1310.3675v1.pdf Study systematics. Show limits vs lifetime and mass Move to analysis for metastable charginos. http://arxiv.org/pdf/1310.3675v1.pdf as illustration

Backup 04/11/2013 C. Gemme – INFN Genova

Cleaning in SUSY Implemented SUSY cleaning: at the EVENT level if ((nt->larError)==2) continue; // Removing LAr error events if ((nt->tileError)==2) continue; // Removing Tile error events if ((nt->coreFlags&0x40000) != 0) continue; // Remove incomplete events due to TTC reset larError, tileError and coreFlags NOT SQUEEZED yet. // TTileTripReader::checkEvent(unsigned int run, unsigned int lbn, unsigned int event) \\Tile trips in periods G-J ????? Also information are missing in SUSY instructions recommend to veto events which have any jet pt>40 && & BCH_CORR_JET > 0.05 && DeltaPhi(MET,Jet)<0.3  cuts 10% of GRL events and with any looser (=BadlooseMinus, 0.15% of jets) jets with pt>20 GeV and any eta  cuts <1% of GRL events (SIMILAR TO THE JET Cleaning that we have used in the candidates events in 2011)