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Search for Supersymmetry with early LHC data David Stuart, UC, Santa Barbara. May 12, 2010.

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Presentation on theme: "Search for Supersymmetry with early LHC data David Stuart, UC, Santa Barbara. May 12, 2010."— Presentation transcript:

1 Search for Supersymmetry with early LHC data David Stuart, UC, Santa Barbara. May 12, 2010

2 2 Outline What is Supersymmetry & why are we looking for it? How do we go about searching for it? When might we find it?

3 3 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings.

4 4 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. W, Z, fermion masses could be generated by Higgs mechanism.

5 5 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. W, Z, fermion masses could be generated by Higgs mechanism. => Search for Higgs at CMS

6 6 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. W, Z, fermion masses could be generated by Higgs mechanism.

7 7 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. W, Z, fermion masses could be generated by Higgs mechanism. But mass values still not explained.

8 8 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. W, Z, fermion masses could be generated by Higgs mechanism. But mass values still not explained. And m H should diverge due to corrections:

9 9 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. W, Z, fermion masses could be generated by Higgs mechanism. Though values not explained. And m H should diverge due to corrections. Would cancel if fermion  boson “super symmetry”. ~ ~ ~ ~

10 10 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. W, Z, fermion masses could be generated by Higgs mechanism. Though values not explained. And m H should diverge due to corrections. Would cancel if fermion  boson “super symmetry”. Cancel the debt by printing more particles. ~ ~ ~ ~

11 11 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. Unification would be nice.

12 12 The Standard Model, an incomplete success Parameters unexplained: masses, mixings, couplings. Unification would be nice, and corrections from the extra “SUSY” particles seem to provide it.

13 13 The Standard Model, an incomplete success The standard model does not explain dark matter.

14 14 The Standard Model, an incomplete success The standard model does not explain dark matter. A conserved SUSY quantum number would. The LSP.

15 15 Supersymmetry, an experimentalists dream Many parameters to measure. Doubled mass spectrum, more mixings. New puzzles to solve. Whence the masses and mixings? Why is the symmetry broken?

16 16 Supersymmetry, an experimentalists dream Many parameters to measure. Doubled mass spectrum, more mixings. New puzzles to solve. Whence the masses and mixings? Why is the symmetry broken? Supersymmetry’s variety of signatures makes it a target representative of many new models.

17 17 How to search for SUSY? Produce super-partners, and detect that we have done so.

18 18 How to search for SUSY? Produce super-partners, and detect that we have done so. Massive, so need energy => LHC

19 19 How to search for SUSY? Produce super-partners, and detect that we have done so. Massive, so need energy => LHC Production via SM like diagrams. For example...

20 20 How to search for SUSY? The same diagram that produces WZ in SM…

21 21 How to search for SUSY? …could produce Winos and Zinos.

22 22 How to search for SUSY? The cross section for weak production is small. But squarks & gluinos would be strongly produced…

23 23 How to search for SUSY? In pairs if RP conserving.

24 24 How to search for SUSY? Cross-section is calculable given masses. Example: 400 GeV squark and gluino gives  ≈40 pb at 7 TeV. ≈ 1/4 of top quark cross-section. Could produce thousands this year.

25 25 Varied signatures Higgs sector LSP squarks gluino sleptons charginos/neutralinos A CMS mSUGRA benchmark, LM0

26 Higgs sector LSP squarks gluino sleptons charginos/neutralinos A CMS mSUGRA benchmark, LM0 26 Varied signatures

27 Higgs sector LSP squarks gluino sleptons charginos/neutralinos A CMS mSUGRA benchmark, LM0 27 Varied signatures

28 28 Many different search modes Multijets + MET Lepton + jets + MET Dileptons + jets + MET Same sign dileptons + jets + MET Trileptons + jets + MET

29 29 Many different search modes Each mode has different backgrounds. Search amounts to predicting these bkgds and looking for an excess above prediction. Multijets + METLepton + jets + MET Dileptons + jets + METSame sign dileptons + jets + MET Trileptons + jets + MET

30 30 Background cross-sections

31 31 Background cross-sections

32 32 Need to predict the Njet and MET tails? But kinematic tails are hard to calculate: higher orders, pdfs, detector effects… e.g., Z+jets q Z ++ --

33 33 How to predict the Njet and MET tails? Monte Carlo predictions? Sophisticated, higher order modeling, e.g., ALPGEN. Elaborate simulation of detector response.

34 34 How to predict the Njet and MET tails? Monte Carlo predictions? Sophisticated, higher order modeling, e.g., ALPGEN. Elaborate simulation of detector response. Both are software…Only trust in so far as validated with data.

35 35 How to predict the Njet and MET tails? Data validation challenges: Slow. Fit away signal?

36 36 How to predict the Njet and MET tails? Data validation challenges: Slow. Fit away signal? Don’t want to wait…

37 37 How to predict the Njet and MET tails? Would like a quick, data-driven method to predict MET in Z+jet events. In this case it is fake MET, from mis-measurement.

