Searching for sneutrinos at the bottom of the MSSM spectrum Arindam Chatterjee Harish-Chandra Research Insitute, Allahabad In collaboration with Narendra Sahu; Nabarun Chakraborty, Biswarup Mukhopadhyay ArXiv: 1407.3030; 1411.7226
Supersymmetry (SUSY) : A hypothetical symmetry relating Bosons and Fermions, has fermionic generators Why SUSY : Solves the Hierarchy problem Unifies the gauge couplings at a high energy scale Haag Lopuzansky Sohnius theorem... The Minimal Supersymmetric extension (MSSM) : has the same gauge group as the SM, SU(3) SU(2) U(1) the particle contents and their gauge quantum numbers follow from that of the SM; an extra Higgs doublet is needed a discrete symmetry, R parity, [( 1)^(3B L 2S)] is assumed; this prevents renormalizable terms responsible for proton decay; and makes the lightest superparticle stable, Dark Matter candidate for free. soft SUSY breaking is assumed.
The LSP and Dark Matter : In MSSM, the lightest neutralino is the only candidate for Dark Matter; usually ``well tempered, co annihilating Or around a resonance at low/medium mass range to achieve the right thermal relic... [Arkani Hamed,Delgado,Giudice'06,...] Left Sneutrino [Hagelin, Kane, Raby'84]: has been ruled out by direct searches upto a mass above which it can not produce the right thermal relic. [Falk,Olive,Srednicki'94].
Can (left )sneutrino still be at the bottom of the (p)mssm spectrum? Various collider (SUSY) search strategies depend on the spectrum and nature of the LSP. A different LSP may lead to new signal and alter several bounds.
Some possibilities I. Small mass splitting between the CP even and CP odd part of the sneutrino LSP [Hall,Moroi,Murayama'98; Tucker Smith and Weiner'01] II. A lighter Gravitino below the sneutrino [dominant decay mode of sneutrino is a neutrino and a gravitino, hard to find in collider; poorly constrined by BBN... ] III. A right sneutrino below the left sneutrino [e.g. in the simplest form with only a Yukawa interaction (y L.Hu N), and a small soft term] Will discuss the first possibility in some detail, before going to the collider implications.
I. Sneutrino(L) mass eigenstates: Before EWSB sneutrino mass comes from the soft SUSY breaking term alone. After EWSB a D term contribution adds up. Also a small mass splitting is generated between the CP even and the CP odd sneutrino states. Note that this contributes to the neutrino mass, needs tuning if the splitting is large. [Grossman,Haber'97; Ma,Sarkar'12] The sneutrino mass matrix after EWSB : With, we have :
Direct Detection : L type Sneutrinos have been ruled out due to their large cross section with quarks, via t channel Z mediation Z couples to a CP even and a CP odd state: In this case there is a mass splitting between these, and the DM is lighter one of these two. To achieve recoil energy ER via Z exchange the minimum speed needed : For splitting of a few hundred kev, it requires very high speed of the incoming DM to excite the heavier state; suppressed by the tail of the (Maxwell Boltzmann) velocity distribution; limited by galactic escape velocity ~ 650 kmps. The Z exchange t channel process does not contribute to the Direct detection.
Direct Detection... LUX Result [arxiv: 1310.8214]
Direct Detection... DM couples to h through D term, and that offers much smaller cross section with nucleon (neutron). The details also depend on the masses of the two CP even Higgses etc. Default values of micromegas, for the strange quark content of the nucleon has been used.
Relic abundance : (Co)annihilation with the bino
(Co)annihilation with the bino... Leading contributions : Z exchange (s channel) and gaugino exchange (t/u channel); followed by W exahange s channel; Nu exchange s channel and snu exchange t/u channel
Benchmarks : MQ = 2 TeV; MQ3=3 TeV; MU3 = 1.5 TeV; Mg = 1.5 TeV Tan beta= 10; ma = 1 TeV; mu = 1 TeV; At = 3.7 TeV.
Collider signature Generic feature : Left sneutrino and left slepton separated by about 10 20 GeV mass splitting, largely created by D term contribution Assume a bino(wino) like neutralino (and chargino), the lightest stop and gluino in the order shown
SS3L from stop pair ( l) j ν j W + W t 1 t b j s t 1 t b j s W W χ 0 1 j s χ 0 1 j s l1 l1 ν 1 ν 1 Majorana gauginos => two same sign leptons can be obtained, one more lepton from the decay of top quark Note that both stops need to decay to neutralinos More possibilities if gluino is not decoupled, can obtain SS3L even when stop has significant branching into b chargino.
Benchmarks
Results Both SS2L and SS3L searches are inclusive, and extra lepton is vetoed.
Results... Some details : We have used MADGRAPH for event generation; PYTHIA for showering and hadronization; FASTJET for jet clustering; DELPHES for (ATLAS) detector simulation and MADANALYSIS For analysing the events.
Results... SM background on SS3L (mostly from t tbar W) [S.Mukhopadhyay, B.Mukhopadhyay; 2011] 0l+MET diluted : Stop mass 1 TeV and 1.2 TeV
Conclusion We consider the possibility of having the lfet sneutrinos as the lightest (p)mssm sparticle. In scenario I, DM can have thermal relic density in a large parameter space starting from about 300 GeV (bino co annihilation). SS3L signal seems to be generic in all 3 scenarios, assuming the lightest stop is not decoupled, and stop >t neutralino (or the corresponding 3 body channel) is open. Scnarios I and II seems to be otherwise weakly, if at all, constrained by cosmology and collider searches. A detail investigation is planned.
Thank You :)
Constraints from neutrino mass : [Grossman, Haber'97; Ma, Sarkar'11] Neutrino (Majorana) mass is generated at one loop level, with both sneutrinos and (gaugino like) neutralinos running in the loops.
Experimental bounds on neutrino mass implies, assuming no significant fine tuning between the bare mass and the renormalized mass: With ~150 KeV
Ma, Sarkar ' 11
Observed rate per unit energy per unit time per unit target mass : Considering v_earth