Status of a Study of High-Mass Muon Pairs from Drell-Yan and Z

Transcription

1 Status of a Study of High-Mass Muon Pairs from Drell-Yan and Z Robert Cousins, Jason Mumford and Slava Valuev University of California, Los Angeles PRS/muon meeting September 24, 22 PRS/Muon meeting September 24, 22

2 Motivation High mass di-muons: Sensitive to many scenarios of physics beyond the Standard Model Relatively simple signature, involving only muons New tools (HLTs, CMSIM) available since last write-ups Seems to be a good entry point for us Previous CMS studies: C.-E. Wulz, CMS-TN/93-7 and DPF/DPB Snowmass (996) Muon TDR (J. Rowe et al. at UC Davis, 997) M. Dittmar, Phys. Rev. D55, 6 (997) V. Palichik and S. Shmatov, talk at CMS physics meeting (4/22) Note added after talk: D. Bourilkov, CMS IN-2/35 and CERN-YR-2-4 PRS/Muon meeting 2 September 24, 22

3 S.M. Drell-Yan muon pairs: number of events Consider M +í > 4 GeV FNAL: ( pp:*/z*) BR(*/Z*: + í ) at s = 96 GeV is ~2 fb for M +í > 4 GeV (~6 fb for M +í > 5 GeV) LHC: (pp:*/z*) BR(*/Z*: + í ): ~24 fb for M +í > 4 GeV dσ/dm (fb/4 GeV) BR (Int. cross-section > M) BR (fb) 2-24, events/year with M +- > 4 GeV at high luminosity M + - µ µ (GeV) M + - µ µ (GeV) PRS/Muon meeting 3 September 24, 22

4 Drell-Yan muon pairs: acceptance Both + and í should be within œœ < 2.4 Acceptance M µ + µ - (GeV) Where are the two muons? 6-95%, depending on the mass Both in barrel Barrelendcap Same endcap Different endcaps 26% 52% 7% 5% PRS/Muon meeting 4 September 24, 22

5 Drell-Yan muon pairs: trigger efficiency Both + and í should pass L, L2 and L3 triggers Use ORCA_6_2_3 Use muon p T thresholds for high luminosity from A. Fanfani et al., PRS/Muon meeting on August 27: Level Level 2 Level 3 Single muon 2 GeV 2 GeV 39 GeV Di-muons 6 GeV; 6 GeV 6 GeV; 6 GeV 4 GeV; 4 GeV Efficiency for all events: 93% Efficiency for events with both muons within < 2.4: 99% If trigger coverage limited to 2.: Efficiency for all events: 9% Efficiency for events with both muons within < 2.4: 97% PRS/Muon meeting 5 September 24, 22

6 Drell-Yan muon pairs: trigger bits A few per cent of events satisfy but not 2; none 2 but not ; most í both L trigger, all events L2 trigger, all events L3 trigger, all events 3 Nent = 3 Nent = Nent = All events failed single mu di-mus Failed mu Both both only only failed single mu di-mus Failed mu Both both only only failed single mu di-mus Failed mu Both both only only L trigger, events in acceptance L2 trigger, events in acceptance L3 trigger, events in acceptance 3 Nent = Nent = Nent = in acceptance failed single mu di-mus Failed mu Both both only only failed single mu di-mus Failed mu Both both only only failed single di-mus Failed mu Both both only only PRS/Muon meeting 6 September 24, 22

7 Drell-Yan muon pairs: HLT analysis Require that there are at least two muons of opposite charge sign: ~6% efficiency loss due to one of the muons not reconstructed charge misassignment is ~.3% (~3% at 3 TeV) Overall selection efficiency: ~65% (~75% at 3 TeV) (L3 P - Gen P)/(Gen P) RMS =.4769 Chi2 / ndf = 34.2 / 79 7 Prob = 5.86e-5 Constant = ± Mean =.284 ±.87 Sigma =.3554 ±.2 5 (L3 Mass-Gen Mass)/(Gen Mass) RMS =.45 Chi2 / ndf = / Prob =.95 Constant = ±.84 3 Mean =.2723 ±.294 Sigma =.2986 ± % overflow: background to high mass PRS/Muon meeting 7 September 24, 22

8 Forward-backward asymmetry A F = FB F + B B, Drell-Yan asymmetry vs mass A FB.8.6 u F B 2 = d σ d(cos dyd(cosθ ) θ 2 = d σ d(cos dyd(cosθ ) θ ) ) d f f : + -, f = u, d, * is the angle in the di-muon C.M. between the í and the quark LHC: 7% uu, 22% dd Mass Formulas from J. Rosner, Phys. Lett. B22, 85 (989) PRS/Muon meeting 8 September 24, 22

9 F-B asymmetry w.r.t. quark direction: Which proton contributes the quark is not directly measured Effect of mistagging from which direction the quark comes: Drell-Yan pairs at Tevatron: Partons before the initial state radiation: 89% uu, 8% dd, 3% others Tag the sign of quark s p L by setting it equal to sign of p L of the (unique) proton; the probability of assigning the correct sign is 99.8%. Drell-Yan pairs at LHC: Partons before the initial state radiation: 2% uu, 7% dd, % uu, 8% ud, 29% gu, 8% gd, 5% gg, 2% others (in PYTHIA with CTEQ 5M) Tag the sign of the quark s p L by setting it equal to that of the di-muon; mistag probability (integrated over y) is ~3% at 4 GeV Recall: dilution in an asymmetry is í2 ( mistag probability ) Asymmetry is further distorted by detector acceptance and resolution PRS/Muon meeting 9 September 24, 22

