 How to trigger on  leptons: practical examples in CMS   identification

1. Search for new physics with taus at the LHC CMS Roberto Chierici CERN  How to trigger on  leptons: practical examples in CMS   identification  the importance of s in SUSY Higgses  the use of s in SUSY searches and measurements Tau04, Nara, September 2004

2. CMS Total weight : 12,500 t Overall diameter : 15 m Overall length : 21.6 m Magnetic field : 4 Tesla CALORIMETERS: SUPERCONDUCTING ECAL Scintillating PbWO4 HCAL Plastic scintillator COIL (B=4 Tesla) TRACKER(s) Crystals copper <3 sandwich <2.4 <5 IRON YOKE MUON BARREL Pixels and Silicon Microstrips MUON ENDCAPS Resistive Plate Drift Tube Chambers (RPC) Chambers (DT)  Cathode Strip Chambers (CSC)  e Resistive Plate Chambers (RPC) 

3. Triggering on taus Triggering on taus Tau04, Nara, September 2004

4. Triggering on s Dedicated High Level Trigger (HLT) algorithms for  identification are essential to select events where s are produced in the final state, down to relatively low ET. (benchmark channel: MSSM Higgs decays A/H, H+) Final state signatures involve either 1 hadronic, 2s hadronic, 1 hadronic and 1 lepton. The trigger of  decays into lepton are part of the e and  triggers. Key features of  detection and trigger:  s decay hadronically 65% of the time and in 77% of these there is only one charged hadron and a number of 0s (one-prong decays)   jets at the LHC are slim, 90% of the energy is is contained in a ‘cone’ of radius R=0.2 around the jet direction for ET>50 GeV Designing a HLT scheme is tough:  cuts must be tuned to reach the allowed rate for a certain channel: for s this is a few Hz from the initial 100KHz  selection must be fast enough to reach the wanted rates  high luminosity conditions are the more demanding for setting up a : on average 17.3 minimum bias events and contribution from 8 out of time bunch crossings are superimposed to every event.

5. Level 1 and 2  trigger with calorimetry A generic jet is first triggered with calorimetry as a 12x12 group of towers whose central 4x4 ET is larger than the ET in all its neighbours. A  jet is a generic jet in which in none of the nine 4x4 regions there are more than 2 towers with ET>2,4GeV One must maintain the  jet L1 trigger rate at a few KHz level  1  jet with ET>90 GeV or 2  jets with ET>60 GeV The level 2 calorimeter  trigger is then based on a cut on the electromagnetic isolation parameter pisol = ETem (R<0.40) – ETem (R<0.13) A,HjetjetX vs QCD pisol<10 GeV A pisol cut of about 5 GeV provides a factor 3 in the trigger rate reduction pisol<1 GeV high lumi low lumi

6. Level 2  trigger using tracking  Reconstruct tracks with pT>1GeV using only pixels  Find primary vertices  The highest pT track (tr1) with good L2 jet matching: -R(j-tr1)< Rm (~0.1) and pT(tr1)> pTm (~3 GeV) defines the primary vertex  count the tracks from the primary vertex in the isolation cone and in the signal cone - Ni: tracks with R(j-track)< Ri (~0.3) - Ns: tracks with R(tr1-track)< Rs (~0.05) - pT(track)> pTi (~1 GeV)  accept as  candidates only if tracks are found in the signal cone (Ns=Ni) Rm,Rs,pTmandpTiare optimized for one and three-prong  decays in A/H  ID with full tracker : the same “isolation” idea , but using tracks found via a regional search with the silicon tracker

7. A/H jet jetTrigger Higgs efficiency vs QCD rejection with varyingRi (0.2-0.5) Calo+Pxl for the leading  jet. Pxl for the second jet high lumi low lumi No strong dependence on the Higgs mass Calo+Pxl vs Calo+Trk Path: efficiency for a Higgs boson of mass 200 GeV/c2 and CPU for background suppression 103 at L = 2 x 1033cm-2s-1 With the same background rejection the Calo+Trk is more robust and efficient, but more time consuming…

8. Other examples Single jet trigger example: H+jet Further criteria to the single  trigger must be added to lower the global rate.  Requirements on the pT of the leading track  Track trigger is the most appropriate Mixed ejet, jet triggers example: A/H l  jet Adding mixed triggers significantly increases the efficiency w.r.t. single lepton triggers  relative 5-10% increase can be easily obtained ET(e) thresholds high lumi

9. Offline  jet identification After HLT there are different ways studied and under study to improve the -jet selection cuts on the jet properties: low multiplicity (1 or 3 charged tracks in a small cone around the jet axis defined with calorimetry) isolation (no other tracks with pT>1GeV/c in a broader cone around the jet axis) momentum of the leading track (typically pTleading>40GeV/c) cuts on the reconstructed  impact parameter: In case of two s the combined IP significance can be used as a discriminant variable  cuts on the  decay vertex: a measure of the flight path can greatly help in QCD rejection  cuts on the vertex mass: work is ongoing on the mass reconstruction… arbitrary units Signal efficiency 3D flightpath in mm Background efficiency

