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CERN | Geneva | Switzerland

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LHCb is trying to crack the Standard Model

LHCb, one of the Large Hadron Collider (LHC) experiments, was designed specifically to study charge-parity (or CP) violation. In simple words, its goal is to explain why more matter than anti-matter was produced when the Universe slowly cooled down after the Big Bang, leading to a world predominantly composed of matter. This is quite puzzling since in laboratory experiments, the measured preference for the creation of matter over antimatter is too small to explain why we only see matter around us today in the Universe. So why did the Universe evolve this way?

One of the best ways to study this phenomenon is with b quarks. Since they are heavy, they can decay (i.e break down in smaller parts) in many different ways, but are light enough for us to produce in copious amounts (unlike the heaviest quark, the top quark). In addition, theorists can make very precise predictions on their decay rates using the Standard Model, the theoretical framework we have to describe most phenomena observed to this day.  Once we have predictions on how often b quarks should decay into one or another decay mode, we can compare this with what is measured with the LHCb detector, and see if there are any deviations from the Standard Model predictions. Such deviations would indicate that this model is incomplete, as every physicist suspects, even though we have not been able to define the nature of the more complex theoretical layer that must be hidden or measure anything in contradiction with the Standard Model.

Here is how LHCb wants to do it: by studying rare decays with a precision never achieved before.

When electrons or protons collide in large accelerators, b quarks are produced, but they do not come alone. They are typically accompanied by one other quark (mostly u, d or s) to form composite particles called B mesons. Such mesons have been produced at several colliders, most abundantly in b-factories in the US and Japan, but also at the Tevatron, an accelerator similar to the LHC and located near Chicago in the US.

Physicists from b-factories studied the decays of B mesons in great detail for more than ten years, but nothing new disproving the Standard Model has been uncovered so far, even after scrutinizing the decays of more than 470 millions B pairs of mesons! All decay modes inspected behaved according to the Standard Model predictions. This means we now need to study even rarer decay modes, the ones the Standard Model predicts will occur only once in a billion times. To do so, we need to look at several billion decays to detect the slightest deviation. This is in these small details that we hope to uncover new physics going beyond the Standard Model.

Recently, the Tevatron experiments, D0 and CDF, took the lead by measuring very rare decays, namely Bs → μμ, where a Bs (a meson made of an anti-b and an s quark) decays to a pair of muons, (denoted m), a particle very similar to electrons, only heavier. CDF saw a small excess of events with respect to Standard Model expectations. And when they look at the angular distributions of Bs à J/Ψ Φ , that is when the Bs meson decays into two other mesons, J/Ψ and Φ, they can measure a parameter called Φs , which is supposed to be zero according to the Standard Model. Both D0 and CDF obtained a non-zero result, but this measurement is not quite accurate enough to really challenge the Standard Model.

And that’s where LHCb, the new kid on the b-physics block, comes into play. With the LHC delivering data at a fast and furious pace, LHCb can already surpass the precision reached at the Tevatron. Already in July, LHCb (and CMS, another LHC experiment) contradicted the CDF claim of anomalous number of Bs → μμ events. They might do it again with the release of their first measurement of Φs, which is expected to be much more precise than the Tevatron result.

Will Φs be equal to zero as predicted by the Standard Model? LHCb will announce this on Saturday at the Lepton-Photon conference in Mumbai. Could LHCb be the first experiment to crack the Standard Model? With the level of precision they are already reaching, even if it’s not now, they will be in the best position to do it in the near future.

Stay tuned. The new results will be added here on Monday.

————————————————————————————————————————-
Addition:
At the Mumbai Lepton Photon conference on Saturday, LHCb presented their new measurement in the decay of Bs → J/ψ φ . They measure the parameter φs to be near zero, as predicted by the Standard Model. Being more precise than the CDF and D0 measurement announced earlier this year, this new measurement shows that the Standard Model holds true even when tested with this unprecedented precision.

However, there is still room for new and unexpected phenomena as the LHCb precision increases as new data are being analysed. LHCb should have about three times more data available by the end of the year, putting the Standard Model under even more rigorous tests.

