B s μ + μ - at the LHC

Transcription

1 s μ + μ - at the LHC Diego artínez antos (Universidade de antiago de Compostela) on behalf of ATLA, C and LHCb collaborations PROGRAA NACIONAL DE ECA FPU 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 1

2 overview otivation for the study of s µµ as an indirect probe of NP Analyses at the LHC: ATLA/C/LHCb How to find such a rare decay and disentangle from background Normalization and Calibration to get a correct R Conclusions 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany

3 indirect approach s µµ can access NP through new virtual particles entering in the loop indirect search of NP Indirect approach can access higher energy scales and see NP effects earlier: ome examples: 3 rd quark family inferred by Kobayashi and askawa (1973) to explain CP V in K mixing (1964). Directly observed in 1977 (b) and 199 (t) Neutral Currents discovered in 1973, Z 0 directly observed in 193 ~30 years till the direct observation 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 3

4 indirect approach s µµ can access NP through new virtual particles entering in the loop indirect search of NP Indirect approach can access higher energy scales and see NP effects earlier: A very early example of how indirect measurements give information about higher scales : Ancient Greece: Earth must be some round object, Eratosthenes measurement of Earth s radius in c. III C (using differences in shadows at different cities) Roundness of Earth not directly observed until ~ ~.3 K years till the direct observation Eratosthenes 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 4

5 Wilson coefficients Hadronic weak decays are often studied in terms of effective hamiltonians of local operators Q i : H eff i C Qˆ i i effective local theory Degrees of freedom of exchanged particles are integrated out giving rise to the Wilson coefficients C i. underlying fundamental theory () An example of similar approach: Fermi s theory of neutron decay R( s µµ) expressed in eff. th. as: R( q ) GF 64 3 V V * tb tq q 3 q f q 1 4m q C P,, (pseudoscalar, scalar and axial) depend on the underlying model (, UY ) q 1 4m q C q C P m q C 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany

6 decay physics () R( q ) GF 64 3 V V * tb tq q 3 q f q 1 4m q q 1 4m q C q C m C, P scalar and pseudo scalar are negligible in C gives the only relevant contribution P q C (q = u, c, t) This decay is very suppressed in : R( s µµ) = (3.3 ± 0.3)x -9 R( d µµ) = (1.03 ± 0.09)x -.lanke et al., JHEP 003,006 Current experimental upper limit (CDF, 3.7fb -1 ) still one order of magnitude to reach such 90% CL: R( s µµ) < 3.6x - R( d µµ) < 6.0x -9 CDF collab., CDF Public Note 99 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 6

7 New Physics effects NP can contribute to this decay rate (specially UY at high tanβ (tanβ = v u /v d )): ore than one Higgs contributions to C,P HD-II : R proportional to tan 4 β UY (): above + extra tan 6 β + RPV UY: tree level diagrams Technicolor (TC), Little Higgs (LHT) modify C. NP can modify the R from < up to current experimental u.l. Whatever the actual value is, it will have an impact on NP searches 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 7

8 NP (II) ome examples from UY -7 x - x -9 J.Ellis et al. JHEP07:09,007 [arxiv: v [hep-ph] ] NUH: best χ of the fit R ~x - J.Ellis et. al. Phys.Rev.D76:11011, 007[ arxiv: v4 [hep-ph] ] (00) CPVFV: Enhancements up to current u.l, but also < depending on the phases C mg ma. Heinemeyer et al., R( s μ + μ - ) ~4.x - ~3.x - ~0.4x - arxiv:00.39v [hep-ph] 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany

9 LHC sensitivity to s μ + μ - 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 9

10 LHC experiments ATLA & C: ATLA General purpose experiments Central detectors η <. High pt physics at L = cm - s -1 physics: high pt muon triggers LHCb: LHCb C physics dedicated experiment Forward spectrometer 1.9< η < 4.9 Lower pt triggers. Efficient also for purely hadronic channels (see talk of Leandro de Paula) Instant Luminosity - x 3 cm - s -1 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany

11 analysis overview Triggered and offline reconstructed (incl. muon identification) signal events per fb -1 (i.e., effective s µµ cross section) ATLA C LHCb # evts/fb For trigger strategy L = 33 L > 3 L = x 3 ain issues: ackground discrimination: offline cuts/ multivariate analysis bb assumed to be 00 µbarn, R( s µµ) = () ATLA/LHCb: 3.3 x -9 C: 3.9 x -9. Artuso et al. Eur. Phys. J. C (00) 7: (see expr. 1) Normalization to another channel with well known R It avoids needing the knowledge of xsections & integrated luminosity Cancelation of systematic uncertainties ATLA analysis: CERN-OPEN [arxiv: ] (-physics chapter) C analysis: C PA PH (009) LHCb analysis: LHCb-PU (007), LHCb-PU (00) 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 11