38 38 Missing E T in Z+jets The Z is well measured. The MET comes from the detector’s response to the jet system.

39 39 Missing E T in Z+jets For each Z+jet event, find an event w/ a comparable jet system and use its MET as a prediction. Huge QCD x-section makes such events SUSY free.

40 40 Missing E T in Z+jets For each Z+jet event, use a MET template measured from events with a comparable jet system in O(1) pb -1. Templates measured in bins of N J and J T =  j E T.

41 41 Missing E T in Z+jets Example of template parameterization Background prediction Data distribution For each data event...

42 42 Missing E T in Z+jets Example of template parameterization Background prediction Data distribution For each data event, look up the appropriate template. Sum these, each with unit normalization, to get the full background prediction N JETS pT>50 GeV sumET Bin 1 sumET Bin 2 sumET Bin 3 sumET Bin 4… 2 3 4…

43 43 Missing E T in Z+jets, MC closure test

44 44 Missing E T in Z+jets, MC closure test

45 45 Missing E T in Z+jets, MC closure test

46 46 Missing E T in Z+jets, MC closure tests “Scaled” includes a low MET normalization, which is important for low N J.

47 47 Missing E T in  +jets, MC closure test

48 48 Missing E T in  +jets, MC closure test

49 49 Missing E T in  +jets, MC closure test

50 50 Missing E T in  +jets, MC closure tests “Scaled” includes a low MET normalization, which is important for low N J.

51 51 Missing E T in Z/  +jets, robustness tests Various detector effects could add MET tails. Check robustness with MC tests, applied equally to all samples.

52 52 Missing E T in Z/  +jets, robustness tests  R=0.8 hole at (h,f)=(0,0) Double gaussian smearing Randomly add GeV “noise jets” Vary n J slope by ±50%. Jet energy scale sensitivity.

53 53 Missing E T in Z/  +jets, robustness tests  R=0.8 hole at (h,f)=(0,0) Double gaussian smearing Randomly add GeV “noise jets” Vary n J slope by ±50%. Jet energy scale sensitivity. Now working to validate this with low E T  +jets from early data.

54 54 Missing E T in W(  )+jets W Can we predict W+jets, and tt  W+jets?

55 55 Missing E T in W(  )+jets Templates can predict the fake MET in W+jet events, but we also need to predict the real MET, i.e., the p T. Can we predict W+jets, and tt  W+jets? 

56 56 Missing E T in W(  +jets Templates can predict the fake MET in W+jet events, but we also need to predict the real MET, i.e., the p T. But, the p T spectrum is ≈ same as the  p T spectrum, if we ignore V-A or randomize W polarization. Can we predict W+jets, and tt  W+jets? 

57 57 Missing E T in  +jets Pretend we could detect and apply templates. Mismatch due to b-jet dominance. But, neutrino p T dominates MET.

58 58 Missing E T in  +jets Combining template prediction with  p T spectrum gives a prediction for the full MET distribution.

59 59 Missing E T in  +jets The same approach predicts W shape, if polarization is not extreme.

60 60 Comparison with signal Benchmark points (LM4 and LM1) stand out with 200/pb at 14 TeV. LM4=(m 0 =210,m 1/2 =285); LM1=(60,250). tan(  )=10.

61 61 But we don’t have 14 TeV.

62 62 But we don’t have 14 TeV. So it will be a bit harder. When will we discover SUSY with 7 TeV?

63 63 But we don’t have 14 TeV. So it will be a bit harder. When will we constrain SUSY with 7 TeV?

64 64 When? Systematic uncertainty assumed to be 50% overall. Separate tight selections for 100 pb -1 and 1 fb -1. Expected limits in multijets + MET search

65 65 When? Similar limits from same-sign dilepton search

66 66 When? So far, we only have a few inverse nanobarns. But, that is a few hundred million events…

67 67 Detector performance encouraging with first data.

68 68 Tracking calibrated with Ks, , ,  J/ , D resonances.

69 69 When? Expect 100 pb -1 by end of this year and 1 fb -1 by end of next year. Tuning up…

70 70 Iron Man 2 © Paramount Pictures

71 71 Summary Potential for quick sensitivity to Supersymmetry If we can obtain robust, data-driven background predictions QCD based templating gives an in situ prediction of MET distribution. Charged lepton p T predicts neutrino p T.

72 72 Acknowledgements MET prediction method by Victor Pavlunin. PRD81: arXiv: Several slides borrowed from Jeff Richman Other material from …and references therein.

73 73 Extra slides

74 74 Dileptons

75 75 How to search for SUSY? Leading order cross section, tan  = 3, A=0,  >0 LM0 LM1 Rough limit from Tevatron

76 76 Typical decay patterns in LM0

77 77 Typical decay patterns in LM0

78 Standard Model backgrounds to Z+jets q Z e+e+ e-e-


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