Exploring Charm Particle Physics: An Overview of the FOCUS Experiment

1. Introduction to the FOCUS Experiment http://lexus.physics.indiana.edu/~focus/project/pptfiles/iu_focus_intro.ppt • FOCUS is a collaboration of about 70 physicists from the US, Italy, Korea, Mexico, Brazil studying charm particle production and decay at the Fermilab Tevatron (Batavia, Illinois) • The acronym stands for FOtoproduction of Charm with an Upgraded Spectrometer (the spelling is half Italian) • It utilizes the worlds highest energy photon beam to produce charm quarks which can be detected using a magnetic spectrometer consisting of wire chambers, silicon detectors, gaseous Cherenkov counters, etc. • The raw data sample was about 25 TB (data taking finished in late ‘97) Rob Gardner / IU Physics Introduction to the FOCUS experiment

2. The Physics of the Charm Quark • The c-quark was discovered in 1974, simultaneously at Brookhaven Lab (Long Island) and at SLAC (Stanford Linear Accelerator Center) • It is a “heavy” quark, which makes it difficult to produce (because of the way cross sections scale). Therefore, data for this object has been slow in coming, making all of the particle physics involving the charm quark difficult to study. • The charm quark is well-behaved in the so-called Standard Model of particle physics. That is to say, SM predictions for weird behavior are tiny. This opens a window for observing physics beyond the SM… “New Physics”. If we can find SM forbidden charm quark decays, we will be onto something really hot in the world of particle physics. (The world at large may also be interested, from a philosophical point of view.) • FOCUS has the worlds largest sample of fully reconstructed charm particle decays and will for the near term future. Introduction to the FOCUS experiment

3. Charm Physics, continued • We study things like: • charm particle lifetimes (gives us information about the interactions between quarks and gauge boson which mediates the “weak” force) • measurements of semileptonic decays -- that is decays of charm quarks which result in leptons in the final state (electrons or muons). These decays can be used to test Quantum Chromodynamics (QCD) which is the theory describing the interactions between quarks and gluons, ie. the forces responsible for binding nucleii. • measurements of “Cabibbo Suppressed” decays which yield information about the couplings between quarks themselves. This is described in the SM by a matrix called the Cabibbo-Kobayashi-Maskawa mixing matrix (CKM for short) which rotates “mass” eigenstates into the physical point-like states (the quarks) which experience both strong and electroweak interactions. • we can look for “CP violation” in charm decay which results in a difference between the decay rate for a charmed meson and its charged conjugate antiparticle state. Introduction to the FOCUS experiment

4. Detectors • Located in the Fixed-Target area (Wide Band Photon Lab) at Fermilab • High energy photon beam (~300 GeV) impinges on beryllium oxide target, producing the charm quarks by “fusing” with a gluon in the target Introduction to the FOCUS experiment

5. D+ D- Charm Signals • Particles containing charm quarks live a long time, about 1picosecond • Since they are travelling at nearly the speed of light in the laboratory, the lifetime is dialated and so the particle travels an observable distance before decaying. • We use very precise silicon strip detectors (s~10m) to measure the trajectories of the daughter particles. These are called tracks. Where they come together is called a vertex. Over 1 million observed by FOCUS These are called golden modes 1cm Introduction to the FOCUS experiment

6. Ds+ Do  (Ds+) =0.506  0.008 ps More charm signals: first results from FOCUS Ds+ and Do have unique non-spectator decays Theory  (Ds+) / (Do) =1.07 1.20 cos K Preliminary:  (Ds+) / (Do) = 1.214 0.017 Introduction to the FOCUS experiment

7. Charm results data processed at Urbana (Jim Wiss): Introduction to the FOCUS experiment

8. p - ~ K + p + p - D 0 _ _ D (recoil) D* + p - p + We tag events which contain two charm mesons Can tag the presence of a D° by observing a right sign  which balances Pt with a reconstructed D . You then count the number of D° decays into a particular final state, correct by efficiency and ratio to find an absolute branching fraction. Low primary vertex multiplicity is a big advantage. 20% FOCUS Proof of Principle 1: Excess of RS over WS events at low Pt Proof 2: We can reconstruct both D’s in an event? Already have a copious sample of very cleanevents with both reconstructed D’s Expect 5000 30% FOCUS

9. Data flow diagram data collection 25 TB Pass1 reconstruction 25 TB skim 1 30 TB skim 2 fnal Introduction to the FOCUS experiment

10. Data facts • There were about 5900 data taking runs in the experiment. Each run lasted for about 1/2 hour, filling a 4 GB exabyte tape (8mm). A total of 6.5 billion physics events were collected. • The raw tapes were processed into about as many PASS1 tapes (raw data is reconstructed into tracks, vertices, particle id codes). Much of the raw detector information was thrown away to make space for the new reconstruction blocks • Skim 1 divided the PASS1 output into 6 superstreams designed to do specific physics studies. There are significant overlaps between the streams (since many events satisfy the same selection criteria) • Each superstream consists of 330-490 tapes. Skim 2 further splits these into substreams, and distributes smaller numbers of tapes (~50) to interested institutions. Introduction to the FOCUS experiment

11. FOCUS Data Store at IU HPSS • We are working with a graduate student (Topher Cawlfield) at UIUC to store data from FOCUS into HPSS • CONTINUES... (data elaboration details) Introduction to the FOCUS experiment