12 useful variables Usual signatures of a given decay: Detached econdary Vertex: large lifetime, distance of flight (DOF), Impact Parameter (IP) of daughters coming from Primary Vertex: small IP, small momentum-to-flight direction ( pointing ) Good quality econdary Vertex: small χ, small DOCA (Distance Of Closest Approach) Isolation ATLA / C: > 1GeV (ATLA) > 0.9 GeV (C) LHCb: Above definition not suitable for LHCb geometry. Isolation is defined per muon as the no. of tracks compatible with a common µ-track V Invariant ass around s: For combinatorial bkg. sensitivity scales as σ ATLA ~ 90 ev, σ C ~ 3 ev, σ LHCb ~ ev 1 DOCA DOF 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 1

13 useful variables uon isolation 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 13

14 atlas / cms bb assumed to be 00 µbarn ATLA Evts/fb R = 3.3x -9 (Efficiencies w.r.t following preselection criteria: 4 < <7.3 GeV, χ <, L xy < cm. Isolation cut in signal also includes a factor 0.46 from trigger efficiency. This cuts are for analysis with L >~ fb -1 ) ATLA is also preparing an analysis based on a boosted decision tree C s µµ bb µµx 4. < <6 GeV ~ cos(α)> DOF > 17 σ χ < Isolation > s < 0 ev Evts/fb R * =3.9 x -9 *. Artuso et al. Eur. Phys. J. C (00) 7: (see expr. 1) C estimates total bkg as ~6.3 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 14

15 LHCb LHCb uses cuts just to get a reasonable rate of events to analyze elected signal candidates are classified in a 3D parameter space, according to: Invariant mass (in a window of 60 ev around s peak) PID likelihood with info from different subdetectors, to get rid of possible remaining misid Geometry likelihood: Combines several variables related candidate geometry est separation power Invariant ass 3D space is binned, so that each bin is treated as an independent experiment Results are combined using odified Frequentist Approach. PID Geometry 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 1

16 IP LHCb How the Geometry likelihood is built: 1. Input variables: min Impact Parameter ignificance (µ +,µ - ), DOCA, Impact Parameter of, lifetime, iso - µ +, iso- µ -. They are transformed to Gaussian through cumulative and inverse error function 3. In such space correlations are more linear-like rotation matrix, and repeat 4. Transformations under signal hyp. χ, under bkg. χ.. Discriminating variable is χ -χ, made flat for better visualization. lifetime G G χ ensitive region GL> 0. χ ignal bb µµx t (ps) G 1 G 1 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 16

17 R( s 0 -> + -) (x -9 ) sensitivities (expected (for R = 3.3e-9) & per fb -1 in each experiment LHCb bins parameter space N experiments) (R = 3.3e-9) =.0 = % CL exclusion sensitivity as a function of L (Only bkg is observed) ass (ev) GL CDF (3.7fb -1 ) prediction 90 % CL exclusion C LHCb privately computed from quoted,, using FA systematics not included C 1fb -1 (official) 1.6x - Expected CDF + D0 (fb -1 ) L (fb -1 ) 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 17

18 R( s 0 -> + -) (x -9 ) sensitivities (expected (for R = 3.3e-9) & per fb -1 in each experiment LHCb bins parameter space N experiments) ass (ev) (R = 3.3e-9) =.0 = 6.3 GL % CL exclusion sensitivity as a function of time Assuming nominal luminosities since the beginning C L = 33 cm - s -1 LHCb L = x 3 cm - s -1 CDF (3.7fb -1 ) prediction 90 % CL exclusion C LHCb privately computed from quoted,, using FA systematics not included Expected CDF + D0 (fb -1 ) Time (nominal years) 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 1

19 R( s 0 -> + -) (x -9 ) sensitivities (expected (for R = 3.3e-9) & per fb -1 in each experiment LHCb bins parameter space N experiments) (R = 3.3e-9) =.0 = 6.3 ignal evidence sensitivity as a function of L (ignal + ackground observed) ass (ev) GL C LHCb privately computed from quoted,, using FA systematics not included evidence prediction L (fb -1 ) 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 19

20 R( s 0 -> + -) (x -9 ) sensitivities (expected (for R = 3.3e-9) & per fb -1 in each experiment LHCb bins parameter space N experiments) ass (ev) (R = 3.3e-9) =.0 = 6.3 GL ignal evidence sensitivity as a function of time Assuming nominal luminosities since the beginning C L = 33 cm - s -1 LHCb L = x 3 cm - s -1 C LHCb privately computed from quoted,, using FA systematics not included evidence prediction Time (nominal years) 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 0

21 R( s 0 -> + -) (x -9 ) LHC tartup LHC first data: Less energy ( TeV) Less instant luminosity % CL TeV Exclusion sensitivity for 40 CDF (3.7fb -1 ) 4% of σ bb w.r.t. 14 TeV (Pythia ratio σ bb_7tev /σ bb_14tev ), so µb 30 0 Expected CDF + D0 (fb -1 ) First months after LHC startup (assumed 300 pb -1 ) This data could allow LHCb to overtake Tevatron limits and impose new constraints on UY models L (pb -1 ) 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 1

22 normalization & Calibration 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany

23 normalization Normalization is needed to convert # events into a R w/o relying on knowledge of σ bb, integrated luminosity or absolute efficiencies R R n n P( b P( b n s ) ) N N n P(b +, d )/P(b s ) implies a ~14 % systematic. Normalization to a s mode would introduce larger errors because of poorly known s R s The fraction of efficiencies (acceptance, trigger, selection, PID ) needs to be computed/cancelled. ATLA/C/LHCb : to + J/Ψ(µµ)K + imilar trigger and muon ID The selection can be made similar to signal ut: Extra track to be reconstructed d J/ΨK * / + J/Ψ(µµ)K + or other similar ratios allow to study this + J/Ψ(µµ)K + ~pb -1 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 3

24 normalization ( kπ) LHCb also uses normalization to h + h - ( d,s Kπ, d ππ, s KK ) ame geometry & kinematics than signal, different trigger (hadronic) and PID How to get rid of the differences: Use hh events Triggered Independently of ignal everal thousands of such events per fb -1 will be available Use b J/ΨX to emulate muon ID and trigger on that sample as a function of p/pt The most suitable mode: d Kπ (well known R, largest statistics ) Λ b pk Λ b pπ It can be separeted from the inclusive sample using the RICH (see talk of Laurence Carson) 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 4

25 calibration LHCb: signal is distributed in several bins of a 3D space We need to know not only overall normalization, also the fraction of signal in each bin Invariant mass Can be calibrated with s KK GL (inclusive) hh triggered independent of signal (TI) PID likelihood J/Ψ taking p, pt distributions from hh TI Red: s µµ lack: hh TI Data: s μμ Red: Fit to data itself lue: Function from calibration 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany

26 Conclusions A measurement/exclusion of R( s µµ) will have an important impact on NP searches LHC offers exceptional conditions for this study, scanning from current upper limit to < prediction LHCb takes advantage of its -physics dedicated trigger, as well as good invariant mass resolution, having the best sensitivity for a given luminosity ATLA/C benefit from their capabilities to run at higher luminosities? The use of control channels such as + J/Ψ(µµ)K + and hh allows to perform a C free analysis 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 6

27 Title of the slide 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 7

28 background level ATLA/C/LHCb: amount of bkg in the signal region has to be known kg is dominated by combinatorial (bb µµx) and hence can be understood from sidebands Linear or exponential fit gives the bkg level in the signal region pecific/peaking bkg is negligible in current simulations 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany

29 LHCb How the Geometry likelihood is built: 1. Input variables: min IP (µ +,µ - ), DOCA, IP of, lifetime, iso - µ +, iso- µ -. They are transformed to gaussian through cumulative and inverse error function 3. In such space correlations are more linear-like rotation matrix, and repeat 4 o 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 9

30 sensitivity to 0 upposing bb mumu is also the dominant bkg at the d window, for each luminosity you can access to 3-4 times smaller R for d than for s. 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 30

31 ROugh ENITIVITY CALCULATION ignal yield σ eff *L bkg under the peak scales linearly with invariant mass resolution σ / eff sig eff bkg L 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 31

32 normalization ( kπ) d Kπ has to be separated from the inclusive sample Use of the RICH system Extra efficiency factor to account for hh can self-calibrate this eff. using ratio d Kπ / d ππ (very well known ratio of xsections) and the number of inclusive hh, as well as the good s - d mass separation in LHCb Alternatively, D* D 0 (Kπ) π reweighting by p,pt, can be also used (see Laurence Carson talk) f(d Kπ) = (C = 0.61) f(d π π) = ± 0.01 (C = 0.17) f(s Kπ) = ± (C = 0.043) f(s KK) = ± (C = 0.) Output of a C experiment using d Kπ / d π π to calibrate RICH effs. 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 3

33 Title of the slide Full expression (µ q the ratio of masses m q /m b ) R( q ) 64 G F 3 sin 4 W V * tb V tq q 3 q f q 1 4m q q 1 4m q C 1 q q C ' q C P 1 q q C ' P m q C A C ' A 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 33

34 Figure -: Correlation in initial and Gaussian space. 1th International Conference on -Physics at Hadron achines, eptember , Heidelberg, Germany 34

35 eparation of d Kπ Extract the fraction of different components of hh, without relying on C PID efficiencies: 1. easure those fractions in a high purity limit (PID cuts > X): (Example for X = 0): KK N kk = 0 Kπ N kπ = 39 ππ N ππ = 7 (Then the true fraction should be): f kk = 0.9 f kπ = 0.71 f ππ = Not necessary the same as in the nonpid hh sample!!! f K f ' KK K f f ' K ' K K K f ' (eparate s Kπ and d Kπ is not an issue because of the mass resolution) f ' K f ' KK f ' K K f ' K 3 3

36 fractions eparation of d Kπ (II). The ratio (ε π /ε K ) thus the right fractions can be easily extracted from d modes, where the R s are known. N( N( 0 d 0 d K ) ) R( R( 0 d 0 d K ) ) To ensure the high purity limit, repeat 1 & until a plateau on the results is reached K ( ) N' N' ( d ) K d 0 ->K f(d Kπ) = (C = 0.61) s ->K 0 d -> 0 s ->K K f(d π π) = ± 0.01 (C = 0.17) f(s Kπ) = ± (C = 0.043) PID cut f(s KK) = ± (C = 0.) 36 36