CMS Bulletin

PHYSICS

In the period since the last CMS Bulletin, the LHC – and CMS – have entered LS1. During this time, CMS Physics Analysis Groups have performed more than 40 new analyses, many of which are based on the complete 8 TeV dataset delivered by the LHC in 2012 (and in some cases on the full Run 1 dataset). These results were shown at, and well received by, several high-profile conferences in the spring of 2013, including the inaugural meeting of the Large Hadron Collider    Physics Conference (LHCP) in Barcelona, and the 26^th International Symposium on Lepton Photon Interactions at High Energies (LP) in San Francisco. In parallel, there have been significant developments in preparations for Run 2 of the LHC and on “future physics” studies for both Phase 1 and Phase 2 upgrades of the CMS detector.

The Higgs analysis group produced five new results for LHCP including a new H-to-bb search in VBF production (HIG-13-011), ttH with H to γγ (HIG-13-015), and two new searches for high-mass Higgses (HIG-13-008/014). They also updated the last of the so-called HPAs (High-Priority Analyses), HIG-13-012 (associated production, VH with H to bb) to the full dataset, wherein a 2.1σ excess over background expectations is now observed as shown in Figure 6.  While these and earlier Higgs measurements continue to strengthen the SM Higgs hypothesis, they are not able to exclude BSM physics, for which direct searches continue at CMS in the SUS, EXO and B2G PAGs.

In the time since the last Bulletin, the SUS PAG carried out several new analyses with the full 8 TeV dataset that further constrain “natural” SUSY scenarios, which require relatively light gluinos and third generation squarks. For example, in the search for top squark (stop) pair production (SUS-13-011), stop masses up to 650 GeV are excluded at 95% CL. On the other hand, one manner in which Nature could be supersymmetric and yet evade these searches is if R-parity is not conserved.  The SUS PAG has recently made significant progress in closing this loop-hole with new dedicated searches (SUS-12-027, SUS-13-003) for scenarios that assume one non-zero R-parity-violating coupling at a time and set stringent limits on these models, as can be seen in Figure 7, where supersymmetric particle masses of up to nearly 2 TeV are excluded at 95% CL. 

Figure 6: 2.1σ excess observed in VH with H-to-bb analysis

In other searches for new physics that have unfortunately also yielded null results, EXO PAG has performed an analysis looking for heavy resonances decaying to bottom-quark final states (EXO-12-023), an analysis looking for evidence of jet “extinction” (EXO-12-051), and an update of the LQ2 analysis to the full dataset. Meanwhile, the B2G group produced two new results with the full 8 TeV dataset for LP:  B2G-12-015 that is an inclusive search for top-partners (as might occur in Little Higgs models, for example), and B2G-12-023, a search for baryon-number-violating top quark decays.

In precision physics, the TOP group has confronted NLO QCD calculations with a measurement of the jet multiplicity in di-leptonic top events (TOP-12-041) as well as performing a search for flavour-changing neutral currents in top quark decays (TOP-12-037), both with the 8 TeV dataset. The SMP group has performed the first inclusive differential jet cross-section measurement at 8 TeV (SMP-12-012), a study of final-state radiation via the ratio between inclusive jet cross-sections with different anti-k_T radius parameters (SMP-13-002), and the first measurement of colour coherence effects at the LHC (SMP-12-010). The BPH group has made measurements of the differential Υ (Upsilon) cross-section (BPH-12-006) and prompt J/ψ and ψ(2S) polarisation (BPH-13-003). The forward physics PAG (FSQ) has produced a number of results for DIS 2013 in Marseilles and LP (FSQ-12-005/002/022/028) including the first result using CMS data triggered by TOTEM, a measurement of charged-particle pseudorapidity and transverse-momentum distributions (FSQ-12-026).

Figure 7: 95% CL mass exclusions for various RPV scenarios

In heavy-ion physics, HIN has performed several analyses on the data from the proton-lead run, a study of di-jets (HIN-13-001), a study of the inclusive production of charged hadrons (HIN-12-016), and a paper with detailed studies of the “ridge” in pPb collisions (HIN-13-002).

Finally, the future physics groups (FTR) have been busy preparing physics projections for both the Phase 1 and Phase 2 upgrades of the CMS detector.  For Phase 1, the L1 Upgrade TDR (CERN-LHCC-2013) has received the endorsement of the LHCC. For Phase 2, using scaled 8 TeV results, parametric and “full” simulations of the CMS detector under several different upgrade scenarios, 14 TeV, 3000 fb^–1 analyses are being performed spanning Higgs, BSM, and SM physics. The earliest of these will go in a whitepaper submitted to Snowmass in late July, with the remainder targeted for the ECFA workshop in October.