Recent results from the LHCb experiment

Transcription

1 Recent results from the LHCb experiment University of Cincinnati On behalf of the LHCb collaboration

2 Brief intro to LHCb

3 The Large Hadron Collider (LHC) proton-proton collisions NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

4 LHCb & Dark Matter, astrophysics, astroparticle physics, The LHCb experiment is a general-purpose detector in the forward region of the proton-proton collider CERN CMS It can contribute and is contributing to the field of dark matter, astrophysics, etc.! - Certainly not something we had thought about when designing the experiment NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

5 Time-dependent CP violation B s D s K The LHCb Detector and Cavern RICH1 MUON CALO RICH2 T MAGNET TT VELO 23 sep :49:24 Run Event NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

6 LHCb versus ATLAS & CMS pros & cons Detector in the forward region - Detects light states also Smaller instantaneous luminosity Limited acceptance but complementary Excellent vertex resolution - Sees B s oscillations at 40 fs Excellent impact parameter and secondary vertex resolutions Excellent mass resolution - ~0.5% on m(mm) up to 20 GeV Real bonus Unique particle identification performance - Thanks to Cherenkov detectors Allows for a variety of studies Good jet reconstruction % energy resolution for jets with pt > 10 GeV - b(c) tagging eff. ~65 (25)% for ~0.3% contamination NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

7 How can LHCb contribute to the field of DM physics? Indirect constraints Flavour physics typically more sensitive to higher mass scales than direct searches Constraints on New Physics couplings Direct searches For Majorana neutrinos For Dark Sector signatures Conventional collider searches Constraints on backgrounds in searches E.g. measurement of antiproton production in p-he collisions NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

8 Muon pairs in the data Note : structure given the numerous trigger lines with different requirements NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

9 Recent publications relevant to DM & co Measurement of antiproton production in phe collisions at s NN =110 GeV [LHCb-CONF ] Search for dark photons produced in 13TeV pp collisions [LHCb-PAPER , arxiv: ] Search for long-lived scalar particles in B + K + χ(μ + μ ) decays [Phys. Rev. D 95, (2017)] Search for hidden-sector bosons in B 0 K μ + μ decays [Phys. Rev. Lett. 115, (2015)] Search for massive long-lived particles decaying semileptonically in the LHCb detector [Eur. Phys. J. C (2017) 77:224] Updated search for long-lived particles decaying to jet pairs [PAPER arxiv: ] Search for long-lived particles decaying to jet pairs [Eur. Phys. J. C75 (2015) 152] Search for Higgs-like bosons decaying into long-lived exotic particles [Eur. Phys. J. C (2016) 76: 664] Search for long-lived heavy charged particles using a ring imaging Cherenkov technique at LHCb [Eur. Phys. J. C 75 (2015) 595] Search for Majorana neutrinos in in B 0 π + μ μ decays [Phys. Rev. Lett. 112, (2014)] Searches for Majorana neutrinos in B decays [Phys. Rev. D 85, (2012)] I will provide a few highlights NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

10 Constraints on backgrounds in astroparticle searches

11 Antiproton production in p-he collisions [JCAP 1509 (2015) no.09, 023] The ഥp/p ratio is a sensitive probe to DM in the Universe Measured by PAMELA & result confirmed by AMS-02 Current data seems compatible with background from standard sources Biggest uncertainties come from ഥp production! How can LHCb contribute? Measurement of antiproton production in p-he collisions! LHCb can be used as a fixed-target experiment: - Exploit our SMOG device for beam-gas imaging - Injection of noble gases in the vertex detector surrounding the interaction region collision of 6.5 TeV p beam with He - Nucleon-nucleon interactions at s = GeV - We acquired 0.4 nb -1 of such data in 2016 (most data from a single 5-hour fill!) NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

12 Antiproton production in p-he collisions LHCb-CONF Selection strategy Good primary vertices (PVs) with < 5 backward-going tracks Good quality negative-charge tracks pointing back to the PV (to suppress material interaction and secondaries) Apply particle identification (PID) to bin antiprotons in p and p T NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

