1. Search for the SM Higgs Boson in the H → γγ Channel with CMS at LHC Marco Pieri UCSD April 4 th 2006

2. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 2 Outline  LHC collider and CMS Detector  Higgs Searches at LHC  H → γγ search with CMS  Trigger  Ecal calibration  Background simulation  Photon isolation  Vertex estimation  Photon conversion identification and π 0 rejection  Selection and background measurement  C.L. for discovery or exclusion  Analysis optimization  Summary and Outlook

3. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 3 LHC Collider  First beams 2007 - Pilot Run  2008 start of physics  Only ~1.5 years to the first collisions  Now mainly studying the low luminosity phase LHC operation (pp s =14 TeV)  Low luminosity phase (Pile-up ~4 events/beam crossing)  ℒ ~ 2 x 10 33 cm -2 s -1  Int ℒ ~ 30 fb -1  High luminosity phase (Pile-up ~20 events/beam crossing)  ℒ ~ 1 x 10 34 cm -2 s -1  Int ℒ ~ 300 fb -1 CMS Atlas LHCb ALICE

4. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 4 CMS Detector MUON BARREL Silicon Microstrips Pixels ECAL Scintillating PbWO4 crystals Cathode Strip Chambers Resistive Plate Chambers Drift Tube Chambers Resistive Plate Chambers SUPERCONDUCTING COIL IRON YOKE TRACKER MUON ENDCAPS Total weight : 12,500 t Overall diameter : 15 m Overall length : 21.6 m Magnetic field : 4 Tesla HCALPlastic scintillator/brass sandwich CALORIMETERS

5. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 5 CMS Magnet  Superconducting coil: length 13m, diameter 5.9 m  Magnetic field 4 Tesla  Energy stored 2.5 GJoule  Coil has been cooled down to 4.5K

6. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 6 DIRECT SEARCHES AT LEP GAVE NEGATIVE RESULTS  SM Higgs boson  M H >114.1 GeV @95% CL  Some hints of possible Higgs signal were reported the last year of LEP running  MSSM neutral Higgs bosons  M h, M A >92.9, 93.3 GeV @95% CL Current Status of Direct Higgs Searches

7. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 7 INDIRECT CONSTRAINTS ON THE SM HIGGS BOSON  SM Electroweak fits to all high Q 2 measurements give:  M H =89 +42 -30 GeV  M H <207 GeV @ 95% CL (taking into account direct LEP limit) Other Constraints on Higgs Mass MSSM HIGGS BOSON  In the MSSM M h ≲ 135 GeV  In the decoupling limit, for M A ≳ 150 GeV  h behaves like H SM  Standard model searches directly apply  H → γγ channel is the most sensitive at LHC

8. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 8 SM Higgs Production at LHC NLO Cross sections M. Spira et al. gg fusion IVB fusion

9. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 9 SM Higgs Decays When WW channel opens up pronounced dip in the ZZ BR …

10. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 10 SM Higgs Search Channels Production DECAY InclusiveVBFWH/ZHttH H → γγ YES H → bb YES H → ττ YES H → WW * YES H → ZZ *, Z  ℓ + ℓ -, ℓ=e,μ YES Low mass M H ≲ 200 GeV H → γγ and H → ZZ* → 4 ℓ are the only channels with a very good mass resolution ~1%

11. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 11 Current status of CMS analysis  Physics TDR (Technical Design Report for the LHCC)  End of last year Volume I  Detector performance, calibration, analysis tools  Now Volume II  Physics channels (more or less detailed)  H → γγ search is being finalized these days  End of the year Volume III Startup physics and activities  All what must be done to start CMS data taking and analysis  Continuous effort on software, data management and computing  The readiness of this (together with hardware performance) will determine the early success of the experiment

12. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 12 forward jets Photons from Higgs decay qqH → qq γγ M H = 120 GeV H→ γγ Signal SIGNAL: two isolated photons with large E t  Gluon-gluon fusion  WW and ZZ fusion (Weak Boson Fusion)  WH, ZH, ttH (additional leptons)  Total σ x BR ~90 fb for M H = 110-130 GeV  Very good mass resolution better than 1% H → γγ M H = 115 GeV Jets from qq are at high rapidity and large Δ η

13. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 13 H→ γγ Background BACKGROUND  ‘irreducible’ backgrounds, two real photons  gg → γγ (box diagram)  qq → γγ (born diagram)  pp → γ+jets (2 prompt γ)  ‘reducible’ backgrounds, at least one fake photons  pp → γ+jets (1 prompt γ + 1 fake γ)  pp → jets (2 fake γ)  pp → ee (Drell Yan) when electrons are mis-identified as photons ProcessP that (GeV)Cross section (pb)Events/1 fb -1 pp → γγ (born)>258282K pp → γγ (box)>258282K pp → γ+jets>3090x10 4 90M pp → jets>251x10 8 1x10 11 Drell Yan ee-4x10 3 4M

14. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 14 Cross section and K-factors  Signal cross sections and BR (NLO M. Spira)  K-factors for the background pp → γγ (born)1.5 pp → γγ (box)1.2 pp → γ+jets (2 prompt)1.72 pp → γ+ jets (1 prompt+ 1 fake)1 pp → jets1 M=115 GeVM=120 GeVM=130 GeVM=140 GeVM=150 GeV σ (gg fusion)(pb) 39.236.431.627.724.5 σ (IVB fusion) (pb) 4.74.54.13.83.6 σ (HW, HZ, Hqq) (pb) 3.83.32.62.11.7 Total (pb) 47.644.238.333.629.7 BR (H → γγ) 2.08x10 -3 2.21x10 -3 2.24x10 -3 1.95x10 -3 1.40x10 -3 Inclusive σ x BR (fb) 99.397.586.065.541.5

15. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 15 Outline of the Analysis  Trigger (Level-1+High Level Trigger)  Calibration of the electromagnetic calorimeter  Background Simulation  Photon isolation  Vertex estimation  Conversion identification  π 0 rejection  Selection, background estimation  C.L. extraction for discovery or exclusion  Effect of systematic errors  Analysis optimization  Results

16. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 16 CMS Trigger Design – Two stages Level 1 hardware trigger High Level Trigger (HLT) “Offline” code running on PC farm 40 MHz 100 kHz 1 Tbit/s 100 Hz Beam crossing rate40 MHz Interaction rate1 GHz Max Level 1 trigger rate100 kHz Event size1 MByte

17. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 17 DAQ Architecture Readout Builders 12.5 kHz+12.5 kHz Data to surface  Aggregate data flow ~1 Tbit/s  In the process of ordering PCs and network elements

18. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 18  Electromagnetic trigger towers are classified in three categories depending on the energy deposition in the calorimeter trigger towers: unidentified, non-isolated, isolated.  Single isolated  E t >23 GeV  Double isolated  E t >12 GeV  Double non-isolated  E t >19 GeV  Total electron+photon Level-1 trigger rate: 4.4 kHz  Level-1 trigger efficiency for H→ γγ larger than 99.5% Level-1 Trigger

19. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 19  H → γγ signal has two isolated photons  Dominant background from di-jets and γ+jet has at least one candidate from jet fragmentation that is not well isolated  We keep early conversions in the double stream  HLT trigger efficiency 88%  Trigger is relatively easy for H→ γγ because of high Et photons  Total rate for photons after HLT ~6 Hz High Level Trigger for Photons HLT photon selection

20. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 20 ECAL Calibration  Use electrons from W →e ν decays  Match the measured ECAL cluster energy with the electron momentum measured in the silicon tracker  Investigating alternative methods that use π 0 or η Calibration precision in barrelEffect on Higgs mass

21. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 21  Events must be pre-selected events at the generator level and we only simulate and reconstruct those events that more likely pass the analysis selection  For jets also the generation is a very heavy task  Generator level selection:  charged track isolation at generator level  allow more than em interacting particle to contribute to the energy of the photon candidate  Results of the selection are verified after simulation and reconstruction using data samples generated with looser pre-selection BG Simulation  Background coming from pp → jets and pp → γ+jets contributes more than half the total background for H → γγ search  The cross section is huge for the process pp → jets ProcessP that cut (GeV)σ (Pythia LO)Events per 1 fb -1 pp → γ+jets>259.0x10 4 pb9.0x10 7 pp → jets>351.0x10 8 pb1.0x10 11

22. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 22 BG Simulation II P that cut (GeV) σ gen (pb) σ sim (pb) Red. factor Ineff. parton cuts (%) Ineff. particle cuts Ineff. total pp → γ+jet259.0x10 4 2.6x10 2 3500.13.43.5 pp → jets301.8x10 8 4.4x10 3 410000.014.1 pp → jets406.0x10 7 4.3x10 3 140001.314.115.4 pp → jets453.7x10 7 4.3x10 3 87003.414.117.5 pp → jets502.5x10 7 4.1x10 3 60006.514.120.6  With this selection it was possible to simulate 5 million jet events corresponding to 1 fb -1 integrated luminosity  Total pre-selection inefficiency ~20%  Events lost are mainly with low E t photons, not very important

23. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 23 Primary Vertex Determination  LHC beams have a longitudinal spread of 7.5 cm  Longitudinal interaction spread ~5 cm  Vertex estimated from the underlying event and recoiling jet  We use a combination of the two methods:  Maximal scalar sum of tracks p t  Maximal vector sum of tracks p t  The efficiency of determining the right vertex is ~83% Higgs events after selection  Efficiency for the different types of background is similar  Can also use identified converted photons – not done yet

24. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 24 Primary Vertex Determination II ProcessEff (%) H → γγ (gg fusion)82 H → γγ (IVB fusion)89 pp → γγ (born)71 pp → γγ (box)72 pp → γ+jet (2 prompt)78 pp → γ+jet (1 prompt + 1fake)86 pp →jets 90 Efficiency of determining the primary vertex within 5 mm from the true one

25. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 25 Photon Conversions  CMS tracker is rather thick  ~30% of the photons convert before reaching the ECAL  Energy resolution somewhat deteriorated  Conversions can be identified in the tracker  Identified conversions may also help to distinguish γ’s from π 0 ’s Total 2 tracks 1 track

26. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 26  R 9 : Sum of 9/cluster energy  Unconverted photons have large R 9  Converted photons, photons in jets and electrons have small R 9  π 0 ’s also have small R 9  Energy resolution is better for large R 9 Shower Shape Variables

27. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 27 0.88<R9< 0.95 Photon Energy Resolution σ fit =0.64% σ fit =1.35% σ fit =1.91% σ fit =0.92% σ fit =1.02% σ fit =0.78% BarrelEndcaps R9>0.95 R9<0.88 Photons with E t > 40 GeV

28. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 28 Photon Isolation  Reducible backrounds (π 0 ’s and mis-identified jets) have other particles near at least one photon candidate  Most of discriminating variables are built by summing up the E t or P t of calorimeter deposits or tracks within a cone ΔR =  (Δη 2 + Δφ 2 )  To study the performance of isolation variables we use individual photon candidates  Signal is: H → γγ gg-fusion 2 nd highest E t cluster with E t >40 GeV matched with a generated photon within ΔR 40 GeV NOT matched with a generated photon  Plot the distribution of the variables for signal and background, move the cut and compute Eff. Sig and Eff. Background ΔRΔR

29. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 29 Combined Isolation Performance Plot EndcapsBarrel  The sum of ECAL, HCAL and Track E t variables can be considered as a global isolation variable  Cone sizes and E t thresholds have been optimized for the different detectors

30. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 30  All isolation variables are more or less correlated  We used a Neural Network with 2, 3 or 5 of following inputs:  ΔR of the 1 st track with P t >1.5 GeV/c  Sum ECAL E t within ΔR<0.3  The shower shape variable R 9  Sum HCAL E t within ΔR<0.35  Sum tracks E t within ΔR<0.2  Did not use kinematical information, easy to combine these variables with reconstructed mass and photons E t in an optimized H → γγ analysis Isolated Photon Identification with NN

31. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 31 Selection for Inclusive Analysis  Photon selection: photon candidates are reconstructed using the hybrid clustering algorithm in the barrel and the island clustering algorithm in the endcaps  E T1, E T2 > 40, 25 GeV  |η|<2.5  Both photon candidates should match L1 isolated triggers with E T > 12 GeV within ΔR < 0.5  Track isolation  No tracks with p t >1.5 GeV present within ΔR<0.3 around the direction of the photon candidate  Calorimeter isolation  Sum of Et of the ECAL basic clusters within 0.06<ΔR<0.35 around the direction of the photon candidate <4 GeV  Sum of Et of the HCAL towers within ΔR<0.3 around the direction of the photon candidate<8 GeV(6 GeV) in barrel (endcaps)  Sum of the 2 less than 10 GeV(8 GeV) in barrel (endcaps)  L1 + HLT inefficiency negligible after selection

32. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 32 Mass Spectrum of Selected Events  All plots are normalized to an integrated luminosity of 1 fb -1 and the signal is scaled by a factor 10  Fraction of signal is very small (signal/background ~0.1)  Use of background MC can be avoided when we will have data  Data + signal MC can be used for optimizing cuts, training NN and precise BG estimation

33. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 33 Results Higgs efficiency for M H =120 GeV Background expectation at M H =120 GeV  Before isolation BG expectation ~ 300 times larger Box (fb/GeV) Born (fb/GeV) γ+ jets 2 prompt (fb/GeV) γ+ jets 1 prompt + 1 fake (fb/GeV) Jets (fb/GeV) Total (fb/GeV) H → γγ (M H =120 GeV) eff. in window of 2.5 GeV (%) 324662516425524.4 M H After photon selectionFinal 120 GeV52.7%34.4%

34. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 34 Discovery Significance/Exclusion C.L.  Use Log Likelihood Ratio frequentistic approach  Log likelihood ratio between the signal+background hypothesis and the BG only hypothesis Mean/Median BG onlyMean/Median Sig + BG

35. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 35 Effect of Systematic Errors Input for CL calculation is:  Background expectation from fit to the data (sidebands)  Signal expectation from MC Origin of systematic errors  Error on the BG estimation (statistical from fit of sidebands + uncertainty of the form of the fitted function)  Error on the signal (theoretical σxBR, integrated luminosity, detector + selection efficiency) Effect of systematic errors  Systematic errors on the signal does not change the expected discovery CL  Systematic error on the signal makes exclusion more difficult  Systematic error on the BG makes exclusion and discovery more difficult

36. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 36 Main Systematic Errors SIGNAL  Theoretical error on cross section times BR (~15%)  Integrated luminosity (5%)  Higgs Q t distribution – effect to be evaluated  Selection efficiency ( ≲ 5%)  For now assume a total of 20% (anyway not important in case of discovery) BACKGROUND  Statistical error on the fit of the sidebands (~0.3% for ~20 fb -1 )  Systematic error on the shape of the fitted function (~0.3%)  No other errors when data available

37. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 37  Large effect on the 5σ discovery of the systematic error on the background (due to the small s/b in this channel)  A signal/background cut is applied at 0.02 Results for Discovery/Exclusion MH=120 GeV 3σ evidence Int L (fb -1 ) 5σ discovery Int L (fb -1 ) 95% exclusion Int L (fb -1 ) Counting 11.331.53.6 Mass distribution 10.7303.4 Counting WITH 0.5% error on BG, 20% Error on Signal 13.253.54.2 Mass distribution WITH 0.5% error on BG, 20% Error on Signal 12.7474.0

38. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 38 How to Improve the Sensitivity  We consider the following:  ‘Reducible’ background tends to have smaller R 9  ‘Reducible’ background contribution is larger in the endcaps  Split the sample into 4 by using the 4 combinations of the requirements:  Both photons in the barrel or not  min(R9 1, R9 2 ) larger or smaller than 0.93  this is equivalent to having different channels  Can also split more the sample by dividing the ECAL into 4 pseudo-rapidity regions and for each region have progressively tightening cuts  When increasing the number of categories the uncertainty on the BG fit should approximately increase by (number of categories)  The uncertainty is basically uncorrelated between the different categories

39. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 39 Four Categories Barrel, min(R9 1, R9 2 )>0.93 Endcap, min(R9 1, R9 2 )>0.93Endcap, min(R9 1, R9 2 )<0.93 Barrel, min(R9 1, R9 2 )<0.93

40. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 40 Discovery/Exclusion with More Categories MH=120 GeV 3σ discovery Int L (fb -1 ) 5σ discovery Int L (fb -1 ) 95% exclusion Int L (fb -1 ) 4 Categories 8222.6 16 Categories 6.618.52.2 4 Categories WITH 1% error on BG, 20% Error on Signal 8.8303.1 16 Categories WITH 1.5% error on BG, 20% Error on Signal 721.52.6  The overall effect of splitting into more categories is a decrease of the effect of the systematic error on the CL (mainly because of the increase of s/b for a fraction of events)

41. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 41 Discovery/Exclusion with 16 Categories  With ~25 fb -1 we can discover the Higgs boson with mass between 115 and 140 GeV

42. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 42 Optimized Analysis  Can do better using the optimized signal/background ratio ordering method technique  I introduced this method in L3 for Higgs searches and has been later used for all Higgs searches at LEP  First of all split sample into 6 categories by using the 6 combinations of the requirements:  Both photons in the barrel or not  min(R9 1, R9 2 ) larger than 0.95, between 0.90 and 0.95 and smaller than 0.90  Then, for barrel and endcap events use a NN with the following mass independent input variables:  Isolation NN γ 1  Isolation NN γ 2  E t1 /M  E t2 /M  P LHiggs  |Δη|  Train the Neural Network using data as background outside the mass region under study

43. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 43 NN Output and Mass mass distribution category 1 Background Signal category 1 NN output without mass information  Compute log(s/b) for each event  Add the NN output and Mass log(s/b)  Than combine all 6 categories into one single plot  Use LLR frequentistic method to evaluate the sensitivity

44. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 44 Results of Optimized Analysis  Now get 5σ significance at M H = 120 GeV with an integrated luminosity of 7 fb -1  Important source of improvement is the exploitation of high s/b Weak Boson Fusion events  Expect some degradation from error on the background but less than in the conventional analysis 4% s/b cut

45. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 45 Summary and Outlook  SM Higgs boson (or MSSM h) can be discovered with CMS in the H → γγ channel with 25 fb -1 at low luminosity, with a conventional cut based analysis in the mass range 115-140 GeV  Optimized likelihood analysis needs ~10 fb -1 luminosity for a 5σ signal in the same mass range Further optimization  Include additional tools for:  Photon conversion identification  π 0 rejection  Largest improvement expected from:  Separation of other γγ channels, WBF, WH, ZH, ttH, exploiting their additional signatures  Then obviously from combination with H → ZZ* →4 lepton channels  Only one and a half years from the beginning of LHC operation, must continue to prepare the real analysis:  based on data  with minimal use of MC information  using all possible control samples to verify the performances of the detector  We will hopefully discover soon a low mass Higgs boson at LHC

46. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 46 End of the talk

47. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 47 EXTRA

48. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 48 ECAL Calibration 5 fb -1

49. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 49 Test beam ECAL resolution

50. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 50 Shower Shape Variable R9 r 9 =S9/E SC non-converted Note that s/b also improves as we select photons that didn’t convert. Jet background Signal categories For highest Et

51. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 51 Analysis flow for each category Isolation NN photon 1 Isolation NN photon 2 (same) ET1/M ET2/M PL higgs  Neural Net Mass Smooth Bkgd Smooth Bkgd Bin Signal and Bkgd In LLR (same way) Define a function of the mass and the NN output and plot events

52. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 52 NN training  Use the background outside the mass region + signal MC  When data available use data for the BG Train Validate Train

53. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 53 Combined Signal/Background Variable ln(s/b) from gg mass From binned histogram. ln(s/b) from gg mass From binned histogram. ln(s/b) from Neural Net From fits to s and b. ln(s/b) from Neural Net From fits to s and b. XX == Log Likelihood per event Rapidly falling background distribution in region with significant signal.

54. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 54 WBF analysis  May tag forward jets and apply the additional following cuts  p T jet > 20 GeV  | jet | < 4.5  R jet > 0.5  | jet1 – jet2 | > 4.0   jet1 * jet2 < 0  p THiggs > 50 GeV and  M j1j2 > 500 GeV  CompHEP background samples  + 3 jets and + 2 jets were produced  PYTHIA underestimates QCD and prompt photon backgrounds when two forward jets are detected  We need more statistics to improve our results with CompHEP

55. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 55 WBF Results  Integrated luminosity needed to reach 5 significance for three different scenarios

56. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 56 WBF P tHiggs

57. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 57 WBF Highest P t Jet

58. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 58 Higgs boson width

59. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 59 H → ZZ* → 4 ℓ H → ZZ* → ℓ + ℓ - ℓ + ℓ - ℓ =e,μ  Irreducible background:  ZZ production  Reducible backgrounds  tt and Zbb  Very good mass resolution ~1%  In this channel (and in the H → γγ ) background can be easily estimated from data by fitting the sidebands  Above M H ~ 2M Z the two Z bosons are real and σxBR is larger  Golden channel for Higgs discovery at LHC Branching ratio dip due to opening of WW channel

60. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 60 Low mass discovery  With 30 fb -1 more than 5 sigma significance for M H >100 GeV  Higgs boson can be discovered in more than one channel, possible to measure its couplings

61. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 61 Whole mass range discovery All mass range accessible at 5σ significance with 10 fb -1 With a few fb -1 possible to discover the Higgs boson with mass between ~150 and ~500 GeV in the WW and ZZ channels  For mass larger than ~200 GeV use ZZ and WW leptonic decays  For mass larger than ~700 GeV use qqH, H → ZZ → ℓℓ νν and H → WW → ℓ ν qq

62. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 62  After discovering the Higgs boson we should measure its parameters  Studies for high luminosity (Int L = 300 fb -1 ) SM Higgs boson mass  direct reconstruction: 4 ℓ, γγ, bb  likelyhood fit WW Measurement of Higgs bosons parameters INT L = 300 fb -1

63. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 63 MSSM Higgs Searches  Two Higgs doublets model  5 Higgs bosons:  2 Neutral scalars h,H  1 Neutral pseudo-scalar A  2 Charged scalars H ±  In the Higgs sector all masses and couplings are determined by two independent parameters  Most common choice:  tanβ – ratio of vacuum expectation values of the two doublets  M A – mass of pseudo- scalar Higgs boson In the MSSM: M h ≲ 135 GeV

64. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 64 Neutral MSSM Higgs bosons  Decoupling limit (M A ≳ 150 GeV)  h behaves like H SM  Standard model searches directly apply  M H ~M A ~M H ±  M A =O(M Z ) and large tanβ  H behaves similarly to SM Higgs (SM searches apply)  In other cases for large tanβ  h(H) → WW,ZZ highly suppressed (A → WW,ZZ never allowed at tree level)  h(H),A almost exclusively decay into bb and ττ and are produced in association with bb pair  Large M A small tanβ  H,A decays almost 100% into tt  for lower masses (200-300 GeV) also H → hh and A → Zh  If SUSY particles are light the Higgs bosons may decay into s- particles

65. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 65 h,H production and decay Decoupling region Large tanβ mainly bb, ττ decays Large tanβ hbb, Hbb (and Abb) production dominates h,H decaysh,H production tanβ = 30

66. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 66 Results from SM Higgs Searches  In a large part of the MSSM parameter space SM Higgs searches are effective to find the MSSM h boson  In the decoupling region if h observed hard to distinguish SM from MSSM CMS 5 σ discovery contours

67. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 67 MSSM h,H decays Decoupling region Large tanβ bb, ττ decays Small tanβ H decays into tt when allowed

68. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 68 MSSM Production processes Large tanβ hbb, Hbb and Abb production dominates

69. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 69 Higgs Bosons visibility in the MSSM All the plane is covered but there is a large area where only h can be seen 4 Higgs observable 3 Higgs observable 2 Higgs observable 1 Higgs observable 5σ discovery regions in the MSSM tanβ – M A plane for M H MAX scenario

70. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 70 Beam Spread  LHC beams have a longitudinal spread of 7.5 cm  Longitudinal interaction spread ~5 cm  Vertex estimated from the underlying event and recoiling jet  Can also use identified converted photons – not done yet Higgs signal (M H =120GeV)

71. 4-Apr-06 Search for the SM Higgs Boson with CMSMarco Pieri 71 Vertex Determination  We use a combination of the two methods:  Maximal scalar sum of tracks p t  Maximal vector sum of tracks p t  The efficiency of determining the right vertex is ~83% Higgs events after selection  Efficiency for the different types of background is similar ProcessEff (%) H → γγ (gg fusion)82 H → γγ (IVB fusion)89 pp → γγ (born)71 pp → γγ (box)72 pp → γ+jet (2 prompt)78 pp → γ+jet (1 prompt + 1fake)86 pp →jets 90 Efficiency of determining the primary vertex within 5 mm from the true one