10. New physics with taus New physics with taus Tau04, Nara, September 2004

11. SUSY heavy Higgs sector and  The SM(-like) Higgs discovery potential has already been discussed in the previous talk. The MSSM Higgs to  couplings are enhanced with tan() (like for b quarks)  for medium-high tan() the dominant production mechanism for the neutral Higgs is in association with b production (90% for tan()=10) Charged Higgses are produced via g-b fusion gbH+t or via g-g fusion ggH+tb. This is particularly convenient for the high mass region. The most promising decay channel is given by H+, especially for high tan() values. Most important backgrounds involve W+jets or Z+jets with  decays of the bosons. QCD is most important when looking at hadronic  decays, bb especially important if leptonic  decays are investigated. Essential tools: IP reconstruction, b tagging, pTmiss resolution

12. MSSM ggbbA/Hbb MSSM H studied in all its decay chain: BR(HeX)  6.3% BR(HeeX+X)  12.5% BR(HjetX+ejetX)  45.6% BR(Hjetjet)  41.5% Main backgrounds: Z,*,ℓℓ tt tW bb W+jet QCD cuts after HLT: lepton isolation stricter  tagging b-tagging jet veto positive E solution The Higgs mass can be reconstructed assuming that the s are emitted along the measured  decay products  project pTmiss onto the directions of the two  jets m() with l+j and two jet modes after selections

13. Discovery potential for neutral H into  Complementary to h (in the low value region of mA). The overall discovery potential heavily depends on this channel. Most of the contribution to the 5 contours comes from the hadronic contribution. The lepton channels suffer from more background. MSSM A/H: discovery reach in mA – tan() plane for mHmax scenario essential agreement between ATLAS and CMS reaches

14. A tan() measurement tan() can be measured by counting H events (assuming known A0, , m1/2, mSUSY) main systematic uncertainties come from theory uncertainties on the cross-sections and branching ratios and on the luminosity The measurement is dominated by A/H whereas H+ gives a factor 2-3 worse statistical error. theory error dominates significance larger than 5

15. MSSM gbH+tt For high mH+, high tan() the BR(H+) is about 10%. For low mH+, H+ dominates Main backgrounds are semileptonic tt decays, W+jets and Wt production where W are involved  polarization in H+ decays is opposite to W+ decays:  in  decays from H+ are preferentially emitted in the direction opposite to the  flight in the  rest frame  harder pions are expected in  jets from H+ ( included) Fully reconstruction of the t hadronic decay and b tagging greatly reduce the backgrounds. A final cut on mT() completely separate the signal and allows a mass reconstruction Low efficiency selection, but very high purities can be reached (>90%)

16. s in SUSY events If SUSY exists et the EW scale, gluinos and squarks will be copiously produced at the LHC In the decay chain the final products are fermions and the undetected LSP (if R-parity is conserved)  production is important because:  Yukawa couplings are larger for the third generation and are also enhanced for high values of tan()  With large values of tan() in mSUGRA the  is predicted to be the lightest slepton  higher probability for producing  in the charginos and neutralinos decay chain. For SUSY events triggering on s is less important than for Higgses because of the distinctive signature of the missing ET from the undetected LSP. 100% 30% 100% ~ For high values of tan() decay into s largely dominate (100%)

17. Proliferation of s Within mSUGRA one can count the expected -jet multiplicity per event. The probability of having at least one -jet per event can go up to 0.8 in certain regions of the parameter space ! A large tan() makes the Yukawa couplings to b and  increase and at the same time increases the mass mixing in the third family, making the  lighter Multi- production also increases drastically with increasing tan() The ridge function of m0, m1/2 corresponds to the allowed phase space points where decays of 20 and 1 into sleptons are allowed The domains where  and b are produced abundantly are complementary and cover most of the parameter space.  Excellent tracking is essential. tanb = 10, m > 0 ~ all gluino and squarks decay modes accounted for tau-jet tanb = 35, m > 0

18. ~  reconstruction Apart from the SUSY discovery itself, it will be important to measure the properties of the supersymmetric particles. The di-lepton invariant mass in the decay chain has a sharp edge because of the two-body decay of the 20.  The mass of the two leptons gives information on the relation between the sparticles involved in the decay. For high tan() using s is a necessity, and the di-lepton edge mass reconstruction is spoiled because of the  decay. Use  hadronic decays (missing ET comes also from the undetected LSP) and subtract same sign di- masses to greatly reduce the MSSM backgrounds. SM backgrounds are suppressed because of the missing ET cuts. Sensitivity to the edge position still possible with about 30/fb.

