Adriano Di Florio on behalf of the CMS collaboration - Adriano Di Florio
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Adriano Di Florio on behalf of the CMS collaboration Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019
The CMS Experiment at LHC The Compact Muon Solenoid (CMS) is a general purpose detector designed for the precision measurement of leptons, photons, and jets, among other physics objects, in proton-proton as well as heavy ion collisions at the CERN LHC facility. Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 01
Muon Reconstruction and Triggering The Compact Muon Solenoid (CMS) is a general purpose detector designed for the precision measurement of leptons, photons, and jets, among other physics objects, in proton-proton as well as heavy ion collisions at the CERN LHC facility. Tracking system Good pT resolution (down to ΔpT pT ≈ 1% in barrel) Tracking efficiency >99% for central muons Good vertex reconstruction & impact parameter resolution O(µm) Muon system Muon candidates reconstructed by matching muon segments and a silicon track in a large rapidity coverage ( < 2.4) Good dimuon mass resolution ( dependent): ΔM M ≈ 0.6 ÷1.5% J ψ : ≈ (20 ÷ 70)MeV Excellent muon-ID: ε (µ | π , K, p) ≤ (0.1÷ 0.2)% Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 02
Run II Data The CMS experiment has recorded 150 fb-1 at 13 TeV of data of which ~143 fb-1 have been certified for physics Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 03
Outline Observation of and ∗ states Observation of ( ) and ( ) states Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 03
Observation of and ∗ states Phys.Rev.Lett. 122, 132001 (2019) arXiv:1902.00571
The family The 3 family consists of charged mesons composed of a beauty antiquark and a charm quark (or vice versa). The ground state 3 was discovered in 1998 by the CDF Collaboration in the 3 → / decay channel [PRL 81 (1998) 2432] Phys. Rev. D 49 (1994) 5845 Theory Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 04
The family The 3 family consists of charged mesons composed of a beauty antiquark and a charm quark (or vice versa). The ground state 3 was discovered in 1998 by the CDF Collaboration in the 3 → / decay channel [PRL 81 (1998) 2432] Phys. Rev. D 49 (1994) 5845 Since the bc mesons cannot annihilate into gluons, the excited states decay to the ground state via the cascade emission of or pairs total widths that are less than a few hundred KeV Their production yields are extremely low since the bc production cross sections is proportional to the GH : two pairs of heavy quarks produced Nevertheless theoretical preditions on 3 excited states proliferates: PRD 49 (1994) 5845 Meson Predicted Mass (MeV) PRD 51 (1995) 3613 PRD 52 (1995) 5229 3 6247 ÷ 6286 PRD 53 (1996) 312 PLB 382 (1996) 131 3∗ 6308 ÷ 6341 PRD 160 (1999) 074006 PRD 67 (2003) 014027 3 (2 ) 6835 ÷ 6882 PRD 70 (2004) 054017 Theory PRL 104 (2010) 022001 3∗ (2 ) 6881 ÷ 6914 PRD 86 (2012) 094510 PRL 121 (2018) 202002 Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 04
The family The 3 family consists of charged mesons composed of a beauty antiquark and a charm quark (or vice versa). The ground state 3 was discovered in 1998 by the CDF Collaboration in the 3 → / decay channel [PRL 81 (1998) 2432] Phys. Rev. D 49 (1994) 5845 Since the bc mesons cannot annihilate into gluons, the excited states decay to the ground state via the cascade emission of or pairs total widths that are less than a few hundred KeV Their production yields are extremely low since the bc production cross sections is proportional to the GH : two pairs of heavy quarks produced Nevertheless theoretical preditions on 3 excited states proliferates: PRD 49 (1994) 5845 Meson Predicted Mass (MeV) PRD 51 (1995) 3613 PRD 52 (1995) 5229 3 6247 ÷ 6286 PRD 53 (1996) 312 PLB 382 (1996) 131 3∗ 6308 ÷ 6341 PRD 160 (1999) 074006 PRD 67 (2003) 014027 ( ) ÷ PRD 70 (2004) 054017 Theory PRL 104 (2010) 022001 ∗ ( ) ÷ PRD 86 (2012) 094510 PRL 121 (2018) 202002 Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 04