LHCb result

LHCb result

The color circles show the LHCb results at different degrees of precision. The theoretical prediction is shown in black with its own uncertainty. At present, the two are in fair agreement. With more data analysed, the uncertainty in the experimental measurement will decrease, allowing for an even more stringent test of the current prediction. (The extra set of circles correspond to the other solution to the equation).

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline

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22 Responses to “LHCb is trying to crack the Standard Model”

  1. Jerry K says:

    Thank you very much, I will be most interested you Monday post

  2. Justin Turner says:

    FINALLY! Possible disproving of the standard model! I’m on the edge of my seat guys. How long is it going to take? :o)

    • CERN (Francais) says:

      Hello Justin,

      even if we find a flaw in the Standard Model and prove with some extremely precise measurement that there are some deviations from the Standard Model, we will not trash it. It already answers so many things and with such precisions.

      Finding a flaw will just tell us we need to add one more layer of complexity to this model. Once we see where the flaws are, it will be easier to see which ones among the many new models proposed corresponds to the way things work. It will be like adding trigonometry to basic geometry. The addition does not prove the first one wrong, it simply allows for more in depth calculations.

      Pauline Gagnon

  3. Tony Lance says:

    Hi there,
    What are the new masses in MeV of the new high precision B Mesons and the
    new High precision antimatter proton published earlier. It would help my work on the Outlandish Particle Periodic Table. Their error margin and charge would help too. A better precision electron mass would be a keystone.

    • Pauline Gagnon says:

      Sorry if that was not clear. LHCb and the other experiments involved in these measurements were not trying to measure the masses of the B mesons they were studying. These are really well known and you can find the whole set of values from the Particle Data Group site:

      http://pdg.lbl.gov/2011/tables/contents_tables.html

      If you click on “mesons”, you’ll find all the values you are looking for. Have fun!

    • Tony Lance says:

      Hi Pauline,
      The mass measurements I already use are as follows;-
      Electron Mass MeV 0.510998902 Nominal Electron Error MeV 1.0D-09
      Electron Mass MeV 0.510998901 Actual Electron Error MeV 2.0D-08
      Electron Mass MeV 0.510998902 Actual Electron Error MeV 2.1D-08
      Electron Mass MeV 0.510998903 Actual Electron Error MeV 2.0D-08
      Electron Mass MeV 0.510998918 Actual Electron Error MeV 4.4D-08
      Electron Mass MeV 0.510998910 Actual Electron Error MeV 1.3D-08
      Muon Mass MeV 105.6583568 Actual Muon Error MeV 5.2D-06
      Muon Mass MeV 105.6583692 Actual Muon Error MeV 9.4D-06
      Muon Mass MeV 105.6583668 Actual Muon Error MeV 3.8D-06
      Muon Mass MeV 105.6583668 Nominal Muon Error MeV 5.0D-05
      Proton Mass MeV 938.2720130 Actual Proton Error MeV .000023
      Proton Mass MeV 938.2720290 Actual Proton Error MeV .000080
      Proton Mass MeV 938.2719980 Actual Proton Error MeV .000038
      Proton Mass MeV 938.2719980 Nominal Proton Error MeV .000200
      These are the best you have got. The nominal ones are in my table.
      Any idea of a timescale for better precision than above?

  4. Martin says:

    Looking forward to tomorrow’s entry! I hope you offer a bit of commentary on the exclusion of supersymmetry below 1000 GeV.

  5. Lucy Haye says:

    The Standar Model was broken many years ago since Dr. Carezani a in his New Paradigm in Physics-Cosmology proved that the Neutrino doesn’t exist confirming a previous experiment by Buechner and Van de Graaff.

    See in the Blog the paper “Never any Detector Detected any Neutrino”” related to the Inia and China problem thinking to construct new Neutrino Detector.
    http://autodynamicslborg.blogspot.com/
    Lucy Haye Ph. D.
    SAA;s representative.

  6. [...] More information: http://www.quantum … ndard-model/ [...]

  7. calimero says:

    Hi,
    in this article,

    http://cdsweb.cern.ch/journal/CERNBulletin/2011/35/News%20Articles/1377392?ln=fr

    Pauline Gagnon says that quarks b are always produced with quarks u, s or c.

    is there a reason why quarks d aren’t produced too ?