19. More Standard Search Methods The standard physics program with s at the LHC is important (W and Z physics,  properties), and new physics can be searched continuing to probe the SM:  g/ge in W decays   rare decays /  forbidden decays Example: the neutrinoless  decay ++- sign of lepton flavour violation, explainable by massive neutrinos or particular mSUGRA models Signal sources are considered as W, Z, mesonX The main backgrounds are found to be bb and cc production. Resonances can be easily suppressed. The best limit is obtained with W decays because of the peculiar high missing ET. The resolution on m() is about 15 MeV CMS, m(), 10/fb signal BR = 1.9 10-6 CMS or ATLAS alone should be able to improve the present experimental limit on the 3 BR (1.9 10-6) by a factor 50 with 30/fb (3.8 10-8)

20. Some other uses of s in new physics GMSB ~ In gauge mediated SUSY breaking the G is the LSP. There are mainly two options as NLSP:  or 10. So  production will represent one of the main possible signatures of the final state. One important feature of GMSB is that the lifetime of the NLSP is directly related to the scale of SUSY breaking and is totally unconstrained.  c » Ldetector:  will appear as heavy muons  c ~ Ldetector: kinks in the detector and the NLSP lifetime can be measured  c « Ldetector: increase of  production cross-section ~ ~ tan()=10 m0=100 GeV m1/2=300 GeV A0=300 GeV LFV in SUSY SUSY models can naturally accommodate lepton flavour violation, which is expected to be larger for the third generation. The best way to observe it in large regions of parameter space (m0≤m1/2) is in the decay channel 2010 The signal is then determined from N()-N(e) (yielding 12 for BR=10% and 10/fb)  more sensitivity than  or  in this region of parameter space. ~ ATLAS, 10/fb

21. Conclusions on  at the LHC How ? An intense activity for the inclusion of the  hadronic decay into the triggering scheme at LHC has lead to very encouraging results.  use of tracking at the HLT level Work on  identification algorithms continues and refines.  This effort will be very helpful for all the searches of new physics at the LHC Why ? Aside standard physics (SM Higgs,  physics) the relevance of  detection at the LHC involves the discovery of supersymmetry on sizeable regions of parameter space:  Higgs boson (neutral and charged) production  evidence for SUSY with high sensitivity in the high tan() regime  search for lepton flavour violation signals  GMSB and other models where staus are NLSPs And the measurement of its properties, if it exists:  Higgs boson masses at high tan()  determination of tan()  sensitivity to the slepton masses

22. Backup Backup Tau04, Nara, September 2004

23. Trigger CPU, rates and speed How to plan a L1 trigger: 100(50) KHz  33(15) KHz safety factor 3  8(4) KHz per physics object CPU per physics object at L1: 1 GHz Intel PIII CPU (=41 SpecInt95)  4092 CPU seconds to cover the full 15 KHz of L1  on average ~300ms/event  considering full 100KHz one needs 30000 PIII  1.2 106 SI95 At the start of LHC (50 KHz+a factor 8 from Moore’s law) 2000 CPUs should be enough = X

24. A more complete view

25. Latest LEP results • Fit individual channel cross-sections without assumptions on lepton universality •  BR(W) clearly higher than BR(We) • and BR(W) • 2*BR(W)- BR(We)- BR(W) differs from 0 by 3.0 (correlations included) • was 2.3 in summer 2003 • is 2.6 if final results only are used • Common effect in all experiments SM: 10.8%

26. A bit of SUSY Supersymmetry postulates the existence of partners of all SM particles differing by those only because their spin is h/2 lower. This mechanism eliminates the radiative corrections quadratic divergencies in the SM. Minimally two Higgs doublets must be introduced The partners of SM particles are called squarks(q), sleptons(ℓ,), gluinos(g), photinos(). zinos(Z), winos(W), Higgsinos(H), gravitino(G). Winos and charged Higgsinos mix to form two charginos(i), photinos, zinos and neutral higgsinos mix to form four neutralinos(i0) which are mass eigenstates. SUSY must be broken: a hidden sector where this happens is introduced and the mediator of the breaking can be gravity (SUGRA) or gauge forces (GMSB) in most popular scenarios. Minimal SUSY model = MSSM. The number of parameters of the model can be reduced to five imposing gaugino and sfermion mass unification at the GUT scale, universal trilinear couplings and the correct EW symmetry scale (mSUGRA): tan() is the ratio of the vacuum expectation values of the two Higgs doublets  is the Higgs mass parameter m1/2 are the unified gaugino masses m0 are the unified sfermion masses mA is the pseudoscalar Higgs mass if R=(-1)3B+L+2S parity is conserved the LSP is stable (typically the i0) and SUSY particles can only be produced in pairs. Best signatures are represented by: ~ ~ ~ ~ ~ ~ ~ ~ ~

27. Higgs discovery potential