Observation of an excitate N meson state by ATLAS PRL 113 (2014) 212004 Using both 7 TeV and 8 TeV Run I collected data ATLAS BC -7 TeV collaboration reported the observation of a a new BC (2S)-7 TeV state whose mass is consistent with predictions for the BC (2S) 3 → / 3 (2 ) → 3 BC -8 TeV PQ(RS) = 22 ± 6 7 TeV PQ(RS) = 35 ± 13 8 TeV BC (2S)-8 TeV For the combined 7 and 8 TeV data set the total significance of the observation is found to be 5.2σ (5.4σ local at fixed mass). Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 05
Search for excited N states by LHCb JHEP01(2018)138 Using 2.9 fb-1of 8 TeV data LHCb collaborations searched for the BC (2S) in the same decay channel used by ATLAS 3 (2 ) → 3 (→ / ) BC BC (2S) BC (2S) With much more Bc candidates (3325 ± 73) they found no evidence of BC (2S) signals and quoted a limit BC (2S) BC (2S) Search sensitivity enhanced by the use of MLP neural network (4 categories) Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 06
N and ∗N reconstruction The 3N 2 decays directly to the 3N ground state : ∆ = 3N 2 → 3N N [ The 3∗N 2 decays to 3∗N state through emission followed by a radiative decay of 3∗N to the 3N ground state with the emission of a soft (E~55 MeV in rest frame): 3∗N 2 → 3∗N (→ 3N ) N [ Having the emitted photon a very low energy, its detection is very challenging, and tipically it is lost. Thus: 3N 2 → 3N N [ + ^_GG emission emission The 3∗N 2 peak should then appear into 3N N [ mass spectrum at the mass ( 3N 2 ) − ∆ where ∆ = ∆ = ∆ c − ∆ d= [ 3∗ 1 − ( 3 1 )] − [ 3∗ 2 − ( 3 2 )] which is predicted positive (∆ ~20MeV) so that the 3∗N 2 peak will be at lower masses than the 3N 2 peak. Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 07
Event Selection Trigger preselection: two µ from / plus a track, with common vertex displaced from interaction point ( t• / •‚ƒ > 3.0) c / n c > 3.5 GeV n µ > 4.0 GeV / rst > 0.1 c n 3 > 15 GeV 3 < 2.4 kv 3 > 100 d d k n d > 0.8 rst > 0.1 k 3 n k > 0.6 3 3N 2 → 3N N [ 3∗N 2 → 3∗N N [ 3N meson momentum required to point to PV in xy plane Tracks and muons satisfy high-quality requirements 6.2 < ( 3 ) < 6.35GeV Among multiple 3N N [ candidates the highest n one is kept The PV is re-fitted excluding the three 3 decay tracls ( c ) d and k are tracks from the refitted PV Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 08
N reconstruction in Run II data Unbinned ML fit Signal modelled using a double gaussian Combinatorial background: first-order Chebyshev polynomial function 2015+2016+2017+2018 3N → / N background: shape determined from simulation studies and a normalization fixed relative to the 3N → / N yield 3N → / N + background: relevant only below 6.2 and is described by a ARGUS function convolved with a Gaussian resolution PQ† = 7629 ± 225 3N = 6371.1 ± 0.5MeV 3N = 33.5 ± 2.5MeV d ˆ_s = 35 ( . . . = 30) Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 09
and ∗ observation 2015+2016+2017+2018 Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 10
and ∗ observation The 3 − 3 + Œv• ( 3 ) distribution is fitted with Gaussian functions for the peaks and a 3rd order Chebyshev polynomial for the background. Mass resolution agrees with MC expectations (~6MeV) and is much lower than ∆ thus allowing a two-peak structure to be observed. 2015+2016+2017+2018 Measured two peaks’ mass difference: ∆ = 29.1 ± 1.5 MeV Given the predicted mass splitting (∆ c − ∆ d> 0), 3N 2 is assumed to be ∗N N the right-most peak 3 (2 ) = 6871.0 ± 1.2 MeV From MC studies: the low-energy emitted in the 3∗N 2 decay has a very small reconstruction efficiency, of order 1% . The photon is not detected and the mass of the 3∗ 2 cannot be measured. Local significance exceeding 6.5 for observing two peaks rather than one. For both single peaks significance is above 5 When fitting each signal with a Breit-Wigner convolved with the gaussian resolution function the natural width ( predicted 50 ÷ 90 KeV ) is consistent with zero: natural widths are much smaller than resolution. d PQ∗† d’ = 67 ± 10 PQ†(d’) = 51 ± 10 ˆ_s = 42 ( . . . = 39) Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 10