13 Antiproton production in p-he collisions LHCb-CONF M reconstructed p-he collisions 1.4M antiprotons Double differential cross-section in p and p T : - Spectrum shape in agreement with EPOS simulation [T. Pierog at al, Phys. Rev. C92 (2015), ] - But absolute production rate ~1.5 larger! - Excess due for 20% to total absolute cross-section larger - Most of excess due to higher antiproton multiplicity in data NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

14 Low-mass particle searches

15 Search for Hidden Sector bosons Phys. Rev. D 95, (2017) Study DM sector with portals to SM - Scalar portal (e.g. inflaton) - Axion portal (only in vector K* meson) Look at B K ( ) χ(μ + μ ) decays - b s transition LHCb has largest samples of B K ( ) χ(μ + μ ) decays Careful selection with efficiency independent of m(mm) and t NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

16 Search for Hidden Sector bosons Phys. Rev. D 95, (2017) Model-independent limit - Branching fraction normalised to rare SM decay - Constraints on lifetimes roughly relate to decay lengths ~30mm to 30 cm [Phys. Rev. Lett. 115, (2015)] Constraints on scalar portal mixing with the SM Higgs inflaton parameter space < 2m t almost ruled out NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

17 Search for Hidden Sector bosons Phys. Rev. D 95, (2017) Supplementary material (tables) can be retrieved from NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

18 Long-lived particle searches

19 Long-lived particle searches motivation SUSY models with long-lived neutralinos - h 0 χ χ, with χ 3 quarks [Phys.Rev.Lett. 99 (2007) , [hep-ph/ ]] Hidden Valley models - h 0 π V π V, with π V b ഥb [Phys.Lett. B651 (2007) ,[hep-ph/ ]] Other models predict semi-leptonic decays which LHCb can look for NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

20 Long-lived part. decaying semileptonically Eur. Phys. J. C (2017) 77:224 Constrain RPV msugra neutralino decaying to a lepton + 2 quarks signature = muon + jets Experimentally, look for a single displaced vertex with several tracks and a high p T muon Probe long-lived particle mass in range [20,80] GeV and lifetime in range [5,100] ps Limits interpreted in a variety of models, see paper Supplementary material (tables) can be retrieved from NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

21 Long-lived particles decaying to jet pairs LHCb-PAPER Constrain model of Hidden Valley dark pions from SM Higgs decay signature = 2 (b-)jets Experimentally, look for a single displaced vertex with 2 b-jets Update analysis with full run-i dataset Limits for different with π V masses and lifetimes - Example of beam-axis displacement R xy bins proxy for the lifetime NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

22 Long-lived particles decaying to jet pairs LHCb-PAPER Observed upper limit versus lifetime on SM Higgs branching fraction for different π V masses and decay modes NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

23 Dark Photons

24 Muon pairs in the 2016 trigger New triggers added in 2016 ability to do both the prompt and the displaced dimuon searches NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

25 Search for dark photons LHCb-PAPER Search for Dark Photons (A ) decaying to a muon pair Kinematic mixing with off-shell photon - inherits production mode - can normalise to off-shell photon data-driven analysis Analysis with 2016 data Two types of search: - Prompt-like : 214 < m(a ) < 350 GeV - Long-lived : mm threshold up to 70 GeV First exclusion limits at a non-beam-dump experiment NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

26 Search for dark photons LHCb-PAPER Prompt-like mass spectrum M(A) = 0.5 GeV NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

27 Search for dark photons LHCb-PAPER First limit on dark photons for m(a ) > 10 GeV NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

28 Looking ahead

29 LHC(b) future NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

30 Future sensitivity studies for A m m with run-iii In run-iii LHCb has the amazing goal of running with a software trigger only! huge gains in sensitivity foreseen NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31

31 In short LHCb is a great general-purpose detector in the forward region - We can do so much more than Flavour Physics LHCb is contributing to the field of DM searches, something that was not anticipated - We provide complementary information to that of the usually named general-purpose detectors ATLAS & CMS So, do not assume upfront that we cannot do some other measurement/study Do get in touch and discuss! 谢谢 Obrigado NCTS Wksp. DM 2017, Shoufeng, Hualien, Taiwan, Oct /31