10 Mistag probability versus M and Y Mistag Mistag versus M Gen. mass mistag fraction.35.3 Mistag versus Y gen rap mistag frac Mistag Mass (GeV) Rapidity PRS/Muon meeting September 24, 22

11 Asymmetry before acceptance cuts Y versus cos * true gen rap vs cos_true, all Y gen versus rap vs cos_cs, * CS all(contains mistags) Rapidity Cos theta Rapidity Cos theta cos * CS is in the Collins-Soper frame (Z* axis bisects the angle between Pbeam and íptarget) PRS/Muon meeting September 24, 22

12 Asymmetry: effects of acceptance cuts gen Y versus rap vs cos_cs, * all CS, all events gen rap vs cos_cs, acc Y versus cos * CS, events in acceptance Rapidity Cos theta Rapidity - -2 The efficiency is ~ inside region, and ~ outside Need to understand well the edges of acceptance! ± cosθ y + log < # cosθ Cos theta PRS/Muon meeting 2 September 24, 22

13 Mistag probability: uncertainty due to PDF Most of the mistags come from gq and gg events X Bj of gluons in mistagged events Gluon parton distribution functions vs X Bj Mistag probability: small differences when compare CTEQ5M with CTEQ5L; CTEQ5 vs CTEQ6 vs MRST: remains to be done PRS/Muon meeting 3 September 24, 22

14 A FB extraction Fit cos * CS in ORCA using an unbinned maximum likelihood dσ 3 ( + b cos 2 θ ) + σ d cosθ The fit takes into account: = A FB cosθ 2(3 + b) production and mistag probability as a function of y; acceptance effects; cos * resolution (R.M.S. of.6 due to * CS vs * true, and of.5 due to momentum resolution) For a sample of 63 events, obtain: A FB =.54 ±.8, b =.2 ±.3 if b is a free parameter; A FB =.53 ±.8 if b is fixed at (S.M. value); A FB =.22 ±.4, b =.2 ±.3 if mistags are not accounted for. (N.B. A FB (S.M.) =.6) PRS/Muon meeting 4 September 24, 22

15 Z : current limits and production rates So far we have generated the following Z s: Z SSM in sequential standard model Z = Z % cos E6 + Z $ sin E6 in E 6 and/or SO() models: Z %, Z $ and Z ( E6 = o ) Current experimental limits (CDF and D): 69 GeV for Z SSM 59 GeV for Z % 595 GeV for Z $ 62 GeV for Z /year above M No decays to exotic particles; unsmeared Z% Drell-Yan in absence of Z Z SSM Z$ M µ + µ - (GeV) PRS/Muon meeting 5 September 24, 22

16 Z width vis-a-vis mass resolution Typical Z width: ~3% Sqrt(Var(L3-Gen Mass)/Gen Mass) vs Gen Mass σ, % of Gaussian fits; typical uncertainty ~% Truncated RMS ± RMS truncated at %; all tracks M µ + µ - (GeV) Mass (GeV) Negligible (< %) bias on mass at all values! PRS/Muon meeting 6 September 24, 22

17 Z mass spectra 3 TeV Z (SSM) events/ GeV/ fb Z SSM (3 TeV) all tracks 3 TeV Zpsi (E6), Qcut events/ GeV/ fb Z % (3 TeV) quality cuts TeV Z (SSM), Qcut events/ GeV/ fb mu+ mu- mass Z SSM (3 TeV) track quality cuts mu+ mu- mass 5 TeV Zpsi (E6), Qcut events/2 GeV/ fb-.4.2 Z % (5 TeV) quality cuts Stat. fluctuations not to scale! mu+ mu- mass mu+ mu- mass Still need to check heavy flavor backgrounds from tt, bb (kin. cuts, isolation) PRS/Muon meeting 7 September 24, 22

18 Z : forward-backward asymmetry A FB A FB Generated (without mistags) M(Z ) = 3 TeV;, events -2-2 Rapidity -2-2 Rapidity A FB A FB Rapidity -2-2 Rapidity As has been extensively discussed in the literature, can be potentially used to distinguish between the models if Z LVVHHQ Remains to be further studied, along with effects of differing u and d couplings, etc. PRS/Muon meeting 8 September 24, 22

19 Summary Results are generally what was expected from prior work by C.-E. Wulz, M. Dittmar, and others, but One can now explore challenges that emerge with the more sophisticated existing simulation and reconstruction. One can now explore what systematics in the angular distribution arise due to acceptance, production, etc. As expected, with any steeply falling spectrum, reducing and understanding way-out tails of resolution is crucial. This work was based on only a crude understanding of the tracker code. One can explore much better ways to use it. We will work to help quantify the above We would like to thank many people who helped us in this study, in particular Norbert Neumeister, Nicola Amapane and Hannes Sakulin PRS/Muon meeting 9 September 24, 22