Systematic Uncertainties Partially reconstructed decays / background contamination: The low-mass edge of signal mass window was varied from 6.2 to Difference seen when normalisation increased by a factor 2: the 6.1, to increase this contamination; the variations in the results difference is negligible are negligible : no systematic uncertainty is considered ( ) fit modeling Alignment of the detector Alternative functions for the signal and the backgrounds • Signal : changed from two Gaussians to two Breit-Wigner functions The possible misalignment of detector biases the measured • Background: changed from a polynomials to a threshold function masses, however for studies with major detector changes (2016 Observed differences in and ∆ are quoted as systematic vs 2017), was found to be negligible uncertainties: 0.8 and 0.7 MeV respectively ∆ ∆ = ∆ c − ∆ d = 29.1 ± 1.5 ± 0.7 3 (2 ) = 6871.0 ± 1.2 ± 0.8 ± 0.8 3 ∆ ( ) world average uncertainty Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 11
Observation of ( ) and ( ) states Phys. Rev. Lett. 121, 092002 (2018) arXiv:1805.11192
The bottomonium family The bottomonium family ( )— plays a special role in understanding how the strong force binds quarks because, due to the high quark mass, allows two important theoretical simplifications 1. the hard-scattering production of a proto-quarkonium quark- antiquark pair can be described in perturbation theory 2. the binding of the quark-antiquark pair can be described in terms of lattice-calculable nonrelativistic potentials Sketch by P.Faccioli Production of œ in the regime Formation of a bound state: of perturbative QCD non relativistic potentials The measurements of the masses of the ˜™ (3 ) triplet states ( = 0,1,2) is especially interesting to probe details of the — interaction in proximity of Picture from : V. Knünz, Measurement of Quarkonium Polariza9on to Probe QCD - DOI 10.1007/978-3-319-49935-2_2 open-beauty threshold Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 13
The ( ) and ( ) states 220 300 -1 http://inspirehep.net/record/1381380 L int = 4.7 fb -1 The ˜ (3 ) was observed by ATLAS in 200 ATLAS 4.4 fb Candidates / 25 MeV pp 7 TeV 180 250 2011 as a new structure in the Phys. Rev. Lett. 108 (2012) 152001 Converted photons Υ (1S) + γ Υ 1 and Υ(2 ) decay modes 160 Events per 10 MeV 200 140 Υ (2S) + γ (1S) Υ (3S) + γ 120 150 CMS saw the ˜ (3 ) in the 100 80 100 Υ( ) radiative decays, in the 7 TeV 60 50 data 40 20 (2S) 9.6 9.8 10 10.2 10.4 10.6 10.8 11 χ 0 M [GeV] 9.6 9.8 10.0 10.2 10.4 10.6 10.8 + - + - Fig. 3.26 m( ) - m( )+m [GeV] 45 Mass spectrum-1of the Y(nS) + γ decay channels, as measured by CMS at 7 TeV, includ- (k S) ing a fit to the DØ,three 1.3distributions fb Events / 50 MeV 90 40 80 LHCb Candidates / 10 MeV Phys. Rev. D 86, 031103 70 8 TeV 35 60 50 30 DØ observed the ˜ (3 ) → Υ(1 ) decay channel. 40 30 25 20 10 20 0 LHCb observed the ˜ (3 ) → Υ(3 ) decay channel 35 Eur. Phys. J. C74 (2014) 3092 Candidates / 10 MeV 15 30 7 TeV 25 10 20 15 5 10 5 0 9.5 10 10.5 11 11.5 0 10.5 10.6 10.7 M μμ - M μμ + m (1S) [GeV ] Y(3S) + photon mass (GeV) Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 14
The ( ) and ( ) reconstruction - selection Based on data, collected from 2015 to 2017 at = and corresponding to ℒ = [ , CMS reported the first observation of resolved ˜c (3 ) and ˜d (3 ) states and the measurement of their masses through the decay channel : ˜ (3 ) → ( ) → µµ decay triggering the event with a µµ pair with two opposite sign µ coming from a common vertex G = 2.0 G = 1.5 candidate: n > 14 < 1.2 High purity ( ) sample achieved with tight mass cuts: (3 ) − G ^ ( ) < µµ < 3 + 2.5 ^ ( ) low 2 contamination / > 0.5 Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 15