    Tx for your reply.

    • Pauline Gagnon says:

      Hello,

      what I said is: a b quark mostly comes with u, d or s quark. These are the lighter quarks and they are easier to produce. So it is possible for a b quark to come with an anti-quark d. You then get a neutral B meson denoted B0.

      A meson is a particle made of one quark and one anti-quark. They only come in combinations that give a full or zero charge, never a fractional charge.
      Take a b quark, which has a charge of -1/3. It can be combined with anti-quark d, the anti-quark s and the anti-quark b. These all have an electric charge of +1/3 (between quarks and anti-quarks, all you need to do is flip the sign of the electric charge). And if you combine a b quark with an anti-u or c quarks, you’d get a charged meson. These have a charge of -2/3. So far, nobody has ever observed a b and t quarks in a meson. These are just too unstable.

      You’ll find a very nice chart showing all the basic constituents of matter and how mesons are formed in here:
      http://www.cpepweb.org/particles.html

      They also have nice interactive material there too, like the “Particle Adventure”. You should find everything you need to understand the basic constituents of matter there.

      Pauline Gagnon

    • calimero says:

      Hi,

      And tx for your kind reply.

      But what I read is that :
      “Voici comment la collaboration LHCb entend s’y prendre : en étudiant les types de désintégrations rares avec la plus grande précision jamais atteinte.

      Les collisions d’électrons ou de protons dans les accélérateurs de particules produisent des quarks b qui s’accompagnent toujours d’autres quarks plus légers (u, s ou c)”

      I am totally noob in physics, to in méca Q all the more so, but as you talk about u (I know that u and d and the lightest ones) something looked strange, for me. Not charmed, but strange ;).

    • CERN says:

      Ah.. I see. indeed, in my French translation, I made this ambiguous. Thank you for spotting it. I corrected it. It is true that b quarks can bind with c quarks, but it is way more common to form light mesons by associating with u and d quarks, as you had thought.

      Pauline Gagnon

  8. [...] not going to attempt to delve into the physics of this – check out the LHCb experiment and Quantum Diaries posts if you’re interested in the nuts and [...]

  9. [...] We are not going to attempt to delve into the physics of this — check out the LHCb experiment and Quantum Diaries posts if you’re interested in the nuts and [...]

  10. Francis says:

    Just some ideas. Im a layman in that field:

    Why do protons and neutrons weigh 100 times more than the quarks they are made of?
    If the Thabet-Lamy postulate is right that in fact any interferences in the “universal” flow of waves does creates Gravity. (the “universal” flow would be a universe where all sub-particles are not connected. Also it would mean a universe where there is no matter but only waves. There are 2 approaches here.
    1. Let’s call it the classical quantum mechanics where the graviton not yet found does exist
    2. The string theory.
    Note: In 8 years, the Fermilab using the LIGO have not recorded a single event (they had a few “ambiguous” events) that could confirm in the classical sense a gravitational wave coming from the gravitational spin of 2 neutron stars. Base on logic, the probable number of inspin neutron stars, black holes (there is at a minimum as many black holes as galaxies) and other yet unknown events capable of producing a GW combined with all their ripple effects, GW should have been recorded on a daily basis. Actually, I will go as far as saying that the laser would have been in constant fluctuation. Unless the instrumentation used was not enough tuned or precise. In such a case, when no event confirming the theory were recorded after 6 months. Well, on your bike my son! But this has been the plague of science for centuries. EGO. What if the theories are wrong? They are not, so we need a graviton to fit the theory and the standard model. I don’t see Gravity as a particle wave-force but as an underlying dynamic.
    If the weight of a 1kg Fe ball is the same, one time at sub zero temperature and another let’s say at 100C.. It’s gravitational force will be the same and therefore could fit the graviton logic but if there is a slight change in masse, therefore gravitational force of the system, the Graviton theory is out. Why? The number of particles that make the 1kg Fe ball would have a corresponding number of Gravitons. By changing its temperature, why would the number of Graviton be different? My view is that the temperature change will modify the frequency of the system, there will be a masse change and that gravity operates at the wave level not at the particle level. This approach might be the key to produce Anti –gravity. Not by changing the temperature but by changing the frequency of a system!
    Another thought experiment in a different area. What would happen to a beam of light (laser) injected and tightly enclosed inside a ball coated with an inner reflexive material? The postulate is that if for some reasons the photons speed up or slow down. We could observe modification in term of Time and maybe even gravity. Of course this is pure speculations until….
    From the string theory approach, the universal flow would be as all strings are on the same frequency, on a carrier wave. At that stage, matter, Quarks, and any other particles are not bound yet by gravity. The speed? Let’s say the speed of light where in this case it should be called the Carrier Wave Speed (CWS) that should be used as a reference. Since a Photon can be either a wave or a particle. At this stage the duality is not yet well explained. We use the speed of light as a reference. For the sake of the argument let’s say that the CWS and the speed of light are the same.
    If the CWS is the singularity, any departure from this “mother” frequency creates particles that form atoms and the cosmological model we see around us. Our Postulate is that: As a new frequency is formed when no longer on the CWS, not only it creates matter but it changes speed since a wave will change frequency and those changes may creates gravity… When 2 separate waves reach the same frequency that’s the “TIME” Gravity is formed. After it is kind of a chain reaction. They attract more waves and more gravity is created. Individual Quarks if made by specific frequencies on the string level, the Nod they make to produce a proton or neutron is the interwoven of those different frequencies creating gravitational force by slowing Time.
    Also, my view point is that a black hole is the return from all different frequencies back to the CWS. The loop and the deterministic view of the universe. Yes and No. The black hole brings back all the frequencies together and the singularity spread them. Maybe but the universe each time is a different one…
    The black hole is basically a defragmenter. The universal flow (UF) could be what’s before the singularity or big bang and after a black hole.
    If Space-Time is one concept, maybe Gravity-Time is another one. Gravity can’t be comprehended without the Time factor and vice versa. This is the hardest part of it. Anyway when talking about waves and specially frequencies it means talking about time!!!!
    One Question: How does the frequency (ies) of a molecular system can be changed? How a particular wave length is influenced by another and therefore merges with it? A river main stream and the smaller rivers merging with it could be a good way to conceptualize it. (To be studied). This should NOT be solely approached from the Fluid mechanics. WRONG. If the waves merger creates gravity, it would mean that once the merger is complete, gravity would no longer be present.

    • CERN says:

      Dear Francis,

      the answer is very simple (and short too!): more than 95% of the weight of a proton or all composite matter comes from the “binding energy”, that is from the forces binding the quarks together inside the proton. Same thing within an atom. The binding energy is the source of the energy released in nuclear fission (when large nuclei are broken into smaller pieces).

      I hope this helps. Pauline Gagnon.

    • João Neto says:

      There’s also the quark’s kinetic energy due to the relativistic speeds they have in order to conform with Heisenberg’s uncertainty principle (since they are within such a small volume).

    • PT Messier says:

      ok I guess i will have to put my 2 cents in and im bored on a sunday evening. First off there was no big bang if you want to associate it with anything as far as a visual rendering you can call it A big spew. This occurs when two or more universes collide with one another in etherical space, which exist some what as a universe nursery. Gravity is dispersed
      equaly according to freq & mass of course to all matter in the universe. An gravity takes on a dual role on dimensional aspects that it not only pulls it also pushes in respect to matter & anti matter nutational freq rates. The reason this all takes place in the first place is what I like to refer to as atomic attraction. Schools out for today God bless you all.

  11. Victor Grauer says:

    It’s possible to conceive of the Big Bang “in such a way as to resolve the dilemma produced by the apparent absence of naturally occurring antimatter in the Universe. The antimatter could be accounted for if we imagine the “white hole” of the original explosion of matter into 3 dimensions . . . to have been accompanied by an “equal but opposite” black hole, formed by an implosion of antimatter into a companion universe defined by three additional, “dimensionally inverse,” dimensions . . . Since the resulting matter and anti-matter are segregated into dimensionally distinct realms, there would have been no possibility of electromagnetic interaction and thus no mutual annihilation.” From my essay, “Is the Universe Expanding into a Black Hole?” See also http://doktorgee.worldzonepro.com/TinyAlice.doc

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