The ( ) and ( ) reconstruction - selection Based on data, collected from 2015 to 2017 at = and corresponding to ℒ = [ , CMS reported the first observation of resolved ˜c (3 ) and ˜d (3 ) states and the measurement of their masses through the decay channel : ˜ (3 ) → ( ) → converted photon with < 1.2 and n > 500 For an higher resolution, at the cost of a reduced yield (w.r.t. calorimetric energy measurements), only e+ e- from a conversion in the beam pipe or in the tracker are considered see arXiv:1210.0875 & arXiv:1409.5761 N.B. the measured low mass peak resolution : • 2.18 ± 0.32 MeV in ( ) mass distribution • 7 MeV and 15 MeV in ( ) and ( ) For a more accurate measure the photon energy scale is calibrated through a 3c → / (→ µµ) sample: d d ¬¬- − ¬¬ Large data sample in the . . . = ( 3c )d − ( / )d same running periods and is used for the event-by-event correction of the photon energy in the computation of the ( ) invariant mass Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 16
The ( ) and mass spectrum 2015+2016+2017 Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 17
The ( ) and mass spectrum Unbinned ML fit 2015+2016+2017 Signal modelled using a double gaussian Combinatorial background: exponential function Total (two peaks) yield is 372 ± 36 The two masses: ˜c 3 = 10513.42 ± 0.41(stat) ± 0.18 MeV ˜d 3 = 10524.02 ± 0.57(stat) ± 0.18 MeV The mass difference between the J = 1,2 states is measured to be: Main systematic uncertainties: ∆ = − = • PES fit function (0.16 MeV) • Fit functions (0.05 MeV) = . ± . ( ) ± . • ( ) mass uncertainty cancels out Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 17
Mass splitting: comparison to theoretical predictions There is a large number of theory predictions for the ∆ mass spliting between the = and = ( ) states 20 CTP 52 (2009) 653 Out of 20 predictions: PRD 86 (2012) 094011; Cornell-I PRD 86 (2012) 094011; Cornell-II PRD 86 (2012) 094011; Screened Cornell-I • 19 range from 8 to 18 MeV 15 PRD 86 (2012) 094011; Screened Cornell-II • 1 prediction is -2 MeV PRD 86 (2012) 094011; Richardson PRD 86 (2012) 094011; pQCD EPJC 72 (2012) 1981 CPC 37 (2013) 023103 CPC 37 (2013) 083101 10 CMS measurement NPA 924 (2014) 65 PRD 90 (2014) 054010 PRD 90 (2014) 054010; GI refit ∆ = 10.60 ± 0.64(stat) ± 0.17 sys MeV PRD 90 (2014) 054010; GI original 5 PRD 92 (2015) 054034 PRD 93 (2016) 074027 has sufficient precision to provide an important constraint to PRD 94 (2016) 034021; SHO the theory models calculating quarkonium spectroscopy levels PRD 94 (2016) 034021; GEM PRD 95 (2017) 074002 arxiv:1702.06774 (2017) 0 1) most of the predictions may be ruled out -5 0 5 10 15 20 2) breaking of the conventional pattern of splittings strongly disfavoured DM (MeV) Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 18
Summary and Conclusions - II Observation of and ∗ states Signals consistent with the ( ) and ∗ states have been separately observed for the first time by investigating the invariant mass spectrum measured by CMS experiment. ∆ and 3 (2 ) have been measured while the mass of the ∗ state remains unknown because the ∗ decays to and the is not reconstructed This analysis is first LHC result based on the full usable Run 2 data of proton-proton collisions at = , corresponding to a total integrated luminosity of 143 fb-1 Both peaks have local significance exceeding 5 , the significance of two peaks with respect to observing only one peak is 6.5 Observation of ( ) and ( ) states Signals consistent with the ( ) and ( ) states have been separately observed for the first time by investigating the ( ) invariant with the photon converting (→ ) in the beam pipe or in the tracker to enhance the mass resolution ∆ , ˜c 3 and ˜d 3 have been measured with sufficient precision to highly support the standard mass hierarchy Two peaks local significance exceeds 5 Both these measurements contribute significantly provide a rich source of information on the non-perturbative QCD processes that bind heavy quarks Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 13
Thank You "I am putting myself to the fullest possible use, which is all I think that any conscious entity can ever hope to do" Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019
Back Up Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019
example event display Adriano Di Florio QWG2019 Cavallerizza Reale, Torino - 15 May 2019 B1
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